TY - JOUR
T1 - Energetics of lanthanide-doped calcium phosphate apatite
AU - Hosseini, S. Mahboobeh
AU - Drouet, Christophe
AU - Al-Kattan, Ahmed
AU - Navrotsky, Alexandra
N1 - Funding Information:
This work was supported by the International Center of Materials Research (ICMR), the National Polytechnical Institute of Toulouse (INPT) and the France-Berkeley Fund (2008 call).
Publisher Copyright:
© 2014 by Walter de Gruyter Berlin/Boston.
PY - 2014/11/1
Y1 - 2014/11/1
N2 - Lanthanides Ln (rare earths) are critical elements found in natural minerals such as calcium phosphate apatites, in sedimentary and igneous settings as well as in skeletal diagenesis. From a medical point of view, nanoparticles of lanthanide-doped apatites can be produced for conferring luminescence properties of interest in cancer cells detection. However, the impact of the substitution of Ln for Ca on the stability and solubility of related apatite phases is still essentially unknown. To investigate the thermochemical effects of such lanthanide substitution for calcium in apatite, we prepared and analyzed four series of apatites with up to 10% lanthanide substitution for calcium. After thorough physicochemical characterization via complementary techniques (XRD, FTIR, TG/DSC, and IPCAES), high-temperature oxide melt solution calorimetry in molten sodium molybdate at 973 K was performed to determine their enthalpies of formation from constituent oxides and from the elements, at 298 K. Our results indicate that although enthalpies of formation are strongly exothermic in all cases, Ln-doping has a destabilizing effect, which increases with dopant concentration and with the size of the incorporated Ln3+ ion. After estimating standard entropies, Gibbs free energies of formation and equilibrium constants for Ca2+/Ln3+ exchange reactions in apatite were then evaluated, for the first time allowing access to quantitative thermodynamic data that may be used in various fields for stability calculations or partitioning estimates between fluids and solids.
AB - Lanthanides Ln (rare earths) are critical elements found in natural minerals such as calcium phosphate apatites, in sedimentary and igneous settings as well as in skeletal diagenesis. From a medical point of view, nanoparticles of lanthanide-doped apatites can be produced for conferring luminescence properties of interest in cancer cells detection. However, the impact of the substitution of Ln for Ca on the stability and solubility of related apatite phases is still essentially unknown. To investigate the thermochemical effects of such lanthanide substitution for calcium in apatite, we prepared and analyzed four series of apatites with up to 10% lanthanide substitution for calcium. After thorough physicochemical characterization via complementary techniques (XRD, FTIR, TG/DSC, and IPCAES), high-temperature oxide melt solution calorimetry in molten sodium molybdate at 973 K was performed to determine their enthalpies of formation from constituent oxides and from the elements, at 298 K. Our results indicate that although enthalpies of formation are strongly exothermic in all cases, Ln-doping has a destabilizing effect, which increases with dopant concentration and with the size of the incorporated Ln3+ ion. After estimating standard entropies, Gibbs free energies of formation and equilibrium constants for Ca2+/Ln3+ exchange reactions in apatite were then evaluated, for the first time allowing access to quantitative thermodynamic data that may be used in various fields for stability calculations or partitioning estimates between fluids and solids.
KW - Calcium phosphate hydroxyapatite
KW - calorimetry
KW - enthalpy of formation
KW - lanthanide substitution
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U2 - 10.2138/am-2014-4930
DO - 10.2138/am-2014-4930
M3 - Article
AN - SCOPUS:84910154365
SN - 0003-004X
VL - 99
SP - 2320
EP - 2327
JO - American Mineralogist
JF - American Mineralogist
IS - 11-12
ER -