Patent ID: 6372806
Filing Date: 2002-04-16
Classification: C01B,D21H

Abstract:
A process for preparing a stable colloidal silica having an S-value of from 20-50 and wherein said silica has a surface area of from about 700 m2/g to about 970 m2/g and comprising:(a) forming an initial composition containing water, an alkali metal silicate having a mole ratio of SiO2 to alkali metal oxide in the range of from 15:1 to 1:1 and a pH of at least 10, and a compound selected from the group consisting of an acid, a corresponding salt thereof and a mixture thereof, said alkali metal silicate and said compound being initially present in a ratio by weight of at least 63:1, while maintaining the temperature of said initial composition below 90 degrees Fahrenheit; (b) slowly and continuously adding to said initial composition an aqueous silicic acid composition having a SiO2 content in the range of from 4.0 to 8.5 percent by weight while maintaining the temperature below 90 degrees Fahrenheit until from one-half to three-quarters of said silicic acid composition has been added to said initial composition; (c) slowly increasing the temperature of said composition to from 115-125 degrees Fahrenheit and maintaining the temperature until the addition of the silicic acid composition is complete; (d) optionally, maintaining the temperature of the composition below 125 degrees Fahrenheit for about an hour; and (e) discontinuing said heating and optionally removing water from said composition until the solids content based on SiO2 of said stable colloidal silica is from about 7 percent by weight to about 20 percent by weight.