Comparative study in use sodium silicate instead of NH4OH as an alkaline basic catalyst to gelation unmodified silica aerogel based on tetraethoxysilane (TEOS)

Abstract

In the present work, nonporous hydrophilic unmodified silica aerogel was synthesized successfully by ambient drying with one step base catalyst by used silica organic initiator tetraethoxysilane (TEOS). Silica aerogel was prepared twice by sol-gel technique; the first one was the gelation that happened under the alkaline catalyst NH4OH, which has a toxic property and dangerous to human health. The second gelation under the effect of the safety inorganic base catalyst sodium silicate (water glass) that used as an inorganic low-cost and environmentally friendly initiator to silica, plays a role in increasing pH as a catalyst and as a new rare co-precursor mixing organic and inorganic silica precursors (TEOS+Na2SiO3). The impurities accompanying water glass and sodium residue were eliminated by a lot of washing. The volume ratio of the (TEOS: ethanol: H2O: base catalyst) fixed respectively at (5.6:50:10:0,01M). The gelation reaction time, the gel properties, it's quality and the amount of the reactant, the density, and the appearance all effect by the type of catalyst used. The comparative study of silica porous aerogel production properties diagnostic achieved by FTIR, XRF, BET, BJH, FESEM and thermal conductivity applied as insulation materials .