Synthesis of Al₂O₃-SiO₂ aerogels with low thermal conductivity and high strength by methyltriethoxysilane as a silica precursor

In this work, Al₂O₃-SiO₂ aerogels with low thermal conductivity and high strength were prepared using methyltriethoxysilane (MTES) as a silica precursor through the sol-gel method and high-temperature calcination. The effects of silica precursor on the thermal conductivity, chemical structure, and pore structure of aerogel as well as the effects of calcination temperature on the thermal conductivity, and mechanical properties of aerogel were investigated. The results indicated that MTES can reduce thermal conductivity by changing the microstructure of aerogel compared with tetraethyl orthosilicate (TEOS). The subsequent high-temperature calcination can further reduce thermal conductivity and improve mechanical properties. The prepared Al₂O₃-SiO₂ aerogels have the characteristics of low thermal conductivity and high strength compared with previous reports. The Al₂O₃-SiO₂ aerogels using MTES as silica precursor and calcined at 800 °C exhibited a density of 0.220 g/cm³, low thermal conductivity of 0.0232 W/(m·K), and a high compressive modulus of 74.29 MPa. In addition, the introduction of MTES can inhibit the sintering and phase transformation of alumina aerogel, and then improve the heat resistance of alumina aerogel. The specific surface areas of Al₂O₃-SiO₂ aerogels before heat treatment, heat-treated at 1000 °C and heat-treated at 1200 °C are 639.68 m²/g, 337.28 m²/g, and 90.67 m²/g, respectively. This work provides a novel method for Al₂O₃-SiO₂ aerogels to reduce thermal conductivity and improve mechanical properties. Graphical Abstract: [Figure not available: see fulltext.]