Synthesis, Polymerization, and Assembly of Nanosilica Particles below the Isoelectric Point.

The particle growth of silica below the isoelectric point plays a key role in oil well cements, production of silica gels and production of nanosilica by dissolving silicates. In this article, we study the particle growth of silica below the isoelectric point using olivine, a silicate mineral, and sodium silicate solutions as silica sources in acid, where the particle size, soluble silica concentration, specific surface area and gelling time were measured. The size of the primary particles detected by laser light scattering is 3 nm in the experiments with sodium silicate solutions. These particles grow then by aggregation forming linear chains which in time will start to branch. The particle growth follows a quadratic polynomial function and particles as large as 100 and 500 nm are detected in the final stages of experiments using sodium silica solutions and olivine, respectively. Based on these findings, a comprehensive model describing the silica particle development below the isoelectric point is proposed. This model gives fundamental information about the growth mechanism and the properties of silica (e.g., particle size of the primary particles, size of the aggregates) at the different growth stages.