US3495120A - Microheating elements,more particularly for cathodes of electron tubes - Google Patents

Microheating elements,more particularly for cathodes of electron tubes Download PDF

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Publication number
US3495120A
US3495120A US706897A US3495120DA US3495120A US 3495120 A US3495120 A US 3495120A US 706897 A US706897 A US 706897A US 3495120D A US3495120D A US 3495120DA US 3495120 A US3495120 A US 3495120A
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United States
Prior art keywords
cathodes
elements
electron tubes
microheating
heating
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Expired - Lifetime
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US706897A
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English (en)
Inventor
Wilhelmus Francisc Knippenberg
Pieter Zalm
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H01J1/22—Heaters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • H01C7/022—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient mainly consisting of non-metallic substances
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/15—Cathodes heated directly by an electric current

Definitions

  • MICROHEATING ELEMENTS MORE PARTICULARLY FUR CATHODES OF ELECTRON TUBES Filed Feb. 20, 1968 INVENTORS WILHELMUS E KNIPPENBERG PIETER ZALM BY M AEmr United States Patent 3,495,120 MICROHEATING ELEMENTS, MORE PARTIC- ULARLY FOR CATHODES OF ELECTRON TUBES 1 Wilhelmus Franciscus Knippenberg, and Pieter Zalm, Em-
  • a microheating element for an electron discharge tube is disclosed as a support of monocrystalline silicon carbide material and a layer of emissive material covering a portion of the surface of the support, whereby said support constitutes the heating element for the cathode.
  • This invention relates to microheating elements, which are to be understood in this specification to mean elements which are not longer than a few millimetres.
  • Such heating elements may especially be used for heating cathodes for small size electron tubes such as used, for example, in mobilophones and transistorised television sets.
  • Heating elements of metal have the disadvantage that their resistivity is comparatively low so that stable elements of a sufliciently high resistance cannot be obtained or with difiiculty only.
  • Semiconductor materials have a higher resistivity. In view of the purpose above referred to, the materials must be able to withstand high temperatures and must also be chemically resistant. This desired combination of properties is found with silicon carbide.
  • micro heating elements could be obtained by grinding olf siliconcarbide crystals, but these are comparatively expensive and diflicult to grind to size. If use is made of considerably cheaper siliconcarbide plates obtained by sintering, then difliculties are encountered in manufacturing large quantities of elements of uniform resistivity. Furthermore, sintered elements of small dimensions are very weak in mechanical respect.
  • the invention relates to a microheating element, especially for cathodes of electron tubes, and is characterized in that the element comprises a filamentary siliconcarbide crystal.
  • Filamentary crystals which are frequently referred to in engineering as whiskers, are to be understood in this specification to mean not only crystals of circular crosssection but also crystals of polygonal cross-section and strip-shaped crystals.
  • Such silicon crystals may, for example, be reproducibly deposited in the required small thickness on the Wall of a space bounded by silicon carbide by recrystallisation and/ or condensation in an inert gas containing lanthanum at temperatures above 2000 C., more particularly between 2200" C. and 2600 C.
  • the whisker crystals are grown on Patented Feb. 10, 1970 a substrate from a gas phase containing silicon and carbon by locally providing finely-divided iron on the substrate and heating to a temperature above 1200 C., during which process silicon and carbon are absorbed from the gas phase by the iron and silicon carbide crystals are deposited on the substrate.
  • heating elements it is important for them to have a positive temperature coeflicient of the resistance. This may in the present example be achieved by carrying out the whisker crystallisation in an atmosphere containing an addition, such as nitrogen.
  • Whiskers of the desired thickness and resistivity can be obtained in the manner described, whereas division of the whiskers in the direction of length provides a large number of heating elements.
  • the siliconcarbide crystal is indicated by 1.
  • Current supply wires 2 may be provided in a simple manner by connecting the ends of a whisker part 1 to a wire of a refactory metal, for example, by means of soldering materal 3 consisting of a gold alloy containing 5% by weight of tantalum.
  • soldering materal 3 consisting of a gold alloy containing 5% by weight of tantalum.
  • Such joints can withstand temperatures up to 1300 C.
  • Suitable soldering materials for higher temperatures may be, for example, nickel containing 5% by Weight of molybdenum (up to 1500 C.) or tungsten (up to 1800" C.).
  • the heating element 1 When using the heating element 1 in a cathode of an electron tube, it is important that the heating circuit should be separated from the emission circuit.
  • this may be achieved in a simple manner by providing an insulating layer 4 which can withstand high temperatures, for example, a layer consisting of oxide or nitride of aluminium or silicon, and applying to this layer a metal layer and a mass 5 of, for example, barium oxide containing an addition of calcium, which emits electrons upon heating.
  • a cathode for an electron discharge tube comprising, a support consisting of monocrystalline silicon carbide, a layer of emissive material covering a portion of the surface of said support, and means for connecting said support to a source of electrical current, whereby said support constitutes a heating element for said cathode 2.
US706897A 1967-03-07 1968-02-20 Microheating elements,more particularly for cathodes of electron tubes Expired - Lifetime US3495120A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL6703548A NL6703548A (ru) 1967-03-07 1967-03-07

Publications (1)

Publication Number Publication Date
US3495120A true US3495120A (en) 1970-02-10

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US706897A Expired - Lifetime US3495120A (en) 1967-03-07 1968-02-20 Microheating elements,more particularly for cathodes of electron tubes

Country Status (7)

Country Link
US (1) US3495120A (ru)
CH (1) CH469351A (ru)
DE (1) DE1639354A1 (ru)
ES (1) ES351239A1 (ru)
FR (1) FR1558677A (ru)
GB (1) GB1222887A (ru)
NL (1) NL6703548A (ru)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5118983A (en) * 1989-03-24 1992-06-02 Mitsubishi Denki Kabushiki Kaisha Thermionic electron source
US5475281A (en) * 1991-02-25 1995-12-12 U.S. Philips Corporation Cathode
US20200066474A1 (en) * 2018-08-22 2020-02-27 Modern Electron, LLC Cathodes with conformal cathode surfaces, vacuum electronic devices with cathodes with conformal cathode surfaces, and methods of manufacturing the same
CN111243917A (zh) * 2020-01-19 2020-06-05 中国科学院电子学研究所 一种阴极热子组件及其制备方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2404128B (en) 2003-07-16 2005-08-24 Kanthal Ltd Silicon carbide furnace heating elements
DE102017101946A1 (de) * 2017-02-01 2018-08-02 Epcos Ag PTC-Heizer mit verringertem Einschaltstrom

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1814759A (en) * 1926-02-10 1931-07-14 Frederick S Mccullough Cathode structure
US3380936A (en) * 1965-10-18 1968-04-30 Matsushita Electric Ind Co Ltd Silicon carbide varistors

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1814759A (en) * 1926-02-10 1931-07-14 Frederick S Mccullough Cathode structure
US3380936A (en) * 1965-10-18 1968-04-30 Matsushita Electric Ind Co Ltd Silicon carbide varistors

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5118983A (en) * 1989-03-24 1992-06-02 Mitsubishi Denki Kabushiki Kaisha Thermionic electron source
US5475281A (en) * 1991-02-25 1995-12-12 U.S. Philips Corporation Cathode
US20200066474A1 (en) * 2018-08-22 2020-02-27 Modern Electron, LLC Cathodes with conformal cathode surfaces, vacuum electronic devices with cathodes with conformal cathode surfaces, and methods of manufacturing the same
CN111243917A (zh) * 2020-01-19 2020-06-05 中国科学院电子学研究所 一种阴极热子组件及其制备方法
CN111243917B (zh) * 2020-01-19 2021-12-07 中国科学院电子学研究所 一种阴极热子组件及其制备方法

Also Published As

Publication number Publication date
ES351239A1 (es) 1969-06-01
NL6703548A (ru) 1968-09-09
FR1558677A (ru) 1969-02-28
GB1222887A (en) 1971-02-17
DE1639354A1 (de) 1970-06-04
CH469351A (de) 1969-02-28

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