Morphology and composition of nanograde calcium phosphate needle-like crystals formed by simple hydrothermal treatment

Nanograde calcium phosphate needle-like crystals are prepared from wet synthesized Ca−P precipitates by simple hydrothermal treatment at 140°C and 0.3 MPa for 2 h. The morphology of these crystals is observed by transmission electron microscopy (TEM). The phase composition is tested through X-ray diffractometer (XRD) and infrared spectroscopy (IR). It is found that the morphology of these crystals is related to the activity or fresh degree of the starting Ca−P precipitates and the added fluorine ions, but is not greatly influenced by the Ca/P ratio of the precipitates. These crystals with a Ca/P ratio between 1.67 and 1.5 show a poorly crystallized apatite structure at room temperature and a biphasic (HA+β−TCP) structure at 1100°C, corresponding to their Ca/P ratio. It is demonstrated that these nonstoichiometric apatite crystals contain lattice-bound water which could play an important role in the formation of bone apatite. The similarity in morphology and composition between these needle-like crystals and the apatite crystals in bone provides a possibility to make a bone-like implant consisting of these needle-like crystals and collagen, etc.