Performance Optimization of Sol-Derived C/Mullite Composites by Reducing the Sintering Shrinkage of Mullite Matrix

C/Mullite composites were fabricated through sol impregnation-drying-heating (SIDH) route using the sol with a high solid content in our previous work, and the composites showed desirable performance. However, it was found that thermal stress caused by sintering shrinkage of mullite matrix is one of the main factors leading to the performance regression of the composites. In present study, the sintering characteristic of Al₂O₃-SiO₂ sol was modified to reduce the thermal stress caused by the sintering shrinkage of mullite matrix, optimizing the performance of the composites. The results showed that the sintering shrinkage of mullite matrix was reduced about 25% after heat treatment at 1600ºC by modifying the sintering characteristic of sol, resulting in that the thermal stress caused by sintering shrinkage of mullite matrix was reduced effectively. Therefore, the strength, modulus and fracture work of the composites were increased by about 19.4%, 24.5% and 24.9% to 318.4 MPa, 62.0 GPa and 6958 J/m², respectively. Furthermore, thermal stability of the composites was also improved obviously in Ar and vacuum environment.