Directly heated cathode for high frequency electron tubes - using graphite substrate covered by inert metal, then tungsten impregnated with aluminate(s), followed by noble metal

摘要

The cathode has a substrate (1) of pyrolytic graphite heated by electric resistance, and covered by an emitter layer (3) of sintered metal, which is impregnated with barium- and calcium- aluminate. Between substrate (1) and layer (3) is a thin film (2) of a material which does not react chemically with carbon; and layer (3) is covered by a layer (4) of a refractory metal with a high work function. Layer (2) is pref. Ir or Re; whereas the metal in layer (3) is pref. pure tungsten, or a mixt. of W plus a refractory metal with a high work function, esp. osmium. The cathode is used esp. in an electron tube for UHF or microwaves. This cathode will operate at the low temp. of 1000-1100 deg. C, as compared with 1400-1500 deg. C required for a cathode using an emitter of LaB6.