Conversion of nacre powders to apatite in phosphate buffer solutions at low temperatures

Apatite (HAP) powders with poor crystallinity were obtained from nacre powders by treatment with phosphate buffer solutions of pH's 6.0-8.0, kept at 37 °C for 1-12 days. The effects of pH values, particle size, and reaction time on the conversion of nacre powders were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Nacre powders are converted to HAP both by treatment with the basic or neutral phosphate solutions, and by treatment with the acidic phosphate solutions without regulating pH values during the reaction using dicalcium phosphate dehydrate (DCPD) or octacalcium phosphate (OCP) as active intermediate phases. Decreasing particle size and prolonging reaction time can improve the conversion percentages of nacre powders to HAP. In addition, the dissolution-recrystallisation mechanism of HAP formation was discussed further in the present work.