Silica aerogel powders were synthesized from inexpensive water glass under ambient-pressure drying (APD). Silica sol was synthesized by using adding hydrochloric acid (HCl) to diluted water glass, the silica sol was rapidly formed hydrogel by the addition of isopropyl alcohol (IPA), a new gelation agent. After solvent exchange and surface modification, silica aerogel powders were obtained by ambient-pressure drying the chemically treated hydrogel. This study especially investigates how the amount of added HCl affects properties of the silica aerogel powders, namely the tap density, specific surface area, pore size and volume, microstructure, and hydrophobicity. The aerogel powders size and density were found to decrease and the specific surface area, pore size and pore volume increase with increasing amounts of added HCl. The aerogel powders synthesized with the largest amount of HCl (volume ratio of HCl to water glass: 0.53) showed the tap density, specific surface area, pore size, pore volume, and thermal conductivity of 0.10 g/cm3, 819 m2/g, 12.00 nm, 3.14 cm3/g, and 0.023 W/mK, respectively. Also, it showed good hydrophobicity and thermal stability. It was evident that HCl addition amount can be one of key parameters to control the physical and thermal properties of silica aerogel.

Keywords: Aerogel, Inorganic acid, Alcohol, Water glass, Ambient-pressure drying