Preparation of three-dimensional braided carbon fiber reinforced mullite composites from a sol with high solid content

To prepare the three-dimensional braided carbon fiber reinforced mullite (3D C/mullite) composites, an Al2O3-SiO2 sol with a solid content of 20% (mass fraction) and an Al2O3-SiO2 mass ratio of 2:1 was selected as the raw material. Characteristics and mullitization of the sol were analyzed throughly. It is found that the formation of mullite is basically completed at 1300 degrees C and the gel powders exhibit favorable sintering shrinkage The 3D C/mullite composites without interfacial coating were fabricated through the route of vacuum impregnation-drying-heat treatment. Satisfied mechanical properties with a flexural strength of 241.2 MPa and a fracture toughness of 10.9 MPa.m(1/2) are obtained although the total porosity reaches 26.0%. Oxidation resistances of the composites at 1200, 1400 and 1600 degrees C were investigated. Due to the further densification of matrix, the 3D C/mullite composites show tiny mass loss and their mechanical properties are well retained after oxidation at 1600 degrees C for 30 min.