Oxidation behaviour of alumina-silicon carbide nanocomposites

Oxidation studies were conducted on Al2O2-SiC nanocomposites at 1400 degree s C. The composites were prepared by hot-pressing mixtures of commercial al umina and ultrafine SiC powders, in amounts of 5, 15 and 30 vol %. Linear k inetics were detected for the oxidation of composites containing 5 vol % Si C. Two stages were observed in composites containing 15 vol % SiC: the firs t linear and the second presumably parabolic. A parabolic behaviour was obs erved in the sample containing 30 vol % SiC. The oxidation rates were sever al orders of magnitude higher than those of monolithic SiC and the observed data we re not consistent with the expected increase in weight associated with the oxidation reaction of SiC to SiO2; in fact the most surprising fea ture is that the sample containing 30 vol % SIC showed a better oxidation r esistance than samples containing 5 and 15vol% SiC. The reaction products w ere alumina and mullite in samples with 5 and 15 vol % SIG, while mullite a nd silica were found on the oxidized surface of samples containing 30 vol % SiC. Explanations are given of the influence of the oxidizable phase amoun t, the presence of impurities, reaction product structure and composition. (C) 1998 Kluwer Academic Publishers.