EFFECT OF IMPURITIES ON MORPHOLOGY OFα-ALUMINA PLATELETS FORMED BY USING SODIUM SULFATE FLUX

摘要

When a powder mixture consisting of {γ-Al_2O_3 (obtained by heating Al_2(SO_4)_3 at 900℃for 12 h) and 2 Na_2SO_4} was heated at 1000℃in an alumina crucible for 3 h, hexagonalα-Al_2O_3 platelets were formed. The effect of impurities on the morphology of theα-Al_2O_3 was investigated. Generally, incomplete hexagonal platelets and/or fine powder ofα-Al_2O_3 were formed when impurities were added to the original material. However, when Cu~(2+), Co~(2+), Ce~(4+) and F- were present in the original material, they had a unique influence on the morphology of theα- Al_2O_3 platelets. When Co~(2+) and Ce~(4+) were present, theα-Al_2O_3 platelets grew along the c-axis. When Cu~(2+) was present, growth of the platelets in both thickness and diameter was promoted. In contrast, when F- was present, growth along the c -axis was suppressed.