Effect of Sintering on Microstructure and Properties of Hydroxyapatite Produced by Different Synthesizing Methods

The aim of this study is to investigate the effect of the sintering schedule on microstructure and properties of hydroxyapatite which is produced by different synthesizing methods. Hence, wet-chemical precipitation and solid-state reaction were performed to prepare nano-sized hydroxyapatite (HA) powders. Powders were then uniaxially pressed and sintered by varying temperatures and times. XRD and SEM were used to identify phases and morphology. Density and porosity of the sintered sample were determined using the Archimedes technique. Flexural strength was measured by a universal testing machine. The results show that density and strength could be improved by increasing the sintering temperature in both HAW and HAD. However, with increasing sintering temperatures, average grain sizes of HAW and HAD samples were not significantly increased. The sintering temperature seems to play a more important role than sintering time in the densification process of hydroxyapatite. In addition, the thermal stability in sintered HAD samples induced a weaker flexural strength of samples in comparison with HAW. Therefore, the optimized microstructure and properties of sintered hydroxyapatite can be prepared by using the suitable synthesizing method together with the workable sintering schedule for each synthesizing process.