The electrochemical behaviour of copper in alkaline solutions containing fluoride, studied by in situ ellipsometry

In situ ellipsometry has been used to reveal a number of interesting features in the growth of passivating films on Cu in 0.1 M KOH containing KF. Fluoride ions are shown to affect the growth of the oxide layer and enhanced dissolution of copper as the Cu-II species occurs as a result of stress corrosion cracking. A restructuring of the oxide film within the passive region is attributed to loss of water and this effect becomes less distinct with increasing F- ion concentration in the electrolyte and disorder in the oxide layer. The enhanced reduction of the conductively inhibited bulk CuO/Cu(OH)(2) layer back to copper found in alkaline solutions containing fluoride would indicate that the formation of this layer is the dominant one for passivation of copper in this medium. The difference between the start and the end Delta-Psi values of the metal surface of the cyclic voltammogram at -1.5 V versus SCE indicates either roughening arising from the oxide formation/reduction or the presence of a residual surface oxide. (C) 1998 Elsevier Science B.V. All rights reserved.