Fabrication and Properties of Three-dimensional Braided Carbon Fiber Reinforced SiOa-rich Mullite Composites

In order to enhance the fracture toughness of mullite, three-dimensional braided carbon fiber reinforced mullite (C/mullite) composites were prepared using the Al2O3-SiO2 sol with a high solid content as raw material. Mullitization behavior of the sol was characterized. Then, the microstructure, mechanical properties and oxidation resistance of C/mullite composites were investigated. It is found that the SiO2-rich mullite with desirable sintering shrinkage can be synthesized at 1 300 degrees C from the sol with an Al(2)0(3)/SiO2 mass ratio of 1:1. The C/mullite composites with a total porosity of 21.5% were fabricated by repeating 18 cycles of vacuum impregnation-drying-heat treatment, showing a flexural strength of 234.5 MPa and a fracture toughness of 13.1 MPa center dot m(1/2). Since carbon fibers were protected by compact matrix, the C/mullite composites show favorable oxidation resistance during 1 200 degrees C-1 600 degrees C even if an open porosity of 10.3% was detected.