Effects of seeds concentration on the formation of colloidal silica

The effects of seed concentration on the mechanism of colloidal silica formation via sodium silicate were studied in this article. When the seed concentration is less than 0.62 wt%, the mechanism of particle formation is dominated by the homogenous nucleation of the active silicate acid. Increasing the seed concentration increases the importance of heterogeneous nucleation via surface growth on seeds. In the seed concentration range of 0.62–1.36 wt%, the formation mechanism is homogenous nucleation parallel to surface growth. Two kinds of particles, one has a small particle size and the other has a large particle size, were observed by transmission electron microscope pictures. A maximum mean particle size of the final product is observed at 0.74 wt% seed concentration. When the seed concentration is in the range of 1.36–2.48 wt%, the mechanism of particle formation is surface growth. The final particles are uniform in diameter. The particles are aggregated and gelled when the seed concentration is greater than 2.48 wt%. The particle size of the final colloidal silica was estimated by the assumption that the additional silica of added as active silicic acid grows on the seeds. The results are compared with the particle size measurement from dynamic light scattering (DLS).