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Near-stoichiometric orthorhombic mullite powders, showing good chemical and thermal stability, were synthesized through a sol-gel process employing diphasic Al2O3-SiO2 sol as starting material.Subsequently, 3D NextelTM440 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 revealed that mullite powder compacts sintered at 1200 ℃ and 1300 ℃ illustrated similar porosity, and both showed porous structure.Mullite powders in N440/p-M composites showed 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 showed typical toughened fracture behavior with improved mechanical properties.Numerous matrices attached to the pullout fibers of N440/p-M composites, indicating that matrix cracks propagate through matrix micro-pores and deflect at the fiber/matrix interface effectively.