The effect of heat-treatment on the physico-chemical properties of silica aerogel prepared by sub-critical drying technique

Synthesis of transparent and crack-free monoliths of silica aerogel by sub-critical drying technique is reported in the present article. Silane ageing with 50% tetraethylorthosilicate:ethanol followed by solvent exchange using ethanol was adopted. The effect of heat-treatment on the textural and physical characteristics of silica aerogel was evaluated. The chosen composition resulted in a high surface area silica aerogel of 1,000 m(2) g(-1)and a pore volume of 1.4 cm3supercript stop g(-1) at room temperature. The aerogel heat-treated at 900 degrees C possessed a surface area of 450 m(2) g(-1) with a pore volume of 0.4 cm(3) g(-1). The decrease in surface area and pore volume was associated with the sintering process. The present technique seems advantageous in preserving the high surface area of the material at high temperatures. The XRD studies showed that the amorphous nature of aerogel matrix was retained till 1,400 degrees C, beyond which it crystallized to phase pure crystoballite.