Preparation of silica gels

Claim 1

The method of claim 1 further comprising: f. calcining the product of step (e).

Claim 19

A method for producing a silica xerogel having a narrow pore diameter distribution primarily within the range of from 300 to 600 A, a surface area within the range of from 200 to 500 m2/g, a pore volume of from 2.2 to 3.0 cm3/g and stability at temperatures up to about 2,000* F. comprising: a. precipitating a silica hydrogel by neutralization of an aqueous solution of a sodium or potassium silicate to provide a silica hydrogel slurry having an SiO2 concentration of from about 8 to about 9 percent by weight while maintaining the pH at from about 5 to about 7 and maintaining the temperature at from about 0* C. to about 10* C., wherein the neutralizing medium is selected from the group consisting of a strong acid, a weak acid, and an ion-exchAnge resin and is added to the aqueous sodium or potassium silicate solution at a rate of up to about 40 percent of the necessary amount in from about 30 to about 120 minutes, and wherein the remaining amount of neutralizing medium necessary to provide an end pH of from about 5 to about 7 is added in a period of time of at least about 20 minutes more, precipitation being under conditions of good agitation, b. heating the product of step (a) at a temperature greater than the temperature of step (a) and at a pH of from about 5 to about 7 for at least about 1 hour, while agitating the product of step (a), c. reducing the sodium or potassium concentration of the product of step (b) by washing the product of step (b) with a liquid which displaces said sodium or potassium until the resulting wash liquor, at equilibrium with the product of step (b), contains less than about 20 ppm sodium or potassium, expressed as an acid-base salt thereof, d. displacing the water from the product of step (c) by replacement of the water with a water miscible organic liquid which reduces the surface tension within the pores of the gel to provide a product with a water content of from about 1 to 6 percent by weight measured as the water content in the displacing organic liquid, and e. drying the product of step (d) to remove the organic liquid and water and provide said silica xerogel.