In-situ investigation of the interplay between microstructure and anodic copper dissolution under near-ECM conditions. Pt.2: The transpassive state

During the anodic dissolution of pure copper in sodium nitrate under near-ECM conditions the influence of the crystallographic orientation of individual grains on the dissolution behaviour was simultaneously investigated. Two different states can be distinguished - the active and the transpassive state. The dissolution shows a continuous transition from one state to the other, depending on the current density j c which itself is determined by the velocity of the electrolyte. For j < j c the active state is marked by an orientation dependant anodic dissolution. Above the critical density j c the crystallographic orientation of the grains is no longer an influencing factor and therefore a homogenous dissolution takes place. This is called the transpassive state which will be analysed in t his paper in detail. For this, in-situ-experiments combining electrochemistry and optical microscopy together with EBSD investigations and current efficiency measurements had been undertaken.