New technology for rapid processing and moulding of silica aerogel materials in prescribed shapes and sizes and their characterization

The new technology has been developed for rapid processing of silica aerogels at a rate 40 times faster than the conventional method and is reported in the present paper. Silica gels were prepared using precursor chemicals Tetramethoxysilane: Methanol: Water (0.05 mol L⁻¹ NH₄OH): Methyltrimethoxysilane at a molar ratio of 1: 12: 4: 0.8, respectively. Mixture of these precursors was stirred and transferred to metallic moulds. These metallic moulds were kept in a 3-liter autoclave with an additional 400 mL of methanol. The autoclave was pre-pressurized to 4 MPa with N₂ gas and heated rapidly at the rate of 8 ^°C/min. to reach supercritical state of methanol. After 10 min, the vessel was depressurized at a rate of 0.45 MPa/min. The sol in the mould when heated rapidly gets transformed to aerogel directly and the crucial alcogel handling step is skipped. We successfully synthesized 50 mm diameter and 15 mm thick disc shaped and 40 mm diameter hemispherical monolithic aerogels using the rapid process method. Retrieved aerogels were characterized for their density, surface area, optical transmittance, fractal size, surface morphology and microstructure using SEM, TEM and SAXS. Aerogels synthesized by rapid process technology shows improved physical properties than the aerogels derived by conventional method.