Fabrication and surface characterization of composite refractory compounds suitable for thermionic converters
Procedures for fabricating high purity single crystals of LaB/sub 6/ and SmB/sub 6/ have been developed. Auger spectroscopy shows that a clean surface can be obtained by thermal heating at 1700 K; such a clean surface gives a value of B/La of 2.3 to 2.6 for the (100) face. The measured thermionic and FERP work functions of the (100) face of LaB/sub 6/ are 2.47 and 2.28 eV, respectively. The electron reflection coefficient for LaB/sub 6/(100) increases near zero primary energy to 0.5. Flash thermal desorption of an oxygen-dosed surface showed that B/sub 2/O/sub 3/ is the desorption product at 1600 to 1700 K. A work function increase of 1.6 eV was observed on oxygen adsorption on LaB/sub 6/(100). Thermal desorption of Co occurs at approximately 1300 K. A reduction of the work function to 1.39 eV was observed on adsorption of a partial monolayer of Cs on LaB/sub 6/(100). The evaporation of LaB/sub 6/ occurs as atomic La and B with a value of B/La of 6 to 3 in the temperature range 1700 to 2000 K. The activation energies of desorption for La and B are 6.3 +- 0.3 and 6.8 +- 0.3 eV, respectively. (auth)
- Research Organization:
- Oregon Graduate Center for Study and Research, Beaverton (USA)
- OSTI ID:
- 7228024
- Report Number(s):
- N-76-21989; NASA-CR-2668
- Country of Publication:
- United States
- Language:
- English
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BACKSCATTERING
BORIDES
BORON COMPOUNDS
COLLISIONS
CRYSTALS
DESORPTION
DIRECT ENERGY CONVERTERS
ELECTRON COLLISIONS
EVAPORATION
FABRICATION
HEATING
LANTHANUM BORIDES
LANTHANUM COMPOUNDS
MATERIALS
MONOCRYSTALS
NESDPS Office of Nuclear Energy Space and Defense Power Systems
PHASE TRANSFORMATIONS
RARE EARTH COMPOUNDS
SAMARIUM BORIDES
SAMARIUM COMPOUNDS
SCATTERING
SURFACE PROPERTIES
THERMIONIC CONVERTERS
VERY HIGH TEMPERATURE
WORK FUNCTIONS