二氧化硅气凝胶以其低密度、高孔隙率等特性在高温隔热领域显示出广阔的应用前景, 但其脆性和高成本的超临界干燥方式限制了其应用。本研究以乙烯基三甲氧基硅烷(VTMS)和乙烯基甲基二甲氧基硅烷(VMDMS)为前驱体, 通过溶胶凝胶、常压干燥制备了具有高柔性的海绵状有机硅气凝胶, 并研究了前驱体摩尔比对气凝胶微观结构和压缩回弹性能的影响, 以及气凝胶分别在高温有氧和无氧环境中的无机化转变过程。结果表明, 随着前驱体中VTMS/VMDMS比例增加, 气凝胶颗粒变小且堆积更紧密, 其压缩回弹性能也随之降低; 在800 ℃空气氛围中, 气凝胶通过侧基的氧化和主链Si-O-Si的断裂、重排转化为无机SiO₂; 在800 ℃ N₂氛围中, 气凝胶通过裂解反应转化为无机SiO₂和游离碳的混合体, 1000~1400 ℃进一步处理后SiO₂和游离碳经碳热还原反应生成SiO₄、SiCO₃、SiC₂O₂和SiC₃O等无定形的Si-O-C结构和少量β-SiC纳米线; 经1200 ℃碳热还原反应生成的Si-O-C结构具有最优的耐高温氧化性能, 可为制备耐高温氧化Si-O-C气凝胶提供参考。

Silica aerogels have wide application prospect in high temperature heat insulation due to their low density and high porosity. However, the brittleness and high cost of supercritical drying restrict their application. In this study, spongy silicone aerogels with high flexibility were prepared via Sol-Gel polymerization and atmospheric pressure drying using vinyltrimethoxysilane (VTMS) and vinylmethyldimethoxysilane (VMDMS) as precursors. The effects of precursor molar ratio on the microstructure and compressive resilience of aerogels, as well as the inorganic transformation process of aerogels in high temperature aerobic and anaerobic environments were studied. The results show that with the increase of VTMS/VMDMS ratio in the precursor, the aerogel particles become smaller and more tightly packed, and the compression resilience of aerogels also decreased. In air at 800 ℃, aerogels were transformed into inorganic SiO₂ by oxidation of organic side groups, fracture and rearrangement of main chain Si-O-Si. In N₂ at 800 ℃, aerogels were transformed into the mixture of inorganic SiO₂ and free carbon by pyrolysis reaction, and after further treatment at 1000-1400 ℃, SiO₂ and free carbon were subjected to carbothermal reduction reaction to form amorphous Si-O-C structures such as SiO₄, SiCO₃, SiC₂O₂, and SiC₃O, and a small amount of β-SiC nanowires. The Si-O-C structure formed by carbothermal reduction reaction at 1200 ℃ has optimal high temperature oxidation resistance, which can provide reference for the preparation of pyro-oxidation resistant Si-O-C aerogels.