Thin Surface Films Over Copper-Nickel Alloy: Corrosion Behavior in Neutral and Acidic Medium in Presence of Chloride Ions

摘要

Oxide films were grown over 90Cu-10Ni alloy using electrochemical polarization. The structure of the films was determined using a variety of surface techniques. Polarization curves were recorded for the alloy in different electrolytes of chloride, sulfate and the corresponding mixtures. It was ascertained that a protective layer consisting mainly of a thin, strongly adherent inner barrier Cu_2O-layer that is followed by a porous and thick outer Cu(II) hydroxide/oxide-layer is formed. Nickel affects the barrier properties of the surface film through a segregation of Ni from the alloy into the Cu_2O layer. The composition of the film formed over 90Cu-10Ni alloy was determined at different polarization times using FE-SEM/EDAX, XPS, ICP-ES, and electrochemical measurements. The ratio of Cu:Ni is maintained in the film composition after few seconds from the inset of polarization in chloride containing electrolytes. Ni-content in the film decreases and then increases after 30 and 60 minutes of the inset of polarization, respectively. In sodium sulfate and sulfuric acid solutions, the Cu:Ni ratio in the film is respected throughout the polarization times.