Review of corrosive environments for copper and its corrosion inhibitors

A. Fateh; M. Aliofkhazraei; A.R. Rezvanian

doi:10.1016/j.arabjc.2017.05.021

View/Download PDF

Buy Reprints

PDF

Translate this page into:

Review

13 (

); 481-544

doi:

10.1016/j.arabjc.2017.05.021

Review of corrosive environments for copper and its corrosion inhibitors

A. Fateh, M. Aliofkhazraei^⁎, A.R. Rezvanian

Department of Materials Engineering, Tarbiat Modares University, P.O. Box: 14115-143, Tehran, Iran

⁎Corresponding author. Fax: +98 21 66960664. maliofkh@gmail.com (M. Aliofkhazraei) khazraei@modares.ac.ir (M. Aliofkhazraei)

Received: 2016-12-25, Accepted: 2017-5-27, Published: 2017-01-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

This review paper deals with corrosion of copper and its alloys in corrosive environments and their corrosion inhibitors. The main corrosion inhibitor groups for copper are introduced and a review of adsorption models is provided. The main part of this work is to investigate different corrosive environments for copper and its alloys and their corrosion inhibitors used in such environments to protect copper. According to the literature, the corrosion inhibition behavior of organic corrosion inhibitors and their derivatives in comparison with inorganic ones are further evaluated. Knowing maximum corrosion inhibition efficiency of a specific corrosion inhibitor in a specific corrosive environment is helpful to choose the most appropriate corrosion inhibitor compound.

Keywords

Azole

Copper

Corrosion

Corrosion inhibitor

Corrosion inhibition efficiency

Isotherm

Show Related Articles from PubMed

1 PBTA: (2-pyrrole carbonyl) benzotriazole
1 TBTA: (2-thienyl carbonyl)-benzotriazole
3 ATA: amino-1,2,4-triazole
3 APP I: methyl-6-oxo-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile
3 APP II: methyl-6-oxo-4-(3-phenoxyphenyl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile
3 APP III: methyl-6-oxo-4-(thiophen-2-yl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile
3,5 DAT: diamino-1,2,4-triazole
3 MTA: mercapto-1H-1,2,4-triazole
4 MePhl: methyl-2-phenyl-imidazole
4 OP: Octylphenol
4: AHMT amino-3-hydrazino-5-mercapto-1,2,4-triazole
5 PTAH: phenyl-1-H-tetrazole
AE: aqueous extract
AMK: amikacin disulfate
AO: Argan Oil
ATA: anisaldehyde-[5-(p-methyl)-phenyl-4-amino-(1,2,4-triazolyl)-2-thiol]-acyldrazone
AV: Adhatoda vasica
BBC: N-benzyl-1H-benzotriazole-1-carbothioamide
BIMD: benzimidazole
BNS: benzothiazole
BTA: benzotriazole
C. siliqua: Ceratonia siliqua
CC: Calligonum comosum
CDs: Capparis decidua seeds
Cys,: cysteine
DFT: density functional theory
DTUr: dithiouracil
EHE: helioscopia linn
E_HOMO: highest occupied molecular orbitals
EIS: electrochemical impedance spectroscopy
EN: electrochemical noise method
FBC: N-(furan-2-ylmethyl)-1H-benzotriazole-1-carbothioamide
HME: Hyoscyamus muticus
IMD: imidazole
LF: Langmuir-Freundlich
MBIMD: mercaptobenzimidazole
MBT: mercaptobenzothiazol
MD: molecular dynamics
MMPB: methyl 3-((2-mercaptophenyl)imino)butanoate
Na-CMC: sodium carboxymethyl cellulose
NH: natural honey
NS: Nigella sativa
NTBC: nitrotetrazolium blue chloride
PP: potentiodynamic–galvanostatic polarization
SAMs: self assembled monolayers
SA: Saraka asoca
SB: (NE)-N-(furan-2-ylmethylidene)-4-({4-[E)-(furan-2-ylmethylidene) amino]phenyl} ethyl) aniline
SDS: sodium dodecyl sulfate
SECM: scanning electrochemical microscopy
STA: salicylal-[5-(p-methyl)-phenyl-4-amino-(1,2,4-triazolyl)-2-thiol]-acylhydrazone
SVET: scanning vibrating electrode technique
TBC: N-(2-thiazolyl)-1H-benzotriazole-1-carbothioamide
VN: Vitex negundo
VTA: vanillin-[5-(p-methyl)-phenyl-4-amino-(1,2,4-triazolyl)-2-thiol]-acylhydrazone
Wl: weight loss measurements
XPS: X-ray photoelectron spectroscopy

1 Introduction

Copper with a reddish orange color is the fifth most usual metal in the earth’s crust which is very useful in pure or alloying form. Brass, copper-nickel and bronze are the most important copper alloys. Copper and its alloys are widely used in industries because of some favorable properties such as good corrosion resistance, high electrical and thermal conductivity, mechanical workability and malleability (Amin and Khaled, 2010; Davis, 2001). Copper and its alloys are highly regarded because of their wide application in production of wire, sheets and pipelines in electronic industries, marine industries, power stations, heat exchangers and cooling towers (Duran et al., 2012; Sherif et al., 2007a). Copper is known as a noble metal which provides appropriate corrosion resistance in the atmosphere and in some of chemical environments due to the formation of a protective passive (oxide) film or nonconductive layer of corrosion products on its surface (Adeloju and Hughes, 1986; Suter et al., 1993).

However, depending on the environmental conditions, the pitting corrosion may be occurred on copper surface in the presence of oxygen and some aggressive anions such as chloride and sulfate ions (Habib, 1998; Souto et al., 1992). The corrosion of copper and formation of corrosion products on its surface have a negative effect on performance of a system constructed from copper and may reduce its efficiency (Attia et al., 2016). According to widespread use of copper in different industries, the issue of corrosion and corrosion protection of copper has attracted a lot of attention and many studies have been conducted to date on this issue and are still ongoing. A schematic illustration of different copper based industries suffering from corrosion attacks is presented in Fig. 1.

Schematic illustration of different copper based industries that suffering from corrosion attacks.

The metallic systems constructed from copper (such as heat exchanger and electrical boards and circuits) usually expose to aggressive environments such as saline water in desalination systems and the corrosive liquids in petroleum pipelines (Abdel-Gaber et al., 2011; Feng et al., 2011; Tan et al., 2011; Wang et al., 2014b; Zanotto et al., 2014 ). Moreover, tidal waves or sea waves which make dry and wet cycles accelerate corrosion of copper due to a decrease in quality of passive layer and/or prevent formation of this passive layer in such conditions (del PB Hernández et al., 2011; El-Mahdy and Kim, 2004; Park et al., 2003; Shi et al., 2006 ). The increasing trend of number of published papers regarding copper corrosion inhibitors in recent years (Fig. 2) shows the importance of this issue for researchers.

Number of published papers around the subject of copper corrosion inhibitor versus year of publication (until 25 November 2016).

Despite corrosion resistive properties, copper as a strategic metal in industrial field suffers from aqueous corrosion by many aggressive ions. So corrosion protection of copper is very important and challenging issue. In this regard, researchers have used wide range of corrosion inhibitors for several decades to minimize the damages arising in corrosive environments (Antonijevic and Petrovic, 2008; Mihajlović and Antonijević, 2015). Another effective approach against destructive effects of corrosion is use of coatings containing corrosion inhibitors; however this review paper just focuses on corrosion inhibitors in aqueous electrolytes and not inside the coatings. Therefore, it was tried to collect principles, theories on copper corrosion, and experimental results of researches about copper corrosion inhibition in different corrosive environments, to present comprehensive insight for researchers with appropriate categories and provide guidance for future researches in this field.

2 Copper corrosion inhibitors

The dissolution and corrosion rate of copper in various environments is controlled by anodic and cathodic reaction rates on copper surface (Kear et al., 2004). The use of corrosion inhibitors is an effective method to reduce the corrosion rate of copper. The possibility of passive film formation on copper surface is low in highly aggressive environments or in the presence of corrosive ions such as chloride and sulfate, and thus corrosion inhibitors are used to control corrosion rate in such aggressive environments. The act of inhibitor to reduce anodic or cathodic reaction or both of them determines the type of corrosion inhibitor (Cao, 1996). If the addition of corrosion inhibitor to corrosive environment reduces anodic dissolution of copper, the corrosion inhibitor provides anodic inhibition, while the cathodic corrosion inhibitors reduce the rate of cathodic reactions (oxygen or hydrogen reduction) on copper surface. Mixed type corrosion inhibitor controls the rate of both anodic and cathodic reactions simultaneously (Khaled and Hackerman, 2003).

According to the literature, most of synthesized nitrogen-containing heterocycles compounds provide a mixed type corrosion inhibition for protection of metal’s surface in acidic solutions (Habib, 1998; Souto et al., 1992). However, in some cases the cathodic reaction has been affected by corrosion inhibitors (Feng et al., 2011). The corrosion inhibition efficiency (which calculated from variation of corrosion rate) is one of the main factors to evaluate the performance of corrosion inhibitor in a specific environment. The corrosion inhibition efficiency depends on chemical composition, structure and electronic (electrostatic) properties of corrosion inhibitor, the nature of metal and different properties of the environment. Considerable efforts have been done to develop corrosion inhibitors and increase their corrosion inhibition efficiency.

The corrosion inhibitors used for copper can also be divided into organic and inorganic corrosion inhibitors. Various inorganic corrosion inhibitors such as chromates ( ${CrO}_{4}^{2 -}$ ), molybdates ( ${MoO}_{4}^{2 -}$ ) and tetraborates ( $B_{4} O_{7}^{2 -}$ ) are used to reduce the corrosion rate of copper, although the use of these compounds was accompanied with some challenges (Muñoz et al., 2004). For instance, chromate is a toxic compound and also increases the corrosion rate by increase in cathodic reaction rate. Molybdate and tetraborate don’t provide an appropriate corrosion inhibition efficiency in solutions containing aggressive anions due to instability of protective layer formed on the metal’s surface (Mustafa and Shahinoor Islam Dulal, 1996). The corrosion inhibition efficiency of these compounds in 850 g/L LiBr solution is as follows (Muñoz et al., 2004): $Molybdate (1.56 %) < TetraBorate (51.0 %) < Chromate (78.6 %)$

In spite of the organic corrosion inhibitors, the changes in corrosion inhibition efficiency of inorganic corrosion inhibitors with variation of time and temperature are negligible. However, most of the inorganic corrosion inhibitors provide weak corrosion inhibition efficiency. In general, the organic corrosion inhibitors and their derivatives are used to protect copper because of their high corrosion inhibition efficiency in comparison with inorganic compounds.

It is necessary for better understanding of corrosion inhibition behavior to have information about properties of an organic compound such as the number of its adsorption sites, charge transfer, molecular dimensions, the type of interaction with metal’s surface and thus formation of metallic complex (Fouda et al., 1986).

The molecular structure of corrosion inhibitor plays a dominant role in interactions between corrosion inhibitor and metal’s surface (Trabanelli, 1991). In this case, the presence of heteroatoms such as nitrogen, oxygen, phosphorus and sulfur as a center of adsorption site promotes the electron exchange between corrosion inhibitor and copper (which has a vacant d orbital). It also develops several bonds between corrosion inhibitor and metal’s surface which increases the possibility to create a stronger bond (chemical type) between them (Zucchi et al., 1996b). In the presence of organic corrosion inhibitor in corrosive environment, the adsorption of its molecules on metal’s surface leads to the formation of an adhesive protective layer on copper surface which prevents from its corrosion (Ravichandran and Rajendran, 2005).

The effectiveness and ability of a corrosion inhibitor to protect copper from corrosion, depends on some factors such as film growth of the inhibitor by polymerization, π-π and Van der Waals interactions, bonding strength with the metal’s surface and the presence of oxygen, nitrogen and sulfur heteroatoms in the molecular structure of corrosion inhibitor. Moreover, the number and type of atoms and bonding group, temperature, pH and stability of aggressive environments are the other effective factors in the corrosion inhibition efficiency of a corrosion inhibitor (Ramesh and Rajeswari, 2005; Szőcs et al., 2005).

The adsorption process of corrosion inhibitor involves two types of interactions (Vashisht et al., 2016). The adsorption process, in physical adsorption, occurs with electrostatic interaction between opposite charged metal surface and corrosion inhibitor components. The chemical adsorption of corrosion inhibitor on metal’s surface is occurred by coordination through the lone pair electrons of heteroatoms (P, N, S, and O) or lone ring in the corrosion inhibitor structure with metal’s surface (Quartarone et al., 2006). In following the adsorption process of corrosion inhibitors and adsorption isotherms will be explained in detail.

Azole compounds (thiazole, benzotriazole, imidazole and thiadiazole), amines, Schiff bases, and amino acid drug compounds can be pointed out as the most important corrosion inhibitors used for protection of copper. Fig. 3 shows usual copper corrosion inhibitors that we have discussed in this review.

Copper corrosion inhibitors commonly used.

2.1

2.1 Benzotriazole

Benzotriazole (BTA) with the chemical structure of C₆H₅N₃ (the molecular structure is shown in Fig. 4) is one of the most important Azole derivatives, which has been known as a very effective corrosion inhibitor used for copper and its alloys, particularly in chloride-containing environments (Hollander and May, 1985).

Chemical structure of benzotriazole (Finšgar and Milošev, 2010).

The flammability and toxicity, which suffers skin and eyes, are the most important diminishing factors (Stupnišek-Lisac et al., 1998). Their toxicity is lower than other organic compounds (Finšgar and Milošev, 2010) and they are cost-effective corrosion inhibitor compounds. Benzotriazole is a five-membered aromatic heterocyclic corrosion inhibitor containing three nitrogen atoms (as shown in Fig. 4). The corrosion inhibition behavior of benzotriazole and its derivatives have been widely studied.

Benzotriazole and its derivatives are efficient and stable corrosion inhibitors for copper in neutral and alkaline environments and their corrosion inhibition effects remain for a long time (Antonijević et al., 2009; Gerengi et al., 2010; Khaled et al., 2010; Khan et al., 2015; Kokalj et al., 2011; Poling, 1970 ). Benzotriazole corrosion inhibitor is used in both stagnant and flow conditions because of its good protective nature. A few researches have been done on the corrosion inhibition of benzotriazole in chloride-containing solutions in hydrodynamic flow condition (Alkire and Cangellari, 1989; Ault, 1995; Khan et al., 2015; Xue and Ding, 1990 ).

It is generally accepted that BTA’s corrosion inhibition mechanism in neutral and alkaline solutions contains the adsorption of BTA molecules on the copper surface (Cu:BTAH(ads)) (Eq. (1)) and the formation of a protective monolayer or multilayer film in the presence of oxidants or by anodic polarization (Eq. (2)). This film has been identified as a polymeric [Cu(I)BTA] complex by spectroscopic techniques (Da Costa et al., 1990; Metikoš-Huković et al., 1998).

(1)

Cu (s) + BTAH (aq) = Cu : BTAH (ads) + H^{+} (aq)

(2)

Cu : BTAH (ads) = Cu (I) BTA (s) + H^{+} (aq) + e^{-}

Despite of its useful and efficient corrosion inhibition in alkaline and near neutral solutions, benzotriazole provides more weak corrosion inhibition efficiency in acidic solutions (in comparison with alkaline and near neutral solutions) due to dissolution of protective layer formed on copper surface in low pH values (Tromans and Sun, 1991). On the other hand, the BTA molecules will be present in the form of protonated molecules (BTAH⁺), which leads to a decrease in chemical adsorption of BTA corrosion inhibitor on copper surface due to repulsion between positive-charged protonated BTA molecules and copper surface (Wu et al., 1993). In these conditions polymeric [Cu(I)BTA] complex and [Cu(I)Cl⁻BTAH] have been found by Raman spectroscopy (Da Costa et al., 1987).

Non-biodegradability of BTA is one of its imperfections (Stupnišek-Lisac et al., 1998) which may allow entrance of wastewater with high quantities of dangerous materials into the general waterways (Gašparac and Stupnisek-Lisac, 1999). Therefore, considerable efforts have been made for possible substitution of other corrosion inhibitors with BTA in acidic media; however reaching high corrosion inhibition efficiency of BTA is hard.

2.2

2.2 Imidazole compounds

Imidazole (IMD) compounds are one of the most important azole derivatives, which provide corrosion inhibition properties and moreover act as anticancer, antibacterial, antifungal and anti-inflammatory agent (Tan et al., 2011; Wang et al., 2014b; Zanotto et al., 2014 ). The IMD is a heterocyclic aromatic compound consisting of three carbon and two nitrogen atoms (distinct from pyridine and pyrrole) which have high solubility in water because of their high polarity (Hofmann, 2009).

IMD compounds are organic compounds with two nitrogen atoms in the heterocyclic ring (Fig. 5) (Gašparac and Stupnisek-Lisac, 1999). This family of azoles has both acidic and basic sites on its structure and thus provides an amphoteric nature in which the nitrogen of pyridine (—N⚌C) is basic site and hydrogen of pyrrole (—HN—C) is acidic site (Kosower, 1968). The IMD molecule shows two anchoring sites suitable for surface bonding: the nitrogen atom with its lonely sp2 electron pair and the aromatic ring (Holze, 1993). The effectiveness of IMD on corrosion inhibition is lower than the other azole-derivatives due to its high solubility in water (Souto et al., 1992). Mechanism of corrosion inhibition of IMD is similar to other azole compounds and contains adsorption of corrosion inhibitor molecules on copper surface and then formation of protective complex with copper.

However, the addition of phenyl groups, a benzene ring or sulfur into the structure of IMD leads to increase in its corrosion inhibition efficiency and tune it to specific applications without any change in the corrosion inhibition mechanism.

Lee (2003) investigated the corrosion inhibition of copper with IMD in 1 M HNO₃ solution. It was proposed that corrosion inhibition mechanism of IMD in 1 M HNO₃ solution contains at first physical adsorption of IMD molecules on cathodic sites of copper surface and then bonding between N—/OH (of IMD) and Cu₂O (oxide layer on copper surface) and formation of protective Cu (N—/OH) complex film. This film is composed of two different layers with different concentrations of N and O. Outer layer that is rich of N, grows constantly than O-rich inner layer, resulting in a stable Cu(N—/OH) complex/Cu₂O bilayer as a barrier to the ion diffusion.

2.3

2.3 Other azole compounds

Since the sulfur atom has a strong tendency for copper, heterocyclic compounds containing mercapto group have been evaluated as corrosion inhibitor for copper (Blajiev and Hubin, 2004; Yan et al., 2000). Therefore, in addition to IMD, the corrosion inhibition behavior of mercapto imidazole compounds such as 2-mercaptobenzimidazole on corrosion of copper has been studied (Finšgar, 2013; Izquierdo et al., 2012; Xue et al., 1991; Zhang et al., 2004b ). In spite of benzotriazole which provides a weak corrosion inhibition efficiency for copper in acidic aerated media such as HCl, 2-mercaptobenzimidazole shows an efficient corrosion inhibition in such environment (Zhang et al., 2004b).

Thiazole (Lee, 2003), thiadiazole (Sherif and Park, 2006a; Xiong et al., 2015), tetrazole (Sherif et al., 2009; Ye et al., 1998; Zucchi et al., 1996a ) and triazole (Al-Shahrani and El-Shazly, 2016) are the other azole derivatives, which inhibit the copper from corrosion efficiently. This behavior is attributed to the flatness and the presence of free electron pairs in heteroatoms which facilitate the adsorption of these atoms on the metal’s surface. Therefore, the molecular structure of these heteroatoms are the main effective factor which has a dominant role in their corrosion inhibition behavior (Al-Amiery et al., 2013). Thiazole and thiadiazole are nontoxic compounds and this eco-friendly feature introduces them as good candidates for substitution with other corrosion inhibitors (Kidwai et al., 2000). The molecular structures of several groups of azoles are presented in Fig. 6.

Molecular structure of main azole family corrosion inhibitors; (a) 1,2,4-triazole, (b) benzotriazole, (c) tetrazole, (d) thiadiazole, (e) pyrazole, and (f) imidazole (Antonijević et al., 2009).

Their corrosion inhibition action depends, among other parameters, on pH of solution, because it may determine a corrosion mechanism, state of copper surface, as well as the state of corrosion inhibitor molecule (protonated or deprotonated). This is one of the reasons that why many efficient corrosion inhibitors for neutral media have not high enough corrosion inhibition in acidic media.

Mechanism of azole corrosion inhibitors family is similar to each other. These compounds contain nitrogen atoms, which coordinate with Cu(0), Cu(I) or Cu(II) through lone pair electrons to form protective complexes after adsorption of its molecules on copper surface (Lakshminarayanan et al., 1994). These complexes with polymeric nature, form an adherent protective film on the copper surface, which acts as a barrier to aggressive ions such as Cl⁻ (Lakshminarayanan et al., 1994).

Various derivatives of different groups of corrosion inhibitors were synthesized for corrosion protection of copper, particularly according to trial and error policy. Some of these most famous and applicable corrosion inhibitors were reviewed in this section.

2.4

2.4 Schiff bases

Recently, the Schiff base compounds have been used as effective corrosion inhibitors to prevent corrosion of copper (Ehteshamzadeh et al., 2006; Li et al., 1999a, 1999b ), aluminum (Aytaç et al., 2012; Chen and Kar, 2012; Muniandy et al., 2011; Şafak et al., 2012; Yurt and Aykin, 2011 ), and carbon steel (Chaitra et al., 2015; Gupta et al., 2016; Saha et al., 2015; Singh and Quraishi, 2016 ) in corrosive environments. The Schiff base compounds with the general formula of R₂C⚌NR are the condensation product of an amine, ketone or aldehyde (Fig. 7).

The corrosion inhibition ability of Schiff bases arises due to the presence of heteroatoms and electrons. They generally contain electronegative nitrogen and oxygen atoms, an electron cloud on aromatic ring and also a long complex chain in acidic aqueous media (Gupta et al., 2014).

Some special interactions between functional groups of schiff bases and metal’s surface that induced due to chemical structure differences play a dominant role on corrosion inhibition behavior of Schiff bases and enable them to be more effective corrosion inhibitors (with higher corrosion inhibition efficiency) in comparison with amines and aldehydes (Desai et al., 1986; Shokry et al., 1998). These interactions induced due to the presence of —C⚌N— groups in molecular structure of schiff bases. The presence of unoccupied π^∗-orbitals in their molecules that enables electron back donation from the transition metal d-orbitals and also stabilizing the existing (metal/corrosion inhibitor) bond is not possible with the amine (Atkins, 2010). Unpaired electrons and benzene ring atoms in schiff bases enable them to have more than one center of chemical adsorption action. Hence, a schiff base can form a stable chelate with copper (Zhang et al., 2010b). The corrosion inhibition action of schiff bases is the result of adsorption of their molecules on copper surface and formation of the complex with Cu⁺ and Cu²⁺ with effective blocking barrier to corrosion (Bhattacharjee et al., 2011; Ma et al., 2002). The ability to the synthesis of schiff bases from inexpensive materials makes them popular corrosion inhibitors.

2.5

2.5 Green corrosion inhibitors

Most of the existing corrosion inhibitors are toxic compounds which should be replaced with environment-friendly compounds (Fouda and Wahed, 2016). Recently, a number of studies have focused on producing and using eco-friendly drug compounds as efficient corrosion inhibitors which decrease the risk of environmental pollution (Abdallah et al., 2012; Aldana-González et al., 2015). Most of the drug and organic compounds play an important role in physiological reactions because of their antispam and antibacterial nature (Abdallah, 2004; El-Naggar, 2007; Samide et al., 2012; Zor, 2014 ). However, due to destructive effects of some corrosion inhibitors on living organism, efforts have been made to produce efficient nontoxic and eco-friendly corrosion inhibitors. These types of corrosion inhibitors usually are named as environment-friendly corrosion inhibitors or green corrosion inhibitors in relative reports (Hamdani et al., 2015; Ramdani et al., 2015). The main advantage of these compounds is their low cost. The use of natural herbs in forms of extracts, oil or pure compounds causes increase in environmental health and immunity and also makes controlling the environmental pollution to be easier. However, the green corrosion inhibitors provide low corrosion inhibition efficiency (Behpour et al., 2012; Hansen et al., 2009).

Unfortunately, most of the common corrosion inhibitors are dangerous for human and the other living organism and decreasing their risks for environment is difficult. To overcome these problems, recent efforts have been concentrated on discovering and developing new green corrosion inhibitors to replace with commercial grades. There are various safe and eco-friendly corrosion inhibitor compounds which can be called green corrosion inhibitors, but the term of green corrosion inhibitor only used for drug corrosion inhibitors and also corrosion inhibitor compounds produced from natural materials and plants.

2.5.1

2.5.1 Natural corrosion inhibitors

Among eco-friendly corrosion inhibitors, the natural materials are of special significance. The extracts of various parts of plants, which are rich source of the chemical compounds have a significant importance (Bagchi et al., 2000; Butler, 2004; Raja and Sethuraman, 2008 ). These compounds can be extracted easily using simple tools at low cost. Moreover, they provide a renewable source for corrosion inhibitors because of their good accessibility and biodegradability. Therefore, investigation to explore natural plants with corrosion inhibition nature became a matter of interest and has great practical and scientific value (Ji et al., 2015; Mehdipour et al., 2015; Odewunmi et al., 2015 ). The corrosion inhibition efficiency of plant extracts from natural plants depends on the geographical location of that plant and the place where the corrosion inhibitor is used.

2.5.2

2.5.2 Pharmaceutical compounds

The development of eco-friendly corrosion inhibitors has been highly regarded in recent years. The corrosion inhibition behavior of active pharmaceutical compounds has been widely investigated and some of these compounds have been used as corrosion inhibitors (Ahamad and Quraishi, 2010; Eddy et al., 2009; Fouda et al., 2013; Hazazi and Abdallah, 2013; Obot and Obi-Egbedi, 2008, 2010; Shukla et al., 2009 ). However, a few number of pharmaceutical compounds have been used for corrosion inhibition of copper and its alloys (Abiola et al., 2011; Eldesoky et al., 2013). The pharmaceutical corrosion inhibitors have carboxyl and heterocyclic groups in their molecular structure and most of them are eco-friendly compounds, besides that they provide high corrosion inhibition efficiency (Enick, 2006).

2.6

2.6 Amino acids

Among the organic compounds used and industrially applied as corrosion inhibitors, nontoxic compounds are strategic materials especially during recent years. These compounds include amino acids (Baba and Kodama, 1999; Moretti and Guidi, 2002), some derivatives as cysteine (Kuruvilla et al., 2013; Matos et al., 2004; Zhang et al., 2010a ), methionine (Barouni et al., 2014; Zhang et al., 2009, 2011b ), glycine (Makarenko et al., 2011), and tannin or isatin that were used for various metals as corrosion inhibitors.

The investigations, deal with corrosion inhibition of amino acids for copper, are increasing progressively. Amino acids are attractive compounds as corrosion inhibitors since they are relatively inexpensive and are easy to produce with purities more than 99% (Liu and Sibi, 2002) and they are soluble in aqueous media. Moreover, these compounds are nontoxic and non-hazardous for health and thus can be classified as environment-friendly corrosion inhibitors (Ashassi-Sorkhabi et al., 2004; Badawy et al., 2006; Ghasemi and Tizpar, 2006; Ismail, 2007 ).

Most of the natural amino acids are the alpha amino acids, which consist of carboxyl and amino-functionalized groups which bonded to the same carbon atom. According to Fig. 8, the properties of R-group in the general structure of amino acids play an important role in their nature and a change in the R-group can change the nature of amino acid. R-group can contain aromatic rings, acids, bases, polar groups, amino-functional groups and even sulfur atoms. There is a considerable variation in R-groups.

Cysteine (cys) and methionine derivatives are parts of sulfur atom containing amino acid corrosion inhibitors that show better corrosion inhibition efficiency than other amino acids in corrosive media. Recent investigations show that formation of donor–acceptor complex between corrosion inhibitors’ free electrons and vacant d orbital of metals is responsible for corrosion inhibition (Khaled, 2010; Zhang et al., 2009). The presence of functional group with high electron donor affinity in molecules’ structure in corrosion inhibitors such as —SH group in cysteine and —S—CH₃ in methionine improves corrosion inhibition efficiency. These groups act as another adsorption center beside nitrogen atom (Barouni et al., 2008; Hammouti et al., 1995).

According to the literature, corrosion inhibition action of cysteine depends on corresponding potentials of formation of ionic derivatives of Cu (Cu²⁺ or Cu⁺). Matos et al. (2004), demonstrated that the main species present on the copper surface at low anodic polarization in sulfate media is the intermediate Cu(I)_ads. So a protective layer forms in the presence of cysteine molecules as following reaction (Eq. (3)):

(3)

{Cu}^{+} + cys = Cu (I) -cys

Cu(I)–cys complex provides appropriate corrosion inhibition due to its high stability constant value (Rigo et al., 2004), but cysteine effect is not significantly high over potentials, where the Cu(II)ads is the main species present on the copper surface. It is unfavorable species for the adsorption of cysteine on copper surface. Also Cu(II)ads influences oxidation of the Cu(I)-cys complex (Quartarone et al., 2003).

2.7

2.7 Self-assembled compounds

The use of an organic corrosion inhibitor, which forms a self-assembled film and self-assembled monolayers (SAMs) on metal’s surface is one of the techniques for protection against corrosion. SAMs are organic films with high molecular order which form on metal’s surfaces by chemical adsorption. SAMs are homogenous and densely packed which can act as a barrier against the dissolution of copper (Appa Rao and Narsihma Reddy, 2014; Fouda and Wahed, 2016; Jennings et al., 2003; Ma et al., 2003b; Ulman, 1996; Wang et al., 2002 ). The ease to prepare and use, and also good persistency are some advantages of SAMs (Love et al., 2005).

3 Corrosion inhibitors efficiency evaluation methods

Several methods are used for monitoring of corrosion. Some of most widely used methods are weight loss measurement, potentiodynamic polarization measurement and electrochemical impedance spectroscopy. These methods are inseparable part of any investigation on corrosion inhibition efficiency. There are also some new methods, such as scanning electrochemical microscopy (SECM) and scanning vibrating electrode technique (SVET). In this part, usage of these methods, for study the effect of corrosion inhibitors on the corrosion phenomena is reviewed. It should be mentioned that surface analysis methods are widely used for study on the mechanism of corrosion inhibition.

3.1

3.1 Weight loss measurements

The most common and simplest method for monitoring the corrosion inhibition efficiency is weight loss. As the result of corrosion, many properties such as mass, electrical resistance, magnetic flux and mechanical properties are changed. The method of using weight loss coupon for determining corrosion damage is very useful for monitoring corrosion and also for investigating the environmental condition which cannot be simulated in laboratory. Of course this method is useful for calculating the corrosion inhibition efficiency. In this low cost method, small samples in a specific duration of time are immersed in corrosive media and then remove from that environment. Difference between mass before and after immersion is important (see ASTM G4 standard). In this method, corrosion rate is estimated by the following relationship:

(4)

R = \frac{K (W_{1} - W_{2})}{A (t_{1} - t_{2}) ρ}

where W₁ and W₂ are initial and final masses (g),

ρ

is the density, t₁ and t₂ are starting and ending times. Also K is a constant and R is corrosion rate.

3.2

3.2 Potentiodynamic–galvanostatic polarization

Since corrosion is an electrochemical process, electrochemical properties of metal/solution interface such as corrosion potential and current density of corrosion have a basic role in monitoring the corrosion. In this method, scan rate of potential or current is very important, scan rate must be slow enough, as much as possible so as to minimize the capacitance of the surface. In this technique, by applying voltage to the working electrode, the current response by varying potential from free corrosion potential is measured (McCafferty, 2011).

Corrosion inhibitors are divided into three different groups (cathodic, anodic and mix type corrosion inhibitor) based on the mechanism of corrosion inhibition (Sastri, 2012). Polarization curve for cathodic corrosion inhibitors is shown in Fig. 9. The cathodic branch of curve in the presence of cathodic corrosion inhibitor is changed.

Schematic curve for comparing the polarization of sample with and without any cathodic corrosion inhibitor.

Similarly, anodic corrosion inhibitors affect the anodic branch of the polarization curve and mix corrosion inhibitors affect both branches of the diagram (Sastri, 2012).

In many studies about the using of corrosion inhibitors for copper, investigators used these diagrams to show the effect of corrosion inhibitors on the corrosion behavior of samples. For example, as can be seen in Fig. 10, in the presence of benzotriazole, current density reduced and also the potential shifts into the anodic direction. Also benzotriazole reduced the cathodic current density significantly, and it caused that both tafel slopes to increase. So investigators suggested that benzotriazole is a mixed type corrosion inhibitor (Liu et al., 2011).

Polarization curves for copper in 17 wt.% TBAB solution in the presence of the following concentrations of BTA (g/l): (1) blank, (2) 0.1, (3) 0.5, (4) 1.0, (5) 2.0, (6) 4.0, and (7) 6.0 (Liu et al., 2011).

Wang et al. (2014a) investigated using of domperidone as a corrosion inhibitor for Copper Fig. 11 shows the polarization curves of copper without and with several concentrations of domperidone.

Potentiodynamic polarization curves for copper in 3.5 wt.% NaCl containing different concentrations of domperidone at 298 K (Wang et al., 2014a).

As can be seen in Fig. 11, potential shifts into the anodic direction and anodic current density reduced significantly, so domperidone is an anodic type corrosion inhibitor.

In another work (Deyab et al., 2015), a novel pyrophosphate is used as corrosion inhibitor for copper. The potential as can be seen in Fig. 12, shifts toward cathodic direction and also difference between potential with and without any pyrophosphate, is less than 80 mV. So this novel pyrophosphate is a mixed type corrosion inhibitor with cathodic effects. The corrosion inhibitor efficiency ( $η_{i} %$ ) is calculating by the following equation:

(5)

η_{i} % = \frac{i_{corr}^{0} - i_{corr}}{i_{corr}^{0}} \times 100

where

i_{corr}^{0}

and i_corr are the corrosion current densities without and with corrosion inhibitor.

Polarization curves for copper in the absence and presence of various concentrations of SNP in seawater in a recirculating system with a solution flow rate of 0.8 ms−1 at 298 K (Deyab et al., 2015).

3.3

3.3 Electrochemical impedance spectroscopy (EIS)

One of the most successful applications of EIS is the study of the mechanism of corrosion inhibition. Changing in R_p due to the reducing of corrosion rate and also capacitance of the electrode, due to the adsorption of corrosion inhibitor molecules can be useful for determining parameters such as corrosion inhibition efficiency. Changing in corrosion mechanism can be recognized by impedance spectra (Marcus and Mansfeld, 2005).

Gopi et al. (2009) studied on the new benzotriazole derivatives as corrosion inhibitors on copper corrosion. They used EIS tests for studying the corrosion inhibition efficiency. The Nyquist and bode plots are shown in Fig. 13.

(a) Nyquist and (b) bode plots of copper in groundwater medium with and without optimum concentration of BTA, 1-(2-thienyl carbonyl)-benzotriazole (TCBT), 1-(2-pyrrole carbonyl)-benzotriazole (PCBT), BTA + TX-100, TCBT + TX-100 and PCBT + TX-100 at 28 °C, (c) equivalent circuit of the studied system (Gopi et al., 2009).

Also the electrical equivalent circuit is presented in Fig. 13C. R_s is the solution resistance, R_P₁ and R_P₂ are polarization resistances and Q₁ and Q₂ are constant phase elements. When the values of CPE decrease, it can be suggested that corrosion inhibitor covers the surface of the metal. Also semicircles at high frequencies are related to relaxation of electrical double layer capacitors and the diameter of the high frequencies semicircles is related to the charge transfer resistant. It is important to mention that as can be seen in bode plot in the presence of corrosion inhibitors, as the corrosion inhibition efficiency increases, the Z parameter increases and in Nyquist plot in the presence of corrosion inhibitor, as the corrosion inhibition efficiency increases, the diameter of curve and also the area increases too. The corrosion inhibition efficiency in this method is calculated with the following equation:

(6)

IE % = \frac{R_{p} - R_{p}^{0}}{R_{p}} \times 100

R_P is the polarization resistance of the corrosion inhibitor and R_P is the polarization resistance of the blank sample.

3.4

3.4 Electrochemical noise method

Ramezanzadeh et al. (2014) used electrochemical noise method for evaluation of the corrosion inhibition efficiency of azole compounds on Cu in H₂SO₄ solution. They mentioned that this method is more accurate than other electrochemical methods such as EIS and DC polarization. Electrochemical noise is a suitable method without applying any external perturbation to the electrode. For calculating the noise resistance, the standard deviations from the current and voltage must be calculated from the following equations:

(7)

Q_{v} = \sqrt{\frac{\sum_{i = 1}^{n} {(V_{i} - m_{v})}^{2}}{2}} m_{v} = \frac{\sum_{i = 1}^{n} V_{i}}{n}

(8)

Q_{i} = \sqrt{\frac{\sum_{i = 1}^{n} {(I_{i} - m_{i})}^{2}}{n}} m_{i} = \frac{\sum_{i = 1}^{n} I_{i}}{n}

where Q_v, Q_i and n are standard deviations from the potential, current and total number of measurements. The noise resistance can be calculated by dividing standard deviations of potential fluctuations to the same quantity associated with current fluctuation.

This resistance is a suitable parameter for calculating the corrosion inhibition efficiency of several corrosion inhibitors. If the noise resistant increases, the corrosion is reduced and so by increasing the concentration of corrosion inhibitor (to an optimum concentration), the noise resistance must increase. For example, by increasing the concentration of BTA and Benzothiazole (BNS), the noise resistance is increased too and increase in resistance was more for BNS.

Another parameter which can be used for studying the effect of corrosion inhibitors is q (the charge in each corrosion event). It can be calculated by following equation by considering current noise signals as packets of charge in frequency domain.

(9)

q = \frac{\sqrt{ψ_{v}} - \sqrt{ψ_{I}}}{B}

where

ψ_{v}

and

ψ_{I}

are low frequencies values of PSD(V) and PSD(I) and B is the Stern–Geary coefficient. As the q increases, the charge transfer during the experiment is increased. So by increasing q, the samples suffer from the stronger corrosion attacks. Corrosion inhibition efficiency in this method can be calculated by the following equation:

(10)

ECN % = \frac{R_{n} - R_{n}^{0}}{R_{n}} \times 100

where R_n and

R_{n}^{0}

are noise resistances for inhibited and uninhibited samples.

3.5

3.5 Scanning electrochemical microscopy (SECM)

SECM is another useful method for studying the corrosion and corrosion inhibitors. In this technique a mobile ultramicroelectrode is moved on the surface and topography, and redox activity of interfaces is studied. Esmaeili et al. (2015) used this method for studying the corrosion inhibition of triazino-benzimidazole-2-thiones in HCl. First step in using this method is studying the approach curve. Approach curve is measured at the open circuit potential. This curve is used for determining the distance in which current reaches the current limit. After determining the point of current limit, SECM test will begin. In this method, the tip current in each point is recorded and corrosion inhibition efficiency is calculated by the following equation:

(11)

{IE}_{SECM} % = (\frac{i_{(\max)} - i_{(\min)}^{'}}{i_{(\max)}}) \times 100

where

i_{tip (\max)}

and

i_{tip (\min)}^{'}

are maximum current densities of the tip in the absence and presence of the corrosion inhibitor. Another data that can be taken from this method are the local concentration of the metallic ions by following equation:

(12)

I = 4 π r_{0} FDC

where n is the number of electrons transferred during the reaction, r₀ is the radius of the UME, F is the Faraday constant, C is the local concentration of metallic ions and D is the diffusion coefficient of the redox species. In the presence of corrosion inhibitors, concentration of metallic ions decreases, so it can be used as a parameter for corrosion inhibition efficiency.

3.6

3.6 Scanning vibrating electrode technique (SVET)

SVET is a new method for investigation on corrosion inhibition efficiency. The merit of SVET is that by using this method, less time and also fewer materials to study the effect of corrosion inhibitor in a selected media is needed. In this method, wire of different metals mounted and then immersed in an ideal solution. The advantage of mounting is that metals are separated from each other and do not have any electrical effect on other metals. These electrodes are immersed in solution and then left at open circuit potential. Also there is a vibrating microelectrode which amplitude in two directions above the surface of samples. SVET measures potential gradients which converts to current density after calibration. Corrosion inhibition efficiency by this method is calculated by the following equation:

(13)

IE % = \frac{I_{0} - I_{inh}}{I_{0}}

where I₀ and I_inh are the current densities in the absence and presence of the corrosion inhibitor.

In this method five parameters are used for calculating the corrosion inhibition efficiency.

(I_max AN): The maximal anodic current (flux of cations)
(I_max CAT): The maximal cathodic current
(I_int AN): Integrated anodic ionic current
(I_int CAT): Integrated cathodic current
(I_int OV): I_int AN + I_int CAT

The integrated ionic currents are calculated by the following equation:

(14)

I_{int} = \sum_{n = 1}^{N} i_{n} \cdot s_{n}

where i_n is the SVET current density measured in point n (at 100 µm above the surface), S_n is the surface area (cm²) and N is the number of data points (anodic, cathodic or overall) considered for calculation. One of the advantages of SVET is that the samples are kept in open circuit potential, so attack less in comparison with potentiodynamic tests (Kallip et al., 2010).

3.7

3.7 Surface analytical methods

Some other surface analytical methods are used for studying the mechanism of corrosion inhibition and interaction between the sample and the corrosion inhibitors. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Secondary ion mass spectrometry (SIMS), Ion Scattering spectroscopy (ISS), RAMAN spectroscopy, Fourier transform infrared (FT-IR) and laser microprobe mass analyzer (LAMMA) are the most usable methods to study about the corrosion inhibitors. In Fig. 14, some methods and their applications can be seen (Holm et al., 1989).

Some surface analysis methods and their application in study of corrosion inhibitors (Holm et al., 1989).

For example, Finšgar and Merl (2014) used XPS for studying the effect of 2-Mercaptobenzoxazole as a copper corrosion inhibitor in HCl solution. They used this method to show that atoms are involved in the surface layer on the copper using 2-Mercaptobenzoxazole and concluded that there are no Cl atoms on the surface layer and also studied the models of adsorption of this corrosion inhibitor on the surface of the copper. They also concluded that connection of Cu ions and corrosion inhibitor by N atoms cause to fabrication of complex which physisorbed to Cu by S (S atom exist in molecular structure of studied corrosion inhibitor too).

4 The adsorption of corrosion inhibitor and its isotherms

The corrosion inhibition behavior of a corrosion inhibitor depends on the adsorption behavior (Rudresh and Mayanna, 1977). The surface of metals in aqueous environments is covered by polar water molecules. The adsorption process of corrosion inhibitor molecules from the bulk of the solution on metal’s surfaces is similar to replacement of pre-adsorbed water molecules by adsorbed corrosion inhibitor molecules (Bockris and Swinkels, 1964). It is accepted that the adsorption process of an organic corrosion inhibitor on the metal’s surface involves the displacement of one or more pre-adsorbed water molecules ( $H_{2} O$ (ads)) by corrosion inhibitor molecules (Org(sol)) on metal/solution interface (Moretti and Guidi, 2002).

(15)

Org (sol) + x H_{2} O (ads) \leftrightarrow Org (ads) + x H_{2} O (sol)

where x is the number of bipolar molecules of water replaced by one corrosion inhibitor molecule. The adsorption process of corrosion inhibitor molecules on the metal’s surface can be described by two types of interactions which involve physical adsorption and chemisorption.

The physical adsorption process requires the presence of both electrically charged surface of the metal and charged species in the bulk of the solution. The presence of electrical charges on the metal’s surface is due to the presence of an electrical field in metal/electrolyte interface. On the other hand, the chemisorption involves charge sharing or charge transfer to form a coordination bond between the metal’s surface and adsorbed molecules of corrosion inhibitor. The adsorption process depends on the electrical structure of metal (electrically charged metal’s surface), the type of electrolyte and molecular structure and electrical characteristics of corrosion inhibitor (Yurt et al., 2014).

According to Fig. 15, the adsorption process of corrosion inhibitor on metal’s surface (with positive charge) may occur as follows: (a) the bipolar interaction between lone pair electrons of metal’s surface and corrosion inhibitor (for example adsorption of BTA on positively charged copper surface represented through (a) in Fig. 15), (b) electrostatic attraction between the electrically charged metal surface and corrosion inhibitor ions (for example adsorption of phosphate on positively charged copper surface represented through (b) in Fig. 15), (c) $π$ -type interaction with metal (for example adsorption of IMD on positively charged copper surface represented through (c) in Fig. 15), and (d) combination of these mechanisms (Schweinsberg et al., 1997).

Schematic illustration of adsorption process of corrosion inhibitor on metal’s surface.

The high corrosion inhibition efficiency of a corrosion inhibitor needs proper thermodynamically and kinetically conditions. The adsorption process of corrosion inhibitor depends on various parameters such as temperature, concentration, the nature of the metal’s surface, electronic and structural properties of corrosion inhibitor.

The corrosion inhibition efficiency of organic corrosion inhibitor compounds depends strongly on their adsorption behavior. The nature of interaction between the surface of metal and corrosion inhibitor molecules can be discussed obviously using various adsorption isotherm models (Khaled, 2008). Understanding adsorption isotherm plays a dominant role in the explanation of adsorption process, because it gives some crucial information about the adsorption process. This information can be used to determine the standard value of adsorption free energy and their relation to surface coverage, the properties of adsorbed layer at metal/electrolyte interface, and properties of interaction between the adsorbate molecules and interaction between metal’s surface atoms and adsorbate molecules.

Over the years, various equilibrium adsorption isotherms such as Langmuir, Freundlich, and Flory-Huggins have been formulated. In this study, some of them that used for corrosion inhibition of copper have been pointed out briefly.

To have a deep understanding of adsorption mechanism, the adsorption isotherm is determined using evaluation of the surface coverage (θ) as a function of corrosion inhibitor concentration (C) and obtaining the best correlation between extracted data and proposed isotherm models. Surface coverage is determined by weight loss, polarization and impedance methods according to the following equation (Eq. (16)):

To calculate the degree of surface coverage in weight loss method (Bastidas, 2006; Lewis, 1981), EIS method (Youda et al., 1990) and polarization curves (Ehteshamzade et al., 2006) Eq. (16) is used

(16)

θ = \frac{(w - w_{0})}{w_{0}} = \frac{(R_{t (inh)} - R_{t})}{R_{t}} = \frac{(J_{corr} - J_{corr (inh)})}{J_{corr}}

where: $w_{0}$ = weight loss value in the absence of corrosion inhibitor (calculated by WL method)
w = weight loss value in the presence of corrosion inhibitor (calculated by WL method)
$R_{t (inh)}$ = charge transfer value in the presence of corrosion inhibitor (calculated by EIS method)
$R_{t}$ = charge transfer value in the absence of corrosion inhibitor (calculated by EIS method)
$J_{corr (inh)}$ = corrosion current density value in the presence of corrosion inhibitor (calculated by PP method)
$J_{corr}$ = corrosion current density value in the absence of corrosion inhibitor (calculated by PP method)

The surface coverage value for a corrosion inhibitor has usually a direct dependency to its corrosion inhibition efficiency, but it may be affected by more phenomena (Cao, 1996). In general, the degree of surface coverage (θ) can be obtained from corrosion inhibition efficiency values extracted from weight loss, polarization and EIS measurements as follows:

(17)

θ = E / 100

In following the most important proposed models for the adsorption process of corrosion inhibitors are discussed briefly.

4.1

4.1 Langmuir adsorption isotherm

In Langmuir isotherm, it is assumed that the adsorbed layer on the metal’s surface has a thickness equal to one molecule diameter and the adsorption process can be occurred on a fixed number of particular local sites (Foo and Hameed, 2010). These localized equilibrium adsorption sites are similar and there are no interactions or vacant places among molecules adsorbed regularly on these sites. Therefore, it can be concluded that Langmuir adsorption isotherm is valid for homogeneous adsorption processes. In this case, the adsorbates have a similar adsorption enthalpy and free energy due to this fact that the adsorption tendency is same for all sites (Kundu and Gupta, 2006). Moreover, each site holds only one adsorbate because it has been reached to the equilibrium state and adsorption would not continue at this preoccupied site.

In each case, the surface coverage values extracted from experimental data will compare with proposed model for adsorption isotherm. Langmuir isotherm, which has a good fit with experimental data, can be given as Eq. (18):

(18)

K_{ads} C = \frac{θ}{1 - θ}

where θ is the fractional surface coverage by corrosion inhibitor molecules,

K_{ads}

is the equilibrium constant for adsorption process and C is the concentration of corrosion inhibitor. Eq. (18) can be rearranged as the following equation in order to show the relation of surface coverage and corrosion inhibitor concentration schematically

(19)

\frac{C}{θ} = C + \frac{1}{K}

The surface coverage values were plotted as a function of the corrosion inhibitor concentration and then different adsorption isotherms were compared to experimental data to find the best suitable adsorption isotherm. Fig. 16 shows the Langmuir adsorption isotherm for adsorption of Purine and Adenine corrosion inhibitors on copper surface. Surface coverage values have been extracted from weight loss measurements (Scendo, 2008).

The Langmuir adsorption plots obtained from weight loss data for copper in 0.5 M NaNo3 solution in the presence of various concentrations of (a) purine and (b) adenine corrosion inhibitors (Scendo, 2008).

According to Fig. 16, a good correlation has been obtained which is understandable from lines with the slopes near to one. The value of $K_{ads}$ parameter which is the equilibrium constant of adsorption process can be obtained from the slope of the lines.

The good proportionality of experimental data with Langmuir isotherm denotes to this fact that adsorption of mentioned corrosion inhibitors obeys Langmuir adsorption isotherm (Scendo, 2008).

4.2

4.2 Freundlich adsorption isotherm

It is well known that Freundlich isotherm describes the nonideal and reversible adsorption process in which the thickness of adsorbed layer may exceed from a monolayer thickness. This experimental model can be used for interpretation of multilayer adsorption process. In this case, there is a heterogeneity in the distribution of active sites and their adsorption energies (Adamson and Gast, 1997; Zeldowitsch, 1934). It can be said that the adsorption energies are equal to the total of adsorption energies of adsorption sites with binding energy. Initially, the adsorption sites with stronger bonds will be occupied which in turn leads to an exponential decrease in adsorption energy due to finishing adsorption process (Zeldowitsch, 1934). The Freundlich adsorption isotherm is widely used in heterogeneous systems, particularly for organic compounds.

With regard to Freundlich adsorption isotherm the degree of surface coverage by corrosion inhibitor species is related to corrosion inhibitor concentration as following (Eq. (20)):

(20)

θ = {kC}^{(1 / n)}

If the logarithmic values of surface coverage will plot as a function of logarithmic concentration values of corrosion inhibitor (as seen in Fig. 17), the variation of log θ versus log C by slope of n indicates that adsorption of corrosion inhibitor obeys Freundlich isotherm. Fig. 17 shows the variation of surface coverage with respect to concentration of Morinda tinctoria leaf extract (used as corrosion inhibitor) at different temperatures (Krishnaveni and Ravichandran, 2015) as an example of Freundlich adsorption isotherm.

Freundlich adsorption isotherm for adsorption of green inhibitor (extract of Morinda tinctoria leaf) on the surface of copper at different concentration in 0.25 M H2SO4 solution (Krishnaveni and Ravichandran, 2015).

4.3

4.3 Langmuir-Freundlich adsorption isotherm

Langmuir-Freundlich (LF) adsorption isotherm which is known as a Sips equation, is a mixed adsorption isotherm. This adsorption isotherm, which has some properties of Langmuir and Freundlich isotherms, has been obtained from the combination of three parameters in an experimental equation (Eq. (21)). According to Eq. (21), the degree of surface coverage is in direct and indirect relation to exponential values with concentration of corrosion inhibitor (as shown by (KC)^h in nominator and denominator) which make it possible to study adsorption processes in a vast range of concentration in both equilibrium and non-equilibrium conditions (Gimbert et al., 2008).

(21)

θ = \frac{{(KC)}^{h}}{1 + {(KC)}^{h}}

where K is the equilibrium constant and h is the non-homogeneity parameter that its value varies between zero and one. The non-homogeneity parameter indicates the distribution of adsorption energy on a heterogeneous surface. In this case, the interactions between the corrosion inhibitor molecules will be regarded.

The LF adsorption isotherm can be used in modeling the adsorption behavior of heterogeneous systems such as adsorption of gas molecules on the surface or adsorption of metallic ions in natural samples (Erdem et al., 2004; Furukawa et al., 2007). With regard to Eq. (21), the LF adsorption isotherm model becomes Freundlich model for low concentration of species in each system. Therefore, LF can be used for modulation of adsorption process for both heterogeneous and homogeneous surfaces.

In each study, if a good proportionality is obtained between experimental data and above mentioned equation, it can be argued that the adsorption process obeys Langmuir-Freundlich adsorption isotherm.

4.4

4.4 Temkin adsorption isotherm

Temkin adsorption isotherm contains a factor that obviously considers the adsorbent–adsorbate interactions. This model by ignoring very low and very high concentration, assumes that the adsorption heat of all adsorbate molecules in adsorbed layer (which is a temperature dependent parameter) decreases linearly with an increase in the surface coverage (Dada et al., 2012). In each case, different adsorption isotherms are evaluated to find the best suitable isotherm with data obtained from experimental tests. The Temkin adsorption isotherm is given as following equation (Deyab and El-Rehim, 2013):

(22)

\exp (- 2 a θ) = K_{ads} C_{inh}

where

C_{inh}

indicates the concentration of corrosion inhibitor in solution, a is the parameter of lateral interaction between the adsorbates molecules which is a good indicator of non-homogeneity of surface, and also

K_{ads}

is equilibrium constant of adsorption. To simplify Eq. (22), it can be rearranged as follows:

(23)

θ = (2.303 / a) (\log K_{ads} + \log C_{inh})

If the surface coverage values are plotted versus logarithmic values of corrosion inhibitor concentration (as shown in Fig. 18), the variation of θ versus (log C) with a slope of 2.303/a indicates that adsorption of corrosion inhibitor obeys Temkin adsorption isotherm. Fig. 18 shows the variation of surface coverage as a function of various concentrations of N-(3-methoxyphenylaminomethyl) phthalimide, N-(3-methylphenylaminomethyl) phthalimide and N-(phenylaminomethyl) phthalimide corrosion inhibitors for copper (Fouda et al., 2006) as example of Temkin adsorption isotherm.

The variation of surface coverage (θ) versus log C for three derivatives of phatalimide after 1 h immersion time in temperature of 30 °C (Fouda et al., 2006).

4.5

4.5 Flory-Huggins adsorption isotherm

The Flory-Huggins model is sometimes used for interpretation of adsorption process of corrosion inhibitor molecules. θ parameter shows the degree of surface coverage (Vijayaraghavan et al., 2006). The equation of Flory–Huggins adsorption isotherm is given as follows (Flory, 1942):

(24)

\frac{θ}{x {(1 - θ)}^{x}} = K_{ads} C

where

K_{ads}

is equilibrium constant of adsorption, x is the number of water molecules replaced by corrosion inhibitor species and C indicates the concentration of corrosion inhibitor in solution. The thermodynamic-kinetic model of Flory–Huggins adsorption isotherm is also given as following equation:

(25)

\log [θ / (x {(1 - θ)}^{x})] = \log K^{'} + y \log C

As seen in Eq. (25), the parameter of y shows the number of molecules, each occupied an active site. $K^{'}$ value can be calculated from Eq. (26) which relates K and y parameters as follows:

(26)

K = K^{' (1 / y)}

Fig. 19 shows the Flory–Huggins adsorption isotherm for the adsorption of pantoprazole sodium at various acidic solutions on the copper surface (Saadawy, 2016). As seen, the Flory–Huggins adsorption isotherm model was not a proper model to justify the adsorption behavior of corrosion inhibitors in HCl and HClO₄ acidic solutions. However, the experimental data were fitted very well with Langmuir adsorption isotherm. The extracted results indicated that the adsorption process of corrosion inhibitor in H₂SO₄ solution on copper surface can be interpreted very well using Flory–Huggins model (Saadawy, 2016).

Flory–Huggins adsorption isotherm for adsorption of pantoprazole sodium inhibitor at various acidic solutions on the copper surface (Saadawy, 2016).

4.6

4.6 Frumkin adsorption isotherm

The adsorption process of corrosion inhibitor may be interpreted using Frumkin adsorption isotherm, which is given as following equation:

(27)

KC = \frac{θ}{1 - θ} e^{- f θ}

where C is the concentration of corrosion inhibitor in the bulk of the solution, θ is degree of surface coverage, f is the constant of attraction and K is the equilibrium constant of adsorption which is directly related to free energy.

The value of f parameter depends on the interaction between the adsorbed molecules and the metal’s surface and also on the degree of surface heterogeneity. This parameter differentiates between Langmuir and Frumkin equations. The positive values of f parameter imply attractive interactions in which the slope of Frumkin equation is more than that of Langmuir equation (Khamis et al., 1995). Moreover, the repulsive interactions deduce from negative values of f parameter and lower slope of Frumkin equation in comparison with Langmuir equation. Therefore, in comparison with Langmuir equation, the slope in the Frumkin equation is modified by a constant f value. Fig. 20 indicates the surface coverage of copper surface as a function of logarithmic concentration values of dithiouracil (DTUr) corrosion inhibitor in NaCl solution. According to Fig. 20, the adsorption of DTUr corrosion inhibitor on copper surface obeys Frumkin adsorption isotherm (Dafali et al., 2003).

The Frumkin isotherm for adsorption of dithiouracil (DTUr) on copper surface in NaCl solution (Dafali et al., 2003).

Several models have been proposed for interpretation of adsorption process, however, as mentioned above, this article focusses on some of these models used for the adsorption process of corrosion inhibitors on copper surface. With regard to proposed models, this is well known that increase in concentration of corrosion inhibitor in the bulk of the solution (to an optimum concentration) causes to increase the degree of surface coverage. The increase in temperature and hydrodynamic flow rate may reduce the degree of surface coverage due to desorption of adsorbed molecules from the surface.

4.7

4.7 Adsorption energy

The adsorption free energy is another important information which can be obtained from adsorption models according to Eq. (28). From the intercept or slope of the straight lines on the different plots for various adsorption models, the equilibrium constant of adsorption can be calculated which is related to adsorption free energy, as given by Eq. (28).

(28)

Δ G_{ads}^{0} = - RT \ln (55.5 K_{ads})

However, if the adsorption free energy is obtained from thermodynamic data, the constant of adsorption can be calculated using the following equation:

(29)

K_{ads} = (1 / 55.5) \exp ((- Δ G_{ads}^{0}) / RT)

The value of 55.5 in Eq. (29), indicates the concentration of water in the solution expressed in molar (mol/l) (Flis and Zakroczymski, 1996).

Large values of $K_{ads}$ imply better corrosion inhibition efficiency due to stronger interaction between the metal’s surface and adsorbed molecules in electrical double layer. The low corrosion inhibition efficiency and interaction of adsorbed corrosion inhibitor species and metal’s surface can be deduced from small values of $K_{ads}$ . In this case, the adsorbed corrosion inhibitor molecules on the metal’s surface can be easily replaced with solution molecules (Khalil et al., 2003).

This is generally accepted that the value of $Δ G_{ads}^{0}$ around −20 kJ/mol or less negative values implies the electrostatic interaction between charged metal’s surface and charged corrosion inhibitor species which indicate a physisorption process. The value of $Δ G_{ads}^{0}$ around −40 kJ/mol or more negative values indicate a chemisorption process in which a charge sharing or charge transfer is occurred to form a coordination bond between the metal’s surface and corrosion inhibitor species (Chadwick and Hashemi, 1977).

5 Corrosive environments for copper

In this section, the investigated corrosive environments for copper and the corrosion inhibitors used for protection of copper in these conditions have been reviewed on the basis of the corrosive environments (acidic, basic and neutral environments).

The corrosion inhibition efficiency of corrosion inhibitors strongly depends on the temperature, concentration of corrosion inhibitor, pH and generally on the condition of the corrosive environment and type of corrosion inhibitor. There is a lot of information about corrosion inhibition efficiency in the literature. Therefore, this paper focuses on the maximum corrosion inhibition efficiency reported for each inhibitor in the studied environment.

5.1

5.1 Copper in acidic environments

According to the literature, many studies have been conducted on the corrosion of copper in acidic media. The corrosion inhibitors in acidic environments (sulfuric acid, hydrochloric acid, phosphoric acid) are commonly used to reduce corrosion attacks in cleaning and descaling processes.

The corrosion products (scales and precipitates) have an attenuator effect on performance of the systems (such as heat exchangers) and decrease their efficiency. To overcome these problems, the scales and precipitates are removed from surface of metal using acid pickling process with HCl or H₂SO₄ solutions. The acid pickling is used in various processes such as acid cleaning of metals and scale removal from metal’s surface, and acidification of oil wells (Ravichandran et al., 2004). Acid cleaning process is commonly used for removing scales and oxides from the surface of metals, however some of the other processes such as galvanizing, coloring, electroplating and cold rolling can be also used for this purpose (Deng et al., 2013).

The absence of depolarizing agents (such as oxygen) in non-oxidizing acids decreases the corrosion rate of copper. Therefore, the corrosion rate of copper in HCl (particularly in moderate concentration) is higher than H₂SO₄ which is due to the formation of soluble compounds such as CuCl²⁻. On the other hand, oxidizing acids such as nitric acid and chromic acid increase the corrosion rate of copper. The presence of oxygen in the acidic solution causes increase in the corrosion attacks on copper surface. In this case, the total corrosion reaction of copper is as follows:

(30)

2 Cu + 4 H^{+} + O_{2} = 2 {Cu}^{2 +} + 2 H_{2} O

However, the corrosion rate of copper does not increase linearly with an increase in oxygen content, probably due to the formation of a protective layer on copper surface (Sathiyanarayanan et al., 2013).

The literature dealing with corrosion inhibition of copper in acidic media on the basis of acid types has been reviewed briefly in the following section.

5.1.1

5.1.1 Sulfuric acid solution

Sulfuric acid is a strong acid with polar molecules in its structure which can bind to each other by hydrogen bonding. This compound is completely soluble in water. Sulfuric acid is used in detergents, painting colors, etc. Various corrosion inhibitor compounds such as azole and amine derivatives, and green corrosion inhibitor have been evaluated for corrosion inhibition of copper in aggressive sulfuric acid media and the corrosion inhibition efficiency of various concentrations of these corrosion inhibitors reported in Table 1. Among industrial acids, only nitric and sulfuric acids have enough oxidizing agent for dissolution of copper. The corrosion reaction of copper in sulfuric acid is as follows:

(31)

Cu (s) + 4 H^{+} (aq) + {SO}_{4}^{2 -} (aq) \to {Cu}^{2 +} (aq) + {SO}_{2} (g) + 2 H_{2} O (l)

Table 1 The results of the study of the efficiency of copper corrosion inhibition in sulfuric acid.

Inhibitor group	Inhibitor	Concentration	Solution	Condition	Adsorption isotherm	Efficiency (%)			Ref
Azole	Pantoprazole sodium	2.5 mM	0.5 M H₂SO₄	303 K	Flory–Huggins	95.1 pp	90.0 EIS		(Saadawy, 2016)
	Benzotriazole (BTA)	600 ppm	1.0 M H₂SO₄		Langmuir	87 pp	90 EIS	92 EN	(Ramezanzadeh et al., 2014)
	Benzothiazole (BNS)	600 ppm	1.0 M H₂SO₄		Langmuir	95	96	97	(Ramezanzadeh et al., 2014)
	Benzotriazole (BTA)	10 mM	0.1 M H₂SO₄	283–298 K		98 pp			(Sameh et al., 2010)
	Benzotriazole (BTA)	10 mM	0.1 M H₂SO₄	100–400 rpm		98 pp			(Sameh et al., 2010)
	2-Mercaptobenzoimidazole (2-MBI) + sodium dodecylbenzenesulfonate (SDBS) SDBS + 2-MBI	0.5 mM 2-MBI	0.5 M H₂SO₄		Langmuir	93 pp	96.77 EIS		(Hosseini et al., 2008)
		0.1 mM 2-MBI + 0.1 mM SDBS	0.5 M H₂SO₄		Langmuir	96 pp	96.80 EIS		(Hosseini et al., 2008)
	5-Phenyl-2-amino-1,3,4-thiadiazole (APT)	6 mM	0.5 M H₂SO₄		Langmuir	87.1 pp	74.3 EIS		(Tang et al., 2009)
	5-(4-Methoxyphenyl)-2-amino-1,3,4-thiadiazole (AMPT)	6 mM	0.5 M H₂SO₄		Langmuir	90.0	86.7		(Tang et al., 2009)
	1-(p-Tolyl)-4-methylimidazole	0.05 M	0.5 M H₂SO₄		Freundlich	86.00 pp			(Stupnišek-Lisac et al., 2002)
	1-Phenyl-4-methylimidazole	0.50 M				94.30 pp
	4-Methyl-5-hydroxymethylimidazole	0.30 M				65.40 pp
	2-Mercapto benzimidazole (MBI) + KI	1 mM MBI	0.5 M H₂SO₄			74.20 wl			(Zhang et al., 2003)
	2-Mercapto benzimidazole (MBI) + KI	0.75 mM MBI + 0.25 mM KI	0.5 M H₂SO₄			95.30 wl
	Benzotriazole (BTA) + KI	10⁻³ M BTA	0.5 M H₂SO₄			58.20 wl
	Benzotriazole (BTA) + KI	0.5 mM BTA + 0.5 mM KI	0.5 M H₂SO₄			67.60 wl
	5-Methyl-2,4-dihydropyrazol-3-one (MHPO)	1 mM	0.1 M H₂SO₄	After 21 days	Langmuir	88.8 EIS	64.7 Wl		(Díaz-Gómez et al., 2014)
	5-Methyl-2-phenyl-2,4-dihydropyrazol-3-one (MPPO)	1 mM	0.1 M H₂SO₄	After 21 days	Langmuir	94.7 EIS	76.47 Wl
	Cyproconazole	1 mM	0.54 mol/L H₂SO₄, 70 ppm Cl⁻ and 0.8 mol/L CuSO₄	293 K		99.9 pp	98.3 EIS		(Li et al., 2014b)
	1-Phenyl-3-hydroxy-1,2,4-triazole	1 mM	0.54 mol/L H₂SO₄, 60 ppm Cl⁻ and 0.88 mol/L CuSO₄			97.7 PP	92.5 EIS		(Li et al., 2014b)
	Nitrotetrazolium blue chloride (NTBC)	1000 ppm	0.1 M H₂SO₄			78.55 PP	90.24 EIS		(Liu et al., 2014)
	5-Methyl-1H-benzotriazole (MBTAH) + potassium sorbate + gelatin	1 g/dm³ MBTAH	0.98 g/dm³ H₂SO₄		Langmuir	87.4 PP			(Tasic et al., 2016)
		1 g/dm³ MBTAH + 1 g/dm³ 20.0 g/dm³ gelatin				95.6 PP
		1 g/dm³ MBTAH + 1 g/dm³ 20.0 g/dm³ potassium sorbate				98.8 PP
Thioles	Benzenethiol SAMs	BT	SAM form in 5 mM solution ethanol, during 1 h	0.5 M H₂SO₄		Langmuir	74.39 pp	74.10bEIS	(Tan et al., 2006)
		4-IP-BT					86.47 pp	90.60 EIS
		4-M-BT					82.53 pp	89.10 EIS
		4-F-BT					80.53 pp	87.10 EIS
		4-AA-BT					66.01 pp	82.60 EIS
		4-A-BT					53.51 pp	76.80 EIS
		3-A-BT					60.25 pp	78.00 EIS
		2-A-BT					72.30 pp	80.40 EIS
Amino acids	Tryptophan (Trp)	0.01 M	0.5 M H₂SO₄	303 K	Bockris–Swinkel	93.40 pp			(Moretti and Guidi, 2002)
	Valine	50 mM	0.5 M H₂SO₄			74.10 pp	72.00 EIS		(Amin and Khaled, 2010)
	Alanine					74.90 pp	73.00 EIS
	Glycine					90.90 pp	92.00 EIS
	Tyrosine					97.90 pp	96.80 EIS
Amin	N-5-chloro-2-furfuryl-p-toluidine		0.5 M H₂SO₄			81.00 pp			(Stupnisek-Lisac et al., 2000)
Amin	N-5-bromo-2-furfuryl-p-toluidine					84.00 pp			(Stupnisek-Lisac et al., 2000)
Schiff bases (self assemble)	Self-assembled films of N,N′-ethylen-bis(salicylidenimine) (S-E-S)	300 ppm	0.5 M H₂SO₄	Exposure time,:30 min	Langmiur	78.00 pp	92.00 EIS		(Ehteshamzade et al., 2006)
Schiff bases (self assemble)	Self-assembled films of N,N′-ortho-phenylenbis(salicylidenimine) (S-o-ph-S)	300 ppm	0.5 M H₂SO₄	Exposure time,:30 min	Langmiur	96 EIS			(Ehteshamzade et al., 2006)
Natural products (green inhibitor)	Morinda tinctoria (leaves extract)		M H₂SO₄ 0.25		Freundlich	Less than 60%			(Krishnaveni and Ravichandran, 2015)
	Azadirachta indica (commercial leaves extract powder form)	1 g/dm³	0.5 M H₂SO₄		Frumkin	86.40 pp			(Valek and Martinez, 2007)
	Cannabis (extract of the flowering tops of plants(	25 ppm	0.5 M H₂SO₄		Langmiur and Flory-Huggins	96.00 pp	91.00 EIS		(Abd-El-Nabey et al., 2013)
	Myrtus communis	100 g/l	0.5 M H₂SO₄		Langmuir	88.5 pp	90.7 EIS		(Bozorg et al., 2014)
Schiff bases	2-((E)-(2-methoxy-4-nitrophenylimino)methyl)phenol + BTA	150 ppm	0.5 M H₂SO₄		Langmuir	83.04 pp	93 EIS	89.93 wl	(Dadgarinezhad and Baghaei Ravari, 2015)
Schiff bases	2-((E)-(2-methoxy-4-nitrophenylimino)methyl)phenol + BTA	150 ppm 2-((E)-(2-methoxy-4-nitrophenylimino)methyl)phenol + 10 ppm (BTA)	0.5 M H₂SO₄		Langmuir	90.86	97	95.56	(Dadgarinezhad and Baghaei Ravari, 2015)
Self-assembled monolayer	Phytic acid (PA) + KI	0.1 mM PA	0.5 M H₂SO₄	After 4 h			84.5		(Shen et al., 2014)
Self-assembled monolayer	Phytic acid (PA) + KI	0.1 mM PA + 5 mM KI	0.5 M H₂SO₄	After 4 h		89.9 pp	90 EIS		(Shen et al., 2014)
Other	Rhodanine (Rdn) + KI	10 mM Rdn	0.5 M H₂SO₄	After 1 h		98.8 EIS			(Solmaz et al., 2011)
		10 mM KI				97.3 EIS
		10 mM KI + 10 mM Rdn				99.9 EIS
Pharmaceutical drug (green inhibitor)	Ciprofloxacin	1 mM	0.5 M H₂SO₄		Langmuir	88 pp	96 EIS		(Thanapackiam et al., 2016)
Other (surfactant)	Cetyl trimethylammonium bromide (CTAB)	10⁻⁴ M	0.5 M H₂SO₄	After 2 h	Langmuir	97.6 EIS			(Ma et al., 2001)
		10⁻³ M				97.9 EIS
		5 × 10⁻³ M				98 EIS
		10⁻² M				97.6 EIS
Carboxylic acids	Indole-3-carboxylic acid (ICA)	2 mM	0.5 M H₂SO₄		Langmuir	81 pp	89 EIS		(Quartarone et al., 2008)
Other (surfactant)	Cetyl trimethylammonium bromide (CTAB)	10⁻⁴ M	0.5 M	2 h		97.6 EIS			(Ma et al., 2003a)
	Sodium dodecyl sulfate (sds)					93.8 EIS
	Sodium oleate					95.3 EIS
	Polyoxyethylene sorbitan monooleate					93.2 EIS
Other	Poly(m-phenylenediamine) (PMPD) film	0.15 M MPD 0.2 M sodium oxalate electrochemical synthesis	0.1 M H₂SO₄	After 24 h		90.69 EIS			(Duran et al., 2012)
Other	Indole	5 × 10⁻³ M	0.5 M H₂SO₄	298 K	Frumkin	95.9			(Quartarone et al., 1998)

In this section, the studies on the corrosion inhibition of copper in sulfuric acid are reviewed. Liu et al. (2014) investigated the corrosion inhibition of nitrotetrazolium blue chloride (NTBC) for copper in 0.1 M H₂SO₄ solution using electrochemical methods, surface analysis and molecular dynamics (MD) simulations. The evaluation of extracted results from EIS and potentiodynamic polarization measurements performed to determine the corrosion inhibition efficiency of this compound for copper in mentioned aggressive media. With regard to EIS curves, the formation of a protective layer on copper surface in the presence of NTBC corrosion inhibitor increased its corrosion resistance.

The corrosion of copper in 0.1 M H₂SO₄ solution in the presence of various concentrations of NTBC corrosion inhibitor was studied. The obtained results from polarization curves (as seen in Fig. 21) are in good agreement with EIS results. According to Fig. 21, the increase in corrosion inhibitor concentration results in a further drop in the corrosion current density values which indicate the increase in corrosion resistance of copper.

Tafel polarization curves for copper immersed in 0.1 M H2SO4 in the absence and presence of various concentrations of NTBC inhibitor (Liu et al., 2014).

Fig. 22 indicates the surface morphology of copper exposed to H₂SO₄ solution in the absence and presence of NTBC corrosion inhibitor (at various concentrations). This is obvious that the presence of corrosion inhibitor in the solution results in a considerable decrease in the corrosion attacks on the copper surface. According to electrochemical tests and surface analysis, the authors concluded that 500 ppm is the optimum concentration of NBTC corrosion inhibitor for protection of copper in 0.1 M H₂SO₄ solution. The results of chemical quantum calculations indicated that nitrogen atoms in IMD rings and oxygen atoms in carbon ring act as the most active sites for adsorption and attachment to the copper surface (Liu et al., 2014).

SEM micrographs of copper foils after 24 h immersion into 0.1 M H2SO4 containing (a) 0 ppm, (b) 100 ppm, (c) 200 ppm, (d) 500 ppm and (f) 1000 ppm NTBC inhibitor at room temperature (Liu et al., 2014).

Krishnaveni and Ravichandran (2015) confirmed the corrosion inhibition effectiveness of Morinda tinctoria leaves extract (as aqueous extract (AE)) for copper in 0.25 M H₂SO₄ using weight loss and electrochemical methods. Morinda tinctoria belongs to the family of Rubiaceae herbs which have pharmaceutical properties. The obtained results from electrochemical measurements revealed that Morinda tinctoria acts as a mixed-type corrosion inhibitor and decreases both of anodic and of cathodic reaction rates. The evaluation of Nyquist plots (Fig. 23) of copper sample in 0.25 M H₂SO₄ in the absence and presence of corrosion inhibitor revealed that the increase in corrosion inhibitor concentration (to an optimum concentration) improves the corrosion inhibition efficiency. From Fig. 23, the radius of Nyquist plots increases by increase in corrosion inhibitor concentration, however the change in corrosion inhibitor concentration has a negligible effect on the shape of Nyquist plots. This implies formation of a protective layer on the copper surface and also indicates that corrosion of copper in this condition is controlled by a charge transfer process.

Nyquist plots for copper in 0.25 M H2SO4 with various concentrations of AE inhibitor (Krishnaveni and Ravichandran, 2015).

The increase in temperature has an attenuator effect for corrosion inhibition efficiency. The adsorption of AE corrosion inhibitor on copper surface obeys Freundlich isotherm. Since the corrosion inhibition efficiency of corrosion inhibitor didn’t reach to 80% in any studied condition, the authors claimed that AE corrosion inhibitor is not a proper compound for the protection of copper surface from corrosion attacks in acidic media. The surface analysis results also proved above mentioned claim. The evaluation of surface morphology of copper in H₂SO₄ solution with different concentrations of corrosion inhibitor with SEM images (as shown in Fig. 24) revealed the negligible effectiveness of corrosion inhibitor on the protection of copper (Krishnaveni and Ravichandran, 2015).

SEM images of (a) polished copper, (b) copper in H2SO4 solution and (c) copper in H2SO4 solution containing AE inhibitor (Krishnaveni and Ravichandran, 2015).

The obtained results of researches on the corrosion inhibition effect of different corrosion inhibitors are used for protection of copper in sulfuric acid given in Table 1.

Due to the results in Table 1, it should be mentioned that using Azol group inhibitors in H₂SO₄ is suggested and also using BNS, BTA and cyproconazole the maximum corrosion inhibition can be reached.

5.1.2

5.1.2 Nitric acid solution

The corrosion of copper in nitric acid results in generation of Cu²⁺ ions which transfer from copper surface into the bulk of the solution. Since the corrosion products and precipitates cannot form a protective layer on copper surface in such aggressive media, it is expected that copper dissolution reaction will be the dominant electrochemical reaction. Joseph and Joseph (2011) discussed the electrochemical reactions for copper in nitric acid as follows:

Anodic reaction:

(32)

Cu \to {Cu}^{2 +} + 2 e^{-}

Cathodic reaction:

(33)

O_{2} + 4 H^{+} + 4 e^{-} \to 2 H_{2} O

Besides, the nitrate ions are readily reduced:

(34)

{NO}_{3}^{-} + 4 H^{+} + 3 e^{-} \to NO + 2 H_{2} O

(35)

{NO}_{3}^{-} + 4 H^{+} + 2 e^{-} \to {HNO}_{2} + H_{2} O

Since the oxidizing power of nitric acid is higher than sulfuric acid, the dissolution rate of copper and thus the concentration of Cu(II) ions in nitric acid is higher.

Copper has a strong tendency to corrode in oxidizing acids such as HCl and HNO₃. The corrosion resistance of copper decreases by increase in corrosivity of solution. Organic and inorganic corrosion inhibitors, azole and its derivatives, Schiff bases, natural products such as green corrosion inhibitors and pharmaceutical drugs are used as corrosion inhibitors for protection of copper in HNO₃ solution.

Savita et al. (2016) investigated the corrosion inhibition effectiveness of Vitex negundo (VN) (Verbenaceae family), Adhatoda vasica (AV) (Acanthaceae family) and Saraka asoca (SA) (Caesalpiniaceae family) leaves extract for corrosion of copper in 3 M HNO₃ solution. The molecular structure and the properties of these corrosion inhibitors are presented in Table 2. The results indicated that an increase in the concentration of corrosion inhibitor in the bulk of the solution (to an optimum concentration) improves the corrosion inhibition efficiency. The evaluation of polarization curves revealed that these corrosion inhibitor compounds have a mix corrosion inhibition nature, near to cathodic corrosion inhibition behavior. It is reported that adsorption of these compounds is a spontaneous process and follows Langmuir adsorption isotherm. AFM images of the copper surface (as shown in Fig. 25) revealed that the presence of corrosion inhibitor compounds in acidic solution decreases the corrosion rate of the copper through formation of a protective layer on its surface. The effect of temperature on corrosion inhibition behavior was also evaluated and the obtained results indicated that corrosion inhibition efficiency decreases by the increase in temperature from 35 to 55 °C.

Table 2 The molecular structure and abbreviation sign of the main components of investigated leaves extract (Savita et al., 2016).

Leaf extract	Major component	Abbreviation
VN	5-Hydroxy-2-(3-hydroxy-4-methoxyphenyl)-3,6,7-trimethoxychromen-4-one	HMPMC
SA	3,4,5 Trihydroxy benzoic acid	HBA
AV	1,2,3,9-Tetrahydropyrrolo[2,1-b] quinazolin-3-o	THPQ

The AFM images of (a) polished copper surface, (b) copper in 3 M HNO3 solution and (c–e) copper in 3 M HNO3 solution with 0.1 g/L VN, SA and AV, respectively (Savita et al., 2016).

Abdallah and Shalabi (2015) studied the corrosion inhibition behavior of Euphorbia helioscopia linn (EHE) extract on corrosion of copper in 1 M HNO₃ solution using polarization and EIS methods. The extracted results from polarization curves revealed that this corrosion inhibitor behaves as a mix-type corrosion inhibitor; however, cathodic reaction is more influenced. They also investigated the effect of temperature and concentration of corrosion inhibitor and reported that an increase in concentration of corrosion inhibitor (to an optimum concentration) leads to increase in corrosion inhibition efficiency, while the increase in temperature decreased the corrosion inhibition efficiency. They claimed that adsorption of this corrosion inhibitor on copper surface obeys Langmuir isotherm. The effectiveness of Hyoscyamus muticus (HME) extract as a green corrosion inhibitor for copper in 1 M HNO₃ solution has been also evaluated. The adsorption process of this compound on copper surface followed Langmuir adsorption isotherm and the maximum corrosion inhibition efficiency reached about 90.45% at concentration of 500 ppm in 25 °C. This is also reported that corrosion inhibition efficiency decreases with increase in temperature (Fouda et al., 2015). Fouda in his research investigated the performance of Ceratonia siliqua (C. siliqua) as a corrosion inhibitor for protection of copper in 1 M HNO₃ solution. The polarization results confirmed the cathodic nature of this corrosion inhibitor compound. As claimed by Fouda et al. (2015), C. siliqua compound can act as an effective corrosion inhibitor for copper and brass in HNO₃ solution. The extracted results from Bode plots (as seen in Fig. 26) revealed that an increase in corrosion inhibitor concentration improves the corrosion inhibition efficiency. This corrosion inhibitor compound obeys Langmuir adsorption isotherm for adsorption on copper surface. SEM images in Fig. 27 indicate the considerable effect of corrosion inhibitor in decreasing the pores on copper surface.

Bode plots for copper immersed 1 M HNO3 in the absence and presence of C. siliqua inhibitor (at various concentrations) (Fouda et al., 2015).

SEM images of the copper surface (a) before immersion in 1 M HNO3, (b) after 24 h immersion in 1 M HNO3 and (c) after 24 h immersion in 1 M HNO3 containing 300 ppm C. siliqua inhibitor (Fouda et al., 2015).

One of the developing corrosion inhibitor compounds used for protection of copper surface in acidic media is Schiff bases. Antipyrine and its derivatives such as 4-(4-methoxy-benzalideneamine) antipyrine, 4-(4-benzalidene-amine) antipyrine and 4-(4-nitro-benzalideneamine) antipyrine are Schiff base compounds which are used as corrosion inhibitor compounds for copper in 2 M nitric acid. The molecular structure and the properties of these compounds are presented in Table 3. According to the obtained results, the corrosion inhibition efficiency increased with corrosion inhibitor concentration and the maximum efficiency reached about 80% was for 4-(4-methoxy-benzalideneamine) antipyrine corrosion inhibitor at concentration of 11 × 10⁻⁶ M.

Table 3 The molecular structure, name and molecular weight of studied inhibitors (Eldesoky et al., 2015).

Compound no.	Name	Mol. wt./mol. formula
(I)	4-(4 methoxybenzalideneamine) antipyrine	321.0/C₁₉H₁₉N₃O₂
(II)	4-(4 benzalideneamine) antipyrine	291.0/C₁₈H₁₇N₃O
(III)	4-(4 nitrobenzalideneamine) antipyrine	336.0/C₁₈H₁₆N₄O₃

The pharmaceutical compounds are also used as corrosion inhibitors for copper. The corrosion inhibition efficiency of three pharmaceutical compounds 6-Chloro-1,1-dioxo-3,4-dihydro2H-1,2,4-benzothiadiazine-7sulfonamide (1), 1-((s)-3-mercapto-2-methyl propanoyl) pyrrolidine-2carboxylic acid (2), and 3-(2-methoxy phenoxy) propane 1,2-diol (3) for corrosion of copper in 2 M HNO₃ have been evaluated. The maximum corrosion inhibition efficiency of 89.7% is obtained for (1) compound at a concentration of 11 × 10⁻⁶ M and the corrosion inhibition efficiency of these compounds at all concentrations increases in the following order: (1) > (2) > (3). The adsorption of these compounds on copper surface can be described using Temkin adsorption isotherm. The extracted results from EIS plots revealed that the presence of corrosion inhibitor compound in the HNO₃ solution decreases the capacity of electrical double layer and the charge transfer resistance (Eldesoky et al., 2013). Karthik and Sundaravadivelu (2016) produce aminoglycoside (antibiotic drug) as corrosion inhibitor called Amikacin disulfate (AMK) for the protection of copper in 1 M HNO₃. The effects of temperature and concentration of corrosion inhibitor were evaluated and as expected the corrosion inhibition efficiency was increased with an increase in concentration and a decrease in temperature. The corrosion inhibition efficiency was reached maximum value of 93.68% at a concentration of 1 M.

The extracted results from the EIS and polarization curves (as seen in Figs. 28 and 29, respectively) show the dependency of AMK concentration to corrosion inhibition efficiency. According to Nyquist plots, the increase in corrosion inhibitor concentration increases the radius of semicircles which indicate improvement of corrosion resistance and corrosion inhibition efficiency. The decrease in corrosion current density and the potential shift toward more noble values (see polarization curves in Fig. 29) correspond to increase in corrosion resistance and corrosion inhibition efficiency.

Nyquist plots of copper samples dipped in (a) 1 M HNO3 and (b) 1 M HNO3 containing different concentrations of AMK inhibitor (Karthik and Sundaravadivelu, 2016).

Tafel polarization curves of copper samples in (a) 1 M HNO3 and (b) 1 M HNO3 containing different concentrations of AMK inhibitor (Karthik and Sundaravadivelu, 2016).

According to SEM images shown in Fig. 30, the presence of corrosion inhibitor in acidic solution decreases the number of pores on the copper surface, probably due to the formation of a protective layer on the surface which act as a barrier against corrosion attacks (Karthik and Sundaravadivelu, 2016).

SEM micrographs of (a) polished copper, (b) copper dipped in 1 M HNO3 containing an optimum quantity of AMK inhibitor and (c) copper immersed in 1 M HNO3 in the absence of inhibitor (Karthik and Sundaravadivelu, 2016).

The evaluation of Ciprofloxacin corrosion inhibition behavior on corrosion of copper in 1 M HNO₃ revealed that this compound has a mixed type nature (cathodic reaction is more influenced) and its adsorption obeys Langmuir adsorption isotherm. Moreover, it is reported that corrosion rate decreases by increase in concentration of corrosion inhibitor and the corrosion inhibition efficiency reaches a maximum value of 77% at a concentration of 1 mM (Thanapackiam et al., 2016). The corrosion inhibition behavior of 3 compounds of Quinoxalines ((Q₁, Q₂, Q₃) as given in Fig. 31) has been evaluated for corrosion of copper in HNO₃ acidic media.

The molecular structure and the names of studied inhibitor compounds (Zarrouk et al., 2014).

The presence of heteroatoms such as O, S, N and P in the structure of Quinoxalines facilitates the adsorption process of these compounds on the metal’s surfaces. Among nitrogen-containing organic corrosion inhibitors, the Quinoxalines are more promising corrosion inhibitors. These corrosion inhibitor compounds are nontoxic, inexpensive, biodegradable, and accessible and can be synthesized easily and also they are similar to mix-type tetrazoles. The increase in concentration of corrosion inhibitor compounds in the bulk of the solution (to an optimum concentration) increases their efficiency and the corrosion inhibition efficiency of these compounds in all concentrations increases in the following order: Q₃ < Q₂ < Q₁. Furthermore, the maximum corrosion efficiency of 96.98% is achieved in a concentration of 1 mM of Q₁.

Sometimes the adsorption of corrosion inhibitor molecules on the surface of metals is weak and thus they need a specific concentration to act as an appropriate corrosion inhibitor. The adsorption mechanisms can be determined by quantum chemical methods. This method can determine the relation between molecular properties (the energy of orbital, charge density, combining energy, etc.) of corrosion inhibitor and its efficiency. The structure, activity, and properties of various compounds can be easily related to each other using calculation methods and some mathematical equations which can exactly describe the studied chemical phenomena.

The structures of Q₁ and Q₂ (which have similar structures) have been evaluated using the quantum chemical calculations, with the density functional theory (DFT) method. The results of calculations revealed that the energy of highest occupied molecular orbitals (E_HOMO) of Q₁ corrosion inhibitor (−4.8 eV) is higher than that of Q₂ corrosion inhibitor (E_HOMO = −5.06 eV). This fact describes the higher corrosion inhibition efficiency of Q₁ corrosion inhibitor than Q₂ corrosion inhibitor. This behavior is attributed to increase in energy of highest occupied molecular orbital. According to obtained results from calculations (see Fig. 32), the value of energy gap ( $Δ E_{gap}$ ) for Q₁ was higher than Q₂. The value of $Δ E_{gap}$ parameter is a criterion for stability of complex formed on copper surface in the presence of corrosion inhibitor compound.

Correlation diagram of frontier molecular orbitals for the studied inhibitors and the calculated values of Δ E ( eV ) (Zarrouk et al., 2014).

Lower values of ΔE imply more stability of formed complex on the surface. With regard to theoretical results, there is no specific relation between ΔE values and corrosion inhibition efficiency. The number of transformed electron (ΔE) has been also calculated. The increase in tendency of offering electron to the unoccupied orbital of the metal leads to increase in corrosion inhibition efficiency and the ability of the corrosion inhibitor to offering electron in Q₁ is greater than Q₂. The dipole moment of the molecule, which used for discussion of polarity, is criteria for the polarity of the polar covalent bonds. The corrosion inhibition efficiency of corrosion inhibitor compound is directly proportional to the polarity of the polar covalent bonds and increases by its increase. The dipole moment of studied corrosion inhibitors can be classified in the following order: Q₃ < Q₂ < Q₁ (see Fig. 33) (Zarrouk et al., 2014).

The correlation of dipole moments (μ) and inhibition efficiency of quinoxalines compounds (Zarrouk et al., 2014).

Azole and its derivatives are widely used for corrosion protection of copper. Azole has various derivatives which some of the most important derivatives were introduced in the introduction. The corrosion inhibition efficiency of thiazole and its derivatives for corrosion of copper in nitric acid solution have been studied. The obtained results from weight loss measurements (3 h immersion in 1 M HNO₃ at 30 °C) indicated that the adsorption process of all derivatives (2-amino-4-(4-chlorophenyl)-thiazole (1), 2-amino-4-(4-bromophenyl)-thiazole (2), 4-(2-aminothiazole-4-yl)-phenol (3), 5,50-(ethane-1,2-diyldisulfanediyl)bis(1,3,4-thiadiazole-2amine) (4) and 5,50-(propane-1,3-diyldisulfanediyl)bis(1,3,4-thiadiazole-2amine) (5)) obey Langmuir adsorption isotherm and the maximum corrosion inhibition efficiency of 97.46% is obtained for 5,50-(propane-1,3-diyldisulfanediyl)bis(1,3,4-thiadiazole-2amine) (5) corrosion inhibitor at a concentration of 200 ppm. It was also reported that generally thiadiazole corrosion inhibitors provide a higher corrosion inhibition efficiency compared to thiazole compounds and corrosion inhibition efficiency depends on changing substituents on the molecules (Tomi et al., 2015). In this regard, Guo et al. (2014) investigated the corrosion inhibition efficiency of triazole derivatives including 3-amino-1,2,4-triazole (ATR), 3,5-diamino-1,2,4-triazole (DAT), and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT), for copper corrosion in 2 M HNO₃ medium theoretically using quantum chemical calculation. They concluded that the energies of the σ-orbitals were decisive for the inhibitor properties and adsorption performance so the E_HOMO of the studied corrosion inhibitors should be in the following order: E_HOMO-1 (AHMT) > E_HOMO-2 (DAT) > E_HOMO-1 (ATR). They observed a good correlation between the related parameters and corrosion inhibition efficiency data reported in the literature (experimental data).

Similarly Zarrouk et al. (2013) evaluated corrosion inhibition of Purpald corrosion inhibitor for copper in acid nitric. The full name and molecular structure of Purpald corrosion inhibitor is shown in Fig. 34. The obtained results indicated that the maximum corrosion inhibition efficiency of this corrosion inhibitor in 2 M HNO₃ reaches 94.7% at corrosion inhibitor concentration of 10 mM. It was also reported that this compound has a mix-type nature and obeys Langmuir adsorption isotherm at a 303–343 °C range of temperature.

Molecular structure of purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT)) (Zarrouk et al., 2013).

Khaled et al. (2010) introduced 3 derivatives of benzotriazole compound with the name of N-(2-thiazolyl)-1H-benzotriazole-1-carbothioamide (TBC), N-(furan-2-ylmethyl)-1H-benzotriazole-1-carbothioamide (FBC) and N-benzyl-1H-benzotriazole-1-carbothioamide (BBC). The extracted results from common corrosion tests revealed a considerable decrease in corrosion rate in the presence of these compounds. Referring to the increased corrosion inhibition efficiency with increase in the concentration of corrosion inhibitor (to an optimum concentration), the increase in corrosion inhibition efficiency of these compounds can be classified as: BBC < FBC < TBC. The corrosion inhibition efficiency reaches a maximum value of 98.10% in the presence of 5 mM TBC corrosion inhibitor in 1 M HNO₃ media. The higher corrosion inhibition efficiency of TBC compound in comparison with the other studied corrosion inhibitor can be attributed to the presence of thiazole ring in its structure which increases the tendency of corrosion inhibitor molecules to adsorption on the copper surface. All of studied corrosion inhibitors behave as a mixed-type corrosion inhibitor and follow Langmuir adsorption isotherm. It should be noted that the obtained results from corrosion tests are in a good agreement with quantum chemical calculations. In this regard, Khaled et al. (2009) studied the corrosion inhibition behavior of three other benzotriazole derivatives (PSB, 3PSB and 2PSB) for copper in 1 M HNO₃ at a temperature of 25 °C using common corrosion tests and quantum chemical molecular dynamic calculations. Corrosion inhibition efficiency increases with increase in inhibitor concentration and the corrosion inhibition efficiency of these compounds increases in the following order: 2PSB < 3PSB < PSB. It is also reported that the presence of heteroatoms such as N, S and P improves the capability of corrosion inhibitors to bond with copper surface. The results of studies on the protection behavior of various corrosion inhibitors used for copper in nitric acid are reported in Table 4.

Table 4 The results of the study of the efficiency of copper corrosion inhibition in nitric acid.

Inhibitor group	Inhibitor			Concentration	Solution	Conditions	Adsorption isotherm	Efficiency (%)			Ref
Other	Phthalimide	N-(3-metoxyphenylaminomethyl) phthalimide (a)		0.1 mM	2 M HNO₃	30 °C	Temkin	93.10 pp			(Fouda et al., 2006)
		N-(3-methylphenylaminomethyl) phthalimide (b)						80.90 pp
		N-(phenylaminomethyl) phthalimide (c)						79.10 pp
Azole	2-Thiobenzylbenzimidazole (TBBI)			1.0 mM	1 M HNO₃	After 1 h 25 °C	Langmuir	90.04 wl			(Radovanović et al., 2012)
	2-Thiomethylbenzimidazole (TMBI)							88.75 wl
	2-Mercaptobenzimidazole (MBI)							87.65 wl
	2-Thiobenzylbenzimidazole (TBBI)			1.0 mM	1 M HNO₃			90.02 wl			(Ramezanzadeh et al., 2014)
	Purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT))			10 mM	2 M HNO₃	303 K	Langmuir	94.7 pp	92.8 EIS	91.7 wl	(Zarrouk et al., 2013)
	N-(2-thiazolyl)-1H-benzotriazole-1-carbothioamide (TBC)			5.0 mM	1 M HNO₃	25 °C	Langmuir	93.08 pp	98.10 EIS	97.4 wl	(Khaled et al., 2010)
	N-(furan-2-ylmethyl)-1H-benzotriazole-1-carbothioamide (FBC)							89.32 pp	92.29 EIS	90.6 wl
	N-benzyl-1H-benzotriazole-1-carbothioamide (BBC)							85.31 pp	90.20 EIS	89.7 wl
	Triazole	3-Amino-1,2,4-trazole (ATR)		0.01 M	2 M HNO₃	303 K		82.2 wl			(Guo et al., 2014)
		3,5-Diamino-1,2,4-triazole (DAT)						86.5 wl
		4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT)						91.7 wl
	Thiazole and thiadiazole derivatives	2-Amino-4-(4-chlorophenyl)-thiazole		250 ppm	1 M HNO₃	After 3 h 30 °C	Langmuir	66.50 wl			(Tomi et al., 2015)
		2-Amino-4-(4-bromophenyl)-thiazole						68.31 wl
		4-(2-Aminothiazole-4-yl)-phenol						82.27 wl
		5,50-(Ethane-1, 2-diyldisulfanediyl) bis (1,3,4-thiadiazole-2-amine)						95.47 wl
		5,50-(Propane-1,3-diyldisulfanediyl)bis(1,3,4-thiadiazole-2-amine)						97.46 wl
	Cyproconazole			1.0 × 10⁻³ M	0.5 M HNO₃	28 °C	Langmuir	99.9 pp		97.9 EIS	(Wang et al., 2015)
	Benzotriazole	1-(Phenylsulfonyl)-1H-benzotriazole (PSB)		5 × 10⁻³ M	1 M HNO₃	25 °C		89.4 TP	92.37 wl		(Khaled et al., 2009)
		1-(3-Pyridinylsulfonyl)-1H-benzotriazole (3PSB)						85.2 TP	87.39 wl
		1-(2-Pyridinylsulfonyl)-1H-benzotriazole (2PSB)						80.3 TP	82.40 wl
	Tetrazole	1-Phenyl-5-mercapto-1,2,3,4-tetrazole (PMT)		10⁻³ M	0.1 M HNO₃	72 h exposure	Langmuir	95.40 pp	97.50 wl		(Mihit et al., 2006)
	Tetrazole	1-phenyl-1,2,3,4-tetrazole (PT)		10⁻³ M	0.1 M HNO₃	72 h exposure	Langmuir	93.70 pp	94.50 wl		(Mihit et al., 2006)
	Tetrazole	Bis [4-amino-5-hydroxy-1, 2, 4-triazol-3-yl] methane (D₁)		5 × 10⁻⁴ M	4.0 M HNO₃	25 °C		99.99 wl			(El-Naggar, 2000)
	Tetrazole	Bis [4-amino-5 hydroxy-1, 2, 4-triazol-3-yl] butane (D₂)		5 × 10⁻⁴ M	4.0 M HNO₃	25 °C		99.99 wl
Amino Acid	l-methionine			5 × 10⁻³ M	1 M HNO₃	25 °C		81.60 pp	88.00 EIS	87.60 wl	(Khaled, 2010)
	l-methionine sulfoxide							87.50 pp	90.20 EIS	91.20 wl
	l-methionine sulfone							90.70 pp	93.50 EIS	94.10 wl
	Methionine			1 × 10⁻³ M	1 M HNO₃	25 °C		80.38 pp	93.98 wl		(Barouni et al., 2014)
Natural products (green inhibitor)	Leaves extract	Verbenaceae	Vitex negundo (VN)	0.1 M	3 M HNO₃	308 K	Langmuir	97 pp	96 EIS	98 wl	(Savita et al., 2016)
		Acanthaceae	Adhatoda vasica (AV)					76 pp	78 EIS	78 wl
		Caesalpiniaceae	Saraka asoca (SA)					85 pp	88 EIS	91 wl
	Euphorbia helioscopia linn (EHE)			500 ppm	1 M HNO₃	25 °C	Langmuir	91.0 pp	88.5 EIS		(Fouda et al., 2015)
	Hyoscyamus muticus Extract (HME)			500 ppm	1 M HNO₃	25 °C	Langmuir	88.65 pp	81.4 EIS	90.45 wl	(Fouda et al., 2015)
	Ceratonia siliqua extract			300 ppm	1 M HNO₃	25 °C	Langmuir	85.09 pp	91.0 EIS	82.8 wl	(Fouda et al., 2015)
	Brass + Ceratonia siliqua extract							98.24 pp	90.3 EIS	97.0 wl
	Azadirachta indica	Acid extract of dry seed		1%	1.0 N HNO₃	After 3 h		95.69 wl			(Sangeetha and Fredimoses, 2011)
	Varthemia iphionoides	Jeceidine		0.1 mM	2 M HNO₃	After 4 h 25 °C	Langmuir	91.60 wl			(Al-Qudah, 2011)
Schiff Bases	Antipyrine derivatives	4-(4-Methoxy-benzalideneamine) antipyrine (I)		11 × 10⁻⁶ M	2 M HNO3	303 K	Temkin	80.0 pp	67.0 EIS	71.46 wl	(Eldesoky et al., 2015)
		4-(4-Benzalidene-amine)antipyrine (II)						73.2 pp	65.5 EIS	64.23 wl
		4-(4-Nitro-benzalideneamine)antipyrine (III)						61.9 pp	61.2 EIS	60.39 wl
Pharmaceutical drug (green inhibitors)	Ciprofloxacin			1 mM	1.0 M HNO₃		Langmuir	77.0 pp	76.0 EIS		(Thanapackiam et al., 2016)
	Aminoglycoside antibiotic drug	Amikacin disulfate (AMK)		1 mM	1.0 M HNO₃		Langmuir	91.50 pp	89.92 EIS	93.68 wl	(Díaz-Gómez et al., 2014)
	6-Chloro-1,1-dioxo-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide (\|)			1.1 × 10⁻⁵ M	2 M HNO₃		Temkin	89.7 pp	60.5 EIS	82.6 wl	(Eldesoky et al., 2013)
	1-((s)-3-Mercapto-2-methyl propanoyl) pyrrolidine-2-carboxylic acid (\|\|)							85.6 pp	43.5 EIS	79.4 wl
	3-(2-Methoxy phenoxy) propane 1,2-diol (\|\|\|)							64.8 pp	32.2 EIS	75.9 wl
Others	1-Butyl-3-methylimidazolium chloride (BMIMCl)			50 × 10⁻³ M	1.0 M Cl⁻ pH 1.0 (NaCl + HCl)		Langmuir	96 pp			(Scendo and Uznanska, 2011)
	1-Butyl-3-methylimidazolium bromide (BMIMBr)			50 × 10⁻³ M	1.0 M Cl⁻ pH 1.0 (NaCl + HCl)		Langmuir	83 pp			(Scendo and Uznanska, 2011)
	Quinoxaline	Ethyl 2-(4-(2-ethoxy-2 oxoethyl)-2-p-tolyliquinoxalin-1(4H)-yl)acetate (Q1)		10⁻³ M	2 M HNO₃	303 K		96.98 quantum chemical calculation based on DFT method			(Zarrouk et al., 2014)
		1-[4-Acetyl-2-(4-chlorophenyl)quinoxalin-1(4H)-yl]acetone (Q2)						91.76 quantum chemical calculation based on DFT method
		2-(4-Methylphenyl)-1,4-dihydroquinoxaline (Q3)						82.76 quantum chemical calculation based on DFT method
	Two quaternary ammonium salts	N1,N2-didodecyl-N1,N1,N2,N2-tetramethylethane-1,2-diaminium bromide (1)		1 × 10⁻³ M	1 M HNO₃	25 °C	Langmuir	93.7 pp	93.9 EIS	94.7 EFM	(Hegazy et al., 2015)
	Two quaternary ammonium salts	N-(2-hydroxyethyl)-N,N-dimethyldodecan-1-aminium bromide (2)		1 × 10⁻³ M	1 M HNO₃	25 °C	Langmuir	90.8 pp	91.7 EIS	91.6 EFM	(Hegazy et al., 2015)
	N-1-naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME)			1.0 mM	2 M HNO₃	303 K		93.53 pp	92.38 EIS	95.26 wl	(Zarrouk et al., 2012)
	(E)-3-(4-methoxyphenyl)-1-phenylprop-2-en-1-one			1.5 × 10⁻⁵ M	1 M HNO₃	30 °C	Temkin	89.3 pp	91.4 EIS	80.2 wl	(Fouda et al., 2014)
	(E)-3-(4-methylphenyl)-1-phenyl prop-2-en-1-one			1.5 × 10⁻⁵ M	1 M HNO₃	30 °C	Temkin	85.7 pp	89.5 EIS	75.0 wl	(Fouda et al., 2014)
	Diaza-adamantane derivatives	6-Hydroxy-5,7-diphenyl-1,3-diazaadamantane (HDDA)		300 ppm	1 M HNO₃	303 K	Langmuir	88.60 pp	88.91 EIS	87.46 wl	(Karthik et al., 2015)
	Diaza-adamantane derivatives	5,7-Diphenyl-1,3-diazaadamantan-6-one (DDA)		300 ppm	1 M HNO₃	303 K	Langmuir	85.22 pp	87.66 EIS	85.22 wl	(Karthik et al., 2015)

According to Table 4, it can be determined that in HNO₃ solution, the highest efficiency is belonged to the thiazole and its derivatives, and then tetrazole and cyproconazole from the azol group and VN (green inhibitor).

5.1.3

5.1.3 Hydrochloric acid solution

The most copper acid pickling process in industry performs in HCl solution, so the corrosion of copper is more investigated in this media. According to the literature (Barcia et al., 1993), anodic dissolution reaction of copper in HCl, rapidly occurs through oxidation of metallic copper to cuprous ion (Eq. (36)):

(36)

Cu \leftrightarrow {Cu}^{+} + e^{-}

Then cuprous ion reacts with chloride ion from solution to precipitate insoluble CuCl on surface:

(37)

{Cu}^{+} + {Cl}^{-} \to CuCl

The formed CuCl does not give enough protection to the copper surface due to poor cohesion, so by combining with another Cl⁻ ion, transforms to soluble cuprous chloride complex, ${CuCl}_{2}^{-}$ (Eq. (38)):

(38)

CuCl + {Cl}^{-} \leftrightarrow {CuCl}_{2}^{-}

Thus dissolution of copper occurs. However this solved complex may oxidize to cupric ions (Eq. (39)) (Sherif, 2012a)

(39)

{CuCl}_{2}^{-} \leftrightarrow {Cu}^{2 +} + 2 {Cl}^{-} + e^{-}

The cathodic reaction in aerated acidic chloride solution is (Eq. (40)) as follows:

(40)

4 H^{+} + O_{2} + 4 e^{-} \to 2 H_{2} O

So total corrosion reaction of copper in acidic chloride solutions is as follows (Eq. (41)):

(41)

2 Cu + 4 H^{+} + 4 {Cl}^{-} + O_{2} \to 2 H_{2} O + 4 {Cl}^{-} + 2 {Cu}^{2 +}

One of the aggressive media for copper is hydrochloric acid and thus the protection of copper from corrosion attacks in this acidic media is important. The corrosion inhibition behavior of various corrosion inhibitor compounds such as green corrosion inhibitors, azole, Schiff bases, and organic and inorganic corrosion inhibitor on the corrosion of copper in HCl solution has been studied. In this section, the inhibition behavior of different compounds used for protection of copper in HCl is reviewed. According to the literature, the corrosion inhibition efficiency of green corrosion inhibitors has been widely studied to provide an eco-friendly and effective compound to decrease corrosion of copper. To aim this purpose, the researchers evaluated the effect of different parameters such as the concentration of corrosion inhibitor, temperature, and pH on corrosion inhibition efficiency. The corrosion inhibition behavior of Calligonum comosum (CC) extract on corrosion of copper in 2 M HCl has been evaluated and it was revealed that maximum corrosion inhibition efficiency of 80.06% is achieved at a concentration of 0.8 g/L. As the concentration of corrosion inhibitor increases, lower values for the capacitance of electrical double layer and higher values for charge transfer are obtained. Fig. 35 indicates the SEM images of copper surface in various conditions. As it is clear from Fig. 35, the presence of corrosion inhibitor in the bulk of the corrosive solution has a dominant role in decreasing the corrosion attacks which is understandable from the considerable decrease in surface pores in the corrosion inhibitor-containing solution. Moreover, the increase in concentration of corrosion inhibitor reduced the surface pores, probably due to more coverage of copper surface and thus more efficiency of corrosion inhibitor compound (Shabani-Nooshabadi et al., 2014b).

SEM micrographs from the surface of (a) polished copper, (b) copper in 2 M HCl after 3 h immersion and (c) copper in 2 M HCl + 0.8 g/L CC extract after 3 h immersion (Shabani-Nooshabadi et al., 2014b).

Many efforts have been done toward using green corrosion inhibitors for protection of copper; however remaining their active component (in environment) is a problem facing with the use of these compounds. In this regard, the corrosion inhibition of Pungent was evaluated in HCl solution and obtained results indicated that PIPERINE, the major pungent component of peppers, provides a good corrosion protection for copper in HCl. The corrosion inhibition efficiency increases with increase in concentration and maximum corrosion inhibition efficiency reached 82% (Cai et al., 2014).

Similarly, Pratihar et al. (2015) investigated corrosion inhibition behavior of Capparis decidua seeds (CDs) ethanol extract on corrosion of copper in 0.5 HCl at 303 ± 1 K. It was found that corrosion inhibition efficiency increases with increasein the concentration of corrosion inhibitor and immersion time (maximum IE was 94.6%). The adsorption process obeys Langmuir adsorption isotherm. The corrosion inhibition nature of this compound is attributed to its chemical structure which contains heteroatoms such as N and O. This atoms improves tendency of corrosion inhibitor for adsorption on the copper surface. Due to its high corrosion inhibition efficiency and cost-effectiveness, this compound can be used as a green and eco-friendly corrosion inhibitor for protection of copper from corrosion attacks in HCl aggressive media (Pratihar et al., 2015). The corrosion inhibition efficiency of Egyptian Licorice for corrosion of copper in 0.1 M HCl has been evaluated by Deyab (2015). Glycyrrhizic acid and Glabridin compounds are the major components of Licorice. The optimized methods for extraction of these compounds are the use of a mixture of water/ethanol in a way that Licorice puts in water/ethanol combination for 60 min at a temperature of 50 °C.

In this regard, Deyab (2015) used various combinations of water/ethanol for extraction of these compounds and the maximum corrosion inhibition efficiency (89.5%) obtained for EXT2 which was a combination of water/ethanol at a ratio of 70/30, 2.93 mg/g of Glycyrrhizic acid and 0.88 mg/g Glabridin. Corrosion inhibition performance was improved by an increase in the concentration of corrosion inhibitor. Also an increase in temperature caused a decrease in the corrosion inhibition efficiency. The adsorption process followed Temkin adsorption isotherm. According to the literature, this compound acts as a mix-type corrosion inhibitor and its good corrosion inhibition efficiency is attributed to the physical adsorption of Glycyrrhizic acid and Glabridin compounds on the copper surface. In addition to green corrosion inhibitors, the phosphate corrosion inhibitor compounds can be used for corrosion protection of copper in HCl solution. Huijing et al. (2014) investigated the corrosion inhibition efficiency of triethyl phosphate and Ce⁴⁺ ions for corrosion of copper in HCl. It was revealed that at a constant concentration of TEP, the corrosion inhibition efficiency of the multicomponent corrosion inhibitor (triethyl phosphate + Ce⁴⁺) increases with increase in concentration of Ce⁴⁺ to a critical value and afterward at this critical concentration of Ce⁴⁺, the corrosion inhibition efficiency of multicomponent corrosion inhibitor improves with an increase in concentration of TEP. According to EIS measurements, the corrosion inhibition efficiency of the multicomponent compound (58.7 mmol/L TEP + 1 mmol/L Ce⁴⁺) reached a maximum value of 80.6% after 1 h of immersion (Huijing et al., 2014).

Mo et al. (2015) used 4-Octylphenol (OP) compound to produce a self-assembled film on copper surface. They investigated the effectiveness of this layer for corrosion of copper in 0.5 M HCl. According to polarization results, this compound behaves as cathodic corrosion inhibitor and its performance increases with increase in concentration (to an optimum concentration). The maximum corrosion inhibition efficiency (91.7%) is obtained at a concentration of 1 mM after 24 h of immersion. However, the corrosion inhibition efficiency decreased at concentrations higher than 1 mM. The time dependency measurements also revealed that the effect of immersion time on corrosion inhibition efficiency is similar to concentration so that at the initial time of immersion, the corrosion inhibition efficiency increases with immersion time and then decreases after 24 h of immersion. The comparison of the contact angle of solution with copper surface in the presence and absence of corrosion inhibitor revealed that the presence of corrosion inhibitor leads to an increase in the contact angle on the surface and thus surface hydrophobicity. Another useful and new compound which can be used as a corrosion inhibitor for copper is Schiff base. With regard to corrosion inhibition behavior of Schiff bases, the effectiveness of heterocyclic furan and a newly synthesized corrosion inhibitor with the name of (NE)-N-(furan-2-ylmethylidene)-4-({4-<E)-(furan-2-ylmethylidene) amino>phenyl}ethyl) aniline (SB) for corrosion of copper in 1 M HCl have been evaluated using EIS and polarization methods. Referring to adsorption of the corrosion inhibitor on the copper surface according to the Langmuir adsorption isotherm, it was also reported that maximum corrosion inhibition efficiency of 94% is achieved at a concentration of 5 mM in 1 M HCl solution. Fig. 36 represents the SEM images of copper surface in HCl solution in the presence and absence of SB corrosion inhibitor. According to Fig. 36, the SB corrosion inhibitor plays a dominant role in decreasing corrosion attacks on the copper surface which are understandable from the considerable decrease in surface pores in the presence of SB corrosion inhibitor in HCl solution (Issaadi et al., 2014).

SEM micrographs of (a) polished copper, (b) copper surface immersed in 1 M HCl in 25 °C and (c) copper surface immersed in 1 M HCl containing 5 × 10−3 M SB inhibitor in 25 °C (Issaadi et al., 2014).

As previously mentioned Azole corrosion inhibitors and its derivatives are widely used for corrosion protection of copper and various studies have been done on corrosion inhibition of these compounds. It is well known that Benzotriazole and its derivatives act as a corrosion inhibitor in aqueous solutions, however, they also used as a volatile corrosion inhibitor. In multimetallic systems which constructed from copper, iron, steel, etc. some other corrosion inhibitor compounds are used that may react with benzotriazole (that used for protection of copper) and leads to the formation of benzotriazole salts. The formation of these salts may increase the corrosion rate of copper and thus understanding the influence of another corrosion inhibitor compound on the performance of benzotriazole using the volatile corrosion inhibitor is necessary (Akyüz and Ergan, 2014). Khadom (2014) studied the corrosion inhibition behavior of benzotriazole on corrosion of Cu-10%Ni in HCl 5% solution at different corrosive solution velocities (fluid flow). He reported that Benzotriazole has a dual function (performance) in such that within providing a good corrosion inhibition efficiency, benzotriazole acts as an improver factor for flow. It was also reported that an increase in the concentration of corrosion inhibitor (to an optimum concentration) increases the corrosion inhibition efficiency of Cu-10%Ni while decreases in temperature and flow rate of HCl 5% solution. The corrosion inhibition effect of three derivatives of Aryl pyrazole pyridine including 3-methyl-6-oxo-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (APP I), 3-methyl-6-oxo-4-(3-phenoxyphenyl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (APP II) and 3-methyl-6-oxo-4-(thiophen-2-yl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (APP III) (Fig. 37) on corrosion of copper in 0.5 HCl has been studied by Sudheer and Quraishi (2015) from polarization results.

Molecular structure of three Aryl pyrazole pyridine derivates as inhibitors (Sudheer and Quraishi, 2015).

It is reported that APP I at a concentration of 1.59 mM provided the maximum corrosion inhibition efficiency of 92.3%. This compound acts as cathodic corrosion inhibitor. Fig. 38 indicates the SEM micrographs of copper surface after 72 h immersion in 0.5 M HCl in the absence and presence of APP I corrosion inhibitor. According to SEM images, the use of corrosion inhibitor considerably reduced corrosion attacks which is understandable from decreasing the pores and cracks on copper surface.

SEM micrographs of copper surface immersed in 0.5 M HCl in the (a) absence and (b) presence of APP I inhibitor (Sudheer and Quraishi, 2015).

Methyl 3-((2-mercaptophenyl)imino)butanoate (MMPB) is one of the synthesized compounds for corrosion inhibition of copper in HCl. The structure of this compound is a combination of azole, thiol, and carboxylate. The maximum corrosion inhibition efficiency of 99.3% at a concentration of 0.01 M in 0.1 M HCl is reported which is reduced to 96.6% after 7 days of immersion. It is reported that the presence of thiol groups in the structure of corrosion inhibitor improves the adsorption interactions. On the other hand, carboxyl group prevents excessive intermolecular stretching (Tansuǧ et al., 2014).

Finally, the corrosion inhibition effect of amines and amino acids (Stupnisek-Lisac et al., 2000) on corrosion of copper in hydrochloric acid is evaluated in this section. In this regard, the corrosion inhibition efficiency of glycine, cysteine, glutamic acid their derivative (glutathione) for corrosion of copper in 0.5 M HCl has been evaluated by various researchers. The obtained results for corrosion inhibition efficiency are given in Table 5. Fig. 39 indicates the molecular structure of amino acid and its derivatives (Zhang et al., 2011a). Similarly, the corrosion inhibition effect of the other amine derivatives such as Serine and Threonine has been evaluated (Zhang et al., 2008a).

Table 5 The results of the study of the efficiency of copper corrosion inhibition in hydrochloric acid solutions.

Inhibitor group	Inhibitor		Concentration	Solution	Conditions	Adsorption isotherm	Efficiency (%)			Ref
Other	Metal organic framework (MOF)	MOF[Ag(qox)NO₃] (MOF 1)	21 × 10⁻⁶ M	1 M HCl	298 K	Langmuir	90.9 pp	61.3 EIS		(Fouda et al., 2016)
	Metal organic framework (MOF)	MOF[Ag(pyzca)] (MOF 2)	21 × 10⁻⁶ M	1 M HCl	298 K	Langmuir	85.8 pp	62.9 EIS
	Aniline oligomers			0.1 M HCl				89		(Shumakovich et al., 2014)
Azole	Aryl pyrazole pyridine derivatives	3-Methyl-6-oxo-4,5,6,7-tetrahydro-2H-pyrazolo [3,4-b]pyridine-5-carbonitrile (APP I)	1.59 mmol L⁻¹	0.5 M HCl			92.3 pp	92.0 EIS		(Sudheer and Quraishi, 2015)
		3-Methyl-6-oxo-4-(3-phenoxyphenyl)-4,5,6,7tetrahydro-2H-pyrazolo[3,4-b]pyridine-5carbonitrile (APP II)					90.5 pp	91.8 EIS
		3-Methyl-6-oxo-4-(thiophen-2-yl)-4,5,6,7tetrahydro-2H-pyrazolo[3,4-b]pyridine-5carbonitrile (APP III)					86.1 pp	91.5 EIS
	2-Amino-5-ethylthio-1,3,4-thiadiazole (AETD)		10 mM	0.5 M HCl	After 12 h		77.00			(Sherif and Park, 2006b)
	Triazole	3-Amino-1,2,4-triazole (ATR)	5 × 10⁻³ M	0.5 M HCl	After 48 h		72.0			(Sherif et al., 2007c)
	3-Amino 5-methylthio 1,2,4-triazole (AMTT) + CTAB + SDS	100 ppm AMTT + 10 ppm CTAB	KH phthalate + HCl	pH = 2	Langmuir			94.62 pp	91.50 wl	(Lalitha et al., 2005)
	3-Amino 5-methylthio 1,2,4-triazole (AMTT) + CTAB + SDS	100 ppm AMTT + 2500 ppm SDS	KH phthalate + HCl	pH = 2	Langmuir			96.15 pp	93.32 wl	(Lalitha et al., 2005)
	Benzotriazole		10⁻² M	0.1 M HCl		Langmuir	90.80 pp			(Khaled and Amin, 2009)
	5-Methyl-benzotriazole						97.87 pp
	5-Chloro-benzotriazole						99.79 pp
	Imidazole	2-Mercapto benzimidazole (MBI)	1 mM	0.5 M HCl	After 4 days 40 °C		91.60 wl			(Antonijevic et al., 2009)
	Methyl 3-((2-mercaptophenyl) imino) butanoate (MMPB)		1 × 10⁻² M	0.1 M HCl			99.30 EIS			(Tansuǧ et al., 2014)
	Methyl 3-((2-mercaptophenyl) imino) butanoate (MMPB)		1 × 10⁻² M		After 7 days		96.60 EIS			(Tansuǧ et al., 2014)
	4-Amino-4H-1,2,4-triazole-3thiol (ATT)		2.58 mM	0.5 M HCl	303 K	Langmuir	92.05 pp	98.64 EIS	87.50 wl	(Sudheer and Quraishi, 2013)
	4-Amino-5-methyl-4H-1,2,4-triazole-3thiol (AMTT)						95.78 pp	98.99 EIS	92.50 wl
	4-Amino-5-ethyl-4H-1,2,4-triazole-3thiol (AETT)						96.09 pp	99.04 EIS	95.00 wl
	N-(2-thiazolyl)-1H-benzotriazole-1-carbothioamide (TBC)		5 × 10⁻² M	0.5 M HCl	30 °C		93.92 pp	97.0 EIS	96.36 wl	(Lei et al., 2014)
	5-(3-Aminophenyl)-tetrazole (APT)		5 × 10⁻³ M	0.5 M HCl	After 72 h		90 wl			(Sherif et al., 2008)
Azole (self assembled)	2,5-Dimercapto-1,3,4-thiadiazole (DMTD) SAM		7.5 mM	0.5 M HCl	After 10 h		90.7 pp	84.2 EIS		(Qin et al., 2011)
	3-Amino-1,2,4-triazole (ATR)		5 × 10⁻³ M	0.5 M HCl	After 48 h		93.8 pp	72 wl		(Wang and Bierwagen, 2009)
	3-Amino-5-mercapto-1,2,4-triazole (AMTA)		5 × 10⁻³ M	0.5 M HCl	After 48 h		84.8 pp	83 wl
	Aryl-triazino-benzimidazole-2-thione	4-Phenyl[1, 3, 5]triazino[1,2-a]benzimidazole-2(1H)-thione (1a)	100 (mg/L)	2 M HCl		Langmuir	90.2 wl			(Esmaeili et al., 2015)
		4-(4-Methylphenyl)[1, 3, 5]triazino[1,2-a]benzimidazole-2(1H)-thione (1b)					93.5 wl
		(4-Methoxyphenyl)[1, 3, 5]triazino[1,2-a]benzimidazole-2(1H)-thione (1c)					95.4 wl
		4-(4-Nitrophenyl)[1, 3, 5]triazino[1,2-a]benzimidazole-2(1H)-thione (1d)					89.0 wl
	Benzotriazole (BTA)		0.1 M	5% HCl	35 °C	Langmuir	91.5 wl			(Khadom, 2014)
	Triazole	Myclobutanil	3.2 × 10⁻⁴ M	1 M HCl	293 K		75.9 pp	84.3 EIS		(Zheng et al., 2014)
Amino acids	2-aminoethanol (A) + N,N-diethylethanamine (D)		10% w/v	1 M HCl	298 K	Langmuir	96 pp			(Fayomi et al., 2014)
Amino acid (self assembled)	4-Amino-3-(octadecylthio)-6-methyl-1,2,4-triazinone (AOTMT)		0.02 M HCl	After 0.5 h, 30 °C			99.00 pp	98.73 EIS		(Appa Rao et al., 2014)
	Cys + glycine + glutamic acid		15 mM Cys	0.5 M HCl			92.90 EIS			(Zhang et al., 2011a)
			5 mM Cys + 5 mM glycine + 5 mM glutamic				90.70 EIS
			10 mM Glutathione				96.40 EIS
	Methionine + Zn²⁺		12 mM Methionine	0.5 M HCl		Langmuir	84.15 pp	76.71 EIS		(Zhang et al., 2009)
	Methionine + Zn²⁺		12 mM Methionine + 0.5 mM Zn²⁺	0.5 M HCl		Langmuir	91.96 pp	87.07 EIS		(Zhang et al., 2009)
	α-Alanine		1 mM	0.5 M HCl	25 °C	Langmuir	94.00 pp			(Gomma and Wahdan, 1994)
	Threonine		1 mM	0.5 M HCl	After 1 h		83.40 pp	87.70 EIS		(Zhang et al., 2008a)
	Glutamic acid		1 mM	0.5 M HCl	After 1 h		90.40 pp	94.50 EIS		(Zhang et al., 2008a)
	Glutamine + KI		0.1 M Glutamine	0.5 M HCl		Langmuir	73.50 EIS			(Zhang et al., 2008b)
	Glutamine + KI		10 mM Glutamine + 5 mM KI	0.5 M HCl		Langmuir	93.74 EIS			(Zhang et al., 2008b)
Amins	N-5-nitro-2-furfuryl-p-toluidine		0.01 M	0.5 M HCl			84.00 pp			(Stupnisek-Lisac et al., 2000)
Amins	N-5-methyl-2-furfuryl-p-toluidine						86.00 pp
Inorganic (phosphate)	Triethyl phosphate (TEP) + Ce⁴⁺		1 mM Ce⁴⁺ + 58.7 mM TEP	0.5 M HCl			80.6 EIS			(Huijing et al., 2014)
Natural products (green inhibitor)	Calligonum comosum (CC)		0.1 g/L	2 M HCl	55 °C	Langmuir	90.36 PP			(Shabani-Nooshabadi et al., 2014b)
	Piperine		3.2 × 10⁻³ M	1 M HCl	298 K	Langmuir	81.8 pp			(Cai et al., 2014)
	Ephedra sarcocarpa (ES)		0.5 M	2.0 M HCl	298 K	Langmuir	94.5 pp	94.8 EIS		(Shabani-Nooshabadi et al., 2014a)
	Ethanolic extract of Capparis decidua Seeds (EECdS)		1.0426 g/L	0.5 M HCl	303 K, After 72 h	Langmuir	94.60 wl			(Pratihar et al., 2015)
	Egyptian licorice extract	EXT2: ethanol/water (30 v/70 v), glycyrrhizic acid (2.93 mg/g), glabridin (0.88 mg/g)	8%(v/v)	0.1 M HCl	298 K	Temkin	89.55 pp	81.22 EIS		(Deyab, 2015)
	Morinda tinctoria (MT) (leaves extracts)		25 M	0.5 M HCl		Freundlich	65.39 pp	79.77 EIS		(Krishnaveni and Ravichandran, 2014)
	Tecomella undulata	Root extract	5%	1 N HCl	After 72 h		86.72 wl			(Mihajlović and Antonijević, 2015)
		Branches extract					89.27 wl
		Leaves extract					86.13 wl
		Seeds extract					93.84 wl
	Commercial non-ionic surfactant plant	Zenthoxylumalatum	800 ppm	1 M HCl	After 2 h 30–40 °C	Langmuir	95.80 pp	98.28 wl		(Chauhan, 2009)
	Ziziphus mauritiana	Plant extract in ethanol	1.288 g/dm³	0.5 N HCl	After 72 h 30 °C	Langmuir	88.58 wl			(Yadav et al., 2013)
Thiole	1,3,4-thiadiazole-2,5-dithiol (bismuthiol)		80 × 10⁻⁵ M	0.5 M HCl	25 °C	Langmuir	84.1 pp			(Baeza et al., 2003)
	(NE)-N-(furan-2-ylmethylidene)-4-({4->E)-(furan-2-ylmethylidene) amino<phenyl}ethyl) aniline (SB)		5 × 10⁻³ M	1 M HCl	298 K	Langmuir	94.0 PP	87.8 EIS		(Issaadi et al., 2014)
	Anionic surfactant complexes	Co²⁺	400 ppm	1.0 M HCl	298 K		79.5 wl			(Tawfik and Zaky, 2015)
		Cu²⁺					85.7 wl
		Zn²⁺					73.5 wl
	Anisalidine derivatives	N-(4-nitro phenyl) p-anisalidine (SB1)	20 mM	2.0 N HCl	30 °C, After 72 h	Langmuir	94.9 wl			(Saxena and Kumar, 2015)
		N-(4-chloro phenyl) p-anisalidine (SB2)					95.4 wl
		N-(4-phenyl) p-anisalidine (SB3)					97.1 wl
		N-(4-methoxy phenyl) p-anisalidine (SB4)					98.1 wl
		N-(4-hydroxy phenyl) p-anisalidine (SB5)					98.8 wl
Schiff bases	N,N0-ethylen-bis(salicylidenimine) [S1]		400 ppm	1 M HCl		Langmuir	91 pp	89.4 EIS	90 wl	(Ehteshamzadeh et al., 2006)
	N,N0-isopropylen-bis(salicylidenimine) [S2]						92 pp	91.5 EIS	95 wl
	N,N0-ortho-phenylen acetyl acetone imine, (2-hydroxy benzophenone imine) [S3]						91 pp	90.8 EIS	86 wl

The molecular structure of amino acid and its derivatives (Zhang et al., 2011a).

The obtained results of different researches on the corrosion inhibition of corrosion inhibitors used for protection of copper in hydrochloric acid solutions are given as Table 5.

Due to the reported efficiency values in Table 5 and the wide range of inhibitors which are used in HCl, for reaching the highest inhibition efficiency Azol group inhibitors (AETT, AMTT, 5-chloro-benzotriazole), and Amino acid group (AOTMT) suggested.

5.1.4

5.1.4 Phosphoric acid solution

Mouni et al. (2015) investigated the corrosion inhibition behavior of Argan Oil (AO) and cosmetic Argan Oil (CAO), which extracted from Argania spinosa herbs, on corrosion of copper in 2 M H₃PO₄ solution containing 0.3 M HCl (the results are given in Table 6). The addition of 7 g/L corrosion inhibitor provided the best corrosion inhibition efficiency. This inhibitor, which acts as a mix-type corrosion inhibitor, protects the copper through physical adsorption.

Table 6 The results of the study of the efficiency of copper corrosion inhibition in phosphoric acid solution.

Inhibitor group	Inhibitor	Concentration	Solution	Condition	Adsorption isotherm	Efficiency (%)			Ref
Natural products (green Inhibitor)	Cosmetic Argan Oil (CAO)	7 g/L	2 M H₃PO₄ + 0.3 M NaCl	298 K	Physisorption	95 PP	97 EIS	98 Wl	(Dadgarinezhad and Baghaei Ravari, 2015)
	Argan Oil (AO)	7 g/L	2 M H₃PO₄ + 0.3 M NaCl	298 K	Physisorption	94 PP	88 EIS	92 wl	(Mouni et al., 2015)
	Extract Artemisia oil	6 g/dm³	2 M H₃PO₄ + 0.3 M NaCl			89.00 pp			(Mounir et al., 2014)

Similarly, they also evaluated the effect of temperature on corrosion inhibition efficiency. Fig. 40 shows the polarization curves of copper immersed in the mentioned solution at different temperatures. It can be seen that increase in temperature from 298 to 323 K leads to increase in corrosion current density and thus decrease in corrosion inhibition efficiency (Mounir et al., 2012).

Potentiodynamic polarization curves for copper immersed in 2 M H3PO4 + 0.3 M HCl solution at various temperatures (Mounir et al., 2012).

The extracted results from studies conducted on corrosion inhibition behavior of different compounds used for protection of copper in phosphoric acid solution are given in Table 6.

As can be seen in Table 6, the highest corrosion inhibition efficiency belongs to the cosmetic argan oil (green inhibitor).

5.2

5.2 Copper in neutral environments

As previously mentioned, most of metallic systems constructed from copper such as heat exchanger of desalination systems are used in neutral environments which may also containing some aggressive ions such as chloride ions. In addition, the presence of these aggressive ions on the copper in electrical equipment or printed circuit boards can increase the corrosion attacks. Most researches on corrosion and corrosion protection of copper have been done in water and NaCl solutions. Žerjav and Milošev (2015) investigated corrosion protection of copper in urban rain. The usual corrosion reactions of copper in chlorinated neutral and acidic environments (such as HCl) are as follows.

The reduction in oxygen (Eq. (42)) is the most common reaction occurred on the copper surface in chlorinated environments (Sherif and Park, 2005):

(42)

O_{2} + 2 H_{2} O + 4 e^{-} \to 4 {OH}^{-}

However, the anodic reactions in above mentioned environment may be as following reactions (Curkovic et al., 2010; Tüken et al., 2012). Initially, the oxidation of copper transforms the copper to Cu⁺ ion (Eq. (43)). In the presence of chloride aggressive ions, the reaction between Cl⁻ and Cu⁺ occurs which produces a soluble film on the surface.

(43)

Cu \to {Cu}^{+} + e^{-}

(44)

{Cu}^{+} + {Cl}^{-} \to CuCl

CuCl is an unstable film and immediately reacts with chloride ions and transforms to ${CuCl}_{2}^{-}$ as follows:

(45)

CuCl + {Cl}^{-} \to {CuCl}_{2}^{-}

5.2.1

5.2.1 Copper in NaCl solutions

Qiang et al. (2015) evaluated the corrosion inhibition efficiency of 5-nitroindazole for corrosion of copper in NaCl solution. They reported that this compound acts as a cathodic corrosion inhibitor and its efficiency increases with concentration. Moreover, the maximum corrosion inhibition efficiency of 99% is obtained in 0.4 mM of corrosion inhibitor concentration.

Tian et al. (2015) synthesized some derivatives of triazolyl-acylhydrazone with names of vanillin-[5-(p-methyl)-phenyl-4-amino-(1,2,4-triazolyl)-2-thiol]-acylhydrazone (VTA), salicylal-[5-(p-methyl)-phenyl-4-amino-(1,2,4-triazolyl)-2-thiol]-acylhydrazone (STA), and anisaldehyde-[5-(p-methyl)-phenyl-4-amino-(1,2,4-triazolyl)-2-thiol]-acyldrazone (ATA) to use as corrosion inhibitors in chlorinated solutions. Afterward, the corrosion inhibition behavior of synthesized compounds was evaluated using weight loss, polarization, and electrochemical tests.

Fig. 41 indicates the polarization curves for copper exposed to NaCl solution in a wet-dry cyclic condition in the absence and presence of these corrosion inhibitor compounds at a concentration of 5 × 10⁻⁴ mol/L. The addition of corrosion inhibitor to NaCl solution causes a considerable decrease in electrochemical reactions, although their effects on decreasing anodic dissolution of copper are more dominant. The corrosion inhibition efficiency values for VTA, STA, and ATA corrosion inhibitors after 8 cycles are obtained as 98.2%, 97.08% and 96.18%, respectively. These values are in a good agreement with results obtained from common weight loss tests in non-cyclic condition (see Table 8). The obtained results confirmed the good corrosion inhibition efficiency of these corrosion inhibitors. Time dependency measurements also indicated the appropriate stability of corrosion inhibition process. The effect of corrosion inhibitor on both anodic and cathodic branches implies to mix nature of corrosion inhibitor, although anodic reaction is more influenced.

The polarization curves of copper after exposure in 1 M NaCl solution containing 5 × 10−4 M in a dry-wet cyclic condition (Tian et al., 2015).

Table 7 The results of the study of the efficiency of copper corrosion inhibition in NaCl solution.

Inhibitor group	Inhibitor		Concentration	Solution	Condition	Adsorption isotherm	Efficiency (%)				Ref
Green inhibitor	Phytic acid (inositol hexaphosphate)		0.1 mM	3 wt.% NaCl	After 6 h		76.9(pp)				(Peca et al., 2014)
Organic	Glycerol		2 M	0.5 M NaCl	pH = 10		83.2 PP	83 EIS			(Chi-Ucán et al., 2014)
	Hexa propylene glycol cyclotriphosphazene (HPGCP)		1 mM	3.5 wt.% NaCl		Langmuir	95 PP	96 EIS			(Dagdag et al., 2015)
	Mono-hydroxamic acid (C12N)		5 mM	3 wt.% NaCl	After 6 h		91 wl				(Ezznaydy et al., 2015)
	Self-assembled film of ammonium pyrrolidine dithiocarbamate (APDTC)		1.0 mM	3 wt.% NaCl	After 8 h	Langmuir	98.7 PP	98.7 EIS			(Zhang et al., 2015)
Azole	Polypyrrole-oxalic acidbenzotriazole (PPy-Ox-BTA)			3.5 wt.% NaCl			Less than 80(wl)				(Lei et al., 2014)
	5-Phenyl-1,3,4-thiadiazole-2-thiol (PTT)		100 mg/l	3.5 wt.% NaCl		Langmuir	97.5 pp	96.6 EIS	98.2 wl		(Tian et al., 2013)
	2-(5-Mercapto-1,3,4-thiadiazole-2-yl)-phenol (MTP)		100 mg/l	3.5 wt.% NaCl		Langmuir	97.1 pp	94.8 EIS	97.7 wl		(Tian et al., 2013)
	Sulfathiazole (ST)		80 ppm	0.1 M NaCl	40 °C	Langmuir	91.17 PP				(Zor, 2014)
	5-(Phenyl)-4H-1,2,4-triazole-3-thiole (PTAT)		1500 ppm	3.5 wt.% NaCl	After 100 h		97 PP				(Zucchi et al., 1996a)
	5-Phenyl-tetrazole (5Ph-T)		1 mM	0.1 M NaCl	313 K		99.40
	5-Mercapto-1-phenyl-tetrazole (5Mc-1Ph-T)						98.40
	5-Mercapto-1-methyl-tetrazole (5Mc-1Me-T)						93.40
	5-Amino-tetrazole (5NH2-T)						85.30
	3-Amino-1,2,4-triazole (ATA)		1.0 mM	3.5 wt.% NaCl	After 50 h		96.1 PP				(Sherif et al., 2007b)
	Bis-(1-benzotriazolymethylene)-(2,5-thiadiazoly)-disulfide (BBTD)		1 mM	3 wt.% NaCl			87.6 wl				(Zhang et al., 2004a)
	4-Methyl-5-imidazolecarbaldehyde		0.3 mM				71.24				(Otmačić and Stupnišek-Lisac, 2003)
	Ethyl-4-methyl-imidazolecarboxylate		1 mM				80.50
	4-Methyl-1(4-methoxyphenyl)imidazole		0.2 mM				83.95
	1-(p-Tolyl)-4-methylimidazole		0.7 mM				93.03
	1-Phenyl-4-methylimidazole		5 mM				94.31
	2-(2′-Phenyl)-2H-benzotriazole	C1(R = —CH₃)	0.15 mM	3.5 wt.% NaCl		Langmuir	59.63(pp)	56.72(EIS)	58.12(wl)		(Gong et al., 2015)
		C2(R = —C₃H₇)	0.15 mM	3.5 wt.% NaCl			71.32	73.79	72.84
		C3(R = —C₄H₉)	0.15 mM	3.5 wt.% NaCl			86.11	88.11	89.98
		C4(R = —C₆H₁₃)	0.15 mM	3.5 wt.% NaCl			94.39	93.98	93.00
		C5(R = —C₇H₁₅)	0.15 mM	3.5 wt.% NaCl			98.12	97.99	98.45
		C6(R = —C₉H₁₉)	0.15 mM	3.5 wt.% NaCl			91.18	93.79	92.93
		C7(R = —C₁₀H₂₁)	0.15 mM	3.5 wt.% NaCl			87.86	90.35	88.18
		C8(R = —C₁₂H₂₅)	0.15 mM	3.5 wt.% NaCl			85.85	87.20	87.37
		C9(R = —C₁₆H₃₃)	0.15 mM	3.5 wt.% NaCl			82.75	85.39	84.98
	(5-Methyl-[1,3,4]thiadiazol-2-ylsulfanyl)-acetic acid (4-hydroxy-3-methoxybenzylidene)-hydrazide (MAH)		100 (mg/l)	3.5 wt.% NaCl		Langmuir	95.67(pp)	96.72(EIS)	95.53(wl)		(Ma et al., 2015)
	5-Nitroindazole		0.4 mM	3 wt.% NaCl		Langmuir	98.9	98.7	97.0		(Qiang et al., 2015)
	Self-assembled monolayer of 2,4,6-trimercapto-1,3,5-triazine (TMTA)		0.1 mM	0.1 M NaCl	After 3 h		92.4 (PP)	93.9 EIS)			(Chen et al., 2014a)
	Self-assembled monolayers of 2-(octadecylthio) benzothiazole		20 mM in ethyl acetate 24 h	0.02 M NaCl	After 0.5 h 303 K	Langmuir	93.5 pp	98.9 EIS			(Appa Rao et al., 2009)
	Self-assembled monolayers of 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium		20 mM 8 h	0.5 M NaCl	328 K		93.8 pp	94.4 EIS			(Chen et al., 2012)
	Self-assembled monolayers of 5-methoxy-2-(octadecylthio) benzimidazole		10 mM (in methanol 24 h)	0.02 M NaCl	303 K After 0.5 h	Chemisorption	99.91 pp	99.3 EIS			(Appa Rao et al., 2010)
	Self-assembled monolayers of 1,2-dihydro-3-(octadecylthio) benzotriazine		2.5 mM (in methanol 24 h)	0.02 M NaCl	303 K After 0.5 h	Chemisorption	99.7 pp	99.4 EIS			(Rao et al., 2014)
	Self-assembled monolayers of 3-mercapto-1H-1,2,4-triazole (MTA)		3.5 wt.% NaCl	After 12 h					83.8 pp		(Rajkumar and Sethuraman, 2016)
	5-Methyl-[1, 3, 4] thiadiazol-2-ylsulfanyl)-acetic acid (4-dimethylamino-benzylidene)-hydrazid (MTYDBH)		100 (mg/l)	3.5 wt.% NaCl	(wl 7 days) pH = 7.5	Langmuir	99.37 EIS	98.48 pp	99.07 w		(Li et al., 2012)
	4-Methyl-1-phenyl imidazole (PMI)		5 mM	0.5 M NaCl	pH = 5.6		93				(Curkovic et al., 2010)
	4-Methyl-1-(p-tolyl) imidazole (TMI)		1 mM	0.5 M NaCl			92
	5-Phenyl-1-H tetrazole (PTAH)		10 mM	0.6 M NaCl			99.41 pp				(Al Kharafi et al., 2012)
	3-Amino-5-mercapto-1,2,4-triazole (AMTA)		1 mM	3.5 wt.% NaCl			81.7 pp	90 wl			(Sherif, 2012b)
	5-(3-Aminophenyl)-tetrazole (APTA)		1 mM	3.5 wt.% NaCl			88.3 pp	95 wl			(Sherif, 2012b)
	Diniconazole ((E)-1-(2,4-dichlorophenyl)-4,4-dimethyl-2-(1,2,4-triazole-1-yl)-1-pentenyl-3-ol)		100 (mg/l)	3.5 wt.% NaCl		Langmuir	99.2 EIS	98.1 pp	96.6 wl		(Hu et al., 2010)
	Triadimefon (1-(4-chlorophenoxy-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)-2-butanone))		100 (mg/l)	3.5 wt.% NaCl		Langmuir	97.3	95.3	96.5		(Hu et al., 2010)
Other	Triazolyl-acylhydrazone derivates	STA	0.5 mM	1 M NaCl		Langmuir–Freundlich	97.3 EIS	98.10 pp	97.6 wl		(Tian et al., 2015)
		ATA					96.9 EIS	96.43 pp	95.7 wl
		VTA					98.4 EIS	98.48 pp	98.2 wl
Amino acid	1-Alkyl-3-methylimidazolium proline ([Omim][Pro])		1 mM	3 wt.% NaCl	303 K		92.79 pp	90.4 EIS			(Chen et al., 2014b)
	Cysteine		10 mM	3.5 wt.% NaCl	pH = 8.5 298 K/328 K		97.080/96.574 EIS				(Kilinççeker and Demir, 2013)
	Cysteine		10 mM + 3.5 wt.% NaCl	3.5 wt.% NaCl	pH = 8.5 298 K/328 K		84.699/94.869 EIS				(Kilinççeker and Demir, 2013)
	Methionine		1 mM	3.5 wt.% NaCl		Langmuir	82.00 pp				(El-Hafez and Badawy, 2013)
Amino acid (self assemble)	Self-assembled films of 4-aminothiophenol		1 mM	3.5 wt.% NaCl	After 12 h		84.8				(Rajkumar et al., 2015)
Natural products (green inhibitor)	Olive mill wastewater (OMW)		200 g/l	3 wt.% NaCl	After 2 years	Langmuir	84.16 PP				(Masmoudi et al., 2015)
Amins	N-phenyl-1,4-phenylenediamine		5 mM	3 wt.% NaCl	Deaerated NaCl		76 EIS				(Sherif and Park, 2005)
					Aerated NaCl		86 EIS
					Oxygenated NaCl		93.3 EIS
Other (ionic liquids)	1-Butyl-3-methylimidazolium chloride (BMIMCl)		50 mM	1.0 M Cl⁻ pH 1.0 (NaCl + HCl)			96 pp				(Scendo and Uznanska, 2011)
Other (ionic liquids)	1-Butyl-3-methylimidazolium bromide (BMIMBr)						83 pp				(Scendo and Uznanska, 2011)
Schiff bases	4-(4-Aminostyryl)-N,N-dimethylaniline (AND)		0.15 mM	3 wt.% NaCl			84.69 pp	89.20 EIS			(Zhou et al., 2015)
Schiff bases	2-((4-(4-(Dimethylamino)styryl)phenylimino)methyl)		0.15 mM				94.50	92.49			(Zhou et al., 2015)
Schiff bases (self assemble)	N-benzylidene-4-dodecylaniline		1 mM	0.5 M NaCl	After 12 h	Langmuir	98.2 PP	97.8 EIS			(Li et al., 2014a)
	Self-assembled films N,N′-ethylen-bis(salicylidenimine) (S-E-S)		300 ppm	0.88 M NaCl	after 30 min		96.00 EIS				(Ehteshamzade et al., 2006)
	N,N′-ortho-phenylenbis(salicylidenimine) (S-o-ph-S)						92.00 pp	99.00 EIS
	Dithiouracil (DTUr)		1 mM 100 mg/l	3 wt.% NaCl		Frumkin	95.40 pp				(Dafali et al., 2003)
	5-Methyl-thiouracil (MTUr)		1 mM 100 mg/l	3 wt.% NaCl		Frumkin	82.00 pp				(Dafali et al., 2003)
	1,4-bis(dodecydipropyl ammonium bromide)-butane (C₁₂C₄C₁₂(C₃)Br₂)	Cationic gemini surfactant		3.5 wt.% NaCl		Langmuir	95.1 pp	89.8 EIS	93.6 wl		(Cao et al., 2014)
	2-Mercapto-4-amino-5-nitroso-6-hydroxy pyrimidine (MAP)		1 mM	3.5 wt.% NaCl			88.9 pp	90.7 EIS	91.6 wl	92.2 EFM	(Khaled, 2011)
	Self-assembled monolayers of 2-(pyridin-2-yliminomethyl)-phenol (HL) SAM		1 mM in ethanol (120 min)	0.1 M NaCl			82.30 pp				(Li et al., 2014a)
	Self-assembled monolayers of sodium diethyldithiocarbamate		1 mM	3 wt.% NaCl			99.3 EIS				(Liao et al., 2011)
Other organic	Gemini surfactant		30 mg/l	3.5 wt.% NaCl			94.5 pp	90.6 EIS	96.3 wl		(Cao et al., 2014)
Pharmaceutical drug (green)	5-Chloro-1-[1-[3-(2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)propyl]-4-piperidinyl]-1,3-dihydro-2H-benzimidazol-2-one	Domperidone	20 mg/l	3.5 wt.% NaCl		Langmuir	93.6 pp	94.2 EIS	92 wl		(Wang et al., 2014b)
Other (purine)	4,6-Diamino-2-mercaptopyrimidine (DAMP)		2 mM	3.5 wt.% NaCl		Langmuir	91.2 pp	90.3 EIS	91 wl		(Cheng et al., 2016)

Table 8 The results of the study of the efficiency of copper corrosion inhibition in other aqueous solutions.

Inhibitor group	Inhibitor		Concentration	Solution	Condition	Adsorption isotherm	Efficiency (%)			Ref
Azole	Tolyltriazole (TTA)		1 ppm (TTA)	Cooling water	pH = 8.5	Langmuir	61.9 pp			(Choudhury et al., 2014)
	Tolyltriazole (TTA)		1 ppm (TTA) + 0.5 ppm (cholorine)	Cooling water	pH = 8.5	Langmuir	39.4 pp
	Benzotriazole. 1-(2-pyrrole carbonyl) benzotriazole (PBTA) + SDS + TBTA	TBTA + SDS + Mo		Groundwater	303 K		94.5 pp			(Gopi et al., 2015)
		PBTA + SDS + Mo		Groundwater	303 K		96.8 pp	96.3 EIS		(Gopi et al., 2015)
	Triazo phosphonates	3-Cinnamyledene amino 1,2,4-triazole phosphonate (CATP)	15 ppm	Lake water	Add inhibitor after 24 h		82.50			(Ramesh and Rajeswari, 2005)
	Tolytriazole (TTA)		10 ppm	Deionized water			95.48			(Al Kharafi et al., 2012)
	Benzotriazole (BTA)		10 ppm	Deionized water	After 24 h, 60 °C	Langmuir	84.48 PP			(Yu et al., 2003)
	Tolytriazole (TTA)		10 ppm	Deionized water	After 24 h, 60 °C	Langmuir	95.48 PP			(Yu et al., 2003)
	1-(2-Pyrrole carbonyl)-benzotriazole (PCBT) + Triton X-100 (TX-100)		0.095 + 0.16 mM	Groundwater	28 °C		91.34 pp	92.07 EIS	91.74 wl	(Kokalj, 2010)
Organic	Carboxylates	Monocarboxylates (C_nH₂_n₊₁COO⁻) n = 10	5 mM	Aerated, mildly saline, near-neutral aqueous	Aerated, mildly saline, near-neutral aqueous		99			(Hefter et al., 1997)
Organic	Carboxylates	α,ω-Dicarboxylate analog (—OOC[CH₂]_nCOO⁻) n = 11	5 mM	Aerated, mildly saline, near-neutral aqueous	Aerated, mildly saline, near-neutral aqueous		98			(Hefter et al., 1997)
Natural inhibitor (green inhibitor)	Nigella sativa (NS)		30 ppm	Aerated make-up water	pH = 7.5	Langmuir	90.30 wl			(Emad and Al-Rasheedi, 2015)
	Natural honey (NH)		900 ppm	Aerated make-up water	pH = 7.5	Langmuir	98.00 wl
	Sodium carboxymethyl cellulose (Na-CMC)		5 g/l	Cooling water	20 °C	Langmuir	77.35 pp	81.72 EIS		(Li et al., 2015)
	Emblica officinalis (AMLA) (leaves extract)		1000 ppm	Natural seawater	30 °C	Langmuir	79.99			(Rani and Selvaraj, 2010a)
	Vitis vinifera	Seed and skin extract 150 g in ethanole	1000 ppm	Natural seawater	After 24 h 25 °C	Langmuir	76.08 wl			(Rani and Selvaraj, 2010b)

The corrosion inhibition efficiency values extracted from both mentioned methods are listed in Table 7. The corrosion inhibition efficiency of corrosion inhibitors at a constant concentration increases as follows: ATA < STA < VTA.

It was reported that corrosion inhibition efficiency of corrosion inhibitors increases with corrosion inhibitor concentration (to an optimum concentration). The best corrosion inhibition efficiency was obtained for corrosion inhibitor compound which can protect copper surface through formation of an adhesive film with hydrophobic properties. Fig. 42 indicates the surface morphology of copper samples immersed in NaCl solution in the absence and presence of corrosion inhibitors (at a concentration of 5 × 10⁻⁴ M). In the absence of corrosion inhibitors, the corrosion attacks destroy most of the surface areas. However, the presence of corrosion inhibitor in solution considerably reduces the corrosion attacks through the formation of a protective layer which acts as a physical barrier against aggressive ions.

Surface morphology of copper samples after 24 h immersion in 1 M NaCl solution in (a) absence and, presence of (b) STA, (c) ATA and (d) VTA inhibitors at a concentration of 5 × 10−4 M (Tian et al., 2015).

All studied compounds act as a mix-type corrosion inhibitor and they adsorb on the copper surface with the contribution of both chemisorption and physisorption, although, chemical adsorption plays more dominant role on corrosion inhibition. Among studied corrosion inhibitors, the adsorption of VTA compound is described as chemisorption. The protective layer which is formed on copper surface in the presence of VTA showed more compactness and homogeneity compared to the protective layer of other compounds (Tian et al., 2015).

Khan et al. (2015) investigated the corrosion inhibition behavior of benzotriazole for corrosion of copper in 3.5% NaCl in flow condition. A continues protective oxide layer is formed on the copper surface in the stagnant condition, although the increase in flow rate may lead to the destruction of this protective layer and causes subsequently localized corrosion of copper. To evaluate the effect of hydrodynamic flow, a rotating cage has been used and flow tests have been conducted at different velocities from 0.5 to 3 m/s. To better understand the effects of flow rate on corrosion inhibition efficiency, the same tests were conducted under stagnant condition. Fig. 43 indicates extracted results from weight loss measurements at different concentrations of corrosion inhibitor in flow condition. The corrosion rate increases with increase in velocity. However the addition of benzotriazole to the solution and an increase in its concentration result in decreasing corrosion rate in all agitation rates. According to the results, the corrosion rate of copper (mpy) in flow condition (at the velocity of 0.5 m/s) increases five times more than the stagnant condition.

Corrosion rates of copper immersed in NaCl solution in the absence and presence of various concentrations of BTA (1–10 mM) at different velocities (0.5–3 m/s) (Khan et al., 2015).

Comparing the SEM images of copper surface at various velocities reveled that increase in flow rate leads to more corrosion/erosion of copper (see Fig. 44). It is also reported that the presence of corrosion inhibitor in solution changes hydrophobic surface to become hydrophilic surface in stagnant condition. The adsorption of benzotriazole on copper surface obeys Langmuir adsorption isotherm.

SEM micrographs of copper immersed in 3.5% NaCl solution at various rotation rates of (a) 0.5 m/s, (b) 2 m/s and (c) 3 m/s (Khan et al., 2015).

Rajkumar and Sethuraman (2016) reported the formation of a self-assembled monolayer (SAM) on the copper surface in 3.5% NaCl solution containing 3-mercapto-1H-1,2,4-triazole (MTA) at different immersion times. The effect of this SAM on the corrosion inhibition of copper has been evaluated using polarization and electrochemical impedance methods in which extracted results are shown in Table 8. Fig. 45 indicates the polarization curves for bare copper samples and also copper samples with SAM monolayer (as formed on the copper surface in MTA ethanol solution) in 3.5% NaCl at different immersion times (1 h, 2 h, 6 h, and 12 h).

Potentiodynamic polarization curves for (a) bare copper and copper samples with self-assembled molecular monolayers of MTA after exposure in 3.5% NaCl solution for (b) 1 h, (c) 2 h, (d) 6 h and (e) 12 h (Rajkumar and Sethuraman, 2016).

The increase in immersion times in MTA solution and the formation of SAM monolayer on the copper surface result in decreasing current density and shifting corrosion potential toward more noble values. The increase in immersion time increases the time for adsorption of SAM monolayers on the copper surface which in turn leads to the formation of a more homogeneous and more compact protective layer. The obtained results indicate that using MTA solution to produce SAM on copper surface can be a proper corrosion protection process for copper in neutral environments (Rajkumar and Sethuraman, 2016).

Finšgar (2015) analyzed the adsorption of 4-methyl-2-phenyl-imidazole (MePhl) on the copper surface in 3.5% NaCl solution using X-ray photoelectron spectroscopy (XPS). They also investigated the corrosion inhibition efficiency of MePhl for corrosion of copper using polarization test and 3D-profilometery analysis. The polarization resistance of copper in NaCl solution in the presence and absence of corrosion inhibitor after 100 h of immersion has been calculated (see Fig. 46).

Potentiodynamic polarization curves of copper immersed in 3 wt.% NaCl solution in the absence and presence of 1 mM MePhl inhibitor (Finšgar, 2015).

The addition of corrosion inhibitor to the solution results in a potential shift toward more noble values and a decrease in corrosion current density. The presence of corrosion inhibitor dominantly reduces anodic reaction rates, indicating anodic nature of corrosion inhibitor. The corrosion inhibition efficiency of 98.9% is obtained for 1 mM MePhi in 3% NaCl solution. The extracted results from 3D-profilometery (see Fig. 47) showed formation of a thin protective layer on the copper surface in the presence of corrosion inhibitor. The corrosion inhibition efficiency reaches a maximum value after 180 days immersion (Finšgar, 2015).

Figure 47 3D profile of copper surface immersed in 3 wt.% NaCl in the presence and absence of 1 mM MePhl for 180 days (Finšgar, 2015).

The results of researches on corrosion inhibition of copper in NaCl solution with various corrosion inhibitor compounds are shown in Table 7.

Due to the efficiency values which reported in Table 7, using organic inhibitor such as APDTC, DDTC and 5-nitroindazole MTYDBH and self-healing inhibitors such as MOTBI, DOTBT and 2-OTBT from the azol group are suggested for using in NaCl.

5.2.2

5.2.2 Copper in other aqueous solutions

Copper is widely used in various industrial systems such as piping and cooling tower systems and also in various aqueous environments such as urban water, wastewater and seawater. Since corrosion is a major problem facing copper used in these environments, and many efforts have been made to produce appropriate corrosion inhibitor. In this section, the corrosion inhibitors used for copper in the aqueous environment are described in two main groups involve azoles and green corrosion inhibitors. In this regard, the corrosion inhibition efficiencies of benzotriazole derivatives (1-(2-Pyrrole carbonyl) benzotriazole (PBTA), 1-(2-thienyl carbonyl)-benzotriazole (TBTA), sodium dodecyl sulfate (SDS) and molybdate for corrosion of copper in groundwater at different temperatures have been evaluated. The results revealed the dominant corrosion inhibition effect of studied corrosion inhibitors on corrosion of copper. The use of a mixture of corrosion inhibitors with their optimum concentration showed a synergistic effect. The maximum corrosion inhibition efficiency of 96.3% is obtained for the multicomponent corrosion inhibitor. From Nyquist plots in Fig. 48, the corrosion resistance increases with increase in the concentration of corrosion inhibitors. The use of multicomponent corrosion inhibitor also improves corrosion inhibition efficiency, while the increase in temperature results in a decrease in corrosion resistance. According to SEM images shown in Fig. 49, the exposure of copper in groundwater in the absence of corrosion inhibitor compounds leads to formation of a non-continues dense layer involve copper oxide, copper chloride and oxychloride. In the presence of PTBA corrosion inhibitor in solution, a crystalline protective layer formed on the copper surface and using a mixture of PTBA and SDS provide a synergistic effect and improve the corrosion inhibition efficiency through the formation of a denser protective layer. Moreover, the use of multicomponent corrosion inhibitor (PBTA + SDS + Mo) results in formation of a dense and homogenous layer which acts as a barrier against corrosion attacks. The extracted results from surface analysis (SEM micrographs) are in a good agreement with corrosion tests (Gopi et al., 2015).

Nyquist plots of copper immersed in the absence and presence of an optimum concentration of MO, SDS, PBTA, PBTA + SDS and PBTA + SDS + MO at temperature of (a) 303 K and (b) 333 K (Gopi et al., 2015).

SEM micrographs of the copper surface after 10 days immersion in (a) inhibitor-free groundwater and groundwater containing an optimum concentration of (b) PBTA, (c) PBTA + SDS and (d) PBTA + SDS + MO (Gopi et al., 2015).

The corrosion inhibition behavior of some triazole derivatives (as given in Fig. 50) on corrosion of copper in lake water in the absence and presence of biocide was studied. The extracted corrosion inhibition efficiency values are given in Table 8. Moreover, nature and adsorption process of corrosion inhibitors on the copper surface have been evaluated (Ramesh and Rajeswari, 2005).

The molecular structure and the abbreviation name of studied triazole derivatives (Ramesh and Rajeswari, 2005).

Al Kharafi et al. (2012) investigated the corrosion inhibition behavior of 5-phenyl-1-H-tetrazole (PTAH) on corrosion of copper in seawater (polluted with sulfide and thiosulfate) and non-polluted seawater. They reported that the free adsorption energy of this corrosion inhibitor is −49.15 kJ/mole and provides corrosion inhibition efficiency of 97% at a temperature of 20 °C.

There are various green corrosion inhibitors used for protection of copper surface from corrosion in aqueous solutions. The corrosion inhibition efficiency of Vitis vinifera extracts for corrosion of copper in seawater has been evaluated (Rani and Selvaraj, 2010b). The effect of temperature, time of immersion and concentration of seed and skin extract has been studied using various corrosion tests. The adsorption process for both of Vitis vinifera extracts obeys Langmuir adsorption isotherm, while the adsorption on Cu–27 Zn alloy can be described by Temkin adsorption isotherm. Sulaiman et al. (2012) investigated the corrosion inhibition behavior of Allium cepa (Onion) on corrosion of copper, nickel, and iron in water and wastewater used in industrial systems. The use of 0.6 g/L Allium cepa provides corrosion inhibition efficiency of 46%, 92% and 88% for copper, iron, and nickel, respectively. From obtained results, it can be concluded that Allium cepa is not a proper corrosion inhibitor for copper in mentioned environment. The corrosion inhibition and adsorption behavior of sodium carboxymethyl cellulose (Na-CMC) on the copper surface in cooling water systems have been investigated. According to EIS results, the maximum corrosion inhibition efficiency of 83.34% is achieved at a concentration of 5 mg/L in 20 °C. Referring to the chemical adsorption of the corrosion inhibitor on the copper surface, it was reported that adsorption process obeys Langmuir adsorption isotherm. According to AFM images shown in Fig. 51, the surface morphology of copper surface in the corrosion inhibitor-containing solution is more homogenous compared to copper surface in the absence of corrosion inhibitor. Furthermore, the average roughness of the copper surface in the presence of corrosion inhibitor is obtained 3.89 nm (1 µm × 1 µm) which is equal to the surface roughness of a polished copper, while the average roughness (Sq) of the copper sample in corrosion inhibitor-free solution is 12.7 nm (1 µm × 1 µm). This can be attributed to the adsorption of corrosion inhibitor on the surface (Li et al., 2015). Similarly, the corrosion inhibition effect of natural honey (NH) and Nigella sativa (NS) for corrosion of copper has been investigated by Emad and Al-Rasheedi (2015). Referring to direct relation between the concentration of corrosion inhibitor and its efficiency, the maximum corrosion inhibition efficiency of 98% and 90.3% is obtained for NH and NS compounds, respectively. It was also reported that the adsorption process of both mentioned compounds obeys Langmuir adsorption isotherm.

AFM images of (a) polished copper (3.5 µm × 3.5 µm), (b) polished copper (1 µm × 1 µm), (c) protected copper (1 µm × 1 µm), (e) copper in simulated cooling water (3.5 µm × 3.5 µm) and (f) copper in simulated cooling water (1 µm × 1 µm) (Li et al., 2015).

The results of researches on corrosion inhibition of copper in other aqueous solution with various corrosion inhibitor compounds are given in Table 8.

5.3

5.3 Copper in alkaline environments

With regard to the effect of corrosion inhibitors on the corrosion of copper in the alkaline environments, many types of researches have been done similar to acidic and neutral environments. Subramanian and Lakshminarayanan (2002) investigated the adsorption and corrosion inhibition behavior of some compounds such as imidazole (IMD), mercaptobenzimidazole (MBIMD), benzimidazole (BIMD), Mercaptobenzothiazol (MBT) and BTA on corrosion of copper in NaOH solution. Referring to following Langmuir adsorption isotherm, the corrosion inhibition efficiency of mentioned compounds increases in the following order: BTA = IMD < BIMD = MBIMD < MBT. The molecular structure of mentioned azoles is shown in Fig. 52.

The structure of azoles (Subramanian and Lakshminarayanan, 2002).

In this regard, the corrosion inhibition of copper corrosion with azole compounds in borate buffers at various pH values (pH = 6.4, 8.4 and 10.4) has been investigated. It is reported that azole corrosion inhibitors act as mix-type corrosion inhibitors and reduce both anodic and cathodic reactions. The corrosion inhibition efficiency increases with pH value and concentration of corrosion inhibitors and the corrosion inhibition efficiency decrease in the following order: MBT > TDA > BIMD = MBIMD > BTA (Altaf et al., 2011).

In addition to azole compounds, the corrosion inhibition effect of cysteine for copper in Na₂SO₄ solution in pH = 9 has been investigated. The presence of corrosion inhibitor results in decreasing corrosion rate due to adsorption of Cu(I)_ads and Cu(II)_ads (at higher anodic potential) on copper surface and formation of Cu(I)-cys protective film. It is also reported that the adsorption process obeys Langmuir adsorption isotherm. From optical microscopic images (shown in Fig. 53), it can be seen that the presence of corrosion inhibitor in solution plays a dominant role in the protection of copper surface and as expected the increase in the concentration of corrosion inhibitor results in increasing darkness of copper surface, indicating more corrosion inhibition performance (Petrović et al., 2012a).

The optical microscopic images of (a) polished copper surface, (b) copper surface in 0.5 M Na2SO4 at pH = 9 and copper surface immersed in 0.5 M Na2SO4 containing, (c) 10−6 M cysteine, (d) 10−4 M cysteine and (e) 10−2 M cysteine after 10 min immersion (Petrović et al., 2012a).

5.4

5.4 Copper in other environments

In addition to mentioned environments, there are some other environments such as Na₂SO₄ which may be aggressive for copper. The addition of different additives to Na₂SO₄ may change its pH values from acidic to alkaline range. Frignani et al. (1999) investigated the effect of alkyl chain on the corrosion inhibition efficiency of 1,2,3-benzotriazole for corrosion of copper in Na₂SO₄. The corrosion inhibition efficiency increases with the length of the alkyl chain up to six carbon atoms. Referring to increasing corrosion inhibition efficiency with the concentration of corrosion inhibitor, the maximum corrosion inhibition efficiency of 99.3% is obtained for hexyl-benzotriazole (C6-BTA) in Na₂SO₄ with pH = 2.5 at 30 °C after 3 h of immersion. The influence of 4- and 5-carboxybenzotriazole isomers (as their atomic structure is shown in Fig. 54) on corrosion of copper in Na₂SO₄ at various pHs, concentrations and immersion times has been investigated. It is reported that 5-CBT isomer provides a better corrosion inhibition performance at lower pH values, while at higher pHs the corrosion inhibition efficiency of 4-CBT isomer is higher than 5-CBT. However, the corrosion inhibition efficiency of both corrosion inhibitors increases with concentration and immersion time. Furthermore, the Electrophilic effect of 5-CBT isomer is lower than 4-CBT which in turn leads to stronger chemisorption adsorption of 5-CBT on the copper surface and coordination through a triazole nitrogen. Thus higher corrosion inhibition efficiency can be achieved. Both isomers indicate anti-tarnishing properties (Huynh et al., 2002; Otieno-Alego et al., 1999).

The molecular structure of (a) 4-CBT and (b) 5-CBT (Otieno-Alego et al., 1999).

Vastag et al. (2001) investigated the corrosion inhibition behavior of some thiazole family including 5-(3′,4′-dimetoxybenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (MBDT), 5-(3′-thenylidene)-2,4-dioxotetrahydro-1,3-thiazole (TDT), 5-(4′-isopropylbenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (IPBDT) and 5-benzylidene-2,4-dioxotetrahydro-1,3-thiazole (BDT) on corrosion of copper in 0.1 M Na₂SO₄. It is reported that IPBDT provides corrosion inhibition efficiency more than the rest at room temperature. The thickness of layers formed on the copper surface in the presence and absence of corrosion inhibitors has been evaluated using quartz crystal microbalance (QCM) measurements.

Minimum thickness reduction is obtained for layer formed in the presence of IPBDT and BDT with 15 and 18 µm/year, respectively.

Beside azoles, the corrosion inhibition behavior of green corrosion inhibitors (Hamed, 2010) and amino acids (Simonović et al., 2014) has been also evaluated for protection of copper in Na₂SO₄. In addition to providing appropriate corrosion inhibition efficiency, these compounds are nontoxic. The corrosion inhibition efficiency of potassium folate for corrosion of copper in Na₂SO₄ has been investigated. Fig. 55 indicates the structure of potassium folate. Referring to the improvement of corrosion inhibition efficiency with increase in concentration and also decrease in temperature and concentration of the solution, the maximum corrosion inhibition efficiency of 73.9% is obtained at a temperature of 15 °C. It was reported that potassium folate acts as anodic corrosion inhibitor through physical adsorption of folate anions on the copper surface. The adsorption process of potassium folate on the copper surface follows Flory–Huggins isotherm. The simultaneous influence of corrosion inhibitor concentration and temperature on corrosion inhibition performance is shown in Fig. 56 (Hamed, 2010).

The structure of potassium folate (Hamed, 2010).

The relation between inhibition efficiency (P%) and logarithmic values of inhibitor concentration in 1 M Na2SO4 at various temperatures (Hamed, 2010).

The corrosion inhibition behavior of benzotriazole on corrosion of copper in tetra-n butylammonium bromide has been investigated by researchers (Liu et al., 2012, 2011). It is reported that corrosion inhibition efficiency increases with the concentration of corrosion inhibitor in 15% (0.534 M) TBTA solution reaching a maximum value of 90%. The adsorption of BTA on the copper surface can be described by Langmuir adsorption isotherm. It is also reported that BTA acts as a mix-type corrosion inhibitor so that both anodic and cathodic reactions are influenced. According to the extracted results from surface analysis (SEM and EDS in Fig. 57), it can be concluded that BTA provides appropriate corrosion inhibition for copper trough formation of a protective layer. The peak density of bromine and CuBr (corrosion products) is decreased due to the formation of a protective film on the copper surface (Liu et al., 2011). In this regard, the synergistic effect of BTA and Na₃PO₄ in the same solution has been evaluated and the maximum corrosion inhibition efficiency of 98.3% has been reported (Liu et al., 2012).

SEM image and EDX spectrum of copper immersed in 17 wt.% TBAB solution without BTA (a, b) and 17 wt.% TBAB solution containing 4 g/L BTA (c, d) (Liu et al., 2012).

The results of researches on corrosion inhibition of copper in various environments with various corrosion inhibitor compounds are given in Table 9.

Table 9 The results of the study of the efficiency of copper corrosion inhibition in other solutions.

Inhibitor group	Inhibitor		Concentration	Solution	Condition	Adsorption isotherm	Efficiency (%)			Ref
Azole	Thiazole derivatives	5-Benzylidene-2,4dioxotetrahydro-1,3-thiazole (BDT)		0.1 M Na₂SO₄	pH = 2.94		86.00 EIS	86.00 wl		(Vastag et al., 2001)
	Thiazole derivatives	5-(4′-Isopropylbenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (IPBDT)		0.1 M Na₂SO₄	pH = 2.94		93.00 EIS	89.00 wl		(Vastag et al., 2001)
	1,2,3-Benzotriazole (BTAH)		0.01 mM	0.1 M Na₂SO₄	pH = 2.5 immersion time = 3 h		83.30 pp			(Frignani et al., 1999)
	Methyl-benzotriazole (C1-BTA)						83.30 pp
	Butyl-benzotriazole (C4-BTA)						97.30 pp
	Hexyl-benzotriazole (C6-BTA)						99.30 pp
	5-Carboxybenzotriazole (5-CBT)		0.7 mM	0.1 M Na₂SO₄	pH ∼ 0 3 days		70.00 wl			(Otieno-Alego et al., 1999)
	4 Isomer-CBTAH-OE (C₈H₁₇ (octyl))		0.1 mM	0.5 M Na₂SO₄	pH = 8		99.10 pp			(Huynh et al., 2002)
	5 Isomer-CBTAH-OE (C₈H₁₇ (octyl))		0.1 mM	0.5 M Na₂SO₄	pH = 8		99.10 pp			(Huynh et al., 2002)
	CBTAH-OE		0.1 mM	0.1 M Na₂SO₄	pH ∼ 0 3 days 30 °C	Langmuir	98.00 wl			(Bartley et al., 2003)
	5-(4′-Dimetyl amino benzylidene)-2,4-dioxotetrahydro-1,3-thiazole (DABDT)		10 mM	0.1 M Na₂SO₄	pH = 3	Langmuir	90 pp	91 wl		(Mihajlović and Antonijević, 2015)
	BTA		0.3 mM	Borate buffer	pH = 8.4	Langmuir	91 pp			(Altaf et al., 2011)
	Mercaptobenzothiazole (MBT)						99 pp
	Thiadiazole (TDA)						96 pp
	Benzimidazole (BIMD)						94 pp
	Mercaptobenzimidazole (MBIMD)						94 pp
	Benzotriazole		6 g/L	17 wt.% tetra-n-butylammonium (TBAB)		Langmuir	93.8 pp	95.9 EIS	94.2 wl	(Liu et al., 2011)
	Benzotriazole (BTA) + Na₃PO₄		2 g/L BTA + 1 g/L Na₃PO₄	17 wt.% tetra-n-butylammonium (TBAB)		Langmuir	98.3 pp	96.4 EIS	96.3 wl	(Liu et al., 2012)
	Benzimidazole (BIMD)		2 mM	0.1 M NaOH		Langmuir	82.00 Cyclic voltammetry (cv)			(Subramanian and Lakshminarayanan, 2002)
	Mercaptobenzimidazole (MBIMD)		2 mM	0.1 M NaOH		Langmuir	74.00 Cyclic voltammetry (cv)			(Subramanian and Lakshminarayanan, 2002)
Amino acid	Cysteine		10 mM	0.5 M Na₂SO₄	pH = 9	Langmuir	88.16 pp			(Petrović et al., 2012a)
Amino acid	Cysteine		10 mM	0.5 M Na₂SO₄	pH = 2	Langmuir	82.73 pp			(Simonović et al., 2014)
Natural products (green extract)	Cassia siamea Lam (root extract)		10 mg/dm³	0.5 M NaOH		Langmuir	78.30			(Mihajlović and Antonijević, 2015)
Pharmaceutical drug (green inhibitors)	Potassium folate		10 mM	1 M Na₂SO₄	15 °C	Flory-Huggins	73.9 pp			(Hamed, 2010)
Other (carboxylic acid)	Myristic acid (MA)			0.2 g/L Na₂SO₄			95			(Žerjav and Milošev, 2014)
Other (purine)	Purine (PU)		10 mM	0.5 M Na₂SO₄	pH = 6.8	Langmuir	91.00 wl			(Scendo, 2007)
	Adenine (AD)		10 mM	0.5 M Na₂SO₄	pH = 6.8	Langmuir	94.00 wl
	Purine (PU)		10 mM	0.5 M Na₂SO₄	pH = 6.8	Langmuir	76.00 pp			(Scendo, 2007)
	Adenine (AD)		10 mM	0.5 M Na₂SO₄	pH = 6.8	Langmuir	91.00 pp
	Purine (PU)		10 mM	0.5 M Na₂SO₄	pH = 7	Langmuir	91.08 pp			(Petrović et al., 2012b)
	Purine (PU)		10 mM	0.5 M NaNO₃	pH = 3	Langmuir	90.00 pp			(Scendo, 2008)
	Adenine (AD)		10 mM	0.5 M NaNO₃	pH = 3	Langmuir	91.00 pp
	Purine (PU)		10 mM	Simulated uterine fluid (SUF)	3 h		99.18 pp			(Alvarez et al., 2012)
Other organic	Cobalt(II) 5,10,15,20tetrakis(2-aminophenyl)		1 mM	0.1 M Na₂SO₄	24 h		97.94 EIS			(Lokesh et al., 2012)

Due to the reported results about the efficiency of different inhibitors in different environments and with regard to the different parameters such as concentration of inhibitor, or pH for Na₂SO₄, Borate buffer and NaOH the best inhibitors are C6-BTA, MBT and BIMD.

6 Conclusions and future trends

According to the results of researches on corrosion protection of copper, various corrosion inhibitor compounds are used for protection of copper from corrosion attacks. However, there are few aggressive environments in which copper is used. Therefore, the review of corrosion inhibitor used for copper in various conditions (the type of environment, temperature, concentration of corrosion inhibitor, pollution) makes it possible to choose an efficient and cost-effective corrosion inhibitor for a particular environment. In general, the acidic or chloride-containing environments are the most aggressive environments for copper. The corrosion inhibition behavior of corrosion inhibitors in the aggressive environment is different. Some of the corrosion inhibitors protect the copper surface through the formation of a protective oxide film and some of them reduce corrosion attack through adsorption and formation of a complex layer. According to extracted results from corrosion tests, the increase in the concentration of corrosion inhibitor in the bulk of the solution (to an optimum concentration) and also increase in immersion time result in improving corrosion inhibition performance. The increase in temperature usually leads to a decrease in corrosion inhibition efficiency. The other point of this review paper was to survey about the molecular structure of various corrosion inhibitors, which are used for protection of copper. The molecular structure of corrosion inhibitor plays a dominant role in its corrosion inhibition efficiency. The presence of heteroatoms such as sulfur, nitrogen and oxygen atoms with free pair electrons, the alkyl chain with high molecular mass and aromatic rings in the structure of corrosion inhibitors plays an important role in their corrosion inhibition performance. Researchers have a special attention on the molecular structure of corrosion inhibitor during synthesizing of organic corrosion inhibitors. In spite of this fact that natural products, extracts, and pharmaceutical drugs can act as corrosion inhibitors because of their nontoxicity and relatively low cost, they cannot widely use in industrial systems due to their low corrosion inhibition efficiency. The most widely used corrosion inhibitor for protection of copper in salt and weak acidic environments is organic compounds from azole family, such as triazole, benzotriazole, and thiazole and for strong acidic media are imidazol and tetrazole. However, it should be noted that amine compounds at high concentrations provide appropriate corrosion inhibition performance, which can act as efficient corrosion inhibitor compound where economic issues are not a priority. In this study, besides survey of the corrosion inhibition of copper in common industrial environments such as acidic media, groundwater or cooling towers in both stagnant and flow conditions, some other corrosive environments such as ionized water (theoretically investigated its corrosivity) for copper have been reviewed. Also, the influence of hydrodynamic flow and the presence of various ions which can form a coordination-cyclic and heterocyclic-complex layer on copper have been studied. The main purpose of researchers is to provide a cost-effective, efficient, nontoxic and eco-friendly corrosion inhibitor to protect copper surface from corrosion attacks in most of the aggressive environments. Therefore, the future studies can be focused on development of organic compounds or production of new natural corrosion inhibitors and also the use of the synergistic effect of multicomponent corrosion inhibitors.

References

Atkins, P., 2010. Shriver and Atkins' inorganic chemistry. Oxford University Press, USA.
Abd-El-Nabey B., Abdel-Gaber A., Ali M.E.S., Khamis E., El-Housseiny S., . Inhibitive action of Cannabis plant extract on the corrosion of copper in 0.5 M H₂SO₄. Int. J. Electrochem. Sci.. 2013;8:5851-5865.
[Google Scholar]
Abdallah M., . Antibacterial drugs as corrosion inhibitors for corrosion of aluminium in hydrochloric solution. Corros. Sci.. 2004;46:1981-1996.
[Google Scholar]
Abdallah M., Zaafarany I., Al-Karanee S.O., Abd El-Fattah A.A., . Antihypertensive drugs as an inhibitors for corrosion of aluminum and aluminum silicon alloys in aqueous solutions. Arab. J. Chem.. 2012;5:225-234.
[Google Scholar]
Abdallah Y., Shalabi K., . Comprehensive study of the behavior of copper inhibition in 1 M HNO₃ by Euphorbia helioscopia linn. extract as green inhibitor. Prot. Met. Phys. Chem. Surf.. 2015;51:275-284.
[Google Scholar]
Abdel-Gaber A., Abd-El-Nabey B., Khamis E., Abd-El-Khalek D., . A natural extract as scale and corrosion inhibitor for steel surface in brine solution. Desalination. 2011;278:337-342.
[Google Scholar]
Abiola O.K., John M.O., Asekunowo P.O., Okafor P.C., James O.O., . 3-[(4-Amino-2-methyl-5-pyrimidinyl) methyl]-5-(2-hydroxyethyl)-4-methyl thiazolium chloride hydrochloride as green corrosion inhibitor of copper in HNO₃ solution and its adsorption characteristics. Green Chem. Lett. Rev.. 2011;4:273-279.
[Google Scholar]
Adamson A., Gast A., . Physical Chemical of Surfaces. New York: Wiley; 1997.
Adeloju S., Hughes H., . The corrosion of copper pipes in high chloride-low carbonate mains water. Corros. Sci.. 1986;26:851-870.
[Google Scholar]
Ahamad I., Quraishi M., . Mebendazole: new and efficient corrosion inhibitor for mild steel in acid medium. Corros. Sci.. 2010;52:651-656.
[Google Scholar]
Akyüz, M.A., Ergan, A.C., 2014. Behaviour of benzotriazole salts in multi metal formulations for corrosion inhibition of copper. In: NACE – International Corrosion Conference Series.
Al-Amiery A.A., Kadhum A.A.H., Mohamad A.B., Junaedi S., . A novel hydrazinecarbothioamide as a potential corrosion inhibitor for mild steel in HCl. Materials. 2013;6:1420-1431.
[Google Scholar]
Al-Qudah M.A., . Inhibition of copper corrosion by flavonoids in nitric acid. J. Chem.. 2011;8:326-332.
[Google Scholar]
Al-Shahrani S., El-Shazly A., . Corrosion inhibition of a gas sparged copper cylinder in a solution of NaCl and Na₂S by using 4-amino-4H-1,2,4-triazole as corrosion inhibitor. J. New Mater. Electrochem. Syst.. 2016;19
[Google Scholar]
Al Kharafi F.M., Ghayad I.M., Abdullah R.M., . Corrosion inhibition of copper in non-polluted and polluted sea water using 5-phenyl-1-H-tetrazole. Int. J. Electrochem. Sci.. 2012;7:3289-3298.
[Google Scholar]
Aldana-González, J., Espinoza-Vázquez, A., Romero-Romo, M., Uruchurtu-Chavarin, J., Palomar-Pardavé, M., 2015. Electrochemical evaluation of cephalothin as corrosion inhibitor for API 5L X52 steel immersed in an acid medium. Arab. J. Chem.
Alkire R., Cangellari A., . Effect of benzotriazole on dissolution of copper in the presence of fluid flow I. Experimental. J. Electrochem. Soc.. 1989;136:913-919.
[Google Scholar]
Altaf F., Qureshi R., Ahmed S., . Surface protection of copper by azoles in borate buffers-voltammetric and impedance analysis. J. Electroanal. Chem.. 2011;659:134-142.
[Google Scholar]
Alvarez F., Schilardi P.L., de Mele M.F.L., . Reduction of the “burst release” of copper ions from copper-based intrauterine devices by organic inhibitors. Contraception. 2012;85:91-98.
[Google Scholar]
Amin M.A., Khaled K., . Copper corrosion inhibition in O₂-saturated H₂SO₄ solutions. Corros. Sci.. 2010;52:1194-1204.
[Google Scholar]
Antonijevic M., Petrovic M., . Copper corrosion inhibitors. A review. Int. J. Electrochem. Sci.. 2008;3:1-28.
[Google Scholar]
Antonijevic M.M., Milic S.M., Dimitrijevic M.D., Petrovic M.B., Radovanovic M.B., Stamenkovic A.T., . The influence of pH and chlorides on electrochemical behavior of copper in the presence of benzotriazole. Int. J. Electrochem. Sci.. 2009;4:962-979.
[Google Scholar]
Antonijević M.M., Milić S.M., Petrović M.B., . Films formed on copper surface in chloride media in the presence of azoles. Corros. Sci.. 2009;51:1228-1237.
[Google Scholar]
Appa Rao B.V., Iqbal M.Y., Kumar K.C., Reddy M.N., . Corrosion protection of copper by self assembled nano film of 4-amino-3-(octadecylthio)-6-methyl-1,2,4-triazinone. Indian J. Chem. Technol.. 2014;21:188-198.
[Google Scholar]
Appa Rao B.V., Iqbal M.Y., Sreedhar B., . Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper. Electrochim. Acta. 2010;55:620-631.
[Google Scholar]
Appa Rao, B.V., Narsihma Reddy, M., 2014. Formation, characterization and corrosion protection efficiency of self-assembled 1-octadecyl-1H-imidazole films on copper for corrosion protection. Arab. J. Chem.
Appa Rao B.V., Yakub Iqbal M., Sreedhar B., . Self-assembled monolayer of 2-(octadecylthio)benzothiazole for corrosion protection of copper. Corros. Sci.. 2009;51:1441-1452.
[Google Scholar]
Ashassi-Sorkhabi H., Majidi M., Seyyedi K., . Investigation of inhibition effect of some amino acids against steel corrosion in HCl solution. Appl. Surf. Sci.. 2004;225:176-185.
[Google Scholar]
Attia A.A., Elmelegy E.M., El-Batouti M., Ahmed A.-M.M., . Anodic corrosion inhibition in presence of protic solvents. Asian J. Chem.. 2016;28:267.
[Google Scholar]
Ault J., . Erosion Corrosion of Nickel Aluminum Bronze in Flowing Seawater. Houston, TX (United States): NACE International; 1995.
Aytaç A., Bilgiç S., Gece G., Ancin N., Öztaş S.G., . Experimental and theoretical study of the inhibition effects of some Schiff bases as corrosion inhibitors of aluminium in HCl. Mater. Corros.. 2012;63:729-734.
[Google Scholar]
Baba H., Kodama T., . Corrosion inhibition and characteristics of the triazinedithiol surface film on copper under potentiostatic anodization. Corros. Sci.. 1999;41:1987-2000.
[Google Scholar]
Badawy W.A., Ismail K.M., Fathi A.M., . Corrosion control of Cu–Ni alloys in neutral chloride solutions by amino acids. Electrochim. Acta. 2006;51:4182-4189.
[Google Scholar]
Baeza, H., Guzman, M., Ortega, P., Vera, L., 2003. J. Chil. Chem. Soc. 48, 23.
Bagchi D., Bagchi M., Stohs S.J., Das D.K., Ray S.D., Kuszynski C.A., Joshi S.S., Pruess H.G., . Free radicals and grape seed proanthocyanidin extract: importance in human health and disease prevention. Toxicology. 2000;148:187-197.
[Google Scholar]
Barcia O., Mattos O., Pebere N., Tribollet B., . Mass-transport study for the electrodissolution of copper in 1 M hydrochloric acid solution by impedance. J. Electrochem. Soc.. 1993;140:2825-2832.
[Google Scholar]
Barouni K., Bazzi L., Salghi R., Mihit M., Hammouti B., Albourine A., El Issami S., . Some amino acids as corrosion inhibitors for copper in nitric acid solution. Mater. Lett.. 2008;62:3325-3327.
[Google Scholar]
Barouni K., Kassale A., Albourine A., Jbara O., Hammouti B., Bazzi L., . Amino acids as corrosion inhibitors for copper in nitric acid medium: experimental and theoretical study. J. Mater. Environ. Sci.. 2014;5:456-463.
[Google Scholar]
Bartley J., Huynh N., Bottle S., Flitt H., Notoya T., Schweinsberg D., . Computer simulation of the corrosion inhibition of copper in acidic solution by alkyl esters of 5-carboxybenzotriazole. Corros. Sci.. 2003;45:81-96.
[Google Scholar]
Bastidas D.M., . Adsorption of benzotriazole on copper surfaces in a hydrochloric acid solution. Surf. Interface Anal.. 2006;38:1146-1152.
[Google Scholar]
Behpour M., Ghoreishi S.M., Khayatkashani M., Soltani N., . Green approach to corrosion inhibition of mild steel in two acidic solutions by the extract of Punica granatum peel and main constituents. Mater. Chem. Phys.. 2012;131:621-633.
[Google Scholar]
Bhattacharjee C.R., Das G., Mondal P., . Novel non-discoid chiral copper (II)-salen type [N₂O₂] donor Schiff base complexes with a cyclohexane diamine spacer: synthesis, electrochemistry, columnar mesomorphism and DFT study. Liq. Cryst.. 2011;38:441-449.
[Google Scholar]
Blajiev O., Hubin A., . Inhibition of copper corrosion in chloride solutions by amino-mercapto-thiadiazol and methyl-mercapto-thiadiazol: an impedance spectroscopy and a quantum-chemical investigation. Electrochim. Acta. 2004;49:2761-2770.
[Google Scholar]
Bockris J.M., Swinkels D., . Adsorption of n-decylamine on solid metal electrodes. J. Electrochem. Soc.. 1964;111:736-743.
[Google Scholar]
Bozorg M., Shahrabi Farahani T., Neshati J., Chaghazardi Z., Mohammadi Ziarani G., . Myrtus communis as green inhibitor of copper corrosion in sulfuric acid. Ind. Eng. Chem. Res.. 2014;53:4295-4303.
[Google Scholar]
Butler M.S., . The role of natural product chemistry in drug discovery. J. Nat. Prod.. 2004;67:2141-2153.
[Google Scholar]
Cai L., Fu Q., Shi R., Tang Y., Long Y.T., He X.P., Jin Y., Liu G., Chen G.R., Chen K., . 'Pungent' copper surface resists acid corrosion in strong HCl solutions. Ind. Eng. Chem. Res.. 2014;53:64-69.
[Google Scholar]
Cao C., . On electrochemical techniques for interface inhibitor research. Corros. Sci.. 1996;38:2073-2082.
[Google Scholar]
Cao K., Sun H.Y., Hou B.R., . Corrosion inhibition of gemini surfactant for copper in 3.5% NaCl. Adv. Mater. Res. 2014:1125-1131.
[Google Scholar]
Chadwick D., Hashemi T., . Benzotriazole adsorption on copper studied by X-ray photoelectron spectroscopy. J. Electron Spectrosc. Relat. Phenom.. 1977;10:79-83.
[Google Scholar]
Chaitra T.K., Mohana K.N.S., Tandon H.C., . Thermodynamic, electrochemical and quantum chemical evaluation of some triazole Schiff bases as mild steel corrosion inhibitors in acid media. J. Mol. Liq.. 2015;211:1026-1038.
[Google Scholar]
Chauhan J.S., . Anticorrosion behaviour of Zenthoxylum alatum extract in acidic media. Asian J. Chem.. 2009;21:1975.
[Google Scholar]
Chen S., Kar T., . Theoretical investigation of inhibition efficiencies of some schiff bases as corrosion inhibitors of aluminum. Int. J. Electrochem. Sci.. 2012;7:6265-6275.
[Google Scholar]
Chen W., Hong S., Luo H.Q., Li N.B., . Inhibition effect of 2,4,6-trimercapto-1,3,5-triazine self-assembled monolayers on copper corrosion in NaCl solution. J. Mater. Eng. Perform.. 2014;23:527-537.
[Google Scholar]
Chen X.D., Gong M., Fu Q.S., Zheng X.W., Feng X.S., . [Omim][Pro] amino acid ionic liquids as a corrosion inhibitor for copper in 3.5% NaCl solution. Appl. Mech. Mater. 2014:47-50.
[Google Scholar]
Chen Z., Huang L., Zhang G., Qiu Y., Guo X., . Benzotriazole as a volatile corrosion inhibitor during the early stage of copper corrosion under adsorbed thin electrolyte layers. Corros. Sci.. 2012;65:214-222.
[Google Scholar]
Cheng Z., Mo S., Jia J., Feng J., Luo H.Q., Li N.B., . Experimental and theoretical studies of 4,6-diamino-2-mercaptopyrimidine as a copper inhibitor in 3.5 wt% NaCl solution. RSC Adv.. 2016;6:15210-15219.
[Google Scholar]
Chi-Ucán S.L., Castillo-Atoche A., Castro Borges P., Manzanilla-Cano J.A., González-García G., Patiño R., Díaz-Ballote L., . Inhibition effect of glycerol on the corrosion of copper in NaCl solutions at different pH values. J. Chem.. 2014;2014
[Google Scholar]
Choudhury M.R., Vidic R.D., Dzombak D.A., . Inhibition of copper corrosion by tolyltriazole in cooling systems using treated municipal wastewater as makeup water. Arab. J. Sci. Eng.. 2014;39:7741-7749.
[Google Scholar]
Curkovic H.O., Stupnisek-Lisac E., Takenouti H., . The influence of pH value on the efficiency of imidazole based corrosion inhibitors of copper. Corros. Sci.. 2010;52:398-405.
[Google Scholar]
Da Costa S., Agostinho S., Rubim J., . Spectroelectrochemical study of passive films formed on brass electrodes in 0.5 m H₂SO₄ aqueous solutions containing benzotriazole (BTAH) J. Electroanal. Chem. Interfacial Electrochem.. 1990;295:203-214.
[Google Scholar]
Da Costa S.L., Rubim J.C., Agostinho S.M., . Spectroelectrochemical study of the corrosion of a copper electrode in deaerated 1.0 M HCl solutions containing Fe (III): effect of the corrosion inhibitor benzotriazole. J. Electroanal. Chem. Interfacial Electrochem.. 1987;220:259-268.
[Google Scholar]
Dada A., Olalekan A., Olatunya A., Dada O., . Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms studies of equilibrium sorption of Zn²⁺ unto phosphoric acid modified rice husk. IOSR J. Appl. Chem.. 2012;3:38-45.
[Google Scholar]
Dadgarinezhad A., Baghaei Ravari F., . Inhibitive effect of a synthetic Schiff base on copper and its modification by benzotriazole in 0.5 M H₂SO₄. Prot. Met. Phys. Chem. Surf.. 2015;51:467-472.
[Google Scholar]
Dafali A., Hammouti B., Mokhlisse R., Kertit S., . Substituted uracils as corrosion inhibitors for copper in 3% NaCl solution. Corros. Sci.. 2003;45:1619-1630.
[Google Scholar]
Dagdag O., El Gouri M., Galai M., Ebn Touhami M., Essamri A., Elharfi A., . Application of hexa propylene glycol cyclotriphosphazene as corrosion inhibitor for copper in 3% NaCl solution. Der Pharm. Chem.. 2015;7:114-122.
[Google Scholar]
Davis J.R., . Copper and Copper Alloys. ASM International; 2001.
del PB Hernández R., Aoki I., Tribollet B., De Melo H., . Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles. Electrochim. Acta. 2011;56:2801-2814.
[Google Scholar]
Deng W., Lin P., Li Q., Mo G., . Ultrafine-grained copper produced by machining and its unusual electrochemical corrosion resistance in acidic chloride pickling solutions. Corros. Sci.. 2013;74:44-49.
[Google Scholar]
Desai M., Desai M., Shah C., Desai S., . Schiff bases as corrosion inhibitors for mild steel in hydrochloric acid solutions. Corros. Sci.. 1986;26:827-837.
[Google Scholar]
Deyab M., El-Rehim S.A., . Influence of polyethylene glycols on the corrosion inhibition of carbon steel in butyric acid solution: weight loss, EIS and theoretical studies. Int. J. Electrochem. Sci.. 2013;8:12613-12627.
[Google Scholar]
Deyab M.A., . Egyptian licorice extract as a green corrosion inhibitor for copper in hydrochloric acid solution. J. Ind. Eng. Chem.. 2015;22:384-389.
[Google Scholar]
Deyab M.A., Essehli R., El Bali B., . Inhibition of copper corrosion in cooling seawater under flowing conditions by novel pyrophosphate. RSC Adv.. 2015;5:64326-64334.
[Google Scholar]
Díaz-Gómez A., Vera R., Molinari A., Oliva A., Aperador W., . 5-Methyl-2,4-dihydropyrazol-3-one and 5-methyl-2-phenyl-2,4-didhydropyrazol-3-one as copper corrosion inhibitors in acidic media. Int. J. Electrochem. Sci.. 2014;10:4004-4019.
[Google Scholar]
Duran B., Bereket G., Duran M., . Electrochemical synthesis and characterization of poly (m-phenylenediamine) films on copper for corrosion protection. Prog. Org. Coat.. 2012;73:162-168.
[Google Scholar]
Eddy N., Odoemelam S., Ekwumemgbo P., . Inhibition of the corrosion of mild steel in H₂SO₄ by penicillin G. Sci. Res. Essays. 2009;4:033-038.
[Google Scholar]
Ehteshamzade M., Shahrabi T., Hosseini M., . Inhibition of copper corrosion by self-assembled films of new Schiff bases and their modification with alkanethiols in aqueous medium. Appl. Surf. Sci.. 2006;252:2949-2959.
[Google Scholar]
Ehteshamzadeh M., Shahrabi T., Hosseini M., . Innovation in acid pickling treatments of copper by characterizations of a new series of Schiff bases as corrosion inhibitors. Anti-Corros. Methods Mater.. 2006;53:296-302.
[Google Scholar]
El-Hafez G.M.A., Badawy W.A., . The use of cysteine, N-acetyl cysteine and methionine as environmentally friendly corrosion inhibitors for Cu–10Al–5Ni alloy in neutral chloride solutions. Electrochim. Acta. 2013;108:860-866.
[Google Scholar]
El-Mahdy G.A., Kim K.B., . AC impedance study on the atmospheric corrosion of aluminum under periodic wet–dry conditions. Electrochim. Acta. 2004;49:1937-1948.
[Google Scholar]
El-Naggar M., . Bis-aminoazoles corrosion inhibitors for copper in 4.0 M HNO₃ solutions. Corros. Sci.. 2000;42:773-784.
[Google Scholar]
El-Naggar M., . Corrosion inhibition of mild steel in acidic medium by some sulfa drugs compounds. Corros. Sci.. 2007;49:2226-2236.
[Google Scholar]
Eldesoky A., Hassan H.M., Fouda A., . Studies on the corrosion inhibition of copper in nitric acid solution using some pharmaceutical compounds. Int. J. Electrochem. Sci.. 2013;8:10376-10395.
[Google Scholar]
Eldesoky A.M., Diab M.A., El-Bindary A.A., El-Sonbati A.Z., Seyam H.A., . Some antipyrine derivatives as corrosion inhibitors for copper in acidic medium: experimental and quantum chemical molecular dynamics approach. J. Mater. Environ. Sci.. 2015;6:2148-2165.
[Google Scholar]
Emad M., Al-Rasheedi M., . Nigella sativa and natural honey as corrosion inhibitors for copper in cooling water systems. J. Mater. Environ. Sci.. 2015;6:201-206.
[Google Scholar]
Enick, O.V., 2006. Do Pharmaceutically Active Compounds have an Ecological Impact? Biological Sciences Department – Simon Fraser University.
Erdem E., Karapinar N., Donat R., . The removal of heavy metal cations by natural zeolites. J. Colloid Interface Sci.. 2004;280:309-314.
[Google Scholar]
Esmaeili N., Neshati J., Yavari I., . Scanning electrochemical microscopy for the investigation of corrosion inhibition of triazino-benzimidazole-2-thiones in hydrochloric acid solution. Res. Chem. Intermed. 2015:1-13.
[Google Scholar]
Ezznaydy G., Shaban A., Telegdi J., Ouaki B., El Hajjaji S., . Inhibition of copper corrosion in saline solution by mono-hydroxamic acid. J. Mater. Environ. Sci.. 2015;6:1819-1823.
[Google Scholar]
Mounir, F., Lh. Bazzi, S.E.I., Salghi, R., Bammou, L., Bazzi1, L., Chihab Eddine, A., Jbara, O., 2012. Copper corrosion behavior in phosphoric acid containing chloride and its inhibition by artemisia oil. IJRRAS 13, 574–587.
Fayomi O.S.I., Popoola A.P.I., Popoola O.M., . Inhibitive action and synergistic performance of 2-amino-ethanol and N,N-diethylethanamine on copper in hydrochloric acid solution. Bull. Chem. Soc. Ethiop.. 2014;28:457-467.
[Google Scholar]
Feng L., Yang H., Wang F., . Experimental and theoretical studies for corrosion inhibition of carbon steel by imidazoline derivative in 5% NaCl saturated Ca(OH)₂ solution. Electrochim. Acta. 2011;58:427-436.
[Google Scholar]
Finšgar M., . 2-Mercaptobenzimidazole as a copper corrosion inhibitor: part I. Long-term immersion, 3D-profilometry, and electrochemistry. Corros. Sci.. 2013;72:82-89.
[Google Scholar]
Finšgar M., . The first X-ray photoelectron spectroscopy surface analysis of 4-methyl-2-phenyl-imidazole adsorbed on copper. Anal. Methods. 2015;7:6496-6503.
[Google Scholar]
Finšgar M., Merl D.K., . 2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: electrochemistry, 3D-profilometry, and XPS surface analysis. Corros. Sci.. 2014;80:82-95.
[Google Scholar]
Finšgar M., Milošev I., . Inhibition of copper corrosion by 1,2,3-benzotriazole: a review. Corros. Sci.. 2010;52:2737-2749.
[Google Scholar]
Flis J., Zakroczymski T., . Impedance study of reinforcing steel in simulated pore solution with tannin. J. Electrochem. Soc.. 1996;143:2458-2464.
[Google Scholar]
Flory P.J., . Thermodynamics of high polymer solutions. J. Chem. Phys.. 1942;10:51-61.
[Google Scholar]
Foo K., Hameed B., . Insights into the modeling of adsorption isotherm systems. Chem. Eng. J.. 2010;156:2-10.
[Google Scholar]
Fouda A., El-Haddad M., Abdallah Y., . Septazole: antibacterial drug as a green corrosion inhibitor for copper in hydrochloric acid solutions. Int. J. Innov. Res. Sci. Eng. Technol.. 2013;2:7073-7085.
[Google Scholar]
Fouda A., Eldesoky A., El-Sonbati A., Salam S., . Prop-2-en-1-one derivatives as corrosion inhibitors for copper in 1 M HNO₃. Int. J. Electrochem. Sci.. 2014;9:1867-1891.
[Google Scholar]
Fouda A., Moussa M., Taha F., Elneanaa A., . The role of some thiosemicarbazide derivatives in the corrosion inhibition of aluminium in hydrochloric acid. Corros. Sci.. 1986;26:719-726.
[Google Scholar]
Fouda A.E.A.S., Etaiw S.E.D.H., El-Bendary M.M., Maher M.M., . Metal-organic frameworks based on silver (I) and nitrogen donors as new corrosion inhibitors for copper in HCl solution. J. Mol. Liq.. 2016;213:228-234.
[Google Scholar]
Fouda A.S., El-Aal A.A., Kandil A.B., . The effect of some phthalimide derivatives on corrosion behavior of copper in nitric acid. Desalination. 2006;201:216-223.
[Google Scholar]
Fouda A.S., Shalabi K., Idress A.A., . Ceratonia siliqua extract as a green corrosion inhibitor for copper and brass in nitric acid solutions. Green Chem. Lett. Rev.. 2015;8:17-29.
[Google Scholar]
Fouda A.S., Wahed H.A.A., . Corrosion inhibition of copper in HNO₃ solution using thiophene and its derivatives. Arab. J. Chem.. 2016;9(Suppl. 1):S91-S99.
[Google Scholar]
Frignani A., Tommesani L., Brunoro G., Monticelli C., Fogagnolo M., . Influence of the alkyl chain on the protective effects of 1,2,3-benzotriazole towards copper corrosion. Part I: inhibition of the anodic and cathodic reactions. Corros. Sci.. 1999;41:1205-1215.
[Google Scholar]
Furukawa H., Miller M.A., Yaghi O.M., . Independent verification of the saturation hydrogen uptake in MOF-177 and establishment of a benchmark for hydrogen adsorption in metal–organic frameworks. J. Mater. Chem.. 2007;17:3197-3204.
[Google Scholar]
Gašparac R., Stupnisek-Lisac E., . Corrosion protection on copper by imidazole and its derivatives. Corrosion. 1999;55:1031-1039.
[Google Scholar]
Gerengi H., Darowicki K., Slepski P., Bereket G., Ryl J., . Investigation effect of benzotriazole on the corrosion of brass-MM55 alloy in artificial seawater by dynamic EIS. J. Solid State Electrochem.. 2010;14:897-902.
[Google Scholar]
Ghasemi Z., Tizpar A., . The inhibition effect of some amino acids towards Pb–Sb–Se–As alloy corrosion in sulfuric acid solution. Appl. Surf. Sci.. 2006;252:3667-3672.
[Google Scholar]
Gimbert F., Morin-Crini N., Renault F., Badot P.-M., Crini G., . Adsorption isotherm models for dye removal by cationized starch-based material in a single component system: error analysis. J. Hazard. Mater.. 2008;157:34-46.
[Google Scholar]
Gomma G.K., Wahdan M.H., . Effect of temperature on the acidic dissolution of copper in the presence of amino acids. Mater. Chem. Phys.. 1994;39:142-148.
[Google Scholar]
Gong Y., Wang Z., Gao F., Zhang S., Li H., . Synthesis of new benzotriazole derivatives containing carbon chains as the corrosion inhibitors for copper in sodium chloride solution. Ind. Eng. Chem. Res.. 2015;54:12242-12253.
[Google Scholar]
Gopi D., Govindaraju K.M., Collins Arun Prakash V., Angeline Sakila D.M., Kavitha L., . A study on new benzotriazole derivatives as inhibitors on copper corrosion in ground water. Corros. Sci.. 2009;51:2259-2265.
[Google Scholar]
Gopi D., Sherif E.S.M., Surendiran M., Angeline Sakila D.M., Kavitha L., . Corrosion inhibition by benzotriazole derivatives and sodium dodecyl sulphate as corrosion inhibitors for copper in ground water at different temperatures. Surf. Interface Anal.. 2015;47:618-625.
[Google Scholar]
Guo L., Dong W., Zhang S., . Theoretical challenges in understanding the inhibition mechanism of copper corrosion in acid media in the presence of three triazole derivatives. RSC Adv.. 2014;4:41956-41967.
[Google Scholar]
Gupta N.K., Verma C., Quraishi M.A., Mukherjee A.K., . Schiff's bases derived from l-lysine and aromatic aldehydes as green corrosion inhibitors for mild steel: experimental and theoretical studies. J. Mol. Liq.. 2016;215:47-57.
[Google Scholar]
Gupta S.R., Mourya P., Singh M., Singh V.P., . Synthesis, structural, electrochemical and corrosion inhibition properties of two new ferrocene Schiff bases derived from hydrazides. J. Organomet. Chem.. 2014;767:136-143.
[Google Scholar]
Habib K., . In-situ monitoring of pitting corrosion of copper alloys by holographic interferometry. Corros. Sci.. 1998;40:1435-1440.
[Google Scholar]
Hamdani I., El Ouariachi E., Mokhtari O., Salhi A., Bouyanzer A., Zarrouk A., Hammouti B., Costa J., . An investigation of mild steel corrosion inhibition in hydrochloric acid medium by environment friendly green inhibitor. Der Pharm. Lett.. 2015;7:109-118.
[Google Scholar]
Hamed E., . Studies of the corrosion inhibition of copper in Na₂SO₄ solution using polarization and electrochemical impedance spectroscopy. Mater. Chem. Phys.. 2010;121:70-76.
[Google Scholar]
Hammouti B., Aouniti A., Taleb M., Brighli M., Kertit S., . l-Methionine methyl ester hydrochloride as a corrosion inhibitor of iron in acid chloride solution. Corrosion. 1995;51:411-416.
[Google Scholar]
Hansen K.B., Hsiao Y., Xu F., Rivera N., Clausen A., Kubryk M., Krska S., Rosner T., Simmons B., Balsells J., Ikemoto N., Sun Y., Spindler F., Malan C., Grabowski E.J.J., Armstrong Iii J.D., . Highly efficient asymmetric synthesis of sitagliptin. J. Am. Chem. Soc.. 2009;131:8798-8804.
[Google Scholar]
Hazazi O.A., Abdallah M., . Prazole compounds as inhibitors for corrosion of aluminum in hydrochloric acid. Int. J. Electrochem. Sci.. 2013;8:8138-8152.
[Google Scholar]
Hefter G., North N., Tan S., . Organic corrosion inhibitors in neutral solutions; part 1 – inhibition of steel, copper, and aluminum by straight chain carboxylates. Corrosion. 1997;53:657-667.
[Google Scholar]
Hegazy M.A., Nazeer A.A., Shalabi K., . Electrochemical studies on the inhibition behavior of copper corrosion in pickling acid using quaternary ammonium salts. J. Mol. Liq.. 2015;209:419-427.
[Google Scholar]
Hofmann K., . The Chemistry of Heterocyclic Compounds, Imidazole and Its Derivatives. John Wiley & Sons; 2009.
Hollander O., May R.C., . The chemistry of azole copper corrosion inhibitors in cooling waters. Corrosion. 1985;41:39-45.
[Google Scholar]
Holm R., Holtkamp D., Kleinstück R., Rother H.J., Storp S., . Surface analysis methods in the investigation of corrosion inhibitor performance. Fresenius' Zeitschrift für analytische Chemie. 1989;333:546-554.
[Google Scholar]
Holze R., . The electrosorption of imidazole on a gold electrode as studied with spectroelectrochemical methods. Electrochim. Acta. 1993;38:947-956.
[Google Scholar]
Hosseini M.G., Tavakoli H., Shahrabi T., . Synergism in copper corrosion inhibition by band 2-mercaptobenzoimidazole. J. Appl. Electrochem.. 2008;38:1629-1636.
[Google Scholar]
Hu L., Zhang S., Li W., Hou B., . Electrochemical and thermodynamic investigation of diniconazole and triadimefon as corrosion inhibitors for copper in synthetic seawater. Corros. Sci.. 2010;52:2891-2896.
[Google Scholar]
Huijing Z., Guangyong L., Huan W., Lixin G., Daquan Z., . Synergistic effect of triethyl phosphate and cerium (IV) ion on corrosion inhibition for copper in hydrochloric acid solution. J. Chin. Soc. Corros. Prot.. 2014;34:271-276.
[Google Scholar]
Huynh N., Bottle S., Notoya T., Schweinsberg D., . Inhibition of copper corrosion by coatings of alkyl esters of carboxybenzotriazole. Corros. Sci.. 2002;44:2583-2596.
[Google Scholar]
Ismail K.M., . Evaluation of cysteine as environmentally friendly corrosion inhibitor for copper in neutral and acidic chloride solutions. Electrochim. Acta. 2007;52:7811-7819.
[Google Scholar]
Issaadi S., Douadi T., Chafaa S., . Adsorption and inhibitive properties of a new heterocyclic furan schiff base on corrosion of copper in HCL 1 M: experimental and theoretical investigation. Appl. Surf. Sci.. 2014;316:582-589.
[Google Scholar]
Izquierdo J., Santana J.J., González S., Souto R.M., . Scanning microelectrochemical characterization of the anti-corrosion performance of inhibitor films formed by 2-mercaptobenzimidazole on copper. Prog. Org. Coat.. 2012;74:526-533.
[Google Scholar]
Jennings G.K., Yong T.-H., Munro J.C., Laibinis P.E., . Structural effects on the barrier properties of self-assembled monolayers formed from long-chain ω-alkoxy-n-alkanethiols on copper. J. Am. Chem. Soc.. 2003;125:2950-2957.
[Google Scholar]
Ji G., Anjum S., Sundaram S., Prakash R., . Musa paradisica peel extract as green corrosion inhibitor for mild steel in HCl solution. Corros. Sci.. 2015;90:107-117.
[Google Scholar]
Joseph B., Joseph A., . Inhibition of copper corrosion in 1 M nitric acid-electro analytical and theoretical study with (E)-(4-(4-methoxybenzylideneamino)-4H-1,2,4-triazole-3,5diyl) dimethanol (MBATD) Portugaliae Electrochim. Acta. 2011;29:253-271.
[Google Scholar]
Kallip S., Bastos A.C., Zheludkevich M.L., Ferreira M.G.S., . A multi-electrode cell for high-throughput SVET screening of corrosion inhibitors. Corros. Sci.. 2010;52:3146-3149.
[Google Scholar]
Karthik G., Sundaravadivelu M., . Amikacin disulfate: an aminoglycoside antibiotic drug as a corrosion inhibitor for copper in 1 M nitric acid medium. J. Adhes. Sci. Technol.. 2016;30:1072-1086.
[Google Scholar]
Karthik G., Sundaravadivelu M., Rajkumar P., Manikandan M., . Diaza-adamantane derivatives as corrosion inhibitor for copper in nitric acid medium. Res. Chem. Intermed. 2015:7593-7615.
[Google Scholar]
Kear G., Barker B.D., Walsh F.C., . Electrochemical corrosion of unalloyed copper in chloride media – a critical review. Corros. Sci.. 2004;46:109-135.
[Google Scholar]
Khadom A.A., . Dual function of benzotriazole as copper alloy corrosion inhibitor and hydrochloric acid flow improver. Surf. Eng. Appl. Electrochem.. 2014;50:157-172.
[Google Scholar]
Khaled K., . Molecular simulation, quantum chemical calculations and electrochemical studies for inhibition of mild steel by triazoles. Electrochim. Acta. 2008;53:3484-3492.
[Google Scholar]
Khaled K., . Corrosion control of copper in nitric acid solutions using some amino acids – a combined experimental and theoretical study. Corros. Sci.. 2010;52:3225-3234.
[Google Scholar]
Khaled K., . Studies of the corrosion inhibition of copper in sodium chloride solutions using chemical and electrochemical measurements. Mater. Chem. Phys.. 2011;125:427-433.
[Google Scholar]
Khaled K., Amin M.A., . Dry and wet lab studies for some benzotriazole derivatives as possible corrosion inhibitors for copper in 1.0 M HNO₃. Corros. Sci.. 2009;51:2098-2106.
[Google Scholar]
Khaled K., Amin M.A., Al-Mobarak N., . On the corrosion inhibition and adsorption behaviour of some benzotriazole derivatives during copper corrosion in nitric acid solutions: a combined experimental and theoretical study. J. Appl. Electrochem.. 2010;40:601-613.
[Google Scholar]
Khaled K., Fadl-Allah S.A., Hammouti B., . Some benzotriazole derivatives as corrosion inhibitors for copper in acidic medium: experimental and quantum chemical molecular dynamics approach. Mater. Chem. Phys.. 2009;117:148-155.
[Google Scholar]
Khaled K.F., Hackerman N., . Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 1 M HCl solutions. Electrochim. Acta. 2003;48:2715-2723.
[Google Scholar]
Khalil N., Mahgoub F., Abd-El-Nabey B., Abdel-Aziz A., . Corrosion of aluminium in perchloric acid in presence of various inorganic additives. Corros. Eng., Sci. Technol.. 2003;38:205-210.
[Google Scholar]
Khamis E., Kandil S., Ibrahim A., . Adsorption action of phosphine inhibitors on the corrosion of steel. Adsorpt. Sci. Technol.. 1995;12:279-291.
[Google Scholar]
Khan P.F., Shanthi V., Babu R.K., Muralidharan S., Barik R.C., . Effect of benzotriazole on corrosion inhibition of copper under flow conditions. J. Environ. Chem. Eng.. 2015;3:10-19.
[Google Scholar]
Kidwai M., Misra P., Bhushan K.R., Dave B., . A novel route to 1,2,4-triazoles. Synth. Commun.. 2000;30:3031-3040.
[Google Scholar]
Kilinççeker G., Demir H., . The inhibition effects of cysteine on the corrosion behaviour of copper in 3.5% NaCl solution. Anti-Corros. Methods Mater.. 2013;60:134-142.
[Google Scholar]
Kokalj A., . Is the analysis of molecular electronic structure of corrosion inhibitors sufficient to predict the trend of their inhibition performance. Electrochim. Acta. 2010;56:745-755.
[Google Scholar]
Kokalj A., Kovačević N., Peljhan S., Finšgar M., Lesar A., Milošev I., . Triazole, benzotriazole, and naphthotriazole as copper corrosion inhibitors: I. Molecular electronic and adsorption properties. ChemPhysChem. 2011;12:3547-3555.
[Google Scholar]
Kosower E.M., . Introduction to Physical Organic Chemistry. John Wiley & Sons; 1968.
Krishnaveni K., Ravichandran J., . Influence of aqueous extract of leaves of Morinda tinctoria on copper corrosion in HCl medium. J. Electroanal. Chem.. 2014;735:24-31.
[Google Scholar]
Krishnaveni K., Ravichandran J., . A study on the inhibition of copper corrosion in sulphuric acid by aqueous extract of leaves of Morinda tinctoria. J. Fail. Anal. Prev.. 2015;15:711-721.
[Google Scholar]
Kundu S., Gupta A., . Arsenic adsorption onto iron oxide-coated cement (IOCC): regression analysis of equilibrium data with several isotherm models and their optimization. Chem. Eng. J.. 2006;122:93-106.
[Google Scholar]
Kuruvilla M., John S., Joseph A., . Electrochemical studies on the interaction of l-cysteine with metallic copper in sulfuric acid. Res. Chem. Intermed.. 2013;39:3531-3543.
[Google Scholar]
Lakshminarayanan V., Kannan R., Rajagopalan S., . Cyclic voltammetric behavior of certain copper-azole systems using carbon paste electrodes. J. Electroanal. Chem.. 1994;364:79-86.
[Google Scholar]
Lalitha A., Ramesh S., Rajeswari S., . Surface protection of copper in acid medium by azoles and surfactants. Electrochim. Acta. 2005;51:47-55.
[Google Scholar]
Lee W.-J., . Inhibiting effects of imidazole on copper corrosion in 1 M HNO₃ solution. Mater. Sci. Eng., A. 2003;348:217-226.
[Google Scholar]
Lei Y.H., Sheng N., Hyono A., Ueda M., Ohtsuka T., . Effect of benzotriazole (BTA) addition on polypyrrole film formation on copper and its corrosion protection. Prog. Org. Coat.. 2014;77:339-346.
[Google Scholar]
Lewis G., . Adsorption isotherm for the copper-benzotnazole system. Br. Corros. J.. 1981;16:169-171.
[Google Scholar]
Li C., Li L., Wang C., Zhu Y., Zhang W., . Study of the protection performance of self-assembled monolayers on copper with the scanning electrochemical microscope. Corros. Sci.. 2014;80:511-516.
[Google Scholar]
Li M.M., Xu Q.J., Han J., Yun H., Min Y., . Inhibition action and adsorption behavior of green inhibitor sodium carboxymethyl cellulose on copper. Int. J. Electrochem. Sci.. 2015;10:9028-9041.
[Google Scholar]
Li Q., Li J., Hu L.T., Zhu L., Han X., Tao Z.H., He W., . Electrochemical study of corrosion inhibition on copper in base electrolyte by 1-phenyl-3-hydroxy-1,2,4-triazole. Adv. Mater. Res. 2014:3-7.
[Google Scholar]
Li S., Chen S., Lei S., Ma H., Yu R., Liu D., . Investigation on some Schiff bases as HCl corrosion inhibitors for copper. Corros. Sci.. 1999;41:1273-1287.
[Google Scholar]
Li S.L., Wang Y.G., Chen S.H., Yu R., Lei S.B., Ma H.Y., Liu D.X., . Some aspects of quantum chemical calculations for the study of Schiff base corrosion inhibitors on copper in NaCl solutions. Corros. Sci.. 1999;41:1769-1782.
[Google Scholar]
Li W., Bai X., Yang F., Hou B., . One derivate of thiadiazole (MTYDBH) as corrosion inhibitors for copper in 3.5% NaCl solution under various conditions. Int. J. Electrochem. Sci.. 2012;7:2680-2694.
[Google Scholar]
Liao Q., Yue Z., Yang D., Wang Z., Li Z., Ge H., Li Y., . Inhibition of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium diethyldithiocarbamate. Corros. Sci.. 2011;53:1999-2005.
[Google Scholar]
Liu A., Ren X., Zhang J., Wang C., Yang P., Zhang J., An M., Higgins D., Li Q., Wu G., . Theoretical and experimental studies of the corrosion inhibition effect of nitrotetrazolium blue chloride on copper in 0.1 M H₂SO₄. RSC Adv.. 2014;4:40606-40616.
[Google Scholar]
Liu M., Sibi M.P., . Recent advances in the stereoselective synthesis of β-amino acids. Tetrahedron. 2002;58:7991-8035.
[Google Scholar]
Liu S., Dong J., Guan W., Duan J., Jiang R., Feng Z., Song W., . The synergistic effect of Na₃PO₄ and benzotriazole on the inhibition of copper corrosion in tetra-n-butylammonium bromide aerated aqueous solution. Mater. Corros.. 2012;63:1017-1025.
[Google Scholar]
Liu S., Duan J., Jiang R., Feng Z., Xiao R., . Corrosion inhibition of copper in tetra-n-butylammonium bromide aqueous solution by benzotriazole. Mater. Corros.. 2011;62:47-52.
[Google Scholar]
Lokesh K.S., De Keersmaecker M., Elia A., Depla D., Dubruel P., Vandenabeele P., Van Vlierberghe S., Adriaens A., . Adsorption of cobalt (II) 5,10,15,20-tetrakis (2-aminophenyl)-porphyrin onto copper substrates: characterization and impedance studies for corrosion inhibition. Corros. Sci.. 2012;62:73-82.
[Google Scholar]
Love J.C., Estroff L.A., Kriebel J.K., Nuzzo R.G., Whitesides G.M., . Self-assembled monolayers of thiolates on metals as a form of nanotechnology. Chem. Rev.. 2005;105:1103-1170.
[Google Scholar]
Ma F., Li W., Tian H., Hou B., . The use of a new thiadiazole derivative as a highly efficient and durable copper inhibitor in 3.5% NaCl solution. Int. J. Electrochem. Sci.. 2015;10:5862-5879.
[Google Scholar]
Ma H., Chen S., Niu L., Zhao S., Li S., Li D., . Inhibition of copper corrosion by several Schiff bases in aerated halide solutions. J. Appl. Electrochem.. 2002;32:65-72.
[Google Scholar]
Ma H., Chen S., Yin B., Zhao S., Liu X., . Impedance spectroscopic study of corrosion inhibition of copper by surfactants in the acidic solutions. Corros. Sci.. 2003;45:867-882.
[Google Scholar]
Ma H., Chen S., Zhao S., Liu X., Li D., . A study of corrosion behavior of copper in acidic solutions containing cetyltrimethylammonium bromide. J. Electrochem. Soc.. 2001;148:B482-B488.
[Google Scholar]
Ma H., Yang C., Yin B., Li G., Chen S., Luo J., . Electrochemical characterization of copper surface modified by n-alkanethiols in chloride-containing solutions. Appl. Surf. Sci.. 2003;218:144-154.
[Google Scholar]
Makarenko N., Kharchenko U., Zemnukhova L., . Effect of amino acids on corrosion of copper and steel in acid medium. Russ. J. Appl. Chem.. 2011;84:1362-1365.
[Google Scholar]
Marcus P., Mansfeld F.B., . Analytical Methods in Corrosion Science and Engineering. Taylor & Francis; 2005.
Masmoudi M., Rahal C., Abdelhedi R., Khitouni M., Bouaziz M., . Inhibitive action of stored olive mill wastewater (OMW) on the corrosion of copper in a NaCl solution. RSC Adv.. 2015;5:101768-101775.
[Google Scholar]
Matos J., Pereira L., Agostinho S., Barcia O., Cordeiro G., D'elia E., . Effect of cysteine on the anodic dissolution of copper in sulfuric acid medium. J. Electroanal. Chem.. 2004;570:91-94.
[Google Scholar]
McCafferty E., . Introduction to Corrosion Science. 3Island Press; 2011.
Mehdipour M., Ramezanzadeh B., Arman S., . Electrochemical noise investigation of Aloe plant extract as green inhibitor on the corrosion of stainless steel in 1 M H₂SO₄. J. Ind. Eng. Chem.. 2015;21:318-327.
[Google Scholar]
Metikoš-Huković M., Babić R., Marinović A., . Spectrochemical characterization of benzotriazole on copper. J. Electrochem. Soc.. 1998;145:4045-4051.
[Google Scholar]
Mihajlović M.B.P., Antonijević M.M., . Copper corrosion inhibitors. Period 2008–2014. A review. Int. J. Electrochem. Sci.. 2015;10:1027-1053.
[Google Scholar]
Mihit M., Salghi R., El Issami S., Bazzi L., Hammouti B., Addi E.A., Kertit S., . A study of tetrazoles derivatives as corrosion inhibitors of copper in nitric acid. Pigm. Resin Technol.. 2006;35:151-157.
[Google Scholar]
Mo S., Qin T.T., Luo H.Q., Li N.B., . Insights into the corrosion inhibition of copper in hydrochloric acid solution by self-assembled films of 4-octylphenol. RSC Adv.. 2015;5:90542-90549.
[Google Scholar]
Moretti G., Guidi F., . Tryptophan as copper corrosion inhibitor in 0.5 M aerated sulfuric acid. Corros. Sci.. 2002;44:1995-2011.
[Google Scholar]
Mouni F., El Issami S., Bazzi L., Salghi R., Abidi N., Jodeh S., Bazzi L., Chihab Eddine A., . Green approach to corrosion inhibition of copper by two oils of Argania spinosa (L.) in phosphoric acid. J. Mater. Environ. Sci.. 2015;6:2066-2075.
[Google Scholar]
Mounir F., El Issami S., Bazzi L., Chihab Eddine A., Jbara O., Hilali M., Salghi R., Bazzi L., . Application of cosmetic argan oil as green corrosion inhibitor for copper in phosphoric acid medium. J. Mater. Environ. Sci.. 2014;5:2478-2483.
[Google Scholar]
Muniandy M.T., Rahim A.A., Osman H., Shah A.M., Yahya S., Raja P.B., . Investigation of some schiff bases as corrosion inhibitors for aluminium alloy in 0.5 M hydrochloric acid solutions. Surf. Rev. Lett.. 2011;18:127-133.
[Google Scholar]
Muñoz A.I., Antón J.G., Guiñón J., Herranz V.P., . Comparison of inorganic inhibitors of copper, nickel and copper–nickels in aqueous lithium bromide solution. Electrochim. Acta. 2004;50:957-966.
[Google Scholar]
Mustafa C., Shahinoor Islam Dulal S., . Molybdate and nitrite as corrosion inhibitors for copper-coupled steel in simulated cooling water. Corrosion. 1996;52:16-22.
[Google Scholar]
Obot I., Obi-Egbedi N., . Fluconazole as an inhibitor for aluminium corrosion in 0.1 M HCl. Colloids Surf., A. 2008;330:207-212.
[Google Scholar]
Obot I., Obi-Egbedi N., . Inhibition of aluminium corrosion in hydrochloric acid using nizoral and the effect of iodide ion addition. J. Chem.. 2010;7:837-843.
[Google Scholar]
Odewunmi N., Umoren S., Gasem Z., . Utilization of watermelon rind extract as a green corrosion inhibitor for mild steel in acidic media. J. Ind. Eng. Chem.. 2015;21:239-247.
[Google Scholar]
Otieno-Alego V., Huynh N., Notoya T., Bottle S., Schweinsberg D., . Inhibitive effect of 4-and 5-carboxybenzotriazole on copper corrosion in acidic sulphate and hydrogen sulphide solutions. Corros. Sci.. 1999;41:685-697.
[Google Scholar]
Otmačić H., Stupnišek-Lisac E., . Copper corrosion inhibitors in near neutral media. Electrochim. Acta. 2003;48:985-991.
[Google Scholar]
Park J., Lee G., Ooshige H., Nishikata A., Tsuru T., . Monitoring of water uptake in organic coatings under cyclic wet–dry condition. Corros. Sci.. 2003;45:1881-1894.
[Google Scholar]
Peca D., Pihlar B., Milosěv I., . Protection of copper surface with phytic acid against corrosion in chloride solution. Acta Chim. Slov.. 2014;61:457-467.
[Google Scholar]
Petrović M.B., Radovanović M.B., Simonović A.T., Milić S.M., Antonijević M.M., . The effect of cysteine on the behaviour of copper in neutral and alkaline sulphate solutions. Int. J. Electrochem. Sci.. 2012;7:9043-9057.
[Google Scholar]
Petrović M.B., Simonović A.T., Radovanović M.B., Milić S.M., Antonijević M.M., . Influence of purine on copper behavior in neutral and alkaline sulfate solutions. Chem. Pap.. 2012;66:664-676.
[Google Scholar]
Poling G., . Reflection infra-red studies of films formed by benzotriazole on Cu. Corros. Sci.. 1970;10:359-370.
[Google Scholar]
Pratihar P.S., Verma M.P.S., Sharma A., . Capparis decidua seeds: potential green inhibitor to combat acid corrosion of copper. Rasayan J. Chem.. 2015;8:411-421.
[Google Scholar]
Qiang Y., Zhang S., Xu S., Yin L., . The effect of 5-nitroindazole as an inhibitor for the corrosion of copper in a 3.0% NaCl solution. RSC Adv.. 2015;5:63866-63873.
[Google Scholar]
Qin T.T., Li J., Luo H.Q., Li M., Li N.B., . Corrosion inhibition of copper by 2,5-dimercapto-1,3,4-thiadiazole monolayer in acidic solution. Corros. Sci.. 2011;53:1072-1078.
[Google Scholar]
Quartarone G., Battilana M., Bonaldo L., Tortato T., . Investigation of the inhibition effect of indole-3-carboxylic acid on the copper corrosion in 0.5 M H₂SO₄. Corros. Sci.. 2008;50:3467-3474.
[Google Scholar]
Quartarone G., Bellomi T., Zingales A., . Inhibition of copper corrosion by isatin in aerated 0.5 M H₂SO₄. Corros. Sci.. 2003;45:715-733.
[Google Scholar]
Quartarone G., Bonaldo L., Tortato C., . Inhibitive action of indole-5-carboxylic acid towards corrosion of mild steel in deaerated 0.5 M sulfuric acid solutions. Appl. Surf. Sci.. 2006;252:8251-8257.
[Google Scholar]
Quartarone G., Moretti G., Bellomi T., Capobianco G., Zingales A., . Using indole to inhibit copper corrosion in aerated 0.5 M sulfuric acid. Corrosion. 1998;54:606-618.
[Google Scholar]
Radovanović M.B., Simonović A.T., Petrović M.B., Milić S.M., Antonijević M.M., . Influence of purine on brass behavior in neutral and alkaline sulphate solutions. Int. J. Electrochem. Sci.. 2012;7:11796-11810.
[Google Scholar]
Raja P.B., Sethuraman M.G., . Natural products as corrosion inhibitor for metals in corrosive media—a review. Mater. Lett.. 2008;62:113-116.
[Google Scholar]
Rajkumar G., Sagunthala R., Sethuraman M.G., . Investigation of inhibiting properties of self-assembled films of 4-aminothiophenol on copper in 3.5% NaCl. J. Adhes. Sci. Technol.. 2015;29:1107-1117.
[Google Scholar]
Rajkumar G., Sethuraman M.G., . A study of copper corrosion inhibition by self-assembled films of 3-mercapto-1H-1,2,4-triazole. Res. Chem. Intermed.. 2016;42:1809-1821.
[Google Scholar]
Ramdani M., Elmsellem H., Elkhiati N., Haloui B., Aouniti A., Ramdani M., Ghazi Z., Chetouani A., Hammouti B., . Caulerpa prolifera green algae using as eco-friendly corrosion inhibitor for mild steel in 1 M HCl media. Der Pharm. Chem.. 2015;7:67-76.
[Google Scholar]
Ramesh S., Rajeswari S., . Evaluation of inhibitors and biocide on the corrosion control of copper in neutral aqueous environment. Corros. Sci.. 2005;47:151-169.
[Google Scholar]
Ramezanzadeh B., Arman S.Y., Mehdipour M., Markhali B.P., . Analysis of electrochemical noise (ECN) data in time and frequency domain for comparison corrosion inhibition of some azole compounds on Cu in 1.0 M H₂SO₄ solution. Appl. Surf. Sci.. 2014;289:129-140.
[Google Scholar]
Rani P.D., Selvaraj S., . Emblica officinalis (AMLA) leaves extract as corrosion inhibitor for copper and its alloy (CU-27ZN) in natural sea water. Arch. Appl. Sci. Res.. 2010;2:140-150.
[Google Scholar]
Rani P.D., Selvaraj S., . Inhibitive action of Vitis vinifera (grape) on copper and brass in natural sea water environment. Rasayan. J. Chem.. 2010;3:473-482.
[Google Scholar]
Rao B.A., Iqbal M.Y., Reddy M.N., Kumar K.C., . Self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio) benzotriazine on copper for corrosion protection. Bull. Mater. Sci.. 2014;37:185-197.
[Google Scholar]
Ravichandran R., Nanjundan S., Rajendran N., . Effect of benzotriazole derivatives on the corrosion and dezincification of brass in neutral chloride solution. J. Appl. Electrochem.. 2004;34:1171-1176.
[Google Scholar]
Ravichandran R., Rajendran N., . Electrochemical behaviour of brass in artificial seawater: effect of organic inhibitors. Appl. Surf. Sci.. 2005;241:449-458.
[Google Scholar]
Rigo A., Corazza A., di Paolo M.L., Rossetto M., Ugolini R., Scarpa M., . Interaction of copper with cysteine: stability of cuprous complexes and catalytic role of cupric ions in anaerobic thiol oxidation. J. Inorg. Biochem.. 2004;98:1495-1501.
[Google Scholar]
Rudresh H., Mayanna S., . Adsorption of n-decylamine on zinc from acidic chloride solution. J. Electrochem. Soc.. 1977;124:340-342.
[Google Scholar]
Saadawy M., . Inhibitive effect of pantoprazole sodium on the corrosion of copper in acidic solutions. Arab. J. Sci. Eng.. 2016;41:177-190.
[Google Scholar]
Şafak S., Duran B., Yurt A., Türkoĝlu G., . Schiff bases as corrosion inhibitor for aluminium in HCl solution. Corros. Sci.. 2012;54:251-259.
[Google Scholar]
Saha S.K., Ghosh P., Hens A., Murmu N.C., Banerjee P., . Density functional theory and molecular dynamics simulation study on corrosion inhibition performance of mild steel by mercapto-quinoline Schiff base corrosion inhibitor. Physica E. 2015;66:332-341.
[Google Scholar]
Sameh S.A., Salih I.K., Alwash S.H., Alwasity A.A., . Eng. Tech. J.. 2010;28:1196.
Samide A., Tutunaru B., Negrila C., Prunaru I., . Surface analysis of inhibitor film formed by 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide on carbon steel surface in acidic media. Spectrosc. Lett.. 2012;45:55-64.
[Google Scholar]
Sangeetha T., Fredimoses M., . Inhibition of mild copper metal corrosion in HNO₃ medium by acid extract of Azadirachta indica seed. J. Chem.. 2011;8:S1-S6.
[Google Scholar]
Sastri V.S., . Green Corrosion Inhibitors: Theory and Practice. John Wiley & Sons; 2012.
Sathiyanarayanan S., Manoharan S., Rajagopal G., Balakrishnan K., . Characterisation of passive films on copper. Br. Corros. J. 2013
[Google Scholar]
Savita, Mourya P., Chaubey N., Singh V.K., Singh M.M., . Eco-friendly inhibitors for copper corrosion in nitric acid: experimental and theoretical evaluation. Metall. Mater. Trans. B. 2016;47:47-57.
[Google Scholar]
Saxena N., Kumar S., . Anisalidine derivatives as corrosion inhibitors of copper in acidic media. Prot. Met. Phys. Chem. Surf.. 2015;51:701-709.
[Google Scholar]
Scendo M., . Inhibitive action of the purine and adenine for copper corrosion in sulphate solutions. Corros. Sci.. 2007;49:2985-3000.
[Google Scholar]
Scendo M., . Inhibition of copper corrosion in sodium nitrate solutions with nontoxic inhibitors. Corros. Sci.. 2008;50:1584-1592.
[Google Scholar]
Scendo M., Uznanska J., . The effect of ionic liquids on the corrosion inhibition of copper in acidic chloride solutions. Int. J. Corros.. 2011;2011
[Google Scholar]
Schweinsberg D., Bottle S., Otieno-Alego V., Notoya T., . A near-infrared FT-Raman (SERS) and electrochemical study of the synergistic effect of 1-[(1′,2′-dicarboxy) ethyl]-benzotriazole and KI on the dissolution of copper in aerated sulfuric acid. J. Appl. Electrochem.. 1997;27:161-168.
[Google Scholar]
Shabani-Nooshabadi M., Hoseiny F.S., Jafari Y., . Corrosion inhibition of copper by Ephedra sarcocarpa plant extract as green corrosion inhibitor in strong acidic medium. Anal. Bioanal. Electrochem.. 2014;6:341-354.
[Google Scholar]
Shabani-Nooshabadi M., Hoseiny F.S., Jafari Y., . Green approach to corrosion inhibition of copper by the extract of Calligonum comosum in strong acidic medium. Metall. Mater. Trans. A. 2014;46:293-299.
[Google Scholar]
Shen S., Zhu C.D., Guo X.Y., Li C.C., Wen Y., Yang H.F., . The synergistic mechanism of phytic acid monolayers and iodide ions for inhibition of copper corrosion in acidic media. RSC Adv.. 2014;4:10597-10606.
[Google Scholar]
Sherif E.-S.M., . Corrosion behavior of copper in 0.50 M hydrochloric acid pickling solutions and its inhibition by 3-amino-1,2,4-triazole and 3-amino-5-mercapto-1,2,4-triazole. Int. J. Electrochem. Sci.. 2012;7:1884-1897.
[Google Scholar]
Sherif E.-S.M., Erasmus R., Comins J., . Corrosion of copper in aerated acidic pickling solutions and its inhibition by 3-amino-1,2,4-triazole-5-thiol. J. Colloid Interface Sci.. 2007;306:96-104.
[Google Scholar]
Sherif E.-S.M., Erasmus R., Comins J., . Inhibition of copper corrosion in acidic chloride pickling solutions by 5-(3-aminophenyl)-tetrazole as a corrosion inhibitor. Corros. Sci.. 2008;50:3439-3445.
[Google Scholar]
Sherif E.-S.M., Potgieter J., Comins J., Cornish L., Olubambi P., Machio C., . Effects of minor additions of ruthenium on the passivation of duplex stainless-steel corrosion in concentrated hydrochloric acid solutions. J. Appl. Electrochem.. 2009;39:1385.
[Google Scholar]
Sherif E., Park S.-M., . Inhibition of copper corrosion in 3.0% NaCl solution by N-phenyl-1, 4-phenylenediamine. J. Electrochem. Soc.. 2005;152:B428-B433.
[Google Scholar]
Sherif E., Park S.-M., . 2-Amino-5-ethyl-1,3,4-thiadiazole as a corrosion inhibitor for copper in 3.0% NaCl solutions. Corros. Sci.. 2006;48:4065-4079.
[Google Scholar]
Sherif E.M., Erasmus R.M., Comins J.D., . Corrosion of copper in aerated synthetic sea water solutions and its inhibition by 3-amino-1,2,4-triazole. J. Colloid Interface Sci.. 2007;309:470-477.
[Google Scholar]
Sherif E.M., Erasmus R.M., Comins J.D., . Effects of 3-amino-1,2,4-triazole on the inhibition of copper corrosion in acidic chloride solutions. J. Colloid Interface Sci.. 2007;311:144-151.
[Google Scholar]
Sherif E.M., Park S.M., . Effects of 2-amino-5-ethylthio-1,3,4-thiadiazole on copper corrosion as a corrosion inhibitor in aerated acidic pickling solutions. Electrochim. Acta. 2006;51:6556-6562.
[Google Scholar]
Sherif E.S.M., . Electrochemical and gravimetric study on the corrosion and corrosion inhibition of pure copper in sodium chloride solutions by two azole derivatives. Int. J. Electrochem. Sci.. 2012;7:1482-1495.
[Google Scholar]
Shi Y., Zhang Z., Su J., Cao F., Zhang J., . Electrochemical noise study on 2024–T3 Aluminum alloy corrosion in simulated acid rain under cyclic wet–dry condition. Electrochim. Acta. 2006;51:4977-4986.
[Google Scholar]
Shokry H., Yuasa M., Sekine I., Issa R., El-Baradie H., Gomma G., . Corrosion inhibition of mild steel by Schiff base compounds in various aqueous solutions: part 1. Corros. Sci.. 1998;40:2173-2186.
[Google Scholar]
Shukla S.K., Singh A.K., Ahamad I., Quraishi M., . Streptomycin: a commercially available drug as corrosion inhibitor for mild steel in hydrochloric acid solution. Mater. Lett.. 2009;63:819-822.
[Google Scholar]
Shumakovich G.P., Otrokhov G.V., Khlupova M.E., Vasil'Eva I.S., Zaitseva E.A., Morozova O.V., Yaropolov A.I., . Laccase-catalyzed synthesis of aniline oligomers and their application for the protection of copper against corrosion. RSC Adv.. 2014;4:30193-30196.
[Google Scholar]
Simonović A.T., Petrović M.B., Radovanović M.B., Milić S.M., Antonijević M.M., . Inhibition of copper corrosion in acidic sulphate media by eco-friendly amino acid compound. Chem. Pap.. 2014;68:362-371.
[Google Scholar]
Singh P., Quraishi M.A., . Corrosion inhibition of mild steel using Novel Bis Schiff's Bases as corrosion inhibitor: electrochemical and Surface measurement. Measur.: J. Int. Measur. Confed.. 2016;86:114-124.
[Google Scholar]
Solmaz R., Altunbaş Şahin E., Döner A., Kardaş G., . The investigation of synergistic inhibition effect of rhodanine and iodide ion on the corrosion of copper in sulphuric acid solution. Corros. Sci.. 2011;53:3231-3240.
[Google Scholar]
Souto R., Sánchez M.P., Barrera M., González S., Salvarezza R., Arvia A., . The kinetics of pitting corrosion of copper in alkaline solutions containing sodium perchlorate. Electrochim. Acta. 1992;37:1437-1443.
[Google Scholar]
Stupnišek-Lisac E., Bozic A.L., Cafuk I., . Low-toxicity copper corrosion inhibitors. Corrosion. 1998;54:713-720.
[Google Scholar]
Stupnisek-Lisac E., Brnada A., Mance A.D., . Secondary amines as copper corrosion inhibitors in acid media. Corros. Sci.. 2000;42:243-257.
[Google Scholar]
Stupnišek-Lisac E., Gazivoda A., Madžarac M., . Evaluation of non-toxic corrosion inhibitors for copper in sulphuric acid. Electrochim. Acta. 2002;47:4189-4194.
[Google Scholar]
Subramanian R., Lakshminarayanan V., . Effect of adsorption of some azoles on copper passivation in alkaline. Corros. Sci.. 2002;44:535-554.
[Google Scholar]
Sudheer, Quraishi M.A., . Electrochemical and theoretical investigation of triazole derivatives on corrosion inhibition behavior of copper in hydrochloric acid medium. Corros. Sci.. 2013;70:161-169.
[Google Scholar]
Sudheer, Quraishi M.A., . The corrosion inhibition effect of aryl pyrazolo pyridines on copper in hydrochloric acid system: computational and electrochemical studies. RSC Adv.. 2015;5:41923-41933.
[Google Scholar]
Sulaiman, S., Nor-Anuar, A., Abd-Razak, A., Chelliapan, S., 2012. A study of using Allium cepa (onion) as natural corrosion inhibitor in industrial chill wastewater system. Res. J. Chem. Sci. ISSN: 2231, 606X.
Suter T., Moser E., Böhni H., . The characterization of the tarnishing of Cu-15Ni-8Sn and Cu-5Al-5Sn alloys. Corros. Sci.. 1993;34:1111-1122.
[Google Scholar]
Szőcs E., Vastag G., Shaban A., Kálmán E., . Electrochemical behaviour of an inhibitor film formed on copper surface. Corros. Sci.. 2005;47:893-908.
[Google Scholar]
Tan Y., Fwu Y., Bhardwaj K., . Electrochemical evaluation of under-deposit corrosion and its inhibition using the wire beam electrode method. Corros. Sci.. 2011;53:1254-1261.
[Google Scholar]
Tan Y., Srinivasan M., Pehkonen S., Chooi S.Y., . Effects of ring substituents on the protective properties of self-assembled benzenethiols on copper. Corros. Sci.. 2006;48:840-862.
[Google Scholar]
Tang Y.M., Yang W.Z., Yin X.S., Liu Y., Wan R., Wang J.T., . Phenyl-substituted amino thiadiazoles as corrosion inhibitors for copper in 0.5 M H₂SO₄. Mater. Chem. Phys.. 2009;116:479-483.
[Google Scholar]
Tansuǧ G., Tüken T., Giray E.S., Findikkiran G., Siǧircik G., Demirkol O., Erbil M., . A new corrosion inhibitor for copper protection. Corros. Sci.. 2014;84:21-29.
[Google Scholar]
Tasic Z.Z., Antonijevic M.M., Petrovic Mihajlovic M.B., Radovanovic M.B., . The influence of synergistic effects of 5-methyl-1H-benzotriazole and potassium sorbate as well as 5-methyl-1H-benzotriazole and gelatin on the copper corrosion in sulphuric acid solution. J. Mol. Liq.. 2016;219:463-473.
[Google Scholar]
Tawfik S.M., Zaky M.F., . Corrosion inhibition performance of some Schiff base anionic surfactant complexes of cobalt(II), copper(II), and zinc(II) on carbon steel in 1.0 M HCl. Res. Chem. Intermed.. 2015;41:8747-8772.
[Google Scholar]
Thanapackiam P., Rameshkumar S., Subramanian S.S., Mallaiya K., . Electrochemical evaluation of inhibition efficiency of ciprofloxacin on the corrosion of copper in acid media. Mater. Chem. Phys. 2016
[Google Scholar]
Tian H., Cheng Y.F., Li W., Hou B., . Triazolyl-acylhydrazone derivatives as novel inhibitors for copper corrosion in chloride solutions. Corros. Sci.. 2015;100:341-352.
[Google Scholar]
Tian H., Li W., Cao K., Hou B., . Potent inhibition of copper corrosion in neutral chloride media by novel non-toxic thiadiazole derivatives. Corros. Sci.. 2013;73:281-291.
[Google Scholar]
Tomi I.H.R., Al-Daraji A.H.R., Aziz S.A., . Synthesis, characterization, and study the inhibitory effect of thiazole and thiadiazole derivatives toward the corrosion of copper in acidic media. Synth. React. Inorg., Met.-Org., Nano-Met. Chem.. 2015;45:605-613.
[Google Scholar]
Trabanelli G., . 1991 Whitney award lecture: inhibitors-an old remedy for a new challenge. Corrosion. 1991;47:410-419.
[Google Scholar]
Tromans D., Sun R.h., . Anodic polarization behavior of copper in aqueous chloride/benzotriazole solutions. J. Electrochem. Soc.. 1991;138:3235-3244.
[Google Scholar]
Tüken T., Kıcır N., Elalan N.T., Sığırcık G., Erbil M., . Self assembled film based on hexane-1,6-diamine and 2-mercapto-ethanol on copper. Appl. Surf. Sci.. 2012;258:6793-6799.
[Google Scholar]
Ulman A., . Formation and structure of self-assembled monolayers. Chem. Rev.. 1996;96:1533-1554.
[Google Scholar]
Valek L., Martinez S., . Copper corrosion inhibition by Azadirachta indica leaves extract in 0.5 M sulphuric acid. Mater. Lett.. 2007;61:148-151.
[Google Scholar]
Vashisht H., Bahadur I., Kumar S., Goyal M.S., Kaur G., Singh G., Katata-Seru L., Ebenso E.E., . Synergistic interactions between tetra butyl phosphonium hydroxide and iodide ions on the mild steel surface for corrosion inhibition in acidic medium. J. Mol. Liq.. 2016;224:19-29.
[Google Scholar]
Vastag G., Szöcs E., Shaban A., Kálmán E., . New inhibitors for copper corrosion. Pure Appl. Chem.. 2001;73:1861-1869.
[Google Scholar]
Vijayaraghavan K., Padmesh T., Palanivelu K., Velan M., . Biosorption of nickel (II) ions onto Sargassum wightii: application of two-parameter and three-parameter isotherm models. J. Hazard. Mater.. 2006;133:304-308.
[Google Scholar]
Wang C.-T., Chen S.-H., Ma H.-Y., Hua L., Wang N., . Study of the ability of self-assembled N-vinylcarbazole monolayers to protect copper against corrosion. J. Serb. Chem. Soc.. 2002;67:685-696.
[Google Scholar]
Wang D., Bierwagen G.P., . Sol-gel coatings on metals for corrosion protection. Prog. Org. Coat.. 2009;64:327-338.
[Google Scholar]
Wang D., Xiang B., Liang Y., Song S., Liu C., . Corrosion control of copper in 3.5 wt.% NaCl Solution by domperidone: experimental and theoretical study. Corros. Sci.. 2014;85:77-86.
[Google Scholar]
Wang S., Tao Z., He W., Xiao D., Tan Z., . Effects of cyproconazole on copper corrosion as environmentally friendly corrosion inhibitor in nitric acid solution. Asian J. Chem.. 2015;27:1107-1110.
[Google Scholar]
Wang Z.L., Zhang J., Wang Z.M., Zhou L., Han X., Li Q.F., Gao S., . Emulsification reducing the corrosion risk of mild steel in oil–brine mixtures. Corros. Sci.. 2014;86:310-317.
[Google Scholar]
Wu Y., Zhang P., Pickering H., Allara D., . Effect of KI on improving copper corrosion inhibition efficiency of benzotriazole in sulfuric acid electrolytes. J. Electrochem. Soc.. 1993;140:2791-2800.
[Google Scholar]
Xiong S., Sun J.L., Xu Y., . Adsorption behavior of thiadiazole as corrosion inhibitors on copper surface. Mater. Sci. Forum. Trans. Tech. Publ. 2015:204-211.
[Google Scholar]
Xue G., Ding J., . Chemisorption of a compact polymeric coating on copper surfaces from a benzotriazole solution. Appl. Surf. Sci.. 1990;40:327-332.
[Google Scholar]
Xue G., Huang X.-Y., Dong J., Zhang J., . The formation of an effective anti-corrosion film on copper surfaces from 2-mercaptobenzimidazole solution. J. Electroanal. Chem. Interfacial Electrochem.. 1991;310:139-148.
[Google Scholar]
Yadav S., Choudhary G., Sharma A., . Green approach to corrosion inhibition of aluminium and copper by Ziziphus mauritiana fruit extract in hydrochloric acid solution. Int. J. ChemTech. Res.. 2013;5:1815-1823.
[Google Scholar]
Yan C., Lin H., Cao C., . Investigation of inhibition of 2-mercaptobenzoxazole for copper corrosion. Electrochim. Acta. 2000;45:2815-2821.
[Google Scholar]
Ye X., Xin X., Zhu J., Xue Z., . Coordination compound films of 1-phenyl-5-mercaptotetrazole on copper surface. Appl. Surf. Sci.. 1998;135:307-317.
[Google Scholar]
Youda R., Nishihara H., Aramaki K., . SERS and impedance study of the equilibrium between complex formation and adsorption of benzotriazole and 4-hydroxybenzotriazole on a copper electrode in sulphate solutions. Electrochim. Acta. 1990;35:1011-1017.
[Google Scholar]
Yu P., Liao D.-M., Luo Y.-B., Chen Z.-G., . Studies of benzotriazole and tolytriazole as inhibitors for copper corrosion in deionized water. Corrosion. 2003;59:314-318.
[Google Scholar]
Yurt A., Aykin Ö., . Diphenolic Schiff bases as corrosion inhibitors for aluminium in 0.1 M HCl: potentiodynamic polarisation and EQCM investigations. Corros. Sci.. 2011;53:3725-3732.
[Google Scholar]
Yurt A., Duran B., Dal H., . An experimental and theoretical investigation on adsorption properties of some diphenolic Schiff bases as corrosion inhibitors at acidic solution/mild steel interface. Arab. J. Chem.. 2014;7:732-740.
[Google Scholar]
Zanotto F., Grassi V., Balbo A., Monticelli C., Zucchi F., . Stress corrosion cracking of LDX 2101® duplex stainless steel in chloride solutions in the presence of thiosulphate. Corros. Sci.. 2014;80:205-212.
[Google Scholar]
Zarrouk A., Hammouti B., Dafali A., Bentiss F., . Inhibitive properties and adsorption of purpald as a corrosion inhibitor for copper in nitric acid medium. Ind. Eng. Chem. Res.. 2013;52:2560-2568.
[Google Scholar]
Zarrouk A., Hammouti B., Dafali A., Bouachrine M., Zarrok H., Boukhris S., Al-Deyab S.S., . A theoretical study on the inhibition efficiencies of some quinoxalines as corrosion inhibitors of copper in nitric acid. J. Saudi Chem. Soc.. 2014;18:450-455.
[Google Scholar]
Zarrouk A., Hammouti B., Dafali A., Zarrok H., Touzani R., Bouachrine M., Zertoubi M., . Inhibition of copper corrosion in acid solution by N-1-naphthylethylenediamine dihydrochloride monomethanolate: experimental and theoretical study: part-1. Res. Chem. Intermed.. 2012;38:1079-1089.
[Google Scholar]
Zeldowitsch J., . Adsorption site energy distribution. Acta Phys. Chim. URSS. 1934;1:961-973.
[Google Scholar]
Žerjav G., Milošev I., . Carboxylic acids as corrosion inhibitors for Cu, Zn and brasses in simulated urban rain. Int. J. Electrochem. Sci.. 2014;9:2696-2715.
[Google Scholar]
Žerjav G., Milošev I., . Protection of copper against corrosion in simulated urban rain by the combined action of benzotriazole, 2-mercaptobenzimidazole and stearic acid. Corros. Sci.. 2015;98:180-191.
[Google Scholar]
Zhang D.-Q., Cai Q.-R., Gao L.-X., Lee K.Y., . Effect of serine, threonine and glutamic acid on the corrosion of copper in aerated hydrochloric acid solution. Corros. Sci.. 2008;50:3615-3621.
[Google Scholar]
Zhang D.-Q., Cai Q.-R., He X.-M., Gao L.-X., Kim G.S., . Corrosion inhibition and adsorption behavior of methionine on copper in HCl and synergistic effect of zinc ions. Mater. Chem. Phys.. 2009;114:612-617.
[Google Scholar]
Zhang D.-Q., Cai Q.-R., He X.-M., Gao L.-X., Zhou G.-D., . Inhibition effect of some amino acids on copper corrosion in HCl solution. Mater. Chem. Phys.. 2008;112:353-358.
[Google Scholar]
Zhang D.-Q., Gao L.-X., Zhou G.-D., . Inhibition of copper corrosion by bis-(1-benzotriazolymethylene)-(2, 5-thiadiazoly)-disulfide in chloride media. Appl. Surf. Sci.. 2004;225:287-293.
[Google Scholar]
Zhang D.-Q., Gao L.-X., Zhou G.-D., . Inhibition of copper corrosion in aerated hydrochloric acid solution by heterocyclic compounds containing a mercapto group. Corros. Sci.. 2004;46:3031-3040.
[Google Scholar]
Zhang D.-Q., Xie B., Gao L.-X., Cai Q.-R., Joo H.G., Lee K.Y., . Intramolecular synergistic effect of glutamic acid, cysteine and glycine against copper corrosion in hydrochloric acid solution. Thin Solid Films. 2011;520:356-361.
[Google Scholar]
Zhang D.-Q., Xie B., Gao L.-X., Joo H.G., Lee K.Y., . Inhibition of copper corrosion in acidic chloride solution by methionine combined with cetrimonium bromide/cetylpyridinium bromide. J. Appl. Electrochem.. 2011;41:491-498.
[Google Scholar]
Zhang D.Q., Gao L.X., Cai Q.R., Lee K., . Inhibition of copper corrosion by modifying cysteine self-assembled film with alkylamine/alkylacid compounds. Mater. Corros.. 2010;61:16-21.
[Google Scholar]
Zhang D.Q., Gao L.X., Zhou G.D., . Synergistic effect of 2-mercapto benzimidazole and KI on copper corrosion inhibition in aerated sulfuric acid solution. J. Appl. Electrochem.. 2003;33:361-366.
[Google Scholar]
Zhang J., Yu W.-Z., Yan Y.-G., Yu L.-J., Ren Z.-J., . Molecular dynamics simulation of the adsorption behavior of imidazoline corrosion inhibitors on a Fe (0 0 1) surface. Acta Phys. Chim. Sin.. 2010;26:1385-1390.
[Google Scholar]
Zhang X.H., Liao Q.Q., Nie K.B., Zhao L.L., Yang D., Yue Z.W., Ge H.H., Li Y.J., . Self-assembled monolayers formed by ammonium pyrrolidine dithiocarbamate on copper surfaces in sodium chloride solution. Corros. Sci.. 2015;93:201-210.
[Google Scholar]
Zheng L., Liu J., Tao Z.H., He W., Xiao D.J., Tan Z., . Electrochemical investigation of myclobutanil as corrosion inhibitor for copper in acid medium. Adv. Mater. Res. 2014:229-233.
[Google Scholar]
Zhou Y., Xu S., Guo L., Zhang S., Lu H., Gong Y., Gao F., . Evaluating two new Schiff bases synthesized on the inhibition of corrosion of copper in NaCl solutions. RSC Adv.. 2015;5:14804-14813.
[Google Scholar]
Zor S., . Sulfathiazole as potential corrosion inhibitor for copper in 0.1 M NaCl. Prot. Met. Phys. Chem. Surf.. 2014;50:530-537.
[Google Scholar]
Zucchi F., Trabanelli G., Fonsati M., . Tetrazole derivatives as corrosion inhibitors for copper in chloride solutions. Corros. Sci.. 1996;38:2019-2029.
[Google Scholar]
Zucchi F., Trabanelli G., Monticelli C., . The inhibition of copper corrosion in 0.1 M NaCl under heat exchange conditions. Corros. Sci.. 1996;38:147-154.
[Google Scholar]

Introduction

Copper corrosion inhibitors

Benzotriazole
Imidazole compounds
Other azole compounds
Schiff bases
Green corrosion inhibitors
Amino acids
Self-assembled compounds

Corrosion inhibitors efficiency evaluation methods

Weight loss measurements
Potentiodynamic–galvanostatic polarization
Electrochemical impedance spectroscopy (EIS)
Electrochemical noise method
Scanning electrochemical microscopy (SECM)
Scanning vibrating electrode technique (SVET)
Surface analytical methods

The adsorption of corrosion inhibitor and its isotherms

Langmuir adsorption isotherm
Freundlich adsorption isotherm
Langmuir-Freundlich adsorption isotherm
Temkin adsorption isotherm
Flory-Huggins adsorption isotherm
Frumkin adsorption isotherm
Adsorption energy

Corrosive environments for copper

Copper in acidic environments
Copper in neutral environments
Copper in alkaline environments
Copper in other environments

Conclusions and future trends

Fulltext Views
12,143

PDF downloads
1,674

View/Download PDF
Download Citations

BibTeX
RIS

Show Sections

[1] Atkins, P., 2010. Shriver and Atkins' inorganic chemistry. Oxford University Press, USA.

[2] Abd-El-Nabey B., Abdel-Gaber A., Ali M.E.S., Khamis E., El-Housseiny S., . Inhibitive action of Cannabis plant extract on the corrosion of copper in 0.5 M H₂SO₄. Int. J. Electrochem. Sci.. 2013;8:5851-5865.
[Google Scholar]

[3] Abdallah M., . Antibacterial drugs as corrosion inhibitors for corrosion of aluminium in hydrochloric solution. Corros. Sci.. 2004;46:1981-1996.
[Google Scholar]

[4] Abdallah M., Zaafarany I., Al-Karanee S.O., Abd El-Fattah A.A., . Antihypertensive drugs as an inhibitors for corrosion of aluminum and aluminum silicon alloys in aqueous solutions. Arab. J. Chem.. 2012;5:225-234.
[Google Scholar]

[5] Abdallah Y., Shalabi K., . Comprehensive study of the behavior of copper inhibition in 1 M HNO₃ by Euphorbia helioscopia linn. extract as green inhibitor. Prot. Met. Phys. Chem. Surf.. 2015;51:275-284.
[Google Scholar]

[6] Abdel-Gaber A., Abd-El-Nabey B., Khamis E., Abd-El-Khalek D., . A natural extract as scale and corrosion inhibitor for steel surface in brine solution. Desalination. 2011;278:337-342.
[Google Scholar]

[7] Abiola O.K., John M.O., Asekunowo P.O., Okafor P.C., James O.O., . 3-[(4-Amino-2-methyl-5-pyrimidinyl) methyl]-5-(2-hydroxyethyl)-4-methyl thiazolium chloride hydrochloride as green corrosion inhibitor of copper in HNO₃ solution and its adsorption characteristics. Green Chem. Lett. Rev.. 2011;4:273-279.
[Google Scholar]

[8] Adamson A., Gast A., . Physical Chemical of Surfaces. New York: Wiley; 1997.

[9] Adeloju S., Hughes H., . The corrosion of copper pipes in high chloride-low carbonate mains water. Corros. Sci.. 1986;26:851-870.
[Google Scholar]

[10] Ahamad I., Quraishi M., . Mebendazole: new and efficient corrosion inhibitor for mild steel in acid medium. Corros. Sci.. 2010;52:651-656.
[Google Scholar]

[11] Akyüz, M.A., Ergan, A.C., 2014. Behaviour of benzotriazole salts in multi metal formulations for corrosion inhibition of copper. In: NACE – International Corrosion Conference Series.

[12] Al-Amiery A.A., Kadhum A.A.H., Mohamad A.B., Junaedi S., . A novel hydrazinecarbothioamide as a potential corrosion inhibitor for mild steel in HCl. Materials. 2013;6:1420-1431.
[Google Scholar]

[13] Al-Qudah M.A., . Inhibition of copper corrosion by flavonoids in nitric acid. J. Chem.. 2011;8:326-332.
[Google Scholar]

[14] Al-Shahrani S., El-Shazly A., . Corrosion inhibition of a gas sparged copper cylinder in a solution of NaCl and Na₂S by using 4-amino-4H-1,2,4-triazole as corrosion inhibitor. J. New Mater. Electrochem. Syst.. 2016;19
[Google Scholar]

[15] Al Kharafi F.M., Ghayad I.M., Abdullah R.M., . Corrosion inhibition of copper in non-polluted and polluted sea water using 5-phenyl-1-H-tetrazole. Int. J. Electrochem. Sci.. 2012;7:3289-3298.
[Google Scholar]

[16] Aldana-González, J., Espinoza-Vázquez, A., Romero-Romo, M., Uruchurtu-Chavarin, J., Palomar-Pardavé, M., 2015. Electrochemical evaluation of cephalothin as corrosion inhibitor for API 5L X52 steel immersed in an acid medium. Arab. J. Chem.

[17] Alkire R., Cangellari A., . Effect of benzotriazole on dissolution of copper in the presence of fluid flow I. Experimental. J. Electrochem. Soc.. 1989;136:913-919.
[Google Scholar]

[18] Altaf F., Qureshi R., Ahmed S., . Surface protection of copper by azoles in borate buffers-voltammetric and impedance analysis. J. Electroanal. Chem.. 2011;659:134-142.
[Google Scholar]

[19] Alvarez F., Schilardi P.L., de Mele M.F.L., . Reduction of the “burst release” of copper ions from copper-based intrauterine devices by organic inhibitors. Contraception. 2012;85:91-98.
[Google Scholar]

[20] Amin M.A., Khaled K., . Copper corrosion inhibition in O₂-saturated H₂SO₄ solutions. Corros. Sci.. 2010;52:1194-1204.
[Google Scholar]

[21] Antonijevic M., Petrovic M., . Copper corrosion inhibitors. A review. Int. J. Electrochem. Sci.. 2008;3:1-28.
[Google Scholar]

[22] Antonijevic M.M., Milic S.M., Dimitrijevic M.D., Petrovic M.B., Radovanovic M.B., Stamenkovic A.T., . The influence of pH and chlorides on electrochemical behavior of copper in the presence of benzotriazole. Int. J. Electrochem. Sci.. 2009;4:962-979.
[Google Scholar]

[23] Antonijević M.M., Milić S.M., Petrović M.B., . Films formed on copper surface in chloride media in the presence of azoles. Corros. Sci.. 2009;51:1228-1237.
[Google Scholar]

[24] Appa Rao B.V., Iqbal M.Y., Kumar K.C., Reddy M.N., . Corrosion protection of copper by self assembled nano film of 4-amino-3-(octadecylthio)-6-methyl-1,2,4-triazinone. Indian J. Chem. Technol.. 2014;21:188-198.
[Google Scholar]

[25] Appa Rao B.V., Iqbal M.Y., Sreedhar B., . Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper. Electrochim. Acta. 2010;55:620-631.
[Google Scholar]

[26] Appa Rao, B.V., Narsihma Reddy, M., 2014. Formation, characterization and corrosion protection efficiency of self-assembled 1-octadecyl-1H-imidazole films on copper for corrosion protection. Arab. J. Chem.

[27] Appa Rao B.V., Yakub Iqbal M., Sreedhar B., . Self-assembled monolayer of 2-(octadecylthio)benzothiazole for corrosion protection of copper. Corros. Sci.. 2009;51:1441-1452.
[Google Scholar]

[28] Ashassi-Sorkhabi H., Majidi M., Seyyedi K., . Investigation of inhibition effect of some amino acids against steel corrosion in HCl solution. Appl. Surf. Sci.. 2004;225:176-185.
[Google Scholar]

[29] Attia A.A., Elmelegy E.M., El-Batouti M., Ahmed A.-M.M., . Anodic corrosion inhibition in presence of protic solvents. Asian J. Chem.. 2016;28:267.
[Google Scholar]

[30] Ault J., . Erosion Corrosion of Nickel Aluminum Bronze in Flowing Seawater. Houston, TX (United States): NACE International; 1995.

[31] Aytaç A., Bilgiç S., Gece G., Ancin N., Öztaş S.G., . Experimental and theoretical study of the inhibition effects of some Schiff bases as corrosion inhibitors of aluminium in HCl. Mater. Corros.. 2012;63:729-734.
[Google Scholar]

[32] Baba H., Kodama T., . Corrosion inhibition and characteristics of the triazinedithiol surface film on copper under potentiostatic anodization. Corros. Sci.. 1999;41:1987-2000.
[Google Scholar]

[33] Badawy W.A., Ismail K.M., Fathi A.M., . Corrosion control of Cu–Ni alloys in neutral chloride solutions by amino acids. Electrochim. Acta. 2006;51:4182-4189.
[Google Scholar]

[34] Baeza, H., Guzman, M., Ortega, P., Vera, L., 2003. J. Chil. Chem. Soc. 48, 23.

[35] Bagchi D., Bagchi M., Stohs S.J., Das D.K., Ray S.D., Kuszynski C.A., Joshi S.S., Pruess H.G., . Free radicals and grape seed proanthocyanidin extract: importance in human health and disease prevention. Toxicology. 2000;148:187-197.
[Google Scholar]

[36] Barcia O., Mattos O., Pebere N., Tribollet B., . Mass-transport study for the electrodissolution of copper in 1 M hydrochloric acid solution by impedance. J. Electrochem. Soc.. 1993;140:2825-2832.
[Google Scholar]

[37] Barouni K., Bazzi L., Salghi R., Mihit M., Hammouti B., Albourine A., El Issami S., . Some amino acids as corrosion inhibitors for copper in nitric acid solution. Mater. Lett.. 2008;62:3325-3327.
[Google Scholar]

[38] Barouni K., Kassale A., Albourine A., Jbara O., Hammouti B., Bazzi L., . Amino acids as corrosion inhibitors for copper in nitric acid medium: experimental and theoretical study. J. Mater. Environ. Sci.. 2014;5:456-463.
[Google Scholar]

[39] Bartley J., Huynh N., Bottle S., Flitt H., Notoya T., Schweinsberg D., . Computer simulation of the corrosion inhibition of copper in acidic solution by alkyl esters of 5-carboxybenzotriazole. Corros. Sci.. 2003;45:81-96.
[Google Scholar]

[40] Bastidas D.M., . Adsorption of benzotriazole on copper surfaces in a hydrochloric acid solution. Surf. Interface Anal.. 2006;38:1146-1152.
[Google Scholar]

[41] Behpour M., Ghoreishi S.M., Khayatkashani M., Soltani N., . Green approach to corrosion inhibition of mild steel in two acidic solutions by the extract of Punica granatum peel and main constituents. Mater. Chem. Phys.. 2012;131:621-633.
[Google Scholar]

[42] Bhattacharjee C.R., Das G., Mondal P., . Novel non-discoid chiral copper (II)-salen type [N₂O₂] donor Schiff base complexes with a cyclohexane diamine spacer: synthesis, electrochemistry, columnar mesomorphism and DFT study. Liq. Cryst.. 2011;38:441-449.
[Google Scholar]

[43] Blajiev O., Hubin A., . Inhibition of copper corrosion in chloride solutions by amino-mercapto-thiadiazol and methyl-mercapto-thiadiazol: an impedance spectroscopy and a quantum-chemical investigation. Electrochim. Acta. 2004;49:2761-2770.
[Google Scholar]

[44] Bockris J.M., Swinkels D., . Adsorption of n-decylamine on solid metal electrodes. J. Electrochem. Soc.. 1964;111:736-743.
[Google Scholar]

[45] Bozorg M., Shahrabi Farahani T., Neshati J., Chaghazardi Z., Mohammadi Ziarani G., . Myrtus communis as green inhibitor of copper corrosion in sulfuric acid. Ind. Eng. Chem. Res.. 2014;53:4295-4303.
[Google Scholar]

[46] Butler M.S., . The role of natural product chemistry in drug discovery. J. Nat. Prod.. 2004;67:2141-2153.
[Google Scholar]

[47] Cai L., Fu Q., Shi R., Tang Y., Long Y.T., He X.P., Jin Y., Liu G., Chen G.R., Chen K., . 'Pungent' copper surface resists acid corrosion in strong HCl solutions. Ind. Eng. Chem. Res.. 2014;53:64-69.
[Google Scholar]

[48] Cao C., . On electrochemical techniques for interface inhibitor research. Corros. Sci.. 1996;38:2073-2082.
[Google Scholar]

[49] Cao K., Sun H.Y., Hou B.R., . Corrosion inhibition of gemini surfactant for copper in 3.5% NaCl. Adv. Mater. Res. 2014:1125-1131.
[Google Scholar]

[50] Chadwick D., Hashemi T., . Benzotriazole adsorption on copper studied by X-ray photoelectron spectroscopy. J. Electron Spectrosc. Relat. Phenom.. 1977;10:79-83.
[Google Scholar]

[51] Chaitra T.K., Mohana K.N.S., Tandon H.C., . Thermodynamic, electrochemical and quantum chemical evaluation of some triazole Schiff bases as mild steel corrosion inhibitors in acid media. J. Mol. Liq.. 2015;211:1026-1038.
[Google Scholar]

[52] Chauhan J.S., . Anticorrosion behaviour of Zenthoxylum alatum extract in acidic media. Asian J. Chem.. 2009;21:1975.
[Google Scholar]

[53] Chen S., Kar T., . Theoretical investigation of inhibition efficiencies of some schiff bases as corrosion inhibitors of aluminum. Int. J. Electrochem. Sci.. 2012;7:6265-6275.
[Google Scholar]

[54] Chen W., Hong S., Luo H.Q., Li N.B., . Inhibition effect of 2,4,6-trimercapto-1,3,5-triazine self-assembled monolayers on copper corrosion in NaCl solution. J. Mater. Eng. Perform.. 2014;23:527-537.
[Google Scholar]

[55] Chen X.D., Gong M., Fu Q.S., Zheng X.W., Feng X.S., . [Omim][Pro] amino acid ionic liquids as a corrosion inhibitor for copper in 3.5% NaCl solution. Appl. Mech. Mater. 2014:47-50.
[Google Scholar]

[56] Chen Z., Huang L., Zhang G., Qiu Y., Guo X., . Benzotriazole as a volatile corrosion inhibitor during the early stage of copper corrosion under adsorbed thin electrolyte layers. Corros. Sci.. 2012;65:214-222.
[Google Scholar]

[57] Cheng Z., Mo S., Jia J., Feng J., Luo H.Q., Li N.B., . Experimental and theoretical studies of 4,6-diamino-2-mercaptopyrimidine as a copper inhibitor in 3.5 wt% NaCl solution. RSC Adv.. 2016;6:15210-15219.
[Google Scholar]

[58] Chi-Ucán S.L., Castillo-Atoche A., Castro Borges P., Manzanilla-Cano J.A., González-García G., Patiño R., Díaz-Ballote L., . Inhibition effect of glycerol on the corrosion of copper in NaCl solutions at different pH values. J. Chem.. 2014;2014
[Google Scholar]

[59] Choudhury M.R., Vidic R.D., Dzombak D.A., . Inhibition of copper corrosion by tolyltriazole in cooling systems using treated municipal wastewater as makeup water. Arab. J. Sci. Eng.. 2014;39:7741-7749.
[Google Scholar]

[60] Curkovic H.O., Stupnisek-Lisac E., Takenouti H., . The influence of pH value on the efficiency of imidazole based corrosion inhibitors of copper. Corros. Sci.. 2010;52:398-405.
[Google Scholar]

[61] Da Costa S., Agostinho S., Rubim J., . Spectroelectrochemical study of passive films formed on brass electrodes in 0.5 m H₂SO₄ aqueous solutions containing benzotriazole (BTAH) J. Electroanal. Chem. Interfacial Electrochem.. 1990;295:203-214.
[Google Scholar]

[62] Da Costa S.L., Rubim J.C., Agostinho S.M., . Spectroelectrochemical study of the corrosion of a copper electrode in deaerated 1.0 M HCl solutions containing Fe (III): effect of the corrosion inhibitor benzotriazole. J. Electroanal. Chem. Interfacial Electrochem.. 1987;220:259-268.
[Google Scholar]

[63] Dada A., Olalekan A., Olatunya A., Dada O., . Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms studies of equilibrium sorption of Zn²⁺ unto phosphoric acid modified rice husk. IOSR J. Appl. Chem.. 2012;3:38-45.
[Google Scholar]

[64] Dadgarinezhad A., Baghaei Ravari F., . Inhibitive effect of a synthetic Schiff base on copper and its modification by benzotriazole in 0.5 M H₂SO₄. Prot. Met. Phys. Chem. Surf.. 2015;51:467-472.
[Google Scholar]

[65] Dafali A., Hammouti B., Mokhlisse R., Kertit S., . Substituted uracils as corrosion inhibitors for copper in 3% NaCl solution. Corros. Sci.. 2003;45:1619-1630.
[Google Scholar]

[66] Dagdag O., El Gouri M., Galai M., Ebn Touhami M., Essamri A., Elharfi A., . Application of hexa propylene glycol cyclotriphosphazene as corrosion inhibitor for copper in 3% NaCl solution. Der Pharm. Chem.. 2015;7:114-122.
[Google Scholar]

[67] Davis J.R., . Copper and Copper Alloys. ASM International; 2001.

[68] del PB Hernández R., Aoki I., Tribollet B., De Melo H., . Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles. Electrochim. Acta. 2011;56:2801-2814.
[Google Scholar]

[69] Deng W., Lin P., Li Q., Mo G., . Ultrafine-grained copper produced by machining and its unusual electrochemical corrosion resistance in acidic chloride pickling solutions. Corros. Sci.. 2013;74:44-49.
[Google Scholar]

[70] Desai M., Desai M., Shah C., Desai S., . Schiff bases as corrosion inhibitors for mild steel in hydrochloric acid solutions. Corros. Sci.. 1986;26:827-837.
[Google Scholar]

[71] Deyab M., El-Rehim S.A., . Influence of polyethylene glycols on the corrosion inhibition of carbon steel in butyric acid solution: weight loss, EIS and theoretical studies. Int. J. Electrochem. Sci.. 2013;8:12613-12627.
[Google Scholar]

[72] Deyab M.A., . Egyptian licorice extract as a green corrosion inhibitor for copper in hydrochloric acid solution. J. Ind. Eng. Chem.. 2015;22:384-389.
[Google Scholar]

[73] Deyab M.A., Essehli R., El Bali B., . Inhibition of copper corrosion in cooling seawater under flowing conditions by novel pyrophosphate. RSC Adv.. 2015;5:64326-64334.
[Google Scholar]

[74] Díaz-Gómez A., Vera R., Molinari A., Oliva A., Aperador W., . 5-Methyl-2,4-dihydropyrazol-3-one and 5-methyl-2-phenyl-2,4-didhydropyrazol-3-one as copper corrosion inhibitors in acidic media. Int. J. Electrochem. Sci.. 2014;10:4004-4019.
[Google Scholar]

[75] Duran B., Bereket G., Duran M., . Electrochemical synthesis and characterization of poly (m-phenylenediamine) films on copper for corrosion protection. Prog. Org. Coat.. 2012;73:162-168.
[Google Scholar]

[76] Eddy N., Odoemelam S., Ekwumemgbo P., . Inhibition of the corrosion of mild steel in H₂SO₄ by penicillin G. Sci. Res. Essays. 2009;4:033-038.
[Google Scholar]

[77] Ehteshamzade M., Shahrabi T., Hosseini M., . Inhibition of copper corrosion by self-assembled films of new Schiff bases and their modification with alkanethiols in aqueous medium. Appl. Surf. Sci.. 2006;252:2949-2959.
[Google Scholar]

[78] Ehteshamzadeh M., Shahrabi T., Hosseini M., . Innovation in acid pickling treatments of copper by characterizations of a new series of Schiff bases as corrosion inhibitors. Anti-Corros. Methods Mater.. 2006;53:296-302.
[Google Scholar]

[79] El-Hafez G.M.A., Badawy W.A., . The use of cysteine, N-acetyl cysteine and methionine as environmentally friendly corrosion inhibitors for Cu–10Al–5Ni alloy in neutral chloride solutions. Electrochim. Acta. 2013;108:860-866.
[Google Scholar]

[80] El-Mahdy G.A., Kim K.B., . AC impedance study on the atmospheric corrosion of aluminum under periodic wet–dry conditions. Electrochim. Acta. 2004;49:1937-1948.
[Google Scholar]

[81] El-Naggar M., . Bis-aminoazoles corrosion inhibitors for copper in 4.0 M HNO₃ solutions. Corros. Sci.. 2000;42:773-784.
[Google Scholar]

[82] El-Naggar M., . Corrosion inhibition of mild steel in acidic medium by some sulfa drugs compounds. Corros. Sci.. 2007;49:2226-2236.
[Google Scholar]

[83] Eldesoky A., Hassan H.M., Fouda A., . Studies on the corrosion inhibition of copper in nitric acid solution using some pharmaceutical compounds. Int. J. Electrochem. Sci.. 2013;8:10376-10395.
[Google Scholar]

[84] Eldesoky A.M., Diab M.A., El-Bindary A.A., El-Sonbati A.Z., Seyam H.A., . Some antipyrine derivatives as corrosion inhibitors for copper in acidic medium: experimental and quantum chemical molecular dynamics approach. J. Mater. Environ. Sci.. 2015;6:2148-2165.
[Google Scholar]

[85] Emad M., Al-Rasheedi M., . Nigella sativa and natural honey as corrosion inhibitors for copper in cooling water systems. J. Mater. Environ. Sci.. 2015;6:201-206.
[Google Scholar]

[86] Enick, O.V., 2006. Do Pharmaceutically Active Compounds have an Ecological Impact? Biological Sciences Department – Simon Fraser University.

[87] Erdem E., Karapinar N., Donat R., . The removal of heavy metal cations by natural zeolites. J. Colloid Interface Sci.. 2004;280:309-314.
[Google Scholar]

[88] Esmaeili N., Neshati J., Yavari I., . Scanning electrochemical microscopy for the investigation of corrosion inhibition of triazino-benzimidazole-2-thiones in hydrochloric acid solution. Res. Chem. Intermed. 2015:1-13.
[Google Scholar]

[89] Ezznaydy G., Shaban A., Telegdi J., Ouaki B., El Hajjaji S., . Inhibition of copper corrosion in saline solution by mono-hydroxamic acid. J. Mater. Environ. Sci.. 2015;6:1819-1823.
[Google Scholar]

[90] Mounir, F., Lh. Bazzi, S.E.I., Salghi, R., Bammou, L., Bazzi1, L., Chihab Eddine, A., Jbara, O., 2012. Copper corrosion behavior in phosphoric acid containing chloride and its inhibition by artemisia oil. IJRRAS 13, 574–587.

[91] Fayomi O.S.I., Popoola A.P.I., Popoola O.M., . Inhibitive action and synergistic performance of 2-amino-ethanol and N,N-diethylethanamine on copper in hydrochloric acid solution. Bull. Chem. Soc. Ethiop.. 2014;28:457-467.
[Google Scholar]

[92] Feng L., Yang H., Wang F., . Experimental and theoretical studies for corrosion inhibition of carbon steel by imidazoline derivative in 5% NaCl saturated Ca(OH)₂ solution. Electrochim. Acta. 2011;58:427-436.
[Google Scholar]

[93] Finšgar M., . 2-Mercaptobenzimidazole as a copper corrosion inhibitor: part I. Long-term immersion, 3D-profilometry, and electrochemistry. Corros. Sci.. 2013;72:82-89.
[Google Scholar]

[94] Finšgar M., . The first X-ray photoelectron spectroscopy surface analysis of 4-methyl-2-phenyl-imidazole adsorbed on copper. Anal. Methods. 2015;7:6496-6503.
[Google Scholar]

[95] Finšgar M., Merl D.K., . 2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: electrochemistry, 3D-profilometry, and XPS surface analysis. Corros. Sci.. 2014;80:82-95.
[Google Scholar]

[96] Finšgar M., Milošev I., . Inhibition of copper corrosion by 1,2,3-benzotriazole: a review. Corros. Sci.. 2010;52:2737-2749.
[Google Scholar]

[97] Flis J., Zakroczymski T., . Impedance study of reinforcing steel in simulated pore solution with tannin. J. Electrochem. Soc.. 1996;143:2458-2464.
[Google Scholar]

[98] Flory P.J., . Thermodynamics of high polymer solutions. J. Chem. Phys.. 1942;10:51-61.
[Google Scholar]

[99] Foo K., Hameed B., . Insights into the modeling of adsorption isotherm systems. Chem. Eng. J.. 2010;156:2-10.
[Google Scholar]

[100] Fouda A., El-Haddad M., Abdallah Y., . Septazole: antibacterial drug as a green corrosion inhibitor for copper in hydrochloric acid solutions. Int. J. Innov. Res. Sci. Eng. Technol.. 2013;2:7073-7085.
[Google Scholar]

[101] Fouda A., Eldesoky A., El-Sonbati A., Salam S., . Prop-2-en-1-one derivatives as corrosion inhibitors for copper in 1 M HNO₃. Int. J. Electrochem. Sci.. 2014;9:1867-1891.
[Google Scholar]

[102] Fouda A., Moussa M., Taha F., Elneanaa A., . The role of some thiosemicarbazide derivatives in the corrosion inhibition of aluminium in hydrochloric acid. Corros. Sci.. 1986;26:719-726.
[Google Scholar]

[103] Fouda A.E.A.S., Etaiw S.E.D.H., El-Bendary M.M., Maher M.M., . Metal-organic frameworks based on silver (I) and nitrogen donors as new corrosion inhibitors for copper in HCl solution. J. Mol. Liq.. 2016;213:228-234.
[Google Scholar]

[104] Fouda A.S., El-Aal A.A., Kandil A.B., . The effect of some phthalimide derivatives on corrosion behavior of copper in nitric acid. Desalination. 2006;201:216-223.
[Google Scholar]

[105] Fouda A.S., Shalabi K., Idress A.A., . Ceratonia siliqua extract as a green corrosion inhibitor for copper and brass in nitric acid solutions. Green Chem. Lett. Rev.. 2015;8:17-29.
[Google Scholar]

[106] Fouda A.S., Wahed H.A.A., . Corrosion inhibition of copper in HNO₃ solution using thiophene and its derivatives. Arab. J. Chem.. 2016;9(Suppl. 1):S91-S99.
[Google Scholar]

[107] Frignani A., Tommesani L., Brunoro G., Monticelli C., Fogagnolo M., . Influence of the alkyl chain on the protective effects of 1,2,3-benzotriazole towards copper corrosion. Part I: inhibition of the anodic and cathodic reactions. Corros. Sci.. 1999;41:1205-1215.
[Google Scholar]

[108] Furukawa H., Miller M.A., Yaghi O.M., . Independent verification of the saturation hydrogen uptake in MOF-177 and establishment of a benchmark for hydrogen adsorption in metal–organic frameworks. J. Mater. Chem.. 2007;17:3197-3204.
[Google Scholar]

[109] Gašparac R., Stupnisek-Lisac E., . Corrosion protection on copper by imidazole and its derivatives. Corrosion. 1999;55:1031-1039.
[Google Scholar]

[110] Gerengi H., Darowicki K., Slepski P., Bereket G., Ryl J., . Investigation effect of benzotriazole on the corrosion of brass-MM55 alloy in artificial seawater by dynamic EIS. J. Solid State Electrochem.. 2010;14:897-902.
[Google Scholar]

[111] Ghasemi Z., Tizpar A., . The inhibition effect of some amino acids towards Pb–Sb–Se–As alloy corrosion in sulfuric acid solution. Appl. Surf. Sci.. 2006;252:3667-3672.
[Google Scholar]

[112] Gimbert F., Morin-Crini N., Renault F., Badot P.-M., Crini G., . Adsorption isotherm models for dye removal by cationized starch-based material in a single component system: error analysis. J. Hazard. Mater.. 2008;157:34-46.
[Google Scholar]

[113] Gomma G.K., Wahdan M.H., . Effect of temperature on the acidic dissolution of copper in the presence of amino acids. Mater. Chem. Phys.. 1994;39:142-148.
[Google Scholar]

[114] Gong Y., Wang Z., Gao F., Zhang S., Li H., . Synthesis of new benzotriazole derivatives containing carbon chains as the corrosion inhibitors for copper in sodium chloride solution. Ind. Eng. Chem. Res.. 2015;54:12242-12253.
[Google Scholar]

[115] Gopi D., Govindaraju K.M., Collins Arun Prakash V., Angeline Sakila D.M., Kavitha L., . A study on new benzotriazole derivatives as inhibitors on copper corrosion in ground water. Corros. Sci.. 2009;51:2259-2265.
[Google Scholar]

[116] Gopi D., Sherif E.S.M., Surendiran M., Angeline Sakila D.M., Kavitha L., . Corrosion inhibition by benzotriazole derivatives and sodium dodecyl sulphate as corrosion inhibitors for copper in ground water at different temperatures. Surf. Interface Anal.. 2015;47:618-625.
[Google Scholar]

[117] Guo L., Dong W., Zhang S., . Theoretical challenges in understanding the inhibition mechanism of copper corrosion in acid media in the presence of three triazole derivatives. RSC Adv.. 2014;4:41956-41967.
[Google Scholar]

[118] Gupta N.K., Verma C., Quraishi M.A., Mukherjee A.K., . Schiff's bases derived from l-lysine and aromatic aldehydes as green corrosion inhibitors for mild steel: experimental and theoretical studies. J. Mol. Liq.. 2016;215:47-57.
[Google Scholar]

[119] Gupta S.R., Mourya P., Singh M., Singh V.P., . Synthesis, structural, electrochemical and corrosion inhibition properties of two new ferrocene Schiff bases derived from hydrazides. J. Organomet. Chem.. 2014;767:136-143.
[Google Scholar]

[120] Habib K., . In-situ monitoring of pitting corrosion of copper alloys by holographic interferometry. Corros. Sci.. 1998;40:1435-1440.
[Google Scholar]

[121] Hamdani I., El Ouariachi E., Mokhtari O., Salhi A., Bouyanzer A., Zarrouk A., Hammouti B., Costa J., . An investigation of mild steel corrosion inhibition in hydrochloric acid medium by environment friendly green inhibitor. Der Pharm. Lett.. 2015;7:109-118.
[Google Scholar]

[122] Hamed E., . Studies of the corrosion inhibition of copper in Na₂SO₄ solution using polarization and electrochemical impedance spectroscopy. Mater. Chem. Phys.. 2010;121:70-76.
[Google Scholar]

[123] Hammouti B., Aouniti A., Taleb M., Brighli M., Kertit S., . l-Methionine methyl ester hydrochloride as a corrosion inhibitor of iron in acid chloride solution. Corrosion. 1995;51:411-416.
[Google Scholar]

[124] Hansen K.B., Hsiao Y., Xu F., Rivera N., Clausen A., Kubryk M., Krska S., Rosner T., Simmons B., Balsells J., Ikemoto N., Sun Y., Spindler F., Malan C., Grabowski E.J.J., Armstrong Iii J.D., . Highly efficient asymmetric synthesis of sitagliptin. J. Am. Chem. Soc.. 2009;131:8798-8804.
[Google Scholar]

[125] Hazazi O.A., Abdallah M., . Prazole compounds as inhibitors for corrosion of aluminum in hydrochloric acid. Int. J. Electrochem. Sci.. 2013;8:8138-8152.
[Google Scholar]

[126] Hefter G., North N., Tan S., . Organic corrosion inhibitors in neutral solutions; part 1 – inhibition of steel, copper, and aluminum by straight chain carboxylates. Corrosion. 1997;53:657-667.
[Google Scholar]

[127] Hegazy M.A., Nazeer A.A., Shalabi K., . Electrochemical studies on the inhibition behavior of copper corrosion in pickling acid using quaternary ammonium salts. J. Mol. Liq.. 2015;209:419-427.
[Google Scholar]

[128] Hofmann K., . The Chemistry of Heterocyclic Compounds, Imidazole and Its Derivatives. John Wiley & Sons; 2009.

[129] Hollander O., May R.C., . The chemistry of azole copper corrosion inhibitors in cooling waters. Corrosion. 1985;41:39-45.
[Google Scholar]

[130] Holm R., Holtkamp D., Kleinstück R., Rother H.J., Storp S., . Surface analysis methods in the investigation of corrosion inhibitor performance. Fresenius' Zeitschrift für analytische Chemie. 1989;333:546-554.
[Google Scholar]

[131] Holze R., . The electrosorption of imidazole on a gold electrode as studied with spectroelectrochemical methods. Electrochim. Acta. 1993;38:947-956.
[Google Scholar]

[132] Hosseini M.G., Tavakoli H., Shahrabi T., . Synergism in copper corrosion inhibition by band 2-mercaptobenzoimidazole. J. Appl. Electrochem.. 2008;38:1629-1636.
[Google Scholar]

[133] Hu L., Zhang S., Li W., Hou B., . Electrochemical and thermodynamic investigation of diniconazole and triadimefon as corrosion inhibitors for copper in synthetic seawater. Corros. Sci.. 2010;52:2891-2896.
[Google Scholar]

[134] Huijing Z., Guangyong L., Huan W., Lixin G., Daquan Z., . Synergistic effect of triethyl phosphate and cerium (IV) ion on corrosion inhibition for copper in hydrochloric acid solution. J. Chin. Soc. Corros. Prot.. 2014;34:271-276.
[Google Scholar]

[135] Huynh N., Bottle S., Notoya T., Schweinsberg D., . Inhibition of copper corrosion by coatings of alkyl esters of carboxybenzotriazole. Corros. Sci.. 2002;44:2583-2596.
[Google Scholar]

[136] Ismail K.M., . Evaluation of cysteine as environmentally friendly corrosion inhibitor for copper in neutral and acidic chloride solutions. Electrochim. Acta. 2007;52:7811-7819.
[Google Scholar]

[137] Issaadi S., Douadi T., Chafaa S., . Adsorption and inhibitive properties of a new heterocyclic furan schiff base on corrosion of copper in HCL 1 M: experimental and theoretical investigation. Appl. Surf. Sci.. 2014;316:582-589.
[Google Scholar]

[138] Izquierdo J., Santana J.J., González S., Souto R.M., . Scanning microelectrochemical characterization of the anti-corrosion performance of inhibitor films formed by 2-mercaptobenzimidazole on copper. Prog. Org. Coat.. 2012;74:526-533.
[Google Scholar]

[139] Jennings G.K., Yong T.-H., Munro J.C., Laibinis P.E., . Structural effects on the barrier properties of self-assembled monolayers formed from long-chain ω-alkoxy-n-alkanethiols on copper. J. Am. Chem. Soc.. 2003;125:2950-2957.
[Google Scholar]

[140] Ji G., Anjum S., Sundaram S., Prakash R., . Musa paradisica peel extract as green corrosion inhibitor for mild steel in HCl solution. Corros. Sci.. 2015;90:107-117.
[Google Scholar]

[141] Joseph B., Joseph A., . Inhibition of copper corrosion in 1 M nitric acid-electro analytical and theoretical study with (E)-(4-(4-methoxybenzylideneamino)-4H-1,2,4-triazole-3,5diyl) dimethanol (MBATD) Portugaliae Electrochim. Acta. 2011;29:253-271.
[Google Scholar]

[142] Kallip S., Bastos A.C., Zheludkevich M.L., Ferreira M.G.S., . A multi-electrode cell for high-throughput SVET screening of corrosion inhibitors. Corros. Sci.. 2010;52:3146-3149.
[Google Scholar]

[143] Karthik G., Sundaravadivelu M., . Amikacin disulfate: an aminoglycoside antibiotic drug as a corrosion inhibitor for copper in 1 M nitric acid medium. J. Adhes. Sci. Technol.. 2016;30:1072-1086.
[Google Scholar]

[144] Karthik G., Sundaravadivelu M., Rajkumar P., Manikandan M., . Diaza-adamantane derivatives as corrosion inhibitor for copper in nitric acid medium. Res. Chem. Intermed. 2015:7593-7615.
[Google Scholar]

[145] Kear G., Barker B.D., Walsh F.C., . Electrochemical corrosion of unalloyed copper in chloride media – a critical review. Corros. Sci.. 2004;46:109-135.
[Google Scholar]

[146] Khadom A.A., . Dual function of benzotriazole as copper alloy corrosion inhibitor and hydrochloric acid flow improver. Surf. Eng. Appl. Electrochem.. 2014;50:157-172.
[Google Scholar]

[147] Khaled K., . Molecular simulation, quantum chemical calculations and electrochemical studies for inhibition of mild steel by triazoles. Electrochim. Acta. 2008;53:3484-3492.
[Google Scholar]

[148] Khaled K., . Corrosion control of copper in nitric acid solutions using some amino acids – a combined experimental and theoretical study. Corros. Sci.. 2010;52:3225-3234.
[Google Scholar]

[149] Khaled K., . Studies of the corrosion inhibition of copper in sodium chloride solutions using chemical and electrochemical measurements. Mater. Chem. Phys.. 2011;125:427-433.
[Google Scholar]

[150] Khaled K., Amin M.A., . Dry and wet lab studies for some benzotriazole derivatives as possible corrosion inhibitors for copper in 1.0 M HNO₃. Corros. Sci.. 2009;51:2098-2106.
[Google Scholar]

[151] Khaled K., Amin M.A., Al-Mobarak N., . On the corrosion inhibition and adsorption behaviour of some benzotriazole derivatives during copper corrosion in nitric acid solutions: a combined experimental and theoretical study. J. Appl. Electrochem.. 2010;40:601-613.
[Google Scholar]

[152] Khaled K., Fadl-Allah S.A., Hammouti B., . Some benzotriazole derivatives as corrosion inhibitors for copper in acidic medium: experimental and quantum chemical molecular dynamics approach. Mater. Chem. Phys.. 2009;117:148-155.
[Google Scholar]

[153] Khaled K.F., Hackerman N., . Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 1 M HCl solutions. Electrochim. Acta. 2003;48:2715-2723.
[Google Scholar]

[154] Khalil N., Mahgoub F., Abd-El-Nabey B., Abdel-Aziz A., . Corrosion of aluminium in perchloric acid in presence of various inorganic additives. Corros. Eng., Sci. Technol.. 2003;38:205-210.
[Google Scholar]

[155] Khamis E., Kandil S., Ibrahim A., . Adsorption action of phosphine inhibitors on the corrosion of steel. Adsorpt. Sci. Technol.. 1995;12:279-291.
[Google Scholar]

[156] Khan P.F., Shanthi V., Babu R.K., Muralidharan S., Barik R.C., . Effect of benzotriazole on corrosion inhibition of copper under flow conditions. J. Environ. Chem. Eng.. 2015;3:10-19.
[Google Scholar]

[157] Kidwai M., Misra P., Bhushan K.R., Dave B., . A novel route to 1,2,4-triazoles. Synth. Commun.. 2000;30:3031-3040.
[Google Scholar]

[158] Kilinççeker G., Demir H., . The inhibition effects of cysteine on the corrosion behaviour of copper in 3.5% NaCl solution. Anti-Corros. Methods Mater.. 2013;60:134-142.
[Google Scholar]

[159] Kokalj A., . Is the analysis of molecular electronic structure of corrosion inhibitors sufficient to predict the trend of their inhibition performance. Electrochim. Acta. 2010;56:745-755.
[Google Scholar]

[160] Kokalj A., Kovačević N., Peljhan S., Finšgar M., Lesar A., Milošev I., . Triazole, benzotriazole, and naphthotriazole as copper corrosion inhibitors: I. Molecular electronic and adsorption properties. ChemPhysChem. 2011;12:3547-3555.
[Google Scholar]

[161] Kosower E.M., . Introduction to Physical Organic Chemistry. John Wiley & Sons; 1968.

[162] Krishnaveni K., Ravichandran J., . Influence of aqueous extract of leaves of Morinda tinctoria on copper corrosion in HCl medium. J. Electroanal. Chem.. 2014;735:24-31.
[Google Scholar]

[163] Krishnaveni K., Ravichandran J., . A study on the inhibition of copper corrosion in sulphuric acid by aqueous extract of leaves of Morinda tinctoria. J. Fail. Anal. Prev.. 2015;15:711-721.
[Google Scholar]

[164] Kundu S., Gupta A., . Arsenic adsorption onto iron oxide-coated cement (IOCC): regression analysis of equilibrium data with several isotherm models and their optimization. Chem. Eng. J.. 2006;122:93-106.
[Google Scholar]

[165] Kuruvilla M., John S., Joseph A., . Electrochemical studies on the interaction of l-cysteine with metallic copper in sulfuric acid. Res. Chem. Intermed.. 2013;39:3531-3543.
[Google Scholar]

[166] Lakshminarayanan V., Kannan R., Rajagopalan S., . Cyclic voltammetric behavior of certain copper-azole systems using carbon paste electrodes. J. Electroanal. Chem.. 1994;364:79-86.
[Google Scholar]

[167] Lalitha A., Ramesh S., Rajeswari S., . Surface protection of copper in acid medium by azoles and surfactants. Electrochim. Acta. 2005;51:47-55.
[Google Scholar]

[168] Lee W.-J., . Inhibiting effects of imidazole on copper corrosion in 1 M HNO₃ solution. Mater. Sci. Eng., A. 2003;348:217-226.
[Google Scholar]

[169] Lei Y.H., Sheng N., Hyono A., Ueda M., Ohtsuka T., . Effect of benzotriazole (BTA) addition on polypyrrole film formation on copper and its corrosion protection. Prog. Org. Coat.. 2014;77:339-346.
[Google Scholar]

[170] Lewis G., . Adsorption isotherm for the copper-benzotnazole system. Br. Corros. J.. 1981;16:169-171.
[Google Scholar]

[171] Li C., Li L., Wang C., Zhu Y., Zhang W., . Study of the protection performance of self-assembled monolayers on copper with the scanning electrochemical microscope. Corros. Sci.. 2014;80:511-516.
[Google Scholar]

[172] Li M.M., Xu Q.J., Han J., Yun H., Min Y., . Inhibition action and adsorption behavior of green inhibitor sodium carboxymethyl cellulose on copper. Int. J. Electrochem. Sci.. 2015;10:9028-9041.
[Google Scholar]

[173] Li Q., Li J., Hu L.T., Zhu L., Han X., Tao Z.H., He W., . Electrochemical study of corrosion inhibition on copper in base electrolyte by 1-phenyl-3-hydroxy-1,2,4-triazole. Adv. Mater. Res. 2014:3-7.
[Google Scholar]

[174] Li S., Chen S., Lei S., Ma H., Yu R., Liu D., . Investigation on some Schiff bases as HCl corrosion inhibitors for copper. Corros. Sci.. 1999;41:1273-1287.
[Google Scholar]

[175] Li S.L., Wang Y.G., Chen S.H., Yu R., Lei S.B., Ma H.Y., Liu D.X., . Some aspects of quantum chemical calculations for the study of Schiff base corrosion inhibitors on copper in NaCl solutions. Corros. Sci.. 1999;41:1769-1782.
[Google Scholar]

[176] Li W., Bai X., Yang F., Hou B., . One derivate of thiadiazole (MTYDBH) as corrosion inhibitors for copper in 3.5% NaCl solution under various conditions. Int. J. Electrochem. Sci.. 2012;7:2680-2694.
[Google Scholar]

[177] Liao Q., Yue Z., Yang D., Wang Z., Li Z., Ge H., Li Y., . Inhibition of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium diethyldithiocarbamate. Corros. Sci.. 2011;53:1999-2005.
[Google Scholar]

[178] Liu A., Ren X., Zhang J., Wang C., Yang P., Zhang J., An M., Higgins D., Li Q., Wu G., . Theoretical and experimental studies of the corrosion inhibition effect of nitrotetrazolium blue chloride on copper in 0.1 M H₂SO₄. RSC Adv.. 2014;4:40606-40616.
[Google Scholar]

[179] Liu M., Sibi M.P., . Recent advances in the stereoselective synthesis of β-amino acids. Tetrahedron. 2002;58:7991-8035.
[Google Scholar]

[180] Liu S., Dong J., Guan W., Duan J., Jiang R., Feng Z., Song W., . The synergistic effect of Na₃PO₄ and benzotriazole on the inhibition of copper corrosion in tetra-n-butylammonium bromide aerated aqueous solution. Mater. Corros.. 2012;63:1017-1025.
[Google Scholar]

[181] Liu S., Duan J., Jiang R., Feng Z., Xiao R., . Corrosion inhibition of copper in tetra-n-butylammonium bromide aqueous solution by benzotriazole. Mater. Corros.. 2011;62:47-52.
[Google Scholar]

[182] Lokesh K.S., De Keersmaecker M., Elia A., Depla D., Dubruel P., Vandenabeele P., Van Vlierberghe S., Adriaens A., . Adsorption of cobalt (II) 5,10,15,20-tetrakis (2-aminophenyl)-porphyrin onto copper substrates: characterization and impedance studies for corrosion inhibition. Corros. Sci.. 2012;62:73-82.
[Google Scholar]

[183] Love J.C., Estroff L.A., Kriebel J.K., Nuzzo R.G., Whitesides G.M., . Self-assembled monolayers of thiolates on metals as a form of nanotechnology. Chem. Rev.. 2005;105:1103-1170.
[Google Scholar]

[184] Ma F., Li W., Tian H., Hou B., . The use of a new thiadiazole derivative as a highly efficient and durable copper inhibitor in 3.5% NaCl solution. Int. J. Electrochem. Sci.. 2015;10:5862-5879.
[Google Scholar]

[185] Ma H., Chen S., Niu L., Zhao S., Li S., Li D., . Inhibition of copper corrosion by several Schiff bases in aerated halide solutions. J. Appl. Electrochem.. 2002;32:65-72.
[Google Scholar]

[186] Ma H., Chen S., Yin B., Zhao S., Liu X., . Impedance spectroscopic study of corrosion inhibition of copper by surfactants in the acidic solutions. Corros. Sci.. 2003;45:867-882.
[Google Scholar]

[187] Ma H., Chen S., Zhao S., Liu X., Li D., . A study of corrosion behavior of copper in acidic solutions containing cetyltrimethylammonium bromide. J. Electrochem. Soc.. 2001;148:B482-B488.
[Google Scholar]

[188] Ma H., Yang C., Yin B., Li G., Chen S., Luo J., . Electrochemical characterization of copper surface modified by n-alkanethiols in chloride-containing solutions. Appl. Surf. Sci.. 2003;218:144-154.
[Google Scholar]

[189] Makarenko N., Kharchenko U., Zemnukhova L., . Effect of amino acids on corrosion of copper and steel in acid medium. Russ. J. Appl. Chem.. 2011;84:1362-1365.
[Google Scholar]

[190] Marcus P., Mansfeld F.B., . Analytical Methods in Corrosion Science and Engineering. Taylor & Francis; 2005.

[191] Masmoudi M., Rahal C., Abdelhedi R., Khitouni M., Bouaziz M., . Inhibitive action of stored olive mill wastewater (OMW) on the corrosion of copper in a NaCl solution. RSC Adv.. 2015;5:101768-101775.
[Google Scholar]

[192] Matos J., Pereira L., Agostinho S., Barcia O., Cordeiro G., D'elia E., . Effect of cysteine on the anodic dissolution of copper in sulfuric acid medium. J. Electroanal. Chem.. 2004;570:91-94.
[Google Scholar]

[193] McCafferty E., . Introduction to Corrosion Science. 3Island Press; 2011.

[194] Mehdipour M., Ramezanzadeh B., Arman S., . Electrochemical noise investigation of Aloe plant extract as green inhibitor on the corrosion of stainless steel in 1 M H₂SO₄. J. Ind. Eng. Chem.. 2015;21:318-327.
[Google Scholar]

[195] Metikoš-Huković M., Babić R., Marinović A., . Spectrochemical characterization of benzotriazole on copper. J. Electrochem. Soc.. 1998;145:4045-4051.
[Google Scholar]

[196] Mihajlović M.B.P., Antonijević M.M., . Copper corrosion inhibitors. Period 2008–2014. A review. Int. J. Electrochem. Sci.. 2015;10:1027-1053.
[Google Scholar]

[197] Mihit M., Salghi R., El Issami S., Bazzi L., Hammouti B., Addi E.A., Kertit S., . A study of tetrazoles derivatives as corrosion inhibitors of copper in nitric acid. Pigm. Resin Technol.. 2006;35:151-157.
[Google Scholar]

[198] Mo S., Qin T.T., Luo H.Q., Li N.B., . Insights into the corrosion inhibition of copper in hydrochloric acid solution by self-assembled films of 4-octylphenol. RSC Adv.. 2015;5:90542-90549.
[Google Scholar]

[199] Moretti G., Guidi F., . Tryptophan as copper corrosion inhibitor in 0.5 M aerated sulfuric acid. Corros. Sci.. 2002;44:1995-2011.
[Google Scholar]

[200] Mouni F., El Issami S., Bazzi L., Salghi R., Abidi N., Jodeh S., Bazzi L., Chihab Eddine A., . Green approach to corrosion inhibition of copper by two oils of Argania spinosa (L.) in phosphoric acid. J. Mater. Environ. Sci.. 2015;6:2066-2075.
[Google Scholar]

[201] Mounir F., El Issami S., Bazzi L., Chihab Eddine A., Jbara O., Hilali M., Salghi R., Bazzi L., . Application of cosmetic argan oil as green corrosion inhibitor for copper in phosphoric acid medium. J. Mater. Environ. Sci.. 2014;5:2478-2483.
[Google Scholar]

[202] Muniandy M.T., Rahim A.A., Osman H., Shah A.M., Yahya S., Raja P.B., . Investigation of some schiff bases as corrosion inhibitors for aluminium alloy in 0.5 M hydrochloric acid solutions. Surf. Rev. Lett.. 2011;18:127-133.
[Google Scholar]

[203] Muñoz A.I., Antón J.G., Guiñón J., Herranz V.P., . Comparison of inorganic inhibitors of copper, nickel and copper–nickels in aqueous lithium bromide solution. Electrochim. Acta. 2004;50:957-966.
[Google Scholar]

[204] Mustafa C., Shahinoor Islam Dulal S., . Molybdate and nitrite as corrosion inhibitors for copper-coupled steel in simulated cooling water. Corrosion. 1996;52:16-22.
[Google Scholar]

[205] Obot I., Obi-Egbedi N., . Fluconazole as an inhibitor for aluminium corrosion in 0.1 M HCl. Colloids Surf., A. 2008;330:207-212.
[Google Scholar]

[206] Obot I., Obi-Egbedi N., . Inhibition of aluminium corrosion in hydrochloric acid using nizoral and the effect of iodide ion addition. J. Chem.. 2010;7:837-843.
[Google Scholar]

[207] Odewunmi N., Umoren S., Gasem Z., . Utilization of watermelon rind extract as a green corrosion inhibitor for mild steel in acidic media. J. Ind. Eng. Chem.. 2015;21:239-247.
[Google Scholar]

[208] Otieno-Alego V., Huynh N., Notoya T., Bottle S., Schweinsberg D., . Inhibitive effect of 4-and 5-carboxybenzotriazole on copper corrosion in acidic sulphate and hydrogen sulphide solutions. Corros. Sci.. 1999;41:685-697.
[Google Scholar]

[209] Otmačić H., Stupnišek-Lisac E., . Copper corrosion inhibitors in near neutral media. Electrochim. Acta. 2003;48:985-991.
[Google Scholar]

[210] Park J., Lee G., Ooshige H., Nishikata A., Tsuru T., . Monitoring of water uptake in organic coatings under cyclic wet–dry condition. Corros. Sci.. 2003;45:1881-1894.
[Google Scholar]

[211] Peca D., Pihlar B., Milosěv I., . Protection of copper surface with phytic acid against corrosion in chloride solution. Acta Chim. Slov.. 2014;61:457-467.
[Google Scholar]

[212] Petrović M.B., Radovanović M.B., Simonović A.T., Milić S.M., Antonijević M.M., . The effect of cysteine on the behaviour of copper in neutral and alkaline sulphate solutions. Int. J. Electrochem. Sci.. 2012;7:9043-9057.
[Google Scholar]

[213] Petrović M.B., Simonović A.T., Radovanović M.B., Milić S.M., Antonijević M.M., . Influence of purine on copper behavior in neutral and alkaline sulfate solutions. Chem. Pap.. 2012;66:664-676.
[Google Scholar]

[214] Poling G., . Reflection infra-red studies of films formed by benzotriazole on Cu. Corros. Sci.. 1970;10:359-370.
[Google Scholar]

[215] Pratihar P.S., Verma M.P.S., Sharma A., . Capparis decidua seeds: potential green inhibitor to combat acid corrosion of copper. Rasayan J. Chem.. 2015;8:411-421.
[Google Scholar]

[216] Qiang Y., Zhang S., Xu S., Yin L., . The effect of 5-nitroindazole as an inhibitor for the corrosion of copper in a 3.0% NaCl solution. RSC Adv.. 2015;5:63866-63873.
[Google Scholar]

[217] Qin T.T., Li J., Luo H.Q., Li M., Li N.B., . Corrosion inhibition of copper by 2,5-dimercapto-1,3,4-thiadiazole monolayer in acidic solution. Corros. Sci.. 2011;53:1072-1078.
[Google Scholar]

[218] Quartarone G., Battilana M., Bonaldo L., Tortato T., . Investigation of the inhibition effect of indole-3-carboxylic acid on the copper corrosion in 0.5 M H₂SO₄. Corros. Sci.. 2008;50:3467-3474.
[Google Scholar]

[219] Quartarone G., Bellomi T., Zingales A., . Inhibition of copper corrosion by isatin in aerated 0.5 M H₂SO₄. Corros. Sci.. 2003;45:715-733.
[Google Scholar]

[220] Quartarone G., Bonaldo L., Tortato C., . Inhibitive action of indole-5-carboxylic acid towards corrosion of mild steel in deaerated 0.5 M sulfuric acid solutions. Appl. Surf. Sci.. 2006;252:8251-8257.
[Google Scholar]

[221] Quartarone G., Moretti G., Bellomi T., Capobianco G., Zingales A., . Using indole to inhibit copper corrosion in aerated 0.5 M sulfuric acid. Corrosion. 1998;54:606-618.
[Google Scholar]

[222] Radovanović M.B., Simonović A.T., Petrović M.B., Milić S.M., Antonijević M.M., . Influence of purine on brass behavior in neutral and alkaline sulphate solutions. Int. J. Electrochem. Sci.. 2012;7:11796-11810.
[Google Scholar]

[223] Raja P.B., Sethuraman M.G., . Natural products as corrosion inhibitor for metals in corrosive media—a review. Mater. Lett.. 2008;62:113-116.
[Google Scholar]

[224] Rajkumar G., Sagunthala R., Sethuraman M.G., . Investigation of inhibiting properties of self-assembled films of 4-aminothiophenol on copper in 3.5% NaCl. J. Adhes. Sci. Technol.. 2015;29:1107-1117.
[Google Scholar]

[225] Rajkumar G., Sethuraman M.G., . A study of copper corrosion inhibition by self-assembled films of 3-mercapto-1H-1,2,4-triazole. Res. Chem. Intermed.. 2016;42:1809-1821.
[Google Scholar]

[226] Ramdani M., Elmsellem H., Elkhiati N., Haloui B., Aouniti A., Ramdani M., Ghazi Z., Chetouani A., Hammouti B., . Caulerpa prolifera green algae using as eco-friendly corrosion inhibitor for mild steel in 1 M HCl media. Der Pharm. Chem.. 2015;7:67-76.
[Google Scholar]

[227] Ramesh S., Rajeswari S., . Evaluation of inhibitors and biocide on the corrosion control of copper in neutral aqueous environment. Corros. Sci.. 2005;47:151-169.
[Google Scholar]

[228] Ramezanzadeh B., Arman S.Y., Mehdipour M., Markhali B.P., . Analysis of electrochemical noise (ECN) data in time and frequency domain for comparison corrosion inhibition of some azole compounds on Cu in 1.0 M H₂SO₄ solution. Appl. Surf. Sci.. 2014;289:129-140.
[Google Scholar]

[229] Rani P.D., Selvaraj S., . Emblica officinalis (AMLA) leaves extract as corrosion inhibitor for copper and its alloy (CU-27ZN) in natural sea water. Arch. Appl. Sci. Res.. 2010;2:140-150.
[Google Scholar]

[230] Rani P.D., Selvaraj S., . Inhibitive action of Vitis vinifera (grape) on copper and brass in natural sea water environment. Rasayan. J. Chem.. 2010;3:473-482.
[Google Scholar]

[231] Rao B.A., Iqbal M.Y., Reddy M.N., Kumar K.C., . Self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio) benzotriazine on copper for corrosion protection. Bull. Mater. Sci.. 2014;37:185-197.
[Google Scholar]

[232] Ravichandran R., Nanjundan S., Rajendran N., . Effect of benzotriazole derivatives on the corrosion and dezincification of brass in neutral chloride solution. J. Appl. Electrochem.. 2004;34:1171-1176.
[Google Scholar]

[233] Ravichandran R., Rajendran N., . Electrochemical behaviour of brass in artificial seawater: effect of organic inhibitors. Appl. Surf. Sci.. 2005;241:449-458.
[Google Scholar]

[234] Rigo A., Corazza A., di Paolo M.L., Rossetto M., Ugolini R., Scarpa M., . Interaction of copper with cysteine: stability of cuprous complexes and catalytic role of cupric ions in anaerobic thiol oxidation. J. Inorg. Biochem.. 2004;98:1495-1501.
[Google Scholar]

[235] Rudresh H., Mayanna S., . Adsorption of n-decylamine on zinc from acidic chloride solution. J. Electrochem. Soc.. 1977;124:340-342.
[Google Scholar]

[236] Saadawy M., . Inhibitive effect of pantoprazole sodium on the corrosion of copper in acidic solutions. Arab. J. Sci. Eng.. 2016;41:177-190.
[Google Scholar]

[237] Şafak S., Duran B., Yurt A., Türkoĝlu G., . Schiff bases as corrosion inhibitor for aluminium in HCl solution. Corros. Sci.. 2012;54:251-259.
[Google Scholar]

[238] Saha S.K., Ghosh P., Hens A., Murmu N.C., Banerjee P., . Density functional theory and molecular dynamics simulation study on corrosion inhibition performance of mild steel by mercapto-quinoline Schiff base corrosion inhibitor. Physica E. 2015;66:332-341.
[Google Scholar]

[239] Sameh S.A., Salih I.K., Alwash S.H., Alwasity A.A., . Eng. Tech. J.. 2010;28:1196.

[240] Samide A., Tutunaru B., Negrila C., Prunaru I., . Surface analysis of inhibitor film formed by 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide on carbon steel surface in acidic media. Spectrosc. Lett.. 2012;45:55-64.
[Google Scholar]

[241] Sangeetha T., Fredimoses M., . Inhibition of mild copper metal corrosion in HNO₃ medium by acid extract of Azadirachta indica seed. J. Chem.. 2011;8:S1-S6.
[Google Scholar]

[242] Sastri V.S., . Green Corrosion Inhibitors: Theory and Practice. John Wiley & Sons; 2012.

[243] Sathiyanarayanan S., Manoharan S., Rajagopal G., Balakrishnan K., . Characterisation of passive films on copper. Br. Corros. J. 2013
[Google Scholar]

[244] Savita, Mourya P., Chaubey N., Singh V.K., Singh M.M., . Eco-friendly inhibitors for copper corrosion in nitric acid: experimental and theoretical evaluation. Metall. Mater. Trans. B. 2016;47:47-57.
[Google Scholar]

[245] Saxena N., Kumar S., . Anisalidine derivatives as corrosion inhibitors of copper in acidic media. Prot. Met. Phys. Chem. Surf.. 2015;51:701-709.
[Google Scholar]

[246] Scendo M., . Inhibitive action of the purine and adenine for copper corrosion in sulphate solutions. Corros. Sci.. 2007;49:2985-3000.
[Google Scholar]

[247] Scendo M., . Inhibition of copper corrosion in sodium nitrate solutions with nontoxic inhibitors. Corros. Sci.. 2008;50:1584-1592.
[Google Scholar]

[248] Scendo M., Uznanska J., . The effect of ionic liquids on the corrosion inhibition of copper in acidic chloride solutions. Int. J. Corros.. 2011;2011
[Google Scholar]

[249] Schweinsberg D., Bottle S., Otieno-Alego V., Notoya T., . A near-infrared FT-Raman (SERS) and electrochemical study of the synergistic effect of 1-[(1′,2′-dicarboxy) ethyl]-benzotriazole and KI on the dissolution of copper in aerated sulfuric acid. J. Appl. Electrochem.. 1997;27:161-168.
[Google Scholar]

[250] Shabani-Nooshabadi M., Hoseiny F.S., Jafari Y., . Corrosion inhibition of copper by Ephedra sarcocarpa plant extract as green corrosion inhibitor in strong acidic medium. Anal. Bioanal. Electrochem.. 2014;6:341-354.
[Google Scholar]

[251] Shabani-Nooshabadi M., Hoseiny F.S., Jafari Y., . Green approach to corrosion inhibition of copper by the extract of Calligonum comosum in strong acidic medium. Metall. Mater. Trans. A. 2014;46:293-299.
[Google Scholar]

[252] Shen S., Zhu C.D., Guo X.Y., Li C.C., Wen Y., Yang H.F., . The synergistic mechanism of phytic acid monolayers and iodide ions for inhibition of copper corrosion in acidic media. RSC Adv.. 2014;4:10597-10606.
[Google Scholar]

[253] Sherif E.-S.M., . Corrosion behavior of copper in 0.50 M hydrochloric acid pickling solutions and its inhibition by 3-amino-1,2,4-triazole and 3-amino-5-mercapto-1,2,4-triazole. Int. J. Electrochem. Sci.. 2012;7:1884-1897.
[Google Scholar]

[254] Sherif E.-S.M., Erasmus R., Comins J., . Corrosion of copper in aerated acidic pickling solutions and its inhibition by 3-amino-1,2,4-triazole-5-thiol. J. Colloid Interface Sci.. 2007;306:96-104.
[Google Scholar]

[255] Sherif E.-S.M., Erasmus R., Comins J., . Inhibition of copper corrosion in acidic chloride pickling solutions by 5-(3-aminophenyl)-tetrazole as a corrosion inhibitor. Corros. Sci.. 2008;50:3439-3445.
[Google Scholar]

[256] Sherif E.-S.M., Potgieter J., Comins J., Cornish L., Olubambi P., Machio C., . Effects of minor additions of ruthenium on the passivation of duplex stainless-steel corrosion in concentrated hydrochloric acid solutions. J. Appl. Electrochem.. 2009;39:1385.
[Google Scholar]

[257] Sherif E., Park S.-M., . Inhibition of copper corrosion in 3.0% NaCl solution by N-phenyl-1, 4-phenylenediamine. J. Electrochem. Soc.. 2005;152:B428-B433.
[Google Scholar]

[258] Sherif E., Park S.-M., . 2-Amino-5-ethyl-1,3,4-thiadiazole as a corrosion inhibitor for copper in 3.0% NaCl solutions. Corros. Sci.. 2006;48:4065-4079.
[Google Scholar]

[259] Sherif E.M., Erasmus R.M., Comins J.D., . Corrosion of copper in aerated synthetic sea water solutions and its inhibition by 3-amino-1,2,4-triazole. J. Colloid Interface Sci.. 2007;309:470-477.
[Google Scholar]

[260] Sherif E.M., Erasmus R.M., Comins J.D., . Effects of 3-amino-1,2,4-triazole on the inhibition of copper corrosion in acidic chloride solutions. J. Colloid Interface Sci.. 2007;311:144-151.
[Google Scholar]

[261] Sherif E.M., Park S.M., . Effects of 2-amino-5-ethylthio-1,3,4-thiadiazole on copper corrosion as a corrosion inhibitor in aerated acidic pickling solutions. Electrochim. Acta. 2006;51:6556-6562.
[Google Scholar]

[262] Sherif E.S.M., . Electrochemical and gravimetric study on the corrosion and corrosion inhibition of pure copper in sodium chloride solutions by two azole derivatives. Int. J. Electrochem. Sci.. 2012;7:1482-1495.
[Google Scholar]

[263] Shi Y., Zhang Z., Su J., Cao F., Zhang J., . Electrochemical noise study on 2024–T3 Aluminum alloy corrosion in simulated acid rain under cyclic wet–dry condition. Electrochim. Acta. 2006;51:4977-4986.
[Google Scholar]

[264] Shokry H., Yuasa M., Sekine I., Issa R., El-Baradie H., Gomma G., . Corrosion inhibition of mild steel by Schiff base compounds in various aqueous solutions: part 1. Corros. Sci.. 1998;40:2173-2186.
[Google Scholar]

[265] Shukla S.K., Singh A.K., Ahamad I., Quraishi M., . Streptomycin: a commercially available drug as corrosion inhibitor for mild steel in hydrochloric acid solution. Mater. Lett.. 2009;63:819-822.
[Google Scholar]

[266] Shumakovich G.P., Otrokhov G.V., Khlupova M.E., Vasil'Eva I.S., Zaitseva E.A., Morozova O.V., Yaropolov A.I., . Laccase-catalyzed synthesis of aniline oligomers and their application for the protection of copper against corrosion. RSC Adv.. 2014;4:30193-30196.
[Google Scholar]

[267] Simonović A.T., Petrović M.B., Radovanović M.B., Milić S.M., Antonijević M.M., . Inhibition of copper corrosion in acidic sulphate media by eco-friendly amino acid compound. Chem. Pap.. 2014;68:362-371.
[Google Scholar]

[268] Singh P., Quraishi M.A., . Corrosion inhibition of mild steel using Novel Bis Schiff's Bases as corrosion inhibitor: electrochemical and Surface measurement. Measur.: J. Int. Measur. Confed.. 2016;86:114-124.
[Google Scholar]

[269] Solmaz R., Altunbaş Şahin E., Döner A., Kardaş G., . The investigation of synergistic inhibition effect of rhodanine and iodide ion on the corrosion of copper in sulphuric acid solution. Corros. Sci.. 2011;53:3231-3240.
[Google Scholar]

[270] Souto R., Sánchez M.P., Barrera M., González S., Salvarezza R., Arvia A., . The kinetics of pitting corrosion of copper in alkaline solutions containing sodium perchlorate. Electrochim. Acta. 1992;37:1437-1443.
[Google Scholar]

[271] Stupnišek-Lisac E., Bozic A.L., Cafuk I., . Low-toxicity copper corrosion inhibitors. Corrosion. 1998;54:713-720.
[Google Scholar]

[272] Stupnisek-Lisac E., Brnada A., Mance A.D., . Secondary amines as copper corrosion inhibitors in acid media. Corros. Sci.. 2000;42:243-257.
[Google Scholar]

[273] Stupnišek-Lisac E., Gazivoda A., Madžarac M., . Evaluation of non-toxic corrosion inhibitors for copper in sulphuric acid. Electrochim. Acta. 2002;47:4189-4194.
[Google Scholar]

[274] Subramanian R., Lakshminarayanan V., . Effect of adsorption of some azoles on copper passivation in alkaline. Corros. Sci.. 2002;44:535-554.
[Google Scholar]

[275] Sudheer, Quraishi M.A., . Electrochemical and theoretical investigation of triazole derivatives on corrosion inhibition behavior of copper in hydrochloric acid medium. Corros. Sci.. 2013;70:161-169.
[Google Scholar]

[276] Sudheer, Quraishi M.A., . The corrosion inhibition effect of aryl pyrazolo pyridines on copper in hydrochloric acid system: computational and electrochemical studies. RSC Adv.. 2015;5:41923-41933.
[Google Scholar]

[277] Sulaiman, S., Nor-Anuar, A., Abd-Razak, A., Chelliapan, S., 2012. A study of using Allium cepa (onion) as natural corrosion inhibitor in industrial chill wastewater system. Res. J. Chem. Sci. ISSN: 2231, 606X.

[278] Suter T., Moser E., Böhni H., . The characterization of the tarnishing of Cu-15Ni-8Sn and Cu-5Al-5Sn alloys. Corros. Sci.. 1993;34:1111-1122.
[Google Scholar]

[279] Szőcs E., Vastag G., Shaban A., Kálmán E., . Electrochemical behaviour of an inhibitor film formed on copper surface. Corros. Sci.. 2005;47:893-908.
[Google Scholar]

[280] Tan Y., Fwu Y., Bhardwaj K., . Electrochemical evaluation of under-deposit corrosion and its inhibition using the wire beam electrode method. Corros. Sci.. 2011;53:1254-1261.
[Google Scholar]

[281] Tan Y., Srinivasan M., Pehkonen S., Chooi S.Y., . Effects of ring substituents on the protective properties of self-assembled benzenethiols on copper. Corros. Sci.. 2006;48:840-862.
[Google Scholar]

[282] Tang Y.M., Yang W.Z., Yin X.S., Liu Y., Wan R., Wang J.T., . Phenyl-substituted amino thiadiazoles as corrosion inhibitors for copper in 0.5 M H₂SO₄. Mater. Chem. Phys.. 2009;116:479-483.
[Google Scholar]

[283] Tansuǧ G., Tüken T., Giray E.S., Findikkiran G., Siǧircik G., Demirkol O., Erbil M., . A new corrosion inhibitor for copper protection. Corros. Sci.. 2014;84:21-29.
[Google Scholar]

[284] Tasic Z.Z., Antonijevic M.M., Petrovic Mihajlovic M.B., Radovanovic M.B., . The influence of synergistic effects of 5-methyl-1H-benzotriazole and potassium sorbate as well as 5-methyl-1H-benzotriazole and gelatin on the copper corrosion in sulphuric acid solution. J. Mol. Liq.. 2016;219:463-473.
[Google Scholar]

[285] Tawfik S.M., Zaky M.F., . Corrosion inhibition performance of some Schiff base anionic surfactant complexes of cobalt(II), copper(II), and zinc(II) on carbon steel in 1.0 M HCl. Res. Chem. Intermed.. 2015;41:8747-8772.
[Google Scholar]

[286] Thanapackiam P., Rameshkumar S., Subramanian S.S., Mallaiya K., . Electrochemical evaluation of inhibition efficiency of ciprofloxacin on the corrosion of copper in acid media. Mater. Chem. Phys. 2016
[Google Scholar]

[287] Tian H., Cheng Y.F., Li W., Hou B., . Triazolyl-acylhydrazone derivatives as novel inhibitors for copper corrosion in chloride solutions. Corros. Sci.. 2015;100:341-352.
[Google Scholar]

[288] Tian H., Li W., Cao K., Hou B., . Potent inhibition of copper corrosion in neutral chloride media by novel non-toxic thiadiazole derivatives. Corros. Sci.. 2013;73:281-291.
[Google Scholar]

[289] Tomi I.H.R., Al-Daraji A.H.R., Aziz S.A., . Synthesis, characterization, and study the inhibitory effect of thiazole and thiadiazole derivatives toward the corrosion of copper in acidic media. Synth. React. Inorg., Met.-Org., Nano-Met. Chem.. 2015;45:605-613.
[Google Scholar]

[290] Trabanelli G., . 1991 Whitney award lecture: inhibitors-an old remedy for a new challenge. Corrosion. 1991;47:410-419.
[Google Scholar]

[291] Tromans D., Sun R.h., . Anodic polarization behavior of copper in aqueous chloride/benzotriazole solutions. J. Electrochem. Soc.. 1991;138:3235-3244.
[Google Scholar]

[292] Tüken T., Kıcır N., Elalan N.T., Sığırcık G., Erbil M., . Self assembled film based on hexane-1,6-diamine and 2-mercapto-ethanol on copper. Appl. Surf. Sci.. 2012;258:6793-6799.
[Google Scholar]

[293] Ulman A., . Formation and structure of self-assembled monolayers. Chem. Rev.. 1996;96:1533-1554.
[Google Scholar]

[294] Valek L., Martinez S., . Copper corrosion inhibition by Azadirachta indica leaves extract in 0.5 M sulphuric acid. Mater. Lett.. 2007;61:148-151.
[Google Scholar]

[295] Vashisht H., Bahadur I., Kumar S., Goyal M.S., Kaur G., Singh G., Katata-Seru L., Ebenso E.E., . Synergistic interactions between tetra butyl phosphonium hydroxide and iodide ions on the mild steel surface for corrosion inhibition in acidic medium. J. Mol. Liq.. 2016;224:19-29.
[Google Scholar]

[296] Vastag G., Szöcs E., Shaban A., Kálmán E., . New inhibitors for copper corrosion. Pure Appl. Chem.. 2001;73:1861-1869.
[Google Scholar]

[297] Vijayaraghavan K., Padmesh T., Palanivelu K., Velan M., . Biosorption of nickel (II) ions onto Sargassum wightii: application of two-parameter and three-parameter isotherm models. J. Hazard. Mater.. 2006;133:304-308.
[Google Scholar]

[298] Wang C.-T., Chen S.-H., Ma H.-Y., Hua L., Wang N., . Study of the ability of self-assembled N-vinylcarbazole monolayers to protect copper against corrosion. J. Serb. Chem. Soc.. 2002;67:685-696.
[Google Scholar]

[299] Wang D., Bierwagen G.P., . Sol-gel coatings on metals for corrosion protection. Prog. Org. Coat.. 2009;64:327-338.
[Google Scholar]

[300] Wang D., Xiang B., Liang Y., Song S., Liu C., . Corrosion control of copper in 3.5 wt.% NaCl Solution by domperidone: experimental and theoretical study. Corros. Sci.. 2014;85:77-86.
[Google Scholar]

[301] Wang S., Tao Z., He W., Xiao D., Tan Z., . Effects of cyproconazole on copper corrosion as environmentally friendly corrosion inhibitor in nitric acid solution. Asian J. Chem.. 2015;27:1107-1110.
[Google Scholar]

[302] Wang Z.L., Zhang J., Wang Z.M., Zhou L., Han X., Li Q.F., Gao S., . Emulsification reducing the corrosion risk of mild steel in oil–brine mixtures. Corros. Sci.. 2014;86:310-317.
[Google Scholar]

[303] Wu Y., Zhang P., Pickering H., Allara D., . Effect of KI on improving copper corrosion inhibition efficiency of benzotriazole in sulfuric acid electrolytes. J. Electrochem. Soc.. 1993;140:2791-2800.
[Google Scholar]

[304] Xiong S., Sun J.L., Xu Y., . Adsorption behavior of thiadiazole as corrosion inhibitors on copper surface. Mater. Sci. Forum. Trans. Tech. Publ. 2015:204-211.
[Google Scholar]

[305] Xue G., Ding J., . Chemisorption of a compact polymeric coating on copper surfaces from a benzotriazole solution. Appl. Surf. Sci.. 1990;40:327-332.
[Google Scholar]

[306] Xue G., Huang X.-Y., Dong J., Zhang J., . The formation of an effective anti-corrosion film on copper surfaces from 2-mercaptobenzimidazole solution. J. Electroanal. Chem. Interfacial Electrochem.. 1991;310:139-148.
[Google Scholar]

[307] Yadav S., Choudhary G., Sharma A., . Green approach to corrosion inhibition of aluminium and copper by Ziziphus mauritiana fruit extract in hydrochloric acid solution. Int. J. ChemTech. Res.. 2013;5:1815-1823.
[Google Scholar]

[308] Yan C., Lin H., Cao C., . Investigation of inhibition of 2-mercaptobenzoxazole for copper corrosion. Electrochim. Acta. 2000;45:2815-2821.
[Google Scholar]

[309] Ye X., Xin X., Zhu J., Xue Z., . Coordination compound films of 1-phenyl-5-mercaptotetrazole on copper surface. Appl. Surf. Sci.. 1998;135:307-317.
[Google Scholar]

[310] Youda R., Nishihara H., Aramaki K., . SERS and impedance study of the equilibrium between complex formation and adsorption of benzotriazole and 4-hydroxybenzotriazole on a copper electrode in sulphate solutions. Electrochim. Acta. 1990;35:1011-1017.
[Google Scholar]

[311] Yu P., Liao D.-M., Luo Y.-B., Chen Z.-G., . Studies of benzotriazole and tolytriazole as inhibitors for copper corrosion in deionized water. Corrosion. 2003;59:314-318.
[Google Scholar]

[312] Yurt A., Aykin Ö., . Diphenolic Schiff bases as corrosion inhibitors for aluminium in 0.1 M HCl: potentiodynamic polarisation and EQCM investigations. Corros. Sci.. 2011;53:3725-3732.
[Google Scholar]

[313] Yurt A., Duran B., Dal H., . An experimental and theoretical investigation on adsorption properties of some diphenolic Schiff bases as corrosion inhibitors at acidic solution/mild steel interface. Arab. J. Chem.. 2014;7:732-740.
[Google Scholar]

[314] Zanotto F., Grassi V., Balbo A., Monticelli C., Zucchi F., . Stress corrosion cracking of LDX 2101® duplex stainless steel in chloride solutions in the presence of thiosulphate. Corros. Sci.. 2014;80:205-212.
[Google Scholar]

[315] Zarrouk A., Hammouti B., Dafali A., Bentiss F., . Inhibitive properties and adsorption of purpald as a corrosion inhibitor for copper in nitric acid medium. Ind. Eng. Chem. Res.. 2013;52:2560-2568.
[Google Scholar]

[316] Zarrouk A., Hammouti B., Dafali A., Bouachrine M., Zarrok H., Boukhris S., Al-Deyab S.S., . A theoretical study on the inhibition efficiencies of some quinoxalines as corrosion inhibitors of copper in nitric acid. J. Saudi Chem. Soc.. 2014;18:450-455.
[Google Scholar]

[317] Zarrouk A., Hammouti B., Dafali A., Zarrok H., Touzani R., Bouachrine M., Zertoubi M., . Inhibition of copper corrosion in acid solution by N-1-naphthylethylenediamine dihydrochloride monomethanolate: experimental and theoretical study: part-1. Res. Chem. Intermed.. 2012;38:1079-1089.
[Google Scholar]

[318] Zeldowitsch J., . Adsorption site energy distribution. Acta Phys. Chim. URSS. 1934;1:961-973.
[Google Scholar]

[319] Žerjav G., Milošev I., . Carboxylic acids as corrosion inhibitors for Cu, Zn and brasses in simulated urban rain. Int. J. Electrochem. Sci.. 2014;9:2696-2715.
[Google Scholar]

[320] Žerjav G., Milošev I., . Protection of copper against corrosion in simulated urban rain by the combined action of benzotriazole, 2-mercaptobenzimidazole and stearic acid. Corros. Sci.. 2015;98:180-191.
[Google Scholar]

[321] Zhang D.-Q., Cai Q.-R., Gao L.-X., Lee K.Y., . Effect of serine, threonine and glutamic acid on the corrosion of copper in aerated hydrochloric acid solution. Corros. Sci.. 2008;50:3615-3621.
[Google Scholar]

[322] Zhang D.-Q., Cai Q.-R., He X.-M., Gao L.-X., Kim G.S., . Corrosion inhibition and adsorption behavior of methionine on copper in HCl and synergistic effect of zinc ions. Mater. Chem. Phys.. 2009;114:612-617.
[Google Scholar]

[323] Zhang D.-Q., Cai Q.-R., He X.-M., Gao L.-X., Zhou G.-D., . Inhibition effect of some amino acids on copper corrosion in HCl solution. Mater. Chem. Phys.. 2008;112:353-358.
[Google Scholar]

[324] Zhang D.-Q., Gao L.-X., Zhou G.-D., . Inhibition of copper corrosion by bis-(1-benzotriazolymethylene)-(2, 5-thiadiazoly)-disulfide in chloride media. Appl. Surf. Sci.. 2004;225:287-293.
[Google Scholar]

[325] Zhang D.-Q., Gao L.-X., Zhou G.-D., . Inhibition of copper corrosion in aerated hydrochloric acid solution by heterocyclic compounds containing a mercapto group. Corros. Sci.. 2004;46:3031-3040.
[Google Scholar]

[326] Zhang D.-Q., Xie B., Gao L.-X., Cai Q.-R., Joo H.G., Lee K.Y., . Intramolecular synergistic effect of glutamic acid, cysteine and glycine against copper corrosion in hydrochloric acid solution. Thin Solid Films. 2011;520:356-361.
[Google Scholar]

[327] Zhang D.-Q., Xie B., Gao L.-X., Joo H.G., Lee K.Y., . Inhibition of copper corrosion in acidic chloride solution by methionine combined with cetrimonium bromide/cetylpyridinium bromide. J. Appl. Electrochem.. 2011;41:491-498.
[Google Scholar]

[328] Zhang D.Q., Gao L.X., Cai Q.R., Lee K., . Inhibition of copper corrosion by modifying cysteine self-assembled film with alkylamine/alkylacid compounds. Mater. Corros.. 2010;61:16-21.
[Google Scholar]

[329] Zhang D.Q., Gao L.X., Zhou G.D., . Synergistic effect of 2-mercapto benzimidazole and KI on copper corrosion inhibition in aerated sulfuric acid solution. J. Appl. Electrochem.. 2003;33:361-366.
[Google Scholar]

[330] Zhang J., Yu W.-Z., Yan Y.-G., Yu L.-J., Ren Z.-J., . Molecular dynamics simulation of the adsorption behavior of imidazoline corrosion inhibitors on a Fe (0 0 1) surface. Acta Phys. Chim. Sin.. 2010;26:1385-1390.
[Google Scholar]

[331] Zhang X.H., Liao Q.Q., Nie K.B., Zhao L.L., Yang D., Yue Z.W., Ge H.H., Li Y.J., . Self-assembled monolayers formed by ammonium pyrrolidine dithiocarbamate on copper surfaces in sodium chloride solution. Corros. Sci.. 2015;93:201-210.
[Google Scholar]

[332] Zheng L., Liu J., Tao Z.H., He W., Xiao D.J., Tan Z., . Electrochemical investigation of myclobutanil as corrosion inhibitor for copper in acid medium. Adv. Mater. Res. 2014:229-233.
[Google Scholar]

[333] Zhou Y., Xu S., Guo L., Zhang S., Lu H., Gong Y., Gao F., . Evaluating two new Schiff bases synthesized on the inhibition of corrosion of copper in NaCl solutions. RSC Adv.. 2015;5:14804-14813.
[Google Scholar]

[334] Zor S., . Sulfathiazole as potential corrosion inhibitor for copper in 0.1 M NaCl. Prot. Met. Phys. Chem. Surf.. 2014;50:530-537.
[Google Scholar]

[335] Zucchi F., Trabanelli G., Fonsati M., . Tetrazole derivatives as corrosion inhibitors for copper in chloride solutions. Corros. Sci.. 1996;38:2019-2029.
[Google Scholar]

[336] Zucchi F., Trabanelli G., Monticelli C., . The inhibition of copper corrosion in 0.1 M NaCl under heat exchange conditions. Corros. Sci.. 1996;38:147-154.
[Google Scholar]

Review of corrosive environments for copper and its corrosion inhibitors

Abstract

Keywords

Azole

Copper

Corrosion

Corrosion inhibitor

Corrosion inhibition efficiency

Isotherm

Abbreviations

1 Introduction

2 Copper corrosion inhibitors

2.1 Benzotriazole

2.2 Imidazole compounds

2.3 Other azole compounds

2.4 Schiff bases

2.5 Green corrosion inhibitors

2.5.1 Natural corrosion inhibitors

2.5.2 Pharmaceutical compounds

2.6 Amino acids

2.7 Self-assembled compounds

3 Corrosion inhibitors efficiency evaluation methods

3.1 Weight loss measurements

3.2 Potentiodynamic–galvanostatic polarization

3.3 Electrochemical impedance spectroscopy (EIS)

3.4 Electrochemical noise method

3.5 Scanning electrochemical microscopy (SECM)

3.6 Scanning vibrating electrode technique (SVET)

3.7 Surface analytical methods

4 The adsorption of corrosion inhibitor and its isotherms

4.1 Langmuir adsorption isotherm

4.2 Freundlich adsorption isotherm

4.3 Langmuir-Freundlich adsorption isotherm

4.4 Temkin adsorption isotherm

4.5 Flory-Huggins adsorption isotherm

4.6 Frumkin adsorption isotherm

4.7 Adsorption energy

5 Corrosive environments for copper

5.1 Copper in acidic environments

5.1.1 Sulfuric acid solution

5.1.2 Nitric acid solution

5.1.3 Hydrochloric acid solution

5.1.4 Phosphoric acid solution

5.2 Copper in neutral environments

5.2.1 Copper in NaCl solutions

5.2.2 Copper in other aqueous solutions

5.3 Copper in alkaline environments

5.4 Copper in other environments

6 Conclusions and future trends

References

Suggested read for related articles: