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Cf/SiO2 composites were prepared by slurry impregnation-hot pressing process, and their mechanical properties, microstructure and surface morphologies were then investigated. The results indicated that the composites showed the best mechanical properties, and the tensile strength, bending curvature, compression strength were 58MPa, 170MPa, 256MPa respectively. XRD spectrums showed that fused quartz appeared no crystallization during the process. Also from the TEM analysis, we can see that the Cf/SiO2 composites exhibited the best compactness. All the tests were carried out on the composites autoclaved at 1400°C for 60min, according to which the best hot pressing process was concluded.

The influences of hexagonal BN content on the porous Si3N4 material was investigated. SEM micrographs showed that the columnar crystal overlapping structure of the porous Si3N4 material with a small BN addition was almost invariant. BN uniformly dispersed in the spaces of crystal overlapping. The experiment showed that the apparent densities of the porous Si3N4 material with a small BN addition marginally increased, the porosity, the strength and the dielectric constant marginally decreased, but The thermal shock resistance was greatly improved.

2.5D and needle-punched performs of silica fiber were studied in the paper,pore structures and slurry diffusion were studied. Mechanical properties of two prefoms composites were different,and influence of pore structures and volume fraction on performance of composites were researched.The results indicated that 2.5D composites had obvious advantages on tensile properties.But needle-punched composites had isotropic properties in their plane ,that were better than 2.5D composites which had anisotropic properties. Needle-punched composites had obvious advantages on compression properties,which overcomed compression strength of was weaker 2.5D composites in some direction.