Excess heat capacity and entropy of mixing along the hydroxyapatite-chlorapatite and hydroxyapatite-fluorapatite binaries

The heat capacity, Cp, of synthetic hydroxyapatite [Ca5(PO4)3OH–OH-Ap], as well as of ten compositions along the OH-Ap-chlorapatite (Cl-Ap) join and 12 compositions along the OH-Ap-fluorapatite (F-Ap) join have been measured using relaxation calorimetry (heat capacity option of the Physical Properties Measurement System—PPMS) and differential scanning calorimetry (DSC) in the temperature range of 5–764 K. Apatites along the Cl-OH and F-OH joins were synthesized at 1100 °C and 300 MPa in an internally heated gas pressure vessel via an exchange process between synthetic fluorapatite or chlorapatite crystals (200–500 μm size) and a series of Ca(OH)2-H2O solutions with specific compositions and amounts relative to the starting apatite. The standard third-law entropy of OH-Ap, derived from the low-temperature heat capacity measurements, is S° = 386.3 ± 2.5 J mol−1 K−1, which is ~ 1% lower than that resulting from low-temperature adiabatic calorimetry data on OH-Ap from the 1950’s. The heat capacity of OH-Ap above 298.15 K shows a hump-shaped anomaly centred around 442 K. Based on published structural and calorimetric work, this feature is interpreted to result from a monoclinic to hexagonal phase transition. Super ambient Cp up to this transition can be represented by the polynomial: $$C_{p}^{{\text{OH - Ap}}} {}_{{298K - 442K}}\left( {{\text{J mol}}^{ - 1} {\text{K}}^{- 1}} \right) = {1013.7-13735.5T^{{ - 0.5}}} + 2.616718\,10^{7} T^{{ - 2}} - 3.551381\,10^{9} T^{{ - 3}} .$$ C p OH - Ap 298 K - 442 K J mol - 1 K - 1 = 1013.7 - 13735.5 T - 0.5 + 2.616718 10 7 T - 2 - 3.551381 10 9 T - 3 . . The DSC data above this transition were combined with heat capacities computed using density functional theory and can be given by the Cp polynomial: $$C_{p}^{{\text{OH - Ap}}} {}_{{ >\,442K}}\left( {{\text{J mol}}^{ - 1} {\text{K}}^{- 1}} \right) = {877.2-11393.7 T^{ - 0.5}} + {5.452030\,10^{7}} \,T^{- {2}} - {1.394125\,10^{10}} \,T^{- {3}}$$ C p OH - Ap > 442 K J mol - 1 K - 1 = 877.2 - 11393.7 T - 0.5 + 5.452030 10 7 T - 2 - 1.394125 10 10 T - 3 . Positive excess heat capacities of mixing, ∆Cpex, in the order of 1–2 J mol−1 K−1, occur in both solid solutions at around 70 K. They are significant at these conditions exceeding the 2σ-uncertainty of the data. This positive ∆Cpex is compensated by a negative ∆Cpex of the same order at around 250 K in both binaries. At higher temperatures (up to 1200 K), ∆Cpex is zero within error for all solid solution members. As a consequence, the calorimetric entropies, Scal, show no deviation from ideal mixing behaviour within a 2σ-uncertainty for both joins. Excess entropies of mixing, ∆Sex, are thus zero for the OH-Ap–F-Ap, as well as for the OH-Ap–Cl-Ap join. The Cp–T behaviour of the OH-Ap endmember is discussed in relation to that of the F- and Cl-endmembers.

The dependence of the boson peak on the thickness of Cu50Zr50 film metallic glasses

In this study, intensive calculations were performed to investigate the behavior of the low-temperature excess heat capacity of Cu50Zr50 ultrathin film metallic glasses.

Deconvoluted plasma DSC curves on patients with psoriasis

Psoriasis is an inflammatory disease that changes plasma composition, and it is detectable by differential scanning calorimetry (DSC). Besides the general change in plasma, the aim of the study was to demonstrate which components are changing and how the anti-psoriatic drug treatment affects back all this. Retrospectively, blood plasma DSC data were analyzed from patients, who have different severities of symptoms and who received steroids (n = 10), or retinoids (n = 10), or biological drug treatment (n = 10). Complex curves were deconvoluted in several individual transitions (Tm1–Tm5), modeling each individual transition. In the examined psoriasis stages, the thermodynamic parameters excess heat capacity and enthalpy of the transitions in proportion corresponded to the targeted treatment and the degree of disease severity, as well as the numbers of transitions were determined from the calorimetric profiles. In conclusion, deconvoluted plasma DSC profiles showed similarities but exhibited marked differences in the thermal denaturation on different treated psoriasis stages. This examination has shown that drug therapy affects the composition of plasma proteins, which should be always considered for the evaluation of DSC results in similar studies.

Recent studies on thermophysical properties of metallic alloys with PROSPECT: Excess properties to construct a solution model

We have developed the system PROSPECT for measuring thermophysical properties at high temperature. Precise thermophysical measurements provide accurate excess functions, which represent non-ideality of solutions. We use excess functions to discuss solution models on the basis of electronic structure and thermodynamics. Pd-Fe systems show positive excess volume VE with negative excess Gibbs energy GE. The phase diagrams of these systems have common features with those of other Pd-X and Pt-X systems (where X is Fe, Ni, Co, or Cu), which means they all have order-disorder transitions. The correlation between VE and GE is discussed in terms of the electronic structure of the alloys, and an energy diagram is proposed to understand this correlation. The excess heat capacity CpE of Fe-Ni melts is positive over a whole composition range and a wide temperature range. We estimate the temperature dependences of the excess enthalpy HE and excess entropy SE of Fe-Ni melts from CpE. The Lupis-Elliott rule is satisfied for HE and SE with positive CpE.

Calculation of the thermodynamic quantities of perovskite metal organics DMAKCr and perovskite HyFe close to the weakly first-order relaxor-like structural transformation using the mean field theory

Weakly first-order or nearly second-order phase transitions occurring in metal–organic frameworks (MOFs), particularly in DMAKCr and perovskite HyFe, are studied under the mean field model by using the observed data from the literature. In this work, mainly thermal and magnetic properties among various physical properties which have been reported in the literature for those MOFs are studied by the mean field theory. By expanding the free energy in terms of the magnetization (order parameter), the excess heat capacity ([Formula: see text]C[Formula: see text]) and entropy ([Formula: see text]S), latent heat (L), magnetization (M) and the inverse susceptibility ([Formula: see text]) are calculated as a function of temperature close to the weakly first-order phase transition within the Landau phenomenological model which is fitted to the experimental data from the literature for C[Formula: see text] (DMAKCr and perovskite HyFe) and for magnetization M (HyFe). Our predictions of the excess heat capacity ([Formula: see text]C[Formula: see text]) and entropy ([Formula: see text]S) agree below T[Formula: see text] with the observed data within the temperature intervals studied for DMAKCr and perovskite HyFe. From our predictions, we find that magnetization decreases continuously whereas the inverse susceptibility decreases linearly with increasing temperature toward the transition temperature in those MOFs as expected for a weakly first-order transition from the mean field model.

Теплофизические и диэлектрические свойства Bi-=SUB=-1-x-=/SUB=-Er-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

The heat capacity and the permittivity of multiferroics Bi_1 – x Er_ x FeO_3 ( x = 0, 0.10, and 0.15) have been studied in the temperature range 130–800 K. It is found that an insignificant substitution of erbium for bismuth significantly increases the heat capacity in a wide temperature range T > 300 K. The temperature dependence of the excess heat capacity is shown to be due to manifestation of the three-level states. An additional anomaly characteristic of a phase transition has been revealed in the temperature dependences of the heat capacity and the permittivity for the compositions with x = 0.15 at T = 587 K. The results of studies are discussed in combination of the data of structural studies.