Dispersion of silica particle agglomerates and process for producing the same

A process for producing a colloidal dispersion of silica particle agglomerates having a specific surface area, as determined by nitrogen adsorption method, of 100 m2/g to 400 m2/g, an average secondary particle diameter of 20 nm to 300 nm and a pore volume of 0.5 ml/g to 2.0 ml/g, which comprises the steps of (i) adding an aqueous active silicic acid solution to water having a temperature of not lower than 50° C. in the solid content (calculated in terms of SiC2) of the aqueous active silicic acid solution of 0.01 to 1.5 parts by weight for 500 parts by weight of the water per minute or (ii) heating an aqueous active silicic acid solution to prepare a colloidal dispersion of silica particle agglomerates having a specific surface area, as determined by nitrogen adsorption method, of 300 m2/g to 1,000 m2/g, and a pore volume of 0.4 ml/g to 2.0 ml/g as a seed dispersion, and adding a mixture of a feed solution comprising at least one of an aqueous active silicic acid solution and alkoxysilanes and an alkali to the seed dispersion in an amount of 0.001 to 0.1 mol/min, in terms of SiC2 per mol of SiO2 contained in the seed particle agglomerates in the seed dispersion or adding the feed solution and the alkali at the same time and growing the primary fine particles of the silica particle agglomerates.

A process for producing a colloidal dispersion of silica particle agglomerates having a specific surface area, as determined by nitrogen adsorption method, of 150 m2/g to 400 m2/g, an average secondary particle diameter of 20 nm to 300 nm and a pore volume of 0.5 ml/g to 2.0 ml/g, which comprises the steps of (i) adding an aqueous active silicic acid solution to water having a temperature of not lower than 50° C. in the solid content (calculated in terms of SiO2) of the aqueous active silicic acid solution of 0.01 to 1.5 parts by weight for 500 parts by weight of the water per minute or (ii) heating an aqueous active silicic acid solution to prepare a colloidal dispersion of silica particle agglomerates having a specific surface area, as determined by nitrogen adsorption method, of 300 m2/g to 1,000 m2/g and a pore volume of 0.5 mug to 2.0 mug as a seed dispersion, adding an alkali to the seed dispersion and then adding a feed solution comprising at least one of an aqueous active silicic acid solution and alkoxysilanes to the seed dispersion in an amount of 0.001 to 0.1 mol/min, in terms of SiO2 per mol of SiO2 contained in the seed particle agglomerates in the seed dispersion and growing the primary fine particles of the silica particle agglomerates.