Corrosion behavior and mechanism of copper soaked in ammonia water

Jinbei He; Lingzhi Chen; Hualiang Huang

doi:10.25259/AJC_416_2025

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ARTICLE IN PRESS

doi:

10.25259/AJC_416_2025

Corrosion behavior and mechanism of copper soaked in ammonia water

Jinbei He^a,b, Lingzhi Chen^a, Hualiang Huang^a,*

aSchool of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan, PR China

bHubei Jingyu Matetial Co., LTD, Wuhan, PR China

*Corresponding author: E-mail address: 51032265@qq.com (H. Huang)

Received: 2025-04-22, Accepted: 2025-10-14, Epub ahead of print: 2026-03-12,

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Abstract

The corrosion behavior and mechanism of Cu soaked in ammonia water were studied at 30°C using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and polarization curve, combined with optical microscopy, scanning electron microscopy (SEM), X-ray powder diffractometer (XRD), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) and other analytical techniques. The findings demonstrated that when the concentration of ammonia water increased from 0.1 wt.% to 1.0 wt.%, the corrosion rate of Cu increased from 21.9 μA/cm² to 32.3 μA/cm², and when the temperature of ammonia water increases from 30°C to 50°C, the corrosion rate of Cu increased from 30.2 μA/cm² to 68.5 μA/cm². The surface of Cu had obvious oxidation discoloration in ammonia water, the corrosion reactions of Cu in ammonia water involved oxidation-reduction and complexation process, and ammonia formed copper-ammonia complexes with Cu (I) and Cu (II), destroying the Cu surface protective film and accelerating oxidation corrosion. In ammonia water, the corrosion products of Cu were Cu₂O, CuO, Cu(OH)₂ and copper-ammonia complexes.

Keywords

Ammonia water

Complexation

Copper

Corrosion

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1. Introduction

Since copper and its alloys offer good electrical, thermal, and ductility properties, they are widely employed in a variety of industries, including electronics, construction, and energy [1-8]. However, in practical applications, copper often face various corrosion problems, which not only affects its service life, but also may cause serious economic losses and security risks [9-11]. Therefore, the study of copper corrosion behavior is of great practical significance for preventing and controlling copper corrosion, improving its service life and economic efficiency.

Among many corrosive media, ammonia, as a common inorganic compound, is widely found in the wastewater of chemical, pharmaceutical, leather manufacturing, and other industries [12,13]. Ammonia water exhibits unique behavior with respect to the corrosion of copper. It chemically interacts with copper to generate a copper ammonia complex, which creates a protective film on the copper surface, preventing copper from corroding [14]. However, this protective effect is not absolute and the corrosion behavior of copper changes with ammonia concentration, temperature, and pH. Monteiro et al. researched the stress corrosion of brass under different concentrations of ammonia [15]. Optical microscopy and scanning electron microscopy (SEM) were utilized to investigate the stress corrosion behavior of copper caused by ammonia. According to the study, the stress corrosion of brass was the most serious in ammonia vapor. SeKwon et al. investigated the galvanic corrosion behavior of copper and gold on printed circuit boards in ammonia water [16]. When the area ratio of gold to copper increased, the galvanic current density between copper and gold increased, and the corrosion of copper intensified.

At present, the few studies on the corrosion of copper in ammonia water mainly focus on its corrosion rate and morphology [17,18]. Moreover, the corrosion mechanism of copper soaked in ammonia water has rarely been reported. In addition, the reaction processes of ammonia and copper may also involve a variety of intermediate products, and the existence of these substances can have an important impact on the corrosion mechanism of Cu.

Therefore, the corrosion behavior and mechanism of copper soaked in ammonia water of different concentrations and temperatures were first studied using electrochemical testing, such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and polarization curve, combined with optical microscopy, The corrosion behavior and mechanism of Cu soaked in ammonia water were studied at 30°C using open circuit potential, electrochemical impedance spectroscopy and polarization curve, combined with optical microscopy, scanning electron microscopy, X-ray powder diffractometer, energy dispersive spectrometer, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy and other analytical techniques., X-ray powder diffractometer (XRD), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FT-IR) and other analytical techniques. By revealing the specific reaction processes between ammonia and copper, the formation and transformation laws of intermediate products were clarified, and a theoretical basis and technical support were provided for preventing and controlling the corrosion of copper in an ammonia environment.

2. Materials and Methods

2.1. Materials

A copper sample was cut into cylindrical specimens, and one end of the copper cylinder was soldered to a copper wire using lead-free solder. Next, a multimeter was used to examine the electrical connectivity between the copper sample and the copper wire. After confirming that the copper wires were attached to the copper specimen, the copper specimen with a bare space of 0.785 cm² was encapsulated with epoxy resin. Before starting the test, the copper electrode’s surface was polished using sandpaper with varying degrees of roughness (600#, 800#, and 1000#). The copper electrode was then cleaned with dilute water, defatted with anhydrous ethanol, and dried at ambient temperature. The corrosive media used in this experiment were ammonia water with different concentrations. The concentrations of ammonia water prepared with analytical grade ammonia and deionized water were 0.1 wt.%, 0.5 wt.%, and 1 wt.%, respectively.

2.2. Electrochemical testing

The OCP, polarization curve, and EIS were measured using a CS350 electrochemistry workstation. A saturated calomel electrode (SCE) as reference electrode (RE), a platinum electrode as counter electrode (CE), and the prepared copper electrode as working electrode (WE). The surface area of the platinum electrode was 1 cm². After the OCP of the WE reached steady state, in a 10^-2 Hz to 10⁵ Hz frequency range of the EIS, amplitude of 10 mV, the polarization experiment was measured with a scan rate of 1.0 mV/s and the scanning potential range of ±200 mV (SCE). All electrochemical experiments should be repeated at least three times.

2.3. UV-vis spectrum tests

After copper was soaked in ammonia water, the UV-vis spectroscopy of ammonia water was detected by an Agilent Cary 60 UV-Vis spectrophotometer every 24 h, which ranged from 500∼800 nm, and the width of the absorbing pore in this region was measured to be 1 cm. Using ultra-pure water as a reference medium, the scanning speed was fast. At room temperature, absorbance values were obtained after three scans of each sample.

2.4. pH tests

The pH value of ammonia before and after copper corrosion was measured by a PHS-3C laboratory pH meter. To ensure the reliability of the measurement results, the pH detector is calibrated with a standard buffer solution. The electrode is immersed in the corrosive medium to be measured, and the pH value of the corrosive medium to be measured is read after the pH of the electrode and the solution is balanced. After each test, clean the electrode in time for the next test.

2.5. Surface characterizations

The surface morphology of the copper samples was examined using SEM (JSM5510LV, JEOL, JPN) after being soaked in ammonia water for 24 h at 30°C. Using a light microscope produced in China, the light morphologies of copper specimens immersed in different concentrations of ammonia water for 24 h, 0.5 wt.% ammonia water for various times, and 0.5 wt.% ammonia water for various temperatures were observed. The compositions of the corrosion products of copper in 0.5 wt.% ammonia water were analyzed by EDS (GeminiSEM 300, Zeiss, GER), XRD (D8 ADVANCE, Bruker, GER), FT-IR (Nicolet 6700, Thermo Fisher, USA), and XPS (ESCALAB XI+, Thermo Fisher, USA). The copper specimen was made, and its surface was cleaned with distilled water before characterization. After copper was soaked in ammonia water for different periods of time and the change in the color of the ammonia water was observed with an iPhone.

3. Results and Discussion

3.1. OCP analysis

Figure 1(a) illustrates the time dependence of the OCP of copper soaked in ammonia water with different concentrations for 1 h at 30°C. On the basis of the corrosion mechanism of Cu in ammonia water, its anodic process involves the dissolution of copper, and its cathodic process is primarily the reduction of oxygen [17]. From Figure 1(a), it is evident that during the corrosion process, the OCP quickly achieves stability, which indicates that its anode and cathode processes quickly reach a stable state. The OCP of copper in 0.1 wt.% ammonia water is -0.11 V (SCE), the OCP of copper in 0.5 wt.% ammonia water is -0.44 V (SCE), and the OCP of copper in 1 wt.% ammonia water is -0.48 V (SCE). The experimental results show that the increase in ammonia water concentration results in a negative shift of the OCP of copper. The more negative OCP usually means that the metal loses electrons more easily, is thus more susceptible to oxidation, and has a greater tendency to corrode [19]. Therefore, with increasing ammonia water concentration, the negative shift of the OCP of copper can be attributed to the acceleration of its anodic process, aggravating the corrosion of copper [17].

The time dependence of the OCP of copper in ammonia water: (a) different concentrations at 30°C, (b) different temperatures at the concentration of 0.5 wt.%.

Figure 1(b) presents the variation of the OCP of copper with time at different temperatures in 0.5 wt.% ammonia water. From Figure 1(b), the OCP of copper also quickly reaches stability at both 40°C and 50°C. Compared with the OCP of copper at 30°C, the OCP of copper undergoes a negative shift at both 40°C and 50°C, which indicates its anodic process is significantly accelerated because of the increase in temperature. However, surprisingly, compared to the OCP of copper at 40°C, the OCP of copper shifts positively at 50°C, which may be explained as follows: at higher temperatures, the rapid removal of corrosion products leads to a significant increase in the oxygen reduction area.

3.2. EIS analysis

The Nyquist and Bode diagrams of copper in various concentrations of ammonia water at 30°C for 1 h have been displayed in Figure 2. From Figure 2(a), the Nyquist diagram for copper in 0.1 wt.% ammonia water consists of three capacitance arcs and corresponds to three temporal parameters. The capacitive loop observed in the high-frequency range constitutes the response from the interior oxidation film, whereas the capacitive arc within the mid-frequency spectrum signifies the response emanating from the external corrosion product film. The capacitive arc in the low-frequency area is associated with charge migration [20]. The Nyquist figures depicting copper in 0.5 wt.% and 1 wt.% ammonia water consist of two capacitive arcs and a Warburg impedance in the low frequency area. The capacitive arc appearing in the high-frequency area is due to the capacitive response of the oxidation film covering the copper surface, whereas the capacitive arc appearing in the mid-frequency area is due to charge migration, and the Warburg impedance is due to the diffusion process of the corrosive substance from the copper surface to the bulk solution [20,21]. The incomplete capacitance arcs in the high-frequency region can be attributed to the formation of a non-uniform oxide film on the copper surface. Additionally, an augmentation in ammonia water concentration leads to a gradual reduction in the diameter of each capacitive arc. The capacitance arc diameter is in direct proportion to the corrosion resistance and in inverse ratio with the rate of metal corrosion in the Nyquist diagram. The diameter of the capacitive arc increases, so does the corresponding corrosion impedance, and a decrease in the corrosion rate. Thus, with the increase of ammonia water concentration, the film impedance and Faraday impedance reduce. Meanwhile, the total diameter of the capacitance arc decreased with escalating ammonia water concentration, showing an acceleration in the corrosion rate of copper. As ammonia water concentration rises, Figure 2(b) demonstrates a gradual decrease in impedance modulus (/Z/) and a positive shift in maximum phase angle (θ), indicating a decrement in total corrosion and film resistance, thereby accelerating the corrosion rate of copper. Therefore, the incremental in the ammonia water concentration speeds up the corrosion of copper.

EIS of copper immersed in different concentrations of ammonia water for 1 h at 30°C: (a) Nyquist plots, (b) Bode plots.

Shown in Figure 3 are the equivalent circuits of the EIS data for the fitting test. Table 1 shows a summary of the fitting parameters. Where, R_s denotes the solution resistance, C_f1 denotes the capacitive behavior of the internal oxidation film, R_f1 denotes the resistance of the internal oxidation film, CPE_f2 denotes the capacitive respond of the outer corrosion induced surface layer, n_f2 denotes the dispersion effect index linked to the outer corrosion induced surface layer, R_f2 denotes the resistance of the outer corrosion induced surface layer, CPE_dl denotes the double-layer capacitance, n_dl denotes the dispersion effect index associated with the double layer capacitance at the electrode-solution interface, W denotes the Warburg impedance, and R_ct denotes the charge transfer resistance. The decrease in the R_f and R_ct observed with increasing ammonia water concentration in Table 2 further confirms that an increase in ammonia water concentration results in an augmentation in the corrosion rate of copper. This may be interpreted as an increase in the ammonia water concentration, results in an increase in ammonia in water, accelerating the dissolution of copper and the removal of oxidation film and corrosion products. Generally, the R_f is a positive relation to the protective capabilities of the film, so a diminution in the R_f implies a decrease in its protective property. Therefore, an increase in ammonia water concentration diminishes the protective property of the film, accelerating copper dissolution. At low ammonia concentrations, an oxide layer may first form on the copper surface, which acts as a barrier and prevents direct contact between copper and ammonia, thus slowing down the corrosion rate. When the concentration of ammonia increases, the oxide layer dissolves due to the chelating effect of ammonia, thus reducing the obstruction of the oxide layer. Therefore, the capacitive time constant decreases with increasing ammonia concentration. Typically, CPE_dl, CPE_f, and the thickness (δ) of film can be calculated using the following Eqs. (1-3) [22,23]:

(1)

C P E_{d l} = Q_{0}^{\frac{1}{n}} {(\frac{1}{R_{s}} + \frac{1}{R_{c t}})}^{\frac{(n - 1)}{n}}

(2)

C P E_{f} = Q_{0}^{\frac{1}{n}} R_{f}^{\frac{(1 - n)}{n}}

(3)

C P E_{f} = \frac{ε^{0} ε}{δ}

(a,b) Equivalent circuit diagrams are used to fit the tested EIS data.

Table 1. The EIS fitting parameters of copper immersed in different concentrations of ammonia water for 1 h at 30°C.

c wt.%	R_s Ω·cm²	C_f1 F·cm^-2	R_f1 Ω·cm²	CPE_f2 S·s^nf2·cm^-2	n_f2	R_f2 Ω·cm²	CPE_dl S·s^ndl·cm^-2	n_dl	R_ct Ω·cm²
0.1	46.46	5.74×10^-9	355.64	4.94×10^-5	0.77	222.2	2.73×10^-3	0.63	406.4
c wt.%	R_s Ω·cm²	C_f F·cm⁻²	R_f Ω·cm²	CPE_dl S·s^ndl·cm^-2	n_dl	R_ct Ω·cm²	W Ω·cm²	-	-
0.5	82.16	2.71×10^-8	235.37	4.52×10^-4	0.75	228.32	394.27	-	-
1	52.83	1.04×10^-8	115.2	4.39×10^-4	0.80	200.9	344	-	-

Table 2. The EIS fitting parameters of copper immersed in 0.5 wt.% ammonia water for different times at 30°C

t h	R_s Ω·cm²	C_f F·cm⁻²	R_f Ω·cm²	CPE_dl S·s^ndl·cm^-2	n_dl	R_ct Ω·cm²	W Ω·cm²
24	49.71	1.07×10^-8	191.35	1.63×10^-4	0.92	324.09	458.37
48	30.93	6.98×10^-9	242.17	1.97×10^-4	0.91	323.19	302.3
72	49.32	1.00×10^-8	172.98	1.83×10^-4	0.93	295.11	236.83
96	51.06	1.16×10^-8	145.75	2.20×10^-4	0.92	323.88	557.92

Here, the Q₀, n, ε, and ε⁰ indicate the CPE, surface inhomogeneity, the dielectric constant, and the vacuum dielectric constant. Thus, the increase in the n_dl is attributable to the decrease in the surface nonuniformity of copper due to the removal of the surface oxidation film and corrosion products, accompanied by a decrease in the R_f and R_ct.

To delve deeper into how corrosion time impacts the corrosion effects of copper’s corrosion behavior when subjected to ammonia water, the EIS of copper soaked in 0.5 wt.% ammonia water at 24 h intervals up to 96 h was performed at 30°C and presented in Figure 4. Observing Figure 4, all Nyquist diagrams of copper always involve two capacitance arcs and a Warburg diffusion, exhibiting two time constants, so the measured EIS data are matched with the equivalent circuit depicted in Figure 3(b), and the pertinent EIS fitting parameters have been compiled in Table 2. From Figure 4, the diameter of the capacitive arc and the /Z/ initially increase and subsequently decrease with time, and the elevated copper corrosion impedance may originate from the generation and buildup of corrosion products. With the extension of the corrosion time, the copper corrosion impedance decreases, which may originate from the removal of corrosion products caused by the formation of copper ammonium complexes. In the advanced stage of corrosion, the continuous dissolution of corrosion products causes a decrease in ammonia water concentration, accompanied by an increase in the W_R, and ultimately, the R_ct of copper increases.

EIS of copper immersed in 0.5 wt.% ammonia water for different time at 30°C: (a) Nyquist plots, (b) Bode plots.

To understand the corrosion behavior of copper in ammonia water, the EIS of copper in 0.5 wt.% ammonia water at varying temperatures for a duration of 1 h was measured and presented in Figure 5. From Figure 5, there are two time constants and one diffusion impedance. The capacitive arc observed in the high-frequency area originates from the capacitive behavior of the oxidation film that coats the copper surface, whereas the capacitive arc appearing in the mid-frequency area can be attributed to the charge transfer resistance coupled with the double layer capacitance. Diffusion occurs in the low-frequency area. Interestingly, at 30°C, the diffusion is semi-infinite, meaning that the length of the pathway for mass transfer can be approximated to be infinite. The solution layer that does not flow (including the absence of convection) is called a “stagnant layer.” Meanwhile, semi-infinite diffusion also refers to the diffusion process in the stagnant flow layer whose thickness can be approximated as infinite [24,25]. In contrast, the diffusion at 40°C and 50°C is finite layer diffusion, and finite layer diffusion means that the thickness of the stagnant flow layer is a finite value [24,26]. In addition, the diameter of each capacitance loop gradually decreases with increasing temperature. From Figure 4(b), the /Z/ also decreases with increasing temperature. This suggests that the film resistance and charge transfer resistance progressively decrease with increasing temperature, causing an elevation in the corrosion rate of copper. The reason for this is that the elevated temperature expedites the corrosion of copper, causing more corrosion products to dissolve into the native solution.

EIS of copper immersed in 0.5 wt.% ammonia water for 1 h at different temperatures: (a) Nyquist plots, (b) Bode plots.

According to the above analysis, the corresponding impedance parameters are derived from using the equivalent circuit presented in Figure 3(b) for the EIS data, which have been shown in Table 3. As can be seen in Table 3, the R_ct undergoes a decrease with a corresponding rise in temperature, signifying an acceleration of the corrosion of copper due to the elevated temperature conditions. In addition, the R_f also decreases with increasing temperature, especially at 50°C, which may be due to the dissolution of corrosion products.

Table 3. The EIS fitting parameters of copper immersed in 0.5 wt.% ammonia water for 1 h at different temperatures.

°C

R_s

Ω·cm²

C_f

F·cm⁻²

R_f

Ω·cm²

CPE_dl

S·s^ndl·cm^-2

n_dl

R_ct

Ω·cm²

82.16

2.71×10^-8

235.37

4.5×10^-4

0.75

228.32

394.27

57.67

8.36×10^-9

228.22

1.86×10^-4

0.86

135.24

382.20

40.90

1.09×10^-8

139.18

2.59×10^-4

0.87

81.65

265.27

3.3. Polarization curve analysis

Figure 6 shows the polarization curves of copper in ammonia water of varying concentrations at 30°C for 1 h. From Figure 6, it is observable that as the concentration of ammonia increases, the self-corrosion potential of copper significantly negatively shifts, and the anodic current densities increase. Studies show that the increase in ammonia concentration obviously speeds up its anodic process. It is generally possible to extrapolate corrosion current density from Tafel’s extrapolation of the polarization curve. Based on the EIS analysis, the anodic processes of copper include the dissolution of copper, the diffusion of corrosive species, and the deposition of corrosion products. However, the cathodic process solely involves oxygen reduction, so the copper polarization curves are fitted using the cathodic Tafel extrapolation [17,27]. The corresponding fitting results for corrosion potential (E_corr), corrosion current density (i_corr), and cathodic Tafel slope (b_c) have been shown in Table 4. In general, the more negative E_corr and the larger i_corr, the faster the corrosion rate. Table 4 shows that with ammonia concentration on the rise, the i_corr of copper increases and the E_corr shifts negatively, which shows that the increasing ammonia concentration promotes its anodization and accelerates its corrosion.

Polarization curves of copper immersed in different concentrations of ammonia water for 1 h at 30°C.

Table 4. Polarization curve fitting parameters of copper immersed in different concentrations ammonia water for 1 h at 30°C.

wt.%

E_corr

b_c

mV/dec

i_corr

A/cm²

0.1

-0.12

-449.3

(2.19±0.12) × 10^-5

0.5

-0.44

-725.85

(3.02±0.27) × 10^-5

-0.49

-1316.6

(3.23±0.07) × 10^-5

Figure 7 is the polarization curves of copper after soaking in 0.5 wt.% ammonia water at 30°C, 40°C, and 50°C for 1 h. From Figure 7 that the current density of the cathode and anode increases with temperature. This shows that the corrosion rate of copper intensifies as the temperature escalates. Table 5 displays the fitting outcomes for various polarization curves. The increase in the i_corr from 3.02×10^-5 A·cm^-2 to 6.85×10^-5 A·cm^-2 with increasing temperature suggests that rising temperature leads to accelerated corrosion of copper.

Polarization curves of copper immersed in 0.5 wt.% ammonia water for 1 h at different temperatures.

Table 5. Polarization curve fitting parameters of copper immersed in 0.5 wt.% ammonia water for 1 h at different temperatures.

°C

E_corr

b_c

mV/dec

i_corr

A/cm²

-0.44

-725.85

(3.02±0.27) × 10^-5

-0.44

-586.96

(5.27±0.05) × 10^-5

-0.44

-710.33

(6.85±0.06) × 10^-5

3.4. UV-Vis analysis

[Cu(NH₃)₄]²⁺ is a dark blue color, and it has specific absorption peaks in the UV-Vis spectral region, so it is possible to determine the concentration of [Cu(NH₃)₄]²⁺ by measuring the absorbance of ammonia water after copper is soaked in ammonia water for different times. Figure 8(a) shows the standard curve of absorbance with [Cu(NH₃)₄]²⁺ concentration. The standard curve equation is y=3.75×10^-4x+2.19×10^-3 (y is absorbance, x is [Cu(NH₃)₄]²⁺ concentration), and the R² is 0.99916. Figure 8(b) shows the UV-vis spectra of 0.5 wt.% ammonia water after copper is soaked in the ammonia water for different times. According to the standard curve equation and the UV-vis spectrum tested at different times, Table 6 lists the concentration and the generation rate of [Cu(NH₃)₄]²⁺ in 0.5 wt.% ammonia water at different times based on Eq. (4).

(4)

v = \frac{c_{after (24 h)} - c_{before (24 h)}}{24 h}

(a,b) UV-vis spectrum of 0.5 wt.% ammonia water with the increase of the corrosion time of copper at 30°C.

Table 6. The concentration and produced rate of [Cu(NH₃)₄]²⁺ in 0.5 wt.% ammonia water with different time

t (h)	Abs	c mg L^-1	v (mg·L^-1·h^-1)
0	0	0	-
24	0.012	26.16	1.09
48	0.020	47.49	0.89
72	0.031	76.83	1.22
96	0.046	116.83	1.67

From Table 6, after copper is soaked in 0.5 wt.% ammonia water for 24, 48, 72, and 96 h, the concentrations of [Cu(NH₃)₄]²⁺ are 26.16 mg/L, 47.49 mg/L, 76.83 mg/L, and 116.83 mg/L, respectively. Thus, the generation rate of [Cu(NH₃)₄]²⁺ is 1.09, 0.89, 1.22 and 1.67 mg·L¹·h^-1, respectively. Clearly, the generation rate of copper decreases first and then increases, which is in accordance with the results of the EIS test.

Figure 9 shows the color change of 0.5 wt.% ammonia water over time after copper is soaked in 0.5 wt.% ammonia water for different times. From Figure 9, with the extension of immersion soaking time, the color of the ammonia water becomes darker and darker, indicating that the concentration of [Cu(NH₃)₄]²⁺ is increasing, which corresponds to the results of the ultraviolet test.

The color change of 0.5 wt.% ammonia water over time with the increase of the corrosion time of copper at 30°C.

3.5. pH analysis

The pH value changes with time after copper immersion in 0.5 wt.% ammonia for different times have been shown in Table 7. From Table 7, as the soaking duration increases, the pH remains almost constant. This may be attributed that [Cu(NH₃)₄]²⁺ is formed and ammonia water has a buffering effect.

Table 7. The change in the pH of 0.5 wt.% ammonia water with the increase of the corrosion time of copper at 30°C.

t (h)	pH
0	11.38
24	11.31
48	11.32
72	11.31
96	11.43

3.6. Surface morphology analysis

Figure 10 illustrates the optical microscope images of copper soaked in varying concentrations of ammonia water at 30°C for 24 h. From Figure 10(a), the copper surface appears black in 0.1 wt.% ammonia water, which may be attributed to insoluble corrosion products (CuO). From Figures 10(b, c), the copper surface appears reddish-brown in 0.5 wt.% or 1 wt.% ammonia water, which may be attributed to insoluble Cu₂O because of the formation of the soluble [Cu(NH₃)₄]²⁺ at high ammonia concentrations. In the ammonia concentration of 1 wt.%, the copper surface presents a deep reddish-brown color. This may be explained as: the higher the ammonia concentration, the more thoroughly the insoluble corrosives will be removed.

Optical microscope images of copper soaked in different concentrations of ammonia water for 24 h at 30°C: (a) 0.1 wt.%, (b) 0.5 wt.%, (c) 1 wt.%.

Figure 11 is the SEM morphologies of copper soaked in various concentrations of ammonia water at 30°C for 24 h. From Figure 11(a), Figures 11(b, c), in the ammonia concentration of 0.1 wt.%, a relatively smooth corrosion product film with cracks and looseness forms on the copper surface. When the ammonia concentration is 0.5 wt.%, a dense and rough corrosion product film forms on the copper surface. When the ammonia concentration is 1 wt.%, a denser and relatively rougher corrosion product film forms on the copper surface. This further confirms the observation results of the above optical microscope.

SEM morphologies of copper immersed in different concentrations of ammonia water for 24 h at 30°C: (a) 0.1 wt.%, (b) 0.5 wt.%, (c) 1 wt.%.

Figure 12 is the optical microscope pictures of copper soaked in 0.5 wt.% ammonia water at 30°C for different times. From Figure 12, as corrosion time increases, the reddish brown color on the copper surface becomes increasingly dark and the white bright spots on the copper surface are increasing, which could be the generated copper monomers, and the relevant reaction was: [Cu(NH₃)₂]⁺↔[Cu(NH₃)₄]²⁺ + Cu, and then the formed copper monomers are oxidized into CuO.

Optical microscope images of copper immersed in 0.5 wt.% ammonia water for different times at 30°C: (a) 24 h, (b) 48 h, (c) 72 h, (d) 96 h.

Figure 13 presents optical microscope pictures of copper soaked in 0.5 wt.% ammonia water at different temperatures for 24 h. From Figure 13, compared to the morphology at 30°C, more white bright spots appear at 40°C. At 50°C, there is a large amount of brown porous and loose corrosion products on the copper surface, which shows that copper corrodes seriously. The results demonstrate a temperature-dependent augmentation in the intensity of copper corrosion, suggesting that the corrosion process intensifies as temperatures elevate.

Optical microscope images of copper immersed in 0.5 wt.% ammonia water at different temperatures for 24 h: (a) 30°C, (b) 40°C, (c) 50°C.

3.7. EDS analysis

Figure 14 shows the surface element distributions and contents of copper before and after corrosion in 0.5 wt.% ammonia water. Comparing Figures 14(a, b), the copper surface becomes rough, and a substantial accumulation of corrosion products occurs after corrosion. The color shading present in the images serves as a representation of the signal intensity within the respective regions. The O image depicted in Figure 14(b) exhibits a brighter intensity compared to that in Figure 14(a), suggesting that the O element content post-corrosion is higher than that pre-corrosion. This can be caused by form on the copper surface corrosion products. Figures 14(c, d) show the content of Cu, O, and N elements. According to Figures 14(c, d), the Cu, O, and N elements pre-corrosion are 99.14%, 0.62%, and 0.24%, and Cu, O, and N post-corrosion are 96.66%, 3.11%, and 0.23%, respectively. This further indicates that the content of the O element increases after corrosion because of the formation of corrosion products.

Elemental distributions and contents of the surface film of copper before and after corrosion in 0.5 wt.% ammonia water: (a) elemental distributions before corrosion, (b) elemental distributions after corrosion, (c) elemental contents before corrosion, (d) elemental contents after corrosion.

3.8. XRD, FT-IR, and XPS analysis

Figure 15 shows the XRD pattern of copper soaked in ammonia water with different concentrations, times, and temperatures. As can be seen in Figure 15, the predominant corrosion products identified are Cu₂O, CuO, and Cu(OH)₂. To further study what the black substance formed on the surface of copper soaked in 0.1 wt.% ammonia water for 24 h is, the black substance is scraped off the surface of copper for FT-IR analysis. The results have been presented in Figure 16. From Figure 16, with two strong absorption peaks at 502.96 cm^-1 and 875.5 cm^-1, which originate from the Cu-O bond of CuO [28].

XRD pattern of copper soaked in ammonia water: (a) different concentration ammonia water at 30°C for 24 h; (b) in 0.5 wt.% ammonia water for different time at 30°C; (c) in 0.5 wt.% ammonia water at different temperatures for 24 h.

FT-IR of the surface film of copper soaked in 0.1 wt.% ammonia water for 24 h at 30°C.

To further substantiate the corrosion products of Cu in ammonia water, the surface film compositions of copper soaked in 0.5 wt.% ammonia water at 30°C for 24 h were investigated by XPS tests. Figure 17 exhibits the XPS measuring spectra and high-resolution spectra. From Figure 17(a), the Cu and O elements can be detected. Figure 17(b) shows the high-resolution spectrum of Cu 2p, which is known to be composed of Cu 2p_1/2 and Cu 2p_3/2 [29]. There are five peaks in the Cu 2p spectrum; the peak at 932.5 eV originates from Cu₂O, the peak at 934.25 eV originates from CuO, and the peak at 934.95 eV originates from Cu(OH)₂ [30]. The peak at 952.29 eV can be from Cu₂O, and the peaks at 954.54 eV are probably derived from Cu (II), which are associated with Cu(OH)₂ and CuO [31,32]. From Figure 17(c), the O 1s spectrum has three peaks, and the peak at 530.41 eV can be derived from O^2-, which indicates the presence of Cu₂O/CuO. The peak at 531.28 eV corresponds to Cu(OH)₂, and the peak at 532.07 eV is associated with adsorbed water molecules [33]. From Figure 17(d), there is no obvious peak in the N 1s spectrum. Therefore, the detected N in the EDS test may originate from the air.

XPS spectrum of copper immersed in 0.5 wt.% ammonia water for 24 h at 30°C: (a) measurement spectrum, (b) Cu 2p, (c) O 1s, (d) N 1s.

3.9. Corrosion mechanism analysis

According to the above experimental data and analysis results, in 0.5 wt.% ammonia water, the corrosion mechanism of copper at 30°C is proposed and presents in Figure 18. The following is a description of the copper corrosion mechanism (Eqs. 5-8):

Corrosion mechanism schematic diagram of copper in 0.5 wt.% ammonia water at 30°C.

The anodic reaction is:

(5)

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

In the presence of ammonia,

(6)

4 {Cu}^{+} + 16 {NH}_{3} + O_{2} + 2 H_{2} O \to 4 {[Cu {({NH}_{3})}_{4}]}^{2 +} + 4 {OH}^{-}

The cathodic reaction is:

(7)

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

The total reaction of Cu in ammonia water is [14,17,34]:

(8)

2 Cu + O_{2} + 8 {NH}_{3} + 2 H_{2} O \to 2 {[Cu {({NH}_{3})}_{4}]}^{2 +} + 4 {OH}^{-}

As can be seen from Eqs. (5-8), in ammonia water, copper loses electrons and forms copper ammonium complexes in the presence of oxygen and ammonia, leading to the dissolution of copper, thus accelerating the corrosion of copper, accompanied by an increase in pH of ammonia solution.

In addition, in the presence of oxygen, copper can be oxidized to form Cu₂O, CuO, and Cu(OH)₂, and then these copper oxides react with ammonia to form copper-ammonia complexes, further promoting the corrosion of copper, as can be seen from Eqs. (9-14):

(9)

4 Cu + O_{2} \to 2 {Cu}_{2} O

(10)

2 Cu + O_{2} \to 2 CuO

(11)

2 Cu + O_{2} + 2 H_{2} O \to 2 Cu {(OH)}_{2}

(12)

{Cu}_{2} O + 4 {NH}_{3} + H_{2} O \to {[Cu {({NH}_{3})}_{2}]}^{+} + 2 {OH}^{-}

(13)

CuO + 4 {NH}_{3} + H_{2} O \to {[Cu {({NH}_{3})}_{4}]}^{2 +} + 2 {OH}^{-}

(14)

Cu {(OH)}_{2} + 4 {NH}_{3} \to {[Cu {({NH}_{3})}_{4}]}^{2 +} + 2 {OH}^{-}

As the corrosion time prolongs, the copper surface appears golden yellow, which may be [Cu(NH₃)₂]⁺ decomposition to generate Cu and [Cu(NH₃)₄]²⁺, as can be seen from Eq. (15):

(15)

2 {[Cu {({NH}_{3})}_{2}]}^{+} \leftrightarrow {[Cu {({NH}_{3})}_{4}]}^{2 +} + Cu

As the soaking time further extends, copper-ammonia complex content increases, and the corrosion of copper becomes increasingly severe.

4. Conclusions

The corrosion behavior and mechanism of copper in ammonia water were investigated by electrochemical tests, surface technologies, and other analytical techniques at 30°C. It is possible to conclude the following:

As ammonia concentration increases, the corrosion current density undergoes an increase from 3.23×10^-5A·cm^-2 to 2.19×10^-5A·cm^-2, while the R_ct undergoes a concurrent decrease from 406.4 Ω·cm² to 200.9 Ω·cm², indicating that the corrosion of copper accelerates.
Upon temperature elevation, the corrosion current density increases from 3.02×10^-5 A·cm^-2 to 6.85×10^-5 A·cm^-2 and the R_ct reduces from 228.32 Ω·cm² to 81.65 Ω·cm², suggesting that the augmentation of temperature expedites the corrosion of copper.
As the soaking duration increases, the pH of ammonia water remains almost constant, which may be ascribed that [Cu(NH₃)₄]²⁺ is formed and ammonia water has a buffering effect.
As the soaking time was prolonged, the corrosion rate of copper underwent an initial decrease followed by an increase. In the early stage of corrosion, the decrease of the corrosion rate of copper may originate from the formation of Cu₂O, CuO, and corrosion products. The corrosion rate of copper increases with time of corrosion, which may originate from the removal of corrosion products resulting from the formation of [Cu(NH₃)₂]⁺ and [Cu(NH₃)₄]²⁺. In the late stage of corrosion, the continuous dissolution of corrosion products causes a decrease in ammonia concentration, a slight increase in copper R_ct, and a slight decrease in copper corrosion rate.
The corrosion products of copper in ammonia water are found to be Cu₂O, CuO, Cu(OH)₂, and copper-ammonia complexes by EDS, XRD, FT-IR, and XPS analyses.

Acknowledgment

The authors thank the support of analytical and testing center of Wuhan Institute of Technology.

CRediT authorship contribution statement

The corresponding author (Hualiang Huang) is responsible for ensuring that the descriptions are accurate and agreed by all authors. Jinbei He and Lingzhi Chen: Data curation, writing and original draft preparation. Hualiang Huang: Validation, reviewing, editing, revising and supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The data that supports the findings of this study are available from the corresponding author upon reasonable request.

Declaration of generative AI and AI-assisted technologies in the writing process

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

References

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Show Sections

[1] Oubahou M., Rbaa M., Lgaz H., Takky D., Naimi Y., Alrashdi A.A., Lee H.. Exploring sustainable corrosion inhibition of copper in saline environment: An examination of hydroquinazolinones via experimental and ab initio DFT simulations. Arabian Journal of Chemistry. 2024;17:105716. https://doi.org/10.1016/j.arabjc.2024.105716
[Google Scholar]

[2] Dhouibi I., Masmoudi F., Bouaziz M., Masmoudi M.. A study of the anti-corrosive effects of essential oils of rosemary and myrtle for copper corrosion in chloride media. Arabian Journal of Chemistry. 2021;14:102961. https://doi.org/10.1016/j.arabjc.2020.102961
[Google Scholar]

[3] Ahmed A.H., Hassan A.M., Gumaa H.A., Mohamed B.H., Eraky A.M., Omran A.A.. Copper(II)-oxaloyldihydrazone complexes: Physico-chemical studies: Energy band gap and inhibition evaluation of free oxaloyldihydrazones toward the corrosion of copper metal in acidic medium. Arabian Journal of Chemistry. 2019;12:4287-4302. https://doi.org/10.1016/j.arabjc.2016.05.015
[Google Scholar]

[4] Fattah-alhosseini A., Molaei M., Kaseem M.. A review on the plasma electrolytic oxidation (PEO) process applied to copper and brass. Surfaces and Interfaces. 2024;46:104179. https://doi.org/10.1016/j.surfin.2024.104179
[Google Scholar]

[5] Pandya M., Patel N.P., Mehta K.P.. Channel formation characteristics under the influence of tool design and comparative analysis on friction stir channeling between copper and aluminum materials. CIRP Journal of Manufacturing Science and Technology. 2024;49:128-149. https://doi.org/10.1016/j.cirpj.2024.01.002
[Google Scholar]

[6] Lytle D.A., Liggett J.. Impact of water quality on chlorine demand of corroding copper. Water Research. 2016;92:11-21. https://doi.org/10.1016/j.watres.2016.01.032
[Google Scholar]

[7] Gancarz T., Berent K.. The applications of Cu substrate in liquid metal cooling systems. Materials Letters. 2018;227:116-119. https://doi.org/10.1016/j.matlet.2018.05.053
[Google Scholar]

[8] Vargas I.T., Fischer D.A., Alsina M.A., Pavissich J.P., Pastén P.A., Pizarro G.E.. Copper corrosion and biocorrosion events in premise plumbing. Materials (Basel, Switzerland). 2017;10:1036. https://doi.org/10.3390/ma10091036
[Google Scholar]

[9] Aklina Z., Tasi Marija B., Petrovi Mihajlovi Milan B., Radovanovi Milan M., Antonijevi. New trends in corrosion protection of copper. Chemical Papers. 2019;73:2103-2132. https://doi.org/10.1007/s11696-019-00774-1
[Google Scholar]

[10] Fateh A., Aliofkhazraei M., Rezvanian A.R.. Review of corrosive environments for copper and its corrosion inhibitors. Arabian Journal of Chemistry. 2020;13:481-544. https://doi.org/10.1016/j.arabjc.2017.05.021
[Google Scholar]

[11] Zhang X., Pehkonen S.O., Kocherginsky N., Andrew Ellis G.. Copper corrosion in mildly alkaline water with the disinfectant monochloramine. Corrosion Science. 2002;44:2507-2528. https://doi.org/10.1016/s0010-938x(02)00021-5
[Google Scholar]

[12] Zhao Y., Wang X., Yuan J., Ji Z., Liu J., Wang S., Guo X., Li F., Wang J., Bi J.. An efficient electrodialysis metathesis route to recover concentrated NaOH-NH₄Cl products from simulated ammonia and saline wastewater in coal chemical industry. Separation and Purification Technology. 2022;301:122042. https://doi.org/10.1016/j.seppur.2022.122042
[Google Scholar]

[13] Abu Hasan H., Sheikh Abdullah S.R., Al-Attabi A.W.N., Nash D.A.H., Anuar N., Abd. Rahman N., Sulistiyaning Titah H.. Removal of ibuprofen, ketoprofen, COD and nitrogen compounds from pharmaceutical wastewater using aerobic suspension-sequencing batch reactor (ASSBR) Separation and Purification Technology. 2016;157:215-221. https://doi.org/10.1016/j.seppur.2015.11.017
[Google Scholar]

[14] Luo Q., Mackay R.A., Babu S.V.. Copper dissolution in aqueous ammonia-containing media during chemical mechanical polishing. Chemistry of Materials. 1997;9:2101-2106. https://doi.org/10.1021/cm970168s
[Google Scholar]

[15] Davalos-Monteiro R.. Observations of corrosion product formation and stress corrosion cracking on brass samples exposed to ammonia environments. Materials Research. 2019;22:e20180077. https://doi.org/10.1590/1980-5373-mr-2018-0077
[Google Scholar]

[16] Oh S.K., Kim Y.J., Jung K.M., Park M.S., Shon M.Y., Kwon H.S.. Galvanic corrosion behaviors of Cu connected to Au on a printed circuit board in ammonia solution. Metals and Materials International. 2018;24:67-72. https://doi.org/10.1007/s12540-017-7262-z
[Google Scholar]

[17] Shi P., Wang Q., Xu Y., Luo W.. Corrosion behavior of bulk nanocrystalline copper in ammonia solution. Materials Letters. 2011;65:857-859. https://doi.org/10.1016/j.matlet.2010.12.014
[Google Scholar]

[18] Namboodhiri T.K.G., Chaudhary R.S., Prakash B., Agrawal M.K.. The dezincification of brasses in concentrated ammonia. Corrosion Science. 1982;22:1037-1047. https://doi.org/10.1016/0010-938x(82)90090-7
[Google Scholar]

[19] Li S., Liang Z., Zhang L.. Corrosion evaluation of prestressed high-strength steel wires with impressed current cathodic protection based on acoustic emission technique. Structural Control and Health Monitoring. 2022;28:e2934. https://doi.org/10.1002/stc.2934
[Google Scholar]

[20] Zhou H., Chen Y., Luo C., Song H., Yan H., Lin L., Hu Z.. Experimental and theoretical study of 2-mercaptopyridine as an effective eco-friendly inhibitor for copper in aqueous NaCl. Journal of Molecular Liquids. 2023;382:121924. https://doi.org/10.1016/j.molliq.2023.121924
[Google Scholar]

[21] Benedeti A.V., Sumodjo P.T.A., Nobe K., Cabot P.L., Proud W.G.. Electrochemical studies of copper, copper-aluminium and copper-aluminium-silver alloys: Impedance results in 0.5M NaCl. Electrochimica Acta. 1995;40:2657-2668. https://doi.org/10.1016/0013-4686(95)00108-q
[Google Scholar]

[22] Wang Y., Huang G., Huang H., Zheng X.. High temperature corrosion behavior of ADC12 aluminum alloy in oxalic acid solution. Corrosion Science. 2024;232:112028. https://doi.org/10.1016/j.corsci.2024.112028
[Google Scholar]

[23] Liu S., Huang H., Huang G., Qu J.. Influence of oxalic acid on the corrosion behavior of AZ91D magnesium alloy in deionized water. Vacuum. 2023;215:112351. https://doi.org/10.1016/j.vacuum.2023.112351
[Google Scholar]

[24] Loew N., Watanabe H., Shitanda I., Itagaki M.. Electrochemical impedance spectroscopy: Simultaneous detection of different diffusion behaviors as seen in finite element method simulations of mediator-type enzyme electrodes. Electrochimica Acta. 2022;421:140467. https://doi.org/10.1016/j.electacta.2022.140467
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[25] Guo F., Duan S., Wu D., Matsuda K., Wang T., Zou Y.. Effect of retrogression re-aging treatment on corrosion behavior of 7055 Al-Zn-Mg alloy. Materials Research Express. 2020;7:106523. https://doi.org/10.1088/2053-1591/abc191
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[26] Aït-Idir W., Wu P., Sgarbi R., Labarde Q., Touhami S., Daoudi M., El kaddouri A., Perrin J.C., Dillet J., Marty C., Micoud F., Chatenet M., Lottin O., Mainka J.. Oxygen diffusion impedance in proton exchange membrane fuel cells – insights into electrochemical impedance spectra and equivalent electrical circuit modeling. Electrochimica Acta. 2023;472:143430. https://doi.org/10.1016/j.electacta.2023.143430
[Google Scholar]

[27] Hsieh M.K., Dzombak D.A., Vidic R.D.. Effect of tolyltriazole on the corrosion protection of copper against ammonia and disinfectants in cooling systems. Industrial & Engineering Chemistry Research. 2010;49:7313-7322. https://doi.org/10.1021/ie100384d
[Google Scholar]

[28] Singh P.K., Kumar P., Hussain M., Das A.K., Nayak G.C.. Synthesis and characterization of CuO nanoparticles using strong base electrolyte through electrochemical discharge process. Bulletin of Materials Science. 2016;39:469-478. https://doi.org/10.1007/s12034-016-1159-1
[Google Scholar]

[29] Finšgar M., Kek Merl D.. An electrochemical, long-term immersion, and XPS study of 2-mercaptobenzothiazole as a copper corrosion inhibitor in chloride solution. Corrosion Science. 2014;83:164-175. https://doi.org/10.1016/j.corsci.2014.02.016
[Google Scholar]

[30] Zhang X., Hu L., Li C., Liu J., Pan G.. Exploring combined effect of nitrilotriacetic acid and inhibitor on copper surface in alkaline solution: Insights from experiments and molecular dynamics simulation studies. Journal of Molecular Liquids. 2021;328:115502. https://doi.org/10.1016/j.molliq.2021.115502
[Google Scholar]

[31] Huang H., Guo X., Bu F., Huang G.. Corrosion behavior of immersion silver printed circuit board copper under a thin electrolyte layer. Engineering Failure Analysis. 2020;117:104807. https://doi.org/10.1016/j.engfailanal.2020.104807
[Google Scholar]

[32] Alhumaimess M.S., Essawy A.A., Kamel M.M., Alsohaimi I.H., Hassan H.M.A.. Biogenic-mediated synthesis of mesoporous Cu₂O/CuO nano-architectures of superior catalytic reductive towards nitroaromatics. Nanomaterials (Basel, Switzerland). 2020;10:781. https://doi.org/10.3390/nano10040781
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[33] Fazal M.A., Haseeb A.S.M.A., Masjuki H.H.. Corrosion mechanism of copper in palm biodiesel. Corrosion Science. 2013;67:50-59. https://doi.org/10.1016/j.corsci.2012.10.006
[Google Scholar]

[34] Li K., Chen Z., Li J., Sun X., Xu F., Xu L.. Corrosion mechanism of copper immersed in ammonium sulfate solution. Materials and Corrosion. 2018;69:1597-1608. https://doi.org/10.1002/maco.201810222
[Google Scholar]

Corrosion behavior and mechanism of copper soaked in ammonia water

Abstract

Keywords

Ammonia water

Complexation

Copper

Corrosion

1. Introduction

2. Materials and Methods

2.1. Materials

2.2. Electrochemical testing

2.3. UV-vis spectrum tests

2.4. pH tests

2.5. Surface characterizations

3. Results and Discussion

3.1. OCP analysis

3.2. EIS analysis

3.3. Polarization curve analysis

3.4. UV-Vis analysis

3.5. pH analysis

3.6. Surface morphology analysis

3.7. EDS analysis

3.8. XRD, FT-IR, and XPS analysis

3.9. Corrosion mechanism analysis

4. Conclusions

Acknowledgment

CRediT authorship contribution statement

Declaration of competing interest

Data availability

Declaration of generative AI and AI-assisted technologies in the writing process

References

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