Long-life cathode with porous two layer emitter - has emitting layer thinner and of lower porosity than supporting layer

摘要

The cathode has a heating filament and a porous two-layer component whose pores contain the electron-emitting material. The layer (4) forming the emitting surface (5) of the component has a lower porosity than the layer beneath (3). The emitting layer has 10-20%, pref. 15%, pores. The layer beneath has 15-50%, pref. 30%, pores so that its total pore volume is roughly twice that of the emitting layer. The emitting layer is thinner than the layer beneath and consists of compressed metal powder of particle size 2-10 microns. The layer underneath consists of compressed metal powder of particle size 10-40 microns.