This report contains a fundamental study about physical and textural properties of silica aerogels prepared by double-catalyzed sol-gel reactions and a supercritical dry by carbon dioxide. The sol-gel reactions to produce wet gels were controlled in condensation reactions by pH while compositions of sols and hydrolysis reactions were kept the same. Silica aerogels produced by the supercritical dry of the wet gels were analyzed in various properties; gelation time decreased exponentially, bulk density decreased significantly, average radius of condensed particles and fractals decreased, but skeletal density increased, volume and size of pores and internal surface area increased when pH in condensation reactions increased. The results were interpreted based on key concepts of condensation reaction rate and developed microstructures that more active condensation in higher pH leads to larger numbers of bonds and junctions for gel networks, and more active elimination of microporosity in higher pH leads to higher skeletal solidity. A combination of these two effects makes the aerogel produced in higher pH resist more to the drying shrinkage. This fundamental study of significant changes of bulk density and porous textures within the same composition of sols was applied further to produce a gradient density aerogel. A new and practical method for producing the gradient density aerogel was introduced in accordance.

Study about structural development of silica aerogles by double-catalyzed sol-gel reactions and gradient density aerogels produced in accordance

248th National Meeting (2014)

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