PREPARATION AND CHARACTERIZATION OF SPHERICAL CALCIUM HYDROXYAPATITE

The preparation of spherical calcium phosphate particles by aging a solution containing CaSO4 and NaH2PO4 at 80 and 100 degrees C in the presence of urea (1 mol/dm(3)) and a surfactant [cetyltrimethylammonium chloride; CTAC] (1.0 x 10(-2) mol/dm(3)) has been investigated, and their properties were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning and transmission electron microscopy (SEM and TEM), N-2 and H2O adsorption measurements, and thermogravimetric-differential thermal analyses (TG-DTA). The size and shape of the particles produced strongly depended on the concentration of the reactants and the aging temperature. Spherical calcium hydroxyapatite particles were precipitated only within a narrow concentration domain of reactants after aging at 100 degrees C for 3 h. The spherical calcium hydroxyapatite particles produced at [CaSO4] = 2.0 x 10(-3) mol/dm(3) and [NaH2PO4] = 7.9 x 10(-4) mol/dm(3) were agglomerates of small platelet particles and were B-type carbonate hydroxyapatite in which 4.8 wt % of CO32- ions are substituted for PO43- ions. The results of chemical analysis and TG identified the formula of the particles as Ca8.5Na1.5(PO4)(5.4)(CO3)(0.8)(OH)(0.7).1.2H(2)O. The texture and crystallinity of the spherical calcium hydroxyapatite particles were sustained up to 1000 degrees C, and the particles showed the selective adsorption of H2O molecules. This selective adsorption was more pronounced after calcining the samples in air.