Oxidation behaviour of Alumina-Silicon carbide nanocomposites

Oxidation studies were conducted on Al2O2ÐSiC nanocomposites at 1400 ¡C. The composites were prepared by hot-pressing mixtures of commercial alumina and ultrafine SiC powders, in amounts of 5, 15 and 30 vol %. Linear kinetics were detected for the oxidation of composites containing 5 vol% SiC. Two stages were observed in composites containing 15 vol% SiC: the first linear and the second presumably parabolic. A parabolic behaviour was observed in the sample containing 30 vol% SiC. The oxidation rates were several orders of magnitude higher than those of monolithic SiC and the observed data were not consistent with the expected increase in weight associated with the oxidation reaction of SiC to SiO2; in fact the most surprising feature is that the sample containing 30 vol% SiC showed a better oxidation resistance than samples containing 5 and 15 vol% SiC. The reaction products were alumina and mullite in samples with 5 and 15 vol% SiC, while mullite and silica were found on the oxidized surface of samples containing 30 vol% SiC. Explanations are given of the influence of the oxidizable phase amount, the presence of impurities, reaction product structure and composition.