Abstract: Aiming at the thermal bridge blocking demand of thermal protection system, carbon aerogel composites with medium-density and high strength were prepared by sol-gel, atmospheric pressure drying and high temperature carbonization processes using carbon/quartz fiber hybrid needle-punched preforms as reinforcement and phenolic resin as carbon precursor, and the microstructure, mechanical properties and thermal insulation performance of the composites were systematically investigated. The results show that the composites has strong mechanical properties (compressive stress approximately 10 MPa at 5% compressive strain) and excellent thermal insulation properties (room temperature thermal conductivity <0.230 W·m^-1·K^-1) with medium density (approximately 0.80 g·cm^-3). As the mass fraction of quartz fibers in the preform increases from 0% to 20%, the equivalent thermal conductivity of the composite decreases from 0.224 W·m^-1·K^-1 to 0.158 W·m^-1·K^-1 at 1 000 ℃, indicating the potential for high-temperature thermal bridge-blocking applications. Further, the lattice Boltzmann method was used to predict the thermal conductivity of the material from room temperature to 1 600 ℃, and the trends of the influence of material structure and environmental factors on the thermal conductivity were found. The increase in the porosity of the carbon aerogel matrix leads to the increase in the resistance of heat transfer, which leads to the decrease in the thermal conductivity of the composite. The increase in the density of the preform leads to the increase in the channels for heat transfer, which makes the thermal conductivity of the composite increase. The increase of quartz fiber content leads to the gradual decrease of thermal conductivity of the composites. When the air pressure is low, the thermal conductivity increases rapidly with the increase of air pressure, while when the air pressure is high, the thermal conductivity is almost unaffected.

Key words: carbon aerogel, composite, mechanical properties, thermal insulation properties, lattice Boltzmann method