Formation of passivating layers by 1,2,4-triazole derivatives on copper in aqueous solutions

Ellipsometry and electrochemical measurements are used to study the adsorption of some substituted 1,2,4-triazoles on copper and their effect on dissolution of copper in aqueous buffer solutions at pH 7.4. It is found that the adsorption of triazole compounds on copper is polymolecular at potential D center dot = 0.0 V, in relation to a normal hydrogen electrode. The first layer is described by the Temkin equation with free adsorption energy (-Delta G (a) (0)) = 55.2-76.3 kJ/mol and an energy heterogeneity factor that varies from 0.91 to 2.5. The maximum value of -Delta G (a) (0) is found for an acid and a hydrogen sulfide corrosion inhibitor that is a mixture of triazole derivatives. The same inhibitor is the one least sensitive to the energy heterogeneity of the surface of a copper electrode, due to its high chemical reactivity and ability to be adsorbed on different active sites. This inhibitor is likely chemisorbed on copper and forms an ultrathin coating in an aqueous solution that is vastly superior to similar coatings produced by the familiar corrosion inhibitors of triazole group compounds in protecting against atmospheric corrosion.