Chemical composition and Mott-Schottky analysis of passive film formed on G3 alloy in bicarbonate/carbonate buffer solution

The chemical composition and semi-conductive properties of passive film on nickelbased alloy (G3 alloy) in bicarbonate/carbonate buffer solution were investigated by Auger electron spectroscopy (AES),X-ray photoelectron spectroscopy (XPS),electrochemical impedance spectra (EIS) and Mott-Schottky plot.AES and XPS results showed that the passive film appeared double-layer structure,in which the inner film was composed of nickel oxide,the mixed nickel-chromium-molybdenum-manganese oxides were the major component of the outer film.The electrochemical results revealed that the factors including frequency,potential,time,temperature and pH value can affect the semi-conductive property,the doping densities decreased with increasing potential and pH value,prolonging time and decreasing temperature.According to the above results,it can be concluded that the film protection on the substrate was enhanced with increasing potential and pH value,prolonging time and decreasing temperature.