Electrochemical and Surface Investigation of Thin-Surface Films Over 90Copper-10Nickel Alloy in Chloride Ion-Containing Electrolytes

The electrochemical behavior of copper-nickel alloy 90Cu-10Ni is studied in various electrolytes of sulfuric acid, sodium sulfate, sodium chloride, and sulfate/chloride-containing electrolytes. The structure and nature of the semi-passivating film formed on the electrode surface depended on the type of electrolyte and exposure time. Relatively high cathodic current densities were measured in sulfuric acid-containing electrolytes with short Tafel regions in the positive side of the steady-state potential. Barrier-thin oxide films mainly composed of Cu⁺ species are formed at the onset of metal exposure to the electrolytes. Nickel incorporation was observed with relative dissolution into the electrolyte side, with the lowest percentage observed in case of sodium sulfate. Scanning electron microscopy showed compact films formed in sulfuric acid and sodium sulfate, and porous ones in chloride-containing solutions. Film structure was examined by x-ray photo-electron spectroscopy, while both copper and nickel ions concentrations in solution were followed by inductively coupled plasma analysis with the time of polarization.