Encapsulation of SiO₂ Nanofibers with Air Interlayer and SiC Shell for High Temperature Thermal Insulating Aerogels

To endure extreme conditions, silica fiber aerogels are expected to maintain ultralow thermal conductivity at high temperatures. However, the weak infrared extinction capacity of SiO₂ fiber aerogels fails to effectively suppress thermal radiation, resulting in high thermal conductivity at high temperatures. Here, SiO₂-air-SiC fibers with high extinction shells, air interlayer, and amorphous core are fabricated by low-pressure carbothermal reduction. Owing to low pressure conditions that reduce Gibbs free energy of the reaction and increase the diffusion rate of the gas molecules, the reaction can occur in seconds. With the mitigation of thermal radiation by the incorporation of SiC shell with high extinction capacity and the weakening of gas-phase heat conduction in air interlayer generated by reaction below the mean free path of gas (70 nm), the aerogel shows ultralow thermal conductivity in a wide temperature range (the thermal conductivity at 1000 °C is 0.108 W m^-1 K^-1). Meanwhile, the ultra-fast reaction rate ensures the amorphous structure of silica core, which can maintain the flexibility of the aerogel by triggering the shear band (up to 80% elastic compressive strain and bending recovery property). The combination of high-temperature thermal insulation and high flexibility shows good potential for thermal insulation applications under extreme conditions.