Alumina-Doped Silica Aerogels for High-Temperature Thermal Insulation

In this study, we used two methods to prepare alumina-doped silica aerogels with the aim of increasing the thermal stability of silica aerogels. The first method was physical doping of α-Al₂O₃ nano powders, and the second method was to create a chemical compound via the co-precursor of TEOS and AlCl₃·6H₂O in different proportions. The shrinkage, chemical composition, and specific surface area (SSA) of samples after heating at different temperatures were analyzed. Our results show that the silicon hydroxyl groups of samples derived from AlCl₃·6H₂O gradually decreased and nearly disappeared after heating at 800 °C, which indicates the complete dehydration of the silicon hydroxyl. Thus, the samples exhibited a large linear shrinkage and decreased SSA after high-temperature heat treatment. By contrast, samples doped with α-Al₂O₃ powders retained abundant silicon hydroxyl groups, and the 6.1 wt.% α-Al₂O₃-doped sample exhibited the lowest linear shrinkage of 11% and the highest SSA of 1056 m²/g after heat treatment at 800 °C. The alumina-doped silica aerogels prepared using a simple and low-price synthesized method pave the way for the low-cost and large-scale production of high-temperature thermal insulation.