Enthalpy measurements on rare earth hafnates RE2O3·2HfO2 (s) (RE = Sm, Eu, Dy)

Thermal Expansion and Thermodynamic Functions of Europium Hafnate at 298–1300 K

“…One can see that curves 1 and 2 lie very closely to each other, although the Neumann-Kopp heat capacity estimate at 298.15 K (242.8 J/(mol K))) is 4.5 J/(mol K) higher than our experimental value. The heat capacities calculated from enthalpy increments [15] (curve 3) are also close to our values (curve 1). The heat capacities calculated by the equation found in [16] as 8.…”

“…The temperature-dependent heat capacity does not feature anomalies due to structural transformations. Figure 3 compares the Eu 2 Hf 2 O 7 heat capacities in the range 300-1300 K taken from various sources: our measurements (curve 1), calculations from Eu 2 O 3 [22] and HfO 2 [23] heat capacities in terms of the Neumann-Kopp rule (curve 2), results borrowed from [15] (curve 3) and from [16] (curve 4). One can see that curves 1 and 2 lie very closely to each other, although the Neumann-Kopp heat capacity estimate at 298.15 K (242.8 J/(mol K))) is 4.5 J/(mol K) higher than our experimental value.…”

“…Model calculations require reliable data on temperature-dependent thermodynamic functions-heat capacity, entropy, enthalpy increment, and Gibbs free energyover the widest possible range of temperatures. The high-temperature heat capacity of Eu 2 Hf 2 O 7 was mea-sured by differential scanning calorimetry (DSC) in a helium atmosphere in the temperature range 373-1073 K [14], and was calculated from drop calorimetry measurements of the enthalpy increment in the ranges 774-1679 K [15] and 977-1738 K [16]. The DSCderived values [14] seem overestimates, and the values derived from drop calorimetry measurements [15] and [16] are not very consistent with each other, especially at temperatures above 1000 K. Thermal expansion parameters are an important characteristic of hightemperature ceramic materials.…”

“…The high-temperature heat capacity of Eu 2 Hf 2 O 7 was mea-sured by differential scanning calorimetry (DSC) in a helium atmosphere in the temperature range 373-1073 K [14], and was calculated from drop calorimetry measurements of the enthalpy increment in the ranges 774-1679 K [15] and 977-1738 K [16]. The DSCderived values [14] seem overestimates, and the values derived from drop calorimetry measurements [15] and [16] are not very consistent with each other, especially at temperatures above 1000 K. Thermal expansion parameters are an important characteristic of hightemperature ceramic materials. This work comprised DSC measurements of the Eu 2 Hf 2 O 7 molar heat capacity in the range 298-1300 K, X-ray diffraction studies of temperature-dependent unit cell parameters, and assessment of thermal expansivities in the range 298-1300 K. EXPERIMENTAL Synthesis, measurement and data processing procedures are described in detail elsewhere [17].…”

Mass spectrometric study of ceramics in the Sm2O3‐ZrO2‐HfO2 system at high temperatures

“…In the Sm 2 O 3 ‐ZrO 2 system, the thermodynamic properties found previously corresponded mainly to the samarium zirconate compound, and they were reviewed by Wang et al 32 and Fabrichnaya and Seifert 33 . The physicochemical properties of samarium hafnate were also obtained using the drop calorimetric method, 42 laser flash analysis, and dilatometry 14 . The vaporization processes and thermodynamic properties of the Sm 2 O 3 ‐HfO 2 and ZrO 2 ‐HfO 2 systems were examined by the high‐temperature mass spectrometric method 38,43 .…”