低密度气凝胶的高温结构变化及其耐温性研究

以正硅酸乙酯为原料，采用二步法制备了密度为30 kg/m³的二氧化硅低密度气凝胶块体材料。将低密度气凝胶分别在100、400、600、700、800、900、1 000 ℃下处理后，使用扫描电子显微镜（SEM）、氮吸附等手段表征高温下低密度气凝胶微观结构变化趋势，并与同等条件下处理的密度为100 kg/m³气凝胶的比表面积进行对比。结果表明：在处理温度超过700 ℃后，低密度气凝胶比表面积出现明显下降，纳米多孔结构出现收缩和坍塌，因此其高温耐受温度为700 ℃。虽然密度为30 kg/m³的二氧化硅气凝胶材料具有更为纤细的网络结构和更高表面活性的纳米组成颗粒，但是由于高温下纳米颗粒反应收缩程度大于纳米颗粒尺寸效应，其表现出与100 kg/m³密度的气凝胶材料相同的耐温性。

Characterization of the high-temperature resistance performance of silica aerogels with different densities

A silica (SiO₂) aerogel with a density of 30 kg/m³ was prepared in a two-step sol-gel process using tetraethoxysilane(TEOS) as a precursor. The porous morphology and structure of the low-density aerogel were characterized by SEM and nitrogen adsorption after heating at 100 ℃、400 ℃、600 ℃、700 ℃、800 ℃、900 ℃ and 1 000 ℃. An aerogel with a higher density of 100 kg/m³ was heated at the same temperatures and characterized by nitrogen adsorption for comparison. The results demonstrated that when the temperature exceeded 700 ℃ the surface area of the low-density aerogel decreased significantly and the nanostructure contracted and rapidly collapsed, showing that its maximum application temperature is 700 ℃. Although the aerogel with a density of 30 kg/m³ possessed a thinner structure and higher surface activity, the contraction resulting from polycondensation of the nanostructure overrode the size effect of nanoparticles, and it showed the same structure and maximum application temperature of 700 ℃ as the high density aerogel.