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U and Th bearing carbides, EuB6 and YB6 were studied to determine how these materials would react in the thermal and chemical environments associated with thermionic applications. Some of the data obtained includes: Thermal shock resistance of the U bearing carbides is, very probably, inadequate for applications which require that the fuel emitter retain structural integrity under thermal cycling and/or severe temperature gradient conditions. Thermophysical properties, thermal conductivity, electrical resistivity, and emissivresponding oxide materials and approach properties exhibited by metallic materials. Vapor pressure properties of the rare earth borides indicate an upper temperature limit in the neighborhood of 1400 C. Work functions of bulk carbides generally fall slightly below that of W. Cs compatibility tests showed the very marked sensitivity of carbon-rich carbide materials to Cs attack in time periods less than 500 hours. TY OF CARBIDE MATERIALS ARE SUPERIOR TO CORRESPONDING OXIDE MATERIALS AND APPROACH PROPERTIES EXHIBITED BY METALLIC MATERIALS. Vapor pressure properties of the rare earth borides indicate an upper temperature limit in the neighborhood of 1400 C. Work functions of bulk carbides generally fall slightly below that of W. Cs compatibility tests showed the very marked sensitivity of carbon-rich carbide materials to Cs attack in time periods less than 500 hours. Boride materials, on the other hand, appear resistant to Cs attack.

The work carried out with the uncooled collector converter was the following: (1) measurement of electrode work functions in vacuo; (2) thermal calibration of the emitter in vacuo; (3) thermal calibration of the emitter in cesium vapor; (4) measurement of current-voltage characteristics and converter efficiencies for a variety of electrode temperatures, electrode spacings, and cesium vapor measures; (5) assemble the cooled collector converter with the new NaK cooled collector. In addition, it was found necessary to do two other calibrations concerned with accurate measurement of the electrode temperatures. One of these calibrations had to do with a reflection effect which resulted in the observed electrode temperatures being higher than their actual values. The second calibration had to do with light absorption in cesium vapor at high pressure., See also AD-601 007.