Citrate was used as chelating or morphology regulating agent in this study. In the presence of regulating agent a two-dimensional monetite phase evolved into  three-dimentional hydroxyapatite microspheres with an average diameter of 4 µm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed the importance of Ca/citrate ratio in regulating the particle morphology. The results indicate that the surface morphology of microspheres can be engineered from nanosheets to nanorods by regulating agent’s concentration.  X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy confirmed crystallinity and purity in the synthesized powders. Brunauer-Emmett-Teller (BET) revealed an increase in the specific surface area with adding citrate. Possible mechanisms are proposed to account for the formation of different morphologies based upon thermodynamic theories.
 

Keywords: Hydroxyapatite, Citrate, Hydrothermal, Morphology.

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