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.
Morphology of silica aerogels obtained from the process catalyzed by NH4F and NH4OHLamgmuir (1997)
Citation InformationJ. 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.