The oxidation of cupronickel alloys—I. XPS study of inter-diffusion

The outer surface of thick oxides formed on the high copper-cupronickel alloys is invariably copper oxide, yet at room temperature the oxide film is entirely nickel oxide. The ESCA (or XPS) technique has been used to determine the temperature at which overgrowth of the initial nickel oxide by cuprous oxide takes place on a alloy. By means of interrupted oxidation runs on a heated probe in the ESCA spectrometer, the physical and chemical displacement of Cu₂O by NiO has been followed. It is concluded that the diffusion step in this displacement reatcion is probably rate controlling during oxidation of the alloy at temperatures up to 650°C.The XPS spectra have been interpreted quantitatively and excellent agreement is found between the calculated stoichiometry and the chemical shifts of the Auger spectra.