EP0794548A1 - Thermionische Kathode und Verfahren zu ihrer Herstellung - Google Patents

Thermionische Kathode und Verfahren zu ihrer Herstellung Download PDF

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Publication number
EP0794548A1
EP0794548A1 EP97400472A EP97400472A EP0794548A1 EP 0794548 A1 EP0794548 A1 EP 0794548A1 EP 97400472 A EP97400472 A EP 97400472A EP 97400472 A EP97400472 A EP 97400472A EP 0794548 A1 EP0794548 A1 EP 0794548A1
Authority
EP
European Patent Office
Prior art keywords
compound
cathode according
thermionic cathode
rare earth
cathode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97400472A
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English (en)
French (fr)
Other versions
EP0794548B1 (de
Inventor
Guy THOMSON-CSF SCPI Clerc
Jean THOMSON-CSF scpi de Cachard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thomson CSF SA
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Publication date
Application filed by Thomson CSF SA filed Critical Thomson CSF SA
Publication of EP0794548A1 publication Critical patent/EP0794548A1/de
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Publication of EP0794548B1 publication Critical patent/EP0794548B1/de
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Classifications

    • 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
    • H01J1/14—Solid thermionic cathodes characterised by the material

Definitions

  • the invention relates to a thermionic cathode intended in particular for electronic tubes, as well as its manufacturing process.
  • Active vacuum components such as grid tubes and microwave tubes have a cathode whose function is to emit electrons in the vacuum by thermionic effect.
  • the surface of a solid has a potential barrier preventing the escape of electrons that do not have enough energy to pull them out.
  • the extraction work W s is a characteristic of the emissive material.
  • the emissive element is a mixture of alkaline earth oxides (barium, calcium, strontium).
  • the oxides are added either by deposition on the surface of the substrate, or by impregnation in the mass of the substrate.
  • large surface cathodes from 10 to more than 1,500 cm 2 ) it is known to produce them from wires, based on a metal with a high melting point (refractory metal) such as, for example, tungsten.
  • refractory metal such as, for example, tungsten.
  • This cylindrical structure is constituted by a kind of mesh which can be obtained for example by welding at their points of intersection two sets of wires arranged obliquely on a cylinder.
  • Thermionic reaction cathodes use this principle. These cathodes are made of a material comprising a substrate containing at least one refractory metal, a compound of an element making an emitting monolayer (monoatomic layer) and a reducing agent which reacts with the compound to release on the surface the element forming monolayer and having effect of reducing the work of extracting electrons from the surface of the cathode.
  • the emitting monolayer element is kept for the life of the cathode, in the volume of the cathode material as a reserve.
  • the monolayer element is released on the surface by reduction and diffusion and this constantly during the lifetime of the cathode with a reaction speed adapted to the evaporation rate of the emitting monolayer.
  • cathodes with high emissivity, of large surface area from tungsten wires (substrate), the electron emission of which is ensured by the presence of approximately 1% of thorium oxide in the composition of the wire.
  • This oxide is dispersed in the form of grains in the volume of the wire and its introduction takes place at the sintering and reduction of the tungsten oxide powder, raw material for the preparation of the wire.
  • a carburetion process a tungsten carbide sheath is created on the surface of the cathode wire which will allow, during the operation of the tube, the reduction of thorium oxide and the diffusion of thorium towards the surface, covering it of a monoatomic emitting layer.
  • cathodes are characterized by a long useful life of more than 20,000 hours and a high operating temperature of the order of 1,700 ° C.
  • the disadvantage of these cathodes lies in the presence of thorium in their composition.
  • Thorium is a radioactive element with an emission period of 1.4 10 10 years which requires handling precautions when it is in powder form and requires recycling of waste at the end of the tubes' life.
  • the mode of action of these cathodes is based on the release of the metal from the rare earths by reduction of the compound based on rare earths and formation of a monoatomic emitting layer on the surface of the cathode.
  • the electronic emission of these types of cathodes is satisfactory at temperatures of the order of 1500 ° C, which is approximately 200 ° C lower than for thoriated tungsten cathodes.
  • the disadvantage of these cathodes, produced in a material based on rare earth oxides, lies in their short lifespan of the order of a few tens of hours, insufficient compared to the minimum 10,000 hours required.
  • the short lifespan of these cathodes is linked to the lack of stability of this type of material subjected to a high temperature.
  • the substrate of which is made of tungsten and comprising a reducing agent in tungsten carbide
  • the tungsten, its carbide and the residual gases act as reducing agents for the earth oxides rare and the metallic elements formed then have a high diffusion speed and quickly reach the surface of the cathode from where they are evaporated.
  • the stability of barium oxide is obtained in two different ways to take account of the respective operating temperatures of 830 ° C and 1050 ° C.
  • the oxide cathodes operate at 830 ° C. and the stability of the barium oxide is obtained by mixing it with the more thermally stable calcium and strontium oxides under vacuum.
  • the impregnated cathodes operate at 1050 ° C. Stability at this temperature is obtained by adding aluminum oxide to the oxides of calcium, strontium and barium.
  • the proportions of these mixtures can vary depending on the desired characteristics of the cathode: lifetime, emission density, evaporation of barium.
  • the electron emission densities required in the electron tubes require, with cathodes based on rare earth oxides, to operate at high temperatures of the order of 1500 ° C. while having a minimum lifespan of the order 10,000 hrs. Under vacuum, few oxides have sufficient stability to be used in admixture with rare earths.
  • the cathode being characterized in that the compound is chosen from rare earth zirconates, rare earth hafnates, rare earth aluminates, rare earth beryls.
  • the compound is obtained from a mixture zirconium oxide (ZrO 2 ) and neodymium oxide (Nd 2 O 3 ).
  • the free enthalpy of formation is characteristic of the stability of the compound.
  • the proportions of the mixtures must be adapted to the characteristics required of the cathodes such as a very long service life or a high emission density.
  • the compound is cerium aluminate produced from approximately 60% aluminum oxide and approximately 40% cerium oxide.
  • a cerium aluminate powder is obtained from a known sol-gel process which, by precipitation, leads to the formation of a powder with the desired particle size.
  • the rest of the known method for manufacturing the cathode is the same.
  • zirconates, hafnates, aluminates or rare earth berylates for the production of the compound is not limited to the examples cited, the thermal stability under vacuum obtained allowing numerous configurations.
  • Figure 1 shows a cross section of a wire 10, for example round, used for the manufacture of a thermionic cathode according to the invention.
  • Compound 14 is introduced in the initial stages of production of the tungsten ingots used for drawing the wire 10 used for the production of the cathode. It is preferable that the compound 14 remains in low proportions, less than about 2% in the tungsten-based wire to allow the wire drawing and keep over the mechanical properties allowing its shaping during the manufacture of the cathode.
  • zirconate, hafnate, aluminate or berylate compound in the form of a deposit in thin layers on a support ensuring direct heating of the emissive cathode.
  • FIG. 2 represents a cross section of a wire 20, for example round, used for the manufacture of a thermionic cathode according to the invention.
  • Compound 24 is reduced by tungsten carbide during operation of the cathode, covering the surface of wire 20 with a monolayer 28 emitting the metal of compound 24.
  • FIG. 3 represents a portion of a massive cathode which is, for example, in the form of a cylinder, heated by a filament.
  • a substrate 32 of refractory metal has on the surface a reducing agent 36 of carbide of the refractory metal.
  • a compound 34 of an element based on rare earths is deposited in thin layers by cathoforesis on the surface of the reducing agent 36 and migrates into the layer of the reducing agent 36.
  • the compound 34 is reduced by the carbide of the refractory metal covering the surface of the cathode 30 with a monolayer 38 emitting the metal of the compound 34.
  • tungsten substrate for its mechanical properties in the form of wires, in the form of a deposit covering a heating element or in solid form
  • other refractory metals can be used such as molybdenum, tantalum, hafnium, graphite.

Landscapes

  • Solid Thermionic Cathode (AREA)
EP97400472A 1996-03-05 1997-02-28 Thermionische Kathode und Verfahren zu ihrer Herstellung Expired - Lifetime EP0794548B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9602743A FR2745951B1 (fr) 1996-03-05 1996-03-05 Cathode thermoionique et son procede de fabrication
FR9602743 1996-03-05

Publications (2)

Publication Number Publication Date
EP0794548A1 true EP0794548A1 (de) 1997-09-10
EP0794548B1 EP0794548B1 (de) 2003-01-15

Family

ID=9489867

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97400472A Expired - Lifetime EP0794548B1 (de) 1996-03-05 1997-02-28 Thermionische Kathode und Verfahren zu ihrer Herstellung

Country Status (4)

Country Link
US (1) US5828165A (de)
EP (1) EP0794548B1 (de)
DE (1) DE69718363T2 (de)
FR (1) FR2745951B1 (de)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2789800B1 (fr) 1999-02-16 2001-05-11 Thomson Tubes Electroniques Generateur radiofrequence de tres grande puissance
US6238122B1 (en) * 1999-03-01 2001-05-29 Exhaust Etiquette Display device and method therefor
KR100315123B1 (ko) 2000-01-10 2001-11-29 김순택 전자빔 장치용 음극 물질
KR100811719B1 (ko) * 2000-09-19 2008-03-11 코닌클리케 필립스 일렉트로닉스 엔.브이. 음극선관 및 산화물 음극
US20090284124A1 (en) * 2008-04-22 2009-11-19 Wolfgang Kutschera Cathode composed of materials with different electron works functions
US10074505B2 (en) * 2016-01-14 2018-09-11 Wisconsin Alumni Research Foundation Perovskites as ultra-low work function electron emission materials
CN108448075B (zh) * 2018-02-05 2020-09-25 河南师范大学 一种锂离子电池锰基复合正极材料及其制备方法
CN115954245A (zh) * 2022-11-30 2023-04-11 朱惠冲 卫星通信高频电磁阴极组件加工工艺

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB182817A (en) * 1921-07-11 1923-08-09 Drahtlose Telegraphie Gmbh Improvements in the cathodes of electric discharge tubes
US1794298A (en) * 1926-09-21 1931-02-24 Gen Electric Thermionic cathode
DE581423C (de) * 1926-09-24 1933-07-27 Aeg Oxydkathode fuer Entladungsgefaesse
US2218381A (en) * 1936-09-03 1940-10-15 Gen Electric Thermionic cathode
EP0210805A2 (de) * 1985-07-19 1987-02-04 Mitsubishi Denki Kabushiki Kaisha Kathode für Elektronenröhre

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB182217A (en) * 1921-03-30 1922-06-30 Karl Rosak Improvements in or relating to grinding machines
DE3148441A1 (de) * 1981-12-08 1983-07-21 Philips Patentverwaltung Gmbh, 2000 Hamburg Verfahren zur herstellung einer thermionischen kathode
JPS58154131A (ja) * 1982-03-10 1983-09-13 Hitachi Ltd 含浸形陰極
NL8803047A (nl) * 1988-12-13 1990-07-02 Philips Nv Oxydekathode.

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB182817A (en) * 1921-07-11 1923-08-09 Drahtlose Telegraphie Gmbh Improvements in the cathodes of electric discharge tubes
US1794298A (en) * 1926-09-21 1931-02-24 Gen Electric Thermionic cathode
DE581423C (de) * 1926-09-24 1933-07-27 Aeg Oxydkathode fuer Entladungsgefaesse
US2218381A (en) * 1936-09-03 1940-10-15 Gen Electric Thermionic cathode
EP0210805A2 (de) * 1985-07-19 1987-02-04 Mitsubishi Denki Kabushiki Kaisha Kathode für Elektronenröhre

Also Published As

Publication number Publication date
FR2745951B1 (fr) 1998-06-05
US5828165A (en) 1998-10-27
DE69718363D1 (de) 2003-02-20
FR2745951A1 (fr) 1997-09-12
EP0794548B1 (de) 2003-01-15
DE69718363T2 (de) 2003-10-16

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