Inhibition of Corrosion of Iron in Acids by Thiourea and Derivatives

The inhibition of corrosion of iron (0.13%C) in hydrochloric acid by thiourea and its derivatives has been investigated. Inhibition is due to adsorption of the molecular species. The maximum of efficiency with low concentrations of thiourea and its N‐substituted derivatives is attributed to the protonation of the inhibitor with consequent acceleration of the hydrogen evolution process. Protonation is high with the simple thiourea and increases with the concentration of the inhibitor and hydrogen ion concentration. S‐substituted derivatives show an increasing efficiency with concentration and are safe inhibitors.