Application of Sol-Gel Derived Mullite in Three-Dimensional Oxide Fiber-Reinforced Composites as Porous Matrix

Near-stoichiometric orthorhombic mullite powders, showing good chemical and thermal stability, were synthesized through the sol-gel process using diphasic Al2O3-SiO2 sol as starting material. Subsequently, three-dimensional (3D) Nextel (TM) 1440 fiber-reinforced porous mullite (N440/p-M) composites were fabricated by the combination of slurry infiltration-sintering and sol-gel processes. Properties of mullite powder compacts and N440/p-M composites were investigated. Results reveal that mullite powder compacts sintered at 1200 and 1300 degrees C possess similar porosity, and both show porous structure. Mullite powders in N440/p-M composites show a ladder-like distribution along the infiltration direction, owing to the shadowing effects of adjacent fiber bundles. Compared to the composites with dense matrix, N440/p-M composites show typical toughened fracture behavior with improved mechanical properties. Numerous matrices attach to pullout fibers of N440/p-M composites, indicating that matrix cracks propagate through micro-pores in the matrix and deflect at the fiber/matrix interface effectively.