Preparation And Properties Of Surface Densified Low-density Quartz Fiber/phenolic Composite

Thermal protection system plays an important role in aerospace industry.In recent years,aerospace vehicles are facing an increasingly harsh reentry environment,and higher requirements have been put forward for the performance of thermal protection materials for long-term service,low ablation,and high thermal blockage.The exploration and Research on the lightweight of materials and the ablation resistance of reinforced materials are also carried out continuously.In this thesis,light quartz fiber/phenolic composites were studied.A surface densification/thermal insulation NQF/PR aerogel composite material was prepared.The surface densification process of quartz fiber preform was optimized.The internal structure,mechanical properties and thermophysical properties of surface densified NQF/PR aerogel composites were studied.The ablation resistance of the material was examined,and the heat insulation and ablation mechanism of the material were discussed.Using ZrB₂,SiO₂ and glass powder as modifiers,polyethylene glycol-400 as dispersant,and phenolic resin solution through mechanical stirring and ultrasonic dispersion to obtain mixed ceramic slurry,the surface densified quartz fiber preform was prepared.The surface densified quartz fiber preform has a smooth appearance without obvious defects,complete microstructure and uniform composition.The quartz fiber preform has a density of 0.20 g/cm³,and the slurry is impregnated to obtain a dense layer with a density of 0.61-0.70 g/cm³.Using phenolic aerogel as the matrix impregnation phase and the dense surface quartz fiber preform as the reinforcement,a dense surface NQF/PR aerogel composite material was prepared.The aerogels with density of 0.20 g/cm3 and porosity of 86.69%were filled with aerogels,and the NQF/PR aerogel composites with a density of 0.29g/cm3 and a porosity of 83.70%were obtained.the dense layer is partially filled with air After gelation,the density increased from 0.62-0.70 g/cm³ to between 0.67-0.75 g/cm³.The mass loss of NQF/PR material in the air atmosphere is less when the temperature is lower than 400?,and the mass loss due to the oxidation of cracked carbon is greater in the range of 400-800?.For the dense layer part,with the increase of ceramic content,the mass residue rate of the material in argon at 1000?increased from 68.02%to71.35%,and the mass residue rate in the air increased from 27.48%to 36.76%.The heat insulation and ablative properties of surface densified NQF/PR aerogel composites were evaluated,and the mechanism of thermal protection and insulation for materials was discussed.The butane flame is used to heat the surface of the material.When the surface temperature exceeds 1100°C,the back temperature is still lower than100°C after heating for 4 minutes,and the peak back temperature is lower than 550°C.The material has good heat insulation performance.The oxygen-acetylene ablation experiment was carried out to assess the ablation resistance of the material.The material has better ablation resistance when the ceramic content is 7%and 9%.During ablation,ZrB₂is oxidized to B₂O₃and Zr O_2.The low-melting liquid phase B₂O₃ can evaporate and absorb heat.The formation of the ZrO₂-SiO₂ layer slows the erosion of the material by the high-temperature airflow,and further improves the ablation resistance of the material.From the ablation of the surface,the carbonized layer,the pyrolysis layer to the original layer,the degree of ablation damage decreases gradually.