Effects of oxidation conditions on the microstructure and texture of NiO in a cube-textured polycrystalline nickel substrate

Surface oxidation behavior of cube-textured polycrystalline nickel was investigated at various oxidation conditions. Cube-textured nickel substrate, which was prepared by rolling and texture anneal, was used. Cube-textured NiO film was formed on a cube-textured polycrystalline nickel regardless of oxidation conditions but different growth behavior of NiO crystals was observed depending on the oxidation conditions. The introduction of water vapor in O-2 did not affect on the texture evolution but rough and porous microstructure was developed. Microstructure of NiO film tends to be denser as the oxygen partial pressure is increased. It is interesting that (111) oriented crystal grew favorably in the substrate oxidized in air atmosphere while (200) plane was major in the substrate oxidized in high purity argon gas. Other crystallographic planes than (200) plane were developed when N2O was used as an oxidant while only (200) plane crystal was formed in dry O-2 atmosphere. The morphology and texture of NiO crystal were changed from smooth one into faceted one when oxidation was performed at 900 degrees C in dry O-2 gas followed by the reduction under a reducing atmosphere. It is thought that absorption behavior of oxygen or OH varies depending on the oxidizing species. (c) 2006 Elsevier B.V. All rights reserved.