Effects of Synthesis Conditions on the Performance of SiO<sub>2</sub> Aerogel Prepared by CO<sub>2</sub> Supercritical Drying

The article presents an investigation about effects of the synthesis conditions on the performance of silica aerogels. Tetraethyl orthosilicates (TEOS) were selected as the silicon source, and two acid-base catalysts were adopted to catalyze the reaction. CO 2 supercritical drying was used to drive out the solvent of alcohols in the wet gels. Semi-transparent monolithic and crack-free SiO 2 aerogels were successfully obtained. The solvents were prepared with a ratio of ethyl orthosilicate: absolute ethanol: H 2 O:HCl:NH 3 ·H 2 O=1:3:5:3×10 -3 :4.8×10 -3 .The single effects of solution pH, water volume, and aging temperature synthesized were investigated. The aerogels were characterized with SEM, specific surface area analysis, thermal constant analysis, thermogravimetric analysis, Raman spectroscopy analysis, N 2 adsorption-desorption analysis, and hydrophobic angle test. The as-synthesized silica aerogels have a porosity of 95.6%, a specific surface area of 756.9m 2 /g, an average pore diameter of 16.22nm, a density of 96.8kg/m 2 , and a thermal conductivity of 0.02W/(m· K). Hydrophobic silica aerogels were also obtained.