Effect of glycerol on monolithicity, density, microhardness and sintering temperature of TMOS silica aerogels

In continuation of our earlier work on silica aerogels, the experimental results on monolithicity, bulk density and Vickers hardness of glycerol 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 tetramethoxysilane (TMOS) precursor were found to be best in between the ranges: 6–12, 0.3–0.83, 3.6 × 10⁻²–1.0 × 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:4H₂O:3.6 × 10⁻³ NH₄OH, respectively. The aerogels of this molar ratio have been characterized by density, Vickers hardness measurements and scanning electron microscopic observations as a function of sintering temperatures. The pore size distribution was found to shift towards the narrow pore radii as the temperature increased above 260°C. The results have been supported by the particle and pore sizes observed using scanning electron microscopy technique and BET surface analyses.