Stress in aerogel during depressurization of autoclave: II. Silica gels

Thierry Woignier, George W. Scherer, Adil Alaoui

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

Although supercritical drying avoids the capillary stresses that tend to warp and crack xerogels, there are other sources of stress that interfere with the preparation of monolithic aerogels. In this paper, we present experimental results showing that there is a limit to the rate at which the pressure can be released from the autoclave without causing cracking, and that the maximum rate decreases as the gel size increases. Using an analysis developed in a companion paper, the stresses generated during depressurization are compared to the modulus of rupture of our aerogels. The calculations require knowledge of the pressure-dependence of the density of the vapor (ethanol, in our experiments), as well as the permeability and modulus of the gel network. Measurements of those properties were performed on a series of silica gels made under basic and neutral conditions. We find that the calculated stresses are large enough to account for the cracking of our gels at high rates of depressurization; moreover, the predicted dependence of stress on gel diameter is in agreement with experiment.

Original languageEnglish (US)
Pages (from-to)141-150
Number of pages10
JournalJournal of Sol-Gel Science and Technology
Volume3
Issue number2
DOIs
StatePublished - Jan 1 1994

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Chemistry(all)
  • Biomaterials
  • Condensed Matter Physics
  • Materials Chemistry

Keywords

  • aerogel
  • drying
  • permeability
  • stress
  • supercritical drying

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