BASIC RESEARCH IN THERMIONICS. PART I. CESIUM PERMEATION THROUGH TANTALUM
TEXAS INSTRUMENTS INC DALLAS
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A plasma thermionic converter concept has been proposed which uses cesium permeation through a tantalum emitter to obtain space charge neutralization of electron current from this emitter. The objective of this project was to determine if the permeation rate of cesium through tantalum was sufficiently large for feasibility of the concept. It has been shown that the concept is not feasible because the permeation rate of Cs through tantalum is too small. Cesium permeation through tantalum has been studied in the temperature range 1400 to 1800 C with cesium pressures up to 13 mm Hg. This phenomenon was investigated for potential application as a hollow, ion-dispensing emitter for a plasma thermionic converter. Three methods were used in this study 1 measurement of ion current from a hollow, polycrystalline tantalum emitter internally connected to a cesium reservoir, 2 measurement of weight-loss from a hollow, polycrystalline tantalum container with a cesium reservoir attached, with both suspended from a microbalance into a radiant furnace, and 3 direct measurement of the diffusion coefficient in single-crystal and polycrystalline tantalum utilizing radioactive Cs-134.
- Metallurgy and Metallography