Electrochemical potential oscillations during galvanostatic passivation of copper in NaNO2 solution and their role in TGSCC mechanism

Abstract

This chapter presents a study in which the potential oscillations of pure copper, galvanostatically polarized in NaNO2 solution under slow strain rate tensile test (SSRT) conditions, are examined. Pure copper (99.998 wt.%) containing less than 75 ppm oxygen was used for the study, where billets of copper were cold-rolled to 1 mm thick strips with intermediate heat treatments. Polarization measurements were performed at room temperature in 0.3M NaNO2 solution (pH 8.3), deaerated by nitrogen gas purging. Saturated calomel type electrode and platinum plate were used as reference and counter electrodes in both electrochemical cells. The study found that electrochemical potential oscillations occurred in pure cooper during its galvanostatic anodic polarization in 0.3M NaNO2 solution in the range of potentials above +50 mVSCE, where an intensive dissolution of the cuprous oxide started to proceed by Cu++ cations at the oxide/solution interface. Potential oscillations are observed in annealed as well as in cold-deformed copper under SSRT, where the average period of oscillations depended on the strain rate of copper substrate.