Geometric influences on the spontaneous passivation of copper in alkaline hexacyanoferrate(III) solutions under conditions of free convection

Abstract

The passivation of copper proceeds in the presence of an oxidizing agent without an external current. Cyclovoltammetric, chronopotentiometric and open-circuit potential measurements show, that in alkaline solution the passivation rate increases with decreasing hydroxide and increasing hexacyanoferrate(III) concentration. The rate increases also by the formation of mixed potentials with NiCrSiO x surfaces and by reduction of the surface area. These effects can be explained by an increase of the diffusion-controlled cathodic partial current in comparison to the anodic partial current. The influence of surface area on the passivation rate is important on surfaces with an extension of about or smaller than the thickness of the diffusion layer.