Influence of Ammonia Concentration on Particle Size Distributions in Seeded Reaction of Hydrolysis and Condensation of Tetraethyl Orthosilicate

Seeded reactions of the hydrolysis and condensation of tetraethyl o-silicate were carried out to determine the influence of NH₃ concentration on particle size distribution. Aggregation of seed particles was observed at a high NH₃ concentration (1 kmole/cu m), while a large number of new particles were formed at a low NH₃ concentration (0.25 kmole/Cu m). An intermediate NH₃ concentration (0.5 kmole/cu m) was suitable for particle growth that was scarcely accompanied with aggregation and new particle formation. Estimation of ionic strength from pH values during the reactions suggested that an increase in the ionic strength with an increase in NH₃ concentration suppressed the new particle formation and led to the particle aggregation. Seeded growth reactions in which KCl of LiCl was added demonstrated that new particle formation was highly suppressed by the addition of the electrolytes.