Preparation of SiO2/Fe2O3 composite aerogels for thermal insulation enhancement

Silica aerogel, with a unique nano-network structure, serves as a high-performance thermal insulation material. However, silica aerogel possesses a high infrared wave transmission ratio above 300 °C, whose thermal conductivity increases and thermal insulation performance further decreases with the increasing temperature. Introducing opacifiers to silica aerogel is a crucial strategy for addressing this issue. In this work, the ferric oxide exerted as an opacifier was incorporated into the main-phase silica aerogel to improve its thermal insulation at high temperatures. The SiO2/Fe2O3 composite aerogels were created via the two-step sol-gel process followed by supercritical drying, which involved doping ferric nitrate nonahydrate as a Fe2O3 precursor into the silica sol generated with tetraethoxysilane. In this way, SiO2/Fe2O3 composite aerogels with low density (0.04 g/cm3), high specific surface area (705 cm2/g), and low thermal conductivity (0.026 W/(m K)) were obtained by structural adjustment. The incorporation of Fe2O3 improves the thermal insulating properties of silica aerogels. After heat treatment at 1100 °C, the thermal conductivity of the SiO2/Fe2O3 composite aerogel was 0.167 W/(m K), lower than that of the pure silica aerogel (0.249 W/(m K)). Furthermore, the SiO2/Fe2O3 composite aerogel maintained its amorphous structure and exhibited a specific surface area of approximately 94.56 cm2/g, which was three times that of the pure silica aerogel. When subjected to five-minute heating at 1000 °C, the maximum surface temperature of the heat delivery surface of the SiO2/Fe2O3 composite aerogel reached 280.8 °C, whereas the pure silica aerogel reached 353.8 °C.