THE EARLY-STAGE OXIDATION-KINETICS OF CEO2 SOL-COATED NICKEL

CeO2 sol with particle diameter of 5 nm was applied to the surface of both chemically and mechanically polished polycrystalline nickel. The oxidation kinetics during early stages of NiO formation have been measured with an ultrahigh vacuum manometric system in the temperature range of 873 to 1073 K and oxygen pressure 5 x 10(-3) Torr. The ceria coatings reduced the nickel oxidation rate by up to a factor of 4, but the extent of the effect depended on coating thickness, substrate surface finish, and preoxidation prior to coating. After oxidation the Auger electron spectroscopy sputter profiles revealed the cerium concentration maximum in the vicinity of the gas-oxide interface. As was determined by scanning and transmission electron microscopy, ceria coatings resulted in formation of more uniform oxide films, with grain size much smaller than that observed on pure nickel. Ceria particles with diameter less than 10 nm were detected both inside nickel oxide grains and at oxide grain boundaries.