CO_2超临界干燥制备SiO_2气凝胶及其表征

Preparation and characterization of silica aerogel by CO_2 supercritical drying

以正硅酸乙酯为原料,应用溶胶—凝胶两步催化法制备SiO2醇凝胶,醇凝胶用CO2超临界干燥后得到SiO2气凝胶.以比表面积和密度为评价标准,以CO2流量、超临界温度、干燥时间和超临界压力为实验因素,设计了四因素三水平的正交实验,研究CO2超临界干燥的工艺条件,并运用SEM、TEM、BET、FTIR对SiO2气凝胶结构、形貌及化学组成进行分析.结果表明:优化的工艺条件为CO2流量12 kg.h-1,干燥压力13 mPa,超临界温度45℃,干燥时间6 h.制得SiO2气凝胶的比表面积为927.37 m2.g-1,密度是0.195 6 g.cm-3,由球形纳米颗粒堆积而成,颗粒尺寸范围在0～20 nm左右,孔径分布主要集中在10 nm左右,是典型的纳米孔材料.

With tetraethoxysilicane as raw material and by addition of catalyst（dilute hydrochloric and aqueous ammonia）,SiO2 alcogel was obtained by sol-gel process.SiO2 alcogel was transformed into SiO2 aerogel via the CO2 supercritical drying technique,which had four parameters—Carbon dioxide flow,supercritical temperature,drying time,and supercritical pressure.A four-factor,three-level orthogonal experiment was designed to investigate the influence of these four parameters on the density and BET of the resultant SiO2 aerogel.In the experiment the microstructure,shape,and composition of SiO2 aerogel were analyzed by SEM,BET,TEM,and FTIR.The experimental results report： the optimized parameters were 12 kg·h-1 of CO2 flow,13 mPa of pressure,45 ℃ of supercritical temperature,and 6 h of supercritical drying time.The prepared SiO2 aerogel was composed of spherical nano-particles with size between 0 nm and 20 nm.Its pore size was around 10 nm,its specific surface area was 927.37 m2·g-1,and its density was 0.195 6 g·cm-3.Therefore,the prepared SiO2 aerogel was a typical nano-mesoporous material.