EP0056749B1 - Directly heated cathode and method of making it - Google Patents

Directly heated cathode and method of making it Download PDF

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Publication number
EP0056749B1
EP0056749B1 EP82400030A EP82400030A EP0056749B1 EP 0056749 B1 EP0056749 B1 EP 0056749B1 EP 82400030 A EP82400030 A EP 82400030A EP 82400030 A EP82400030 A EP 82400030A EP 0056749 B1 EP0056749 B1 EP 0056749B1
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EP
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Prior art keywords
tungsten
oxide
cathode
mixture
rare earths
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EP82400030A
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German (de)
French (fr)
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EP0056749A3 (en
EP0056749A2 (en
Inventor
Guy Clerc
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Thales SA
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Thomson CSF SA
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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
    • H01J1/14—Solid thermionic cathodes characterised by the material

Definitions

  • the subject of the present invention is a cathode for a high frequency electronic tube, and more particularly a thermoelectronic emission cathode with direct heating.
  • the cathodes are generally produced from tungsten or thoriated tungsten wires for reasons of thermoelectronic emissivity, the operating temperature is then between 1,900 and 2,000 ° K.
  • Mechanical problems then arise due to the difference in thermal behavior of the materials, problems imperfectly resolved by expensive mechanical assemblies. It has been proposed to avoid thermo-mechanical problems inside the tube while ensuring good thermo-electronic emissivity by introducing direct heating from a pyrolytic graphite support and by depositing a material on the graphite surface. emitting at a lower temperature than tungsten or thoriated tungsten such as lanthanum hexaboride La B 6 for example.
  • Such a structure makes it possible to obtain electronic emission at a temperature between 1,400 and 1,500 ° C.
  • emissive materials such as lanthanum hexaboride is their high chemical activity vis-à-vis hot graphite, which can lead to the destruction of the cathode.
  • Application FR-A-2,445,605 discloses a direct heating cathode comprising a pyrolytic graphite support heated by the Joule effect and an emissive layer based on lanthanum hexaboride which is separated from the support by an intermediate layer.
  • the present invention relates to a direct heating cathode working at the same temperature as the lanthanum hexaboride cathode, but not requiring an intermediate layer between the graphite and the emissive layer.
  • the advantage lies in the elimination of the intermediate layer.
  • the present invention relates to a direct heating cathode comprising a support cut out of pyrolytic graphite heated by the Joule effect and an emissive coating, characterized in that this coating consists of an emissive layer composed of a mixture of tungsten and rare earth oxide.
  • the present invention relates to a direct heating cathode comprising a support cut out of pyrolytic graphite heated by the Joule effect and an emissive coating, characterized in that this coating consists of an emissive layer and a surface layer, the emissive layer being composed of a mixture of tungsten and rare earth oxide and the surface layer consisting of tungsten hemicarbide.
  • the present invention relates to a direct heating cathode comprising a support cut out of pyrolytic graphite heated by the Joule effect and an emissive coating, characterized in that this coating consists of an emissive layer composed of a mixture of tungsten , rare earth oxide and tungsten carbide.
  • This comprises a support 1 of pyrolytic graphite with a thickness of approximately 200 ⁇ m, on which is deposited, by plasma or by cathode sputtering, or by any other means known to those skilled in the art, a homogeneous layer 2 of a mixture of tungsten and lanthanum oxide, the latter being in proportions of between 0.5% and 10%, the thickness of layer 2 can be between 50 and 100 ⁇ m.
  • the tungsten of the emissive layer can be transformed in its surface part 3, over a thickness of 10 to 20 k tm, into tungsten hemicarb W 2 C. This transformation is carried out in the usual way by heating the cathode in vapors of hydrocarbon at a temperature of about 1,800 ° C.
  • tungsten carbide can be codeposited with tungsten and lanthanum oxide, in a proportion ranging from 10% to 50% carbide, 0.5 to 10% lanthanum oxide, the balance being made by tungsten. This variant eliminates the carburetion process of tungsten.

Description

La présente invention a pour objet une cathode pour tube électronique haute fréquence, et plus particulièrement une cathode à émission thermo-électronique à chauffage direct.The subject of the present invention is a cathode for a high frequency electronic tube, and more particularly a thermoelectronic emission cathode with direct heating.

Dans les tubes électroniques haute fréquence du type triode, tétrode ou pentode, qui comportent une cathode, une anode et une, deux ou trois grilles, il est avantageux de réaliser les grilles en graphite pyrolytique, matériau connu pour ses qualités mécaniques et thermiques.In high frequency electronic tubes of the triode, tetrode or pentode type, which comprise a cathode, an anode and one, two or three grids, it is advantageous to produce the grids in pyrolytic graphite, a material known for its mechanical and thermal qualities.

Toutefois, dans ces mêmes tubes les cathodes sont généralement réalisées en fils de tungstène ou de tungstène thorié pour des raisons d'émissivité thermo-électronique, la température de fonctionnement est alors comprise entre 1 900 et 2 000 °K. Il se pose alors, en fonctionnement, des problèmes mécaniques du fait de la différence de comportement thermique des matériaux, problèmes résolus imparfaitement par des montages mécaniques coûteux. On a proposé d'éviter les problèmes thermo-mécanique à l'intérieur du tube tout en assurant une bonne émissivité thermo-électronique en introduisant un chauffage direct à partir d'un support en graphite pyrolytique et en déposant à la surface du graphite un matériau émettant à plus basse température que le tungstène ou le tungstène thorié tel l'hexaborure de lanthane La B6 par exemple. Une telle structure permet d'obtenir l'émission électronique à une température comprise entre 1 400 et 1 500 °C. Toutefois, un inconvénient de matériaux émissifs tels l'hexaborure de Lanthane est leur grande activité chimique vis-à-vis du graphite à chaud, qui peut conduire à la destruction de la cathode. On est contraint de ce fait à introduire une couche intermédiaire entre le graphite et l'hexaborure de Lanthane formant barrière de diffusion entre ces deux matériaux.However, in these same tubes the cathodes are generally produced from tungsten or thoriated tungsten wires for reasons of thermoelectronic emissivity, the operating temperature is then between 1,900 and 2,000 ° K. Mechanical problems then arise due to the difference in thermal behavior of the materials, problems imperfectly resolved by expensive mechanical assemblies. It has been proposed to avoid thermo-mechanical problems inside the tube while ensuring good thermo-electronic emissivity by introducing direct heating from a pyrolytic graphite support and by depositing a material on the graphite surface. emitting at a lower temperature than tungsten or thoriated tungsten such as lanthanum hexaboride La B 6 for example. Such a structure makes it possible to obtain electronic emission at a temperature between 1,400 and 1,500 ° C. However, a drawback of emissive materials such as lanthanum hexaboride is their high chemical activity vis-à-vis hot graphite, which can lead to the destruction of the cathode. We are therefore forced to introduce an intermediate layer between graphite and lanthanum hexaboride forming a diffusion barrier between these two materials.

Par la demande FR-A-2.445.605, on connaît une cathode à chauffage direct comportant un support en graphite pyrolytique chauffé par effet Joule et une couche émissive à base d'hexaborure de lanthane qui est séparée du support par une couche intermédiaire.Application FR-A-2,445,605 discloses a direct heating cathode comprising a pyrolytic graphite support heated by the Joule effect and an emissive layer based on lanthanum hexaboride which is separated from the support by an intermediate layer.

Par la demande de brevet FR-A-2.237.303 on connaît en particulier les deux modes de réalisation suivants :

  • a) une cathode chaude constituée d'un substrat contenant au moins un métal à point de fusion élevé et d'une substance active comportant de l'oxyde de lanthane, et un réducteur formé au moins en partie d'un carbure d'un métal à point de fusion élevé que la substance du substrat contient (voir revendications 1 à 3) ;
  • b) une cathode chaude constituée d'une plaquette formée d'un mélange de tungstène et d'oxyde de lanthane, cette plaquette étant soumise à une carburation de surface, dans un mélange de benzène et d'hydrogène (voir page 4, ligne 6).
The following two embodiments are known in particular from patent application FR-A-2,237,303:
  • a) a hot cathode consisting of a substrate containing at least one metal with a high melting point and an active substance comprising lanthanum oxide, and a reducing agent formed at least in part from a carbide of a metal high melting point that the substrate substance contains (see claims 1 to 3);
  • b) a hot cathode consisting of a plate formed of a mixture of tungsten and lanthanum oxide, this plate being subjected to surface carburetion, in a mixture of benzene and hydrogen (see page 4, line 6 ).

La présente invention a pour objet une cathode à chauffage direct travaillant à la même température que la cathode en hexaborure de lanthane, mais ne nécessitant pas de couche intermédiaire entre le graphite et la couche émissive.The present invention relates to a direct heating cathode working at the same temperature as the lanthanum hexaboride cathode, but not requiring an intermediate layer between the graphite and the emissive layer.

Par rapport à une cathode couramment utilisée dans l'art antérieur, les principaux avantages entraînés sont :

  • - une température de fonctionnement plus faible ;
  • - une meilleure tenue mécanique.
Compared to a cathode commonly used in the prior art, the main advantages entailed are:
  • - a lower operating temperature;
  • - better mechanical strength.

Par rapport à une cathode en hexaborure de lanthane, l'avantage réside dans la suppression de la couche intermédiaire.Compared to a lanthanum hexaboride cathode, the advantage lies in the elimination of the intermediate layer.

Selon la revendication 1, la présente invention concerne une cathode à chauffage direct comportant un support découpé en graphite pyrolytique chauffé par effet Joule et un revêtement émissif, caractérisée en ce que ce revêtement est constitué d'une couche émissive composée d'un mélange de tungstène et d'oxyde de terres rares.According to claim 1, the present invention relates to a direct heating cathode comprising a support cut out of pyrolytic graphite heated by the Joule effect and an emissive coating, characterized in that this coating consists of an emissive layer composed of a mixture of tungsten and rare earth oxide.

Selon la revendication 2, la présente invention concerne une cathode à chauffage direct comportant un support découpé en graphite pyrolytique chauffé par effet Joule et un revêtement émissif, caractérisée en ce que ce revêtement est constitué d'une couche émissive et d'une couche superficielle, la couche émissive étant composée d'un mélange de tungstène et d'oxyde de terres rares et la couche superficielle étant constituée d'hémicarbure de tungstène.According to claim 2, the present invention relates to a direct heating cathode comprising a support cut out of pyrolytic graphite heated by the Joule effect and an emissive coating, characterized in that this coating consists of an emissive layer and a surface layer, the emissive layer being composed of a mixture of tungsten and rare earth oxide and the surface layer consisting of tungsten hemicarbide.

Selon la revendication 7, la présente invention concerne une cathode à chauffage direct comportant un support découpé en graphite pyrolytique chauffé par effet Joule et un revêtement émissif, caractérisée en ce que ce revêtement est constitué d'une couche émissive composée d'un mélange de tungstène, d'oxyde de terres rares et de carbure de tungstène.According to claim 7, the present invention relates to a direct heating cathode comprising a support cut out of pyrolytic graphite heated by the Joule effect and an emissive coating, characterized in that this coating consists of an emissive layer composed of a mixture of tungsten , rare earth oxide and tungsten carbide.

D'autres objets, caractéristiques et résultats de l'invention ressortiront de la description suivante annexée par la figure unique qui représente une vue en coupe d'un mode de réalisation de la cathode selon l'invention.Other objects, characteristics and results of the invention will emerge from the following description appended by the single figure which represents a sectional view of an embodiment of the cathode according to the invention.

Celle-ci comporte un support 1 en graphite pyrolytique d'une épaisseur d'environ 200 ¡.Lm, sur lequel on dépose, par plasma ou par pulvérisation cathodique, ou par tout autre moyen connu de l'homme de l'art, une couche homogène 2 d'un mélange de tungstène et d'oxyde de lanthane ce dernier étant dans des proportions comprises entre 0,5 % et 10 %, l'épaisseur de la couche 2 peut être comprise entre 50 et 100 ¡.Lm.This comprises a support 1 of pyrolytic graphite with a thickness of approximately 200 μm, on which is deposited, by plasma or by cathode sputtering, or by any other means known to those skilled in the art, a homogeneous layer 2 of a mixture of tungsten and lanthanum oxide, the latter being in proportions of between 0.5% and 10%, the thickness of layer 2 can be between 50 and 100 µm.

Le tungstène de la couche émissive peut être transformé dans sa partie superficielle 3, sur une épaisseur de 10 à 20 ktm, en hémicarbure de tungstène W2C. Cette transformation est réalisée d'une manière usuelle par chauffage de la cathode dans des vapeurs d'hydrocarbure à une température d'environ 1 800 °C.The tungsten of the emissive layer can be transformed in its surface part 3, over a thickness of 10 to 20 k tm, into tungsten hemicarb W 2 C. This transformation is carried out in the usual way by heating the cathode in vapors of hydrocarbon at a temperature of about 1,800 ° C.

Dans une autre variante, le carbure de tungstène peut être codéposé avec le tungstène et l'oxyde de lanthane, en proportion allant de 10 % à 50% de carbure, de 0,5 à 10% d'oxyde de lanthane, la balance étant faite par le tungstène. Cette variante permet d'éliminer le processus de carburation du tungstène.In another variant, tungsten carbide can be codeposited with tungsten and lanthanum oxide, in a proportion ranging from 10% to 50% carbide, 0.5 to 10% lanthanum oxide, the balance being made by tungsten. This variant eliminates the carburetion process of tungsten.

La cathode selon l'invention peut être obtenue par un procédé comportant les étapes suivantes :

  • a) mélange de poudres de tungstène et d'oxyde de terres rares ;
  • b) pressage du mélange sous une pression d'environ 3 000 bars ;
  • c) frittage à une température de 2 000 °C environ ;
  • d) dépôt dudit mélange par pulvérisation cathodique sur un support en graphite pyrolytique ;
  • e) chauffage à une température d'environ 1 800 °C sous pression réduite d'hydrocarbure.
The cathode according to the invention can be obtained by a process comprising the following steps:
  • a) mixture of tungsten powders and rare earth oxide;
  • b) pressing the mixture under a pressure of approximately 3000 bars;
  • c) sintering at a temperature of approximately 2000 ° C;
  • d) depositing said mixture by sputtering on a pyrolytic graphite support;
  • e) heating to a temperature of approximately 1,800 ° C. under reduced hydrocarbon pressure.

Claims (10)

1. Direct heating cathode comprising a carrier (1) cut from pyrolytic graphite and heated by the Joule effect, and an emissive coating, characterized in that this coating is formed of an emissive layer (2) composed of a mixture of tungsten and an oxide of rare earths.
2. Direct heating cathode comprising a carrier
(1) cut from pyrolytic graphite heated by Joule effect, and an emissive coating, characterized in that this coating is formed of an emissive layer (2) and a superficial layer (3), the emissive layer (2) being composed of a mixture of tungsten and an oxide of rare earths, while the superficial layer (3) is formed of tungsten hemicarbide.
3. Cathode according to claim 1 or 2, characterized in that the oxide of rare earths forming the emissive layer (2) is lanthanum oxide.
4. Cathode according to any of claims 1 to 3, characterized in that the proportions of the rare earths oxide forming the emissive layer (2) are comprised between 0.5 % and 10 % of the weight of the mixture.
5. Cathode according to any of claims 1 to 4, characterized in that the thickness of the emissive layer (2) is comprised between 50 µm and 100 µm.
6. Method of producing a cathode according to any of claims 2 or 3 to 5 depending on claim 2, comprising the following successive steps :
a) mixing powders of tungsten and an oxide of rare earths ;
b) compressing the mixture at a pressure of about 3 000 bars ;
c) sintering at a temperature of about 2 000 °C ;
d) deposition of said mixture (2) on a carrier (1) of pyrolytic graphite by cathode sputtering ;
e) heating to a temperature of about 1 800 °C under reduced hydrocarbone pressure.
7. Direct heating cathode comprising a carrier (1) cut from pyrolytic graphite heated by Joule effect, and an emissive coating, characterized in that this coating is formed of an emissive layer (2) composed of a mixture of tungsten, an oxide of rare earths and tungsten carbide.
8. Cathode according to claim 7, characterized in that the oxide of rare earths is lanthanum oxide.
9. Cathode according to any of claims 7 and 8, characterized in that the proportions of the emissive layer (2) are from 10% to 50% of tungsten carbide and 0.5 to 10 % of rare earths oxide, the balance being made up by the tungsten.
EP82400030A 1981-01-16 1982-01-08 Directly heated cathode and method of making it Expired EP0056749B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8100782A FR2498372A1 (en) 1981-01-16 1981-01-16 DIRECT HEATING CATHODE, METHOD FOR MANUFACTURING SAME, AND ELECTRONIC TUBE INCLUDING SUCH A CATHODE
FR8100782 1981-01-16

Publications (3)

Publication Number Publication Date
EP0056749A2 EP0056749A2 (en) 1982-07-28
EP0056749A3 EP0056749A3 (en) 1982-08-25
EP0056749B1 true EP0056749B1 (en) 1984-10-17

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EP82400030A Expired EP0056749B1 (en) 1981-01-16 1982-01-08 Directly heated cathode and method of making it

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US (1) US4577134A (en)
EP (1) EP0056749B1 (en)
JP (1) JPS57138744A (en)
DE (1) DE3260969D1 (en)
FR (1) FR2498372A1 (en)

Families Citing this family (10)

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DE3148441A1 (en) * 1981-12-08 1983-07-21 Philips Patentverwaltung Gmbh, 2000 Hamburg METHOD FOR PRODUCING A THERMIONIC CATHODE
US4810926A (en) * 1987-07-13 1989-03-07 Syracuse University Impregnated thermionic cathode
DE4026300A1 (en) * 1990-08-20 1992-02-27 Siemens Ag Electron emitter for X=ray tube - is of material contg. rare earth element covering support layer of large flat surface withstanding vibration
DE69409306T2 (en) * 1993-07-29 1998-07-30 Nec Corp Thermally emitting cathode, manufacturing method of such a thermally emitting cathode and electron beam device
FR2733856B1 (en) * 1995-05-05 1997-08-29 Thomson Tubes Electroniques CATHODE FOR GRID ELECTRON CANON, GRID TO BE ASSOCIATED WITH SUCH A CATHODE AND ELECTRON CANON INCLUDING SUCH CATHODE
FR2775118B1 (en) 1998-02-13 2000-05-05 Thomson Tubes Electroniques GRID FOR ELECTRONIC TUBE WITH AXIAL BEAM WITH IMPROVED PERFORMANCE
FR2789800B1 (en) 1999-02-16 2001-05-11 Thomson Tubes Electroniques VERY HIGH POWER RADIO FREQUENCY GENERATOR
DE102008020187A1 (en) * 2008-04-22 2009-10-29 Siemens Aktiengesellschaft Cathode, has flat emitter emitting electrons, and emission layer with circular cross section arranged on emitter, where material of emission layer has lower emission function than that of material of emitter
JP5881741B2 (en) 2011-12-20 2016-03-09 株式会社東芝 Tungsten alloy and tungsten alloy parts, discharge lamp, transmitter tube and magnetron using the same
US20170330725A1 (en) * 2016-05-13 2017-11-16 Axcelis Technologies, Inc. Lanthanated tungsten ion source and beamline components

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US3389977A (en) * 1964-08-05 1968-06-25 Texas Instruments Inc Tungsten carbide coated article of manufacture
US3719856A (en) * 1971-05-19 1973-03-06 O Koppius Impregnants for dispenser cathodes
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Also Published As

Publication number Publication date
JPS57138744A (en) 1982-08-27
EP0056749A3 (en) 1982-08-25
FR2498372A1 (en) 1982-07-23
EP0056749A2 (en) 1982-07-28
FR2498372B1 (en) 1983-07-22
US4577134A (en) 1986-03-18
DE3260969D1 (en) 1984-11-22

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