Method of making colloidal silica

  • US 6,372,806 B1
  • Filed: 02/14/2000
  • Issued: 04/16/2002
  • Est. Priority Date: 03/06/1998
  • Status: Expired due to Term
First Claim
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1. 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.

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