Synthesis, characterization, and dispersion properties of hydroxyapatite prepared by mechanochemical-hydrothermal methods

Thermodynamic modeling was utilized to identify reaction conditions to prepare phase-pure hydroxyapatite particulates (HA) by mechanochemical-hydrothermal (M-H) methods using Ca(OH)(2) and (NH4)(2)HPO4 as precursors. The resulting HA powders were characterized by X-ray diffraction, infra-red spectroscopy, thermogravimetry, and transmission electron microscopy, nitrogen adsorption and dynamic light scattering methods. Choosing reaction conditions in the 99% yield region of the CaO-P2O5-NH4OH-H2O phase-pure equilibrium system, nearly stoichiometric and nanostructured HA powders were prepared at room temperature in as little as 1 h. The minimum time to obtain phase-pure HA was 8 h from the conventional attrition mill. As-prepared powders were found to be highly agglomerated with a mass-weighted mean diameter of 2.6 mum in deionized water and average agglomeration number (AAN) as high as 4.5x10(6). Dispersion studies revealed that the appropriate use of dispersants could reduce the mass-weighted mean diameter and AAN. In the presence of sodium polyacrylate, the mass-weighted mean diameter and AAN were 217 nm and 1600, respectively.