Indirectly heated cathode and cathode-ray tube comprising the same

摘要

In an indirectly heated cathode (8) comprising a heater (13) having an alumina electrical insulating layer formed by layering and sintering alumina particles on a surface of a metal wire (14) and an electron-emitting part (9) that receives heat from the heater (13) and emits thermoelectrons, and a cathode-ray tube comprising the indirectly heated cathode (8), the alumina particles contained in the alumina electrical insulating layer have a purity of at least 99.7 wt% and the alumina particles used for forming the alumina electrical insulating layer have a Na content of 20ppm or less or a Si content of 100ppm or less, thus enabling stable production, avoiding the occurrence of cracks in the alumina electrical insulating layer and heater deformation even in the practical operation of the cathode-ray tube, and lengthening the life of the heater.