Silica particle growth in metastable supersaturation solution
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Jun-Kyung Kim Division of Polymer Research, Korea Institute of Science and Technology, Seoul, 134, Korea
Woo-Sik Kima) Department of Chemical Engineering, Kyunghee University, Suwon, 449-701, Korea (Received 20 March 2000; accepted 8 November 2000)
In a metastable solution the particle growth rate of silicon dioxide increased with an increase in the initial supersaturation of the metastable solution and agitation speed in the ranges of 2.5 × 10−4 to 2.0 × 10−3 M and 300–1500 rpm, respectively. Based on a power law expression, the particle growth rate order was estimated as 2.0 independent of the initial supersaturation and agitation speed. Meanwhile, the particle growth rate coefficient was enhanced from 2.0 × 10−3 to 1.4 × 10−2 with increase in the agitation speed from 300 to 1500 rpm. From the experimental data, it would appear that the enhanced particle growth rate resulted from the promotion of molecular transport due to the agitation and driving force of the supersaturation in the particle growth process. A slight addition of sodium chloride into the metastable solution caused a marked reduction of the particle growth rate due to the inhibition of growth process by sodium chloride adsorbed on the particle. This effect of sodium chloride on the particle growth appeared in a significant drop of the particle growth rate coefficient from 4.5 × 10−3 to 8.0 × 10−4 with increase in the sodium chloride concentration from zero to 5.0 × 10−3 M, but not in the particle growth rate order. The influence of sodium chloride on the particle growth process of silicon dioxide predicted with a Langmuir isotherm matched with the experimental data.
I. INTRODUCTION
Since the synthesis of a spherical silicon dioxide particle by Stober et al.1 using the sol-gel method, particle size control and morphology have become the most important concerns in the production of fine ceramic powders. Accordingly, a lot of research has focused on investigating the particle growth rate and mechanism in the sol-precipitation. Many mechanisms describing the particle growth process of silicon dioxide in a sol-precipitation have been suggested. Among them, LaMer and Dinegar2 developed a solute molecular addition model for silicon dioxide particle growth in a sol-precipitation. According to this model, the silicon dioxide produced by the reaction in the solution is transferred from the bulk to the particle and then integrated on the particle surface, thereby causing particle growth. To mathematically predict the particle size produced in the sol-precipitation, Matsuokas and Gulari introduced the molecular addition model.3,4 In this a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 2, Feb 2001
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model, it is assumed that during the initial stage of the precipitation, the particle is nucleated with the product of the hydrolysis and condensation of tetraethylorthosilicate (TEOS); thereafter, most of the reaction product is consumed by partic
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