Effect of Thioureas and Triazoles on Hydrogen Penetration Rates in Iron

The rates of hydrogen penetration in annealed iron in 1N H₂SO₄ containing various thiourea and triazole compounds have been measured by the electrochemical technique. Corrosion rates were measured by the polarization method. The organic compounds selected for this study are thiourea, phenylthiourea, tolylthiourea, triazole, benzotriazole, and tolyltriazole. At lower organic concentrations, thiourea, phenylthiourea, tolylthiourea, and triazole were corrosion accelerators, while at all concentrations studied, benzotriazole and tolyltriazole were corrosion inhibitors. All three thiourea compounds accelerated the hydrogen penetration rate in iron, while the three triazole compounds were hydrogen penetration inhibitors. Thiourea accelerated and tolyltriazole inhibited hydrogen penetration to the greatest extent. Correlations between the open circuit hydrogen penetration rate and the corrosion rate have been obtained for the two groups of organic compounds. For the thiourea compounds, open circuit hydrogen penetration increased as corrosion decreased. In contrast, the open circuit hydrogen penetration decreased as corrosion decreased for the three triazole compounds.