Hydrothermal conversion of coral into hydroxyapatite

Porous coralline hydroxyapatite (CHA) was prepared by the hydrothermal conversion of Porites skeleton (aragonite) with and without the use of the mineralizer KH2PO4. X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were employed to characterize the exchange process. The complete conversion was achieved after 10 and 17 days, respectively, with and without the mineralizer. When the mineralizer was present, the exchange process involved only the direct conversion of aragonite into HA. Without the presence of the mineralizer, there were, in addition, intermediary conversions of aragonite into calcite and calcite into β-tricalcium phosphate (β-TCP). The research study also showed that the presence of the mineralizer accelerated the conversion process and preserved the interconnecting microstructure of the coral better.