[en] The high-temperature enthalpies of plutonium monocarbide and plutonium sesquicarbide have been determined with a copper-block calorimeter of the isoperibol type. The experimental enthalpy data, which was measured relative to 298 K, covered the temperature range from 400 to 1500 K. The calculation of the temperature rise of the calorimeter takes into account the added heat evolution from the radioactive decay of the plutonium samples. These enthalpy results, combined with the heat capacity and entropy of the respective carbide at 298 K available from the literature, has made it possible to generate tables of thermodynamic functions for the plutonium carbides. The behavior of the heat capacity of both of the plutonium carbides, i.e., a relatively steep increase in the heat capacity as the temperature increases, may be attributed to a premelting effect with the formation of vacancies within the crystal lattice although a theoretical treatment of this phenomenon is not given

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[en] The heat capacity of delta-stabilized plutonium (Pu - 3.2 at. % Ga) has been determined from 330 to 700₀K by an adiabatic calorimeter. The heat capacity for this alloy may be expressed by: Cp (Pu-3.2 at. % Ga)/(J K^-₁ mol^-₁) = 39.249 - 0.0264 (T/K) + 3.595 x 10₅ (T/K)₂ - 2.506 x 10₅ (K/T)₂. It was found that a large contribution to the heat capacity is due to the electronic heat capacity. The thermal functions for this plutonium-gallium alloy are calculated to 700₀K

[en] For over twenty years, the International Atomic Energy Agency has played a major role in furthering the exchange of information on the thermodynamics of nuclear materials between scientists all over the world. The methodology used by the Agency to achieve this exchange has been to convene five international symposia on the thermodynamics of nuclear materials (1962, 1965, 1967, 1974 and 1979). These symposia not only served as a means for scientific exchange of experimental results, but also provided a mechanism whereby various scientists could collaborate on pertinent topics. Under the sponsorship of the Agency, several panels have been held resulting in the publication of several technical reports specifically related to thermochemical assessment, e.g. UC and PuC (1962), UO₂ (1964), and PuO₂ and UPuO₂ (1964). On a broader front, publication of two series of monographs on thermodynamic assessment has recently been undertaken; one consists of a special series of the Atomic Energy Review and the other is a series on The Chemical Thermodynamics of Actinide Elements and Compounds. During the past three years, the Agency has also sponsored a coordinated research programme between Member States. It deals with thermodynamic and transport properties of nuclear materials

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[en] The high-temperature enthalpies of plutonium monocarbide and plutonium sesquicarbide have been determined with a copper-block calorimeter of the isoperibol type. The experimental enthalpy data, which were measured relative to 298 K, covered the temperature range from 400 to 1500 K. The calculation of the temperature rise of the calorimeter takes into account the added heat evolution from the radioactive decay of the plutonium samples. These enthalpy results, combined with the heat capacity and entropy of the respective carbide at 298 K available from the literature, have made it possible to generate tables of thermodynamic functions for the plutonium carbides. The behaviour of the heat capacities of both of the plutonium carbides, i.e., a relatively steep increase in the heat capacity as the temperature increases, may be attributed to the formation of vacancies within the crystal lattice although a theoretical treatment of this phenomenon is not given. (orig.)

[en] Equilibrium, kinetic and x ray diffraction data show the existence of two stability regimes in the Pu-H system. A metastable solid solution between CaF₂-type PuH₁₉ and anti-Fe₃Al-type PuH₃₀ forms at low temperature and behaves as an ideal solid solution. Equilibrium and calorimetric results show that the enthalpy of formation varies linearly from -38 to -50 kcal/mol between the lower phase boundary and the trihydride. The phase relationships established at high temperature are similar to those of the lanthanide difluoride-lanthanide trifluoride systems. A series of CaF₂-related phases apparently forms between PuH₁₉ and PuH₂₅; a nonstoichiometric hexagonal (LaF₃-type) hydride exists in the range PuH₂₉-PuH₃₀. A procedure for preparing pure hexagonal puH₃₀₀ is described, and the hysteresis behavior of the Pu-H system is discussed