Tin oxide gel shrinkage during CO2 supercritical drying
Journal
Journal of Non-Crystalline Solids
Journal Volume
224
Journal Issue
3
Pages
259-266
Date Issued
1998
Author(s)
Abstract
Shrinking behavior of tin oxide gels during solvent exchange in CO2 supercritical drying was investigated. The drying process consisted of two solvent-exchanging steps, including a first replacement of water by acetone and a second of acetone by liquid CO2. Gels prepared from a basic sol with a ζ-potential of -75 mV exhibited extensive shrinkage during both steps, while those from an acidic hydrous precipitate of lower potential (| ζ-potential| < 35 mV) shrank only during the second step. The shrinkage during the first step correlates with the ξ-potential reduction with increasing acetone concentration, while that during the second step for both gels can be attributed to osmotic compressive pressure that arises from an increase in the liquid-solid (gel skeleton) interfacial energy with increasing CO2 concentration. Dramatically different aerogel microstructures were obtained by controlling the gel surface potential in conjunction with different combinations of solvent-evaporating and supercritical drying. © 1998 Elsevier Science B.V.
SDGs
Type
journal article