Oxidation of an amorphous Ni77P23 alloy in air and dry oxygen at 300 °C

The oxidation behaviour of an amorphous Ni77P23 alloy, prepared by electrodeposition, was investigated in air and in dry oxygen at 300 °C. The morphology, structure and composition of the oxide developed on the alloy were examined by X-ray photoelectron spectrometry, secondary-ion mass spectrometry (SIMS), and by high resolution transmission electron microscopy of ultramicrotomed sections. With successful preparation of extremely thin ultramicrotomed sections, between 5 and 10 nm thick, the microstructure of the oxide grown on the alloy and the oxide-alloy interface were revealed clearly, at atomic scale resolution, for the first time. SIMS depth profiling analysis has shown that the oxide films, grown in air and dry oxygen, consist mainly of NiO. However, the oxide growth rate in air was found to be considerably less than that in dry oxygen. High resolution cross-sectional transmission electron microscopy has shown that the difference in oxidation rates appears to be due to the distinctly different mosaic structure of the oxide films grown in air and dry oxygen which, in turn, affects the length of easy paths for Ni2+ diffusion during oxide growth.