R. Babu

Thermodynamic functions of barium and strontium zirconates from calorimetric measurements

Abstract Enthalpy increment measurements have been carried out on BaZrO 3 and SrZrO 3 in the temperature range 1030–1700 K using a high-temperature differential calorimeter. From the measured enthalpy increment values, other thermodynamic functions, such as heat capacity, entropy and free energy functions, of these compounds have been calculated. The free energies of formation of BaZrO 3 and the equilibrium barium partial pressures for the formation reactions have been computed and compared with literature data. The equilibrium strontium pressures for the formation reactions of SrZrO 3 have also been computed.

Thermodynamic properties of ternary oxides of fission products from calorimetric measurements

Abstract The alkaline earth elements barium and strontium, which are produced in a mixed oxide fuel during irradiation, can combine with other major fission products such as zirconium, molybdenum and cerium under favourable conditions of temperature and oxygen potential. As a part of our programme to investigate the thermodynamic properties of these fission product compounds, we have already reported thermodynamic data on BaZrO 3 , SrZrO 3 , BaMoO 4 and BaCeO 3 . To complete the series, enthalpy increment measurements were carried out on SrCeO 3 , SrMoO 4 , CaZrO 3 and CaMoO 4 using a high temperature microcalorimeter. These data along with the derived thermodynamic functions are reported in this paper. The stabilities of the whole set of fission product compounds, under conditions of oxygen potentials and temperature prevalent in the mixed oxide fuel, are examined in the light of all the data mentioned above.

Enthalpy of formation of UZr2 by calorimetry

Abstract The enthalpy of formation of the intermetallic compound UZr2 at 298 K was determined by high temperature solution calorimetry in which liquid aluminium was used as the solvent. The thermal effects of dissolution of U, Zr and UZr2 in liquid aluminium were measured in separate experiments by dropping the samples held at ambient temperature into liquid aluminium maintained at 991 K in the calorimeter. The thermal effects of dissolution of the samples in liquid aluminium at infinite dilution were derived from these measurements, and based on these data the enthalpy of formation of UZr2 at 298 K was computed as −4.0 kJ mol−1. The partial enthalpy of solution of zirconium in liquid aluminium at infinite dilution was also computed and the value thus obtained was −(257.7 ± 9.5) kJ mol−1.

THERMODYNAMIC PROPERTIES OF COMPOUNDS OF ALKALINE EARTH ELEMENTS WITH OTHER FISSION PRODUCTS

Abstract The alkaline earth fission products barium and strontium can combine with other major fission product elements such as Mo, Ce and Zr in a mixed oxide fuel pin of a fast breeder reactor to form compounds such as molybdates. cerates and zirconates. In order to understand the condition of their formation in the fuel pin basic thermodynamic data on these compounds applicable to the relevant temperature range are required. In this work enthalpy increments of BaMoO 4 , BaCeO 3 and (Ba, Sr)ZrO 3 were determined relative to room temperature using a high temperature differential calorimeter. The experimentally measured enthalpy data covered the temperature range of 985–1750 K. From these enthalpy values other thermodynamic functions such as heat capacities, entropies and free energy functions were generated using C p 298 0 and S 298 0 values of the compounds available in the literature. The free energies of formation of these compounds and the equilibrium barium partial pressures for the formation reactions have been computed in the temperature range of 500–2000 K and in the oxygen potential range of −376.56 kJ mol −1 to −502.08 kJ mol −1 .

Enthalpies of formation of UAl4 and UAl3 by calorimetry

Abstract Enthalpies of formation of the intermetallic compounds UAl 4 and UAl 3 at 298.15 K were determined by high temperature solution calorimetry in which liquid aluminium was used as the solvent. The thermal effects of dissolution of UAl 4 , UAl 3 and U in liquid aluminium were measured in separate experiments by dropping the samples held at the ambient temperature into liquid aluminium maintained at 980 K in the calorimeter. The thermal effects of dissolution of these samples at infinite dilution in liquid aluminium were derived from these measurements and based on this data the enthalpies of formation of UAl 4 and UAl 3 at 298.15 K were computed. The values obtained are ΔH 0 f ,298.15 ( UAl 4 ) = − 126.5 ± 13.3 kJ mol −1 and ΔH 0 f ,298.15 ( UAl 3 ) = − 118.1 ± 8.2 kJ mol −1 . The integral enthalpies of formation of U-Al alloys at 978 K, 1078 K and 1094 K were measured by dropping U samples maintained at the ambient temperature into liquid aluminium in the calorimeter at the experimental temperature. From the integral enthalpies of formation of U-Al alloys in the two phase regions, { U - Al } + 〈 UAl 4 〉 and { U - Al } + 〈 UAl 3 〉, the enthalpies of formation of UAl 4 and UAl 3 , respectively, at the temperatures of measurement were derived. These results are discussed in comparison with the literature data.

Enthalpies of formation of CeNi2 and CeNi5 by calorimetry

Abstract The enthalpies of formation of the intermetallic compounds, CeNi2 and CeNi5 at 298.15 K have been determined by high temperature solution calorimetry. The thermal effects of dissolution of nickel, cerium and the intermetallic compounds in liquid aluminum at 1095.15 K were determined as a function of concentration of the solutes from which the respective thermal effects of dissolution at infinite dilution were derived. The enthalpies of formation of the compounds at 298.15 K were computed from these values of thermal effects of dissolution at infinite dilution. The enthalpies of formation of CeNi2 and CeNi5, at 298.15 K thus obtained are −115.8 ± 7.3 and −201.9 ± 11.9 kJ mol−1, respectively. The present enthalpy of formation of CeNi5 is compared with the earlier literature values. In the case of CeNi2 the study provides the only experimental data for the enthalpy of formation.

Enthalpies of formation of UNi5, UNi2 and UFe2 by solution calorimetry

Abstract The enthalpies of formation of the intermetallic compounds UNi5, UNi2 and UFe2 at room temperature were determined by high temperature solution calorimetry in which liquid aluminium was used as the solvent. The “thermal effects of dissolution” of Ni, Fe, UNi5, UNi2 and UFe2 in liquid aluminium were measured in separate experiments by dropping the samples, held at ambient temperature, into liquid aluminium maintained at 994 K in a high temperature differential calorimeter. The thermal effects of dissolution of the samples in liquid aluminium at infinite dilution were derived from these measurements, and based on these data, the enthalpies of formation of UNi5, UNi2 and UFe2 at room temperature were computed as −(39.54 ± 8.6), −(37.89 ± 4.4) and −(38.73 ± 5.4) kJ (g-atom)−1, respectively. The partial enthalpies of solution at infinite dilution, ( Δ H ∞ ) for Ni and Fe in liquid aluminium were also derived from the measured data as −(147.26 ± 1) and −(114.71 ± 1.2) kJ mol−1, respectively.

Enthalpies of formation of UGa2 and UGa3 by calorimetry

Abstract Enthalpies of formation of the intermetallic compounds, UGa 2 and UGa 3 , at 298.15 K were determined by using high-temperature liquid gallium solution calorimetric measurements at 1427 K to be −40.4±6.0 and −38.3±4.4 kJ gatom −1 , respectively. The enthalpies of formation of UGa 2 at 1563 K and UGa 3 at 1038 K were determined to be −79.1±2.5 and −40.6±1.5 kJ gatom −1 by using the precipitation calorimetric method. The enthalpies of formation of UGa 3 at 298.15 and at 1038 K are found to be in agreement with each other, whereas that of UGa 2 at 1563 K is highly exothermic compared to that at 298.15 K.

Thermodynamic functions of alkaline earth monouranates from calorimetric measurements

Abstract High temperature differential calorimetry was used to determine the enthalpy increments of BaUO 4 , α-SrUO 4 and CaUO 4 relative to room temperature. The measurements covered the temperature range 1000–1735 K. From these enthalpy values other thermodynamic functions, such as C XXX p T , S XXX T and -( G XXX T - H XXX 298 )⧸ T , were deduced using C XXX p298 and S XXX 298 from the literature. The high temperature C XXX p T values for the monouranates obtained in this study are discussed in relation to the low temperature data available in the literature.

Standard enthalpies of formation of lanthanum gallides by high temperature reaction calorimetry

Abstract The standard enthalpies of formation (Δ f H 0 298.15 ) of Ce 3 Ga 2 , CeGa, CeGa 2 and CeGa 6 at 298.15 were determined by high temperature liquid gallium solution calorimetry to be −(71.1±2.7), −(84.1±1.9), −(51.5±1.4) and −(48.2±3.7) kJ gatom −1 respectively. The enthalpies of formation of Ce 0.21 Ga 0.79 at 1125 K and CeGa 6 at 876 K were determined by using precipitation calorimetry to be −(36.7±2.9) and −(52.8±3.0) kJ gatom −1 . The partial enthalpies of solution of cerium in liquid gallium at infinite dilution (ΔH ∞ Ce ) at 874 K and 1094 K were determined to be −(186.4±5.4) and −(213.0±3.7) kJ gatom −1 respectively.