Sintering and mechanical properties of nanocrystalline hydroxyapatite

Nanocrystalline hydroxyapatite powder (Ca10(PO4)6(OH)2, HAp) was produced by solid-state reaction using the mechanical alloying method. The nanocrystalline and Micron (HA, Merk>98%) powders were pressed and sintered at various temperatures in the range of 800-1200°C. Measurements of compression strength, microhardness and density were performed at the same condition. The phase analysis was carried out using X-ray diffraction (XRD) technique. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to study the morphology of powders and sintered hydroxyapatite. Hydroxyapatite grains gradually increased in size from ~90 nm to 2 µm when temperature increased from 800 to 1200◦C, reaching to a density of 83.20% theoretical density and 230 MPa Compressive strength compared with micron hydroxyapatite, reaching to a density of 70% theoretical density and 125 MPa compressive strength