Heat-resistant, strong alumina-modified silica aerogel fabricated by impregnating silicon oxycarbide aerogel with boehmite sol

Highlights: • The inexpensive boehmite sol was used as alumina source to prepare Al₂O₃-SiO₂ aerogel. • The partial sintering of aerogel during its preparation process endows the aerogel with high elastic modulus of 78 MPa. • The carbon in silicon oxycarbide can act as a pore former by oxidizing with O₂ during preparation process. • The resultant alumina-modified silica aerogel exhibits a much higher heat resistance than silica aerogel. In order to overcome the fragility and sintering behavior of silica aerogel at high temperature, heat-resistant and strong alumina-modified silica aerogel was fabricated by impregnating silicon oxycarbide (SiOC) aerogel with industrial boehmite sol. The partial sintering of SiOC aerogel during its pyrolysis endowed alumina-silica aerogel its high strength. Meanwhile, the carbon in SiOC can also act as a pore former due to oxidation with O₂ during the subsequent calcination in air. This approach is straightforward and economical. The as-prepared composite aerogel exhibited high surface area (278 m²/g) and compressive strength of up to 2.17 MPa. Compared to SiO₂ aerogel prepared using the same method, the composite aerogel was found to be more heat resistant. After being heated to 1000 °C and 1200 °C for 2 h, the surface area of composite aerogel reached up to 183 and 22 m²/g, respectively. On the other hand, the corresponding values for linear shrinkage were as low as 6.93% (for 1000 °C) and 18.90% (for 1200 °C). The XRD patterns indicated that amorphous SiO₂ and γ-Al₂O₃ remained in the composite aerogel after heat-treatment at 1200 °C.