Effect of Silicon Powder on Properties of SiO2 Gel/Alumina-silica Fibers Composites

SiO2 gel/alumina-silica fibers composites were prepared by impregnation method. Silicon powder with different mass fractions of 0%, 0.2%, 0.4%, 0.6% and 0.8% was added in the slurry, and the effects of silicon powder on the microstructure, bulk density, compression-resilience ratio and phase compositions of the SiO2 gel/alumina-silica fiber composites were investigated. The results show that when the mass fraction of the silicon powder is lower than 0.6%, the volume expansion of silicon resulting from the silicon oxidation fills the cracks between fibers and gel, the volume density of the composites increases from 0.468g/cm3 to 0.723g/cm3, and the resilience ratios increase from 43.1% to 59.6%. Besides, it is found that the mechanical property is improved and the degree of high-temperature damage for the composites is decreased by the silicon crystallization, which restrains the fibers crystallization and facilitates the generation of pyroxene. However, when the mass fraction of silicon powder is 0.8%,the compression-resilience ratio of the composites significantly declines to 44.5%, which is attributed to the big cracks generated from the excessive volume expansion of silicon powder at high temperature.