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Morphology of silica aerogels obtained from the process catalyzed by NH4F and NH4OH
Lamgmuir (1997)
  • Janusz J. Malinowski
  • J. Mrowiec-Bialon
  • L. Pajak
  • A. B. Jarzebski
  • A. I. Lachowski
Abstract

Twelve samples of silica aerogels were synthesized using different concentrations of catalysts (NH4F,NH4OH), and their morphology was investigated by means of small-angle X-ray scattering (SAXS), N2 adsorption, and transmission electron microscopy. Both SAXS and the nitrogen adsorption method consistently show a different influence of the catalysts; fluoride anions promote formation of a tenuous branched-polymeric structure, with mass fractal dimension Dm = 2.3-2.5, while addition of hydroxyl ions results in a sparser structure (Dm = 2.1-2.2) self-similar over a narrower range. The morphology of aerogels obtained from the process catalyzed by fluoride hydroxide resembles that of aerogels produced by the two-step method. This may suggest similar mechanisms of gel formation in both processes, and, consequently, a dramatic acceleration of the hydrolysis reaction caused by NH4F.

Disciplines
Publication Date
1997
Citation Information
J. Mrowiec-Bialon, L. Pajak, A. B. Jarzebski, A. I. Lachowski, J. J. Malinowski. "Morphology of silica aerogels obtained from the process catalyzed by NH4F and NH4OH" Lamgmuir 13(23) (1997): 6310-6314.