Sol-Gel Transition of Acid Silica Sols Produced by a Y-shaped Reactor

We have developed a new production method for silica sols using a Y-shaped reactor. Diluted sodium silicate and sulfuric acid were forced to collide against each other at the intersection of the reactor. Silica sols with the appropriate viscosity produced by this method could be used as waste water treatment agents and retention aids for papermaking. In this study, the gelation process of silica sols was considered by dynamic viscoelastic measurements. Furthermore, we observed directly observed the gel surface using a scanning probe microscope (SPM). From the results, the onset time of gelling was strongly affected by both the concentration of SiO2 and the excessive rate of sulfuric acid. The gel surface structure produced with different conditions was also characterized. It was found that larger coalescence of silica particles presented in gels and the coalescence rate depended on the excessive rate of sulfuric acid.