An effective route to the synthesis of carbonated apatite crystals with controllable morphologies and their growth mechanism

Carbonated hydroxyapatite (CHAp) powders with controllable morphologies and sizes were successfully synthesized via hydrothermal treatment by using hexamethylenetetramine (HMT) as a hydroxide anion-generating agent in a phosphate-surplus precursor solution. The products were characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction. The results revealed that the morphologies (such as microrods, sheet-like-assembled flowers, shaft wheel-like structures, bur-like spheres, dumbbell-shaped structures, and microspheres) of the products could be well tailored by regulating the reaction acidity and time. A possible growth mechanism accompanied by the effects of HMT on crystal nucleation and growth was preliminarily proposed for the formation of the controllable structures. This work indicated that the use of HMT as a hydroxide anion-adjusting agent is an effective strategy to finely control the morphology of CHAp crystals.