Structural analysis and thermochemistry of “A” type phosphostrontium carbonate hydroxyapatites

“A” type phosphostrontium carbonate hydroxyapatites, having the general formula Sr 10 (PO 4 ) 6 (OH) (2−2 x ) (CO 3 ) x with 0 ≤ x ≤ 1, were synthesised by solid gas reaction at high temperature. The samples were characterised by X-ray diffraction and infrared spectroscopy. Analysis of carbonate was achieved by coulometry and Rietveld refinement of the structure. Using an isoperibol calorimeter, the heat of solution of these products was measured at 298 K in 9 wt% nitric acid solution. Thermochemical cycle was proposed and complementary experiences were performed to reach the standard enthalpies of formation of these compounds. The results showed a decrease of the enthalpy of formation with the amount of carbonate introduced in the lattice, suggesting an increase of stability due to this kind of substitution.