V. E. Gorbunov

Low-temperature heat capacity and thermodynamic properties of four boron nitride modifications

Abstract A short review of the low-temperature heat capacity studies of four boron nitride (BN) modifications is presented. C p versus ( T ) dependences of high-ordered hexagonal and disordered (turbostratic) modifications were studied by adiabatic calorimetry. The influence of disordering on the heat capacity of boron nitride is shown. The values of thermodynamic properties (heat capacity, entropy, enthalpy, and formation enthalpy) of four BN modifications is reported.

Calorimetric study of alkali metal tetrafluoroborates

Abstract Adiabatic calorimetric investigation of the low-temperature heat capacity of sodium tetrafluoroborate as well as a DSC study of the thermal behavior of potassium tetrafluoroborate and of lithium tetrafluoroborate and its hydrates were carried out. Temperatures and enthalpies of phase transitions at temperature above ambient were determined for potassium tetrafluoroborate, lithium tetrafluoroborate, and lithium tetrafluoroborate mono- and trihydrate. It was demonstrated that lithium tetrafluoroborate has only one phase transition in the solid at 300 K.

Low-temperature heat capacity and thermodynamic functions of AlH3 and AlD3

The thermodynamic properties of AlH3 and AlD3 were evaluated from low-temperature heat capacity measurements. For α-AlH3 , C0p(298.15 K) = 41.14 ± 0.13 J/(mol K), S0(298.15 K) = 30.62 ± 0.14 J/(mol K), H0(298.15 K) – H0(0) = 5527 ± 15 J/mol, and Φ0(298.15 K) = 12.08 ± 0.06 J/(mol K). For α-AlD3 , C0p(298.15 K) = 50.82 ± 0.04 J/(mol K), S0(298.15 K) = 36.74 ± 0.12 J/(mol K), H0(298.15 K) – H0(0) = 6801 ± 10 J/mol, and Φ0(298.15 K) = 13.93 ± 0.04 J/(mol K).

Thermodynamic Properties and Decomposition of Lithium Hexafluoroarsenate, LiAsF6

The heat capacity of lithium hexafluoroarsenate is determined in the temperature range 50–750 K by adiabatic and differential scanning calorimetry techniques. The thermodynamic properties of LiAsF6 under standard conditions are evaluated: Cp0(298.15 K) = 162.5 ± 0.3 J/(K mol), S0(298.15 K) = 173.4 ± 0.4 J/(K mol), Φ0(298.15 K) = 81.69 ± 0.20 J/(K mol), and H0(298.15 K) – H0(0) = 27340 ± 60 J/mol. The Cp(T) curve is found to contain a lambda-type anomaly with a peak at 535.0 ± 0.5 K, which is due to the structural transformation from the low-temperature, rhombohedral phase to the high-temperature, cubic phase. The enthalpy and entropy of this transformation are 5.29 ± 0.27 kJ/mol and 10.30 ± 0.53 J/(K mol), respectively. The thermal decomposition of LiAsF6 is studied. It is found that LiAsF6 decomposes in the range 715–820 K. The heat of decomposition, determined in the range 765–820 K using a sealed crucible and equal to the internal energy change ΔUr(T), is 31.64 ± 0.08 kJ/mol.

Thermodynamic Properties of the Ni0.333Zr0.667 Alloy in Amorphous and Crystalline States

The heat capacity of the Ni0.667Zr0.333 alloy in amorphous and crystalline states is measured by adiabatic calorimetry from 12 to 325 K. The thermal behavior of the amorphous alloy is studied by differential scanning calorimetry between room temperature and 900 K. Amorphous Ni0.667Zr0.333 is found to crystallize in the range 817–874 K, with a heat evolution maximum at 841 K and an enthalpy increment ΔcrH = 3.58 kJ/mol. The heat capacity data are used to evaluate the thermodynamic properties of the Ni0.667Zr0.333 alloy in amorphous and crystalline states in the temperature range 12–325 K.The heat capacity of the Ni0.333Zr0.667 alloy in amorphous and crystalline states is measured by adiabatic calorimetry from 13 to 326 K. The thermal behavior of the amorphous alloy is studied by differential scanning calorimetry between room temperature and 800 K. Amorphous Ni0.333Zr0.667 is found to crystallize in the range 628–686 K, with a heat evolution maximum at 655 K and an enthalpy increment ΔcrH = 2.91 kJ/mol. The heat capacity data are used to evaluate the thermodynamic properties of the Ni0.333Zr0.667 alloy in amorphous and crystalline states in the temperature range 15–320 K.