Thermally insulating, fiber-reinforced alumina–silica aerogel composites with ultra-low shrinkage up to 1500 °C

Highly porous, heat resisting and thermal insulating alumina-based aerogel materials are considered as promising high-temperature thermal insulations. The major obstacles for their applications are poor mechanical strengths, transparency to infrared radiation and complex preparation processes. In this study, a direct sol-immersion-gel (SIG) and supercritical fluid drying (SCFD) strategy for synthesizing mullite fiber reinforced alumina–silica aerogel composites (MFASs) was developed to overcome these problems. No tedious operation such as solvent exchange or gel modification was needed. The MFASs, with bulk density less than 0.4 g/cm3, experienced no deformation and ultra-low dimensional shrinkage even under 1500 °C exposure at air atmosphere, also exhibit good compressive strength and toughness. Thanks to cooperation of mullite fibers and the alumina–silica aerogel (ASA), the MFASs show quite low thermal conductivity (0.082 W/(m·K) at 1200 °C) and proved to be extremely thermal insulating during the quartz lamp heating test at 1500 °C. The light-weight, strong MFASs with superior heat resistance and thermal insulating performances can satisfy the urgent need for high-temperature thermal insulations such as thermal protection system (TPS) for space vehicles.