Influence of CaO or CeO_2 coatings on oxidation of nickel polycrystals

摘要

The present study is concerned with the influence of CaO, or CeO_2, sputter coatings on the oxidation behavior of specpure Ni polycrystals. The experiments were performed between 800° and 1200°C. The CeO_2-coated specimens show a more pronounced decrease of the oxidation kinetics than those coated with CaO. The beneficial influence of these coatings is first explained by the presence of CaO, or CeO_2 precipitates near the position of the initial metal surface. For the CeO_2-coated specimens, the lower oxidation rates are also due to the decrease of the vacancy diffusion coefficient, while for the CaO coatings, it results of the decrease of the driving force of diffusion, due to the shift of the Ni/NiO phase boundary to higher PO_2.