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 H₂ absorbed by cold-rolled mild steel in 1 N H₂SO₄ at 40°C was studied. Inhibitor efficiency increased with increases in molecular weight and inhibitor concentration. Higher inhibitor concentrations decreased H₂ pickup. Thiourea accelerated corrosion reactions and H₂ 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.