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.