Research Progress on Alumina Aerogel Composites for High-temperature Thermal Insulation

As a nano-porous material with high porosity, low density, high specific surface area, excellent heat-resistance, and low thermal conductivity, the alumina aerogel shows broad application prospect in high-temperature thermal insulating areas such as the thermal protective system for space vehicles and the thermal insulation for industrial kilns. However, pristine alumina aerogels cannot be directly used because of their relatively poor thermal resistance above 1000 , mechanical strengths and high-temperature thermal insulating performance. They need to be improved by introducing reinforcements and opacifiers (namely the alumina aerogel composite). This paper summarizes the latest research progress of synthesis of heat-resistant alumina aerogels, and preparation and properties of alumina aerogel composites. Researchers improved the thermal stability of alumina aerogels by modifications such as in-situ doping, deposition, organic chains or carbon coatings. The introduction of whiskers, particles, porous skeletons or fibers into alumina aerogels contributes to considerable improvement of mechanical performance. The cooperation of fibers and opacifiers helps to increase the inhibition of infrared radiation and lower the high-temperature thermal conductivity of alumina aerogels. The future of alumina aerogel composites is also proposed: a) finely tailoring the bulk density, micro structures, and introducing proper foreign elements and opacifiers, are supposed to further optimize the thermal stability of alumina aerogels and thermal insulating performance of their composites; b) deeper attention should also be paid on the evolution of structure and properties of composites at elevated temperatures, and on the interaction between alumina aerogel and reinforcement. As a novel thermal insulation, alumina aerogel composites are expected to take their advantages and be widely applied in the future.