Ostwald ripening silicate

The Si02 walls are built up by condensation processes, for which the anchored silicate species act as nucleation points. The enrichment of the oxide at the templating crystals occurs by an Ostwald ripening mechanism the particles grow in size at the tube walls and highly soluble very small silica particles re-dissolve to the reaction solution. The polycondensation reaction is finished within about I2h. 

To obtain a final product with larger ultimate particles, before the particles are aggregated, it may be desirable to increase their size beyond that reached by spontaneous Ostwald ripening which is around 5 nm at 2S C and 10 nm at 80-I00 C. Ways of growing discrete particles have been described in Chapter 4 and the procedure when making silica from acid and sodium silicate was particularly discussed (402). This or another equivalent procedure is needed as an intermediate step prior to aggregation and structural reinforcement if the final product is to have a particle size much larger than 12-15 nm. 

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