The effects of sintering temperature on the properties of hydroxyapatite

The sintering behaviour of hydroxyapatite (HA), the resulting microstructure and properties are influenced not only by the characteristics and impurities of the raw materials but also were found to be dependent on the thermal history during the fabrication process. This work is concerned with the effects of grain size on the relative density and hardness. A commercially available HA powder was cold isostatically pressed at 200 MPa and sintered at temperatures ranging from 1000 to 1450°C with a dwell time of 2 hours. It has been found that, at the optimum sintering temperature of 1250°C where the material is composed of pure hydroxyapatite phase, the samples exhibited densities >99% of theoretical value and possessed a hardness value of 6.08 GPa. Decomposition of HA starts to occur at ∼1400°C with the formation of TCP phase. The change in hardness was found to be dependent on the relative density up to a certain grain size limit. However, above this grain size limit, no correlation exists between the two properties. Porosity and grain size were found to play an important role in determining the properties of sintered hydroxyapatite compacts.