Effect of aging time and concentration of aging solution on the porosity characteristics of subcritically dried silica aerogels

Subcritical drying technique has emerged as effective and convenient method for the synthesis of silica aerogels compared to the conventional supereritical route. One of the important steps in this method is aging of the wet gel which leads to dissolution and reprecipitation of silica monomers to the gel structure and results in stronger gels with desired pore characteristics. This paper deals with effect of concentration of aging solution and duration of aging on the development of pore characteristics of silica aerogels. The specific surface area, pore size and pore volume increase with an increase in concentration of TEOS in the aging solution. With an 80% tetraethoxysilane in isopropanol at 50 degrees C, a surface area of 1098 m(2)/g, pore volume 1.3 cm(3) g(-1) and an average pore size of 47.7 angstrom were obtained. Time of aging also has a similar effect on bulk density, surface area and pore volume as the concentration of aging solution. Under the reported experimental conditions, a duration of 48 h for aging has been most favourable, after which there appears a negative effect. The result presented in this paper provides data for designing the mesoporous silica gels through subcritical drying technique. (c) 2005 Elsevier Inc. All rights reserved.