1998 Volume 45 Issue 12 Pages 1122-1130
An overall development of microstructure during sintering of high purity sub-micron alumina is investigated. The alumina is compacted by the High-Speed Centrifugal Compaction Process (HCP alumina). An alumina powder with a purity of 99.99 mass% and mean particle size of 0.22μm is dispersed in 25 mass% of ion-exchanged water, compacted applying a centrifugal force of 10, 000-20, 000 g for 3 ks, and sintered at 1473-1623 K for 0-172.8 ks in air.
The microstructure of sintered HCP alumina has particular combination of its density and grain size in each sintering condition, and they make single grain-size/relative-density trajectory. The location of the trajectory shifts toward smaller in grain size and higher in density compared to previously reported ones.
The grain-size/relative-density trajectory is divided into three stages as the microstructure morphology changes. In the stage I, the microstructure is composed of open pore network, and its trajectory shows a straight line with low gradient. In the stage II, the microstructure has closed pores and the trajectory curves upward. After the density almost reaches uppermost limit, the morphological development enters to stage III, and steep straight trajectory is observed.
The sintered compact at the boundary of stage II and III shows the highest strength. The microstructure of that body has a density of about 99 % and homogeneous fine grains with equi axed isolated pores located at the four-grain corners.
