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  • Author or Editor: Mohamed Jemal x
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Abstract

Phosphobaryum carbonate hydroxyapatites Ba10(PO4)6(OH)(2−2x)(CO3)x with 0 ≤ x ≤ 1, were synthesized in this study by solid gas reaction at a high temperature. Carbonate content was determined by thermogravimetric analysis and X-ray diffraction. The heat of the solution in a 3 wt% nitric acid solution was measured at 298 K using an isoperibol calorimeter. The combination of the enthalpies of solution with the enthalpies of formation of the reactants allowed us to determine the standard enthalpies of formation of the studied apatites. The result showed a decrease in formation enthalpy with the carbonate amount introduced in the lattice, suggesting an increase in stability of these compounds as the ratio of the substitution increases.

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Abstract

A series of “B” type carbonate fluorapatites (B–CO3–Fap) have been synthesized and characterized by X-ray diffraction, infrared spectroscopy, and chemical analysis. The thermochemical study of phosphoric acid attack of the products was performed by a 19% w/w P2O5 solution on raw and deconvoluted curves. The calculated thermogenesis curves show one, two, or four peaks, depending on the mass of dissolved solid and the carbonate content in B–CO3–Fap. The plot of the quantity of heat measured by integrating the raw signal as a function of the dissolved mass in the same volume solution presents three straight segments for low-carbonated and two segments for moderately carbonated ones. From the slopes of line segments, it was possible to determine the enthalpies of dissolution of “B” type carbonate fluorapatites and to deduce that of precipitation of CaF2 and Ca(H2PO4)2·H2O, which have been compared to directly measured or literature data.

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Abstract

“A” type phosphostrontium carbonate hydroxyapatites, having the general formula Sr10(PO4)6(OH)(2−2x)(CO3)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.

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