PURPOSE: To obtain an aggregate of polyhedral corundum particles having a narrow particle size distribution by mixing alumina hydrate as a starting material with fine corundum particles having a specified shape factor and by hydrothermally treating the mixture to deposit alumina on the surfaces of the particles.
CONSTITUTION: Particles of alumina hydrate such as aluminum hydroxide as a starting material are mixed with fine corundum particles adjusted to 1.0W1.4 shape factor by classification as seed crystals. The mixture is hydrothermally treated to deposit alumina in the alumina hydrate as corundum on the surfaces of the fine corundum particles. To the hydrothermal synthetic reaction system may be added a boron compound such as sodium borate. By this method the desired aggregate of polyhedral corundum particles havong a narrow particle size distribution is obtd.
HASEGAWA HIKARI
SAKAIDA TOSHIAKI
YAMAGUCHI KATSUNOBU
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