Tensile and Ablation Properties of Fiber-Reinforced Si-Modified Phenolic Aerogel Composites

This study realizes the synergistic improvement in mechanical properties and ablation resistance of Si-modified phenolic aerogel composites with preserved lightweight characteristics and excellent thermal insulation. The resin matrix forms a uniform nanoporous structure, providing prominent thermal insulation performance. The composite with a fiber density of 0.62 g/cm3 has a low thermal conductivity of 0.086 W/(m·K). The material exhibits reliable tensile strength within a wide temperature range, and its tensile strength rises significantly with an increase in fiber density. The composite with a fiber density of 0.62 g/cm3 delivers a tensile strength of 129 MPa at 20 °C and 102 MPa at 300 °C, which are 79.4% and 122.2% higher than those of the composite with a fiber density of 0.36 g/cm3. In addition, methyltriethoxysilane and quartz fiber knitted felts form in situ SiO2 and SiC ceramic cladding layers under high-temperature ablation, effectively enhancing the ablation resistance of the composites. Higher fiber density greatly reduces the linear ablation rate. With an oxygen flow of 950 L/h and acetylene flow of 700 L/h, the linear ablation rate of the composite with a fiber density of 0.62 g/cm3 is only 0.13 mm/s, 23.1% lower than the composite with a fiber density of 0.36 g/cm3.