Inhibition of steel corrosion by thiourea derivatives

The thiourea group of sulfur compounds has important theoretical and practical applications. Thioureas have been studied extensively, but their inhibition mechanism is not fully understood. The effect of thiourea; allylthiourea; N,N'-diethylthiourea; N,N'-di-isopropylthiourea; phenylthiourea; thiocarbanilide; and symdiotolylthiourea on the corrosion reaction and on the amount of H-2 absorbed by cold-rolled mild steel in 1 N H2SO4 at 40-degrees-C was studied. Inhibitor efficiency increased with increases in molecular weight and inhibitor concentration. Higher inhibitor concentrations decreased H-2 pickup. Thiourea accelerated corrosion reactions and H-2 pickup at higher concentrations. Potential studies showed cathodic reactions was inhibited at lower concentrations and anodic reactions were inhibited at higher concentrations. Results were based on the adsorption theory, and all inhibitors studied followed the Langmuir isotherm.