Consolidation of different hydroxyapatite powders by SPS: Optimization of the sintering conditions and characterization of the obtained bulk products

The difference in purity, particle size, microstructure, and thermo-chemical stability of three commercially available hydroxyapatite powders are found to play an important role during their consolidation using spark plasma sintering (SPS) as well as strongly affect the characteristics of the resulting sintered bodies. A fully dense material without secondary phases was obtained by SPS at 900 °C, when using the relatively small sized, with refined grains and high purity powders. The sintered product, consisting of sub-micrometer sized hydroxyapatite grains, displayed optical transparency and good mechanical properties.In contrast, the higher temperature levels (up to 1200 °C) needed to sinter powders with larger particles, or finer ones which contain additional phases, lead to products with coarser microstructures and/or significant amount of β-TCP as a result of HAp decomposition. Optical characteristics, hardness and elastic modulus of the resulting sintered samples are correspondingly worsened.