Thermionic Emitters Consisting of BaO–UO2 Dispersed in a Tungsten Matrix

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Abstract
Thermionic emitters fabricated with various concentrations of BaO and UO2 dispersed in tungsten have been operated at temperatures up to 1400°C. A tentative phase diagram for the BaO–UO2 system has been constructed from microstructure and x‐ray analysis. Electron‐emission studies, emitter‐life tests, and barium‐transpiration studies have been conducted on eleven different BaO–UO2 tungsten compositions. The emission studies have indicated current‐density capabilities of 10 A/cm2. Work‐function measurements at 1100°C on the various emitters tested ranged from 2.03 eV for the high‐barium‐content samples to 2.56 eV for the low‐barium‐content samples. The barium transpiration rate of the emitters was evaluated for various barium contents and compositional forms. For a given quantity of barium, the transpiration rate was lower from the BaUO3+UO2 system than from the BaUO3+BaO system. At a temperature of 1200°C one type of BaO–UO2 tungsten material had a transpiration rate of 20 μg/cm2·h.

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