Fundamental studies of copper anode passivation during electrorefining .2. Surface morphology

Passivation of commercial copper anodes and pure copper has been previously analyzed by performing electrochemical measurements. Chronopotentiometry results revealed four characteristic regions involving I-active dissolution, II-prepassivation, III-passivation onset, and IV-passivation, for commercial copper anodes, while only active dissolution was observed for pure copper under the conditions employed. In order to establish the relationship between surface morphology and passivation response, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS) were applied to characterize morphology of the product layers formed on a commercial copper anode surface for the distinctive electrochemical regions. The morphology studies suggested that the formation and stability of copper oxide surface films are critical to the onset and development of passivation. The structure and porosity of the slimes layer present in the outer layer of the anode influence the stability of copper oxide surface films which dominantly control the passivation response.