Green Approach to Corrosion Inhibition of Mild Steel in Hydrochloric Acid by 1-[Morpholin-4-yl(thiophen-2-yl)methyl]thiourea

Abstract

The inhibition effect of novel Mannich base 1-[morpholin-4-yl(thiophen-2-yl)methyl]thiourea on the corrosion of mild steel in 0.5 M hydrochloric acid solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements and surface examination through scanning electron microscope (SEM) technique. The results showed that Mannich base is an effective corrosion inhibitor and the inhibition efficiency increases with increase in concentration of the inhibitor. The corrosion behavior of mild steel in 0.5 M HCl without and with the inhibitor at various concentrations was studied at the temperature range of 303–333 K. Potentiodynamic polarization measurements showed that the Mannich base is a mixed-type inhibitor. EIS plots indicated that the presence of the inhibitor increases the charge transfer resistance of the corrosion process, increasing the inhibition efficiency. Temperature studies revealed that inhibition efficiency increased up to 323 K and beyond which inhibitor efficiency decreased because of desorption of inhibitor. The adsorption of inhibitor on mild steel surface is an endothermic reaction and is best described by the Langmuir adsorption isotherm. The surface adsorbed film was analyzed using SEM.