Reduction of processing time by mechanical shaking of the ambient pressure dried TEOS based silica aerogel granules

Abstract

The present paper deals with preparation of silica aerogel granules by two step acid–base sol–gel process involving ambient pressure drying of alcogels with additional use of mechanical shaker to accelerate the solvent exchange process and characterization of the yielded aerogels granules to study their physical properties. The conventional ambient pressure drying of alcogels is crucial since it needs tedious repetitive gel washing and solvent exchanges (10 times) which consumes total process time of 4 days. We have succeeded to synthesize aerogels within 2 days by making use of alcogels shaking. To get good quality aerogels in terms of low density, high optical transparency, low volume shrinkage, various base catalysts and their combinations were used. The optimal molar ratio of precursor chemicals Tetraethoxysilane (TEOS): Methanol (MeOH): Oxalic acid: NH4OH: NH4F: Trimethylchlorosilane (TMCS) found to be 1: 16.5: 0.49: 0.58: 0.60: 0.98, respectively. Among six catalyst studied, combination of NH4OH and NH4F resulted in low density and transparent aerogels. Hydrophobicity was achieved by surface silylation using TMCS silylating agent but lead to decrease in transparency due to chloride precipitation. We have improved transparency of aerogels by methanol washing of alcogels prior to silylation. The hydrophobicity has been studied by FTIR analysis and contact angle measurements. The thermal analysis indicates thermal stability of hydrophobicity up to 318 °C and the Surface morphology of aerogel has been studied by FESEM.