THE PREPARATION AND GROWTH OF COLLOIDAL PARTICLES OF CONCENTRATED SILICA SOLS

Concentrated acidic (pH 3-4) and basic (pH 9-10) silica sols (30-40 wt .%, particle diameter D = 10-20 nm) have been prepared from water-glas s. Both products are very stable in the presence of an appropriate amo unt of stabilizer. It is suggested that the growth of SiO2 particles i n basic solution proceeds by the reaction of neutral surface silanol g roups with monosilicic acid anions, and of surface Si-O- groups with m onosilicic acid molecules. The rate of growth of the colloidal particl es can be described by the following equation, in good agreement with experimental results: V(D) = K(D) 10(-865/T) (r2 + 56.4rD - 126D2)(r 30 + 5D)/D6r(r2 + 126D2) where K(D) is the rate constant, D is the di ameter of colloidal particles, r is the SiO2/Na2O mole ratio and T is the temperature in kelvins.