氟离子催化疏水性气凝胶的常压制备与性能研究

PREPARATION AND PROPERTIES OF HYDROGENATED AEROGELS CATALYZED BY FLUORIDE ION AT NORMAL PRESSURE

目前常用的气凝胶凝胶过程为酸碱催化,水解时间长且操作过程烦琐。本文以正硅酸四乙酯为硅源,以氟离子作为催化剂,采用溶胶-凝胶法制备湿凝胶,经正己烷溶剂置换、三甲基氯硅烷表面改性后,经常压阶梯升温干燥制备二氧化硅气凝胶,使用导热系数分析仪、扫描/透射电镜等手段研究了不同氟离子含量对所制备气凝胶性能的影响。实验表明:所制得的气凝胶密度最低为0.032W/(m·K),平均比表面积为628.7m^2/g,平均孔径为17.2nm;随着氟离子用量的增多,正硅酸四乙酯水解更加彻底,但对湿凝胶后期表面改性不利,从而导致接触角变小,导热系数增加。

At present, the commonly used aerogel gel process is acid-base catalysis, and the hydrolysis time is long and the operation process is cumbersome. In this paper, tetraethyl orthosilicate was used as the silicon source, and the wet gel was prepared by sol-gel method using fluoride ion as the catalyst. After the solvent was replaced by n-hexane solvent and the surface was modified by trimethylchlorosilane, the silica aerogel was prepared by stepwise heating at room temperature. Silica aerogels were studied by means of thermal conductivity analyzer, scanning/transmission electron microscopy and other methods to study the effect of different fluoride ion content on the properties of the prepared aerogels. Experiments show that the aerogel has a minimum density of 0.032 W/(m·K), an average specific surface area of 628.7m^2/g, and an average pore diameter of 17.2 nm. Moreover, with the increase of the amount of fluoride ion, the tetraethyl orthosilicate is more thoroughly hydrolyzed, but it is unfavorable for the surface modification of the wet gel, which leads to a smaller contact angle and an increase in thermal conductivity.