THE EFFECT OF THERMAL ANNEALING ON THE PROPERTIES OF ALUMINA FILMS PREPARED BY METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION AT ATMOSPHERIC-PRESSURE

Thin films deposited at 330-degrees-C by metal organic chemical vapour deposition on stainless steel, type AISI 304, were annealed in a nitr ogen atmosphere for 1, 2 and 4 h at 600, 700 and 800-degrees-C. The fi lm properties, including the protection of the underlying substrate ag ainst high temperature corrosion, the chemical composition of the film and the microstructure, were investigated. Corrosion experiments perf ormed at 450-degrees-C in a hydrogen sulphide containing gas, showed t hat the cracks in the alumina films almost completely disappeared afte r a post-deposition heat treatment, probably as a result of stress rel axation. The porosity of the alumina films was not affected by this he at treatment. X-ray diffraction measurements of these films, deposited at 330-degrees-C, revealed an amorphous structure. Owing to the therm al annealing process, the amorphous alumina films were converted to ga mma-alumina, and OH-groups disappeared.