Preparation And Characterization Of Silicon Oxycarbide Aerogel/flexibel Ceramic Fiber Composite

The performance of thermal protection materials is one of the key factors influencing the design and service performance of hypersonic aircraft.It is necessary to develop new flexible materials with low density,low thermal conductivity,low price,reusable and high temperature stability because of the need for large area coverage in the high temperature range and low temperature zone of hypersonic vehicles.The flexible ceramic fiber insulation felt just meets these requirements.In this paper,SiOC aerogels were prepared by sol-gel technique in deionized water and ethanol co-solvent.The precursors were TEOS and MTMS.The SiOC aerogels prepared by this process can be formed a nano porous structure,and the product phase after sintering can be formed by using the two-step method.Hydrolysis under acidic conditions and polycondensation under alkaline conditions.Mainly for the amorphous amorphous SiOC structure and cluster-like uniform distribution of free carbon.In the non-inert atmosphere,the content of free carbon is an important factor affecting the performance of SiOC aerogels.After sintering at 1100 ?,the free carbon content in SiOC increases with the increase of C / Si ratio,When the C / Si ratio of 0.33,the carbon content of 3.4%,C / Si ratio of 0.83,the carbon content of 8.83%.The SiOC aerogels / flexible ceramic fiber matrix composites synthesized by in situ impregnation method are poor in flexibility and are basically rigid.Well the composite material prepared by atmospheric spraying method is flexible,so its performance is emphatically characterized.If the application environment is below 600 ?,the porous composite material has good hydrophobicity,and the hydrophobicity is reduced after sintering.The structure of the composites showed a significant decrease in the hygroscopicity of the composites compared with the quartz fibers without the addition of SiOC aerogels,and only 2.15% in the 90% humidity environment by 35 days.The thermal conductivity of the composite was about 0.035 Wm-1K-1 with a C / Si ratio of 0.67.After oxidation experiments,it was found that the weight loss of this composite material was only 2% after 3h static oxidation at 1200 ?,and the composition of Si O2 microcrystals was found after oxidation.The thermal conductivity of the composites was increased 20% after oxidation.