Hydroxyapatite transformed hydrothermally from natural porous material

The chalky layer from the oyster shell studied,was found to be a natural micro-porous structure material calcite,with which the hydroxyapatite was synthesized in the phosphatic solution at 90℃ water bath heating and atmospheric press.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),and scanning electron microscopy(SEM) were employed to characterize the products prepared by chalky layer.The results show that the hydroxyapatite would be formed as long as the reactants underwent only 15min hydrothermal reaction at atmospheric press.After 48h reaction,the chalky layer almost converted entirely to hydroxyapatite and the hydroxyapatite still retained the original integrity of the micro-porous structure.This conversion included two reaction processes.The exterior calcite converted to hydroxyapatite via dissolution-recrystallization;meanwhile the interior calcite-conversion referred to a solid-state topotactic ion exchange reaction.