Anodic Behavior of Copper in Chloride/Tolytriazole and Chloride/Benzotriazole Solutions

Potentiodynamic techniques were used to compare the effects of tolytriazole (TTAH) and benzotriazole (BTAH) corrosion inhibitors on anodic polarization behavior of copper in 1 M sodium chloride (NaCl). Variations in experimental procedure included the injection of inhibitor before commencing the potential scan, injecting the inhibitor during the scan, and scribing the surface of the copper electrode in the presence of the inhibitor. Results were compared to the behavior of copper in the absence of inhibitor and interpreted with respect to aqueous thermodynamic equilibria in the copper-chloride-water (Cu-Cl⁻-H₂O) system. Both inhibitors exhibited adsorption behavior in the active region where copper was dissolving as cuprous chloride complex (CuCl₂^–). Adsorption of TTAH was more pronounced, had more effect on the apparent Tafel slope, and moved the kinetics of active dissolution from a mass transfer-kinetic controlled process, involving transport of CuCl₂⁻ in the liquid phase, to a charge-transfer controlled process at the electrode surface. At higher potentials, both inhibitors caused an active-to-passive transition by reacting with CuCl₂⁻ to form films of cuprous tolytriazole (CuTTA) and cuprous benzotriazole (CuBTA) on an oxide-free surface. Effects of pH were discussed in relation to the mechanism of passive film formation. Anodic behavior in the passive region was considered to be determined by movement of ions through the film. The range of potentials over which passivity occurred varied, and a limiting potential was predicted above which repassivation was unlikely to occur in the event of local film breakdown.