On the Mechanism of Operation of the Barium Aluminate Impregnated Cathode

Abstract

Emission and evaporation characteristics of a porous tungsten cathode impregnated with the composition 5BaO·2Al2O3 are presented and are interpreted in terms of the cathode mechanism. Barium necessary for activation is generated by the reaction, 23 Ba3Al2O6+13 W=13 BaWO4+23 BaAl2O4+Ba,and is transported through partially clogged pores, the length of which increases with time, predominantly via Knudsen flow. During transport, oxygen is acquired from the tungsten, leading to a substantial content of BaO in the evaporant. The BaAl2O4 component of the impregnant is inert. Emission is substantially lower than that of an L cathode, presumably because of release of a poisoning agent accompanying the activator.