Understanding the Adsorption of Quinoxaline Derivatives as Corrosion Inhibitors
The anti-corrosive properties of (E)-3-styrylquinoxalin-2(1H)-one (STQ), (E)-1-benzyl-3-(4-methoxystyryl) quinoxalin-2(1H)-one (BMQ) and (E)-3-(2-(furan-2-yl) vinyl) quinoxalin-2(1H)-one (FVQ) were analyzed by different techniques such as: potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss (WL) and molecular modeling by DFT method and Monte Carlo simulation studies. All quinoxaline derivatives showed appreciable inhibition efficiency. Among the quinoxaline derivatives studied, BMQ exhibited the best inhibition efficiency. The results from the experimental and theoretical investigations show that the order of inhibition efficiency by the quinoxaline derivatives follow the order BMQ > FVQ> STQ.
The experimental results suggest that the three tested inhibitors function as mixed-type compounds and the inhibition efficiency increases with the increase in inhibitor concentration and decreased with temperature. Adsorption of the three compounds on mild steel (MS) surface obeys Langmuir’s isotherm model. The theoretical study by DFT method, Monte Carlo simulation and radial distribution function (RDF) provided strong evidence that the inhibition efficiency of quinoxaline derivatives is due to their ability to adsorb strongly at the MS surfaces, which is supportive of the obtained experimental results.
Mild steel is an iron-containing alloy, considered as one of important constructional materials extensively used in different applications. Generally, acid solution (especially hydrochloric acid) plays a significant role in many fields of industry such as pickling, descaling and oil well acidification, its price is generally low and more consistent. In the few last decades the use of chemical compounds as corrosion inhibitors is considered as one of the efficient and practical methods to protect the metals surfaces against aggressive mediums such as acidic solutions.
The effectiveness of these molecules is mainly from their ability to adhere to metal surfaces. The use of synthetic inhibitors also appears to be economically viable and promising because of their simplicity in application, and they’re relatively cheaper. Meanwhile, the adsorption of these inhibitors produces a protective insoluble film on the MS surface, which reduces contact with the corrosive mediums and consequently the degree of metal attack. The presence of N, O, S atoms and conjugates aromatic nucleus are responsible for their essential characteristics.
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