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Effect of aging on silica aerogel properties

  • Iswar, Subramaniam Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland - Adolphe Merkle Institute, University of Fribourg, Switzerland
  • Malfait, Wim J. Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
  • Balog, Sandor Adolphe Merkle Institute, University of Fribourg, Switzerland
  • Winnefeld, Frank Laboratory for Concrete and Construction Chemistry, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
  • Lattuada, Marco Department of Chemistry, University of Fribourg, Switzerland
  • Koebel, Matthias M. Laboratory for Building Energy Materials and Components, Swiss Federal Laboratories for Materials Science and Technology, Empa, Dübendorf, Switzerland
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    15.03.2017
Published in:
  • Microporous and Mesoporous Materials. - 2017, vol. 241, p. 293–302
English Silica aerogels’ unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO2. Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying.
Faculty
Faculté des sciences et de médecine
Department
Département de Chimie
Language
  • English
Classification
Chemistry
License
License undefined
Identifiers
Persistent URL
https://folia.unifr.ch/unifr/documents/305540
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