科研之友
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摘要
Dissolution of the synthetic hydroxylapatite (HAP) and fluorapatite (FAP) was studied at 25 degrees C at different pH in a series of batch experiments. The XRD, FT-IR and FE-SEM analyses indicated that the HAP and FAP were found to have no obvious variation after dissolution except that the existence of OH groups in FT-IR spectra for FAP after 7200h dissolution at constant pH 2 was observed. During the HAP and FAP dissolution at constant pH 2 and initial pH 2, the release of calcium and phosphate increased and reached a steady state after 1000h. For the dissolution at initial pH 5.6 and 9, the aqueous pH, calcium and phosphate concentrations increased rapidly and reached the peak values after 12-24h and then decreased gradually with time until a steady state was attained. The aqueous calcium and phosphate concentrations during the FAP dissolution were significantly lower than those during the HAP dissolution. The mean logK(sp) values were calculated by using PHREEQC for HAP of -57.72 (-57.39 similar to -58.05) and for FAP of -59.08 (-58.65 similar to -59.75) at 25 degrees C at initial pH 2, the free energies of formation Delta G(f)(o)[HAP] and Delta G(f)(o)[FAP] were calculated to be -6310.98 and -6440.64 kJ/mol respectively.
