Electrochemical potential oscillations during galvanostatic passivation of copper in NaNO_2 solution and their role in TGSCC mechanism

摘要

Auto-oscillations of the electrochemical potential around its average value close to +100 mV_(SCE) under galvanostatic polarization of pure copper in 0.3M NaNO_2 solution were studied in annealed state of copper and during slow strain rate tensile tests of cold-deformed copper. The oscillations occur in the potential range where the passivation current increases dramaticaly due to Cu~(++) cation generation in the semi-coherent oxide film on the copper substrate. Parameters of the oscillations were measured depending on the polarization conditions. It was supposed that the observed oscillations represent a nonlinear relaxation process in the passive oxide film interacting with the metal substrate at the semi-coherent oxide/metal interface. Based on the idea that cation vacancy balance at the Cu_2O/Cu interface depends on the stresses induced in the metal substrate by the interface conditions, a model of the observed nonlinear phenomena was formulated.