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« A » type carbonate phosphocalcium hydroxyapatites having the general formula Ca 10 (PO 4 ) 6 (OH) (2-2x) (CO 3 ) x with 0 ⩽ x ⩽ 1, were prepared by solid gas reaction in the temperature range of 700–1000 °C. The obtained materials were characterized by X-ray diffraction and infrared spectroscopy. The carbonate content has been determined by C–H–N analysis. The heat of solution of these products was measured at T = 298 K in 9 wt% nitric acid solution using an isoperibol calorimeter. A thermochemical cycle was proposed and complementary experiences were performed in order to access to the standard enthalpies of formation of these phosphates. The results were compared to those previously obtained on apatites containing strontium and barium and show a decrease with the carbonate amount introduced in the lattice. This quantity becomes more negative as the ratio of substitution increases. Estimation of the entropy of formation allowed the determination of standard Gibbs free energy of formation of these compounds. The study showed that the substitution of hydroxyl by carbonate ions contributes to the stabilisation of the apatite structure. [ABSTRACT FROM AUTHOR]

'A' type phosphostrontium carbonate hydroxyapatites, having the general formula Sr(PO)(OH)(CO) 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. [ABSTRACT FROM AUTHOR]

A brown and transparent ionic liquid (IL), [C4mim][FeCl4], was prepared by mixing anhydrous FeCl3 with 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), with molar ratio 1/1 under stirring in a glove box filled with dry argon. The molar enthalpies of solution, Δs H m, of [C4mim][FeCl4], in water with various molalities were determined by a solution-reaction isoperibol calorimeter at 298.15 K. Considering the hydrolyzation of anion [FeCl4]− in dissolution process of the IL, a new method of determining the standard molar enthalpy of solution, Δs H , was put forward on the bases of Pitzer solution theory of mixed electrolytes. The values of Δs H and the sum of Pitzer parameters: $$ (4\beta _{Fe,Cl}^{(0)L} + 4\beta _{C_4 mim,Cl}^{(0)L} + \Phi _{Fe,C_4 mim}^L ) $$ and $$ (\beta _{Fe,Cl}^{(1)L} + \beta _{C_4 mim,Cl}^{(1)L} ) $$ were obtained, respectively. In terms of thermodynamic cycle and the lattice energy of IL calculated by Glasser’s lattice energy theory of ILs, the dissociation enthalpy of anion [FeCl4]−, Δ H dis≈5650 kJ mol−1, for the reaction: [FeCl4]−( g)→Fe3+( g)+4Cl−( g), was estimated. It is shown that large hydration enthalpies of ions have been compensated by large the dissociation enthalpy of [FeCl4]− anion, Δd H m, in dissolution process of the IL. [ABSTRACT FROM AUTHOR]

Abstract: The molar solution enthalpies of ionic liquids (IL) EMIBF4 (1-methyl-3-ethylimidazolium tetrafluoroborate), EMIC (1-methyl-3-ethylimidazo-lium chloride) and ionic solid NaBF4 at various molalities were determined by the solution-reaction isoperibol calorimeter in water at 298.15K. In terms of a Debye–Hückel limiting term, the molar solution enthalpies of EMIBF4, EMIC and NaBF4 at infinite dilution, , were obtained. Then the values of apparent relative molar enthalpy were calculated. Hydration heat of both cation EMI+ and anion BF4 − was discussed. In terms of values of , the reaction heat of NaBF4 +EMIC→EMIBF4 +NaCl was estimated. [Copyright &y& Elsevier]

Abstract: The ionic liquid BMIInCl4 was prepared by mixing 1-methyl-3-butylimidazolium chloride (BMIC) with InCl3. The molar solution enthalpies of BMIC and BMIInCl4 at various molalities were determined by the solution reaction isoperibol calorimeter in water at 298.15K. In terms of Pitzer''s electrolyte solution theory, the molar solution enthalpy of BMIC and BMIInCl4 at infinite dilution, and the parameters: were obtained. Then the values of apparent relative molar enthalpy ϕ L and relative partial molar enthalpies of solute (BMIC and BMIInCl4), L 2, were calculated, respectively. In terms of values of of BMIC, BMIInCl4 and InCl3, the enthalpy change for the reaction: BMIC+InCl3 →BMIInCl4 was obtained. [Copyright &y& Elsevier]

Abstract: The molar enthalpies of solution of ionic liquid 1-methyl-3-butylimidazolium tetrafluoroborate (BMIBF4) in water at various molalities were determined by calorimetry at 298.15K. Pitzer''s electrolyte solution theory was used to obtain the molar solution enthalpy of BMIBF4 at infinite dilution, . [Copyright &y& Elsevier]

Enthalpy of solution of calcium hydroxyapatite Ca10(PO4)6(OH)2 (CaHap) in hydrochloric and perchloric acid solutions is measured by an isoperibol calorimeter and a C80 microcalorimeter. The former device is adapted to reactions occurring in concentrated acid solutions, whereas the microcalorimeter is suitable for slow processes happening in diluted acid solutions. Some solution mechanisms are suggested for different pH ranges. They are confirmed by complementary solution in the same solvent of the entities produced by the reaction between CaHap and the acid. These entities are CaCl2; Ca(ClO4)2· nH2O; Ca(H2PO4)2 and H3PO4. Extrapolation of solution enthalpies to pH=7 leads to the solution enthalpy of (CaHap) in pure water, which is -406.2 kJ mol-1 from HCl and -437.3 kJ mol-1 from HClO4. [ABSTRACT FROM AUTHOR]