Pressure-induced crystalline to amorphous transition in hydroxylapatite

Hydroxylapatite, prepared by the reaction of an aqueous suspension of Ca(OH)2 with H3PO4 at pH>7 and sintered at 700°C was subjected to various pressures in a Bridgman anvil apparatus, and the retrieved material was examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) methods. The studies showed that the crystalline hydroxylapatite transforms irreversibly to an amorphous phase 2 GPa. The transformation occurs through an intermediate phase and is completed at around 10 GPa pressure.