EP0056749A2 - 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
EP0056749A2
EP0056749A2 EP82400030A EP82400030A EP0056749A2 EP 0056749 A2 EP0056749 A2 EP 0056749A2 EP 82400030 A EP82400030 A EP 82400030A EP 82400030 A EP82400030 A EP 82400030A EP 0056749 A2 EP0056749 A2 EP 0056749A2
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Prior art keywords
tungsten
mixture
layer
cathode
cathode according
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German (de)
French (fr)
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EP0056749A3 (en
EP0056749B1 (en
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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 1900 and 2000 ° 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 on the graphite surface a material emitting at a lower temperature than tungsten or thoriated tungsten such as hexaborure lanthanum LaB 6 for example.
  • Such a structure makes it possible to obtain electronic emission at a temperature between 1400 and 1500 ° 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.
  • the present invention relates to a direct heating cathode working at the same temperature as the hexa cathode lanthanum boride, but not requiring an intermediate layer between the graphite and the emissive layer.
  • the advantage lies in the elimination of the intermediate layer.
  • the cathode according to the invention comprises a pyrolytic graphite support heated by the Joule effect and an emissive coating composed of a mixture of tungsten and rare earth oxide (lanthanum oxide for example).
  • the emissive layer can be carburized on the surface to improve the emission.
  • This comprises a support 1 of pyrolytic graphite with a thickness of about 200 p, on which a homogeneous layer 2 is deposited, by plasma or by cathode sputtering, or by any other means known to those skilled in the art.
  • a homogeneous layer 2 is deposited, by plasma or by cathode sputtering, or by any other means known to those skilled in the art.
  • the thickness of layer 2 can be between 50 and 100 ⁇ .
  • the tungsten of the emissive layer can be transformed in its surface part 3, over a thickness of 10 to 20 u, into tungsten hemicarb W 2 C. This transformation is carried out in the usual way by heating the cathode in vapors. hydrocarbon at a temperature of around 1800 ° C.
  • tungsten carbide can be codeposited with tungsten and lanthanum oxide, in proportions ranging from 10% to 50% carbide, from 0.5 to 10% lanthanum oxide, the balance being made by tungsten. This variant allows you to choose undermine the carburetion process of tungsten.

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  • Solid Thermionic Cathode (AREA)

Abstract

La cathode selon l'invention comporte un support (1) en graphite pyrolytique et un revêtement émissif (2) constitué d'un mélange de tungstène et d'oxyde de lanthane, le tungstène étant transformé dans sa partie superficielle (3) en hemicarbure de tungstène. L'invention s'applique notamment aux tubes haute fréquence du type triode, tétrode ou pentode.

Figure imgaf001
The cathode according to the invention comprises a support (1) in pyrolytic graphite and an emissive coating (2) consisting of a mixture of tungsten and lanthanum oxide, the tungsten being transformed in its surface part (3) into hemicarbide of tungsten. The invention applies in particular to high frequency tubes of the triode, tetrode or pentode type.
Figure imgaf001

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 1900 et 2000°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-mécaniques 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 LaB6 par exemple. Une telle structure permet d'obtenir l'émission électronique à une température comprise entre 1400 et 1500°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 1900 and 2000 ° 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 on the graphite surface a material emitting at a lower temperature than tungsten or thoriated tungsten such as hexaborure lanthanum LaB 6 for example. Such a structure makes it possible to obtain electronic emission at a temperature between 1400 and 1500 ° 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.

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 hexa cathode lanthanum boride, 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 entrainés sont :

  • - une température de fonctionnement plus faible.
  • - une meilleure tenue mécanique.
Compared to a cathode commonly used in the prior art, the main advantages 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.

La cathode selon l'invention comporte un support en graphite pyrolytique chauffé par effet Joule et un revêtement émissif composé d'un mélange de tungstène et d'oxyde de terres rares (oxyde de lanthane par exemple).The cathode according to the invention comprises a pyrolytic graphite support heated by the Joule effect and an emissive coating composed of a mixture of tungsten and rare earth oxide (lanthanum oxide for example).

La couche émissive peut être carburée en surface pour améliorer l'émission.The emissive layer can be carburized on the surface to improve the emission.

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 200p, 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 100µ.This comprises a support 1 of pyrolytic graphite with a thickness of about 200 p, on which a homogeneous layer 2 is deposited, by plasma or by cathode sputtering, or by any other means known to those skilled in the art. 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 μ.

Le tungstène de la couche émissive peut être transformé dans sa partie superficielle 3, sur une épaisseur de 10 à 20 u, 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 1800° C.The tungsten of the emissive layer can be transformed in its surface part 3, over a thickness of 10 to 20 u, into tungsten hemicarb W 2 C. This transformation is carried out in the usual way by heating the cathode in vapors. hydrocarbon at a temperature of around 1800 ° 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 proportions ranging from 10% to 50% carbide, from 0.5 to 10% lanthanum oxide, the balance being made by tungsten. This variant allows you to choose undermine 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 ton- nes/cm2,
  • c) Frittage à une température de 2000°C environ,
  • d) Dépôt dudit mélange par pulvérisation cathodique sur un support en graphite pyrolytique ,
  • e) chauffage à une température d'environ 1800°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 of the mixture under a pressure of approximately 3 tons / cm 2,
  • 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 1800 ° C. under reduced hydrocarbon pressure.

Claims (6)

1. Cathode à chauffage direct, caractérisée par le fait qu'elle comporte un support (1) découpé en graphite pyrolytique chauffé par effet Joule, et un revêtement émissif constitué d'une couche (2) composée d'un mélange de tungstène et d'oxyde de terres rares.1. Direct heating cathode, characterized in that it comprises a support (1) cut from pyrolytic graphite heated by the Joule effect, and an emissive coating consisting of a layer (2) composed of a mixture of tungsten and d rare earth oxide. 2. Cathode selon la revendication 1, caractérisée en ce que l'oxyde de terres rares constituant la couche (2) est de l'oxyde de lanthane.2. Cathode according to claim 1, characterized in that the rare earth oxide constituting the layer (2) is lanthanum oxide. 3. Cathode selon l'une des revendications 1 ou 2, caractérisée en ce que la partie supérieure (3) de la couche (2) est constituée d'hémicarbure de tungstène.3. Cathode according to one of claims 1 or 2, characterized in that the upper part (3) of the layer (2) consists of tungsten hemicarbide. 4. Cathode selon l'une des revendications 1 à 3, caractérisée en ce que les proportions d'oxyde de terres rares constituant la couche (2) sont comprises entre 0,5% et 10% du poids du mélange.4. Cathode according to one of claims 1 to 3, characterized in that the proportions of rare earth oxide constituting the layer (2) are between 0.5% and 10% of the weight of the mixture. 5. Cathode selon l'une des revendications 1 à 4, caractérisée en ce que l'épaisseur de la couche (2) est comprise entre 50y et 100p.5. Cathode according to one of claims 1 to 4, characterized in that the thickness of the layer (2) is between 50y and 100p. 6. Procédé de fabrication d'une cathode selon l'une des revendications 1 à 5, comportant les étapes successives suivantes : a) Mélange de poudres de tungstène et d'oxyde de terres rares, b) Pressage du mélange sous une pression d'environ 3 ton- nes/cm2, c) Frittage à une température de 2000°C environ, d) dépôt dudit mélange (2) par pulvérisation cathodique sur un support en graphite pyrolytique (1), e) chauffage à une température d'environ 1800° C sous pression réduite d'hydrocarbure. 6. Method for manufacturing a cathode according to one of claims 1 to 5, comprising the following successive steps: a) Mixture of tungsten powders and rare earth oxide, b) pressing of the mixture under a pressure of approximately 3 tons / cm 2, c) Sintering at a temperature of approximately 2000 ° C., d) depositing said mixture (2) by sputtering on a pyrolytic graphite support (1), e) heating to a temperature of approximately 1800 ° C. under reduced hydrocarbon pressure.
EP82400030A 1981-01-16 1982-01-08 Directly heated cathode and method of making it Expired EP0056749B1 (en)

Applications Claiming Priority (2)

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

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

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

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4533852A (en) * 1981-12-08 1985-08-06 U.S. Philips Corporation Method of manufacturing a thermionic cathode and thermionic cathode manufactured by means of said method
EP0637046A1 (en) * 1993-07-29 1995-02-01 Nec Corporation Thermoionic emissive cathode method of fabricating the same thermoionic emissive cathode and electron beam apparatus

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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 OF A X-RAY TUBE
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
CN103998635B (en) * 2011-12-20 2017-01-18 株式会社东芝 Tungsten alloy, and tungsten alloy parts, discharge lamps, emission tubes and magnetrons using the tungsten alloy
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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FR2445605A1 (en) * 1978-12-27 1980-07-25 Thomson Csf DIRECT HEATING CATHODE AND HIGH FREQUENCY ELECTRONIC TUBE COMPRISING SUCH A CATHODE

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4533852A (en) * 1981-12-08 1985-08-06 U.S. Philips Corporation Method of manufacturing a thermionic cathode and thermionic cathode manufactured by means of said method
EP0637046A1 (en) * 1993-07-29 1995-02-01 Nec Corporation Thermoionic emissive cathode method of fabricating the same thermoionic emissive cathode and electron beam apparatus

Also Published As

Publication number Publication date
DE3260969D1 (en) 1984-11-22
EP0056749A3 (en) 1982-08-25
FR2498372A1 (en) 1982-07-23
EP0056749B1 (en) 1984-10-17
FR2498372B1 (en) 1983-07-22
JPS57138744A (en) 1982-08-27
US4577134A (en) 1986-03-18

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