HIGH TEMPERATURE PHASE EQUILIBRIA IN THE SYSTEM CARBON-OXYGEN-URANIUM

Journal Article · Sun Jul 01 04:00:00 EDT 1962 · Dissertation Abstr.

DOI:https://doi.org/10.1021/je60015a002· OSTI ID:4791838

Piazza, J R

Equilibrium relationships among uranium monocarbide, uranium dicarbide, graphite, uranium dioxide, and carbon monoxide were investigated in the temperature range be tween 1400 and 1700 deg C and at pressures below one atmosphere. The two univariant equilibria UO/sub 2/ + 4C = UC/sub 2/ + 2CO and UO/sub 2/ + 3UC/sub 2/ = 4UC + 2CO were found to exist over the temperature range studied. Carbon monoxide equilibrium pressure as a function of temperature was determined for both equilibria. Pressure-temperature data were used to formulate analytical expressions for the carbon monoxide equilibrium pressures. The expressions were determined as log/sub 10PCO/ = - 18000/T + 8.23 and log/sub 10PCo/= -16600/T + 7.26 for the first and second equilibria, respectively. Experiments were made to assess the activity of the solid phases involved in the equilibria and to determine the order of magnitude of errors due to the presence of nitrogen in the system. The experiments included precision lattice parameter determinations at room temperature of the monocarbide and dioxide phases in the solid residues. The activities of the monocarbide and dicarbide were estimated as 0.95 plus or minus 0.05 throughout the range of temperatures investigated. It was concluded from the study of the effect of nitrogen that the errors in the carbon monoxide equilibrium pressures for the first equilibria are negligible and that those for the second amount to 10% or less. Expressions for standard Gibbs free energies of reaction in calories for the reactions UO/sub 2/ + 4C yields UC/sub 2/ + 2CO, UO/sub 2/ +3UC/sub 2/ yields 4UC +2CO, UO/sub 2/+3C yields UC + 2CO, and UC + C yields UC/sub 2/, were determined as 164,500-74.23T, tively. The effects of nitrogen indicate that, at temperatures in the range studied, uranium mononitride will coform with uranium monocarbide if nitrogen is present in the gas phase. The resuIts also indicate that lowering of the monocarbide activity stabilizes mixtures of the monocarbide and graphite with respect to the dicarbide. The extent to which the monocarbide activity need be lowered to equilibrate graphite, the monocarbide and the dicarbide is indicated by the free energy of reaction for UC + C yields UC/sub 2/ given by 3100-2.20T calories. (auth)

• Research Organization: Univ. of Michigan, Ann Arbor
• Sponsoring Organization: USDOE
• NSA Number: NSA-16-029399
• OSTI ID: 4791838
• Journal Information: Dissertation Abstr., Journal Name: Dissertation Abstr. Vol. Vol: 23
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CARBON
CARBON MONOXIDE
CHEMICAL REACTIONS
EQUATIONS
ERRORS
GASES
GRAPHITE
HIGH TEMPERATURE
LATTICES
METALS, CERAMICS, AND OTHER MATERIALS
MIXING
NITROGEN
PHASE DIAGRAMS
PRESSURE
QUANTITATIVE ANALYSIS
REACTION KINETICS
RESIDUES
SOLUBILITY
TEMPERATURE
TESTING
THERMODYNAMICS
URANIUM CARBIDES
URANIUM DIOXIDE
URANIUM NITRIDES