The effect of a 1,1’-(2-phenylquinoxaline-1,4-diyl)diethanone (PQE) on the corrosion of carbon steel in 1.0 M HCl solution has been investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. Inhibition efficiencies of PQE increased as the concentration of quinoxaline derivative increases, but decreased with increases in temperature. The Langmuir adsorption isotherm was found to be the best isotherm that described the adsorption characteristics of the inhibitor. Also, the activation and thermodynamic parameters of dissolution were calculated and discussed. Electrochemical polarization measurements revealed that PQE acted as a mixed-type inhibitor and the results of electro-chemical impedance spectroscopy have shown that the change in the impedance parameters, charge transfer resistance and double layer capacitance, with the change in concentration of the inhibitor is due to the adsorption of the molecule leading to the formation of a protective layer on the surface of mild steel. The adsorption was assumed to occur on the steel surface through the active centers of the molecule. Density functional theory calculations of quantum parameters were used to explain efficiency in relation with molecular structure.
