Preparation and characterization of silica aerogel by CO_2 supercritical drying

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.