Protection of mild steel corrosion with new thia-derivative Salens in 0.5 M H2SO4 solution

The corrosion inhibition of mild steel in 0.5 M sulfuric acid by two newly synthesized Schiff bases namely, 4-X-2-{[2-(2-pyridin-2-yl-ethylsulfanyl) ethylimino] methyl}-phenol [X = -NO2 (S-1) and -OMe (S-2)] has been investigated in the temperature range 298-318 K using Tafel polarization and electrochemical impedance spectroscopy (EIS) methods. The inhibition efficiency of both S-1 and S-2 increases with increase in inhibitor concentration. The variation in inhibition efficiency depends on the type of functional group substituted in the benzene ring. It was found that the presence of the methoxy group in the Schiff base (S-2) better facilitates the adsorption of molecules on the surface than is the case with S-1. Tafel polarization showed that both Schiff bases are mixed corrosion inhibitors. The Temkin isotherm was found to provide an accurate description of the adsorption behavior of the Schiff bases. Calculation of thermodynamic parameters such as Delta G(ads)(0), Delta H-ads(0) and Delta S-ads(0) shows that the inhibitive action of the inhibitors is in the following order S-1 < S-2.