Sublimation thermodynamics of the URu3 compound

Abstract

The sublimation behavior of the URu3 intermetallic compound has been studied with a mass spectrometer–target collection apparatus. The sublimation reaction proceeded by dissociation to the elements up to the solidus temperature of the condensed phase. Vapor pressures of gaseous 233U effusing from the Knudsen cell over the temperature range 1690–2100 K were measured by target collection and radioanalysis of the targets. A second-law treatment of the data yielded ΔH° (1896 K) and ΔS° (1896 K) of sublimation of 563.4±13.4 kJ mole−1 (134.6±3.2 kcal mole−1) and 147.8±7.1 JK−1 mole−1 (35.3±1.7 cal K−1 mole−1), respectively. The corresponding ΔH° (1896 K) and ΔS° (1896 K) of formation were −79.5±20.9 kJ mole−1 (−19.0±5.0 kcal mole−1) and −35.2±10.5 JK−1 mole−1 (−8.4±2.5 cal K−1 mole−1), respectively. Third-law treatment with estimated free energy functions yielded ΔH° (298 K) of sublimation and ΔH° (298 K) of formation of 572.2±8.0 kJ mole−1 (136.8±1.9 kcal mole−1) and −49±22 kJ mole−1 (−12±5 kcal mole−1),respectively.