Electron Emission From Oxide Coated Filaments

Abstract

Emission from oxide coated filaments.—(1) Effect of various gases. Platinum iridium filaments were coated with oxides of Ba and Sr by repeatedly dipping in a solution of the nitrates and burning in a C${\mathrm{O}}_2$ atmosphere. Under good vacuum conditions the emission corresponds to the equation $I=a{T}^2{e}^{-\frac{b}{T}}$ where $a=.\mathrm{}00107\mathrm{}$ amp/${\mathrm{cm}}^2$ and $b=12,100\mathrm{}$ deg. for the filaments studied. The presence of oxygen in small amounts (${10}^{-3\mathrm{}}$ mm) decreases the emission ten to a thousand fold, depending on the temperature, while argon, hydrogen, CO and C${\mathrm{O}}_2$ cause a great increase. These results indicate that the emission is due not to the oxides but to a film of metal. (2) Positive ion bombardment also increases the emission, probably by reducing some of the oxide. (3) Flashing at 1600°K for 1 to 5 min. de-activates the filament, but heating at lower temperatures (900°K) restores the activity. (4) Distribution of initial velocities was found to follow Maxwell's law, but the average energy came nearly 30 per cent higher than that corresponding to the temperature of the filament.