High Temperature Resistant Calcium-doped Silica Aerogels with Enhanced Thermal Insulation <i>via</i> Sol-Gel Hydrothermal Route

Silica aerogel has a broad application in the field of high-temperature thermal insulation due to its low density, low thermal conductivity and high stability.However, its thermal insulation performance deteriorates significantly at elevated temperatures exceeding 600 , primarily due to the collapse of pore structure.Meanwhile the shielding capacity of SiO2 aerogel to the infrared radiation at high temperature is rather low due to the intrinsic properties of SiO2.Herein, we explored to improve the high-temperature stability and infrared shielding properties of SiO2 aerogel via Ca doping.Calcium-doped silica aerogel (CSA) powders were prepared by sol-gel, hydrothermal, and atmospheric pressure drying (APD) techniques using water glass and anhydrous calcium chloride as precursors and trimethylchlorosilane (TMCS) as a hydrophobic modifier.The effects of Ca/Si molar ratio in the precursor and hydrothermal conditions (temperature and pH) on the crystalline properties, microscopic morphology and pore structure of calcium-doped silica aerogels were investigated.The results show that the Ca/Si molar ratio and hydrothermal treatment have significant effects on the microstructure and heat resistance of calcium-doped silica aerogels in the temperature range of 400-1000 .The samples sintered at 1000 have a high specific surface area of 100.1 m 2 /g and a pore volume of 0.8705 cm 3 /g, thereby indicating that the calcium-doped silica aerogel has good heat resistance.One-side insulation tests at temperatures up to 600 C show that the sample with a Ca/Si molar ratio of 1.0 has the best insulation performance, with a cold surface temperature of 450 C, which is 27 C lower than that of the pure silica aerogel.