Oxidation study of a polycrystalline Ni/Cr alloy. I. Room-temperature exposure to O2

The changes induced at a cleaned polycrystalline Ni/Cr alloy surface upon increasing oxygen exposure (0 to 100 L) at room temperature were studied by Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS), and X-ray photoelectron spectroscopy (XPS). Cr oxides, NiO and hydroxides form near the surface during the initial 5 L exposure. More of the oxygen present is bonded as NiO than Cr oxide, but a larger fraction of the near-surface Cr is oxidized. The Cr oxide formed consists of a mixture of CrO2, Cr2O3 and CrO3 with CrO2 as the predominant form. With increasing exposure to 100 L, both metallic Cr and Ni become increasingly oxidized, but most of the Ni within 3.5 nm of the surface remains in metallic form after a 100 L exposure. ISS data indicate that the outermost atomic layer becomes enriched in Cr with oxygen exposure, while AES data indicate a small enrichment of Cr in the near-surface region sampled by this technique. AES data also indicate that the oxygen uptake is rapid to 20 L and then slow above that exposure. (orig.)