Examination of the total pressure over hypostoichiometric uranium dioxide
The standard free energy of formation of stoichiometric UO$sub 2$ is reevaluated. An altered valent cation model, descriptive of the oxygen potential throughout the hypostoichiometric domain of urania, is integrated analytically so that activities of (U) and of (UO$sub 2$) and the free energies of formation of [UO/sub 2-x/] can be evaluated. By including separately determined values for the vapor pressure of uranium and the free energy of formation of (UO$sub 3$) and by imposing the independence of composition of $delta$$G$$sup 0$/sub integral/(UO) as a condition, the latter and p$sup 0$(UO$sub 2$) are determined from observations of the total pressure of uranium bearing species. This resolution of the total pressure of uranium-bearing species plus the starting equations for the oxygen potential enable determination of the congruently vaporizing compositions, which are found to be much nearer stoichiometry than are experimental results. By including separately determined mass spectrometric observations of (I$sup +$T) at the lower phase boundary, evaluations are made of the instrument sensitivities for the various species in the gas phase. While the model well describes the observations of oxygen potential, it leads to obviously erroneous contributions to the enthalpy of stoichiometric uranium dioxide. 11 figures, 60 references. (auth)
- Research Organization:
- Argonne National Lab., IL
- NSA Number:
- NSA-33-009741
- OSTI ID:
- 4131797
- Journal Information:
- High Temp. Sci., v. 7, no. 2, pp. 81-102, Journal Name: High Temp. Sci., v. 7, no. 2, pp. 81-102; ISSN HITSA
- Country of Publication:
- United States
- Language:
- English
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Cermets & Refractories-- Physical Properties
CHEMICAL COMPOSITION
ENTHALPY
EQUATIONS
EVAPORATION
FORMATION FREE ENERGY
N50130* --Metals
Ceramics
& Other Materials--Ceramics & Cermets--Properties
Structure & Phase Studies
QUANTITY RATIO
STOICHIOMETRY
TEMPERATURE DEPENDENCE
VAPOR PRESSURE
VERY HIGH TEMPERATURE