Modulation of hydroxyapatite crystals formed from α-tricalcium phosphate by surfactant-free hydrothermal exchange

In the present work, an unusual precursor, α-tricalcium phosphate [Ca3(PO4)2, α-TCP] was used for the modulation of hydroxyapatite [Ca10(PO4)6(OH)2, HA] crystals. Micro-structure and morphology controllable HA crystals were successfully synthesized via direct hydrothermal treatment of α-TCP particles in the absence of any surfactants or additives, and were investigated by field emission scanning electron microscopy, field emission transmission electron microscopy, X-ray diffraction, X-ray fluorescence spectroscopy and Fourier transform infrared spectroscopy. Well developed HA crystals with different structures and morphologies (chrysanthemum-like HA microflowers, enamel-like HA microparticles, rectangle shaped HA microplates and HA microrods) could be obtained by adjusting the reaction temperature and the concentration of Ca2+ ions. The experimental results showed that different aggregation routes of HA nanorods which grow along the c-axis were the reason for the formation of various micro-structures and morphologies. The possible mechanism of the formation of HA crystal was based on the Cluster Growth Model. This study suggested that the hydrothermal phase transformation from α-TCP to HA could be a promising way for the delicate morphology control of HA crystals.