alpha -ALUMINA

摘要

A powdery alpha -alumina comprising single-crystal alpha -alumina grains which are homogeneous and free from any crystal seed inside, form an at least eight-sided polyhedron, and have a D to H ratio of 0.5 to 3.0 (wherein D is the maximum grain diameter in parallel with the hexagonal lattice plane of the alpha -alumina having a hexagonal closest lattice structure and H is the grain diameter perpendicular to the hexagonal lattice plane thereof), a number-average grain diameter of longer than 5 mu m up to 30 mu m, a sodium content of less than 0.05 wt.% in terms of Na2O and an alumina purity of 99.90 wt.% or above. The powdery alpha -alumina of the invention comprises single-crystal alpha -alumina grains which are highly pure, fine and homogeneous, have a narrow grain size distribution, are not aggregated, and form an at least eight-sided polyhedron. It is suitable as the raw materials of abrasive, sinter, plasma spraying material, filler, single crystal, catalyst support, phosphor, sealing material and ceramic filter, thus being remarkably useful from the industrial viewpoint. In particular, it has such a high purity that it can be used as the raw material of single crystals of, for example, yttrium aluminum garnet (YAG), sapphire and ruby, which cannot be prepared from low-purity alpha -alumina, and as the raw material of high-purity sinter.