Patent ID: 8585791

Claim:
A method of producing a nodular silica sol, comprising the steps of: preparing a polymerized silicic acid solution with viscosity of a silicic acid in a range from 0.9 to 100 mPa-s by aging a silicic acid solution with pH in a range from 1.0 to 7.0 and silica concentration in a range from 0.05 to 3.0% by weight at a temperature in a range from 1 to 98° C.; preparing a seed liquid by adding an alkali to the polymerized solution to adjust the pH to a range from 10 to 12.5 and heating the resultant mixture solution at a temperature in a range from 50 to 150° C.; adding an alkali, according to the necessity, to the obtained seed liquid to adjust the pH in a range from 9 to 12.5; dropping a silicic acid solution or a highly purified silicic acid solution to the seed liquid at a temperature in a range from 20 to 98° C. continuously or intermittently for building up; and condensing a mixture of the acid solution and the seed liquid, so that the nodular silica sol has characteristics such that a ratio of an average particle diameter (r) obtained through measurement by means of a dynamic light scattering method versus a particle diameter (r′) converted to that of an equivalent sphere computed from an average specific surface area measured by a nitrogen absorption method (r/r′, referred to as “association ratio”) is in a range from 1.2 to 10, the particle diameter (r′) is in a range from 5 to 200 nm, a specific surface area is in a range from 13 to 550 m 2 /g, and contents of Ca and Mg calculated as those of oxides contained in the nodular silica particles are below 100 ppm against SiO 2 respectively.