High-temperature thermodynamic properties of the thorium-oxygen system
The thermodynamic properties of the thorium-oxygen system at high temperatures have been investigated by means of mass effusion, mass spectrometric, and transpiration techniques over compositions ranging from the congruently vaporizing composition to the lower phase boundary composition. A very sharp decrease in oxygen potential occurs when stoichiometric thoria is reduced but slightly from the stoichiometric composition. The small extent of reduction over a wide range of oxygen potentials measured in the temperature range 2400 to 2655/sup 0/K is a clear illustration of the higher stability of the ThO/sub 2-x/ phase compared with actinide-oxides such as UO/sub 2-x/, PuO/sub 2-x/, as well as other metal oxide systems. Estimates of ..delta.. anti H/sub O/sub 2//, ..delta.. anti S/sub O/sub 2//, and the standard free energy of formation of bivariant ThO/sub 2-x/ compositions have been made. A substantial increase in the total pressure of thorium-bearing species occurs when stoichiometric thoria is reduced toward the lower phase boundary. The increase in pressure can be attributed primarily to the increasing contribution of the ThO gaseous species. Total pressures of thorium-bearing species above ThO/sub 2-x/ compositions calculated by means of experimental oxygen potentials and the known or estimated free energy of formation values of the gaseous species and condensed phase are in reasonable agreement with experimental values. 8 figures, 3 tables.
- Research Organization:
- Argonne National Lab., IL
- OSTI ID:
- 6041969
- Journal Information:
- High Temp. Sci.; (United States), Vol. 13:1
- Country of Publication:
- United States
- Language:
- English
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