THE FORMATION OF ANODIC LAYERS ON ANNEALED COPPER SURFACES IN PHOSPHATE-CONTAINING SOLUTIONS AT DIFFERENT PH

The electrochemical behaviour of Cu in different phosphate buffers is studied through electrochemical techniques combined with scanning electron microscopy and energy dispersive X-ray analysis. At pH 6.0 and 8.0 the onset of passivation is due to the anodic formation of a basic Cu(II) phosphate, whereas at pH 11.5 the passivating layer corresponds to a duplex Cu(I) oxide-Cu(II) oxide layer. The potentiostatic anodic current transients can be reproduced by a model involving the initial growth of a thin anodic layer and the simultaneous electrodissolution of Cu. The electrodissolution of passivated Cu takes place through the passivating layer. This reaction contributes to the thickening of the outer part of the passivating layer.