EFFECT OF GLYCEROL ON MONOLITHICITY, DENSITY, MICROHARDNESS AND SINTERING TEMPERATURE OF TMOS SILICA AEROGELS

In continuation of our earlier work on silica aerogels, the experiment al results on monolithicity, bulk density and Vickers hardness of glyc erol modified silica aerogels as a function of sintering temperatures are reported. The molar ratios of methanol (MeOH) solvent, glycerol (G ) additive, ammonia (NH4OH) catalyst and water (H2O) to the tetrametho xysilane (TMOS) precursor were found to be best in between the ranges: 6-12, 0.3-0.83, 3.6 x 10(-2)-1.0 x 10(-1) and 4-8, respectively, for the production of monolithic silica aerogels. The best quality silica aerogels in terms of monolithicity, transparency and low density have been obtained with the molar ratio of 1TMOS:0.83G:12MeOH:4H(2)O:3.6x10 (-3) NH4OH, respectively. The aerogels of this molar ratio have been c haracterized by density, Vickers hardness measurements and scanning el ectron microscopic observations as a function of sintering temperature s. The pore size distribution was found to shift towards the narrow po re radii as the temperature increased above 260 degrees C. The results have been supported by the particle and pore sizes observed using sca nning electron microscopy technique and BET surface analyses. (C) 1997 Elsevier Science B.V.