Performance and theoretical study on corrosion inhibition of 2-(4-pyridyl)-benzimidazole for mild steel in hydrochloric acid
Highlights
► Excellent inhibition efficiency of 2-(4-pyridinyl)-benzimidazole (PBI). ► Effects of temperature and concentration of acidic media. ► Active sites and capability of adsorption. ► Nearby flat orientation of PBI on iron surface and highest interaction energy.
Introduction
Acid solutions are, especially hydrochloric acid, widely used in various industrial processes such as oil well acidification, the petrochemical processes, acid pickling and acidic cleaning [1], [2], [3], which generally leads to serious metallic corrosion. As the most effective and economic method, inhibitors are applied in these acid solutions to control the metal dissolution [4], [5]. There is a considerable amount of effort devoted to develop novel and efficient corrosion inhibitors. Organic compounds usually serve as inhibitors, and generally protect the metal from corrosion by forming a protection film on the metal surface [6]. Most of the well-known organic inhibitors are the compounds containing nitrogen, sulfur, oxygen atoms and π-bonds [7]. Those structures with the polar groups, which can act as the reactive centers, play an important role in the adsorption of inhibitor molecules on the metal surface. Benzimidazole and its derivatives have received considerable attention on their inhibition properties for metallic corrosion over the past years [8], [9], [10]. Benzimidazole is a heterocyclic organic compound, and the nitrogen atom and the aromatic ring in molecular structure are likely to facilitate the adsorption of the compounds on the metal surface [11]. Some derivatives of benzimidazole have been demonstrated as excellent inhibitors for metals and alloys in acidic solution, and exhibit different inhibition performance with the difference in substituent groups and substituent positions on the imidazole ring [12], [13], [14], [15], [16], [17], [18].
The efficiency of organic inhibitors depends on their structure, especially chemical/electronic structure. Those structural parameters can be obtained from quantum chemical methods, which have been extensively used to study reaction mechanism. Several groups [19], [20], [21], [22], [23] have studied the inhibition mechanism of some organic molecules by quantum chemical calculations, and a nonlinear model based on multiple regressions has successfully been established to probe the relationship between the quantum chemical parameters of inhibitor molecule and inhibition efficiency [24], [25], [26]. For quantum chemical study, however, it is difficult to give the information on the interaction between metal surface and inhibitor molecule, which is essential to understand the inhibition performance of inhibitors.
In recent years, the molecular dynamics (MD) simulations have been used to study the interaction between inhibitors and metal surface. MD simulations can illustrate the adsorption of the molecules onto the corroding metal surface at molecular level, and present the conformation of organic molecule adsorbed onto metal surface and the interaction energy between inhibitor and metal surface [27], [28], [29], [30], [31]. Therefore, molecular dynamics simulations provide insights into the design of inhibitor systems with superior properties, and the interaction energy between organic molecule and metal surface can explain the difference in inhibition efficiency between different organic inhibitors [32], [33], [34].
In this paper, the corrosion inhibition performance of 2-(4-pyridyl)-benzimidazole (PBI, Fig. 1) for mild steel in hydrochloric acid solutions was investigated by weight loss and electrochemical techniques. Density Functional Theory (DFT) calculations and MD simulations were performed to study the electronic structure and the adsorption of PBI onto Fe (1 1 0) plane, respectively. To understand the inhibition mechanism of PBI for mild steel more explicitly, the inhibition actions of benzimidazole (BI) and pyridine (Py) were also studied using the quantum chemical method and MD simulations.
Section snippets
Materials
Mild steel containing 0.17 wt.% C, 0.20 wt.% Si, 0.37 wt.% Mn, 0.03 wt.% S, 0.01 wt.% P, and balance iron was used for weight-loss and electrochemical tests. For weight loss tests, the rectangular coupons with the size of 5.0 × 2.5 × 0.2 cm were used. A columned steel specimen, embedded in Teflon holder using epoxy resin with an exposed area of 0.785 cm2, was used as the working electrode for electrochemical measurements. The coupons and electrodes were abraded with wet SiC paper (up to 1200 grit),
Weight loss measurements
The inhibition efficiency (η) and corrosion rate (v) with different concentrations of PBI for mild steel in 1.0 M HCl solution at 25 °C were summarized in Table 1. The inhibition efficiency was calculated from the following equation:where v0 and v are the corrosion rates without and with inhibitor, respectively.
It is very clear from Table 1 that the corrosion rate of mild steel decreases sharply and the inhibition efficiency increases when the concentration of PBI increases. Maximum
Conclusion
PBI is a good inhibitor for mild steel corrosion in 1.0 M HCl, and inhibition efficiency increases with the increase in the concentration of PBI. However, inhibition efficiency of PBI for mild steel corrosion is affected by temperature and concentration of aggressive solution. As a mixed-type inhibitor with predominant cathodic effectiveness, PBI inhibits the reduction of H+ ions by merely blocking the reaction sites of mild steel surface. For the anodic dissolution, the presence of PBI results
Acknowledgements
The authors gratefully acknowledge the National Natural Science Foundation (21176116) and the Natural Science Foundation of Jiangsu Province (BK2011800) for financial support.
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