INVESTIGATIONS OF CARBIDES AS CATHODES FOR THERMIONIC SPACE REACTORS. Quarterly Progress Report for Period Ending November 30, 1961
The physico-chemical properties of mixed carbides of uranium and zirconium are being measured at temperatures up to 2400 deg K. Vapor-loss measurements were conducted for specimens with nominal compositions of 20 mol-% UC-80 mol-% ZrC and 90 mol-% UC-l0 mol-% ZrC at 2300 deg plus or minus 11 deg K in a vacuum of 4 x 10/sup -9/ mm Hg to establish if residual oxide layers were influencing weight-loss measurements. Comparison of the data obtained with measurements performed in vacuums of 1 x 10/sup -5/ mm Hg showed that no change was effected by the difference in vacuum. After a 95-hr exposure at 2300 deg K, the weight loss of the specimen with a nominal composition of 90 mol-% UC-10 mol- % ZrC continued to decrease at a constant rate. Preliminary experiments to determine the influence of a cesium-vapor environment on the weight loss are described. Electrical-resistivity measurements are being conducted for mixed- carbide specimens of differing U: Zr ratios from room temperature to 2400 deg K. The resistivity data obtained are represented as a linear function of temperature. A technique selected for thermal-conductivity measurements is presented and the requisite apparatus is described. A technique was developed for simultaneously studying the interdiffusion between uranium carbides and four refractory metals -- -tungsten, niobium, tantalum, and molybdenum. The interactions between these metals and UC/sub 2/--UC mixtures were studied at 1800 deg C for times up to 50 hr. Using carbon contents greater than stoichiometric UC suppressed liquid-phase formation. The growth of uniform carbide layers was found to proceed according to a parabolic rate law, and layers as thick as 1000 mu were found after 50 hr. In addition to the formation of uniform carbide layers, severe carbide penetration of the grain boundaries was observed in niobium, tantalum, and molybdenum. Investigation of the interaction between UZrC (6.0 mol-% U-45.8 mol- % Zr-48.2 mol-% C) and the same four refractory metals at 1800 deg C after 50 hr showed that the stabilization of the carbide phase by the addition of zirconium dramatically improves the diffusion characteristics. (auth)
- Research Organization:
- General Atomic Div., General Dynamics Corp., San Diego, Calif.
- NSA Number:
- NSA-16-005078
- OSTI ID:
- 4823041
- Report Number(s):
- GA-2670
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CARBON
CESIUM
DIAGRAMS
DIFFUSION
EFFICIENCY
ELECTRIC CONDUCTIVITY
ELECTRODES
FILMS
GRAIN BOUNDARIES
HIGH TEMPERATURE
LABORATORY EQUIPMENT
LOSSES
MATERIALS TESTING
MEASURED VALUES
METALS
MIXING
MOLYBDENUM
NESDPS Office of Nuclear Energy Space and Defense Power Systems
NIOBIUM
OXIDES
PHASE DIAGRAMS
QUALITATIVE ANALYSIS
REFRACTORIES
SPACE APPLICATIONS AND TECHNOLOGY
TANTALUM
TEMPERATURE
THERMAL CONDUCTIVITY
THERMIONICS
THICKNESS
TUNGSTEN
URANIUM ALLOYS
URANIUM CARBIDES
USES
VACUUM
VAPORS
WEIGHT
ZIRCONIUM ALLOYS
ZIRCONIUM CARBIDES