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Abstract

Procedure for making Al.sub.2 O.sub.3 spheroids, 600 micrometers in diameter or less, utilizes an AlOOH sol containing 0.25% weight percent MgO (in the form of Mg(NO.sub.3).sub.2 .multidot.6H.sub.2 O) and HNO.sub.3. The sol is dispersed into droplets in a particle forming fluid (e.g., 2-ethylhexanol) where gelling occurs. The gelled spheroids are collected, dried and pre-fired in air at temperatures less than 1,200.degree. C. for up to about 12 hours. The dried and prefired beads are fired in a 2-step process at temperatures of about 1,850-1,950.degree. C. in the following sequence: a first dry oxygen firing for about ten minutes, followed by a wet hydrogen firing for up to 350 minutes. Reasonably transparent microspheres having crystallites in the range of 5-100 micrometers are obtained with little intergranular porosity, and their density is estimated to be near theoretical.

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First Claim