Preparation of Al₂O₃-SiO₂ composite aerogel and the influence of modifier on its structure and thermal insulation properties

Low cost, impurity-free and low thermal conductivity Al₂O₃-SiO₂ composite aerogel were prepared from AlCl₃·6H₂O derived gel through ion exchange technology and sol-gel method by dipping silicon in tetraethyl orthosilicate (TEOS), subsequently surface modification and ambient pressure drying were employed. The effects of different organosilane modifiers on the structure and thermal insulation properties of the Al₂O₃-SiO₂ composite aerogels were explored. The results show that Al₂O₃-SiO₂ composite aerogel shows the most uniform microstructure in the neutral (pH=7) modified environment of trimethoxy methylsilane (MTMS). The SiO₂ and Al₂O₃ phases mainly exist in amorphous form. MTMS is more effective in reducing the -OH group on the surface of Al₂O₃-SiO₂ wet gel to form Si-O-Si and Al-O-Si groups. The specific surface area and pore volume of Al₂O₃-SiO₂ aerogels are as high as 574 m²/g and 2.3 cm³/g, respectively, and the thermal conductivity is as low as 0.029 W(m·K)^-1. The above research provides support for the application of aerogel materials in the field of thermal insulation.