The Peculiarities of Silica Aerogel Production Using Azeotropic Mixtures.

At the first time it was carried out the theoretical researches regarding pathways to get into a supercritical region at the ambient pressure with the main aim to avoid expensive and hazardous supercritical drying process and to make a silica aerogel production in whole more economical and commercial. These investigations based on fundamental knowledge about the critical phenomena in multicomponent systems. The representation of phase states in such systems by graphical images was used for the estimation ofLV(xL = xV) azeotrope influence onSLVandL˭Vequilibria. In the course of empiric selection of azeotropic mixtures the negative azeotropes advantage over positive ones was determined and grounded in theory. We report on the synthesis of hydrophobic silica aerogel by ambient pressure drying (APD) procedure, which involves two-step sol–gel process with tetraethyl orthosilicate (TEOS) as a silica precursor and isopropanol as the solvent and an elaborated flow chart using both types of azeotropes as the pore fluids. Guided by receiving our theoretical investigation, we obtained transparent crack-free silica aerogel samples with specific surface in the range of 711–913 m2/g, average pore diameter of ∼95–137 nm, and density of ca. 0.39–0.081 g/cm3. [ABSTRACT FROM PUBLISHER]