INVESTIGATIONS OF CARBIDES AS CATHODES FOR THERMIONIC SPACE REACTORS. Fourth Interim Progress Report for the Period from March 1 through May 31, 1962
The physicochemical properties of mixed carbides of uranium and zirconium are being measured to determine the usefulness of these materials as nuclear-heated thermionic emitters or as the nuclear fuel for refractorymetal thermionic cells. Property measurements of other carbide systems having potential as thermionic emitters are also being performed. Vapor-loss data were obtained in vacuum for a specimen of nominal composition 90 mole% UC--10 mole-% ZrC over the temperature range 1988 to 2083 deg K. The rate of weight loss can be expressed as follows: log w(dot on top) = 9.72--3.05 x 10/sup 4/ (2/T), where w(dot on top) is t he rate of weight loss in mg/cm/sup 2/sec and T is the absolute temperature. A cesium-vapor environment at a pressure of 0.06 to 0.09 mm Hg at 1990 deg plus or minus 14 deg K was not found to significantly change the rate of weight loss of this specimen from the rate of weight loss measured in vacuum at the same temperature. Depletion of the surface uranium content by over 30% of the bulk concentration (based on weight percentages) was found by electron- microprobe techniques in specimens of low UC content whose rate of weight loss was previously studied. The rate of weight loss of a specimen of nominal composition 20 mole-% UC--80 mole-% HfC was found to be 1.59 x 10/sup -5/ mg/cm/ sup 2/sec at 2063 plus or minus 11 deg K. Electron emission in vacuum was determined as a function of temperature for specimens of nominal composition 90 mole-% UC--10 mole-% ZrC and 20 mole-% UC--80 mole% HfC. Diffusion experiments showed that rhenium and tungsten--25 wt-% rhenium barrier layers are ineffective in stopping carbon diffusion between UC/sub 2/ and molybdenum or tungsten at 1800 deg C. However, ZrC provides an effective barrier. Studies of the containment of 10 mole-% UC--90 mole-% ZrC by tantalum were made using electron-emission measurements from the tantalum surface as the monitoring technique. These studies showed that at 1680 deg C less than 57 hr is required for sufficient diffusion of the fuel components through the tantalum to cause a significant change in the electronemission characteristics. Electron-microprobe analyses were employed to gain further data on UC--ZrC, ZrC --W, and UC --W interactions. Electrical-resistivity measurements were completed for a specimen of nominal composition 80 mole-% UC--20 mole-% ZrC over the temperature range from room temperature to 2400 deg K. Thermalconductivity measurements were obtained for ZrC in the temperature range 1100 deg to 1200 deg C. The average value obtained from three different specimens is 0.107 calcm/sup -2/-cm-sec/sup -1/- deg C/sup -1/. (auth)
- Research Organization:
- General Atomic Div., General Dynamics Corp., San Diego, Calif.
- DOE Contract Number:
- NAS 5-1253
- NSA Number:
- NSA-16-024154
- OSTI ID:
- 4820297
- Report Number(s):
- GA-3254
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- United States
- Language:
- English
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INVESTIGATIONS OF CARBIDES AS CATHODES FOR THERMIONIC SPACE REACTORS. Quarterly Progress Report No. 3, December 1, 1961 through February 28, 1962
INVESTIGATIONS OF CARBIDES AS CATHODES FOR THERMIONIC SPACE REACTORS. Quarterly Progress Report for Period Ending November 30, 1961
Related Subjects
BARRIERS
CARBIDES
CARBON
CESIUM
CHEMICAL REACTIONS
DIFFUSION
ELECTRIC CONDUCTIVITY
ELECTRON PROBES
ELECTRONS
EMISSION
ENVIRONMENT
EQUATIONS
FUELS
HEATING
HIGH TEMPERATURE
INTERACTIONS
LAYERS
MEASURED VALUES
METALS
MIXING
MOLYBDENUM
MONITORING
NUCLEATE BOILING
PHASE DIAGRAMS
PRESSURE
QUANTITY RATIO
REFRACTORIES
RHENIUM
SURFACES
TANTALUM
TEMPERATURE
TENSILE PROPERTIES
THERMAL CONDUCTIVITY
THERMIONICS
THERMODYNAMICS
TUNGSTEN
URANIUM
URANIUM CARBIDES
VACUUM
VAPORS
WEIGHT
ZIRCONIUM CARBIDES
NESDPS Office of Nuclear Energy Space and Defense Power Systems