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Corrosion inhibition of aluminum by 1,1(lauryl amido)propyl ammonium chloride in HCl solution
Materials Chemistry and Physics 70 (2001) 64–72
Corrosion inhibition of aluminum by 1,1(lauryl amido)propyl ammonium chloride in HCl solution Sayed S. Abd El Rehim∗ , Hamdy H. Hassan, Mohammed A. Amin Chemistry Department, Faculty of Science, Ain Shams University, Abbassia, Cairo, Egypt Received 26 January 2000; received in revised form 20 May 2000; accepted 21 July 2000
Abstract The corrosion inhibition characteristics of 1,1(lauryl amido)propyl ammonium chloride, as a cationic surfactant (CS), on aluminum in HCl solution have been studied in the temperature range 10–60◦ C by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. Results obtained show that the inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. The surfactant acts predominately as anodic inhibitor. The inhibition efficiency increases with an increase in the surfactant concentration, but decreases with an increase in temperature. Maximum inhibition is observed around its critical micelle concentration (CMC). Frumkin isotherm fits well the experimental data. Thermodynamic functions for both dissolution and adsorption processes were determined. Results obtained from the three methods are in good agreement. © 2001 Published by Elsevier Science B.V. Keywords: Acid inhibitor; Surfactant; Aluminum and protection efficiency
1. Introduction
2. Experimental
The inhibition of corrosion of Al and its alloys are the subject of tremendous technological importance due to the increased industrial applications of these materials. Several authors [1–4] have studied the corrosion of aluminum and its alloys and their inhibition by organic inhibitors in acid solutions. Various aliphatic and aromatic amines as well as nitrogen-heterocyclic compounds are being studied as corrosion inhibitors for pure Al in acid media [5–9]. Hydrazine compounds [10–12], organic acids and their salts [13,14], dicyandiamide and some of its related compounds [15], ethoxylated fatty acids [16] and Shiff bases [17] were also found to inhibit the corrosion of Al in HCl solution. The main object of the present work is to investigate the influence of the selected cationic surfactant (CS) as an inhibitor for the acid corrosion of aluminum. Careful examination of the literature reveals that the studied surfactant has not yet been studied as corrosion inhibitor. The study employed weight loss, potentiodynamic and impedance techniques.
For the weight loss measurements, spec pure aluminum sheet of the following chemical composition (wt.%): Al (99.79%), Cu (0.05%), Mg (0.05%), Si (0.05%), Mn (0.05%) and Zn (0.01%) and of size 1×1 cm2 was used. The samples were polished successively with fine grade emery papers, cleaned with acetone, washed with doubly distilled water and finally dried. The weight loss, expressed in mg cm−2 , was determined by weighing the cleaned samples before and after immersion in 1.0 M HCl solution at different immersion times. Weight loss was determined in the absence and presence of various concentrations of 1,1(lauryl amido)propyl ammonium chloride and at different temperatures. The CS has the following structure:
∗ Corresponding author. Fax: +20-2-831836. E-mail address: [email protected] (S.S. Abd El Rehim).
For electrochemical measurements, the cell used is a conventional three-electrode Pyrex glass cell with a platinum
0254-0584/01/$ – see front matter © 2001 Published by Elsevier Science B.V. PII: S 0 2 5 4 - 0 5 8 4 ( 0 0 ) 0 0 4 6 8 - 5
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wire counter electrode and a saturated calomel electrode (SCE) as reference to which all potentials are referred. All solutions were prepared from analytical grade chemical reagents using doubly distilled water and were used without further purification. The critical micelle concentration (CMC) of the surfactant was determined at each temperature by measuring the electrical conductivity using “conductivity meter LF 538 WTW”. For each run, a freshly prepared solution as well as a cleaned set of electrodes was used. Each run was carried out in stagnant solution purged with purified argon for 30 min at the required temperature. The working electrode was embedded in Araldite so that its cross-sectional area (0.785 cm2 ) was in contact with the solution. Prior to each experiment, the working electrode was polished successively with fine grade emery papers, then the polished metal surface was rinsed with acetone, distilled water, and finally dipped in the electrolytic cell. The potentiodynamic current–potential curves were recorded by changing the electrode potential automatically from −2.0 to 2.0 V with scan rate of 10 mV s−1 . EIS measurements were carried out using AC signals of amplitude 5 mV peak-to-peak at the open circuit potential in the frequency range of 100 kHz to 10 Hz. A potentiostat/galvanostat (EG&G model 273), lock-in amplifier (model 5210) and a personal computer were used. M352 corrosion software and M398 impedance software from EG&G Princeton Applied Research were used for the potentiodynamic polarization measurements and the EIS measurements, respectively.
3. Results and discussion 3.1. Weight loss measurements
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Fig. 1. Weight loss vs. immersion time for Al in 1.0 M HCl solution containing various concentrations of the surfactant at 30◦ C: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M; (7) 0.006 M; (8) 0.010 M.
temperatures. The plots have S-shaped adsorption isotherm. The inhibition efficiency increases when the concentration of the surfactant increases and tends to attain a maximum value when the concentration reaches a value close to its CMC value (≈ 2 × 10−3 M at 30◦ C). The surfactant seems to function as inhibitor by being adsorbed on the metal surface. In acid medium, adsorption is due to electrostatic attraction between the two ammonium N+ groups of the surfactant and the negatively charged metal surface [18,19]. However, the inhibition efficiency decreases with
Fig. 1 represents the straight line relation of the weight loss (mg cm−2 ) as a function of the immersion time for Al in 1.0 M HCl solution with and without the addition of different concentrations (from 2×10−4 up to 0.01 M) of the surfactant at 30◦ C. The slope of each line (weight loss per unit time (mg cm−2 min−1 )) represents the corrosion rate of Al at the specified conditions. However, Fig. 2 shows the influence of temperature on the weight loss/immersion time relation for Al in (1.0 M HCl + 0.002 M surfactant). As can be seen from Figs. 1 and 2, the addition of the surfactant retards the rate of dissolution and inhibits the acid corrosion of Al. The inhibition efficiency P% at different inhibitor concentrations and temperature was calculated from the equation: W (1) P % = 100 × 1 − W0 where W0 and W are the weight loss per unit time in the absence and presence of the surfactant, respectively. Fig. 3 illustrates the plots of the inhibition efficiency vs. the logarithmic concentration of the inhibitor at various
Fig. 2. Weight loss vs. immersion time for Al in 1.0 M HCl solution containing 0.002 M surfactant at different temperatures: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
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Fig. 4. Arrhenius plot of the corrosion rate of Al in 1.0 M HCl solution in the presence and absence of different concentrations of the surfactant: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M.
Fig. 3. Variation of the protection efficiency with the logarithmic concentration of the surfactant for Al in 1.0 M HCl solution at different temperatures: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
an increase in temperature. This can be due to decreasing surfactant adsorption at higher temperatures. This suggests that physical adsorption may be the type of adsorption of the inhibitor on the metal surface. It has been reported by a number of authors [20–22] that for Al corrosion in acid solution, the logarithm of the corrosion rate (mg cm−2 min−1 ) is a linear function with 1/T (Arrhenius equation): log(Rate) =
−Ea0 +A 2.303RT
(2)
where Ea0 is the apparent effective activation energy, R the general gas constant and A the Arrhenius pre-exponential factor. A plot of the logarithm of the corrosion rate of Al obtained from weight loss measurements vs. 1/T gave straight lines as shown in Fig. 4. The values of Ea0 obtained from the slope of the lines are given in Table 1. An alternative formula of the Arrhenius equation is the transition state equation: 1S 0 1H 0 RT exp exp − (3) Rate = Nh R RT where h is the Planck’s constant, N the Avogadro’s number, 1S0 the entropy of activation, and 1H0 the enthalpy of activation. A plot of log(rate/T) vs. 1/T should give a straight line (Fig. 5) with a slope of (−1H0 /2.303R) and an intercept of [(log(R/Nh)) + (1S 0 /2.303R)], from which the values of 1S0 and 1H0 were calculated and listed in Table 1. The data show that the thermodynamic activation functions (Ea and 1H0 ) of the corrosion of Al in 1 M HCl solution in the presence of the surfactant are higher than those in the free acid solution. Ea and 1H0 enhance with increasing inhibitor concentration, indicating more energy barrier for
the reaction in the presence of the inhibitor is attained. The entropy of activation 1S0 in the absence and presence of the inhibitor is large and negative. This indicates that the activated complex in the rate determining step represents an association rather than a dissociation step, meaning that, a decrease in disordering takes place on going from reactants to the activated complex [23]. 3.2. Potentiodynamic polarization measurements Fig. 6 shows the effect of surfactant concentration on the potentiodynamic anodic and cathodic polarization curves for Al in 1.0 M HCl solution at 30◦ C, while Fig. 7 illustrates the influence of temperature on the anodic and cathodic polarization curves of Al in 1.0 M HCl solution containing 0.002 M surfactant. The addition of the surfactant displaces
Fig. 5. Plot of log (corrosion rate/T ) vs. 1/T for the corrosion of Al in 1.0 M HCl solution in the presence and absence of different concentrations of surfactant: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M.
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Fig. 6. Effect of surfactant concentration on the anodic and cathodic potentiodynamic polarization response of Al in deaerated 1.0 M HCl at a scan rate of 10 mV s−1 and 30◦ C: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M; (7) 0.006 M; (8) 0.010 M.
Fig. 7. Effect of solution temperature on the anodic and cathodic potentiodynamic polarization response of Al in 1.0 M HCl in the presence of 0.002 M surfactant scan rate of 10 mV s−1 : (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
the open circuit corrosion potentials Ecorr to more positive values. The inhibitor increases also both of the anodic and cathodic overpotentials but its influence on the cathodic side is much less obvious. These results indicate that this inhibitor acts predominately as anodic inhibitor. The electrochemical parameters (jcorr , Ecorr , bc and ba ) associated with polarization measurements and the inhibitor efficiency P% of the surfactant at different inhibitor concentrations and temperatures are listed in Tables 2 and 3, respectively, where jcorr , ba and bc are the corrosion current density, and anodic and cathodic Tafel slopes, respectively, in the potential range ±50 mV form Ecorr . These parameters were determined simultaneously by a computer program (M352 corrosion software from EG&G Princeton Applied Research). Since the corrosion rate is directly related to the corrosion current jcorr , the inhibition efficiency P% at different inhibitor concentrations and temperatures were calculated from the equation: (jcorr )i (4) P % = 100 × 1 − (jcorr )0
ciency increases with inhibitor concentration but decreases with temperature. The higher inhibition efficiencies are observed when the concentration reaches values close to its CMC. The slopes of the anodic (ba ) and cathodic (bc ) Tafel lines are approximately equal. These results indicate that this inhibitor acts by simply blocking the available surface area. In other words, the inhibitor decreases the surface area for dissolution without affecting the mechanism of the dissolution of Al and only causes inactivation of a part of the surface with respect to the corrosive medium.
where (jcorr )0 and (jcorr )i are the corrosion current densities in the absence and presence of the inhibitor. According to the data of Tables 2 and 3, it is seen that the inhibition effi-
3.3. Electrochemical impedance measurements The effects of the inhibitor concentration and temperature on the impedance behavior of Al in 1.0 M HCl solution have been studied and the results are given in Figs. 8 and 9, respectively. Inspections of the data reveal that the impedance spectra consists of a large capacitive loop at high frequencies (HFs) followed by a small inductive one at low frequency (LF) values. The LF capacitive loop is usually related to the charge transfer of the corrosion process and the double layer behavior, and the inductive loop may be attributed to the relaxation processes in the oxide film covering the
Table 2 Effect of surfactant concentration (C) on kinetic parameters determined simultaneously by a computer program (M352 corrosion software from EG&G Princeton Applied Research) for potentiodynamic polarization curves of Al in 1.0 M HCl in the absence and presence of surfactant at 30◦ C C (M)
ba (mV decade−1 )
−bc (mV decade−1 )
Rp (k)
jcorr (A cm−2 )
−Ecorr (mV)
P%
0.0 2 × 10−4 4 × 10−4 6 × 10−4 2 × 10−3 4 × 10−3 6 × 10−3 1 × 10−2
190.7 185.5 184.5 180.5 181.1 180.5 179.4 180.4
432.5 421.1 419.3 410.4 412.8 411.8 407.9 411.6
17.26 21.84 27.97 38.33 112.0 241.7 373.8 662.0
4.49 3.47 2.69 1.93 0.67 0.32 0.21 0.12
1109 1065 1033 996.7 966.8 928 900 864
– 22.80 40.00 54.00 85.00 93.00 95.40 97.30
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Table 3 Effect of solution temperature (T) on kinetic parameters determined simultaneously by a computer program (M352 corrosion software from EG&G Princeton Applied Research) for potentiodynamic polarization curves for Al in 1.0 M HCl in the absence and presence of 0.002 M surfactant T (K)
ba (mV decade−1 )
−ba (mV decade−1 )
Rp (k)
jcorr (A cm−2 )
−Ecorr (mV)
P%
283 293 303 313 323 333
189.4 183.1 181.1 179.1 177.2 175.4
437.6 419.6 412.8 406.7 401.1 395.4
467.8 188.4 112.0 78.5 55.6 36.0
0.17 0.41 0.67 0.95 1.33 2.02
1150 1078 966.8 915 870 827
93.10 89.50 85.00 83.00 78.30 74.00
electrode surface [4,24–26]. It is worthy noting that the presence of the inhibitor does not alter the profile of the impedance behavior, suggesting similar mechanisms for the dissolution of Al in HCl in the absence and presence of the inhibitor. The equivalent circuit model used to fit the experimental results is given in Fig. 10 as previously reported [27,28]. The measured complex-plane impedance plot is similar to that calculated by the equivalent circuit model, as shown in Fig. 8 (the solid line). The polarization resistance Rp and the double layer capacitance Cdl for the CS were determined by analysis of the complex-plane impedance plots
and the equivalent circuit models. Values of Rp and Cdl at different inhibitor concentrations and temperatures are given in Tables 4 and 5, respectively. Complete inspection of Tables 4 and 5 reveals that Rp values increase with an increase in the inhibitor concentration, but decrease with an increase in temperature. On the other hand, the values of Cdl decrease with an increase in the inhibitor concentration, but increase with an increase in temperature. This is due to the increasing surface coverage by the inhibitor which leads to an increase in the inhibition efficiency with increasing inhibitor concentration. Since electrochemical theory shows
Fig. 8. Effect of surfactant concentration on the impedance behavior of Al at its open circuit potential in deaerated 1.0 M HCl solution at 30◦ C: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M; (7) 0.006 M; (8) 0.010 M.
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Fig. 9. Effect of solution temperature on the impedance behavior of Al at its open circuit potential in deaerated (1.0 M HCl + 0.002 M surfactant) solution: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
that Cdl is proportional to the corrosion rate [29], the inhibition efficiencies at different inhibitor concentrations and temperatures were calculated using the following equation: ! Cdl (5) P% = 1 − 0 Cdl 0 and C are the double layer capacitance of the where Cdl dl electrode without and with the inhibitor, respectively. The calculated values of P% are listed in Tables 4 and 5. The activated thermodynamic functions (Ea , 1H0 and 1S0 ) of the corrosion of Al in 1 M HCl solution in the absence and presence of different concentrations of the surfactant can be calculated by applying Eqs. (2) and (3) for the two electrochemical techniques used and the results are listed in Table 3. The corrosion rate in these equations is taken as jcorr for the potentiodynamic polarization technique and Cdl for EIS technique at different surfactant concentrations and solution temperatures as given in Tables 2–5, respectively. The three different techniques gave the same trend of inhibition of the surfactant and yield nearly the same values of P%. Moreover, the activated thermodynamic functions (Ea , 1H0 , 1S0 and 1G0 ) for the corrosion process are in good agreement (Table 1).
3.4. Adsorption isotherms In order to get more information about the mode of adsorption of the surfactant on the metal surface at different
Fig. 10. The equivalent circuit model used to fit the experimental results.
Table 4 Effect of surfactant concentration (C) on kinetic parameters obtained from EIS of Al in 1.0 M HCl in the absence and presence of surfactant at 30◦ C C (M)
Rp (k)
Cdl (F)
P%
0.0 2 × 10−4 4 × 10−4 6 × 10−4 2 × 10−3 4 × 10−3 6 × 10−3 1 × 10−2
16.23 20.35 26.62 34.16 110.5 239.4 381.8 667.1
4.51 3.50 2.66 2.03 0.63 0.29 0.18 0.10
– 22.40 41.00 57.00 86.00 93.60 96.00 97.70
temperatures, the data obtained from the three different techniques have been tested with several adsorption isotherms. “Frumkin” [30] isotherm was found to fit well with our experimental data. The adsorption isotherm relationship of Frumkin is represented by the following equation: θ = ln K + 2aθ (6) ln C(1 − θ ) where θ is the surface coverage (θ = P /100), C the inhibitor concentration in the bulk of solution, a 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 can Table 5 Effect of solution temperature (T) on kinetic parameters obtained from EIS of Al in 1.0 M HCl in the absence and presence of 0.002 M surfactant T (K)
Rp (k)
Cdl (F)
P%
283 293 303 313 323 333
425.1 176.2 110.5 76.4 53.1 28.3
0.17 0.40 0.63 0.90 1.28 2.37
92.90 89.50 86.00 84.00 79.00 69.30
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Fig. 11. Curve fitting of the weight loss data of Al in 1.0 M HCl solution containing various concentrations of the surfactant to Frumkin isotherm at different temperatures: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
have both positive and negative values. The more positive the value of a, the steeper is the adsorption isotherm. K is the binding constant of the adsorption reaction. Curves fitting of weight loss data are shown in Fig. 11. Similar results were obtained from the data of the other two techniques (the figures are not presented here). The calculated values of K are given in Table 6. It is seen that there is a good agreement between the values of K obtained from the three different methods used. Small values of K, however, compromise that such interactions by the adsorbing molecules and the metal surface are weaker, indicating that the molecules are easily removable from the surface by the solvent molecules. Generally speaking, the K value of adsorption was found to be lowered with increasing temperature, confirming the suggestion that this inhibitor is physically adsorbed on the metal surface and the strength of the adsorption decreases with temperature. The molecular interaction a which depends on the molecular interaction in the adsorption layer and the degree of heterogeneity of the sample is also included in Table 6. The values of a were found to be positive.
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Fig. 12. The relation between log (binding constant) and 1/T for the adsorption of the surfactant on Al in 1.0 M HCl solution containing various concentrations of the surfactant in the 10–60◦ C temperature range.
This has been interpreted [31] to imply that the interactions between molecules with positive a value cause an increase in the adsorption energy with the increase of θ. 0 and The average thermodynamic parameters (1Hads 0 1Sads ) for the surfactant adsorption on the Al surface in 1.0 M HCl in the 10–60◦ C temperature range were determined from the slopes and intercepts of the lines of log K vs. l/T plots (Fig. 12) according to the following equation [32]: log K = −
0 0 1Sads 1Hads + 2.303RT 2.303R
(7)
0 and 1S 0 are the enthalpy and entropy of the where 1Hads ads adsorption process, respectively. The calculated values for 0 , 1S 0 and 1G0 are listed in Table 7 (1G0 = 1Hads ads ads ads 0 − T 1S 0 ). The thermodynamic functions of the ad1Hads ads sorption process obtained from the three methods are in good agreements. The calculated values of 1G0ads are low suggesting that the nature of the inhibitor adsorption is mainly physisorption and their negative sign indicating spontaneous
Table 6 0 0 The thermodynamic parameters of adsorption obtained by applying Eq. (7) and Gibbs equation (1G0ads = 1Hads − T 1Sads ) on the weight loss, potentiodynamic polarization and impedance data of Al in 1.0 M HCl + 0.002 M surfactant at 30◦ C T (K)
283 293 303 313 323 333
a
K
Weight loss data
Potentiodynamic data
Impedance data
Weight loss data
Potentiodynamic data
Impedance data
0.78 0.51 0.54 0.54 0.65 0.65
0.77 0.55 0.60 0.58 0.64 0.65
0.78 0.54 0.70 0.56 0.67 0.64
1527.0 1460.5 1121.4 981.0 659.3 496.0
1515.5 1452.6 1068.0 975.0 648.0 480.0
1522.8 1450.0 1043.0 963.5 651.5 477.4
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Table 7 The parameters obtained applying Frumkin model Eq. (5) on the weight loss, potentiodynamic polarization and impedance data of Al in 1.0 M HCl + 0.002 M surfactant Technique used
0 −1Hads (kJ mol−1 )
0 −1Sads (J mol−1 K −1 )
−1G0ads (kJ mol−1 )
Weight loss data Potentiodynamic data Impedance data
19.10 18.95 19.14
24.73 24.68 25.36
17.68 17.53 17.51
interaction of inhibitor molecule with the corroding Al 0 indicates that surface [17,33]. The negative value of 1Hads the adsorption of inhibitor molecules is an exothermic pro0 and 1S 0 cess [34]. The magnitude of the values of 1Hads ads are characteristic of the occurrence of a replacement process during adsorption of inhibitor molecules on the metal surface [35].
4. Conclusions • 1,1(Lauryl amido)propyl ammonium chloride behaves as an anodic inhibitor. • The inhibition is due to the adsorption of the surfactant on Al surface and blocking its active sites. • The inhibition efficiency increases with the increase of inhibitor concentration but decreases with the increase of temperature. • The data obtained fit well the Frumkin isotherm. • The data obtained from the three different methods, namely, weight loss, potentiodynamic polarization and EIS, are in good agreements. References [1] F. Ovari, L. Tomcsanyi, T. Turmezey, Electrochim. Acta 33 (1988) 323. [2] L. Tomcsanyi, K. Varga, I. Bartik, G. Horanyi, E. Maleczki, Electrochim. Acta 34 (1989) 855.
[3] R.M. Stevanovic, A.R. Despic, D.M. Drazic, Electrochim. Acta 33 (1988) 397. [4] S.E. Frers, M.M. Stefenel, C. Mayer, T. Chierchie, J. Appl. Electrochem. 20 (1990) 996. [5] I.L. Rozenfeld, Corrosion Inhibitors, McGraw-Hill, New York, 1981, p. 182. [6] M.N. Desai, B.C. Thakar, P.M. Chiaya, M.H. Gandi, Corros. Sci. 16 (1976) 9. [7] N. Hackerman, A.C. Makrides, Ind. Eng. Chem. 46 (1954) 523. [8] S.L. Granese, B.M. Rosales, Proceedings of the Seventh European Symposium on Corrosion Inhibitors, Vol. 9, Ann. Univ. Ferrara N.S., Sez. V, 1990, p. 73. [9] N. Hackerman, H. Kaesche, J. Electrochem. Soc. 105 (1958) 191. [10] Y.A. El-Awady, A.I. Ahmed, J. Ind. Chem. 24A (1985) 601. [11] M.N.H. Moussa, F.I.M. Taha, M.M. Gouda, G.M. Singab, Corros. Sci. 16 (1976) 379. [12] I.M. Issaa, M.N.H. Moussa, M.A.A. Ghondoura, Corros. Sci. 13 (1973) 79. [13] D. Bracher, A.D. Mercer, Br. Corros. J. 3 (1968) 120. [14] H. Mihara, Y.H. Kawa, Denki Kagaku 36 (1968) 657; Chemical Abstract 70 (1969) 14022. [15] A. Maitra, S. Barua, Corros. Sci. 14 (1974) 587. [16] M.M. Osman, S.S. Abdel Rehim, J. Mater. Chem. Phys. 53 (1998) 34. [17] G.K. Gomma, M.H. Wahdan, J. Mater. Chem. Phys. 39 (1995) 209. [18] A.K. Vijh, J. Phys. Chem. 72 (1968) 1148. [19] M.N. Desai, Werkestoffi und Korosion 23 (1972) 475. [20] M.A.B. Christopher, A.R.G. Isabel, P.S.M. Jenny, Corros. Sci. 36 (1994) 15. [21] C.B. Breslin, W.M. Carrol, Corros. Sci. 34 (1993) 327. [22] M.G.A. Khedr, M.S. Lashien, Corros. Sci. 33 (1992) 137. [23] M.K. Gomma, M.H. Wahdan, Mater. Chem. Phys. 39 (1995) 209. [24] F.M. Al-Kharafi, W.A. Badawy, Electrochim. Acta 40 (1995) 1811. [25] C.M.A. Brett, J. Appl. Electrochem. 20 (1990) 1000. [26] C.M.A. Brett, Corros. Sci. 33 (1992) 203. [27] A. El-Sayed, Corros. Prev. Control 43 (1996) 29. [28] I. Sekine, M. Sabongi, H. Hagiuda, T. Oshibe, M. Yuasa, T. Imahoma, Y. Shibata, T. Wake, J. Electrochem. Soc. 139 (1992) 3167. [29] W.J. Lorenz, F. Mansfeld, Corros. Sci. 21 (1981) 647. [30] A.N. Frumkin, Z. Phys. Chem. 116 (1915) 166. [31] M. Kaminki, Z. Szklarska-Smialowska, Corros. Sci. 13 (1973) 557. [32] B. Ateya, B. El-Anadouli, F. El-Nizamy, Corros. Sci. 24 (1984) 509. [33] J. Marsh, Advanced Organic Chemistry, 3rd Edition, Wiley Eastern, New Delhi, 1988. [34] B.A. Abd-El-Nabey, E. Khamis, M.Sh. Ramadan, A. El-Gindy, Proceedings of the Eighth European Symposium on Corrosion Inhibitors, Ann. Univ. Ferrara N.S., Sez. 10, 1995, p. 299. [35] M.J. Lampinen, M. Fomino, J. Electrochem. Soc. 140 (1993) 3537.
Corrosion inhibition of aluminum by 1,1(lauryl amido)propyl ammonium chloride in HCl solution Sayed S. Abd El Rehim∗ , Hamdy H. Hassan, Mohammed A. Amin Chemistry Department, Faculty of Science, Ain Shams University, Abbassia, Cairo, Egypt Received 26 January 2000; received in revised form 20 May 2000; accepted 21 July 2000
Abstract The corrosion inhibition characteristics of 1,1(lauryl amido)propyl ammonium chloride, as a cationic surfactant (CS), on aluminum in HCl solution have been studied in the temperature range 10–60◦ C by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. Results obtained show that the inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. The surfactant acts predominately as anodic inhibitor. The inhibition efficiency increases with an increase in the surfactant concentration, but decreases with an increase in temperature. Maximum inhibition is observed around its critical micelle concentration (CMC). Frumkin isotherm fits well the experimental data. Thermodynamic functions for both dissolution and adsorption processes were determined. Results obtained from the three methods are in good agreement. © 2001 Published by Elsevier Science B.V. Keywords: Acid inhibitor; Surfactant; Aluminum and protection efficiency
1. Introduction
2. Experimental
The inhibition of corrosion of Al and its alloys are the subject of tremendous technological importance due to the increased industrial applications of these materials. Several authors [1–4] have studied the corrosion of aluminum and its alloys and their inhibition by organic inhibitors in acid solutions. Various aliphatic and aromatic amines as well as nitrogen-heterocyclic compounds are being studied as corrosion inhibitors for pure Al in acid media [5–9]. Hydrazine compounds [10–12], organic acids and their salts [13,14], dicyandiamide and some of its related compounds [15], ethoxylated fatty acids [16] and Shiff bases [17] were also found to inhibit the corrosion of Al in HCl solution. The main object of the present work is to investigate the influence of the selected cationic surfactant (CS) as an inhibitor for the acid corrosion of aluminum. Careful examination of the literature reveals that the studied surfactant has not yet been studied as corrosion inhibitor. The study employed weight loss, potentiodynamic and impedance techniques.
For the weight loss measurements, spec pure aluminum sheet of the following chemical composition (wt.%): Al (99.79%), Cu (0.05%), Mg (0.05%), Si (0.05%), Mn (0.05%) and Zn (0.01%) and of size 1×1 cm2 was used. The samples were polished successively with fine grade emery papers, cleaned with acetone, washed with doubly distilled water and finally dried. The weight loss, expressed in mg cm−2 , was determined by weighing the cleaned samples before and after immersion in 1.0 M HCl solution at different immersion times. Weight loss was determined in the absence and presence of various concentrations of 1,1(lauryl amido)propyl ammonium chloride and at different temperatures. The CS has the following structure:
∗ Corresponding author. Fax: +20-2-831836. E-mail address: [email protected] (S.S. Abd El Rehim).
For electrochemical measurements, the cell used is a conventional three-electrode Pyrex glass cell with a platinum
0254-0584/01/$ – see front matter © 2001 Published by Elsevier Science B.V. PII: S 0 2 5 4 - 0 5 8 4 ( 0 0 ) 0 0 4 6 8 - 5
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wire counter electrode and a saturated calomel electrode (SCE) as reference to which all potentials are referred. All solutions were prepared from analytical grade chemical reagents using doubly distilled water and were used without further purification. The critical micelle concentration (CMC) of the surfactant was determined at each temperature by measuring the electrical conductivity using “conductivity meter LF 538 WTW”. For each run, a freshly prepared solution as well as a cleaned set of electrodes was used. Each run was carried out in stagnant solution purged with purified argon for 30 min at the required temperature. The working electrode was embedded in Araldite so that its cross-sectional area (0.785 cm2 ) was in contact with the solution. Prior to each experiment, the working electrode was polished successively with fine grade emery papers, then the polished metal surface was rinsed with acetone, distilled water, and finally dipped in the electrolytic cell. The potentiodynamic current–potential curves were recorded by changing the electrode potential automatically from −2.0 to 2.0 V with scan rate of 10 mV s−1 . EIS measurements were carried out using AC signals of amplitude 5 mV peak-to-peak at the open circuit potential in the frequency range of 100 kHz to 10 Hz. A potentiostat/galvanostat (EG&G model 273), lock-in amplifier (model 5210) and a personal computer were used. M352 corrosion software and M398 impedance software from EG&G Princeton Applied Research were used for the potentiodynamic polarization measurements and the EIS measurements, respectively.
3. Results and discussion 3.1. Weight loss measurements
65
Fig. 1. Weight loss vs. immersion time for Al in 1.0 M HCl solution containing various concentrations of the surfactant at 30◦ C: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M; (7) 0.006 M; (8) 0.010 M.
temperatures. The plots have S-shaped adsorption isotherm. The inhibition efficiency increases when the concentration of the surfactant increases and tends to attain a maximum value when the concentration reaches a value close to its CMC value (≈ 2 × 10−3 M at 30◦ C). The surfactant seems to function as inhibitor by being adsorbed on the metal surface. In acid medium, adsorption is due to electrostatic attraction between the two ammonium N+ groups of the surfactant and the negatively charged metal surface [18,19]. However, the inhibition efficiency decreases with
Fig. 1 represents the straight line relation of the weight loss (mg cm−2 ) as a function of the immersion time for Al in 1.0 M HCl solution with and without the addition of different concentrations (from 2×10−4 up to 0.01 M) of the surfactant at 30◦ C. The slope of each line (weight loss per unit time (mg cm−2 min−1 )) represents the corrosion rate of Al at the specified conditions. However, Fig. 2 shows the influence of temperature on the weight loss/immersion time relation for Al in (1.0 M HCl + 0.002 M surfactant). As can be seen from Figs. 1 and 2, the addition of the surfactant retards the rate of dissolution and inhibits the acid corrosion of Al. The inhibition efficiency P% at different inhibitor concentrations and temperature was calculated from the equation: W (1) P % = 100 × 1 − W0 where W0 and W are the weight loss per unit time in the absence and presence of the surfactant, respectively. Fig. 3 illustrates the plots of the inhibition efficiency vs. the logarithmic concentration of the inhibitor at various
Fig. 2. Weight loss vs. immersion time for Al in 1.0 M HCl solution containing 0.002 M surfactant at different temperatures: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
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Fig. 4. Arrhenius plot of the corrosion rate of Al in 1.0 M HCl solution in the presence and absence of different concentrations of the surfactant: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M.
Fig. 3. Variation of the protection efficiency with the logarithmic concentration of the surfactant for Al in 1.0 M HCl solution at different temperatures: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
an increase in temperature. This can be due to decreasing surfactant adsorption at higher temperatures. This suggests that physical adsorption may be the type of adsorption of the inhibitor on the metal surface. It has been reported by a number of authors [20–22] that for Al corrosion in acid solution, the logarithm of the corrosion rate (mg cm−2 min−1 ) is a linear function with 1/T (Arrhenius equation): log(Rate) =
−Ea0 +A 2.303RT
(2)
where Ea0 is the apparent effective activation energy, R the general gas constant and A the Arrhenius pre-exponential factor. A plot of the logarithm of the corrosion rate of Al obtained from weight loss measurements vs. 1/T gave straight lines as shown in Fig. 4. The values of Ea0 obtained from the slope of the lines are given in Table 1. An alternative formula of the Arrhenius equation is the transition state equation: 1S 0 1H 0 RT exp exp − (3) Rate = Nh R RT where h is the Planck’s constant, N the Avogadro’s number, 1S0 the entropy of activation, and 1H0 the enthalpy of activation. A plot of log(rate/T) vs. 1/T should give a straight line (Fig. 5) with a slope of (−1H0 /2.303R) and an intercept of [(log(R/Nh)) + (1S 0 /2.303R)], from which the values of 1S0 and 1H0 were calculated and listed in Table 1. The data show that the thermodynamic activation functions (Ea and 1H0 ) of the corrosion of Al in 1 M HCl solution in the presence of the surfactant are higher than those in the free acid solution. Ea and 1H0 enhance with increasing inhibitor concentration, indicating more energy barrier for
the reaction in the presence of the inhibitor is attained. The entropy of activation 1S0 in the absence and presence of the inhibitor is large and negative. This indicates that the activated complex in the rate determining step represents an association rather than a dissociation step, meaning that, a decrease in disordering takes place on going from reactants to the activated complex [23]. 3.2. Potentiodynamic polarization measurements Fig. 6 shows the effect of surfactant concentration on the potentiodynamic anodic and cathodic polarization curves for Al in 1.0 M HCl solution at 30◦ C, while Fig. 7 illustrates the influence of temperature on the anodic and cathodic polarization curves of Al in 1.0 M HCl solution containing 0.002 M surfactant. The addition of the surfactant displaces
Fig. 5. Plot of log (corrosion rate/T ) vs. 1/T for the corrosion of Al in 1.0 M HCl solution in the presence and absence of different concentrations of surfactant: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M.
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Fig. 6. Effect of surfactant concentration on the anodic and cathodic potentiodynamic polarization response of Al in deaerated 1.0 M HCl at a scan rate of 10 mV s−1 and 30◦ C: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M; (7) 0.006 M; (8) 0.010 M.
Fig. 7. Effect of solution temperature on the anodic and cathodic potentiodynamic polarization response of Al in 1.0 M HCl in the presence of 0.002 M surfactant scan rate of 10 mV s−1 : (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
the open circuit corrosion potentials Ecorr to more positive values. The inhibitor increases also both of the anodic and cathodic overpotentials but its influence on the cathodic side is much less obvious. These results indicate that this inhibitor acts predominately as anodic inhibitor. The electrochemical parameters (jcorr , Ecorr , bc and ba ) associated with polarization measurements and the inhibitor efficiency P% of the surfactant at different inhibitor concentrations and temperatures are listed in Tables 2 and 3, respectively, where jcorr , ba and bc are the corrosion current density, and anodic and cathodic Tafel slopes, respectively, in the potential range ±50 mV form Ecorr . These parameters were determined simultaneously by a computer program (M352 corrosion software from EG&G Princeton Applied Research). Since the corrosion rate is directly related to the corrosion current jcorr , the inhibition efficiency P% at different inhibitor concentrations and temperatures were calculated from the equation: (jcorr )i (4) P % = 100 × 1 − (jcorr )0
ciency increases with inhibitor concentration but decreases with temperature. The higher inhibition efficiencies are observed when the concentration reaches values close to its CMC. The slopes of the anodic (ba ) and cathodic (bc ) Tafel lines are approximately equal. These results indicate that this inhibitor acts by simply blocking the available surface area. In other words, the inhibitor decreases the surface area for dissolution without affecting the mechanism of the dissolution of Al and only causes inactivation of a part of the surface with respect to the corrosive medium.
where (jcorr )0 and (jcorr )i are the corrosion current densities in the absence and presence of the inhibitor. According to the data of Tables 2 and 3, it is seen that the inhibition effi-
3.3. Electrochemical impedance measurements The effects of the inhibitor concentration and temperature on the impedance behavior of Al in 1.0 M HCl solution have been studied and the results are given in Figs. 8 and 9, respectively. Inspections of the data reveal that the impedance spectra consists of a large capacitive loop at high frequencies (HFs) followed by a small inductive one at low frequency (LF) values. The LF capacitive loop is usually related to the charge transfer of the corrosion process and the double layer behavior, and the inductive loop may be attributed to the relaxation processes in the oxide film covering the
Table 2 Effect of surfactant concentration (C) on kinetic parameters determined simultaneously by a computer program (M352 corrosion software from EG&G Princeton Applied Research) for potentiodynamic polarization curves of Al in 1.0 M HCl in the absence and presence of surfactant at 30◦ C C (M)
ba (mV decade−1 )
−bc (mV decade−1 )
Rp (k)
jcorr (A cm−2 )
−Ecorr (mV)
P%
0.0 2 × 10−4 4 × 10−4 6 × 10−4 2 × 10−3 4 × 10−3 6 × 10−3 1 × 10−2
190.7 185.5 184.5 180.5 181.1 180.5 179.4 180.4
432.5 421.1 419.3 410.4 412.8 411.8 407.9 411.6
17.26 21.84 27.97 38.33 112.0 241.7 373.8 662.0
4.49 3.47 2.69 1.93 0.67 0.32 0.21 0.12
1109 1065 1033 996.7 966.8 928 900 864
– 22.80 40.00 54.00 85.00 93.00 95.40 97.30
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Table 3 Effect of solution temperature (T) on kinetic parameters determined simultaneously by a computer program (M352 corrosion software from EG&G Princeton Applied Research) for potentiodynamic polarization curves for Al in 1.0 M HCl in the absence and presence of 0.002 M surfactant T (K)
ba (mV decade−1 )
−ba (mV decade−1 )
Rp (k)
jcorr (A cm−2 )
−Ecorr (mV)
P%
283 293 303 313 323 333
189.4 183.1 181.1 179.1 177.2 175.4
437.6 419.6 412.8 406.7 401.1 395.4
467.8 188.4 112.0 78.5 55.6 36.0
0.17 0.41 0.67 0.95 1.33 2.02
1150 1078 966.8 915 870 827
93.10 89.50 85.00 83.00 78.30 74.00
electrode surface [4,24–26]. It is worthy noting that the presence of the inhibitor does not alter the profile of the impedance behavior, suggesting similar mechanisms for the dissolution of Al in HCl in the absence and presence of the inhibitor. The equivalent circuit model used to fit the experimental results is given in Fig. 10 as previously reported [27,28]. The measured complex-plane impedance plot is similar to that calculated by the equivalent circuit model, as shown in Fig. 8 (the solid line). The polarization resistance Rp and the double layer capacitance Cdl for the CS were determined by analysis of the complex-plane impedance plots
and the equivalent circuit models. Values of Rp and Cdl at different inhibitor concentrations and temperatures are given in Tables 4 and 5, respectively. Complete inspection of Tables 4 and 5 reveals that Rp values increase with an increase in the inhibitor concentration, but decrease with an increase in temperature. On the other hand, the values of Cdl decrease with an increase in the inhibitor concentration, but increase with an increase in temperature. This is due to the increasing surface coverage by the inhibitor which leads to an increase in the inhibition efficiency with increasing inhibitor concentration. Since electrochemical theory shows
Fig. 8. Effect of surfactant concentration on the impedance behavior of Al at its open circuit potential in deaerated 1.0 M HCl solution at 30◦ C: (1) 0.00 M; (2) 0.0002 M; (3) 0.0004 M; (4) 0.0006 M; (5) 0.002 M; (6) 0.004 M; (7) 0.006 M; (8) 0.010 M.
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Fig. 9. Effect of solution temperature on the impedance behavior of Al at its open circuit potential in deaerated (1.0 M HCl + 0.002 M surfactant) solution: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
that Cdl is proportional to the corrosion rate [29], the inhibition efficiencies at different inhibitor concentrations and temperatures were calculated using the following equation: ! Cdl (5) P% = 1 − 0 Cdl 0 and C are the double layer capacitance of the where Cdl dl electrode without and with the inhibitor, respectively. The calculated values of P% are listed in Tables 4 and 5. The activated thermodynamic functions (Ea , 1H0 and 1S0 ) of the corrosion of Al in 1 M HCl solution in the absence and presence of different concentrations of the surfactant can be calculated by applying Eqs. (2) and (3) for the two electrochemical techniques used and the results are listed in Table 3. The corrosion rate in these equations is taken as jcorr for the potentiodynamic polarization technique and Cdl for EIS technique at different surfactant concentrations and solution temperatures as given in Tables 2–5, respectively. The three different techniques gave the same trend of inhibition of the surfactant and yield nearly the same values of P%. Moreover, the activated thermodynamic functions (Ea , 1H0 , 1S0 and 1G0 ) for the corrosion process are in good agreement (Table 1).
3.4. Adsorption isotherms In order to get more information about the mode of adsorption of the surfactant on the metal surface at different
Fig. 10. The equivalent circuit model used to fit the experimental results.
Table 4 Effect of surfactant concentration (C) on kinetic parameters obtained from EIS of Al in 1.0 M HCl in the absence and presence of surfactant at 30◦ C C (M)
Rp (k)
Cdl (F)
P%
0.0 2 × 10−4 4 × 10−4 6 × 10−4 2 × 10−3 4 × 10−3 6 × 10−3 1 × 10−2
16.23 20.35 26.62 34.16 110.5 239.4 381.8 667.1
4.51 3.50 2.66 2.03 0.63 0.29 0.18 0.10
– 22.40 41.00 57.00 86.00 93.60 96.00 97.70
temperatures, the data obtained from the three different techniques have been tested with several adsorption isotherms. “Frumkin” [30] isotherm was found to fit well with our experimental data. The adsorption isotherm relationship of Frumkin is represented by the following equation: θ = ln K + 2aθ (6) ln C(1 − θ ) where θ is the surface coverage (θ = P /100), C the inhibitor concentration in the bulk of solution, a 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 can Table 5 Effect of solution temperature (T) on kinetic parameters obtained from EIS of Al in 1.0 M HCl in the absence and presence of 0.002 M surfactant T (K)
Rp (k)
Cdl (F)
P%
283 293 303 313 323 333
425.1 176.2 110.5 76.4 53.1 28.3
0.17 0.40 0.63 0.90 1.28 2.37
92.90 89.50 86.00 84.00 79.00 69.30
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Fig. 11. Curve fitting of the weight loss data of Al in 1.0 M HCl solution containing various concentrations of the surfactant to Frumkin isotherm at different temperatures: (1) 10◦ C; (2) 20◦ C; (3) 30◦ C; (4) 40◦ C; (5) 50◦ C; (6) 60◦ C.
have both positive and negative values. The more positive the value of a, the steeper is the adsorption isotherm. K is the binding constant of the adsorption reaction. Curves fitting of weight loss data are shown in Fig. 11. Similar results were obtained from the data of the other two techniques (the figures are not presented here). The calculated values of K are given in Table 6. It is seen that there is a good agreement between the values of K obtained from the three different methods used. Small values of K, however, compromise that such interactions by the adsorbing molecules and the metal surface are weaker, indicating that the molecules are easily removable from the surface by the solvent molecules. Generally speaking, the K value of adsorption was found to be lowered with increasing temperature, confirming the suggestion that this inhibitor is physically adsorbed on the metal surface and the strength of the adsorption decreases with temperature. The molecular interaction a which depends on the molecular interaction in the adsorption layer and the degree of heterogeneity of the sample is also included in Table 6. The values of a were found to be positive.
71
Fig. 12. The relation between log (binding constant) and 1/T for the adsorption of the surfactant on Al in 1.0 M HCl solution containing various concentrations of the surfactant in the 10–60◦ C temperature range.
This has been interpreted [31] to imply that the interactions between molecules with positive a value cause an increase in the adsorption energy with the increase of θ. 0 and The average thermodynamic parameters (1Hads 0 1Sads ) for the surfactant adsorption on the Al surface in 1.0 M HCl in the 10–60◦ C temperature range were determined from the slopes and intercepts of the lines of log K vs. l/T plots (Fig. 12) according to the following equation [32]: log K = −
0 0 1Sads 1Hads + 2.303RT 2.303R
(7)
0 and 1S 0 are the enthalpy and entropy of the where 1Hads ads adsorption process, respectively. The calculated values for 0 , 1S 0 and 1G0 are listed in Table 7 (1G0 = 1Hads ads ads ads 0 − T 1S 0 ). The thermodynamic functions of the ad1Hads ads sorption process obtained from the three methods are in good agreements. The calculated values of 1G0ads are low suggesting that the nature of the inhibitor adsorption is mainly physisorption and their negative sign indicating spontaneous
Table 6 0 0 The thermodynamic parameters of adsorption obtained by applying Eq. (7) and Gibbs equation (1G0ads = 1Hads − T 1Sads ) on the weight loss, potentiodynamic polarization and impedance data of Al in 1.0 M HCl + 0.002 M surfactant at 30◦ C T (K)
283 293 303 313 323 333
a
K
Weight loss data
Potentiodynamic data
Impedance data
Weight loss data
Potentiodynamic data
Impedance data
0.78 0.51 0.54 0.54 0.65 0.65
0.77 0.55 0.60 0.58 0.64 0.65
0.78 0.54 0.70 0.56 0.67 0.64
1527.0 1460.5 1121.4 981.0 659.3 496.0
1515.5 1452.6 1068.0 975.0 648.0 480.0
1522.8 1450.0 1043.0 963.5 651.5 477.4
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Table 7 The parameters obtained applying Frumkin model Eq. (5) on the weight loss, potentiodynamic polarization and impedance data of Al in 1.0 M HCl + 0.002 M surfactant Technique used
0 −1Hads (kJ mol−1 )
0 −1Sads (J mol−1 K −1 )
−1G0ads (kJ mol−1 )
Weight loss data Potentiodynamic data Impedance data
19.10 18.95 19.14
24.73 24.68 25.36
17.68 17.53 17.51
interaction of inhibitor molecule with the corroding Al 0 indicates that surface [17,33]. The negative value of 1Hads the adsorption of inhibitor molecules is an exothermic pro0 and 1S 0 cess [34]. The magnitude of the values of 1Hads ads are characteristic of the occurrence of a replacement process during adsorption of inhibitor molecules on the metal surface [35].
4. Conclusions • 1,1(Lauryl amido)propyl ammonium chloride behaves as an anodic inhibitor. • The inhibition is due to the adsorption of the surfactant on Al surface and blocking its active sites. • The inhibition efficiency increases with the increase of inhibitor concentration but decreases with the increase of temperature. • The data obtained fit well the Frumkin isotherm. • The data obtained from the three different methods, namely, weight loss, potentiodynamic polarization and EIS, are in good agreements. References [1] F. Ovari, L. Tomcsanyi, T. Turmezey, Electrochim. Acta 33 (1988) 323. [2] L. Tomcsanyi, K. Varga, I. Bartik, G. Horanyi, E. Maleczki, Electrochim. Acta 34 (1989) 855.
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