Kelly R. Brown

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)2HPO4 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 µm in deionized water and average agglomeration number (AAN) as high as 4.5 × 106. 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.