Method for making high purity, devitrification resistant, amorphous silica fibers

Claim 1

A double leaching process for making amorphous silica fibers having excellent resistance to devitrification at temperatures up to 2500° F. comprising: providing a mass of glass fibers having a composition, on a weight basis, of about 72.6-75% silica, at least about 23.5% soda, about 0.02-0.16% alumina, and less than about 0.01% titanium dioxide, into a digestor, leaching the fibers in a first leaching cycle comprising: forming in said digestor a slurry comprising said fibrous mass and a leaching solution, said fibrous mass being covered with said leaching solution, heating said slurry to a temperature within the range of about 180°-205° F. and during said heating withdrawing leaching solution from the digestor at a point below said fibrous mass and reintroducing the leaching solution to the top surface of the fibrous mass, and periodically gently stirring said slurry to prevent settling of the fibers and channeling and to fluff the fibers up into a loose mass to facilitate uniform flow of the leaching solution through the entire mass, draining the leaching solution from the digestor, rinsing the fibrous mass in an initial rinsing cycle in order to remove residue leaching solution and soluble salts and during said rinsing periodically gently stirring said fibrous mass to prevent channeling and settling of the fibers and to fluff up the fibrous mass to facilitate uniform flow of the rinsing solution through the fibrous mass, leaching said fiber in a second leaching cycle comprising: again forming in said digestor a slurry comprising said fibrous mass and a leaching solution, said fibrous mass again being covered with said leaching solution, again heating said slurry to a temperature within the range of about 180°-205° F. and during said heating withdrawing leaching solution from the digestor at a point below said fibrous mass and reintroducing the leaching solution to the top surface of the fibrous mass, and periodically gently stirring said slurry to prevent settling of the fibers and channeling and to fluff the fibers up into a loose mass to facilitate uniform flow of the leaching solution through the entire mass, again draining the leaching solution from the digestor when the batch of fibers is leached to the desired extent, again rinsing the fibrous mass in a final rinsing cycle to remove residue leaching solution and soluble salts and during said rinsing periodically gently stirring said fibrous mass to prevent channeling and settling of the fibers and to fluff up the fibrous mass to facilitate uniform flow of the rinsing solution through the fibrous mass, and drying the fibrous mass.