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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.degree. 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. % Na.sub.2 O 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.

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First Claim