INVESTIGATIONS OF CARBIDES AS CATHODES FOR THERMIONIC SPACE REACTORS. Quarterly Progress Report No. 3, December 1, 1961 through February 28, 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. Vapor-loss data, as determined by the Langmuir free- evaporation technique in the temperature range from 2130 deg to 2400 deg K, for three separate specimens with ZrC contents in the range from 8l to 86 mol-% ZrC can be expressed as follows: log w = 8.3- 3.03 x 10/sup 4/(1/T), where w is the rate of weight loss in mg/cm/sup 2//sec and T is the absolute temperature. The rate of weight loss for a specimen of nominal composition 90 mol-% UC- 10 mol-% ZrC was found to be l.15 x 10-/sup 5/ mg/cm/sup 2//sec at 2073 deg K. In contrast to results obtained for a similar specimen at 2300 deg K, the rate of weight loss remained constant with exposure time and no surface uranium depletion was obscrved. Studies of the compatibility of tungsten and uranium monocarbide to temperatures as high as 2000 deg C indicated that this combination of materials shows great promise as a nuclear-heated thermionic cathode. The kinetics of the interaction between mixtures of UC/sub 2/-UC and four refractory metals, niobium, tantalum, tungsten, and molybdenum, were further defined at 1800 deg C, and studies of these materials were extended to 1200 deg C. Electron-microprobe analyses of refractory-metal specimens which were placed in contact with UZrC(6.0 mol-% U-45.8 mol-% Zr-48.2 mol-% C) at 1800 deg C showed that uranium and zirconium penetrate deeply into niobium and tantalum in a period of 50 hr, but molybdenum and tungsten are less affected. Interdiffusion between UC and ZrC is being investigated to see if structures graded from a high-UC core to a high-ZrC surface would be stable for long periods of time at operating temperatures. Measurements of the electrical resistivities of uranium-carbon alloys in the composition range from UC to UC/sub 2/ were completed at temperatures to 2400 deg K. Work is progressing on the measurement of the electrical resistivities of mixed carbides of uranium and zirconium over the same temperature range. Procedures for thermal-conductivity measurement of the carbides were developed, and the necessary equipment was constructed and calibrated against a standard material (tantalum). (auth)
- Research Organization:
- General Atomic Div., General Dynamics Corp., San Diego, Calif.
- NSA Number:
- NSA-16-014350
- OSTI ID:
- 4801417
- Report Number(s):
- GA-3007
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHEMICAL REACTIONS
DIFFUSION
EFFICIENCY
ELECTRIC CONDUCTIVITY
ELECTRODES
ELECTRON MICROSCOPY
EVAPORATION
HIGH TEMPERATURE
LABORATORY EQUIPMENT
LOSSES
MEASURED VALUES
METALS
MOLYBDENUM
NESDPS Office of Nuclear Energy Space and Defense Power Systems
NIOBIUM
PLANNING
RADIOISOTOPES
REACTION KINETICS
REFRACTORIES
SPACE APPLICATIONS AND TECHNOLOGY
STABILITY
STANDARDS
SURFACES
TANTALUM
TEMPERATURE
THERMIONICS
THERMOELECTRIC CELLS
TUNGSTEN
URANIUM ALLOYS
URANIUM CARBIDES
VAPORS
WEIGHT
ZIRCONIUM ALLOYS
ZIRCONIUM CARBIDES