Asymmetrical Schiff bases as inhibitors of mild steel corrosion in sulphuric acid media

Two newly synthesised Schiff bases [H2A3, N,N′-ortho-phenylene(salicylaldimine-acetylacetone imine) and H2A4, N,N′-ortho-phenylene(salicylaldimine-2-hydroxy-1-naphthaldimine)] were studied as inhibitors for the corrosion of mild steel in 0.5 mol dm−3 sulphuric acid. Results of weight loss, electrochemical impedance and Tafel polarisation measurements consistently identify both compounds as good inhibitors, with efficiencies of around 95% at a concentration of 400 ppm. The inhibition is in both cases of a mixed anodic–cathodic nature. Differences in inhibition efficiency between H2A3 and H2A4 are correlated with their chemical structures. Several adsorption isotherms are assessed, and the Temkin isotherm is found to provide an accurate description of the adsorption behaviour of the investigated Schiff bases.