Search

The temperature dependence of the heat capacity of Tm2Ti2O7 and Lu2Ti2O7 compounds over the range of 4.5–320 K has been researched by adiabatic calorimetry. Based on the experimental data, the basic thermodynamic functions of the compounds over the range of 5–320 K have been determined. Tm2Ti2O7 sample has revealed an additional component in the heat capacity associated with the presence of the Schottky anomaly. The temperature dependence behavior of the Debye characteristic temperature of Lu2Ti2O7 sample indicates the absence of anomalies in the heat capacity. Standard thermodynamic functions at 298.15 K are: for Tm2Ti2O7 – Cp,298.15 = 221.0 ± 1.2 J·mol−1·K−1, S298.15 = 261.3 ± 2.4 J·mol−1·K−1, ΔH0298.15 = 39.45 ± 0.29 kJ·mol−1; for Lu2Ti2O7 – Cp,298.15 = 206.9 ± 1.1 J·mol−1·K−1, S298.15 = 229.8 ± 2.2 J·mol−1·K−1, ΔH0298.15 = 35.70 ± 0.26 kJ·mol−1.

The heat capacity of natural chalcanthite (copper sulfate pentahydrate, CuSO4·5H2O) from the deposit Kosmurun has been measured by the method of low-temperature adiabatic calorimetry over the temperature range of (4.3–320) K. The identity of the mineral was proved by methods of XRD, EMPA, IR and Raman spectroscopy. The thermodynamic functions have been calculated based on the experimental data on the heat capacity. The lattice component of heat capacity below 20 K was extracted. The standard values of the heat capacity and entropy for natural chalcanthite are as follows: C°p,m = 288.0 ± 0.4 J·mol−1 K−1, S°m = 295.2 ± 0.8 J mol−1 K−1.

The temperature dependence of the heat capacity of pyrochlore-like compounds CaLa2MoO7 and MgLa2MoO7 has been investigated over the range of 4.4–320 K by adiabatic calorimetry. The main thermodynamic functions and fractal properties of the compounds over the range of 5–320 K have been determined based on the experimental data. We have revealed the heat capacity anomaly in the sample CaLa2MoO7 in the area below 10 K. Standard thermodynamic functions at T = 298.15 K are: for CaLa2MoO7 C p,m(298.15) = 222.1 ± 0.4 J mol−1K−1, S m(298.15) = 246.0 ± 0.8 J mol−1K−1, H m(298.15)−H m(0) = 39.20 ± 0.10 kJ mol−1; for MgLa2MoO7 C p,m(298.15) = 216.6 ± 0.3 J mol−1K−1, S m(298.15) = 231.1 ± 0.6 J mol−1K−1, H m(298.15) − H m(0) = 37.09 ± 0.08 kJ mol−1.

The investigation of a magnetic component of the heat capacity of natural samples of copper sulfates antlerite Cu3SO4(OH)4 in the temperature range below 40 K and brochantite Cu4SO4(OH)6 below 55 K has been carried out. A regular component of the heat capacity has been calculated from experimental data of adiabatic calorimetry. In the low-temperature area of (0 to 55) K two peaks of magnetic heat capacity for brochantite have been registered. The contributions of anomalous component ΔStr into entropy of the minerals are (11 ± 3) J·mol–1·K–1 for antlerite and (5.3 ± 1.5) J·mol–1·K–1 for brochantite.

The heat capacity of natural strontium sulfate – mineral celestine – has been measured over the range of 5–320 K by the method of adiabatic calorimetry and its thermodynamic functions have been determined. The methods of X-ray phase analysis, Raman spectroscopy and electron probe microanalysis have confirmed the adequacy of the sample to mineral celestine. The standard values of thermodynamic functions were: C°p(298.15) = 100.30 ± 0.11 J mol−1 K−1, S°298.15 = 123.44 ± 0.28 J mol−1 K−1 and ΔH°298.15 = 18, 406 ± 33 J mol−1. The heat capacity and thermodynamic functions of celestine have also been calculated by means of methods of semi-empirical quantum-chemical calculation and the theory of crystal lattice dynamics.

The investigation of the heat capacity of a natural specimen of copper phosphate—pseudo-malachite Cu5(PO4)2(OH)4 in the temperature range between 4.2 K and 320 K has been carried out by the method of low-temperature adiabatic calorimetry. Tabulated values of the heat capacity and thermodynamic functions of the mineral including the changes of entropy and enthalpy and the Gibbs function of free energy have been calculated. The standard values of thermodynamic functions of pseudo-malachite at T = 298.15 K are C p , m ° = ( 385.43 ± 0.41 ) J mole − 1 K − 1 , Δ 0 T S m ° = ( 412.16 ± 0.61 ) J mole − 1 K − 1 , Δ 0 T H m ° = ( 63681.5 ± 57.0 ) J mole − 1 , F m ° = ( 198.57 ± 0.47 ) J mole − 1 K − 1 . In the low-temperature area 0

The heat capacity of natural lead molybdate (wulfenite, PbMoO4) has been measured by the method of vacuum adiabatic calorimetry over the temperature range of (4.3 to 80) K, and its thermodynamic functions in the range from (0 to 320) K have been calculated. The obtained standard values are as follows: Cpo(298.15) = (119.4 ± 0.13) J·mol−1·K−1, S°(298.15) = (161.5 ± 0.3) J·mol−1·K−1, and ΔH°(298.15) = (23018 ± 23) J·mol−1. The experimental data have been compared with the calculated values of the heat capacity obtained previously by different methods. The greatest correspondence of the thermodynamic functions has been obtained when employing the method of interatomic potentials using the computer program LADY.

The heat capacity of natural mineral, pyromorphite Pb5(PO4)3Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy, and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The standard thermodynamic functions of the mineral are Cp298.15o = 414.98 ± 0.44 J/(mol K), S298.15o = 585.31 ± 0.99 J/(mol K), H298.15o − H0o = 80.90 ± 0.08 kJ/mol, and Φ298.15o = 313.97 ± 0.84 J/(mol K).

Measurements of the heat capacity of standard specimens of copper, benzoic acid, and heptane and their thermodynamic functions of molar heat capacity, change in entropy, and enthalpy have been carried out at a low-temperature thermal-physical installation in the temperature range (4.2 up to 320) K using the method of adiabatic calorimetry. The obtained data are in good agreement with the recommended values. The relative uncertainty limits of the calorimetric unit: ± 1.43 % at T = 5 K, ± 0.75 % at T = 10 K, ± 0.23 % at T = 40 K, and less than ± 0.11 % for the temperature range (90 up to 298.15) K have been determined according to the experimental data of measurements of the certified measure of oxygen-free electronic (OFE) grade copper heat capacity. According to the heptane heat capacity measurement, the values of its enthalpy and entropy of fusion at Tfus = 182.54 K, ΔHfus = (14047 ± 19.6) J·mol−1 and ΔSfus = (76.96 ± 0.11) J·mol−1·K−1, have been determined. These values are also in a satisfactory agreem...

The temperature dependence of heat capacity of a natural zinc silicate, hemimorphite Zn4Si2O7(OH)2·H2O, over the temperature range 5–320 K has been investigated by the method of low-temperature adiabatic calorimetry. On the basis of the experimental data on heat capacity over the whole temperature interval, its thermodynamic functions C p (T), S(T) and H(T) − H(0) have been calculated. The existence of a phase transition in the area of 90–105 K determined on the basis of vibrational spectra has been confirmed, and changes of entropy ΔS tr. and enthalpy ΔH tr. of the phase transition have been calculated. Hemimorphite heat capacity has also been determined by the calculation methods according to the valence force field model in LADY program. The values of force constants of valence bonds and angles have been calculated by semi-empirical method PM5. The calculated IR and Raman spectra concordant with the experimental spectra have been obtained. The heat capacity values calculated according to the found vibrational states satisfactorily agree with those experimentally obtained with an accuracy of ±1.7% in the area of 120–200 K, and not more than ±0.8% for the interval of 200–300 K. This fact testifies that the calculation of thermodynamic characteristics is correct.