Corrosion Inhibition and Adsorption Behavior of Some Thioamides on Mild Steel in Sulfuric Acid

Abstract

Abstract The objective of this work was to evalulate the effect of changing functional and structural groups on the protection efficiency imparted by the various inhibitor molecules. It was found that the molecules which include a thiocarbonyl group e.g. thiourea (TU), thioacetamide (TA), and thiosemicarbazide (TSC) exhibited much higher protection efficiencies than the corresponding compounds which do not e.g. semicarbazide, guanidine, and aminoguanidine. Furthermore, it made only little difference whether the thiocarbonyl group was attached to two amino groups as in thiourea, an amino and a methyl group as in thioacetamide or an amino and a methyl group as in thioacetamide above certain concentrations both TU and TA lose their efficiency and eventually become corrosion promotors. The adsorption behavior of TU and TA was quist complicated whereas that of TSC points towards complete coverage at high concentrations. The differences in behaviour between TSC, TU, and TA have been explained on the basis of delocalization or resonance stabilization energy.