Effect of aging temperature on the porosity characteristics of subcritically dried silica aerogels

Silica aerogels were synthesised by subcritical drying technique which involves controlled solvent exchange and aging of the wet gel in silane solution followed by drying under controlled conditions. Effect of temperature of aging in silane solution on the porosity characteristics of silica aerogels and the thermal pore stability of the resultant gels were investigated. Aging in silane solution leads to an increased degree of condensation reactions, siloxane crosslinking and the dissolution and reprecipitation of silica monomers to the gel structure and enhances the total strength of the gel. Thermal aging of the wet gel have a pronounced effect on bulk density, linear drying shrinkage, surface area and pore volume. As the temperature of aging increases the bulk density decreases whereas the surface area and pore volume were found to increase. We could achieve a surface area of 1040 m2/g, pore volume 1.2 cc/g and an average pore size of 49 A corresponding to an aging temperature of 70 °C. Thermal pore stability of the gel was found to be up to 700 °C above which densification of SiO2 gel starts. The novel findings will help in tailoring the process parameters to prepare mesoporous oxides from sol–gel precursors with specific pore features.