高速遠心成形法による高純度アルミナの焼結中における気孔組織の変化

Abstract

To elucidate the causes of the superior mechanical properties of the alumina developed by the high-speed centrifugal compaction process, its microstructure development during sintering is investigated. A high purity alumina powder with a purity of 99.99% and a mean particle size of 0.22μm is dispersed in 25 mass% of ion-exchanged water, compacted applying acentrifugal force of 10, 000-20, 000g for 3ks, and sintered at 1423-1773 K for 5.4ks in air.Homogeneous sintered compacts with a relative density of 99% or more and free from abnormal grain growth are obtained without using any additives in a wide range of sintering conditions. On tens of fracture surfaces observed, no sign of inhomogeneity such as large grain, large pore, or inclusion is observed. Instead, each specimen contains a little intergranular porosity. At low sintering temperatures, pores remain at the fbur-grain corners which. are thermodynamically the most stable sites. As the sintering temperature increases, the pores change their locations gradually from four-grain corners to three-grain edges, then to two-grain boundaries.The strongest specimen, the one sintered at 1503K for 5.4ks, shows homogeneous equiaxed grains with equiaxed and simple-shaped pores located at four-grain comers.