Fabrication of Spherical Silica Aerogel Granules from Water Glass by Ambient Pressure Drying

Spherical silica aerogel granules were fabricated from water glass. A silicic acid solution was mixed with n ‐hexane and a surfactant, which was used as a stabilizer, to produce silicic acid droplets in n ‐hexane. Ammonia was used to gelate the silicic acid droplets and the silica hydrogel droplets were subsequently surface‐modified using a TMCS (trimethylchlorosilane)/ n ‐hexane solution followed by solvent exchange from water to n ‐hexane. Silica wet gel droplets were dried at 80°C under ambient pressure. A perfect spherical silica granule between 230 and 123 μm in diameter was obtained and its size can be controlled by surfactant content. On the other hand, the surfactant had little effect on the particle size distribution and its uniformity lies between 0.332 and 0.454. The tapping density, pore volume, and BET surface area of the silica aerogel granule were ~0.08 g/cm 3 , 3.0 cm 3 /g, and 700 m 2 /g, respectively. FT‐IR spectrum analysis showed that the surface of the silica granules was modified by Si–CH 3 groups, which allowed the aerogel to be hydrophobic.