Influence of different seeds on transformation of aluminum hydroxides and morphology of alumina grains by hot-pressing

The influence of different seeds on transformation of aluminum hydroxides and morphology of alumina grains was investigated. There are two kinds of alumina seeds used separately, alumina milling ball abrasive seeds and ultra-fine alumina powder seeds. Abrasive seeds were introduced to the starting materials by wet-grinding of high-purity alumina milling balls. The alumina powder seeds were directly added into raw materials. First, the introduction of different seeds can lower the transformation temperature from κ phase to α phase. The phase transformation from aluminum hydroxide to α-Al2O3 was completed at 1100 °C in 2 h when a certain amount of seeds were employed. Second, seeds also changed the sintering behaviour and microstructure of alumina ceramics. For the hot-pressed sample with alumina powder seeds added directly, the microstructure with platelets was observed. However, the anisotropic growth of alumina grains is favored in the presence of alumina abrasives as seeds. The elongated grains were developed in the sample with abrasive seeds introduced.