Corrosion inhibition of aluminum with a series of aniline monomeric surfactants and their analog polymers in 0.5 M HCl solution

M.M. El-Deeb; S.M. Sayyah; S.S. Abd El-Rehim; S.M. Mohamed

doi:10.1016/j.arabjc.2013.09.018

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ORIGINAL ARTICLE

8 (

); 527-537

doi:

10.1016/j.arabjc.2013.09.018

Corrosion inhibition of aluminum with a series of aniline monomeric surfactants and their analog polymers in 0.5 M HCl solution

Part II: 3-(12-sodiumsulfonate dodecyloxy) aniline and its analog polymer

M.M. El-Deeb^{^a,^c,*}, S.M. Sayyah^{^a}, S.S. Abd El-Rehim^{^b}, S.M. Mohamed^{^a}

a Chemistry Department, Faculty of Science, Beni Suef University, 62514 Beni Suef, Egypt

b Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt

c Chemistry Department, Faculty of Science, Ha’il University, Ha’il, Saudi Arabia

*Corresponding author at: Chemistry Department, Faculty of Science, Beni Suef University, 62514 Beni Suef, Egypt. Tel.: +966 530 176 588 eldeebm@yahoo.com (M.M. El-Deeb)

Received: 2013-2-18, Accepted: 2013-9-7, Published: 2013-07-01

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

Available online 19 September 2013

Peer review under responsibility of King Saud University.

Abstract

The inhibition effect of 3-(12-sodiumsulfonate dodecyloxy) aniline monomeric surfactant (MC₁₂) and its analog polymer Poly 3-(dodecyloxy sulfonic acid) aniline (PC₁₂) on the corrosion of aluminum in 0.5 M HCl solution was investigated using weight loss and potentiodynamic polarization techniques. The presence of these two compounds in 0.5 M HCl inhibits the corrosion of aluminum without modifying the mechanism of corrosion process. It was found that these inhibitors act as mixed-type inhibitors with anodic predominance as well as the inhibition efficiency increases with increasing inhibitor concentration, but decreases with raising temperature. Langmuir and Frumkin adsorption isotherms fit well with the experimental data. Thermodynamic functions for both dissolution and adsorption processes were determined. The obtained results from weight loss and potentiodynamic polarization techniques are in good agreement with contact angle measurements.

Keywords

Polymers

Electrochemical techniques

Adsorption

Corrosion

Contact angle

Aluminum

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1 Introduction

Aluminum and its alloys have a remarkable economic and attractive material for engineering applications owing to its low cost, light weight, high thermal and electrical conductivity. The resistance of aluminum against corrosion in aqueous media can be attributed to a rapidly formed surface oxide film. Therefore, aluminum has been known to exhibit widely different electrochemical properties in different aqueous electrolytes.

Hackerman and Sudbury (1950), Hackerman and Markrides (1954), Hackerman (1962) showed that, the adsorption of surfactant molecules on the metal surface can markedly change the corrosion resisting property of the metal. Various surfactants as well as octyl sulfate sodium salt are being studied as a corrosion inhibitor for aluminum in acidic media (Elewady et al., 2008; Zhao and Mu, 1999). Many of organic compounds such as electroactive conducting polymers (Perucki and Chandrasekhar, 2001; Breslin et al., 2005; Gelling et al., 2001; Epstein et al., 1999; Yang et al., 2002 ), carboxylic organic acids (Muller, 2004; Bereket and Yurt, 2001), fatty acids (Foad El-Sherbini et al., 2003) dicyandiamide and some of its related compounds (Maitra and Barua, 1974), hydrazine compounds (Moussa et al., 1976), triazole and thiazole derivatives (Zheludkevich et al., 2004) were also found to inhibit the corrosion of aluminum.

The inhibition of most these compounds occurs via their adsorption on the metal surfaces which can markedly change the corrosion – resisting property of the metal and so the study of the relations between the adsorption and corrosion inhibition is of great importance.

Abd El Rehim et al. (2001) studied the effect of sodium dodecyl benzene sulfonate on the corrosion of aluminum and its alloy in 1 M HCl. The data show that, the addition of this surfactant inhibits the hydrochloric acid corrosion of aluminum and the inhibition occurs through adsorption of the surfactant on the metal surface and fits Frumkin adsorption isotherm.

EL-Deeb and Mohamed (2011) studied the effect of 3-(10-sodiumsulfonate decyloxy) aniline monomeric surfactant and its analog polymer on the corrosion of aluminum in 0.5 M HCl. The results show that, the inhibition occurs through the adsorption of surfactant molecules on the aluminum surface as well as the inhibition efficiency increases with increasing inhibitor concentrations and decreases with raising temperature.

The present study aims to investigate the inhibition effect of 3-(12-sodiumsulfonate dodecyloxy) aniline monomeric surfactant (MC₁₂) and its analog polymer Poly 3-(dodecyloxy sulfonic acid) aniline (PC₁₂) on the corrosion of aluminum in 0.5 M HCl solution using weight-loss and potentiodynamic polarization techniques as well as the thermodynamic functions for the dissolution and adsorption were investigated.

2 Experimental

2.1

2.1 Materials

3-Aminophenol, potassium persulfate and 1,12-dibromododecane were obtained from Aldrich Chemical Co., England. Sodium sulfite used in the synthetic process was obtained from Merck chemical Co., (Germany). Concentrated hydrochloric acid was chemically pure grade products provided by Prolabo-Chemical Co., (U.K.). Twice distilled water was used as a medium for the polymerization reactions.

2.2

2.2 Weight loss measurements

Aluminum metal provided by the Egyptian Aluminum Company, Naghammady of the following chemical composition: 99.57% Al, 0.31% Fe, 0.07% Si, 0.015% Ti%, 0.0016% Zn, 0.0003% Cr, 0.0019% Mg, 0.0021% Mn and 0.0007 Cu and the diminutions of the tested samples 2 × 2 × 0.1 (thickness) is used in this study. The samples were polished successively with fine grade emery papers, cleaned with acetone, washed with doubly distilled water and finally dried, weighed and then introduced into test solution.

2.3

2.3 Potentiodynamic polarization measurements

The working electrode made from aluminum rod has the same composition as mentioned in Section 2.2. The rod is axially embedded in araldite holder to offer an active flat disk shaped surface of an area of 0.785 cm⁻². Prior to each experiment, the working electrode was polished successively with fine emery paper. The polished metal surface was rinsed with acetone and distilled water before dipping it into the electrolytic cell. A platinum wire was used as the counter electrode and a saturated calomel electrode as a reference electrode to which all potentials are referred.

The electrochemical experiments are performed using the Potentiostat/Galvanostat Wenking PGS95, connected to computer. I–E curves are recorded using computer software (model ECT). The experiments were carried out by changing the electrode potential automatically from the starting potential toward more positive values at the required scan rate till the end of the experiments.

2.4

2.4 Synthesis of monomeric 3-(12-sodiumsulfonate dodecyloxy) aniline (MC₁₂)

3-(12-Bromododecyloxy) aniline was prepared by the equilomolar reaction, between 3-aminophenol and 1,12-dibromododecane in the presence of sodium ethoxide. The product 3-(12-Bromododecyloxy) aniline was reacted with sodium sulfite to produce 3-(12-sodiumsulfonate dodecyloxy) aniline.

2.5

2.5 Synthesis of Poly 3-(dodecyloxy sulfonic acid) aniline (PC₁₂)

The amount of 3-(12-sodiumsulfonate dodecyloxy)aniline in 25 ml 2.0 M HCl solution was introduced into a well stoppered conical flask of 250 ml capacity followed by the addition of the required amount of potassium per sulfate dissolved in 25 ml 2.0 M HCl solution to the reaction mixture under nitrogen atmosphere. The order of addition of substances was kept constant in all the performed experiments. The stoppered conical flask was then placed in an automatically controlled thermostat at 25 °C. The flask was shaken (50 shakings/10 s/15 min) for one hour by using an automatic shaker. The flask was left for 72 h at room temperature to continue the reaction and then filtrated using a Buchner funnel. Then the solid was washed with distilled water, and finally dried under vacuum at room temperature until constant weight.

2.6

2.6 Elemental and spectroscopic analysis

Elemental analysis of the prepared monomeric and polymeric surfactant was carried out in the microanalytical laboratory at the Cairo University by using oxygen flask combustion and a dosimat E415 titrator (Switzerland). The elemental analysis of the prepared monomeric and polymeric surfactant is summarized in Table 1. Infrared spectroscopic analysis of the prepared MC₁₂ and PC₁₂ was carried out in the microanalytical laboratory at the Cairo University by using a shimadzu FTIR-430 Jasco Spectrophotometer and KBr disk techniques. IR absorption bands and their assignments (Silversyein et al., 1974) of MC₁₂ and PC₁₂ are summarized in Table 2. Data of Tables 1 and 2 show that, there is a good agreement with the suggested structures present in Scheme 1.

Table 1 Elemental analysis of the prepared MC₁₂ and PC₁₂.

Name	C%		H%		Cl%		S%		N%
	Cal.	Found	Cal.	Found	Cal.	Found	Cal.	Found	Cal.	Found
MC₁₂	73.22	72.93	10.17	10.02	^–	^–	10.85	10.63	4.75	7.66
PC₁₂	54.65	55.37	7.97	7.69	4.44	4.51	8.10	8.04	3.54	3.52

Table 2 Infrared absorption bands and their assignments for MC₁₂ and PC₁₂.

Wave number (cm⁻¹)		Assignments Silversyein et al. (1974)
MC₁₂	PC₁₂	Assignments Silversyein et al. (1974)
510^b	493^s	Bending deformation of NH in primary aromatic amines
628^sh	–	Out-of-plane bending deformation of CH in 1,3-disubstituted benzene ring
753^s	758^b	In-plane rocking vibration for CH in aliphatic chain
–	818^m	Out-of-plane bending deformation of CH in 1,3,4-trisubstituted benzene ring
920^m	974^s	Symmetric stretching vibration for S–O or C–N group
–	1056^sh	Symmetric stretching vibration for C–O group
1121^b	1126^b	Symmetric stretching vibration for C–O group
1329^w	1325^w	Symmetric stretching vibration for S⚌O group
1457^s	1405^s	Scissoring deformation for CH in methylene group
–	1566^m	Stretching vibration for quinoide structure in benzene ring
1617^s	1624^b	Stretching vibration for C⚌C in benzene ring
2839^sh	2840^w	Symmetric stretching vibration for CH group in aliphatic chain
3042^sh	3041^sh	Symmetric stretching vibration for CH group in benzene ring
3235^m	3148^b	Stretching vibration for OH group in SO₃H group strongly hydrogen bond
3414^m	–	Symmetric stretching vibration for NH in aromatic amine
3478^m	3400^b	Asymmetric stretching vibration for NH in aromatic amine
3550^m	–	Stretching vibration for free OH group in SO₃H group

Abbreviations: s, sharp; m, medium; w, weak; sh, shoulder.

Structure of monomeric and polymeric surfactants.

2.7

2.7 Critical micelle concentration and contact angle

Critical micelle concentration (CMC) of the prepared MC₁₂ and PC₁₂ was measured by using K100 Tensiometer (KRUSS Type) for the hydrochloric form of synthesized monomeric and polymeric surfactants using different concentrations.

3 Results and discussion

3.1

3.1 Weight loss measurements

Weight loss (in mg cm⁻²) of aluminum in 0.5 M HCl solution in the absence and presence of different concentrations of 3-(12-sodiumsulfonate dodecyloxy) aniline (MC₁₂) monomeric surfactant and its analog polymer Poly 3-(dodecyloxy sulfonic acid) aniline (PC₁₂) at 30 °C was determined as a function of the immersion time and the data are graphically represented in Fig. 1. The slope of each line (mg cm⁻² min⁻¹) represents the corrosion rate of aluminum at the specified conditions. From these data, the weight loss (and hence rate of corrosion) of aluminum enhances with the immersion time.

Weight loss vs. immersion time for aluminum in 0.5 M HCl solution in the absence and presence of different concentrations of MC12 (a) and PC12 (b) at 30 °C.

On one hand, the dissolution of aluminum in HCl solution is slow and increases with the immersion time as indicated by increasing the weight loss by time, this may by due to the presence of a pre-immersion hydrate Al₂O₃ film on the metal surface (Osman and Abd El Rehim, 1998). On the other hand, the addition of (MC₁₂) monomeric surfactant and its polymer (PC₁₂) retards the rate of dissolution and inhibits the acid corrosion of aluminum. The inhibition efficiency values (P%) at different inhibitor concentrations and temperatures were calculated from the following equation:

(1)

P % = 100 \times [1 - (W / W_{0})]

where W₀ and W are the weight loss per unit time in the absence and presence of the inhibitors, respectively and the data are summarized in Table 3. Data of Table 3 indicate that the inhibition efficiency of PC₁₂ is higher than that of MC₁₂. The inhibition efficiency increases with increasing concentration of the two surfactants and reaches maximum value at critical concentration (1.32 × 10⁻⁵ mol/L in case of MC₁₂ and 3.19 × 10⁻⁶ mol/L in case of PC₁₂). Beyond this critical concentration, the efficiency tends to achieve steady state values. It is seen that, the maximum efficiency is obtained at concentration less than the respective CMC (CMC is 2.51 × 10⁻⁴ mol/L in case of MC₁₂ and 1 × 10⁻⁴ mol/L in case of PC₁₂). This means that, the adsorption of these surfactants on the aluminum surface reaches equilibrium before the formation of micelles (The aggregation of these surfactant long chains into fairly large charged units).

Table 3 Variation of inhibition efficiency (P%) and contact angle of aluminum at different inhibitor concentrations using weight loss and polarization measurements at 30 °C.

Conc. (ppm)	P%				Contact angle
	Weight loss		Polarization		Contact angle
	MC₁₂	PC₁₂	MC₁₂	PC₁₂	MC₁₂	PC₁₂
1	28.1	35.5	25.8	36.2	83.16	76.91
3	43.5	48.6	42.0	50.9	50.12	47.12
5	55.0	71.3	56.5	69.0	16.82	10.78
10	49.0	56.1	50.0	55.1	22.34	21.45

The contact angle is the angle formed when a liquid droplet is placed on the solid surface. The contact angle values vary from 0° (perfectly wetting) to 180° (completely non-wetting). The values of the contact angle for MC₁₂ and PC₁₂ at 30 °C are given in Table 3. The data clearly show that, the inhibition efficiency of these two inhibitors increases as their contact angles decrease. Moreover, it is observed that the contact angles for PC₁₂ are lower than those for MC₁₂ confirming the suggestion that PC₁₂ is more effective than MC₁₂ for inhibiting the acid corrosion of aluminum.

Fig. 2 shows the influence of temperature on the weight loss for aluminum in 0.5 M HCl in the absence and presence of 10 ppm of MC₁₂ and PC₁₂. As can be seen from the figure, the weight loss (and hence the rate of corrosion) of aluminum sample enhances with the immersion time and the addition of both inhibitors retards the rate of dissolution at all ranges of the investigated temperatures. The data show that the weight loss increases with increasing temperature. This can be due to the decrease in the strength of adsorption process with increasing temperature suggesting that physical adsorption may be the type of adsorption of the inhibitor on the sample surface. It has been reported that (EL-Deeb and Mohamed, 2011; Sayyah et al., 2001; Abd El Rehim et al., 2010 ), for acid corrosion of metals, the logarithm of the corrosion rate (in mg cm⁻² min⁻¹) is a linear function with 1/T (following Arrhenius equation type):

(2)

\log (rate) = - E_{a} / 2.303 RT + A

where E_a is the apparent effective activation energy, R is the universal gas constant and A is the Arrhenius pre-exponential factor. The corrosion rate for each concentration from 1 to 10 ppm of the monomeric and its polymeric surfactant was calculated at different temperatures and the logarithm of the corrosion rate was plotted against 1/T for each concentration and the value of E_a was calculated and tabulated in Table 4. An alternative formula of the Arrhenius equation is the transition state equation:

(3)

Rate = RT / Nh \exp (Δ S ° / R) \exp (- Δ H ° / RT)

where h is the Planck’s constant, N is the Avogadro’s number, ΔS° is the entropy of the activation, and ΔH° is the enthalpy of activation. The plot of log (Rate/T) vs. 1/T gives a straight line with a slope of (−ΔH°/2.303 R), from which the value of ΔH° was calculated and listed in Table 4. These values indicate that the presence of the additives increases the activation energy and the activation enthalpy, for the corrosion process. The addition of inhibitors modified the values of the activation energy and the activation enthalpy. This may be attributed to the adsorption of inhibitors on the aluminum surface and this adsorption makes an energy barrier and this energy barrier of the corrosion reaction increases as the concentration of the inhibitor is increased.

Weight loss vs. immersion time for aluminum in 0.5 M HCl solution in the presence of 10 ppm of MC12 (a) and PC12 (b) at different temperatures.

Table 4 Effect of MC₁₂ and PC₁₂ concentrations on the thermodynamic of the dissolution process of Al in 0.5 M HCl solution.

Conc. (ppm)	E_a (kJmol⁻¹)				ΔH° (kJmol⁻¹)
	Weight loss		Polarization		Weight loss		Polarization
	MC₁₂	PC₁₂	MC₁₂	PC₁₂	MC₁₂	PC₁₂	MC₁₂	PC₁₂
Blank	57.4	57.4	57.3	57.3	55.5	55.5	54.7	54.7
1	64.5	66.6	62.6	65.3	62.3	64.1	59.9	62.9
3	67.3	73.7	66.4	72.5	65.1	70.5	64.3	68.9
5	72.8	82.5	72.0	80.4	70.0	80.1	68.9	76.8
10	70.1	80.1	69.8	76.2	68.5	78.6	67.6	70.2

3.2

3.2 Potentiodynamic polarization measurements

Potentiodynamic polarization measurements of aluminum in 0.5 M HCl containing different concentrations of both MC₁₂ and PC₁₂ at different temperatures with a scan rate of 25 mVs⁻¹ are graphically represented in Figs. 3 and 4 and the electrochemical parameters (l_corr, E_corr, β_c and β_a) are listed in Tables 5 and 6. The data clearly show that the addition of MC₁₂ and PC₁₂ enhances both the anodic and cathodic overpotential and decreases the corresponding partial anodic (dissolution of the metal) and partial cathodic (evolution of hydrogen) current densities as well as decreases the values of I_corr confirming the inhibition of the corrosion process. Moreover, the corrosion potentials are displayed to more positive values in the presence of the inhibitors revealing that these surfactants predominately act as anodic inhibitors. This could be interpreted on the basis that the potential at the anodic sites is more positive than that at the cathodic sites and consequently the adsorption of the surfactant is much more negative anion surfactant likely to adsorb at the anodic sites.

Effect of MC12 and PC12 concentrations on the cathodic and anodic polarization of Al in 0.5 M HCl solution with a scan rate of 25 mV/s at 30 °C.

Effect of temperature on the cathodic and anodic polarization of Al in 0.5 M HCl in the presence of 10 ppm of MC12 and PC12 with a scan rate of 25 mV/s.

Table 5 Electrochemical parameters associated with polarization measurements for Al in 0.5 M HCl solution in the absence and presence of different concentrations of PC₁₂ at different temperatures.

C (ppm)	E_Corr (V)	I_Corr (μA cm⁻²)	β_a (mV dec⁻¹)	−β_c (mV dec⁻¹)
At 30 °C
Blank	−0.82	95.22	−0.34	0.04
1	−1.04	60.80	−0.26	0.33
3	−0.60	46.73	−0.36	0.26
5	−0.74	29.79	−0.29	0.08
10	−0.70	42.82	−0.32	0.13

At 40 °C
Blank	−0.98	368.00	−0.39	0.12
1	−0.94	256.70	−0.32	0.11
3	−0.84	216.20	−0.39	0.11
5	−0.89	186.30	−0.34	0.15
10	−0.93	193.10	−0.43	0.09

At 50 °C
Blank	−1.03	574.20	−0.46	0.13
1	−0.95	440.50	−0.45	0.11
3	−0.97	401.10	−0.41	0.11
5	−0.98	366.50	−0.35	0.15
10	−0.90	383.40	−0.43	0.09

At 60 °C
Blank	−1.21	783.00	−0.48	0.13
1	−0.95	632.30	−0.55	0.12
3	−0.97	602.50	−0.43	0.14
5	−0.98	578.60	−0.46	0.14
10	−0.90	603.20	−0.56	0.10

Table 6 The electrochemical parameters associated with polarization measurements for Al in 0.5 M HCl solution in the absence and presence of different concentrations of MC₁₂ at different temperatures.

C (ppm)	E_Corr (V)	I_Corr (μA cm⁻²)	β_a (mV dec⁻¹)	−β_c (mV dec⁻¹)
At 30 °C
Blank	−0.82	95.22	−0.34	0.044
1	−0.72	70.65	−0.24	0.119
3	−0.71	55.26	−0.317	0.122
5	−0.82	41.45	−0.31	0.114
10	−0.75	47.61	−0.315	0.084

At 40 °C
Blank	−0.98	368	−0.114	0.39
1	−0.97	270.4	−0.146	0.314
3	−0.931	227.5	−0.118	0.42
5	−0.818	199.1	0.221	0.51
10	−0.812	206.3	0.181	0.099

At 50 °C
Blank	−1.033	574.2	−0.128	0.46
1	−0.912	432.7	−0.137	0.41
3	−1.03	401.6	−0.132	0.454
5	−0.917	356.4	−0.119	0.45
10	−0.915	378.1	0.154	0.71

At 60 °C
Blank	−1.21	783	−0.13	0.48
1	−1.11	675.6	−0.161	0.45
3	−0.963	653.7	−0.127	0.461
5	−0.96	623.1	−0.121	0.46
10	−0.923	635.4	−0.141	0.41

The inhibition efficiency (P%) was calculated at different inhibitor concentrations and the data are given in Table 3. It is seen that, the inhibition efficiency increases with increasing surfactant concentrations up to critical concentrations but decreases with raising temperature. The presence of these inhibitors does not change significantly the values of cathodic and anodic Tafel line slopes. These results indicate that these inhibitors act by simply blocking the available surface area for the corrosion process. In other words, each inhibitor decreases the surface area for corrosion without affecting the mechanism of the corrosion process and only causes inactivation of a part of the aluminum surface with respect to the corrosive medium.

3.3

3.3 Adsorption isotherm

In order to get more information about the mode of adsorption of the inhibitors on the metal surface at different temperatures, the data obtained from the two different techniques have been tested with several adsorption isotherms. Langmuir adsorption isotherm was found to fit well with our experimental data. Fig. 5 represent curves fitting of MC₁₂ and PC₁₂ using data obtained from potentiodynamic polarization measurements respectively. Similar results were obtained from weight loss technique. The adsorption isotherm relationship of Langmuir is represented by the following equation (EL-Deeb and Mohamed, 2011; Migahed et al., 2004):

(4)

C_{i} / θ = 1 / K_{ads} + C_{i}

where C_i is the concentration of the inhibitor in bulk solution, θ is the surface coverage (θ = P/100) and K_ads is the adsorption equilibrium constant_.

Langmuir adsorption isotherm of MC12 (a) and PC12 (b) based on polarization data at different temperatures.

Frumkin isotherm (Frumkin, 1915) was also found to fit well with the obtained experimental data. The adsorption isotherm relationship of Frumkin is represented by the following equation:

(5)

\ln θ / C_{i} (1 - θ) = \ln K_{ads} + 2 a θ

where (a) is the lateral interaction term describing the molecular interactions in the adsorption layer and the heterogeneity of the surface and is a measure for the steepness of the adsorption isotherm. It may be positive or negative values. The more positive the value of (a), the steeper is the adsorption isotherm. Curves fitting of the weight loss data for MC₁₂ and PC₁₂ are graphically represented in Fig. 6. Similar results are obtained from the data of the polarization technique.

Frumkin adsorption isotherm of MC12 (a) and PC12 (b) based on weight loss data at different temperatures.

The adsorption thermodynamic parameters (ΔH_ads and ΔS_ads) for the surfactant adsorption on the aluminum surface in 0.5 M HCl at different temperatures were determined from the slopes and intercepts of the lines of log K_ads vs. 1/T plots using the following equation:

(6)

\log K_{ads} = - Δ H_{ads} / 2.303 RT + Δ S_{ads} / 2.303 R

where ΔH_ads and ΔS_ads are the enthalpy and entropy of the adsorption process respectively. The calculated values for ΔH_ads, ΔS_ads and ΔG_ads are listed in Table 7 (ΔG_ads = ΔH_ads − TΔS_ads). The thermodynamic functions of the adsorption process which obtained from two different techniques confirm each other. The calculated values of ΔG_ads are low suggesting that the nature of the inhibitor adsorption is mainly physical adsorption and their negative sign indicating spontaneous interaction of the inhibitor with the aluminum surface (Ateya et al., 1984). The negative value of ΔH_ads indicates that the adsorption of the inhibitors on the aluminum surface is an exothermic process. The values of ΔH_ads and ΔS_ads are characteristic of the occurrence of a replacement process during the adsorption of inhibitor compound on the metal surface (Iampinen and Fomino, 1993).

Table 7 Thermodynamic parameters of the adsorption process based on Frumkin isotherm.

Surfactant	Weight loss			Polarization
Surfactant	−ΔH_ads (kJmol⁻¹)	−ΔS_ads (kJmol⁻¹ K⁻¹)	−ΔG_ads (kJmol⁻¹)	−ΔH_ads (kJmol⁻¹)	−ΔS_ads (kJmol⁻¹ K⁻¹)	−ΔG_ads (kJmol⁻¹)
MC₁₂	65.95	0.1105	32.47	67.21	0.1128	33.01
PC₁₂	46.32	0.0298	37.28	45.57	0.0301	36.45

4 Conclusion

Addition of MC12 and PC12 surfactants inhibits the corrosion of aluminum in 0.5 M HCl solution.
The inhibition efficiency of polymeric surfactant is higher than that of monomeric surfactant.
The inhibition efficiency of the two surfactants increases with an increase in inhibitor concentration but decreases with an increase in temperature.
The data obtained from weight loss and polarization technique fit well the Langmuir and Frumkin isotherms.
The data obtained from contact angle, weight loss and potentiodynamic polarization techniques are in good agreements.

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Abd El Rehim S.S., Sayyah S.M., El-Deeb M.M., Kamal S.M., Azooz R.E., . Mater. Chem. Phys.. 2010;123:20.
Migahed M.A., Azzam E.M., Al-Sabagh A.M., . Mater. Chem. Phys.. 2004;85:273.
Frumkin A.N., . Z. Phys. Chem.. 1915;116:166.
Ateya B., El-anadouli B., El–Nizamy F., . Corros. Sci.. 1984;24:509.
Iampinen M.J., Fomino M., . J. Electrochem. Soc.. 1993;140:3537.

Show Sections

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