Abstract
Synthetic carbonate lead hydroxyapatite Pb5(PO4,CO3)3(OH,CO3) was precipitated from aqueous solution and characterized. The maximum content of CO32− ion in lead apatites does not exceed 2.25 wt%. For precipitation from aqueous solutions this is even lower and controlled by the solubility of cerussite PbCO3. Carbonate substitution occurs simultaneously in two structural positions: at OH− sites (A-type substitution) and at PO43− sites (B-type substitution). This is the most pronounced in FTIR (Fourier Transform Infrared Spectroscopy) spectra at 865 cm−1 and within the range of 1300–1500 cm−1. The substitution results in slight increase of the unit cell parameter a from 9.874 to 9.904 A. The presence of CO32− in two structural positions results in two stages of the release of CO2 upon heating: at 300–350 °C and at 400 °C. The presence of carbonates has little effect on thermal decomposition of lead hydroxyapatite which starts at about 450 °C resulting in the formation of lead pyrophosphate.
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