Abstract
The pore structures and microstructures of silica gel monoliths derived from the polycondensation of tetramethoxysilane (TMOS) in basic pH were characterized after various stages of sintering, using N{sub 2} gas adsorption-desorption, mercury porosimetry, and TEM. Gels dried by supercritical drying, i.e., aerogels and gels dried slowly in air have different pore structures and sinter with contrasting results when heat-treated under identical conditions. The air-dried gels do not sinter to full density and exhibit bloating on heating to high temperatures (1,100{degree}C), whereas under the same condition aerogels sinter to dense, transparent glass without bloating. Transmission electron microscopy shows that the microstructure of gels is composed of 5- to 10-nm primary spherical particles which clustered to form large (100 nm) spherical aggregates loosely bound to each other. In aerogels, two types of porosity exit: macroporosity and ultraporosity.
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