Task-specific ionic liquids as corrosion inhibitors on carbon steel in 0.5 M HCl solution: An experimental and theoretical study

Corrosion Science 153 (2019) 301–313

Contents lists available at ScienceDirect

Corrosion Science journal homepage: www.elsevier.com/locate/corsci

Task-specific ionic liquids as corrosion inhibitors on carbon steel in 0.5 M HCl solution: An experimental and theoretical study ⁎⁎

Shuyun Caoa, Dan Liub, , Hui Dingc, Jinghui Wangb, Hui Lud, Jianzhou Guia,b,

T

⁎

a State Key Laboratory of Separation Membranes and Membrane Processes & School of Material Science and Engineering, Tianjin Polytechnic University, Tianjin, 300387, PR China b School of Chemistry and Chemical Engineering & Tianjin Key Laboratory of Green Chemical Technology and Process Engineering, Tianjin Polytechnic University, Tianjin, 300387, PR China c School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, PR China d State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: Ionic liquid Corrosion Acid inhibition Brønsted acid Carbon steel

This study investigated corrosion inhibition of task-specific ionic liquids, 1-(4-sulfonic acid) butyl-3-ethyl imidazolium hydrogen sulfate and 1-(4-sulfonic acid) butyl-3-decyl imidazolium hydrogen sulfate, for carbon steel in 0.5 M HCl by electrochemical tests, SEM, UV–vis, XPS, contact angle measurements, molecular orbital theory, and MD simulations. The inhibition efficiency of both ionic liquids increased with concentration, and the latter one shows higher inhibition efficiency of 97.9% due to the weaker hydrophilicity caused by increased alkyl tail. The mechanism of inhibition was found to be through adsorption onto the steel surface with cycling donation and back-donation of electrons.

1. Introduction Metal corrosion in any environment is inevitable given the rules of thermodynamics; however, corrosion can be mitigated. Reducing corrosion of metal is crucial for many industrial applications. Acid solutions are aggressive media that are extensively used the industries of oil well acidification, chemical cleaning and processing, and pickling, etc. [1]. Various corrosion prevention measures exist, including corrosion inhibition, coating, cathodic or anodic protection, metal selection, and design improvement. Corrosion inhibition is widely used in various fields because of its low cost, high efficiency, and easy operation [2–5]. Organic corrosion inhibitors generally act by adsorption onto the metal surface through heteroatoms with O, N, P, and S in a conjugated system, which serve as adsorption centers and allow physical adsorption (mainly electrostatic interaction of the charged inhibitor molecules and the charged metal surface), chemisorption (by forming coordinate type bond), or both. The adsorption of these inhibitors onto the metal surface leads to the formation of a protective layer that prevents mass and charge transfer and the subsequent attack of aggressive media toward the metal [6,7]. Ionic liquids (ILs) have attracted considerable attention as potential

functional materials in various fields due to their low vapor pressure, nontoxicity, and environmental friendliness [8–11]. Task-specific ionic liquids (TSILs) with different physicochemical properties can be designed and optimized by selecting the appropriate cation/anion combinations to satisfy diverse needs. Despite the versatility of TSILs, few have been reported as corrosion inhibitors. Imidazole-based ILs, as organic corrosion inhibitors, feature effective inhibition efficiency in some aggressive media [12–14]. Likhanova et al. studied the inhibitory effect of two ILs with different cations (N-octadecylpyridinium bromide and dioctadecylimidazolium bromide) for carbon steel in sulfuric acid solution and demonstrated that they were chemically adsorbed onto the steel surface. The latter ionic liquid (IL) obtained higher inhibition efficiency (88%) than the former (82%), owing to the additional long octadecyl chain of N-octadecylpyridinium bromide [15]. Another study by Zhou et al. reported the IL, 1-butyl-3-methyl imidazolium tetrafluoroborate, as a corrosion inhibitor for carbon steel in alkaline chloride solution. They found that it effectively suppressed cathodic and anodic processes with the highest inhibition efficiency of 97% at an optimal concentration by adsorption onto the steel surface, which fits the Langmuir adsorption isotherm well [16]. Palomar-Pardavé et al. utilized ILs (2-amino-5-alkyl-1, 3, 4-thiadiazole compounds) as

⁎

Corresponding author at: State Key Laboratory of Separation Membranes and Membrane Processes & School of Material Science and Engineering, Tianjin Polytechnic University, Tianjin, 300387, PR China. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (D. Liu), [email protected] (J. Gui). https://doi.org/10.1016/j.corsci.2019.03.035 Received 14 May 2018; Received in revised form 27 February 2019; Accepted 22 March 2019 Available online 26 March 2019 0010-938X/ © 2019 Elsevier Ltd. All rights reserved.

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

(m, 2 H), 4.06 (m, 2 H), 4.13 (t, 2 H) 4.73 (t, 2 H), 7.39 (s, 1 H), 7.46 (s, 1 H), 8.80 (s, 1 H). 13C NMR (126 MHz, DMSO-d6) δ: 13.60, 20.89, 22.33, 25.05, 28.58, 28.89, 31.07, 48.95, 50.07, 122.55, 135.67. The surface active properties of C2-IMIC4-S and C10-IMIC4-S by the critical micelle concentration (CMC) measurements, as the function of concentrations in 0.5 M HCl solution, are shown in the supporting information (see Fig. S4). It is shown that the surface tensions decrease with increasing IL concentration at lower concentrations. However, only C10-IMIC4-S has the relatively stable values of surface tensions at higher concentrations. The intersection of the lower concentration region and higher concentration region shows the CMC value where micelles are formed. Accordingly, only C10-IMIC4-S has a CMC, which is 3.5 ± 1.5 mM. Carbon steel specimens with dimensions of 10 × 10 × 2 mm were used for the experiments with weight percentage composition shown as follows: C, 0.4–0.5; Ni, ≤ 0.3; Cr, ≤ 0.2; Si, 0.2–0.4; Cu, ≤ 0.2; Mn, 0.5-0.8; Fe for balance. All experiments, including electrochemical experiments and immersion tests used for surface analysis and solution examination, were carried out in 0.5 M HCl solution at 298 K, which was prepared using 37% HCl solution (AR grade) and distilled water. The concentration range of ILs studied was 1–15 mM (for C2-IMIC4-S) and 0.5–15 mM (for C10-IMIC4-S).

corrosion inhibitors for mild steel in 1 M H2SO4 solution. Their results showed that the alkyl chain length contributed to nice inhibition ability of ILs. Due to the hydrophobic characteristic of long alkyl chains, they can help block the attack of water and other corrosive ions from the metal to some extent; however, the inhibition efficiency might not simply increase with alkyl chain length [17]. Thus, an in-depth study of the inhibition mechanism of different ILs with different alkyl chain lengths is necessary. Several studies have reported the effects of individual functional groups on the inhibition behavior of organic molecules [13–17]. However, little is known about the influence of possessing different donating-accepting centers or varying alkyl tail length on corrosion inhibition performance [18]. While many factors, such as the type of metal, aggressive media and inhibitors play roles in inhibition effectiveness, the chemical structure of inhibitors is of critical importance [19]. In our previous work, the Brønsted acid ionic liquids (BAILs) were found to be effective inhibitors in strong acidic media regardless of their acidity [20]. The specific interest of this study in TSILs involves their structural design with respect to cation/anion pairs to meet the requirements of good inhibitors. Accordingly, we synthesized TSILs by modifying BAILs to include an imidazolium ring, sulfonic acid group, and different lengths of the alkyl tail for testing as corrosion inhibitors. The corrosion inhibition performance of two TSILs, 1-(4-sulfonic acid) butyl-3-ethylimidazolium hydrogen sulfate (C2-IMIC4-S) and 1-(4-sulfonic acid) butyl-3-decylimidazolium hydrogen sulfate (C10-IMIC4-S), has been evaluated by electrochemical techniques in this study. Here we investigate surface morphology, solution analysis, and theoretical study to reveal the effect of different functional groups on their roles in corrosion inhibitions. Finally, the corrosion inhibition mechanism was elucidated. Experimental results were found to agree well with the results of the theoretical study based on frontier molecular orbital theory and molecular dynamics simulations.

2.2. Electrochemical experiments Electrochemical experiments were performed using an electrochemical workstation (CHI760E), in a three-electrode-type glass cell with an electrolyte volume of 200 mL. The carbon steel mentioned above, with an exposed surface area of 1 cm2, was employed as the working electrode (WE). The saturated calomel electrode (SCE), which is connected via a long Luggin’s capillary, and a graphite plate with the large area were used as the reference electrode (RE) and counter electrode (CE), respectively. Before each experiment, the WE was abraded with wet silicon carbide abrasive paper of steadily increasing grade of # 360, #600, #1000, #1500, and #2000, then rinsed with distilled water, then degreased with anhydrous acetone, and, finally dried. Electrochemical impedance spectroscopy (EIS) experiments were performed after the immersion of carbon steel in unaerated HCl solution for 1 h. These experiments were performed at the corrosion potential (Ecorr) in a frequency range from high frequency (100 kHz) to low frequency (50 mHz), with an amplitude perturbation of 10 mV. After the measurements, the EIS data obtained were interpreted using ZSimpwin software. The polarization tests using the Tafel extrapolation method were then performed at ± 250 mV versus SCE at Ecorr at a constant sweep rate of 0.5 mV s−1. The corrosion potential and the corrosion current density were collected by extrapolation at Tafel segments of the obtained anodic and cathodic polarization curves.

2. Experimental 2.1. Experimental preparation Two BAILs were synthesized by our group, according to the references [21,22]. Their chemical structures are shown below in Fig. 1. Their structures were characterized by FTIR spectroscopy, 1H NMR, and 13 C NMR, which are shown in the supporting information (see Figs. S1–S3), and the spectral data were as follows: C2-IMIC4-S: IR (KBr, v/cm−1): 3415, 3159, 3107, 2955, 2460, 1564, 1461, 1198, 1037, 883 cm−1. 1H NMR (500 MHz, D2O) δ: 1.13 (t, 3 H), 1.37 (m, 2 H), 1.66 (m, 2 H), 2.57 (m, 2 H), 3.88 (t, 2 H), 3.91 (t, 2 H), 7.15 (s, 1 H), 7.16 (s, 1 H), 8.43 (s, 1 H). 13C NMR (126 MHz, DMSO-d6) δ: 14.34, 20.53, 27.86, 44.61, 48.68, 50.04, 122.18, 134.52. C10-IMIC4-S: IR (KBr, v/cm−1): 3405, 3148, 3105, 2925, 2460, 1563, 1456, 1170, 1037, 883 cm−1. 1H NMR (500 MHz, D2O) δ: 0.62 (t, 3 H), 1.05 (m, 14 H), 1.58 (m, 2 H), 1.73 (m, 2 H), 1.87 (m, 2 H), 2.73

Fig. 1. Chemical structures of C2-IMIC4-S and C10-IMIC4-S. 302

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

2.3. Surface analyses The surface morphology test of the steel was performed using X Flash Detector 5010 BRUKER Nano model scanning electron microscopy (SEM). The surface analysis was investigated by ESCALAB 250 model X-ray photoelectron spectroscopy (XPS) using a monochromatic Al-Kα source (hν = 1486.6 eV). For XPS analysis, the binding energy reference was set at the C 1 s peak of carbon, 284.7 eV. Prior to each immersion experiment, the surfaces of the steel specimens were abraded and cleaned as previously described, and then immersed in 0.5 M HCl aqueous solution with and without ILs for 24 h. After the immersion experiments, all the steel surfaces were rinsed with acetone, dried in cool air, and taken for surface examination. i.e., SEM and XPS. The contact angle (CA) measurements of a water droplet by POWEREACH of Shanghai zhongchen digital technology apparatus Co., Ltd. were performed at 25 °C with three repetitions of each sample. The volumes of the droplets were fixed at 2 μL. 2.4. Solution analyses UV–vis spectrophotometry (Thermo Scientific™ Evolution 300) was carried out to further probe the possible interaction mechanism between the IL molecules and the steel surface. The UV–vis spectra were obtained using quartz cells of light pass length 1 cm in the 200–600 nm range. 2.5. Computational calculations 2.5.1. Frontier molecular orbital (FMO) study The frontier molecular orbitals have been calculated after the geometric optimization of the inhibitors by Density Functional Theory (DFT). All the calculations were completed using Materials Studio software (Accelrys Inc.) and performed by the function of the generalized gradient approximation (GGA) combined with the Lee Yang Parr correlation (BLYP) using DMol3.

Fig. 2. Nyquist plots for carbon steel in 0.5 M HCl solution uninhibited and inhibited with different concentrations of C2-IMIC4-S (a) and C10-IMIC4-S (b).

the real axis can be observed, indicating that the steel surface is rough and inhomogeneous. The depressed capacitive loops present in Fig. 2 also indicate that the corrosion process of carbon steel with and without the ILs in 0.5 M HCl solution is mainly controlled by the process of charge transfer at the electrode/solution interface [24]. In Fig. 2, the semicircle plots for carbon steel in the IL-inhibited HCl solution are larger than that in the uninhibited HCl solution, and the diameter of the semicircles increase with increases in IL concentration. Generally, the bigger the semicircle, the higher the inhibition performance. Therefore, the above results indicate that the investigated ILs can lessen the corrosion. Fig. S5 shows that the value of the phase angle is higher for the steel in the inhibited solution, and in a wider frequency range, compared with those of the uninhibited solution. Figs. 2 and S5 plot attributes mentioned above are related to the enhanced corrosion resistance for the inhibited system, which is more evident in the presence of C10-IMIC4-S. Based on the Bode plots, the equivalent circuit model with one-time constant shown in Fig. 3 is advantageous to use to fit the EIS data for analysis. In the equivalent circuit model, Rs and Rct refer to the solution resistance, and the charge transfer resistance of the carbon steel/bulk

2.5.2. Molecular dynamics (MD) simulations Molecular dynamics (MD) simulations of the IL molecules interacting with the Fe(001) surface were investigated using a Forcite module with Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force-field. The simulations of the interactions between the IL molecules and the Fe(001) surface were conducted in a simulation box (28.7 × 28.7 × 25.2 Å) with periodic boundary conditions, a time step of 1 fs, using a simulation time of 1000 ps, and under NVT ensemble at 298 K. The MD simulation box consisted of a Fe slab, 1 IL molecule, and a vacuum layer with 15.00 Å height, as well as the other box, containing an additional layer comprised of water, hydrogen chloride, and inhibitor molecule. In the latter box, the additional layer consisted of 100 H2O molecules, 1 IL molecule, 5 H3O+ ions, and 5 Cl− ions and was constructed first by the Amorphous cell program, then the simulation box was built by placing the constructed Amorphous cell onto the Fe(001) surface using the “build layers” tool. 3. Results and discussion 3.1. Electrochemical impedance spectroscopy (EIS) EIS is a useful and important technology that can provide information about the kinetics of electrochemical processes occurring at the interface of a metal surface and an aggressive medium to determine the corrosion rate [23]. Fig. 2 shows the Nyquist plots for carbon steel in 0.5 M HCl solution with and without four different concentrations of C2-IMIC4-S and C10IMIC4-S. The relevant Bode diagrams are shown in Fig. S5. In Fig. 2, single depressed capacitive loops with all of their center located below

Fig. 3. Equivalent circuit model used to fit the EIS experimental data. 303

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

test condition of this study, and the inhibition efficiency increases obviously with its concentration. While a solution of C10-IMIC4-S at around its CMC or above forms micelles, making the inhibition efficiency increase very slowly, and even at a slightly lower concentration (1 mM), still shows a relative high inhibition efficiency (96.6%). However, further decreasing the concentration to 0.5 mM, the inhibition efficiency decreased dramatically to 76.1%. C10-IMIC4-S offers higher inhibition efficiency than C2-IMIC4-S, with 97.9% for C10IMIC4-S and 80.8% for C2-IMIC4-S at the concentration of 15 mM. This can be attributed to the increased length of the alkyl tail. In order to investigate the effect of immersion time, EIS tests were performed in 0.5 M HCl solution with and without 15 mM ILs after 24 h immersion. Their Nyquist and Bode plots are shown in Figs. S6 and S7. As compared to short time immersion, EIS plots with long immersion time do not show significant differences and the same equivalent circuit model in Fig. 3 can be used to fit the EIS data based on the Bode plots shown in Fig. S7. The electrochemical parameters are presented in Table S1. Rct value in shorter immersion time (1 h) in inhibited solution is higher than that without inhibitors, while slightly lower than that after 24 h immersion with inhibitors, meaning that longer immersion time (24 h) with inhibitors leads to the decrease in iron dissolution rate over time. This can be demonstrated in the results of inhibition efficiencies, and longer immersion time leads to higher inhibition efficiency.

electrolyte interface, respectively. The constant phase element, CPE/Q, instead of the double layer capacitance (Cdl) is employed to deal with the non-ideal capacitance response (which leads to the non-ideal semicircle), so that better-fitting curves can be obtained [17,21]. The impedance function of the constant phase element, CPE, is presented as follows [25]:

ZCPE = Y 0−1 (jω)−n

(1)

where Y0 represents the CPE/Q constant, and n refers to the CPE exponent, which can be described as follows: −1 ≤ n ≤ 1. j is an imaginary number, which equals (−1)1/2. ω is the angular frequency, which equals 2πf. Cdl can be calculated as follows [25]:

Cdl = Y0 (2πfmax )(n−1)

(2)

where fmax is the maximum frequency shown in the impedance spectrum. Cdl can also be calculated as follows:

Cdl =

ε 0εS d

(3)

where d represents the thickness of the double layer formed at the carbon steel/electrolyte interface, ε° and ε are the permittivity of air and the local dielectric constant, respectively, and S refers to the area of the studied electrode surface. Therefore, the decrease of Cdl can indicate a decrease in ε and/or an increase in d. The inhibition efficiency (IEEIS%) obtained by EIS tests at different IL concentrations was obtained by applying the following expression [25]:

R ct(IL) − R ct IEEIS % = × 100 R ct(IL)

3.2. Tafel extrapolation method Fig. 4 depicts the polarization curves of carbon steel in 0.5 M aqueous HCl solution with and without different concentrations of the studied ILs. As can be seen in Fig. 4, the cathodic and anodic current densities decrease with the corrosion potential (Ecorr), shifting to a more negative value. Fig. 4 also shows that the maximum Ecorr, in the presence of ILs, shifts less than ± 85 mV from that of the uninhibited solution. These findings indicate that both C2-IMIC4-S and C10-IMIC4-S exhibit mixed-inhibition behavior, i.e., they can reduce both anodic Fe dissolution and retard the cathodic hydrogen evolution reaction [16]. The inhibition efficiency (IETafel%) was estimated using icorr values generated from the data of polarization tests by the following equation [25,26]:

(4)

where Rct and Rct(IL) represent the charge transfer resistance of the carbon steel/electrolyte interface without and with IL inhibitors, respectively. Table 1 presents the details of the electrochemical parameters obtained using the equivalent circuit from the Nyquist plots. The Rct values increase; however, the Cdl values simultaneously decrease by and large. This effect becomes more evident when increasing IL concentration, which might be due to the effective displacement of a certain number of water molecules and/or other cation or anion ions preferentially adsorbed onto the steel surface by ILs, thereby prevents the steel surface from further corrosive attack. In addition, it should be mentioned that the adsorption of organic molecules onto the steel surface can modify the electrical double layer by changing ε and/or d. Therefore, the increase in Rct and the decrease in Cdl are generally related to the adsorption behavior of IL molecules onto the steel surface, accompanied by the displacement of water molecules (having higher dielectric constant compared to inhibitor molecules), which helps decrease the attack of aggressive species, thus increasing the inhibition efficiency of the ILs [4]. The IL C2-IMIC4-S cannot form micelles in the

IETafel % =

i corr − i corr(IL) × 100 i corr

(5)

where icorr and icorr(IL) denote the corrosion current density for carbon steel without and with IL inhibitors, respectively. The relevant electrochemical parameters, including icorr, Ecorr, IE%, anodic slope (βa), and cathodic slope (βc), were obtained by extrapolating the Tafel line (Fig. 4), are presented in Table 2. The icorr(IL) values for steel in the inhibited solution are much smaller than the icorr value in the uninhibited solution. In addition, the icorr(IL) values decrease with the increase in IL concentration. As expected, IETafel%, in

Table 1 Electrochemical parameters obtained from EIS data for carbon steel in HCl solution containing different concentrations of C2-IMIC4-S and C10-IMIC4-S at OCP after one-hour immersion at 25 °C. Inhibitor name

Conc. (mM)

Rs (Ω cm2)

Y0 (μΩ−1 Sn cm−2)

Cdl (μFcm−2)

n

Rct (Ω cm2)

Blank C2-IMIC4-S

0 1 5 10 15 0.5 1 5 10 15

2.2 1.7 1.8 1.4 1.4 1.5 2.1 1.8 3.7 1.7

146.7 371.7 116.6 115.8 222.7 109.7 64.7 93.4 63.5 72.3

250.1 544.3 108.3 116.0 132.4 217.3 84.2 60.3 53.4 102.7

0.98 0.99 0.90 0.91 0.91 0.91 0.82 0.74 0.77 0.83

21.9 45.3 87.2 102.2 114.2 91.6 639.3 738.1 1013 1034

C10-IMIC4-S

304

IE (%)

51.7 68.0 78.6 80.8 76.1 96.6 97.0 97.8 97.9

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

in an aqueous solution, especially in an acidic solution, can be explained by adsorption of inhibitor molecules onto the metal surface, accompanied by displacement of water molecules. Water molecules are preferentially adsorbed onto the studied steel surface. This displacement process can be described using the following equation [17]:

Inhi (sol) + x H2 O(ads) ↔ Inhi (ads) + x H2 O(sol)

(6)

where Inhi(ads) is the inhibitor molecule adsorbed on the steel surface, H2O(sol) represents water molecules in the bulk aqueous solution, and x refers to the ratio of water molecules effectively replaced by one inhibitor molecule. In addition, the adsorption mechanisms include three types: physical adsorption, chemisorption, and both. Thus, adsorption isotherms are of great importance for understanding the interaction mechanism between IL inhibitors and the investigated steel surface. The inhibition efficiency is concentration dependent and increases with IL concentration, which is probably because more IL molecules would be adsorbed onto the studied steel surface at higher IL concentrations, thereby increasing surface coverage (θ) and enhancing inhibition efficiency [27]. The Langmuir, Frumkin, Temkin, and Frundlich adsorption isotherms were tested, and the Langmuir adsorption isotherm was identified as the best fit to describe the adsorption behavior of the ILs. The Langmuir adsorption isotherm is defined as follows [28]:

Cinh 1 = + Cinh(IL) θ K ads

(7)

Where Cinh(IL) is IL concentration, θ (define θ = IE%/100) is the surface coverage caused by IL, and Kads represents the equilibrium constant. The plot of Cinh(IL)/θ as a function of Cinh(IL) is shown in Fig. 5. As can be seen from Fig. 5, the slope of the Langmuir adsorption isotherm for the two ILs is near 1, with the linear correlation coefficient (R2) reaching over 0.99. In addition, the standard free energy (ΔG°ads) of inhibitor adsorbed on the metal surface was calculated as follows [29]:

Fig. 4. Polarization curves for carbon steel in 0.5 M HCl solution uninhibited and inhibited with different concentrations of C2-IMIC4-S (A) and C10-IMIC4-S (B).

ѳ ΔGads = −RT (ln(55.5 × K ads) −1

(8)

−1

Where R (8.314 J mol K ) represents the universal gas constant, 55.5 refers to the molar concentration of pure water, and T denotes the thermodynamic temperature in Kelvin. The Kads and △Gѳads values obtained from Langmuir adsorption isotherm through EIS and Tafel tests are shown in Table 3. The higher the Kads values for the studied ILs, the stronger the adsorption ability of IL on the steel surface. Meanwhile, the negative values of △Gѳads indicate the spontaneous adsorption process of IL molecules towards the studied steel surface. When △Gѳads > −20 kJ mol−1, the physical adsorption can be assumed to occur between the charged inhibitor molecules and the charged steel surface. Meanwhile, △Gѳads < −40 kJ mol−1 indicates chemisorption on the metal surface and △Gѳads −40 kJ - −20 kJ mol−1 indicates combined physical adsorption and chemisorption [30–32]. However, some researchers have reported that in the adsorption process, the adsorption behavior of inhibitor molecules cannot be simply deemed as physisorption or chemisorption, but that

the presence of C2-IMIC4-S and C10-IMIC4-S, increases with increasing IL concentration and reaches the maximum values of 88.0% and 97.7% at the maximum concentration of 15 mM, respectively. The slopes of the Tafel curves are changed in varying degrees for each IL, with the anodic slope (βa) being more affected, especially for C10-IMIC4-S, compared to the change in the cathodic slope (βc), which might indicate a small difference in inhibition mechanism between the two ILs. Collectively, the data presented in Table 2 show that ILs can act as effective inhibitors with their inhibition efficiencies (IETafel%) increasing with IL concentration, and the data are therefore in good agreement with those obtained from the above EIS results. 3.3. Adsorption isotherm The inhibition mechanism for organic inhibitors of metal corrosion

Table 2 Electrochemical parameters obtained from polarization curves for carbon steel in HCl solution containing different concentrations of C2-IMIC4-S and C10-IMIC4-S after one-hour immersion at OCP and EIS test at 25 °C. Inhibitor name

Conc.(mM)

Ecorr (V)

Icorr (μA cm−2)

βc (mAdec−1)

βa (mAdec−1)

IE%

Blank C2-IMIC4-S

0 1 5 10 15 0.5 1 5 10 15

−0.45 −0.48 −0.48 −0.48 −0.49 −0.49 −0.48 −0.49 −0.48 −0.49

919.2 239.8 220.1 171.1 109.9 275.0 47.1 41.8 27.3 20.9

7.09 8.48 8.47 7.76 9.39 6.06 9.85 10.50 9.82 10.37

11.38 13.70 11.46 14.78 14.82 7.29 3.62 3.03 5.46 6.32

73.9 76.1 81.4 88.0 70.1 94.9 95.5 97.0 97.7

C10-IMIC4-S

305

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

Table 4 XPS analysis results of the steel surfaces after 24-hour immersion in 0.5 M HCl solution with and without 15 mM C2-IMIC4-S and C10-IMIC4-S. Element

Without IL

With C2-IMIC4-S

With C10-IMIC4-S

Fe

709.6 eV Fe° 710.5 ± 0.1 eV Ferrous compounds 712.1 ± 0.1 eV Ferric compounds 529.6 eV O2− bonded to ferric oxides 531 eV FeOOH

709.6 eV Fe° 710.5 ± 0.1 eV Ferrous compounds 712.1 ± 0.1 eV Ferric compounds 530.0 eV O2− bonded to ferric oxides 531.4 eV FeOOH 198.3 ± 0.1 eV Cl− 199.9 ± 0.1 eV FeCl3 168.1 ± 0.2 eV Fe-S complex 169.4 ± 0.2 eV SO42− 284.7 eV C–C aliphatic bonds 285.4 ± 0.1 eV C–N 288.1 ± 0.1 eV C=N 400.1 eV -NR3 401.6 eV NR4+

709.6 eV Fe° 710.5 ± 0.1 eV Ferrous compounds 712.1 ± 0.1 eV Ferric compounds 530.0 eV O2− bonded to ferric oxides 531.4 eV FeOOH

O

Cl

S

C

N

198.3 ± 0.1 eV Cl− 199.9 ± 0.1 eV FeCl3

198.3 ± 0.1 eV Cl− 199.9 ± 0.1 eV FeCl3 168.1 ± 0.2 eV Fe-S complex 169.4 ± 0.2 eV SO42− 284.7 eV C–C aliphatic bonds 285.4 ± 0.1 eV C–N 288.1 ± 0.1 eV C=N 400.1 eV -NR3 401.6 eV NR4+

Fig. 5. Langmuir adsorption plots for carbon steel in 0.5 M HCl solution containing different concentrations (1–15 mM) of C2-IMIC4-S (a) and C10-IMIC4-S (b) obtained from EIS and polarization results. Fig. 6. UV–vis spectra of C2-IMIC4-S and C10-IMIC4-S and the resulting solution after 24 h of carbon steel immersion.

Table 3 Thermodynamic adsorption parameters. Inhibitor name

C2-IMIC4-S C10-IMIC4-S

ΔGѳads (kJ)

Kads

EIS

Tafel

EIS

Tafel

−9.8 −18.6

−11.1 −16.2

0.95 33.33

1.59 12.50

C2-IMIC4-S and C10-IMIC4-S with and without 24 h of immersion of carbon steel are shown in Fig. 6. As depicted in Fig. 6, one broad absorption band at 205–240 nm appears in the optical spectra of C2IMIC4-S and C10-IMIC4-S. This band can be assigned to the π–π* transition in the imidazolium structural motif of ILs. Meanwhile, the optical spectrum of 0.5 M HCl solution without IL after 24 h immersion of carbon steel shows a characteristic weak absorption band at around 344 nm, which can be ascribed to the interaction between Fe2+ and Cl− to form the complex. After addition of carbon steel into the inhibited solution, the absorption band in the range of 205–240 nm is broadened to 205–270 nm, which might be attributed to the interaction between IL and Fe2+ from solution, because the bands can extend over to a higher wavelength region because of conjugation [34]. These data suggest that ILs can coordinate with Fe2+ in solution to form a complex. The addition of steel into the inhibited solution also leads to a weaker absorption band at 344 nm, compared with that in the uninhibited HCl solution, indicating the effectiveness of the IL inhibitors. Therefore, the ILs can be confirmed to adsorb onto the investigated steel surface through chemical and physical adsorption.

physisorption could be the first adsorption process to occur on the metal surface against HCl attack [33]. As also seen in Table 4, C2-IMIC4-S and C10-IMIC4-S showed △Gѳads values of −9.8 and −18.6 kJ mol−1 by EIS and −11.1 and −16.2 kJ mol−1 by polarization test, respectively. These results suggest that physical adsorption is mainly involved in the presence of C2-IMIC4-S and both physisorption and chemisorption are probably involved in the presence of C10-IMIC4-S (−18.5 and −16.2 kJ mol−1 are around the value of −20 kJ mol−1). Moreover, the adsorption capability of C10IMIC4-S is stronger than that of C2-IMIC4-S, as indicated by the higher K value.

3.4. UV–vis spectra analysis The UV–vis spectra of 0.5 M HCl solution in the presence of 15 mM 306

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

Fig. 7. SEM images of carbon steel before (a) and after 24 h immersion in 0.5 M HCl solution uninhibited (b) and inhibited with 15 mM C2-IMIC4-S (c) and C10IMIC4-S (d).

ILs. The positions of the two peaks are located at 529.6 and 531 eV without ILs, which are ascribable to the O2− and −OH of hydrous iron oxides (such as FeOOH), respectively [39,40]. The peaks move to higher binding energies (530 and 531.4 eV) in the presence of ILs, corresponding to the strong interaction between IL and the steel surface through O atom, facilitating the electron transfer between metal and IL [41]. The Cl 2p spectra (Fig. 8C) show two peaks. One peak at 198.3 ± 0.1 eV can be ascribed to Cl−, and the other peak, appearing at 199.9 ± 0.1 eV, is attributed to FeCl3 [15], suggesting that the Cl− ion is adsorbed onto the steel surface. In addition, in the presence of the ILs, the absorption strength of Cl− is higher than that in the blank solution. Accordingly, to some extent, Cl− might help the adsorption of inhibitors. The S 2p spectra (Fig. 8D) show two main peaks in the presence of ILs. The peak at 168.1 ± 0.2 eV can be assigned to the Fe–S complex and the peak at 169.4 ± 0.2 eV can be ascribed to SO42− [42]. In the C 1s spectra (Fig. 8E), three peaks can be seen at 284.7 ± 0.1 (CeC aliphatic bonds), 285.4 ± 0.1 (CeN), and 288.1 ± 0.1 eV (C] N) [16], indicating that the skeleton of the imidazolium motif may present on the steel surface. In the N 1 s spectra (Fig. 8F), the peak at approximately 400.1 eV can be assigned to the amine group (–NR3), whereas the peak at 401.6 eV (coordinated nitrogen atom and C-N-metal connection) can be ascribed to quaternary nitrogen (NR4+) [16]. From the combination of the peaks of C 1s and N 1s spectra, it can be seen that C and N species bond in different ways with the iron surface, indicating that IL molecules and/or the anion of the ILs can be

3.5. SEM analysis Fig. 7 shows the SEM morphology of the steel surface before and after immersion for 24 h in 0.5 M HCl solution with and without 15 mM C2-IMIC4-S and C10-IMIC4-S. As depicted in Fig. 7, the steel surface before immersion is smooth with many grinding scratches and becomes severely corroded after immersion in the uninhibited solution with many deep cracks. However, in the presence of ILs, as expected, the corrosion damage of the steel surface is distinctly decreased, and the surface in the presence of C10-IMIC4-S is smoother than that of C2IMIC4-S. Accordingly, this result indicates that addition of IL markedly decreases the corrosion and that the inhibition by C10-IMIC4-S is more effective than that of C2-IMIC4-S. 3.6. XPS analysis Fig. 8 shows the XPS spectra for Fe 2p, Cl 2p, O 1s, S 2s, N 1s and C 1s elements on the steel surface after 24 h immersion with and without 15 mM IL in 0.5 HCl solution. The detailed XPS results are listed in Table 4. In Fig. 8, the Fe 2p spectra (Fig. 8A) show three peaks at 709.6 ± 0.1, 710.5 ± 0.1, and 712.1 ± 0.1 eV for Fe 2p3/2, which can be attributed to Fe°, ferrous (such as FeO, Fe2O3), and ferric compounds (such as Fe2O3, FeOOH and FeCl3), respectively [35–38]. The formation of a stable and insoluble layer (Fe2O3 and/or FeOOH) can act as a protective film and thus decrease the corrosion rate of the steel in acidic solution. The O 1 s spectra (Fig. 8B) show two main peaks with and without 307

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

Fig. 8. XPS spectra of the steel surface after 24 h immersion in 0.5 M HCl solution uninhibited and inhibited with 15 mM C2-IMIC4-S and C10-IMIC4-S.

efficiency. As others have reported, inhibitors with a longer alkyl tail are less hydrophilic or hydrophobic [43]. The substance showing water contact angle > 90° is considered to possess water repelling property while water contact angle < 90° exhibits the characteristic wetting property [44,45]. Herein, in the presence of ILs in this study, all the steel surfaces show wetting characteristics, and the steel surface is less hydrophilic in the presence of C10-IMIC4-S compared to C2-IMIC4-S. The protective layer formed by the adsorption of ILs is of importance on corrosion inhibition, i.e., the adsorption layer formed by C10-IMIC4-S gives more effective protection than that of C2-IMIC40S, resulting in better inhibition efficiency.

integrally adsorbed onto the steel surface. Thus, chemical adsorption is possible, as confirmed by the above results obtained from thermodynamic calculations, UV–vis spectra observations, and XPS analyses. 3.7. Contact angle measurements Fig. 9 shows the cross-sectional optical images of water droplets on inhibited and uninhibited surfaces. For the fresh steel, the average surface contact angle is 75°. The average surface contact angles in 0.5 M HCl solution with ILs are higher (45° for C2-IMIC4-S and 82° for C10IMIC4-S) than that of the uninhibited solution (26°). This indicates that the steel surface is efficiently inhibited by ILs. In addition, C10-IMIC4-S with longer alkyl tail length can displace water molecules more effectively compared to that with C2-IMIC4-S, leading to better inhibition 308

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

Fig. 9. The cross sectional optical images of water droplets on (a) fresh grinded steel surface, (b) uninhibited steel surface, (c) the steel surface inhibited with 15 mM C2-IMIC4-S, (d) the steel surface inhibited with 15 mM C10-IMIC4-S for 24 h immersion.

3.8. Frontier molecular orbital theory (FMOT) study

represents the energy of the IL molecule, and Esurface denotes the energy of the Fe(001) surface. Under the consideration of the solution effect, the interactions between the IL molecules and the Fe(001) surface can be obtained as follows [48]:

The above results of the thermodynamic parameters and the XPS analyses showed that the respective ILs were adsorbed onto the steel surface to retard corrosion. To further understand and explain the interaction between inhibitor molecule and the steel surface, FMOT study has been carried out. In addition to HOMO/LUMO, three additional orbitals above the LUMO and below the HOMO level have been computed. Suitable inhibitors are those that can not only perform as electron donors to the unoccupied d orbital of the metal, but act as electron acceptors from the d orbital of the metal [34]. As for the two studied ILs, their difference in corrosion resistance capability must be caused by their cations, since they possess the same anion (i.e., bisulfate). According to FMOT, the HOMO of the inhibitor usually donates electrons to metal; meanwhile, the LUMO of the inhibitor can accept electrons readily from the metal surface by electron back donation, finally leading to effective inhibition by surface adsorption [46]. Images of the optimized molecular structures, the HOMOs, and LUMOs for the cations of IL molecules are shown in Fig. 10. The LUMOs of both cations are located in the imidazolium motif, and the HOMO of C2-IMIC4-S and HOMO-3 (where HOMO-3 means 3th molecular orbitals below the HOMO) of C10-IMIC4-S are mainly located in the -SO3H group; while the HOMO of the C10-IMIC4-S is illustrated on the end-alkyl tail with a small energy difference of 0.27 eV compared with the HOMO-3. According to the symmetry match and maximum overlapping principle, it is hard for the end alkyl tail to form a bond with the metal surface. Therefore, cycling adsorption through electron donation from-SO3H group to metal and back donation from iron to the imidazolium motif occurs.

(10)

Einteraction = Etotal − (Esurface+soluiton + EIL+solution ) + Esolution

(11)

where Esurface+solution is the total energy of the system without IL molecule, EIL+solution denotes the total energy of the system without considering the Fe(001) surface, and Esolution refers to the energy of the solution without the Fe(001) surface but including the presence of the IL molecule. The Ebinding is the reciprocal of the interaction energy or adsorption energy, which can be calculated as follows [47,48]:

Ebinding = −Einteraction/adsorption

(12)

Fig. 11 shows the equilibrium configuration for the adsorption of the cations of C2-IMIC4-S and C10-IMIC4-S on the Fe(001) surface in vacuum slabs. As shown in Fig. 11, the adsorption configurations of the cations of C2-IMIC4-S and C10-IMIC4-S are inclined to parallel arrangement, which favors high coverage and effective inhibition efficiency. The calculated adsorption energies of the cations of C2-IMIC4-S and C10-IMIC4-S on the Fe(001) surface are −479.75 and −797.99 kJ mol−1, respectively. Fig. 12 displays the equilibrium configurations for the cations of C2-IMIC4-S and C10-IMIC4-S on the Fe (001) surface in an aqueous system. As can be seen, the imidazole ring of both molecules still tends to remain parallel to the Fe(001) surface. The adsorption energy is in the order of C10-IMIC4-S (-1110.74 kJ mol−1) < C2-IMIC4-S (−237.30 kJ mol−1) when considering the solution effect. A more negative value of Einteraction or a more positive value of Ebinding of IL suggests that the adsorption of the cation of the IL molecule on the Fe(001) surface is more stable and can lead to higher inhibition performance [49]. Therefore, the inhibition efficiency for the two studied ILs, with and without considering the solvent effect, is C10IMIC4-S > C2-IMIC4-S in both cases. In addition, the adsorption system for C10-IMIC4-S in an aqueous system is more stable than that without considering the solution effect, but the trend is opposite for C2IMIC4-S. The increase of alkyl trail length (hydrophobic group) of ILs

3.9. Molecular dynamics (MD) simulations MD simulations were carried out to provide useful information on the interactions of ILs with the iron surface. The interactions between the IL molecules and the Fe(001) surface can be well determined by interaction energy, calculated as follows [47]:

Einteraction/adsorption = Etotal − (Esurface + EIL )

Einter = Etotal − (Esur+sol + Einh+sol ) + Esol

(9)

Where Etotal refers to the energy of the entire stable system, EIL 309

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

Fig. 10. Optimized structures, HOMOs and LUMOs of both BAIL cations.

molecules on the Fe(001) surface. Radial distribution function (RDF) is used to further illustrate the difference between the adsorption performance of C2-IMIC4-S and C10IMIC4-S on the Fe(001) surface. The highest peak of the RDF curve represents the most probable distance between each kind of atom in IL

facilitates steric hindrance and helps expel water away from the steel surface. In addition, the interaction energies of both cations of C2IMIC4-S and C10-IMIC4-S are more negative than that of H2O (−23.67 kJ mol−1), which indicates that the adsorption of the IL cations is a replacement process that can occur by displacing water

Fig. 11. Equilibrium configurations for the cation adsorption of C2-IMIC4-S (a) and C10-IMIC4-S (b) on the Fe(001) surface in vacuum slabs (Inset: on-top views). 310

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

Fig. 12. Equilibrium configurations of the cations of C2-IMIC4-S (a) and C10-IMIC4-S (b) on the Fe(001) surface in aqueous systems (Inset: top-down views).

π-electron system (conjugated double bonds, triple bonds and aromatic motifs) and the unoccupied d-orbital of the metal [51]. For C2-IMIC4-S, physisorption is predominant, but for C10-IMIC4-S, chemisorption is more likely. In addition, an IL with a longer alkyl tail has greater inhibition efficiency due to its good ability to expel water away from the Fe surface to form a protective layer. Therefore, large ionic radius and weak hydrophilicity play important roles in the adsorption process [52,53]. The higher corrosion efficiency of C10-IMIC4-S with long alkyl tail might be caused by the compact adsorption protective film, thus enhancing the adsorption process by displacing water molecules when adsorbing onto the steel surface. ILs form cycling adsorption of electrons with the Fe surface according to FMOT (i.e., the frontier molecular orbital located on the -SO3H group donates electrons to the unoccupied d-orbital of Fe (of electron configuration [Ar]3d64s2) while the imidazolium ring accepts electrons from Fe through back-donation). The cations of the ILs may lose some of the H+ ions from their –SO3H groups to form the zwitterion in acidic solution; however, this does not affect the inhibition efficiency much.

Table 5 The distances between N, S, O, and C atoms and the Fe atom in the simulation systems. Distance (Å)

C2-IMIC4-S

C10-IMIC4-S

N-Fe S-Fe O-Fe

2.2 15 2.7

2.1 14.9 2.2

and Fe atoms. Table 5 shows the most probable distance between N, S and O atoms, interacting with Fe atoms. As can be seen from Table 5, the distances between N, S, O atoms, and Fe atoms for C2-IMIC4-S and C10-IMIC4-S are 2.2 Å and 2.1 Å; 15 Å and 14.9 Å; and 2.7 Å and 2.2 Å, respectively, which confirms that the closest contacts between the cations of C2-IMIC4-S and C10-IMIC4-S with the Fe(001) surface are both N-Fe. The lower distances for C10-IMIC4-S, compared to those of C2IMIC4-S, indicate the stronger interaction between C10-IMIC4-S and the iron surface. As can be seen, the theoretical calculations results are in accordance with the electrochemical data and confirm that this is a powerful method in the investigation of inhibitor behavior.

4. Conclusions The inhibition of steel corrosion in 0.5 M HCl solution by task-specific ionic liquids, possessing an imidazolium structural motif, sulfonic acid group, and an alkyl tail, was analyzed. The above findings, based on electrochemical tests, SEM, XPS, UV–vis, contact angle measurements, molecular orbital theory, and MD simulations, allow the following conclusions:

3.10. Corrosion inhibition mechanism The possible inhibition performance of the respective ILs was evaluated and discussed using experimental tests, surface examinations (such as SEM, XPS, and surface contact angle method), solution examinations (UV–vis spectra), and molecular orbital study, as well as MD simulations. The results indicate that ILs exhibit effective inhibition for steel corrosion and their inhibition efficiency enhances with increased length of the alkyl tail. The cations of the ILs can be adsorbed onto the charged steel surface in the HCl aqueous solution by physisorption and/or chemisorption [50]. Chemisorption occurs through the electron donation–back donation between the lone electron pairs of heteroatoms (N, S, O, etc.), the

(1) TSILs, C2-IMIC4-S and C10-IMIC4-S, are effective inhibitors for carbon steel regardless of their acid characteristics in acidic solution. Inhibition efficiency increases with their concentration and alkyl tail length. The maximum inhibition efficiency is 80.8% and 97.9% at the maximum concentration of 15 mM, respectively, as obtained by EIS. (2) Polarization results show that both C2-IMIC4-S and C10-IMIC4-S

311

Corrosion Science 153 (2019) 301–313

S. Cao, et al.

act as mixed-type inhibitors, which suppress both the anodic and cathodic processes by physical adsorption only, and physiochemical adsorption, respectively. Adsorption of the ILs on the steel surface follows the Langmuir adsorption model. (3) UV–vis results confirm the interaction between Fe2+ and ILs in 0.5 M HCl solution, suggesting the possibility of chemisorption between the ILs and the iron surface, forming a metal-inhibitor protective layer. (4) The results of SEM and XPS confirm the protection of the steel surface by the two ILs in 0.5 M HCl solution. Meanwhile, contact angle measurements demonstrate the weak hydrophilicity of the long alkyl tail. The length of the alkyl tail plays an important role, and the longer the alkyl tail length, the higher the corrosion mitigation efficiency. (5) MD simulations agree with the experimental results, solution analysis, and surface examinations. The frontier molecular orbitals of ILs interact with the Fe surface by a cycling adsorption style, which can enhance the adsorption process, thus leading to effective inhibition efficiency.

[16] [17]

[18]

[19]

[20]

[21]

[22]

[23]

Acknowledgements [24]

The authors thank Dr. Nigel Daniels from Ohio University for the assistance with the preparation of this paper, and are grateful for the financial support from the National Natural Science Foundation of China (No.21576211), Program for Tianjin Innovative Research Team in Universities (Grant No. TD13-5031) and Tianjin 131 Research Team of Innovative Talents.

[25]

[26]

[27]

Appendix A. Supplementary data [28]

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.corsci.2019.03.035.

[29]

References [30] [1] X.H. Li, X.G. Xie, S.D. Deng, G.B. Du, Inhibition effect of two mercaptopyrimidine derivatives on cold rolled steel in HCl solution, Corros. Sci. 92 (2015) 136–147. [2] M. Abdallah, B.H. Asghar, I. Zaafarany, A.S. Fouda, The inhibition of carbon steel corrosion in hydrochloric acid solution using some phenolic compounds, Int. J. Electrochem. Sci. 7 (2012) 282–304. [3] M.I. Khaled, Evaluation of cysteine as environmentally friendly corrosion inhibitor for copper in neutral and acidic chloride solutions, Electrochim. Acta 52 (2007) 7811–7819. [4] E.E. Oguzie, Y. Li, F.H. Wang, Effect of surface nanocrystallization on corrosion and corrosion inhibition of low carbon steel: synergistic effect of methionine and iodide ion, Electrochim. Acta 52 (2007) 6988–6996. [5] I.B. Obot, D.D. Macdonald, Z.M. Gasem, Density functional theory (DFT) as a powerful tool for designing new organic corrosion inhibitors. Part 1: an overview, Corros. Sci. 99 (2015) 1–30. [6] M.R. Vinutha, T.V. Venkatesha, Review on mechanistic action of inhibitors on steel corrosion in acidic media, Electrochim. Acta 34 (2016) 157–184. [7] S.Kr. Saha, A. Dutta, P. Ghosh, D. Sukulc, P. Banerjee, Adsorption and corrosion inhibition effect of Schiff base molecules on the mild steel surface in 1 M HCl medium: a combined experimental and theoretical approach, Phys. Chem. Chem. Phys. 17 (2015) 5679–5690. [8] P. Wasserscheid, W. Keim, Ionic liquids–new “solutions” for transition metal catalysis, Angew. Chem. Int. Ed. 39 (2000) 3772–3789. [9] T. Welton, Room-temperature ionic liquids. Solvents for synthesis and catalysis, Chem. Rev. 99 (1999) 2071–2084. [10] P. Wasserscheid, T. Welton (Eds.), Ionic Liquids in Synthesis, Wiley, Weinheim, 2003. [11] J. Hulsbosch, D.E.D. Vos, K. Binnemans, R. Ameloot, Biobased ionic liquids: solvents for a green processing industry? ACS Sustain. Chem. Eng. 4 (2016) 2917–2931. [12] R. Gasparac, C.R. Martin, E. Stupnisek-Lisac, In situ studies of imidazole and its derivatives as copper corrosion inhibitors. I. Activation energies and thermodynamics of adsorption, J. Electrochem. Soc. 147 (2000) 548–551. [13] M.A. Quraishi, M.Z.A. Rafiquee, S. Khan, N. Saxena, Corrosion inhibition of aluminium in acid solutions by some imidazoline derivatives, J. Appl. Electrochem. 37 (2007) 1153–1162. [14] K.F. Khaled, The inhibition of benzimidazole derivatives on corrosion of iron in 1 M HCl solutions, Electrochim. Acta 48 (2003) 2493–2503. [15] N.V. Likhanova, M.A. Domínguez-Aguilar, O. Olivares-Xometl, N. Nava-Entzana, E. Arce, H. Dorantes, The effect of ionic liquids with imidazolium and pyridinium

[31]

[32]

[33] [34]

[35]

[36] [37]

[38]

[39]

[40]

[41]

[42] [43]

312

cations on the corrosion inhibition of mild steel in acidic environment, Corros. Sci. 52 (2010) 2088–2097. X. Zhou, H.Y. Yang, F.H. Wang, [BMIM]BF4 ionic liquids as effective inhibitor for carbon steel in alkaline chloride solution, Electrochim. Acta 56 (2011) 4268–4275. M. Palomar-Pardavé, M. Romero-Romo, H. Herrera-Hernández, M.A. AbreuQuijano, Natalya V. Likhanova, J. Uruchurtu, J.M. Juárez-García, Influence of the alkyl chain length of 2 amino 5 alkyl 1, 3, 4 thiadiazole compounds on the corrosion inhibition of steel immersed in sulfuric acid solutions, Corros. Sci. 54 (2012) 231–243. E.E. Oguzie, Y. Li, F.H. Wang, Corrosion inhibition and adsorption behaviour of methionine on mild steel in sulfuric acid and synergistic effect of iodide ion, J. Colloid Interface Sci. 310 (2007) 90–98. M. Mahdavian, A.R. Tehrani-Bagha, E. Alibaakhshi, S. Ashhari, M.J. Palimi, S. Farashi, S. Javadian, F. Ektefa, Corrosion of mild steel in hydrochloric acid in the presence of two gemini surfactants with and without hydroxyl substituted spacers, Corros. Sci. 137 (2018) 62–75. S.Y. Cao, D. Liu, P. Zhang, L.X. Yang, P. Yang, H. Lu, J.Z. Gui, Green Brönsted acid ionic liquids as novel corrosion inhibitors for carbon steel in acidic medium, Sci. Rep. 7 (2017) 8773–8786. J.Z. Gui, X.H. Cong, D. Liu, X.T. Zhang, Z.D. Hu, Z.L. Sun, Novel Brønsted acidic ionic liquid as efficient and reusable catalyst system for esterification, Catal. Commun. 5 (2004) 473–477. A.C. Cole, J.L. Jensen, I. Ntai, K.L.T. Tran, K.J. Weaver, D.C. Forbes, J.H. Davis, Novel Brønsted acidic ionic liquids and their use as dual solvent-catalysts, J. Am. Chem. Soc. 124 (2002) 5962–5963. D.V. Ribeiro, C.A.C. Souza, J.C.C. Abrantes, Use of electrochemical impedance spectroscopy (EIS) to monitoring the corrosion of reinforced concrete, Rev. Ibracon Estrut. Mater. 8 (2015) 529–546. K.F. Khaled, N. Hackerman, Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 1 M HCl solutions, Electrochim. Acta 48 (2003) 2715–2723. A. Popova, E. Sokolova, S. Raicheva, M. Christov, AC and DC study of the temperature effect on mild steel corrosion in acid media in the presence of benzimidazole derivatives, Corros. Sci. 45 (2003) 33–58. A.K. Satapathy, G. Gunasekaran, S.C. Sahoo, K. Amit, P.V. Rodrigues, Corrosion inhibition by Justicia gendarussa plant extract in hydrochloric acid solution, Corros. Sci. 51 (2009) 2848–2856. E.E. Oguzie, Y. Li, F.H. Wang, Corrosion inhibition and adsorption behavior of methionine on mild steel in sulfuric acid and synergistic effect of iodide ion, J. Colloid Interface Sci. 310 (2007) 90–98. M. Lebrini, F. Bentiss, H. Vezin, M. Lagrenee, The inhibition of mild steel corrosion in acidic solutions by 2, 5-bis(4-pyridyl)-1, 3, 4-thiadiazole: structure–activity correlation, Corros. Sci. 48 (2006) 1279–1291. K.F. Khaled, M.M. Al-Qahtani, The inhibitive effect of some tetrazole derivatives towards Al corrosion in acid solutions: chemical electrochemical and theoretical studies, Mater. Chem. Phys. 113 (2009) 150–158. I.B. Obot, N.O. Obi-Egbedi, Inhibitory effect and adsorption characteristics of 2, 3Diaminonaphthalene at aluminum/hydrochloric acid interface: experimental and theoretical study, Surf. Rev. Lett. 15 (6) (2008) 903–910. E.E. Ebenso, H. Alemu, S.A. Umoren, I.B. Obot, Inhibition of mild steel corrosion in sulphuric acid using alizarin yellow GG dye and synergistic iodide additive, Int. J. Electrochem. Sci. 3 (2008) 1325–1339. R. Solmaza, G. Kardas, M. Culha, B. Yazıcı, M. Erbil, Investigation of adsorption and inhibitive effect of 2-mercaptothiazoline on corrosion of mild steel in. hydrochloric acid media, Electrochim. Acta 53 (2008) 5941–5952. E. McCafferty, Introduction to Corrosion Science, Springer, New York, Dordrecht, Heidelberg, London, New York, 2010. M.A. Bedair, M.M.B. El-Sabbah, A.S. Fouda, H.M. Elaryian, Synthesis, electrochemical and quantum chemical studies of some prepared surfactants based on azodye and Schiff base as corrosion inhibitors for steel in acid medium, Corros. Sci. 128 (2017) 54–72. M.A. Pech-Canul, P. Bertolo-Perez, Inhibition effects of N-phosphono-methyl-glycine/Zn2+ mixtures on corrosion of steel in neutral chloride solutions, Surf. Coat. Technol. 184 (2004) 133–140. V.S. Sastri, M. Elboujdaini, J.R. Brown, J.R. Perumareddi, Surface analysis of inhibitor films formed in hydrogen sulfide medium, Corrosion 52 (1996) 447–452. A.P. Grosvenor, B.A. Kobe, M.C. Biesinger, N.S. Mclntyre, Investigation of multiplet splitting of Fe 2p XPS spectra and bonding in iron compound, Surf. Interface Anal. 36 (2004) 1564–1574. F.Z. Bouanis, F. Bentiss, M. Traisnel, C. Jama, Enhanced corrosion resistance properties of radiofrequency cold plasma nitrided carbon steel: gravimetric and electrochemical results, Electrochim. Acta 54 (2009) 2371–2378. S. Garai, S. Garai, P. Jaisankar, J.K. Singh, A. Elango, A comprehensive study on crude methanolic extract of Artemisia pallens. (Asteraceae) and its active component as effective corrosion inhibitors of mild steel in acid solution, Corros. Sci. 60 (2012) 193–204. S.J. Gao, C.F. Dong, H. Luo, K. Xiao, X.M. Pan, X.G. Li, Scanning electrochemical microscopy study on the electrochemical behavior of CrN film formed on 304 stainless steel by magnetron sputtering, Electrochim. Acta 114 (2013) 233–241. W. Temesghen, P.M.A. Sherwood, Analytical utility of valence band X-ray photoelectron spectroscopy of iron and its oxides, with spectral interpretation by cluster and band structure calculations, Anal. Bioanal. Chem. 373 (2002) 601–608. The Characterization of Passive Films on Chromium Electrodes by XPS, 36, 1994; 2159–2167. A. Alagta, I. Felhosi, I. Bertoti, et al., Corrosion protection properties of hydrox-amic aicd self-assembled monolayer on carbon steel, Corros. Sci. 50 (2008) 1644–1649.

Corrosion Science 153 (2019) 301–313

S. Cao, et al. [44] P. Wang, D. Zhang, R. Qiu, J. Wua, Y. i Wan, Super-hydrophobic film prepared on zinc and its effect on corrosion in simulated marine atmosphere, Corros. Sci. 69 (2013) 23–30. [45] E. Vazirinasa, R. Jafari, G. Momen, Application of superhydrophobic coating as a corrosion barrier: a review, Surf. Coa. Technol. 341 (2018) 40–56. [46] M. Finsgar, A. Lesar, A. Kokalj, I. Milosev, A comparative electrochemical and quantum chemical calculation study of BTAH and BTAOH as copper corrosion inhibitors in near neutral chloride solution, Electrochim. Acta 53 (2008) 8287–8297. [47] B. Xu, Y. Liu, X.S. Yin, W.Z. Yang, Y.Z. Chen, Experimental and theoretical study of corrosion inhibition of 3-pyridinecarbozalde thiosemicarbazone for mild steel in hydrochloric acid, Corros. Sci. 74 (2013) 206–213. [48] L. Li, X. Zhang, S. Gong, H. Zhao, Y. Bai, Q. Li, L. Ji, The discussion of descriptors for the QSAR model and molecular dynamics simulation of benzimidazole derivatives as corrosion inhibitors, Corros. Sci. 99 (2015) 76–88.

[49] X.H. Li, X.G. Xie, G.B. Du, Inhibition effect of two mercaptopyrimidine derivatives on cold rolled steel in HCl solution, Corros. Sci. 92 (2015) 136–147. [50] X.M. Wang, H.Y. Yang, F.H. Wang, An investigation of benzimidazole derivative as corrosion inhibitor for mild steel in different concentration HCl solutions, Corros. Sci. 53 (2011) 113–121. [51] H. Lgaz, R. Salghi, K.S. Bhat, A. Chaouiki, Shubhalaxmi, S. Jodeh, Correlated experimental and theoretical study on inhibition behavior of novel quinoline derivatives for the corrosion of mild steel in hydrochloric acid solution, J. Mol. Liq. 244 (2017) 154–168. [52] E.E. Oguzie, G.N. Onuoha, A.I. Onuchukwu, Inhititory mechanism of mild steel corrosion in 2 M sulphuric acid solution by methylene blue dye, Mater. Chem. Phys. 89 (2005) 305–311. [53] Y.I. Kuznetsov, N.N. Andreev, Corrosion 96, NACE International, Houston, 2019 paper No. 214.

313