Sodium and carbonate distribution in substituted calcium hydroxyapatite

Hydroxyapatites containing sodium and carbonate are prepared according to a double decomposition method. Two samples have been investigated by IR absorption spectroscopy and X-ray powder pattern fitting methods. Results confirm that both compounds pertain to the apatite family crystallising in a hexagonal system, space group P6(3)/m. The cell parameters of the lower carbonate content apatite are a = 9.3892(4) and c = 6.9019(3) Angstrom, while those of the higher one are a = 9.3249(1) and c = 6.9213(1) Angstrom. Occupancy factors show that sodium is localised mainly in a 6h cationic site. Furthermore, carbonate ions occupy phosphate sites leading to a B-type carbonate apatite. These simultaneous substitutions affect the OH- position in the channel, as well as the metal-oxygen interatomic distances. The substitution mechanism can be described using two of the six known elementary mechanisms. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.