The Poisoning of Barium-Nickel Matrix Cathodes†

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Abstract
This paper describes an experimental study of the poisoning of the thermionic emission from barium-nickel matrix cathodes activated by aluminium and titanium hydride. Gases which poison the emission are oxygon, carbon dioxide and water vapour, while nitrogen, hydrogen, the inert gases and carbon monoxide do not. The emission deteriorates rapidly when once a critical partial pressure of a poisoning gas is exceeded, this pressure being higher for higher cathode temperatures. The critical pressures of the poisoning gases are each about 10−7 torr for normal cathode temperatures, but they decrease considerably with repeated poisonings. The cathodes can be reactivated completely after a number of poisonings, before permanent impairment is observed. The speed of reactivation increases with temperature and decreases with repeated poisoning. The results are largely explained on the basis of the probability of gas adsorption and its subsequent removal by free barium, being produced by the activator.

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