Comparative study of N-[(4-methoxyphenyl) (morpholin-4-yl)methyl]acetamide (MMPA) and N-[morpholin-4-yl(phenyl)methyl]acetamide (MPA) as corrosion inhibitors for mild steel in sulfuric acid solution

Two Mannich bases namely, N-[(4-methoxyphenyl)(morpholin-4-yl)methyl]acetamide (MMPA) and N-[morpholin-4-yl(phenyl)methyl]acetamide (MPA) were synthesized and their influence on the inhibition of corrosion of mild steel in 1.0 M H2SO4 was investigated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and FT-IR spectroscopy. The weight loss measurements showed that these inhibitors have excellent inhibiting effect at a concentration of 0.01 M. The inhibitor efficiency was found to depend on both concentration and molecular structure of the inhibitor. Both the compounds have been found to be relatively good inhibitors. Potentiodynamic polarization curves revealed that the studied inhibitors represent a mixed-type, predominantly cathodic control. An equivalent circuit is suggested based on an analysis of EIS data. The negative value of standard free energy of adsorption in the presence of inhibitor suggests spontaneous adsorption of inhibitors on the mild steel surface. The activation energy of corrosion and other thermodynamic parameters were calculated to elaborate the mechanism of corrosion inhibition. The Temkin isotherm was found to provide an accurate description of the adsorption behavior of the inhibitors. Surface analysis using scanning electron microscope (SEM) shows a significant morphological improvement on the mild steel surface with the addition of inhibitors. FT-IR spectra revealed the interaction between inhibitor molecules and mild steel surface.