2,2′-Dithiobis(3-cyano-4,6-dimethylpyridine): A new class of acid corrosion inhibitors for mild steel

The title compound (PyS)2 has been synthesized and its inhibiting action on the corrosion of mild steel in 1–5 M H2SO4 solutions at 35–50 °C has been investigated by polarization resistance (Rp), polarization curves and electrochemical impedance spectroscopy (EIS). (PyS)2 showed excellent performance and its efficiency did not affect either by increasing the acid concentration or rise of temperature. Polarization curves indicated that (PyS)2 behaves mainly as anodic inhibitor in 1 M H2SO4 solutions and as a mixed-type inhibitor in 3 and 5 M H2SO4 solutions at different temperatures. Adsorption of (PyS)2 on the steel surface followed Temkin’s adsorption isotherm with a very high negative value of the free energy of adsorption (ΔGads0). The activation parameters of the corrosion process were calculated. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions.