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Abstract: Molecular dynamics simulations of monoclinic (P21/b) hydroxy- and chlorapatite were undertaken in the range 498K< T <1298K, and for pressures up to 7.5GPa. The all-atom Born–Huggins–Mayer force field, that had been previously used to successfully describe the room temperature isotherms of both compounds, was also used in this work. The isothermal sets of p–V data generated by simulation were each fitted to the three-parameter form of the isothermal Parsafar and Mason equation of state (EoS) with an accuracy better than 0.07%. Taking the temperature dependence of the coefficients into account, it was found that the MD data are satisfactorily reproduced by the universal EoS. The isothermal compressibility coefficient dependence with pressure can be described by a linear relation. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations of molten hydroxyapatite were performed, for the first time, in the range 2000K< T <3000K and pressures up to 20GPa. The all-atom Born–Huggins–Mayer potential energy function employed had been previously used to study the thermodynamic properties of the solid compound. High-temperature simulation runs were used to generate the p–V m –T surface of the melt, from which properties like the isobaric thermal expansion coefficient, α p and the isothermal compressibility, κ T , could be evaluated. The heat capacity at room pressure, C p , in the range 2000–3000K, was estimated from the plot of the molar enthalpy of the melt as a function of temperature, H m = A 0 + AT + BT 2 + C/T (A 0 =−3.7490×104 kJmol−1, A =3.5842kJmol−1 K−1, B =−5.6989×10−4 kJmol−1 K−2, C =−3.0061×105 kJmol−1 K). C p varies from 1373Jmol−1 K−1 (T =2000K) to 180Jmol−1 K−1 (T =3000K). The intermolecular atom–atom distribution functions, at several temperatures and pressures, were also investigated. A universal EoS proposed by Parsafar et al. was shown to give a good account of the MD data, the precision being better than 0.5%. Likewise, the Parsafar–Mason regularity which assumes a linear dependence of (Z −1)V 2 on ρ 2, has been established for molten hydroxyapatite. [Copyright &y& Elsevier]

Abstract: The standard (p ∘ =0.1MPa) molar enthalpies of formation in the crystalline state of hydroxyapatite, chlorapatite and a preliminary value for bromapatite, at T =298.15K, were determined by reaction-solution calorimetry as: . A critical assessment of these results and of previously published data is made. Finally, the standard molar enthalpy of formation of iodapatite is estimated as , from a linear correlation of (X=OH, F, Cl, Br) against the corresponding . [Copyright &y& Elsevier]