Effect of Organic Inhibitor on Corrosion of Mild Steel in Hydrochloric Acid

The inhibition effect of thiourea, hexamethylenetecramine and N-N I -dicyclohexylthiourea on mild steel corrosion in hydrochloric acid solutions has been examined by means of a hydrogen-evolution measurement and the surface observation of corroded specimens. The evoiltion -rate of hydrogen by the steel was kept constant in the acid solution with thiourea. In contrast, the evo- 1ution-rate redueced with time in the acid solution with the other inhibitors. The inhibitor concentration at which the inhibitor efficiency was over 90% was 500ppm for thiourea and only 50ppm for the other inhibitors. The surface of corroded specimens was much smoother in the acid solution with hexamethylenetetramine than in the acid solution with thiourea, regardless of the corrosion-rate. Thus, hexamethylenetetramine has been found as an excellent inhibitor for the corrosion of mild steel in hydrochloric acid solution