Preparation and characterization of monolithic Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> aerogel

Al2O3–SiO2 aerogel was prepared through mixed sol–gel process and ethanol supercritical drying technology using aluminum chloride hexahydrate (AlCl3·6H2O) and tetraethoxysilane (TEOS) as precursors. Under the condition of the propylene oxide used as gelation initiators, during the process, a kind of Al2O3–SiO2 aerogel with porous and large specific surface area were achieved in our experiments. Structures and properties of Al2O3–SiO2 aerogel are investigated by means of X-ray Diffraction, Nitrogen adsorption/desorption analysis, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscope, and Thermogravimetry-Differential Thermal analysis. The results showed that the Al2O3–SiO2 aerogel with the mole ratio of Al/Si = 3/1 possessed better heat-insulation performance and high-temperature stability. And it possessed a porous network structure made up of leaf shape particles. At the same time, Al2O3–SiO2 aerogel showed a low density of 0.071 g/cm3 at room temperature, specific surface areas of 708 m2/g at 600°C, as well as 255 m2/g at 1200°C. The Al2O3–SiO2 aerogel is the polycrystalline boehmite (γ-AlOOH) phase at room temperature. As the temperature growing, it transferred to γ-Al2O3 at 600°C, and mullite phase at 1200°C.