Steady-stage growth of NiO scales on ceria-coated polycrystalline nickel

The effect of CeO2 ceramic coatings with thicknesses in the range of 14 to 42 nm on the oxidation of high purity polycrystalline nickel at 973 K in 1 atm O-2 has been studied. The ceria coatings decrease the Ni oxidation rate after 125 h bg a factor up to 45, which is significantly higher than the reduction achieved during early stages. Growth features, including oxide thickness, surface morphology, and the texture for both the pure and CeO2 modified NiO, demonstrate a definite dependence on the crystallographic orientation of the Ni substrate. Oxides with thicknesses of up to 1 mu m developed on CeO2-coated Ni consisted of three sublayers. The Ce-rich part, composed of small NiO grains and CeO2 particles, was located inside the scale and shifted deeper into the scale with increased oxidation time. The growth kinetics and microstructural evolutions of modified NiO are discussed in terms of the mechanism of inhibition of grain boundary diffusion in NiO by Ce+4 ions.