Preparação e caracterização de mulita pelo processo sol-gel

Abstract

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We present a new sol-gel method to prepare gels of mullite (3Al2O3∙2SiO2) using as precursors a mixture of Si and Al alkoxides and a slow hydrolysis process. The gels have a polymeric structure with a high chemical homogeneity and crystallize at low temperature (980°C). X ray diffraction data indicate, at this temperature, the presence of a mixture of mullite and Al-Si spinel phases. The Al-Si spinel phase disappears at 1180°C and pure, well organized orthorhombic mullite is obtained at 1450°C. Ceramics prepared under uniaxial or isostatic pressing and sintered at 1550°C present, however, poor mechanical properties with apparent densities of the order of 70 to 80% of the theoretical density (3.17 g cm(-2)).