Supercritical drying of gels
| Autor: | David Wilfred Johnson, R.A Laudise |
|---|---|
| Rok vydání: | 1986 |
| Předmět: |
Materials science
Supercritical drying Condensed Matter Physics medicine.disease Supercritical fluid Electronic Optical and Magnetic Materials Autoclave Cracking chemistry.chemical_compound Volume (thermodynamics) chemistry Alkoxide Materials Chemistry Ceramics and Composites medicine Dehydration Composite material Sol-gel |
| Zdroj: | Journal of Non-Crystalline Solids. 79:155-164 |
| ISSN: | 0022-3093 |
| DOI: | 10.1016/0022-3093(86)90043-8 |
| Popis: | Crack free dry gels provide a possibly advantageous route to glasses for, for example, optical fibers. Cracking of condensed alkoxide silica gels occurs during drying when strains are produced because some capillaries are liquid filled while others have dried. If drying is carried out at or near supercritical conditions such strains are reduced. Gels formed from ethylorthosilicate were autoclave dried by various pressure-temperature-time paths. To avoid cracks the initial fill of the autoclave had to be well above the critical fill for ethyl alcohol and the temperature had to be brought above the critical temperature, T c , before the pressure was released. The best results (crack free dried gels) occured when the autoclave was filled to 100% of volume with alcohol, the pressure was brought above p c (H 2 O) and the temperature was slowly raised above T c (H 2 O) while pressure was held constant. Pressure was then slowly dropped and finally the autoclave was furnace cooled. This procedure precluded the presence of vapor+liquid during both heating and drying. |
| Databáze: | OpenAIRE |
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