Diffusion Porosity in Films of Impregnated M-Type WBa Thermionic Cathodes and its Influence on Cathode Emission Characteristics

摘要

The paper examines how the emission characteristics of impregnated M-type cathodes depend on variation in the film composition and structure in the cathode operation process. Diffusion porosity has been established to appear in the 49.5% Os-49.5% Ir-1% Al and 50% Os-50% W films, and its influence on the emission characteristics of the M-type cathodes has been studied. It is assumed that the diffusion porosity decreases the M-type cathode work function because the total emitting area of the film increases and promotes faster delivery of barium and its compounds to the emitting layer through mass transfer facilitated by both Knudsen flow of atoms through pores and surface diffusion along pore walls. Degradation in the emission characteristic of the M-type cathode is due to the film structural failure. The experiments confirm the existence of three-dimensional barium-containing crystallites on the emitting surface of the M-type WBa cathode film.