Sol-gel control of matrix net-shape sintering in 3D fibre reinforced ceramic matrix composites

The origin of thermochemical degradation of 3D reinforced ceramic matrix composites has been analysed by dilatometry, pore-size distribution and electron microscopy and correlated to the cracking arising from the matrix shrinkage in an invariant 3D fibre network. The matrix shrinkage of an alumina matrix composite has been delayed zip to a higher temperature (+200 degrees C) by post-infiltration with pure alkoxide which was subsequently in situ hydrolysed, polycondensed and pyrolysed. Mechanical strength of the composites has been increased four times by optimizing alkoxides. The tensile and flexural mechanical strengths of these alumina matrix composites are similar to those obtained from SiC matrix composites prepared by the CVI process using the same 3D carbon preform. (C) 1997 Elsevier Science Limited.