非超临界干燥法制备块状SiO2气凝胶

以正硅酸乙酯为原料，去离子水和异丙醇为溶剂，丙三醇为干燥控制化学添加剂，盐酸和氨水为催化剂，通过酸／碱两步溶胶-凝胶法合成SiO2醇凝胶，经过老化、表面修饰和溶剂交换等工艺后，在常压分级干燥条件下制备块状SiO2气凝胶。不均匀的毛细管力是非超临界干燥过程中造成凝胶破裂的原因，从减小不均匀毛细管力及提高凝胶强度2个方面确定工艺，采用非超临界干燥法制备具有优良性能的块状SiO2气凝胶。应用X射线衍射、扫描电镜、热失重-差热等分析手段及吸附-脱附技术对所得气凝胶样品进行结构分析和性质表征。结果表明，用此方法可以制备具有优良性能的块状气凝胶样品，该气凝胶充满两端开放的管状中孔，具有较大的孔隙率（97．1％）及比表面积（614．3m^2／g），孔径分布均匀并且集中。

Preparation of block silica aerogels via non-supercritical drying

Silica aerogels were synthesized by the two-step sol-gel method. In the synthesis, tetraethyoxysilane was used as raw material, isopropanol and H2O which was distilled after ion exchange were used as solvent, HCl and NH4 OH were used as hydrolysis and condensation catalysts, glycerol was used as drying control chemical agent. After aging, surface modification, exchanging solvent, silica aerogels were obtained by gradual drying under normal atmosphere. The reason of the eraeking in non-supereritieal drying is the uneven eapillary strength. Two measures are taken in order to obtain silica aerogels with good properties by non-supereritieal drying, one is to decrease the uneven capillary strength and the other is to increase the intension of the sample. The resulting aerogels were characterized by means of X-ray diffraction, scanning electron microscopy and thermal gravity-differential thermal analysis and adsorption-desorption technique. It is found that the aerogels made by this method have high porosity and speeifie surfaee area, their pore size distribution is narrow and uniform.