Surface analytical examination of passive layers on Cu-Ni alloys .2. Acidic solutions

The formation and chemical structure of passive layers on Cu-50Ni and Cu-20Ni in acidic electrolytes have been examined with X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). Phthalate buffer pH 5.0 and 0.005 M H2SO4 + 0.995 M K2SO4 pH 2.9 have been used for passivation. The corrosion behaviour of the alloys is characterized by the characteristic properties of both alloy components, i.e. increased dissolution of Cu and passivating properties of Ni in acidic electrolytes. A similar multilayer structure with an outer hydroxide and an inner oxide with lower valent cations in an inner position is found as for alkaline solutions. The incorporation of Cu-ions in the outer hydroxide part is extremely small and approaches zero for low pH as a consequence of the increased dissolution rate of Cu2+ for acidic electrolytes. Copyright (C) 1996 Published by Elsevier Science Ltd.