EFFECT OF SOL-GEL PROCESSING PARAMETERS ON THERMAL-PROPERTIES OF SILICA AEROGELS

The dependence of thermal conductivity (lambda) and heat capacity per unit volume (rho C-p) of silica aerogels on the sol-gel processing par ameters for a fixed temperature ranging from 300 to 360 K have been st udied. The silica aerogels were made in circular shapes by varying one of the three molar ratios of ammonia (NH4OH)/tetramethoxysilane (TMOS ), methanol (MeOH)/TMOS and water (H2O)/TMOS by keeping the other two molar ratios constant. The measurements were performed by using transi ent hot-wire probe method. The variation of NH4OH/TMOS molar ratio res ulted in a slow change in lambda and rho C-p values whereas MeOH/TMOS and H2O/TMOS molar ratios resulted in marked changes as a function of temperature. The results have been discussed by taking into account of the chemistry and the resulting porosities of the aerogels.