Preparation of Silica Aerogel by Ambient Pressure Drying Process using Rice Husk Ash as Raw Material

Abstract

Silica aerogel was prepared from rice husk ash by sol-gel process followed by ambient pressure drying. Silica was extracted from ash as sodium silicate by boiling it in sodium hydroxide solution.Sodium silicate was neutralized with nitric acid to form silica gel. To prepare aerogel, first the pore water of the gel was exchanged by ethanol and then surface modification was done by aging alcogel in tetraethylorthosilicate (TEOS)/ethanol solution. Before drying, TEOS/ethanol solvent was exchanged with n-heptane. Capillary stress and shrinkages were greatly reduced due to the low surface tension of n-heptane. The prepared aerogel was a light and crack-free solid, with bulk density of 0.67 g.cm–3,porosity of about 80%, total pore volume of 3.1 cm3.g–1 and specific surface area of about 273 m2.g–1. The nature of surface modification and thermal stability of the aerogel was studied by FTIR and DSC/TG respectively.