STRUCTURAL-ANALYSIS OF SILICA AEROGELS

Silica aerogels have numerous properties which suggest many applications such as ultrahigh-efficiency thermal insulation, and performance in these applications relates directly to the aerogel pore size distribution. The micro and meso pore size range can be investigated by normal small-angle X-ray scattering and possibly nitrogen adsorption. The measurement of larger pores (> 500 Angstrom) is accomplished by using combined small-angle scattering (both light and X-ray) techniques. These techniques were employed to study the change in wet gel pore structure during partial drying of alkoxide-prepared aerogel precursor gels as well as for aerogels produced from those wet gel of different solids content prepared by supercritical CO2 drying. Aerogels made with density varying from 0.17 to similar or equal to 0.6 g/cm(3) as well as the wet gel precursors showed a loss of the largest pores first during partial drying. As the degree of drying shrinkage increased, both the large pores surrounding individual aggregates and mesopores within the aggregates decreased in size,These results agree with earlier scattering studies on colloidal silica aerogels which had been isostatically compacted to different densities.