Abstract: A method of preparing colloidal zirconium oxide sols having substantially uniformly spherical particles in the size range of from about 0.01 to about 2.0 microns is described. The process comprises the steps of(A) preparing a liquid mixture comprising at least one zirconium salt and a compatible liquid vehicle;(B) contacting said liquid mixture with an anion exchange resin for a period of time sufficient to form a zirconium hydrate sol having a pH of at least about 5.0; and(C) recovering the zirconium hydrate sol from the resin. Colloidal size zirconium oxide powders can be prepared from the colloidal zirconium oxide sols by drying and calcining the sols at an elevated temperature. The zirconium oxide powders obtained in accordance with the present invention can be stabilized by the incorporation of certain stabilizers such as yttrium oxide, lanthanum oxide, cerium oxide, calcium oxide and magnesium oxide.

Abstract: A filter element for aerosols and finely divided solid particles suspended in a gas, is formed by depositing a septum of microscopic and submicroscopic unsintered fibers of fibrillatable polytetrafluoroethylene (hereinafter referred to as PTFE) as a random network on a supporting screen. The filter so formed is especially effective to remove liquid and solid particles of micron and submicron size suspended in a gaseous medium to be filtered.A process is described for separating contaminant solid and liquid particles less than about 5 .mu. (micron) in diameter from the gas in which the particles are suspended, comprising introducing primary particles of fibrillatable PTFE less than about 1 .mu.