The chemical thermodynamics of nuclear materials: IV. The high-temperature enthalpies of plutonium monocarbide and plutonium sesquicarbide

Abstract

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.