Characteristics of 3D mullite fibre reinforced silica rich mullite matrix composites fabricated by sol-gel process

Three-dimensional mullite fibre reinforced silica rich mullite matrix (Mu(f)/S-Mu) composites were fabricated by sol-gel process employing silica rich mullite sols. The structural evolution of the mullite precursors and effects of sintering temperature on the mechanical and dielectric properties and microstructure of the composites were investigated. The results showed that the long club shaped orthorhombic mullite grains embedded in amorphous SiO2 were obtained for the gels sintered at 1200 degrees C. The composite fabricated at 1200 degrees C shows an obvious brittle failure behaviour, and the flexural strength of which is 54.2 MPa. The permittivity of the composites fabricated at 1200 degrees C is 5.41-10 11 at 8.2 GHz, and almost constant within measured frequency. between 8.2 and 12.4 GHz. Because of the enhancement of the matrix densification, the real part of permittivity of all composites increases as fabrication cycle increases from 8 to 13.