An electrochemical study of the passive film formed on Ni-Cr (80/20) coating

The passive state of Ni-Cr (80/20) coatings prepared by a plasma beam sputter deposition process was studied using cyclic voltammetry and impedance spectroscopy techniques. The highly protective quality of the film formed in acetate buffer, pH = 5.7, is probably based on chromic species. The nickel content in the film was very low and influenced only the electronic properties of the film. The appearance of a distinct transition in the capacitance potential characteristic may be correlated with the presence of higher valent chromium species. Cyclic voltammetry demonstrated that Cr(VI) was incorporated into the outer part of the oxide film, or was tenaciously adsorbed on the electrode surface. Its formation and reduction were reversible. (orig.)