Lanthanated thermionic cathodes
AssigneeBBC Brown, Boveri & Company, Limited
InventorsRobert Bachmann, Charley Buxbaum, Gernot Gessinger
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Abstract
A thermionic cathode of tungsten or molybdenum is made with an activating content of lanthanum oxide and is supplied with a carbonaceous reducing agent either by incorporation in the bulk material of the cathode body or by carburizing, so that the reducing agent comprises at least in part a carbide of the carrier metal. Lower operating temperatures and higher emissivity are obtained compared to thoriated tungsten filaments and longer useful life compared to other cathodes activated by other rare earth oxides. The temperature-emissivity characteristics are such that good results are obtainable even within the temperature range in which molybdenum is usable as a carrier material.
Claims20
A thermionic cathode comprising a body surrounded by an emitting surface, said body consisting essentially of a high-melting metal, between 0.2% and 5% by weight lanthanum oxide distributed throughout said body and close to the emitting surface of said body and between 0.05% and 18% by weight of a carbon containing-reducing agent which is effective in reducing the lanthanum oxide to lanthanum during operation of the thermionic cathode and replenish the lanthanum which has evaporated at the emitting surface of the body.
A thermionic cathode consisting essentially of a body surrounded by a freely exposed emitting surface and containing dispersed throughout said body to a location near to the region of the emitting surface between 0.2% and 5% by weight lanthanum oxide and between 0.05% and 18% by weight of a carbon containing-reducing agent, said lanthanum oxide being reduced, during operation of the thermionic cathode, by the carbon containing-reducing agent to lanthanum in order to continually replenish lanthanum evaporating from the emitting surface of the body so as to maintain a substantially monatomic layer of lanthanum at the emitting surface of the cathode, said thermionic cathode possessing higher emissivity in comparison to a thoriated tungsten filament.
A method of producing a thermionic cathode comprising the steps of:
- a. forming a cathode body of a metallic carrier material consisting essentially of at least one high-melting metal an activating material containing lanthanum oxide in an amount between 0.2% by weight and 5% by weight of said cathode body;
- b. said lanthanum oxide being dispersed in said cathode body up to the region of the outer surface of said cathode body;
- and
- c. subjecting the body so formed to carburization to introduce therein a carbon-containing reducing agent in an amount between 0.05% and 18% by weight.
Dependencies are inferred from the claim text.