Effect of operation conditions on HA synthesized by the hydrothermal method

This paper reports the influence of aging time and reaction temperature on the surface morphology and mechanical properties of hydroxyapatite (HA) synthesized by a hydrothermal method. Calcium nitrate and ammonium orthophosphate solutions were premixed and fed to an autoclave and reacted to temperatures varying between 25-250°C for 2-10 h. Results indicate the strong positive influence of reaction temperature on the HA particle aspect ratio. The density of the discs pressed from these samples reached 85-90% of the theoretical density after calcination at 1200°C for 1 h. Sintered density and flexural strength were found to increase with increasing aging time and reaction temperature. A maximum flexural strength of 78 MPa was observed for the sample synthesized at 170°C for 5 h with the predicted average at these conditions being 65 MPa.