Abstract
Thin amorphous alumina films were deposited on AISI 304 by thermal decomposition at low pressure (0.17 kPa (1.25 Torr)) of aluminium-tri- sec-butoxide (ATSB). The effect of the deposition temperature (within the range 200–380 °C) has been studied in relation to film properties including the protection of the underlying substrate against high-temperature corrosion, the chemical composition of the film, the microstructure and its refractive index. The activation energy for the heterogeneous reaction was 65 ± 2 kJ mol −1. Corrosion experiments, performed at 450 °C in a hydrogen sulphide gas, showed that the alumina coatings giving the best protection were obtained at a deposition temperature of 280 °C. The alumina films showed an amorphous structure, in agreement with the index of refraction. Transmission electron microscopy analysis revealed extremely fine grains of γ- Al 2O 3 AlO(OH) . Only OH groups were found as an “impurity” in the oxide film. Carbon was not detected.
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