Preparation, Characterization, and Thermal Stability of Lead Hydroxyapatite

Lead hydroxyapatites (PbHAp) have been prepared from H3PO4and Pb(NO3)2·5PbO (1), the latter of which was obtained through dehydration of basic lead nitrates such as 2Pb(NO3) 2·5Pb(OH)2(2) and Pb(NO3)2·5Pb(OH)2(3). The amount of 2 with respect to 3, as well as the quantity of an unidentified water-soluble compound (4), decreased with increasing reaction time. The dehydration of 2 and 3, but not of 4, yielded the desired compound with expected X-ray diffraction pattern and infrared spectra. When the prepared PbHAp was heated at 773, 973, and 1173 K for 3 h, the XRD patterns showed the apatite structure, respectively, but PbHAp heated at 1173 K was partly converted to an amorphous compound. At 1473 K, PbHAp completely melted. X-ray absorption fine structure analyses showed that the nearest-neighbor distance of the Pb-O bond in PbHAp was 2.18 ?, which was shorter than that of the Ca-O bond of calcium hydroxyapatite and Sr-O bond of strontium hydroxyapatite.