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.
