US 6,203,773 B1 · Low temperature mineralization of alumina

Abstract

Alpha alumina particles are made by heating particles of alumina with an aqueous solution containing a dissolved fluorine-containing compound and an acid; separating the particles from the solution and then calcining the particles at a temperature not greater than about 1025° C. The alumina particles preferably have an LOI in the range of about 1-20 wt. %; more preferably about 1-6 wt. %. Alpha alumina particles of the invention are more readily ground into smaller particles than alpha alumina particles made by calcining at higher temperatures. The remaining soda in the alpha alumina is found to be highly soluble in hot water. The process produces low soda content (0.01 wt. % Na2O or less) alpha alumina crystals from alumina feedstocks with 0.5 wt. % or more initial soda levels. The alpha alumina crystals produced are as large as 30-40 microns. Most typically; the size range is between 2 and 8 microns. Because of the low mineralization temperature, the particles require significantly less grinding time to separate the component alpha crystals.

Claims16

Dependent claims

A process for making alpha alumina particles comprising:

(a) treating particles of alumina having an LOI of less than about 20 wt. % with an aqueous solution containing a dissolved fluorine-containing compound and an acid;
(b) separating the treated alumina particles from the solution;
and
(c) calcining the alumina particles at a temperature in the range of about 950°-1025° C. for a sufficient time to convert at least most of the alumina to alpha alumina;
and
(d) comminuting the calcined particles to an average particle size of less than about 10 microns.

3 more elements

Dependencies are inferred from the claim text.

Low temperature mineralization of alumina

Life of this patent

Low temperature mineralization of alumina

Life of this patent

Abstract

Claims16