Application of electrochemical frequency modulation for monitoring corrosion and corrosion inhibition of iron by some indole derivatives in molar hydrochloric acid

The corrosion inhibition effect of four indole derivatives, namely indole (IND), benzotriazole (BTA), benzothiazole (BSA) and benzoimidazole (BIA), have been used as possible corrosion inhibitors for pure iron in 1 M HCl. In this study, electrochemical frequency modulation, EFM was used as an effective method for corrosion rate determination in corrosion inhibition studies. By using EFM measurements, corrosion current density was determined without prior knowledge of Tafel slopes. Corrosion rates obtained using EFM, were compared to that obtained from other chemical and electrochemical techniques. The results obtained from EFM, EIS, Tafel and weight loss measurements were in good agreement. Tafel polarization measurements show that indole derivatives are cathodic-type inhibitors. Molecular simulation studies were applied to optimize the adsorption structures of indole derivatives. The inhibitor/iron/solvent interfaces were simulated and the adsorption energies of these inhibitors were calculated. Quantum chemical calculations have been performed and several quantum chemical indices were calculated and correlated with the corresponding inhibition efficiencies.