A commercial hydroxyapatite, which has been regarded as a powder with low sinterability, was ground by four kinds of wet ball-milling in order to improve the sinterability. The effect of the grinding on the sinterability was investigated by comparing the four methods. When the powder was ground under water as a dispersion media, fine particles generated by the grinding cohere to reconstruct aggregates, then milling effects disappear. The fine particles without reconstructed aggregates can be obtained by ball-milling under ethyl alcohol as a dispersion media. The grinding efficiency can be improved by using balls with a high true density. The sizes of aggregates were diminished to 0.1-0.2μm by ball-milling using nylon coated iron balls. The powder ground by the nylon coated iron ball was formed into disks and then heated at 1200°C for 1 h. The bulk density of the sintered body was >98% of the theoretical density.
