Thermodynamic, chemical and electrochemical investigations of 2-mercapto benzimidazole as corrosion inhibitor for mild steel in hydrochloric acid solutions

The inhibiting action of 2-mercapto benzimidazole (2MBI) on mild steel in 1.0 M hydrochloric acid has been investigated at 308 K using weight loss measurements and electrochemical techniques (impedance spectroscopy and potentiodynamic polarisation). Inhibition efficiency increases with 2MBI concentration to attain 98% at 10−3 M. Polarisation curves indicate that 2MBI acts as a mixed-type inhibitor. Inhibition efficiency values obtained from various methods were in good agreement. EIS measurements showed an increase of the transfer resistance with the inhibitor concentration. The temperature effect on the corrosion behaviour of steel in 1.0 M HCl without and with the 2MBI at various concentrations was studied in the temperature range from 308 to 353 K. Thermodynamic parameters such as heat of adsorption (ΔHads∘), entropy of adsorption (ΔSads∘) and adsorption free energy (ΔGads∘) have been calculated. Kinetic parameters for the corrosion reaction at different concentrations of 2MBI were determined. Adsorption of 2MBI on the mild steel surface in 1.0 M HCl follows the Langmuir isotherm model.