Pitting corrosion of copper in sulphate solutions:: inhibitive effect of different triazole derivative inhibitors

The inhibitive effect of 3-amino 1,2,4-triazole (ATA) on the pitting corrosion of copper induced by sulphate ions was compared to that obtained with benzotriazole (BTAH) and 1-hydroxybenzotriazole (BTAOH) and to previous results obtained in chloride media. It was concluded that the inhibitive action of these compounds towards pitting corrosion was dependent on the aggressive species. For BTAH and BTAOH, the inhibitive efficiency was greater towards pitting induced by sulphate than towards pitting induced by chloride which was explained by referring to the surface area covered by the organic molecules and to the size of the aggressive species. For ATA, an opposite behaviour was observed and was explained by quantum chemical calculations. First, the binding energy between clusters of Cu+ ions and Cl- was much weaker than that between clusters of Cu+ ions and SO42-. Secondly, the adsorption of Cl- on ATA linked to copper ions was more favourable than its adsorption on copper oxide. Moreover, the sulphate ion had a larger adsorption energy on copper ions than on ATA linked to copper ions.