The Heat Capacities of Uranium, Uranium Trioxide, and Uranium Dioxide from 15°K to 300°K

Abstract

Heat capacity measurements have been made over the temperature range 15–300°K for uranium metal, uranium trioxide, and uranium dioxide. A maximum was observed at 28.7°K in the heat capacity curve of UO2 which is probably the result of the changing population of the magnetic quadrivalent uranium ions among their available energy states. The entropies of these substances at 298.16°K are 12.03, 23.57, and 18.63 cal deg−1 mole−1, respectively. The free energies of formation of UO3 and UO2 are −273.1±3 and −246.6±0.6 kcal mole−1, respectively.