Anomalous Size-Induced Crystalline to Amorphous Uphill Phase Transformation of Hydroxyapatite Nanoparticles

The objective of the present paper was to produce nanoscale hydroxyapatite at room temperature under 10 nm through a simple method that requires no specialized equipment, surfactants, or additives. The Ca(C2H3O2)2-K3PO4-H2O synthesis system explored in previous literature was employed and the nanoscale powder product completely characterized through x-ray diffraction, transmission electron microscopy, BET nitrogen surface area adsorption, helium pycnometry, TGA and Karl Fisher titration. In accordance with other materials, it was found that hydroxyapatite under 5 nm produced by this chemistry undergoes an uphill phase transformation when left in dry storage over 5 months. Although it is possible to produce hydroxyapatite (and other materials) in this size range, it is imperative that care is taken through storage alterations to prevent any undesirable changes in structure or surface chemistry