Abstract: Using tetraethyl orthosilicate (TEOS) and aluminum chloride hexahydrate (AlCl₃·6H₂O) as the mixed precursor and propylene oxide as the network trapping agent, the aerogel with different molar ratios of Al₂O₃-SiO₂ was prepared by sol-gel process and carbon dioxide supercritical drying method without adding chelating agent. The samples were heat-treated at 600 ℃, 800 ℃, 1 000 ℃ and 1 200 ℃ respectively, and the micro-morphology, structure and thermal stability of the Al₂O₃-SiO₂ composite aerogel were characterized by Fourier infrared spectroscopy, scanning electron microscopy, X-ray diffractometer, specific surface area analyzer, thermogravimetric differential thermal analyzer and other instruments. The results show that when AlCl₃·6H₂O∶TEOS=8∶1, the thermal conductivity of Al₂O₃-SiO₂ aerogel samples after heat treatment at 1 000 ℃ and 1 200 ℃ is 0.062 1 W/m·K and 0.080 3 W/m·K, respectively. The pore size is more uniform and the mesoporous structure is preserved above 1 000 ℃. At normal temperature and 1 200 ℃, the specific surface area is 617.14 m²/g and 102.9 m²/g, with uniform mesoporous structure (pore diameter is 8~32 nm), and the pore size is lower than the average free path of air at normal temperature. After heat treatment at 1 200 ℃, the total weight loss rate of the sample is 16.3%, which proves the sample has good high temperature thermal stability.

Key words: Al₂O₃-SiO₂ composite aerogel, heat treatment, microstructure, thermal stability, composites