A New Approach to Study the Synergistic Inhibition Effect of Cationic

Article pubs.acs.org/IECR

A New Approach to Study the Synergistic Inhibition Effect of Cationic and Anionic Surfactants on the Corrosion of Mild Steel in HCl Solution Ali Yousefi,† Soheila Javadian,*,† and Jaber Neshati‡ †

Department of Chemistry, Faculty of Science, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran Corrosion Department, Coating Research Center, Research Institute of Petroleum Industry (RIPI), P.O. Box 18745-4163, Tehran, Iran

‡

S Supporting Information *

ABSTRACT: The corrosion inhibition characteristics of cation-rich and anion-rich catanionic mixtures of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as corrosion inhibitor for mild steel (MS) in aqueous solution of 2 M HCl were investigated. The interaction between the two surfactants in the solid−liquid interface was analyzed on the basis of regular solution theory for the first time. Mixed surfactants showed good inhibition properties due to strong adsorption on the surface and formation of a protective film. Adsorption of the inhibitors obeyed the Flory−Huggins isotherm. Potentiodynamic polarization investigations indicated that the inhibitors studied were mixed-type inhibitors.

1. INTRODUCTION Acid solutions are extensively employed in industries; some of the important fields of application are acid pickling of steel, chemical improvement and processing or production, and oil well acidification.1 These operations typically induce serious corrosion of equipment, tubes, and pipelines made of steel.2 Corrosion within the oil industry is one of the main problems. Of explicit concern is internal corrosion, such as that of pipes and storage tanks.3 To minimize the internal corrosion of industrial equipment, it is very important to protect the internal surface of the materials.3 These chemicals, when added in small quantities, stop or slow corrosion of the metallic surface.3,4 Up to now, various compounds have been used as corrosion inhibitors for steel in acidic media (HCl, H2SO4, and H3PO4), such as dyes,5,6 ionic liquids,7−9 bis-thiadiazole derivatives,10 glycine derivative,11 n-alkyl-quaternary ammonium salts,12−14 pyridine derivatives,15,16 amino acids,3,17 etc. Several studies have suggested that these chemicals are adsorbed on the metal surface, displacing water molecules from the surface and forming a compressed film as a barrier. In other words, the adsorbed corrosion inhibitor might sterically block the surface, thus either restricting the contact of corrosion species to the surface or transferring the corrosion product from it.18 Addition of surfactants to destructive media like acid solutions is one of the methods for achieving this goal.18 Surfactants also displace water from the metal surface, interact with anodic or cathodic reaction sites to slow the oxidation and reduction corrosion reaction, and prevent transportation of water and corrosionactive species to the surface.19 Various surfactants are reported to be good corrosion inhibitors in acidic media, such as anionic surfactants,20,21 cationic surfactants,22,23 nonionic surfactants,24,25 and gemini surfactants.2 Xianghong Li et al.26 have studied the effects of different surfactants as corrosion inhibitors in hydrochloric acidic media. Although the anionic surfactants studied showed good inhibitive performance, they © 2014 American Chemical Society

are poor bactericides, are easily destroyed by strong electrolyte, and produce the salting-out effect. On the other hand, cationic surfactants are cost-effective, stable in acid and base solutions, and are good bactericides. It is found that cationic surfactants13,27 show high inhibition efficiency for steel corrosion in acid solutions. However, few studies have been carried out on inhibition of steel corrosion in acid solutions by mixtures of surfactants. Mixtures of surfactants have several applications in technology. The mixtures usually show synergistic effects, which are evidence of nonideal behavior and are the reason for their widespread use in industry.18 Synergistic inhibition is an effective means to improve the inhibitive force of the inhibitor, to decrease the quantity of usage, and to diversify the application of the inhibitor in acidic media. It is necessary for corrosion scientists to discover, explore, and use synergism in complicated corrosive media. R. Fuchs-Godec18 has studied the corrosion inhibition characteristics of cationic and zwitterionic surfactants as corrosion inhibitors for stainless steel in aqueous solutions of 2 M H2SO4. He has found that mixtures of the surfactants acted as mixedtype inhibitors, adsorbing on the stainless steel surface in agreement with the Flory−Huggins adsorption isotherm. It has also been reported that the mixtures showed good inhibition properties and the adsorption in mixtures was stronger. In another work, Godec et al.28 have investigated the synergistic inhibition offered by halide ions and nonionic surfactant to the corrosion of stainless steel X4Cr13 (SS) in sulphuric acid. They showed that there is a significant synergistic effect between TRITON-X-405 and KBr or C4H12NI. Polarization and electrochemical impedance spectroscopy (EIS) measurements Received: Revised: Accepted: Published: 5475

August 4, 2013 February 18, 2014 February 24, 2014 February 24, 2014 dx.doi.org/10.1021/ie402547m | Ind. Eng. Chem. Res. 2014, 53, 5475−5489

Industrial & Engineering Chemistry Research

Article

electrode specimens were polished with emery papers then degreased with acetone and washed with deionized water. After being weighed accurately, the specimens were immersed in hydrochloric acid solutions with and without addition of different concentrations of surfactants. The average weight losses of two parallel mild steel sheets were calculated. The weight-loss measurements and the corresponding corrosion rate were carried out as described according to the ASTM (G 01) standard. Surface tension measurements were made under atmospheric pressure by the ring method with a Krüss K12 tensiometer.30 The platinum ring was thoroughly cleaned and flame-dried before each measurement. Immersion corrosion analysis of mild steel samples in the acidic solutions with and without the optimal concentration of the inhibitors was performed using scanning electron microscopy (Hitachi S4160).

indicated that single TRITON-X-405 can relatively inhibit the corrosion of SS in 2.0 M H2SO4 (η% = 84−89) successfully. Nevertheless, the inhibition efficiencies markedly increased by the addition of KBr (η% = 91−95) and much more by addition of C4H12NI (η% = 97−99) into the 2.0 M H2SO4 containing TRITON- X-405. The data indicated that the inhibition efficiencies were increased with the help of synergistic effect between halide ions and TRITON-X-405. In similar research, the synergistic effect of mixed solutions of CTAB-TX100 and CTAB-TX305 was investigated, and the results exhibited a synergistic effect at low concentrations and an antagonistic effect at high concentrations.29 It was suggested that the synergistic effect is due to the additional interaction between the hydrocarbon chains of adsorbed TX molecules and adsorbed CTA+ ions. The antagonistic effect, which occurs at high concentrations, is believed to result from the formation of mixed micelles in the bulk solution. The synergistic effect of mixed surfactants as corrosion inhibitors of metal has not been widely studied. The objective of the present work was to study the synergistic effect of mixed surfactants on mild steel (MS). The purpose of this research is to maximize the surfactant adsorption onto MS while minimizing the aqueous surfactant concentration by using mixed anionic and cationic surfactants. Hence, in the present study, we investigated the inhibition and adsorption behaviors of SDS/CTAB with an excess of cationic or anionic surfactant in an aqueous solution of 2.0 M HCl on MS. Also, this research demonstrates for the first time the usefulness of regular solution theory for obtaining the nature and strength of interactions between surfactant mixtures on the metal surface.

3. THEORETICAL BACKGROUND 3.1. Approaches for Evaluating the Interaction Parameter in Mixed Adsorption Layers and Micelles: Model of Nonideal Interaction in Binary Surfactant Mixtures. When the values of β parameters are calculated using the nonideal interaction in binary surfactant mixtures (NIBSM) model of Rosen et al., the interaction strength between two surfactants in binary mixed systems can be determined.31−33 The mentioned parameter related to mixed monolayer formation at the solution−solid interface, βS, can be calculated according to eqs 1 and 2 (See Section S.1 of Supporting Information). Z12 ln(α1C12/Z1C10)

2. MATERIALS AND METHODS 2.1. Materials. Cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and hydrochloric acid (HCl) were prepared from Merck Company and used without purification. The mild steel sheets (composition: 0.081 wt % C, 0.020 wt % Si, 0.40 wt % Mn, 0.0098 wt % P, 0.0094 wt % S, 0.056 wt % Al, 0.031 wt % Ni, 0.0061 wt % Co, 0.028 wt % Cu; reminder was iron) of 1 × 1 × 1 cm3 were hand-polished successively using emery papers of grade 220, 600, 800, 1000, 1200, and finally 2000. The metal surface was degreased in acetone and rinsed with deionized water prior to each experiment. 2.2. Methods. Electrochemical experiments were carried out in a conventional three-electrode cell with a platinum counter electrode (CE) and an Ag/AgCl reference electrode. Impedance measurements were performed at open circuit potential (Eocp) with the AC voltage amplitude 10 mV in the frequency range from 100 kHz to 10 mHz. All the measurements were carried out after immersion time of 90 min with potentiostat/galvanostat EG&G model 273 connected with a personal computer. The potential of the potentiodynamic polarization curves was scanned from −250 mV versus OCP to 250 mV versus OCP at a sweep rate of 0.1 mV s−1. The OCP time was 30 min for our experimentation. A rotating disk electrode is a hydrodynamic working electrode used in a three-electrode system. The electrode rotates during experiments, inducing a flux of analyte to the electrode. These working electrodes are used in electrochemical studies when investigating reaction mechanisms related to the redox chemistry. The active geometrical surface area of a steel disk electrode was 0.12 cm2. Weight-loss measurements were performed using 1 × 1 cm2 mild steel sheets. Two steel

0 (1 − Z1)2 ln[(1 − α1)C12 /(1 − Z1)C20]

βS =

=1 (1)

0 ln(α1C12 /Z1C10)

(1 − Z1)2

(2)

where Z1 is the mole fraction of component 1 in mixed monolayer and C01, C02, and C012 are the molar concentrations in the aqueous phases containing components of surfactant 1, surfactant 2, and their mixture, respectively, at the mole fraction α1 of surfactant 1 required to have a specific inhibition efficiency (IE) value. In the present work, C01, C02, and C012 were determined to obtain IE = 55%. Equation 1 was numerically solved for Z1, which is then put into eq 2 to obtain βS. Similarly, the interaction parameter of mixed micelle formation in solution, βM, is obtained through eqs 3 and 4:31−33 M (X1M )2 ln(α1C12 /X1C1M) M (1 − X1M)2 ln[(1 − α1)C12 /(1 − X1M)C2M]

βM =

=1 (3)

M ln[α1C12 /X1C1M]

CM 1,

(1 − X1M)2

CM 2,

(4)

CM 12

where and are the critical micelle concentrations related to surfactant 1, surfactant 2, and their mixture, respectively, at the mole fraction α1 and XM 1 is the mole fraction of surfactant 1 in the total surfactant in the mixed micelle. Because the β parameter value is dependent upon the mixing free energy of the system, a negative β value shows an attractive interaction between two different surfactants that is stronger than that between surfactants of the same type and, in contrast, a weaker repulsive interaction between different surfactants 5476

dx.doi.org/10.1021/ie402547m | Ind. Eng. Chem. Res. 2014, 53, 5475−5489


Article

Figure 1. continued

5477



Article

Figure 1. Nyquist and Bode plots for mild steel in 2 M HCl solution containing (a) CTAB, (b) SDS, (c) CTAB/SDS 90:10, and (d) CTAB/SDS 10:90 at 298 K. 5478



Article

different concentrations. The high-frequency phase angle range (104−105 Hz) of the impedance spectra corresponds to the properties of an outer layer; the middle-frequency range (100− 104 Hz) reflects the properties of an inner barrier layer, while the low-frequency range (less than 100 Hz) corresponds to the properties of the double-electrical layer information. Increases in the high- and middle-frequency phase angle occurs with the high-frequency phase angle increases at higher inhibitor concentrations (especially for CTAB and mixtures). Thus, a more complex EEC was needed to analyze the impedance plots (Figure 2b) where Rs represents the ohmic resistance between the working and the reference electrode and Rct represents the charge transfer resistance related to the corrosion reaction at OCP. Rp can be prescribed to the pseudoresistance of the surface-adsorbed layer, and CPE1 is the capacitance of the electric double-layer at the electrode−electrolyte interface; the element CPE2 is its pseudocapacitance.36−38 A CPE was used instead of double-layer capacitance (Cdl) in the equivalent circuits in order to fit the data more accurately.39,40 Constant phase elements have been used extensively to account for deviations brought about by surface roughness. The impedance of CPE is given by eq 541

compared to that between pure surfactant components. Similarly, a positive value of β indicates that the attractive interaction between the two different surfactants is weaker than the attractive interaction between each type of surfactant and another molecule of the same type. In this work, negative value of the interaction parameter indicates the strength of the attractive interaction between two different surfactants compared to the self-attraction between the individual ones. An ideal mixing of two surfactants bears an interaction parameter near zero. The interaction parameter between surfactants is overwhelmed by the electrostatic interaction between the hydrophilic head groups of the two different surfactants.34 As can be easily seen, the interaction strength of two surfactants in a mixed monolayer of those surfactants at the surface depends upon the surface type and also the molecular medium (e.g., the temperature and ionic strength of the solution phase).

4. RESULTS AND DISCUSSION 4.1. Electrochemical Impedance Spectroscopy Measurements. The Nyquist and Bode plots of MS for CTAB, SDS, 90:10, and 10:90 CTAB/SDS mixtures are shown in Figure 1. The impedance diagrams show a capacitive loop that arises from the time constant of the electrical double layer and charge-transfer resistance in low concentrations. The plots obtained were not perfect semicircles at higher concentrations of the surfactants. This feature is attributed to frequency dispersion and inhomogeneity of the electrode surface arising from surface roughness or interfacial phenomena. When the surfactant concentrations are increased and also when they are mixed, aggregates start to form and change the processes of adsorption and desorption on the surface.35 In both cationicrich and anionic-rich mixtures, formation of aggregates occurs in lower concentrations. With regard to the bode plots, in the lower concentration of SDS, CTAB, and their mixtures, the impedance curves were fitted to the one time constant equivalent electrical circuits (EEC) (Figure 2a). In the higher concentration, deviation from

ZCPE =

1 1 × Y0 (jω)n

(5)

where Y0 is the magnitude of the CPE, n the CPE exponent (phase shift), and ω the angular frequency (ω = 2πf, where f is the AC frequency). Here, j is the imaginary unit. The correction of capacity to its real values is calculated from eq 6 Cdl = Y0(ωmax )n − 1

(6)

where ωmax is the frequency at which the imaginary part of impedance (Zim) has a maximum. The data are summarized in Table 1. Also, charge-transfer resistance was used to calculate the inhibition efficiency (η) and surface converge (θ) from the following equation:2 η(%) = θ × 100

(7)

R − R0 R

(8)

θ=

where R0 and R are charge-transfer resistances in the absence and presence of the inhibitor, respectively. As can be seen from Table 1, the R or η values increased while Cdl values decreased by addition of the surfactant concentration. The decrease in capacitance and increase of resistance can be attributed to the decrease in local dielectric constant and/or the increase in the thickness of the electrical double layer, signifying that the molecule acts by adsorption at the metal−solution interface.42 The change of R and Cdl values was caused by the gradual replacement of water molecules by adsorption of the inhibitor molecules on the metal surface, reducing the extent of acidic dissolution for the mild steel.43 Table 1 shows the inhibition efficiency for CTAB, SDS, 10:90 SDS/CTAB, and 10:90 CTAB/SDS mixtures. According to Figure 3, a curve with three regions was found. At low surfactant concentration, the slight increase in R is attributed to the adsorption of surfactants on MS. This adsorption is due to the electrostatic interaction between surfactant monomers and the solid surface. A decrease in the corrosion rate (or increase in R) was found as the surfactant concentration was increased. In this region, surfactant monomers begin to form surface aggregates and

Figure 2. Electrical equivalent circuit diagram used for modeling steel−solution interface in 2 M HCl solution in (a) low concentrations and (b) high concentrations of surfactants.

the semicircular may suggest formation of a more compact surface film. Also, the Bode plot exhibited two distinct capacitive time constants. This new time constant at higher frequencies could be related to formation of this film. The first time constant at high frequencies can be described by the charge transfer resistance (Rct), which corresponds to the electron-transfer reactions occurring in the mild steel−solution interface, and the other time constant at low frequencies is related to the film resistance (Rp), which can be ascribed to the adsorption of inhibitor and other accumulated kinds. The corresponding corrosion resistance is equivalent to the sum of the charge-transfer and layer resistance, R = Rct + RP. Figure 1 shows the changes of phase angle for different surfactants with 5479



Article

Table 1. Electrochemical Parameters of Impedance, Potentiodynamic Polarization Results, and the Corrosion Inhibition Efficiencies of Surfactants Concentration in HCl 2 M at 298 K 2 M HCl + x mM blank 1 5 10 30 50 100 150 200 x mM blank 1 5 10 30 50 100 400 1000 1200 1800 x mM blank 0.6 1 5 10 30 50 100 150 x mM blank 1 5 10 20 30 50 100 150 a

Cdl (× 105 F cm−2)

n

η%

icorr (μA cm−2)

26 − 48 67 − 86(15)a 159(55)a − 125(26)a

568 − 87 62 − 958(51)a 776(45)a − 604(51)a

0.82 − 0.79 0.81 − 0.74 0.57 − 0.62

− − 45 61 − 75 88(69)b − 83

678 456 423 338 228 196 63 117 96

26 − − − − 34 35 39 48(5)a 62(19)a 48(14)a

568 − − − − 496 412 163 413(170)a 370(153)a 356(161)a

0.82 − − − − 0.73 0.77 0.80 0.78 0.78 0.81

− − − − − 23 25 33 51 68(46)b 58

26 − − 130(88)a − − 221(41)a 99(44)a 148(14)a

568 − − 15(85)a − − 12(17)a 2.1(29)a 2.9(34)a

0.82 − − 0.64 − − 0.59 0.63 0.62

26.2 − 40.5 − − − 43.8 105.2(7.2)a 89.4(9.3)a

568 − 381 − − − 300 1.7(220)a 2.2(290)a

0.82 − 0.72 − − − 0.75 0.71 0.72

R (Ω cm2)

−E (mV)

IE %

bc (mVdec−1)

ba (mVdec−1)

409 429 431 435 436 437 434 432 435

− 33 38 50 66 71 91(53)b 83 86

161 146 128 167 154 166 202 146 161

91 124 110 148 126 118 139 119 91

678 570 535 481 468 409 399 258 148 159 164

409 407 432 417 414 425 434 437 436 439 437

− 16 21 29 46 40 41 62 78 76(49)b 76

161 126 146 117 148 141 117 127 141 112 132

91 95 79 101 84 96 93 88 74 91 86

− − − 88 − − 90(77)b 82 84

678 290 227 207 196 174 128 181 193

409 410 419 425 432 441 452 461 453

− 57 66 69 71 74 81(77)b 73 71

161 146 145 191 145 165 127 176 145

91 112 95 116 88 97 81 125 104

− − 35 − − − 40(26)b 77 73

678 357 366 389 326 275 290 272 240

409.53 422.74 429.12 425.39 420.98 426.74 468.39 452.64 448.49

− 47 46 43 52 60 57(33)b 60 65

161 144 127 133 141 145 151 135 160

91 88 92 119 107 91 93 103 119

× 103 CTAB

× 103 SDS

× 103 CTAB(90)/SDS(10)

× 103 CTAB(10)/SDS(90)

The values in parentheses are the parameters of the second time constant. bThe values are obtained by rotating disc electrode.

occurs at the critical micelle concentration of the surfactant systems, the CMC values of the surfactant systems were also determined through the impedance technique. The results are in agreement with the CMC values for these systems obtained using the surface tension technique (Figure 4 and Table 2). As shown in Table 1, the maximum inhibition efficiency of CTAB, 87.7%, was higher than the maximum inhibition efficiency of SDS, 67.8%. It can be shown that CTAB, which is a cationic surfactant, can absorb better and increase the inhibition efficiency more than an anionic surfactant (SDS) on the surface of the metal. This increase is due to a strong interaction between the polar head groups of the surfactant and the metal surface. The other reason is that hydrophobic chains of cationic surfactant are longer than SDS and cover the steel surface

colloids, including hemimicelles and admicelles because of hydrophobic interactions. As a result, the adsorption density or inhibition efficiency exhibits an increase in this region. Also, deviation from the semicircular suggests formation of a protective inhibitor film on the steel surface, especially at high concentrations. The second equivalent circuit with two time constants is appropriate for this behavior (Figure 2b). Table 1 also shows that as the surfactant concentration was further increased, the corrosion rate remained approximately constant. In some cases, the corrosion rate increased. When the surfactant reaches critical micelle concentration (CMC), the surfactant monomer activity becomes constant and further increase in the concentration contributes only to the micellization in solution. Because the maximum efficiency 5480



Article

Figure 3. Plot of inhibition efficiency versus total concentration for CTAB/SDS (10:90) at 298 K.

Figure 4. Surface tension versus total concentration in 2 M HCl solution at 298 K.

Table 2. Critical Micelle Concentration and Synergism Parameters of Mild Steel in HCl 2.0 M at 298 K

a

inhib. type

CMC (× 102 mM)a

CMC (× 102 mM)b

CMC (× 102 mM)c

βS

ZCTAB

βM

XCTAB

Save θ

CTAB SDS CTAB(90)/SDS(10) SDS(90)/CTAB(10)

9 79 4 21

10 120 5 10

10 100 5 15

− − −20.43 −5.81

− − 0.61 0.53

− − −7.67 −2.99

− − 0.72 0.49

− − 1.23 0.71

The values obtained from surface tension measurements. potentiodynamic polarization measurements.

b

The values obtained from EIS measurements. cThe values obtained from

cationic−anionic mixtures exhibited synergy at the solid−liquid interface. In our previous work,44 we showed that CTAB/SDS mixtures formed nano spherical and cylindrical aggregates in low concentrations because of attractive electrostatic interactions between their two oppositely charged polar groups. Hence, in 10:90 SDS/CTAB, more hemispheric and hemi spherical cylinder micelles can also be absorbed on the metal surface and enhance the inhibition efficiency (Table 1). Furthermore, Ducker et al.45 showed that cationic and zwitterionic surfactant mixtures form surface aggregates with a structure intermediate between the structures formed by each

more. Also, the low concentration of CTAB in comparison to that of SDS was used to obtain the maximum inhibition efficiency. An increase in inhibition efficiency was obtained in the cases of CTAB/SDS mixtures in comparison with SDS and CTAB used alone as the inhibitor. The 10:90 SDS/CTAB system provided the highest inhibition efficiency (90%) at very low concentration (C = 0.05 mM). This concentration was approximately equal to the CMC (Table 2) and two times lower than the CMC of CTAB. The maximum adsorption also occurred for 90:10 SDS/CTAB at low concentration compared to the adsorption of single surfactants (SDS). Adsorption of 5481



Article

Figure 5. Potentiodynamic polarization curves for mild steel in 2 M HCl solution without and with different concentrations of CTAB at 298 K.

Figure 6. Plot of inhibition efficiency versus total concentration in HCl 2 M solution at 298 K.

imental situations, the cathodic branch signifies the hydrogen evolution reaction, whereas the anodic branch represents the iron dissolution reaction. The values of associated electrochemical parameters, i.e., corrosion potential (Ecorr), corrosion current density (icorr), cathodic Tafel slopes (bc), anodic Tafel slopes (ba), and percentage of inhibition efficiency (IE %) values were calculated from the polarization curves and are listed in Table 1. The inhibition efficiency IE % was calculated from polarization measurements according to eq 9:35

of the pure surfactants. At higher concentrations of CTAB and in the case of mixture CTAB(10)/SDS(90), a decrease in n values was found. This phenomenon can be related to the change in the morphology of the electrode surface arising from surface heterogeneity, interfacial phenomena, and formation of large or nonspherical aggregates. 4.2. Tafel Polarization Measurements. Tafel polarization measurements were made to complement and confirm the data obtained from EIS measurements. From the present response recorded and using the electron-transfer-kinetic theory (Tafel theory),46 kinetic parameters associated with the rate of the corrosion reaction(s) were found in the presence and absence of cationic, anionic, and mixed surfactants. The potentiodynamic polarization curves for mild steel in 2 M HCl solution (in different concentrations of CTAB) at 298 K after immersion time of 90 min are shown in Figure 5 (color curves are in Section S.2 of Supporting Information). Under the exper-

IE(%) = θ × 100 θ=

/ icorr − icorr icorr

(9)

(10)

where icorr and i/corrare uninhibited and inhibited corrosion current densities, respectively, and are determined by 5482



Article

Figure 7. Plot of inhibition efficiency versus different inhibitors in Re = 0 and Re = 3256.

corrosion is the transfer of metal ions from the surface into the solution and the cathodic reaction is the reduction of hydrogen ions to produce hydrogen molecules or to reduce oxygen. An inhibitor usually affects the redox reactions.49 The surfactants anodic and cathodic Tafel slopes (ba and bc) were changed as the inhibitor concentration changed, implying the effect of inhibitor on both mentioned reactions.47 It is concluded that the reactions of cathodic hydrogen evolution and also anodic iron dissolution were both inhibited by the inhibitor through completely occupying the reaction sites of mild steel surface. Therefore, the mentioned compounds can be classified as mixed-type inhibitors.2 The inhibitory action of corrosion inhibitors is expressively explained through the adsorption mechanism. There are two paths by which an inhibitor can affect the corrosion rate: reducing the accessible reaction surface, the so-called geometric blocking effect, and changing the activation energy of redox reactions. Specifying the dominant contribution of the two mentioned effects is too difficult. No change of Ecorr is theoretically observed after the corrosion inhibitor addition if the geometric blocking effect is dominant compared to the energy effect.50 No change in Ecorr upon surfactant addition implies that the geometric blocking contribution is more effective compared that of the energy effect.50 We also used the rotating disc electrode (RDE) to investigate the stability of systems studied. For optimized concentrations of CTAB, SDS, and their mixtures, electrochemical impedance and Tafel polarization measurements were carried out with the rotating electrode. Experiments performed within the RDE rotation in 700 rpm A rotating disk electrode (RDE) give the arrangement that allows the electrolyte to get transported first perpendicularly to the electrode surface and then to flow over the surface in a circular-parallel pattern. The RDE configuration also permits excellent control of the electrolyte hydrodynamics and is frequently used in electrode kinetics and mass-transport electrochemical studies. Reynolds number (Re) for the RDE was calculated using the following equation:17

extrapolation of Tafel lines to the respective corrosion potentials. It can be observed from Figure 6 that IE % increased with increase in the inhibitor concentration until it reached a maximum value corresponding to the critical micelle concentration (Table 2). These results also confirm the findings obtained from EIS measurements. As described in the previous section, the protective behavior of SDS, CTAB, and their mixtures can be explained by adsorption of surfactant on the metal surface. At low surfactant concentration, the surfactant monomers are individually adsorbed on the surface with a low coverage percentage. As surfactant concentration increases, the amount adsorbed increases leading to a higher degree of coverage and consequently higher corrosion inhibition. At higher surfactant concentration (C > CMC), the efficiency is reduced. This behavior may be due to saturation of the surfactant adsorbed layer and formation of free micelles. An increase in inhibition efficiency was also obtained in the cases of CTAB/SDS mixtures in 2 M HCl solutions in comparison with SDS and CTAB alone in acidic solutions. According to Table 1 and polarization measurements, the efficiency of mixed surfactants at low concentration is higher than that of pure surfactants in both cationic-rich and anionicrich mixtures, while at higher concentrations, the efficiency of mixed systems is higher than CTAB and SDS in cationic-rich only mixtures. The corrosion potential did not obviously change before and after addition of CTAB, SDS, and their mixtures, suggesting that the compounds act as a mixed-type inhibitor and the inhibition action is caused by the geometric blocking effect. Similar results have been reported elsewhere for other organic compounds in HCl solution.47,48 Moreover, the corrosion potential of the inhibitor-containing solution nearly equals that in the solution without the inhibitor, indicating that the inhibition effect is caused by the adsorbed inhibiting species. As shown in Table 1, it is clear that an increase in the amounts of CTAB, SDS, and their mixtures led to a decrease in current densities. This shows that the addition of surfactants reduces anodic dissolution and also retards the hydrogen evolution reaction, which indicates that these surfactants are mixed-type inhibitors and control both the anodic and cathodic reactions (Section S.3 of Supporting Information).7 The Tafel slope values (ba, bc) change as the surfactant concentration is changed. In acidic solutions, the oxidation

Re =

r 2ω v

(11)

where r is the radius of the RDE electrochemically active surface area (cm), ω the angular velocity (rad s−1), and v the 5483



Article

Figure 8. Flory−Huggins adsorption plots for mild steel in 2.0 M HCl solution at 298 K in different concentrations of pure and mixed surfactants.

electrolyte kinematic viscosity (cm2 s−1). Because the Reynolds number for the transition from laminar to turbulent flow is Re > 105, the low Reynolds number (Re = 3256) shows that EIS experiments were made in the laminar flow regime. With an increase in Re from (Re = 0) to (Re = 3256), the corresponding inhibition efficiency decreases for CTAB, SDS, and SDS(90)/ CTAB(10), whereas the inhibition efficiency of CTAB(90)/ SDS(10) does not change significantly. At high rotations, inhibitors cannot adsorb well on the solid surface and effect on IE except CTAB(90)/SDS(10) mixed system. Comparison to the results in Figure 7, in cationic-rich mixture, the protective film formed under this condition on the surface is much more stable than that formed in other systems. The results are in agreement with other works.17,37 As shown in Table 1 and Figure 7, using a rotating electrode reduces inhibition efficiency between 15 and 20%; therefore, the surfactants are rather stable in a perturbed medium and can be used as good inhibitors in such systems. 4.3. Surfactant−Surfactant Interaction in Micellar Phase and Monolayer at Liquid−Solid Interface. In this work, C01, C02 and C012 were determined that correspond to a corrosion current of IE = 55% or icorr = 300 μA cm−2 (see Figure 6). The interaction between two different surfactant components in the mixed monolayer formed on metallic medium and also in mixed micellar system was investigated using the approaches defined in Theoretical Background. In the NIBSM model, the interaction parameter was obtained using eqs 2 and 4 as shown in Table 2. As mentioned before, the interaction parameter value is taken into account as an index of interaction strength between two surfactants. The obtained values of the surface interaction parameter, βS, were negative, indicating a strong synergism between surfactants at the liquid−solid interface in the mixed monolayer. Additionally, the βS and βM values were both negative, indicating that the interaction between CTAB and SDS after mixing is more attractive than that before mixing. The ionic surfactant molecules, CTAB or SDS, have a strong electrostatic selfrepulsion in pure solution. Calculations using Rubingh’s regular solution theory reveal that the βS value is more negative than βM, indicating a synergism in the solid−aqueous solution interface that is stronger than that of the mixed micelle. This corresponds with the prediction that interacting hydrophobic

groups will be more easily accommodated at the planar solid− aqueous solution interface compared to the interior of a spherical or cylindrical micelle or the curved micelle surface. As shown in Table 1, the corrosion inhibition efficiencies for solutions of mixed surfactants are higher than those of pure solutions. This reflects that the CTAB/SDS system has a synergistic effect on the corrosion process of mild steel in 2.0 M HCl solution. This can be explained by the strong adsorption of CTAB/SDS on the metal surface.41,51 The inhibitor molecules are then adsorbed by columbic attraction on the metal surface. Stabilization of the adsorbed inhibitor leads to greater surface coverage and thereby greater inhibition. According to Table 2, ZCTAB and XCTAB decrease slightly, which can be attributed to the strong interaction between surfactants in mixed micelles and monolayer. We also calculated the synergism parameters using the relationship given by Aramaki and Hackerman as shown by the following equation:52 Sθ =

1 − θ1 + 2 1 − θ1/+ 2

θ1 + 2 = (θ1 + θ2) − (θ1θ2)

(12) (13)

θ/1+2

where θ1, θ2, and are the surface coverage by CTAB, SDS, and both CTAB and SDS, respectively. Average values of the synergism parameters (Sθave) for both the cationic-rich and anionic-rich regions of mixed surfactants are given in Table 2. Generally, Sθ < 1 implies that antagonistic behavior prevails, which may lead to competitive adsorption, whereas Sθ > 1 indicates a synergistic effect.41 The mixed surfactants enhance stability of the inhibitor on the metal surface by a coadsorption mechanism, which may be either competitive or cooperative. For competitive adsorption, the anion and cation inhibitors are adsorbed at different sites on the metal surface. In cooperative adsorption, the anion is chemisorbed on the metal surface and the cation is adsorbed on a layer of the anion and vice versa. Both competitive and co-operative mechanisms may occur simultaneously.41 4.4. Adsorption Isotherm. It has been understood that surfactants and their mixtures establish their inhibition action using adsorption of the inhibitor onto the metal surface. The potency of surfactants as an effective corrosion inhibitor mainly depends on their adsorption ability at the metal−solution 5484



Article

Figure 9. Arrhenius plots for mild steel in 2.0 M HCl solution without and with surfactants.

can be concluded that mixed surfactants have greater values than pure surfactants, which can be a result of more attraction between head groups and the fact that more inhibitors can be adsorbed on the surface. The negative value of ΔG0ads shows a strong interaction of the inhibitor molecule onto the mild steel surface. It has been accepted that the values of ΔG0ads on the order of −20 kJ mol−1 or less negative are associated with an electrostatic interaction between the charged inhibitor molecules and the charged metal surface (physical adsorption); those of −40 kJ mol−1 or more negative involve charge distribution or transfer from the inhibitor molecules to the metal surface to form a coordinate covalent bond (chemical adsorption).35,41 The values of ΔG0ads suggest a combination of both physisorption and chemisorptions occurs on the surface, with predominant control by chemical adsorption.35 The data of |ΔG0ads| showed that mixed surfactants have standard free energy of adsorption that is greater than that of pure surfactants because of strong interaction between oppositely charged surfactants. 4.5. Effect of Temperature. The temperature range from 298 to 338 K in the presence of 0.1, 1.2, and 0.005 mM of CTAB, SDS, and 90:10 CTAB/SDS solutions was studied. Comparing the activation energy in the presence and absence of the inhibitor helps us to study the effect of temperature on the corrosion parameter. The Arrhenius plot was used to determine the activation energy (Ea), activation enthalpy (ΔHa), and activation entropy (ΔSa) for the corrosion of mild steel in 2.0 M HCl. The activation energy can be obtained using the following equation:41

interface that takes place through the substitution of water molecules by inhibitors. Therefore, it is essential to understand the mode of adsorption and the adsorption isotherm.41 Generally, two modes of adsorption can be considered. Physical adsorption requires the presence of electrically charged metal surface and charged species within the bulk of the solution. The chemisorption process involves charge transfer from the inhibitor molecules to the metal surface. The presence of related molecules having comparatively loosely bound electrons or heteroatoms with lone-pair electrons with a transition metal having a vacant and low-energy electron orbital facilitates this adsorption. To better understand the adsorption mechanism, the following Flory−Huggins isotherm equation was used:41 ⎛ θ ⎞ log⎜ ⎟ = log(xK ads) + x log(1 − θ ) ⎝ C inh ⎠

(14)

where θ is the surface coverage, which was determined from the polarization measurements and Cinh is the molar concentration of the inhibitor. Kads is the standard adsorption equilibrium constant, related to the standard free energy of adsorption (ΔG0ads) by the following equation: 0 ΔGads = −RT ln(55.5K ads)

(15)

where R is the universal gas constant and T is the absolute temperature. According to the Flory−Huggins model, plots of log (θ/Cinh) versus log (1 − θ) produce straight lines of slope x and intercept log (xKads), as shown in Figure 8.53,54 The data indicate that the values of x were approximately 2 with pure surfactants and around 7 and 12 with mixed surfactants. This suggests that one molecule of CTAB or SDS adsorbed on the metal surface replaces 2 water molecules. However, in mixed systems, the ion pair of CTAB and SDS replaces 7 and 12 water molecules in anionic-rich and cationic-rich regions, respectively, with the help of a synergistic effect between the two ionic surfactants. The results are in agreement with the synergistic effect between KBr and TRITON-X-405, which was studied by Godec.18 From eq 15, the calculated ΔG0ads values in the presence of CTAB, SDS, 90:10 CTAB/SDS, and 90:10 SDS/CTAB were −41.66, −31.88, −45.56, and −43.86 kJ mol−1, respectively. The high amounts of standard adsorption equilibrium indicated the high adsorption ability of surfactants on the steel surface. It

⎛ E ⎞ icorr = A exp⎜ − a ⎟ ⎝ RT ⎠

(16)

where icorr is corrosion current, A the constant, Ea the activation energy of the metal dissolution reaction, R the gas constant, and T the temperature. The Ea value can be determined from the slopes of the plot of ln (icorr) against 1/T (Figure 9). Furthermore, the Arrhenius equation can be renewed an alternative equation as follows:41,55 icorr =

⎛ ΔS ⎞ ⎛ −ΔHa ⎞ RT ⎟ exp⎜ a ⎟ exp⎜ ⎝ R ⎠ ⎝ RT ⎠ hN

(17)

where N is Avogadro’s constant, h Plank’s constant, ΔSa the entropy of activation, and ΔHa the enthalpy of activation. A 5485



Article

plot of ln (icorr/T) against 1/T (Section S.4 of Supporting Inoformation) should give a straight line with a slope of (ΔHa/ R) and intercept of [ln (R/Nh) + (ΔSa/R)]. Ea, ΔHa, and ΔSa were calculated and tabulated in Table 3. As can be seen in

Table 4. Weight-Loss Results of Mild Steel Corrosion without and with Different Concentrations of Surfactants at 298 K inhib. type

Table 3. Calculated Thermodynamic Parameters of Adsorption (Activation Energy Ea, Enthalpy ΔHa, and Entropy ΔSa) in the Absence and Presence of Different Surfactants inhib. type blank CTAB SDS CTAB(90)/ SDS(10)

blank CTAB SDS

con. (mM × 103)

Ea (kJ mol−1)

ΔHa (kJ mol−1)

ΔSa (J mol−1 K−1)

− 100 120 5

60.94 66.65 63.68 71.32

55.25 64.02 58.22 71.23

−124.23 −107.25 −118.64 −76.32

CTAB(90)/ SDS(10) CTAB(10)/ SDS(90)

Table 3, the activation energy increases in the presence of the inhibitor. The increasing activation energy in the presence of inhibitor indicates that physical adsorption (electrostatic) occurs in the first stage.56,57 The Ea value is greater than 20 kJ mol−1 in both the presence and absence of the inhibitor, which reveals that the entire process is controlled by the surface reaction.58 The values of ΔHa and Ea are nearly the same and are higher in the presence of the surfactants. This indicates that the energy barrier of the corrosion reaction increases in the presence of the inhibitor without changing the mechanism of dissolution. The entropy of activation ΔSa in the absence and presence of the inhibitor is negative and tends to become positive in mixed surfactants.59 4.6. Weight Loss. Weight-loss tests were carried out by weighing the mild steel specimens before and after immersion in 50 mL acid solutions without and with surfactants for 270 min at 25 °C. The corrosion rate (W) and the percentage protection efficiency IEw (%) were calculated according to the following equations:60,61

W = Δm /St IE w (%) =

corrosion rate, W (g cm−2 h−1)

inhibition efficiency, IEW (%)

− 5 50 5 50 5

0.0131 0.0084 0.0076 0.0106 0.0099 0.0076

− 36.19 41.52 19.04 24.57 41.71

50 5

0.0073 0.0084

44.01 36.19

50

0.0081

38.47

possible reason may be due to the difference in immersion time. Similar observation has been reported by several authors.60,62 4.7. Scanning Electron Microscopy (SEM). The morphologies of mild steel surface immersed in the corrosion solution in the absence and presence of CTAB, SDS, and their mixture at 298 K after immersion time of 90 min are displayed in Figure 10. It can be observed that the mild steel surface was damaged in the absence of inhibitor (Figure 10a), while the mild steel surface exposed to different kinds of surfactants was smooth (Figure 10b−d). This is could be due to the involvement of the inhibitor molecules in the interaction with the reaction sites of iron surface.2,43 It can be concluded from Figure 10 that corrosion occurs slowly in the presence of an inhibitor; hence, corrosion was inhibited when the inhibitor was present in the hydrochloric acid.63

5. CONCLUSION The corrosion of MS in 2 M HCl solution can be inhibited by the use of CTAB, SDS, and their mixtures. CTAB/SDS 90:10 mixtures showed a very high inhibitive efficiency for MS in 2 M HCl solution. The principal conclusions are as follows: (1) CTAB, SDS, and their mixtures inhibit both anodic and cathodic reactions by adsorption on the MS surface and hence behave like mixed-type inhibitors. (2) Compared to the adsorption of single surfactants, adsorption of mixtures of SDS/CTAB exhibit synergism at interfaces. As a new approach, we stressed the potential significance of regular solution theory in the quantitative interpretation of the interaction between the two surfactants at the solid−liquid interface. (3) The driving force for adsorption of surfactants and their mixtures at the solid−liquid interface is a combination of electrostatic and chain−chain interactions. (4) The impedance and polarization curves show that the inhibition efficiency of the studied systems increases with increase in the concentration of surfactant until it reaches a maximum value around their CMC. (5) The adsorption model obeys to the Flory−Huggins adsorption isotherm, and the high negative values of the Gibbs free energy suggest chemical adsorption ability of surfactants on steel surface. (6) The SEM images reveal a good inhibition on the surface and confirm the highest inhibition efficiency of mixed surfactants.

(18)

W0 − W × 100 W0

conc. (× 103 mM)

(19)

where Δm (g) is the mass loss, S (cm ) the area, and t (h) the immersion period; W0 (g cm−2 h−1) and W (g cm−2h−1) are the corrosion rates of mild steel without and with the inhibitor, respectively. As shown in Table 4, the surfactants inhibit the corrosion of mild steel at all concentrations in 2 M HCl. In both static and flow conditions, results reveal that the inhibition efficiency increases with increasing the concentration of the inhibitors and that mixed surfactants are better inhibitors than both CTAB and SDS. The inhibition efficiency values in the absence and presence of different concentrations of CTAB, SDS, and their mixtures, which were calculated from weightloss measurements, are compared with electrochemical methods. It was also concluded that mixed cationic-rich surfactants are more stable on the surface than other systems and can be used as good inhibitors in both static and flow conditions. However, the exact values of inhibition efficiency obtained by the two measurements remain different. The difference can be attributed to the fact that the weight-loss method gives average corrosion rates, whereas the electrochemical method gives instantaneous corrosion rates. Another 2

5486



Article

Figure 10. SEM images for the mild steel surface in 2 M HCl (a) without surfactant, (b) with 0.05 mM of CTAB, (c) with 0.05 mM of SDS, and (d) with 0.05 mM of 90:10 CTAB/SDS.

■

(9) Likhanova, N. V.; Domínguez-Aguilar, M. A.; Olivares-Xometl, O.; Nava-Entzana, N.; Arce, E.; Dorantes, H. The effect of ionic liquids with imidazolium and pyridinium cations on the corrosion inhibition of mild steel in acidic environment. Corros. Sci. 2010, 52, 2088. (10) Singh, A. K.; Quraishi, M. A. The effect of some bis-thiadiazole derivatives on the corrosion of mild steel in hydrochloric acid. Corros. Sci. 2010, 52, 1373. (11) Amin, M. A.; Ibrahim, M. M. Corrosion and corrosion control of mild steel in concentrated H2SO4 solutions by a newly synthesized glycine derivative. Corros. Sci. 2011, 53, 873. (12) Li, X.; Deng, S.; Fu, H. Benzyltrimethylammonium iodide as a corrosion inhibitor for steel in phosphoric acid produced by dihydrate wet method process. Corros. Sci. 2011, 53, 664. (13) Elachouri, M.; Hajji, M. S.; Kertit, S.; Essassi, E. M.; Salem, M.; Coudert, R. Some surfactants in the series of 2-(alkyldimethylammonio) alkanol bromides as inhibitors of the corrosion of iron in acid chloride solution. Corros. Sci. 1995, 37, 381. (14) Qiu, L. G.; Xie, A. J.; Shen, Y. H. The adsorption and corrosion inhibition of some cationic gemini surfactants on carbon steel surface in hydrochloric acid. Corros. Sci. 2005, 47, 273. (15) Xiao-Ci, Y.; Hong, Z.; Ming-Dao, L.; Hong-Xuan, R.; Lu-An, Y. Quantum chemical study of the inhibition properties of pyridine and its derivatives at an aluminum surface. Corros. Sci. 2000, 42, 645. (16) Schweinsberg, D. P.; Ashworth, V. The inhibition of the corrosion of pure iron in 0.5 M sulphuric acid by n-alkyl quaternary ammonium iodides. Corros. Sci. 1988, 28, 539. (17) Ghareba, S.; Omanovic, S. The effect of electrolyte flow on the performance of 12-aminododecanoic acid as a carbon steel corrosion inhibitor in CO2-saturated hydrochloric acid. Corros. Sci. 2011, 53, 3805. (18) Fuchs-Godec, R. Effects of surfactants and their mixtures on inhibition of the corrosion process of ferritic stainless steel. Electrochim. Acta 2009, 54, 2171. (19) Badawi, A. M.; Hegazy, M. A.; El-Sawy, A. A.; Ahmed, H. M.; Kamel, W. M. Novel quaternary ammonium hydroxide cationic surfactants as corrosion inhibitors for carbon steel and as biocides for sulfate reducing bacteria (SRB). Mater. Chem. Phys. 2010, 124, 458.

ASSOCIATED CONTENT

S Supporting Information *

Detailed explanations about surfactant−surfactant interaction (Section S.1), color plots for potentiodynamic polarization curves (Section S.2), mechanism of corrosion inhibition (Section S.3), and plot of ln (icorr/T) versus 1/T in HCl 2 M solution (Section S.4). This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 0098(21)82883455. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Deng, S.; Li, X.; Fu, H. Alizarin violet 3B as a novel corrosion inhibitor for steel in HCl, H2SO4 solutions. Corros. Sci. 2011, 53, 3596. (2) Wang, X.; Yang, H.; Wanga, F. A cationic gemini-surfactant as effective inhibitor for mild steel in HCl solutions. Corros. Sci. 2010, 52, 1268. (3) Ghareba, S.; Omanovic, S. 12-Aminododecanoic acid as a corrosion inhibitor for carbon steel. Electrochim. Acta 2011, 56, 3890. (4) Shein, A. B.; Denisova, A. V. Choice of effective corrosion inhibitors for acid treatment of wells. Prot. Met. 2006, 42, 34. (5) Deng, S.; Li, X.; Fu, H. Acid violet 6B as a novel corrosion inhibitor for cold rolled steel in hydrochloric acid solution. Corros. Sci. 2011, 53, 760. (6) Ebenso, E. E.; Oguzie, E. E. Corrosion inhibition of mild steel in acidic media by some organic dyes. Mater. Lett. 2005, 59, 2163. (7) Zhang, Q. B.; Hua, Y. X. Corrosion inhibition of mild steel by alkylimidazolium ionic liquids in hydrochloric acid. Electrochim. Acta 2009, 54, 1881. (8) Zhang, Q.; Hua, Y. Corrosion inhibition of aluminum in hydrochloric acid solution by alkylimidazolium ionic liquids. Mater. Chem. Phys. 2010, 119, 57. 5487



Article

(20) Rehim, S. S. A. E.; Hassaan, H. H.; Amin, M. A. The corrosion inhibition study of sodium dodecylbenzene sulphonate to aluminium and its alloys in 1.0 M HCl solution. Mater. Chem. Phys. 2002, 78, 337. (21) Maayta, A. K.; Al-Rawashdeh, N. A. F. Inhibition of acidic corrosion of pure aluminum by some organic compounds. Corros. Sci. 2004, 46, 1129. (22) Saleh, M. M.; Atia, A. A. Effects of structure of the ionic head of cationic surfactant on its inhibition of acid corrosion of mild steel. J. Appl. Electrochem. 2006, 36, 899. (23) Atia, A. A.; Saleh, M. M. Inhibition of acid corrosion of steel in cetylpyridinium chloride. J. Appl. Electrochem. 2003, 33, 171. (24) El-Sherbini, E. E. F.; Abd-El-Wahab, S. M.; Deyab, M. A. Studies on corrosion inhibition of aluminum in 1.0 M HCl and 1.0 M H2SO4 solutions by ethoxylated fatty acids. Mater. Chem. Phys. 2003, 82, 631. (25) Branzoi, V.; Golgovici, F.; Branzoi, F. Aluminium corrosion in hydrochloric acid solutions and effect of some organic inhibitors. Mater. Chem. Phys. 2002, 78, 122. (26) Li, X.; Deng, S.; Fu, H. Inhibition by tetradecylpyridinium bromide of the corrosion of aluminium in hydrochloric acid solution. Corros. Sci. 2011, 53, 1529. (27) Vasudevan, T.; Muralidharan, S.; Alwarappan, S.; Iyer, S. V. K. The influence of N-hexadecyl benzyl dimethyl ammonium chloride on the corrosion of mild steel in acids. Corros. Sci. 1995, 37, 1235. (28) Fuchs-Godec, R.; Pavlovic, M. G. Synergistic effect between non-ionic surfactant and halide ions in the forms of inorganic or organic salts for the corrosion inhibition of stainless steel X4Cr13 in sulphuric acid. Corros. Sci. 2012, 58, 192. (29) Huang, Z.; Gu, T. Mixed Adsorption of Nonionic and Cationic Surfactants on Silica Gel and Methylated Silica Gel. Colloids Surf. 1987, 28, 159. (30) Ruiz, C. C.; Molina-Boliver, J. A.; Aguiar, J.; Macisaac, G.; Moroze, S.; Palepu, R. Thermodynamic and structural studies of Triton X-100 micelles in ethylene glycol−water mixed solvents. Langmuir 2001, 17, 6831. (31) Rosen, M. J.; Hua, X. Y. Surface Concentrations and Molecular Interactions in Binary Mixtures of Surfactants. J. Colloid Interface Sci. 1981, 86, 164. (32) Rosen, M. J.; Zhou, Q. Surfactant−Surfactant Interactions in Mixed Monolayer and Mixed Micelle Formation. Langmuir 2001, 17, 3532. (33) Zhou, Q.; Rosen, M. J. Molecular interactions of surfactants in mixed monolayers at the air/aqueous solution interface and in mixed micelles in aqueous media: The regular solution approach. Langmuir 2003, 19, 4555. (34) Rosen, M. J. Synergism in mixtures containing zwitterionic surfactants. Langmuir 1991, 7, 885. (35) Deyaba, M. A.; El-Rehimb, S. S. A.; Keeraa, S. T. Study of the effect of association between anionic surfactant and neutral copolymer on the corrosion behaviour of carbon steel in cyclohexane propionic acid. Colloids Surf., A 2009, 348, 170. (36) Felhosi, I.; Telegdi, J.; Palinkas, G.; Kalman, E. Kinetics of selfassembled layer formation on iron. Electrochim. Acta 2002, 47, 2335. (37) Alexiadis, A.; Cornell, A.; Dudukovic, M. P. Comparison between CFD calculations of the flow in a rotating disk cell and the Cochran/Levich equations. J. Electroanal. Chem. 2012, 669, 55. (38) Georges, C.; Rocca, E.; Steinmetz, P. Synergistic effect of tolutriazol and sodium carboxylates on zinc corrosion in atmospheric conditions. Electrochim. Acta 2008, 53, 4839. (39) Khaled, K. F. Corrosion control of copper in nitric acid solutions using some amino acids − A combined experimental and theoretical study. Corros. Sci. 2010, 52, 3225. (40) Behpour, M.; Ghoreishi, S. M.; Soltani, N.; Salavati-Niasari, M. The inhibitive effect of some bis-N,S-bidentate Schiff bases on corrosion behaviour of 304 stainless steel in hydrochloric acid solution. Corros. Sci. 2009, 51, 1073. (41) Musa, A. Y.; Mohamad, A. B.; Kadhum, A. A. H.; Takriff, M. S.; Tien, L. T. Synergistic effect of potassium iodide with phthalazone on the corrosion inhibition of mild steel in 1.0 M HCl. Corros. Sci. 2011, 53, 3672.

(42) Mcafferty, E.; Hackerman, N. Double layer capacitance of iron and corrosion inhibition with polymethylene diamines. J. Electrochem. Soc. 1972, 119, 146. (43) Muralidharan, S.; Phani, K. L. N.; Pitchumani, S.; Ravichandran, S.; Iyer, S. V. K. Polyamino-Benzoquinone Polymers: A New Class of Corrosion Inhibitors for Mild Steel. J. Electrochem. Soc. 1995, 142, 1478. (44) Yousefi, A.; Javadian, S.; Gharibi, H.; Kakemam, J.; RashidiAlavijeh, M. Cosolvent Effects on the Spontaneous Formation of Nanorod Vesicles in Catanionic Mixtures in the Rich Cationic Region. J. Phys. Chem. B 2011, 115, 8112. (45) Ducker, W. A.; Wanless, E. J. Surface-Aggregate Shape Transformation. Langmuir 1996, 12, 5919. (46) Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, 2nd ed.; Wiley: New York, 2001. (47) Bentiss, F.; Traisnel, M.; Lagrenee, M. The substituted 1, 3, 4oxadiazoles: A new class of corrosion inhibitors of mild steel in acidic media. Corros. Sci. 2000, 42, 127. (48) Elkadi, L.; Marnari, B.; Traisnel, M.; Bentiss, F.; Lagrenee, M. The inhibition action of 3,6-bis(2-methoxyphenyl)-1,2-dihydro1,2,4,5-tetrazine on the corrosion of mild steel in acidic media. Corros. Sci. 2000, 42, 703−719. (49) Mayanna, S. M. Adsorption isotherm of iodide ions on copper single crystal planes in sulfuric acid. J. Electrochem. Soc. 1975, 122, 251. (50) Musa, A. Y.; Kadhum, A. A. H.; Mohamad, A. B.; Takriff, M. S.; Daud, A. R.; Kamarudin, S. K. On the inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol. Corros. Sci. 2010, 52, 526. (51) Rehim, S. S. A.; Hazzazi, O. A.; Amin, M. A.; Khaled, K. F. On the corrosion inhibition of low carbon steel in concentrated sulphuric acid solutions. Part I: Chemical and electrochemical (AC and DC) studies. Corros. Sci. 2008, 50, 2258. (52) Aramaki, K.; Hackerman, N. Inhibition mechanism of mediumsized polymethyleneimine. J. Electrochem. Soc. 1969, 116, 568. (53) Solmaz, R.; Sahin, E. A.; Döner, A.; Kardas, G. The investigation of synergistic inhibition effect of rhodanine and iodide ion on the corrosion of copper in sulphuric acid solution. Corros. Sci. 2011, 53, 3231. (54) Obot, I. B.; Obi-Egbedi, N. O.; Umoren, S. A. The synergistic inhibitive effect and some quantum chemical parameters of 2,3diaminonaphthalene and iodide ions on the hydrochloric acid corrosion of aluminum. Corros. Sci. 2009, 51, 276. (55) Amin, M. A.; Ibrahim, M. M. Corrosion and corrosion control of mild steel in concentrated H2SO4 solutions by a newly synthesized glycine derivative. Corros. Sci. 2011, 53, 837. (56) Solmaz, R.; Kardas, G.; Yazıcı, B.; Erbil, M. Adsorption and corrosion inhibitive properties of 2-amino-5-mercapto-1,3,4-thiadiazole on mild steel in hydrochloric acid media. Colloids Surf., A 2008, 312, 7. (57) Ashassi-Sorkhabi, H.; Shaabani, B.; Seifzadeh, D. Effect of some pyrimidinic Shciff bases on the corrosion of mild steel in hydrochloric acid solution. Appl. Surf. Sci. 2005, 50, 3446. (58) Moretti, G.; Guidi, F.; Grion, G. Tryptamine as a green iron corrosion inhibitor in 0.5 M deaerated sulphuric acid. Corros. Sci. 2004, 46, 387. (59) Ouali, I. E.; Hammouti, B.; Aouniti, A.; Ramli, Y.; Azougagh, M.; Essassi, E. M.; Bouachrine, M. Thermodynamic characterisation of steel corrosion in HCl in the presence of 2- phenylthieno (3, 2-b) quinoxaline. J. Mater. Environ. Sci. 2010, 1, 1. (60) Abboud, Y.; Abourriche, A.; Saffaja, T.; Berrada, M.; Charrouf, M.; Bennamara, A.; Hannache, H. A novel azo dye, 8-quinolinol-5azoantipyrine as corrosion inhibitor for mild steel in acidic media. Desalination 2009, 237, 157. (61) Tebbji, K.; Bouabdellah, I.; Aouniti, A.; Hammouti, B.; Oudda, H.; Benkaddour, M.; Ramdani, A. N-Benzyl-N,N-bis[(3,5-dimethyl1H-pyrazol-1-yl)methyl]amine as corrosion inhibitor of steel in 1 M HCl. Mater. Lett. 2007, 61, 799. (62) El-Sherbini, E. E. F.; Abd-El-Wahab, S. M.; Deyab, M. A. Mater. Chem. Phys. 2003, 75, 82. 5488



Article

(63) Prabhu, R. A.; Venkatesha, T. V.; Shanbhag, A. V.; Kulkarni, G. M.; Kalkhambkar, R. G. Inhibition effects of some Schiff’s bases on the corrosion of mild steel in hydrochloric acid solution. Corros. Sci. 2008, 50, 3356.

5489


A New Approach to Study the Synergistic Inhibition Effect of Cationic

Recommend Documents