OXIDE COATED HOT-CATHODE

PURPOSE:To prolong the service life by adding Ni alloy powder of reducing agent such as W, Mg, Si, etc., in an oxide layer in an oxide coated hot-cathode having the oxide layer consisting of an oxide of alkaline earth metal. CONSTITUTION:An Ni based metal 3, containing, for example, 4wt.% of reducing agent such as W, Mg, Si, etc., is disposed on the upper end of an Ni metal cylinder 2 having a built-in heater 1. Further, an oxide layer 4 is applied thereon, whereas alloy powder consisting of reducing agent such as W, Mg, Si, etc., and Ni is added into this oxide layer 4. The alloy power of the reducing agent and Ni in this case is added by 1-50wt.% relative to the solid component of the oxide layer, and the grain diameter thereof is made not larger than about 70% of the thickness of the oxide layer 4, i.e., because the thickness of the oxide layer 4 is about 70mum, the grain diameter is made not larger than about 50mum. In this hot-cathode, reaction, which takes place at the interface between the oxide layer 4 and the base metal, takes place even in the oxide layer 4 due to current feeding to the heater 1 for heating, to effect electron emission, and because Ni alloy is added in the powder state, the contact area between BaO and the alloy is increased so that a longer life is achieved.