MULLITE AND ALUMINA SILICA MATRICES FOR COMPOSITES BY MODIFIED SOL-GEL PROCESSING

An alumina-silica gel of stoichiometric mullite (3Al2O3.2SiO2) composi tion, prepared using submicrometre alumina powder and colloidal silica sol as precursors, was sintered to over 98% of full density at 1300-d egrees-C, as a result of the viscous sintering of the silica. Almost f ull mullitisation was achieved at 1600-degrees-C after 2 h. Unidirecti onal fibre composites were synthesised by single stage infiltration of carbon fibres with the alumina-silica sol. The composite was hot-pres sed to over 97% of full density at 1400-degrees-C and exhibited a non- brittle failure with a mean flexural strength of 766 MPa.