high-temperature mechanical behaviour. The strength is Alumina/SiC nanocomposites were produced by mechanical mixture of commercial powders. The preparation steps involved the vigorous mixing of the powders and drying under conditions where the homogeneous mixture was kept stable. Pressureless sintering of die-pressed powders achieved reasonable densities (~9 7 % theoretical density) for 2.5wt% of Sic on sintering at 2073 K. Higher Sic contents strongly reduced the sintered density. The use of a more reactive alumina (finer matrix powder) gave similar results. Hot pressing at 19 73 K / 1 h/25 MPa produced highdensity materials for Sic contents as high as 20 wt%. Transmission and scanning electron microscopy analysis showed that the Sic particles were well distributed and were situated both inside the grains and on the grain boundaries of the alumina matrix. The Sic strongly inhibited grain growth in the matrix in keeping with the Zener model. The bend strength increased as the Sic content increased, a result partly explained by the grain size refinement. The strength improvement of 20% over monolithic was explained in terms of the change to an intergranular fracture mode.

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Neste trabalho foram utilizadas matérias-primas naturais para a obtenção de pós Al2O3/SiC através da redução carbotérmica das mesmas por um agente rico em carbono. Os aluminossilicatos estudados foram caulim, cianita e ilita-moscovita, sendo que os mesmos foram reduzidos ou por negro de fumo ou por grafite. Os pós resultantes da reação foram caracterizados por microscopia eletrônica de varredura e transmissão, difração de raios X e picnometria de hélio. Durante a reação, as diferenças existentes tanto na estrutura das matérias-primas quanto na composição química produziram pós com morfologia diversa. Foram encontradas estruturas como grandes aglomerados esféricos, whiskers, partículas e aglomerados fibrosos.

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