| 摘要 |
PURPOSE: To obtain flocculated large-sized silica particles by incorporating an aqueous dispersion composed of an aqueous medium and noncrystalline silica particles with hydrosilicofluoric acid or a slat thereof and an alkali enough to form silica to effect conducting a reaction. CONSTITUTION: First, an aqueous dispersion of silica particles is prepared by dispersing under agitation 0.5-30 pts.wt., in terms of SiO2 , of noncrystalline silica particles each 5-1000nm in average diameter in 100 pts.wt. of an aqueous medium such as water. Secondly, the aqueous dispersion is heated to about 40-100 deg.C and then incorporated, under agitation, with such an amount of hydrosilicofluoric acid or a salt thereof as to form 0.05-25wt.% of free fluorine ions based on the SiO2 content of the noncrystalline silica particles and such an amount of an aqueous alkali solution such as NH4 OH as to be enough to maintain 0.5-25 pts.wt. of the whole SiO2 based on 100 pts.wt. of the aqueous medium, to effect conducting a reaction to produce an aqueous dispersion of flocculated large-sized silica particles. Subsequently, the aqueous dispersion is filtered, and the flocculated large-sized silica particles are filtered off and washed with water and dried, thus obtaining the objective flocculated large-sized silica particles each having 0.1-10μm diameter determined by centrifugal sedimentation method.
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