Preparation and Properties of Silica Aerogels Reinforced Carbon Foam Composites

Carbon foam composites with a unique porous structure can be widely used in the fields of thermal insulation, energy storage, and absorption. In order to improve their mechanical and thermal-insulation properties, carbon foam composites were modified. Silica (SiO₂) aerogels reinforced carbon foam composites were prepared via compression molding and carbonization with zirconium modified phenolic resin as a carbon origin, SiO₂ aerogels as a reinforcement, and phenolic hollow microspheres as a closed phase. The effect of SiO₂ aerogels amount on the microstructure, compressive and oxidation resistance of carbon foam composites was investigated by scanning electron microscopy, universal testing machine, specific surface area analysis and pore size distribution measurement, respectively. The thermal conductivity of pure carbon foam and modified carbon foam composites were characterized by laser-flash thermal conductivity measurement, and their high-temperature heat transfer behavior was then analyzed. The results show that SiO₂ aerogels disperse in the ligaments or on the surface of microspheres, and barely contribute to cell structure of carbon foams. When the SiO₂ aerogels amount is 2% (in mass fraction), the maximum compressive strength and specific compressive strength both reach 19.39 MPa and 42.17 MPa·cm³/g, respectively. Compared to the pure carbon foam, the compressive strength and specific compressive strength of carbon foam are increased by 106.7% and 79.8%, respectively. A proper addition of SiO₂ aerogels can restrict the heat transfer path and internal radiative heat transfer. When the SiO₂ aerogels amount is 5%, carbon foam composites have the optimum thermal insulation and oxidation resistance. The thermal conductivity at 800 ℃ is 0.447 W/(m·K), which is 38.9% lower than that of pure carbon foam. The optimum oxidation resistance can be obtained, i.e., the mass loss of 18% during the isothermal oxidation at 700 ℃ for 30 min.