Patent ID: 6242854
Filing Date: 2001-06-05
Classification: H01J

Abstract:
An indirectly heated cathode comprising a heater having an alumina electrical insulating layer formed by layering and sintering alumina particles on a surface of a metal wire and an electron-emitting part that receives heat from the heater and emits thermoelectrons,wherein the alumina particles contained in the alumina electrical insulating layer have a purity of at least 99.7 wt % and alumina particles with a particle size of 2 .mu.m or less included in the alumina particles used for forming the alumina electrical insulating layer have a Na content of 20 ppm or less, andwherein the alumina particles with a particle size of 2 .mu.m or less arc present in the alumina particles as a whole in a ratio of 10-50 wt %.