Title: Gelation rate of silica nanoparticles at different supersaturation with and without ammonium fluoride additive

Authors: E.A. Abdel-Aal, M.M. Rashad, R.M. Mohamed

Addresses: Central Metallurgical Research and Development Institute, P.O. Box 87 Helwan, Cairo, Egypt. ' Central Metallurgical Research and Development Institute, P.O. Box 87 Helwan, Cairo, Egypt. ' Central Metallurgical Research and Development Institute, P.O. Box 87 Helwan, Cairo, Egypt

Abstract: Silica nanoparticles have been synthesised using sol gel technique. The effect of ammonium fluoride NH₄F addition on the gelation rate of silica was studied under supersaturation ranging from 8.72 to 13.34. The results showed that the gelation times were decreased by increasing the supersaturation and by addition of NH₄F. Surface energy between the formed gel and the solution was calculated as 17.28 and 16.11 mJ/m² with and without NH₄F addition. The gelation rate was increased and the Gibbs free energy change for the formation of critical nucleus was decreased by increasing the supersaturation and by addition of NH₄F. The critical radius of the nucleus was decreased from 6.42 and 5.60 Å without and with addition of ammonium fluoride to 5.70 and 4.85 Å when the supersaturation was increased from 8.72 to 13.34. This approach can be used to discuss the effect of any additives on enhancing or inhibition the gelation rate.

Keywords: A1; nucleation; A2; growth from solution; b1; nanomaterials; gelation rate; silica nanoparticles; supersaturation; ammonium fluoride; nanotechnology; sol gel; additives.

DOI: 10.1504/IJNP.2010.034852

International Journal of Nanoparticles, 2010 Vol.3 No.2, pp.192 - 203

Published online: 25 Aug 2010 *

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