EFFECT OF GEL PARAMETERS ON MONOLITHICITY AND DENSITY OF SILICA AEROGELS

As part of continuing investigation of the preparation and characterization of silica aerogels, detailed experimental results on monolithicity and density of the aerogels as a function of catalysts and their concentrations, molar ratios of tetraethylorthosilicate (TEOS), ethanol (EtOH) and H2O, gel pH and gel ageing, are reported. With large concentrations of catalysts, lower and higher aged alcogels have been found to produce opaque, cracked and high-density silica aerogels; however, good-quality monolithic, transparent and low-density aerogels have been obtained at lower catalyst concentration (0.01 N HCl) with alcogel ageing periods between 9 and 30 days. The best quality silica aerogels, in terms of transparency and monolithicity, have been obtained using TEOS: EtOH: H2O in the molar ratio of 1:5:8.