Influence of temperature and concentration on the sintering behavior and mechanical properties of hydroxyapatite

Abstract Human bone mineral contains calcium-deficient crystalline hydroxyapatite (HA) embedded in collagen fibers. Research over the past two decades has focused on preparing synthetic HA, which closely resembles bone apatite and exhibits excellent osteoconductivity. This paper describes the synthesis of nano-HA particles via a wet precipitation method. The concentration of the reactants (0.5, 1.0 and 2.0 g/dL) and the temperature of the reaction (25, 70 and 100 °C) were varied. FESEM images were used to determine the size and shape of the resulting nano-particles. The length and breadth of the HA particles were found to increase with the temperature, while the aspect ratio increased with both the concentration and the temperature. The average length of the particles was in the range 53–165 nm and the average breadth in the range 29–52 nm. Agglomerates of HA precipitates were formed during the synthesis process. HA precipitated at 25 °C and concentration 0.5 g/dL resulted in large agglomerates with a specific surface area of 79.8 m 2 /g. HA agglomerates synthesized at each condition were pressed into discs and sintered at 1200 °C. It was found that there was a positive correlation ( p = 0.015) between sintered density and biaxial flexural strength. A maximum strength of 57.4 MPa was observed for the specimens 2.0–70 which also attained the highest density, 92%. XRD results indicated that most of the sintered discs had slightly decomposed. The decomposition of the specimens and their resulting microstructures also contributed to the mechanical strength drop of the specimens.