Sol-gel processing of controlled porosity silica films: From aerogels to molecular sieves
- Sandia National Lab., Albuquerque, NM (United States)
In sol-gel processed materials, the structure of the dried gel or xerogel depends on the structure of the wet gel and its response to capillary stresses exerted during drying. This paper first describes experiments conducted to elucidate the formation of porous ceramic files from liquid-based precursors in situ using novel techniques such as imaging ellipsometry, fluorescence mapping and capillary stress profiling. We then report on several non-hydrothermal routes to prepare microporous silica films with pore sizes and transport properties similiar to zeolites and describe a process to prepare highly porous aerogels films (>98% porosity) that avoids supercritical conditions. In general to achieve this wide spectrum of structural variations at ambient pressures, we use catalytic conditions and organic substitution to control the gel modulus, pore fluid composition and relative pressures to control the capillary stress, and surface derivatization to control the reversabiltiy of drying shrinkage. When mechanically weak gels are subjected to high capillary stress, the gel network collapses (normally irreversibly) to create micropores. Alternatively, when prior to drying, the pore surfaces are derivatized with non-hydrolyzable groups, e.g. -SiMe{sub 3} drying shrinkage can be followed by expansion of {open_quotes}springback{close_quotes} re-creating some or all of the porosity of the wet gel state.
- OSTI ID:
- 370178
- Report Number(s):
- CONF-960376--
- Country of Publication:
- United States
- Language:
- English
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