Preparation, characterization, and thermal stability of lead hydroxyapatite

Lead hydroxyapatites (PbHAp) have been prepared from H3PO4 and Pb(NO3)(2). 5PbO (1), the latter of which was obtained through dehydration of basic lea d 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 uniden tified water-soluble compound (4), decreased with increasing reaction time. The dehydration of 2 and 3, but not of 4, yielded the desired compound wit h expected X-ray diffraction pattern and infrared spectra, When the prepare d 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 dis tance of the Pb-O bond in PbHAp was 2.18 Angstrom, which was shorter than t hat of the Ca-O bond of calcium hydroxyapatite and Sr-O bond of strontium h ydroxyapatite, (C) 1999 Academic Press.