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EP0516503A1 - Oxide cathode and method of its manufacture - Google Patents

Oxide cathode and method of its manufacture Download PDF

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Publication number
EP0516503A1
EP0516503A1 EP92401339A EP92401339A EP0516503A1 EP 0516503 A1 EP0516503 A1 EP 0516503A1 EP 92401339 A EP92401339 A EP 92401339A EP 92401339 A EP92401339 A EP 92401339A EP 0516503 A1 EP0516503 A1 EP 0516503A1
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EP
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Prior art keywords
oxide
alkaline earth
oxides
scandium
cathode according
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EP92401339A
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German (de)
French (fr)
Inventor
Arvind Shroff
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Thales Electron Devices SA
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Thomson Tubes Electroniques
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/04—Manufacture of electrodes or electrode systems of thermionic cathodes
    • H01J9/042—Manufacture, activation of the emissive part
    • 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
    • H01J1/142—Solid thermionic cathodes characterised by the material with alkaline-earth metal oxides, or such oxides used in conjunction with reducing agents, as an emissive material

Definitions

  • the present invention relates to oxide cathodes. These cathodes are used in particular in grid microwave tubes, in tubes with longitudinal interaction, in magnetrons or in cathode ray tubes.
  • the invention also relates to a method of manufacturing such a cathode.
  • These cathodes which have been known for a long time, comprise a support generally made of nickel, covered with thermoemissive material.
  • This thermoemissive material is a mixture of alkaline earth metal oxides.
  • These cathodes are produced by brushing the support with a suspension of carbonates of alkaline earth metals in an organic binder. The painting can be done with a brush or a spray gun. The thickness deposited is of the order of 40 to 50 micrometers. Often double or triple carbonates are used, for example barium and calcium carbonates or barium, calcium and strontium carbonates.
  • the binder is often collodion dissolved in butyl acetate.
  • the cathode is then placed under vacuum and activated by heating it.
  • the carbonates are transformed into oxides.
  • a poorly conductive layer is formed, known as an interface layer.
  • This layer increases the cathode resistance, causes a drop in voltage between the cathode and the anode and significant dissipation of energy. This layer evolves over time and its disadvantages are amplified.
  • thermoemissive material is a mixture of alkaline earth metal oxides with scandium oxide.
  • the level of scandium oxide is relatively high. They are made by brushing the support with a suspension of carbonates of alkaline earth metals and scandium oxide in an organic binder and then activating the cathode. But there is the appearance of detachments between the oxide layer and the support. These detachments disrupt the emission of electrons. They are detrimental to the reliability of the cathode and reduce its lifespan.
  • the present invention aims to remedy these drawbacks. To this end, it proposes a cathode comprising a support covered with a layer of one or more oxides of alkaline earth metals. This layer is covered with a mixture of one or more oxides of alkaline earth metals and scandium oxide.
  • the separation zones are removed and the interface layer, without completely disappearing, has a reduced thickness and is blocked in its evolution.
  • the mixture of alkaline earth metal oxides and scandium oxide contains a weight content of scandium oxide less than or equal to 5%, without however being zero.
  • the mixture of alkaline earth metal oxides and scandium oxide can be formed from a succession of layers, two successive layers containing a different content by weight of scandium oxide.
  • the successive layers may contain an increasing rate of scandium oxide by weight the further away from the support or on the contrary a decreasing rate.
  • Double or triple oxides of alkaline earth metals can be used, for example, barium and calcium oxides, or barium, calcium and strontium oxides.
  • a nickel support is chosen.
  • the thickness of the layer of alkaline earth metal oxides is substantially equal to the thickness of the mixture of alkaline earth metal oxides and scandium oxide.
  • the suspension of alkaline earth metal carbonates and scandium carbonate can be deposited in several successive stages, using several projection devices, so as to form a succession of layers.
  • the organic binder can be collodion dissolved in butyl acetate.
  • the cathode shown is a cathode for a tube with longitudinal interaction. This example is not limitative. The invention is not limited to this type of cathode.
  • a cathode according to the invention could be cylindrical and serve in a magnetron or have a substantially planar emissive surface and serve in a cathode ray tube.
  • FIG 1 we see a concave support 1, cup-shaped, mounted on a cylindrical skirt 2.
  • the support 1 and the skirt 2 are metallic, in nickel for example.
  • a heating filament 3 is held in the skirt 2.
  • the support instead of being concave could be substantially planar.
  • the concave part of the support 1 forms an emissive face of the cathode.
  • the support 1 is covered with a layer 4 of thermoemissive material.
  • the filament 3 heats the emissive material, which produces, from a certain temperature, the emission of electrons.
  • the thermoemissive material is generally a compound of alkaline earth metal oxides. Double oxides are often used: barium oxide and calcium oxide or triple oxides: barium oxide, calcium oxide and strontium oxide.
  • the thermosemissive material is deposited from a suspension of carbonates of alkaline earth metals (barium and calcium or barium, calcium and strontium) in an organic binder. This deposit is done by brushing with a brush or by spraying with a gun. Collodion dissolved in butyl acetate is often chosen as the organic binder.
  • the thickness of the deposited layer 4 is of the order of 40 to 50 micrometers.
  • the cathode is activated by heating it under vacuum and the carbonates are transformed into oxides.
  • the weight ratios of the various oxides are of the order of 55% barium oxide, 35% strontium oxide and 10% calcium oxide.
  • FIG. 2 represents an oxide cathode according to the invention.
  • thermoemissive material comprises, from the support 3, a layer 20 of one or more oxides of alkaline earth metals.
  • This layer 20 can be of the same nature as above, but its thickness is only 10 to 20 micrometers.
  • This layer 20 is covered with a mixture of one or more oxides of alkaline earth metals and scandium oxide. In practice, to obtain a satisfactory emission of electrons, double or triple alkaline earth metal oxides are used. In the following description, we keep this hypothesis.
  • the mixture is formed of a single layer 21. The thickness of the layer 21 is substantially equal to that of the layer 20. It may well be envisaged that the mixture is formed of a succession of layers. This variant is shown in Figure 3.
  • the content by weight of scandium oxide is preferably less than or equal to 5%, without however being zero.
  • the alkaline earth metal oxides can be, as before, barium and calcium oxides or barium, calcium and strontium oxides.
  • layers 20 and 21 may contain the same alkaline earth metal oxides.
  • the layer 20 can be in double oxides and the layer 21 in triple oxides.
  • the weight ratio of alkaline earth metal oxides of layer 21 is greater than or equal to 95%.
  • the mixture of alkaline earth metal oxides and oxide of scandium can be formed from a succession of layers 31,32,33.
  • the content by weight of scandium oxide can vary from one layer to another while preferably remaining less than or equal to 5%.
  • the first deposited layer 31 may contain 1% of scandium oxide, the second 32 3% and the third 33 5 %. This is just an example.
  • the weight content of scandium oxide can decrease the further one moves away from the support 1.
  • Other distributions are still possible, for example, layers rich in scandium oxide can be alternated with layers poor in oxide of scandium.
  • the weight content of scandium oxide contained in the poor layers will be, for example, around 1% and the weight content contained in the rich layers around 5%.
  • the thickness of the successive layers is chosen so that the total thickness of the heat-emissive material is of the order of 40 to 50 micrometers.
  • the thickness of the layer of alkaline earth metal oxides will be substantially equal to the thickness of the mixture of alkaline earth metal oxides and scandium oxide.
  • the presence of the layer 20 of alkaline earth metal oxides directly on the support 1 promotes good bonding between the oxides and the support.
  • a relatively thin interface layer is formed, but its development is blocked by the mixture of alkaline earth metal oxides and scandium oxide.
  • the disadvantages associated with the detachment of oxides containing a relatively high level of scandium oxide are eliminated while the disadvantages linked to the interface layer are limited.
  • Figures 4a and 4b show a part of an installation making it possible to produce cathodes by the process of the invention.
  • a number of metal supports 41 are placed in a suction hood 40.
  • a first projection device 42 such as a compressed air paint gun
  • a suspension of carbonates of alkaline earth metals in an organic binder is deposited.
  • the first layer 43 is scandium-free.
  • a second projection device 44 a suspension of alkaline earth metal carbonates and scandium carbonate is deposited in the organic binder.
  • a second layer 45 is formed.
  • the binder can be collodion dissolved in butyl acetate.
  • the second layer 45 contains scandium.
  • the cathode comprises a succession of layers of oxides of alkaline earth metals and of scandium oxide, as shown in FIG. 3, it is possible to use several pistols 44, each projecting a suspension having a weight ratio of suitable scandium. We thus obtain a succession of layers with scandium. After these sprays, the cathode is placed under vacuum and activated by heating it, the carbonates are transformed into oxides.
  • the oxide cathodes according to the invention have a long service life and a high current density.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)

Abstract

The present invention relates to oxide-containing cathodes comprising, on the support (1), a layer (20) of one or more oxides of alkaline earth metals, covered with a mixture (21) of one or more oxides of alkaline earth metals and of scandium oxide. Preferably, the mixture of oxides of alkaline earth metals and of scandium oxide contains a proportion by weight of scandium oxide less than or equal to 5%, without however being zero. Moreover, the mixture of oxides of alkaline earth metals and of scandium oxide may be formed by a succession of layers, two successive layers containing a different proportion by weight of scandium oxide. Application to oxide-containing cathodes having a long life and a high current density. <IMAGE>

Description

La présente invention concerne les cathodes à oxydes. Ces cathodes sont notamment utilisées dans des tubes hyperfréquences à grille, dans des tubes à interaction longitudinale, dans des magnétrons ou dans des tubes à rayons cathodiques.The present invention relates to oxide cathodes. These cathodes are used in particular in grid microwave tubes, in tubes with longitudinal interaction, in magnetrons or in cathode ray tubes.

L'invention concerne aussi un procédé de fabrication d'une telle cathode. Ces cathodes, connues depuis longtemps comportent un support généralement en nickel, recouvert de matériau thermoémissif. Ce matériau thermoémissif est un mélange d'oxydes de métaux alcalino-terreux. Ces cathodes sont réalisées en badigeonnant le support avec une suspension de carbonates de métaux alcalino-terreux dans un liant organique. Le badigeonnage peut se faire au pinceau ou au pistolet. L'épaisseur déposée est de l'ordre de 40 à 50 micromètres. On utilise bien souvent des carbonates doubles ou triples, par exemple des carbonates de barium et de calcium ou des carbonates de barium, de calcium et de strontium. Le liant est souvent du collodion dissous dans de l'acétate de butyle.The invention also relates to a method of manufacturing such a cathode. These cathodes, which have been known for a long time, comprise a support generally made of nickel, covered with thermoemissive material. This thermoemissive material is a mixture of alkaline earth metal oxides. These cathodes are produced by brushing the support with a suspension of carbonates of alkaline earth metals in an organic binder. The painting can be done with a brush or a spray gun. The thickness deposited is of the order of 40 to 50 micrometers. Often double or triple carbonates are used, for example barium and calcium carbonates or barium, calcium and strontium carbonates. The binder is often collodion dissolved in butyl acetate.

La cathode est ensuite placée sous vide et activée en la chauffant. Les carbonates se transforment en oxydes.The cathode is then placed under vacuum and activated by heating it. The carbonates are transformed into oxides.

Lors de cette transformation les composés qui apparaissent réagissent avec les impuretés nécessairement présentes dans le métal du support. Il se forme une couche peu conductrice, connue sous le nom de couche d'interface. Cette couche augmente la rèsistance de cathode, provoque une chute de tension entre la cathode et l'anode et une importante dissipation d'énergie. Cette couche évolue au cours du temps et ses inconvénients s'amplifient.During this transformation, the compounds which appear react with the impurities necessarily present in the metal of the support. A poorly conductive layer is formed, known as an interface layer. This layer increases the cathode resistance, causes a drop in voltage between the cathode and the anode and significant dissipation of energy. This layer evolves over time and its disadvantages are amplified.

D'autres cathodes à oxydes sont aussi connues. Le matériau thermoémissif est un mélange d'oxydes de métaux alcalino-terreux avec de l'oxyde de scandium. Le taux d'oxyde de scandium est relativement élevé. Elles sont réalisées en badigeonnant le support avec une suspension de carbonates de métaux alcalino-terreux et d'oxyde de scandium dans un liant organique puis en activant la cathode. Mais il y a apparition de décollements entre la couche d'oxydes et le support. Ces décollements perturbent l'émission d'électrons. Ils sont préjudiciables à la fiabilité de la cathode et réduisent sa durée de vie.Other oxide cathodes are also known. The thermoemissive material is a mixture of alkaline earth metal oxides with scandium oxide. The level of scandium oxide is relatively high. They are made by brushing the support with a suspension of carbonates of alkaline earth metals and scandium oxide in an organic binder and then activating the cathode. But there is the appearance of detachments between the oxide layer and the support. These detachments disrupt the emission of electrons. They are detrimental to the reliability of the cathode and reduce its lifespan.

La présente invention vise à remédier à ces inconvénients. A cette fin, elle propose une cathode comportant un support recouvert d'une couche d'un ou plusieurs oxydes de métaux alcalino-terreux. Cette couche est recouverte d'un mélange d'un ou plusieurs oxydes de métaux alcalino-terreux et d'oxyde de scandium.The present invention aims to remedy these drawbacks. To this end, it proposes a cathode comprising a support covered with a layer of one or more oxides of alkaline earth metals. This layer is covered with a mixture of one or more oxides of alkaline earth metals and scandium oxide.

Les zones de décollement sont supprimées et la couche d'interface, sans disparaître totalement, a une épaisseur réduite et est bloquée dans son évolution.The separation zones are removed and the interface layer, without completely disappearing, has a reduced thickness and is blocked in its evolution.

De préférence, le mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium contient un taux pondéral d'oxyde de scandium inférieur ou égal à 5%, sans toutefois être nul.Preferably, the mixture of alkaline earth metal oxides and scandium oxide contains a weight content of scandium oxide less than or equal to 5%, without however being zero.

Le mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium peut être formé d'une succession de couches, deux couches successives contenant un taux pondéral d'oxyde de scandium différent.The mixture of alkaline earth metal oxides and scandium oxide can be formed from a succession of layers, two successive layers containing a different content by weight of scandium oxide.

Les couches successives peuvent contenir un taux pondéral d'oxyde de scandium croissant plus on s'éloigne du support ou au contraire un taux décroissant.The successive layers may contain an increasing rate of scandium oxide by weight the further away from the support or on the contrary a decreasing rate.

On peut aussi définir des couches paires ayant un premier taux d'oxyde de scandium et des couches impaires ayant un deuxième taux d'oxyde de scandium, le premier et le deuxième taux étant relativement éloignés l'un de l'autre.It is also possible to define even layers having a first level of scandium oxide and odd layers having a second level of scandium oxide, the first and second rates being relatively distant from each other.

Des oxydes doubles ou triples de métaux alcalino-terreux peuvent être utilisés, par exemple, des oxydes de barium et de calcium, ou des oxydes de barium, de calcium et de strontium.Double or triple oxides of alkaline earth metals can be used, for example, barium and calcium oxides, or barium, calcium and strontium oxides.

De préférence, on choisit un support en nickel.Preferably, a nickel support is chosen.

L'épaisseur de la couche d'oxydes de métaux alcalino-terreux est sensiblement égale à l'épaisseur du mélange d'oxydes métaux alcalino-terreux et d'oxyde de scandium.The thickness of the layer of alkaline earth metal oxides is substantially equal to the thickness of the mixture of alkaline earth metal oxides and scandium oxide.

L'invention concerne aussi un procédé de réalisation d'une telle cathode. Il comporte au moins les étapes suivantes :

  • dépôt sur le support, à partir d'un dispositif de projection, d'une suspension d'un ou plusieurs carbonates de métaux alcalino-terreux dans un liant organique;
  • dépôt immédiatement après, à partir d'au moins un autre dispositif de projection, d'une suspension d'un ou plusieurs carbonates de métaux alcalino-terreux et de carbonate de scandium, dans un liant organique;
  • activation de la cathode, sous vide, en la chauffant pour transformer les carbonates en oxydes.
The invention also relates to a method for producing such a cathode. It includes at least the following steps:
  • depositing on the support, from a projection device, a suspension of one or more carbonates of alkaline earth metals in an organic binder;
  • immediately after deposition, from at least one other spraying device, of a suspension of one or more carbonates of alkaline earth metals and of scandium carbonate, in an organic binder;
  • activation of the cathode, under vacuum, by heating it to transform the carbonates into oxides.

La suspension de carbonates de métaux alcalino-terreux et de carbonate de scandium peut être déposée en plusieurs étapes successives, à partir de plusieurs dispositifs de projection, de manière à former une succession de couches.The suspension of alkaline earth metal carbonates and scandium carbonate can be deposited in several successive stages, using several projection devices, so as to form a succession of layers.

Le liant organique peut être du collodion dissous dans de l'acétate de butyle.The organic binder can be collodion dissolved in butyl acetate.

Les caractéristiques et avantages de l'invention apparaîtront à la lecture de la description suivante illustrée des figures qui représentent :

  • la figure 1 une cathode à oxydes de type connu;
  • la figure 2 une cathode à oxydes selon l'invention;
  • la figure 3 une variante d'une cathode à oxydes selon l'invention;
  • la figure 4 une installation pour la réalisation d'une cathode à oxydes selon le procédé de l'invention.
The characteristics and advantages of the invention will appear on reading the following description illustrated by the figures which represent:
  • Figure 1 an oxide cathode of known type;
  • FIG. 2 an oxide cathode according to the invention;
  • Figure 3 a variant of an oxide cathode according to the invention;
  • Figure 4 an installation for the production of an oxide cathode according to the method of the invention.

Sur ces figures, dans un souci de clarté les échelles ne sont pas respectées.In these figures, for the sake of clarity, the scales are not respected.

Sur les différentes figures les mêmes éléments portent le même repère. Sur les figures 1, 2, 3, la cathode représentée est une cathode pour tube à interaction longitudinale. Cet exemple n'est pas limitatif. L'invention n'est pas limitée à ce type de cathode. Une cathode selon l'invention pourrait être cylindrique et servir dans un magnétron ou avoir une surface émissive sensiblement plane et servir dans un tube à rayons cathodiques.In the different figures, the same elements bear the same reference. In FIGS. 1, 2, 3, the cathode shown is a cathode for a tube with longitudinal interaction. This example is not limitative. The invention is not limited to this type of cathode. A cathode according to the invention could be cylindrical and serve in a magnetron or have a substantially planar emissive surface and serve in a cathode ray tube.

Sur la figure 1, on voit un support 1 concave, en forme de coupelle, monté sur une jupe 2 cylindrique. Le support 1 et la jupe 2 sont métalliques, en nickel par exemple.In Figure 1, we see a concave support 1, cup-shaped, mounted on a cylindrical skirt 2. The support 1 and the skirt 2 are metallic, in nickel for example.

Un filament 3 de chauffage est maintenu dans la jupe 2. Le support au lieu d'être concave pourrait être sensiblement plan.A heating filament 3 is held in the skirt 2. The support instead of being concave could be substantially planar.

La partie concave du support 1 forme une face émissive de la cathode. Le support 1 est recouvert d'une couche 4 de matériau thermoémissif. Le filament 3 chauffe le matériau émissif, ce qui produit, à partir d'une certaine température, l'émission d'électrons.The concave part of the support 1 forms an emissive face of the cathode. The support 1 is covered with a layer 4 of thermoemissive material. The filament 3 heats the emissive material, which produces, from a certain temperature, the emission of electrons.

Le matériau thermoémissif est généralement un composé d'oxydes de métaux alcalino-terreux. On utilise souvent des oxydes doubles : oxyde de barium et oxyde de calcium ou des oxydes triples : oxyde de barium, oxyde de calcium et oxyde de strontium. Le matériau thermosémissif est déposé à partir d'une suspension de carbonates de métaux alcalino-terreux (barium et calcium ou barium, calcium et strontium) dans un liant organique. Ce dépot se fait par badigeonnage au pinceau ou par projection avec un pistolet. On choisit souvent comme liant organique du collodion dissous dans de l'acétate de butyle.The thermoemissive material is generally a compound of alkaline earth metal oxides. Double oxides are often used: barium oxide and calcium oxide or triple oxides: barium oxide, calcium oxide and strontium oxide. The thermosemissive material is deposited from a suspension of carbonates of alkaline earth metals (barium and calcium or barium, calcium and strontium) in an organic binder. This deposit is done by brushing with a brush or by spraying with a gun. Collodion dissolved in butyl acetate is often chosen as the organic binder.

L'épaisseur de la couche 4 déposée est de l'ordre de 40 à 50 micromètres.The thickness of the deposited layer 4 is of the order of 40 to 50 micrometers.

La cathode est activée en la chauffant sous vide et les carbonates se transforment en oxydes.The cathode is activated by heating it under vacuum and the carbonates are transformed into oxides.

Les taux en poids des différents oxydes (dans le cas d'oxydes triples) sont de l'ordre de 55 % d'oxyde de barium, 35 % d'oxyde de strontium et 10 % d'oxyde de calcium.The weight ratios of the various oxides (in the case of triple oxides) are of the order of 55% barium oxide, 35% strontium oxide and 10% calcium oxide.

La figure 2 représente une cathode à oxydes selon l'invention.FIG. 2 represents an oxide cathode according to the invention.

On retrouve comme précédemment le support 1 métallique solidaire d'une jupe 2 et le filament 3 de chauffage. Le support 1 est recouvert de matériau thermoémissif. Ce matériau comporte, à partir du support 3, une couche 20 d'un ou plusieurs oxydes de métaux alcalino-terreux. Cette couche 20 peut être de même nature que précédemment, mais son épaisseur n'est que de 10 à 20 micromètres. Cette couche 20 est recouverte d'un mélange d'un ou plusieurs oxydes de métaux alcalino-terreux et d'oxyde de scandium. Dans la pratique, pour obtenir une émission d'électrons satisfaisante, on utilise des oxydes de métaux alcalino-terreux doubles ou triples. Dans la suite de la description on garde cette hypothèse. Sur la figure 2, le mélange est formé d'une seule couche 21. L'épaisseur de la couche 21 est sensiblement égale à celle de la couche 20. On peut bien sur envisager que le mélange soit formé d'une succession de couches. Cette variante est représentée à la figure 3.We find as before the metal support 1 secured to a skirt 2 and the heating filament 3. The support 1 is covered with thermoemissive material. This material comprises, from the support 3, a layer 20 of one or more oxides of alkaline earth metals. This layer 20 can be of the same nature as above, but its thickness is only 10 to 20 micrometers. This layer 20 is covered with a mixture of one or more oxides of alkaline earth metals and scandium oxide. In practice, to obtain a satisfactory emission of electrons, double or triple alkaline earth metal oxides are used. In the following description, we keep this hypothesis. In FIG. 2, the mixture is formed of a single layer 21. The thickness of the layer 21 is substantially equal to that of the layer 20. It may well be envisaged that the mixture is formed of a succession of layers. This variant is shown in Figure 3.

Le taux pondéral d'oxyde de scandium est de préférence inférieur ou égal à 5%, sans toutefois être nul. Les oxydes de métaux alcalino-terreux peuvent être comme précédemment des oxydes de barium et de calcium ou des oxydes de barium, de calcium et de strontium. Dans un souci de simplification, les couches 20 et 21 peuvent contenir les mêmes oxydes de métaux alcalino-terreux. D'autres choix sont possibles, par exemple la couche 20 peut être en oxydes doubles et la couche 21 en oxydes triples.The content by weight of scandium oxide is preferably less than or equal to 5%, without however being zero. The alkaline earth metal oxides can be, as before, barium and calcium oxides or barium, calcium and strontium oxides. For the sake of simplification, layers 20 and 21 may contain the same alkaline earth metal oxides. Other choices are possible, for example the layer 20 can be in double oxides and the layer 21 in triple oxides.

Le taux pondéral d'oxydes de métaux alcalino-terreux de la couche 21 est supérieur ou égal à 95 %.The weight ratio of alkaline earth metal oxides of layer 21 is greater than or equal to 95%.

Selon une variante, représentée à la figure 3, le mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium peut être formé d'une succession de couches 31,32,33. Le taux pondéral d'oxyde de scandium peut varier d'une couche à l'autre tout en restant de préférence inférieur ou égal à 5%. Par exemple, on peut envisager que le taux pondéral d'oxyde de scandium augmente plus on s'éloigne du support 1. La première couche déposée 31 peut contenir 1% d'oxyde de scandium, la seconde 32 3% et la troisième 33 5%. Ce n'est qu'un exemple. Au contraire, le taux pondéral d'oxyde de scandium peut diminuer plus on s'éloigne du support 1. D'autres répartitions sont encore possibles, par exemple, on peut alterner des couches riches en oxyde de scandium avec des couches pauvres en oxyde de scandium. Le taux pondéral d'oxyde de scandium contenu dans les couches pauvres sera, par exemple, d'environ 1 % et le taux pondéral contenu dans les couches riches d'environ 5 %.According to a variant, represented in FIG. 3, the mixture of alkaline earth metal oxides and oxide of scandium can be formed from a succession of layers 31,32,33. The content by weight of scandium oxide can vary from one layer to another while preferably remaining less than or equal to 5%. For example, it is conceivable that the weight content of scandium oxide increases the further one moves away from the support 1. The first deposited layer 31 may contain 1% of scandium oxide, the second 32 3% and the third 33 5 %. This is just an example. On the contrary, the weight content of scandium oxide can decrease the further one moves away from the support 1. Other distributions are still possible, for example, layers rich in scandium oxide can be alternated with layers poor in oxide of scandium. The weight content of scandium oxide contained in the poor layers will be, for example, around 1% and the weight content contained in the rich layers around 5%.

L'épaisseur des couches successives est choisie pour que l'épaisseur totale du matériau thermo-émissif soit de l'ordre de 40 à 50 micromètres. De préférence, l'épaisseur de la couche d'oxydes de métaux alcalino-terreux sera sensiblement égale à l'épaisseur du mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium.The thickness of the successive layers is chosen so that the total thickness of the heat-emissive material is of the order of 40 to 50 micrometers. Preferably, the thickness of the layer of alkaline earth metal oxides will be substantially equal to the thickness of the mixture of alkaline earth metal oxides and scandium oxide.

Sur la figure 3, on a représenté trois couches successives, ce n'est qu'un exemple non limitatif. On peut envisager de déposer seulement deux couches ou jusqu'à quatre ou cinq par exemple.In Figure 3, there are shown three successive layers, this is only a non-limiting example. We can consider depositing only two layers or up to four or five for example.

La présence de la couche 20 d'oxydes de métaux alcalino-terreux directement sur le support 1 favorise un bon accrochage entre les oxydes et le support. Il y a formation d'une couche d'interface relativement peu épaisse, mais son évolution est bloquée grâce au mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium. Les inconvénients liés au décollement des oxydes contenant un taux relativement élevé d'oxyde de scandium sont supprimés tandis que les inconvénients liés à la couche d'interface sont limités.The presence of the layer 20 of alkaline earth metal oxides directly on the support 1 promotes good bonding between the oxides and the support. A relatively thin interface layer is formed, but its development is blocked by the mixture of alkaline earth metal oxides and scandium oxide. The disadvantages associated with the detachment of oxides containing a relatively high level of scandium oxide are eliminated while the disadvantages linked to the interface layer are limited.

Les figures 4a et 4b représentent une partie d'une installation permettant de réaliser des cathodes par le procédé de l'invention. On place dans une hotte 40 d'aspiration un certain nombre de supports 41 métalliques. On dépose à l'aide d'un premier dispositif de projection 42, tel qu'un pistolet à peinture à air comprimé, une suspension de carbonates de métaux alcalino-terreux dans un liant organique. La première couche 43 est sans scandium. Immédiatement après, on dépose à l'aide d'un second dispositif de projection 44, une suspension de carbonates de métaux alcalino-terreux et de carbonate de scandium dans le liant organique. On forme une deuxième couche 45. Le liant peut être du collodion dissous dans de l'acétate de butyle. La deuxième couche 45 contient du scandium. Si l'on désire que la cathode comporte une succession de couches d'oxydes de métaux alcalino-terreux et d'oxyde de scandium, comme représenté sur la figure 3, on pourra utiliser plusieurs pistolets 44, chacun projettant une suspension ayant un taux pondéral de scandium approprié. On obtient ainsi une succession de couches avec du scandium. Après ces pulvérisations, la cathode est placée sous vide et activée en la chauffant, les carbonates se transforment en oxydes.Figures 4a and 4b show a part of an installation making it possible to produce cathodes by the process of the invention. A number of metal supports 41 are placed in a suction hood 40. Using a first projection device 42, such as a compressed air paint gun, a suspension of carbonates of alkaline earth metals in an organic binder is deposited. The first layer 43 is scandium-free. Immediately afterwards, using a second projection device 44, a suspension of alkaline earth metal carbonates and scandium carbonate is deposited in the organic binder. A second layer 45 is formed. The binder can be collodion dissolved in butyl acetate. The second layer 45 contains scandium. If it is desired that the cathode comprises a succession of layers of oxides of alkaline earth metals and of scandium oxide, as shown in FIG. 3, it is possible to use several pistols 44, each projecting a suspension having a weight ratio of suitable scandium. We thus obtain a succession of layers with scandium. After these sprays, the cathode is placed under vacuum and activated by heating it, the carbonates are transformed into oxides.

Les cathodes à oxydes selon l'invention ont une longue durée de vie et une forte densité de courant.The oxide cathodes according to the invention have a long service life and a high current density.

Claims (13)

1 - Cathode à oxydes comportant un support (1) recouvert d'un matériau thermoémissif, caractérisée en ce que le matériau thermoémissif comporte, à partir du support (1) , une couche (20) d'un ou plusieurs oxydes de métaux alcalino-terreux recouverte d'un mélange (21) d'un ou plusieurs oxydes de métaux alcalino-terreux et d'oxyde de scandium. 1 - Oxide cathode comprising a support (1) covered with a thermoemissive material, characterized in that the thermoemissive material comprises, from the support (1), a layer (20) of one or more alkali metal oxides- earthy coated with a mixture (21) of one or more alkaline earth metal oxides and scandium oxide. 2 - Cathode à oxydes selon la revendication 1, caractérisée en ce que le mélange contient un taux pondéral d'oxyde de scandium inférieur ou égal à 5 % sans toutefois être nul. 2 - Oxide cathode according to claim 1, characterized in that the mixture contains a weight content of scandium oxide less than or equal to 5% without however being zero. 3 - Cathode à oxydes selon l'une des revendications 1 ou 2, caractérisée en ce que le mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium est formé d'une succession de couches, deux couches successives contenant un taux pondéral d'oxyde de scandium différent. 3 - Oxide cathode according to one of claims 1 or 2, characterized in that the mixture of alkaline earth metal oxides and scandium oxide is formed by a succession of layers, two successive layers containing a rate by weight of different scandium oxide. 4 - Cathode à oxydes selon la revendication 3, caractérisée en ce que les couches successives contiennent un taux pondéral d'oxyde de scandium croissant plus on s'éloigne du support. 4 - Oxide cathode according to claim 3, characterized in that the successive layers contain a weight content of scandium oxide increasing the further away from the support. 5 - Cathode à oxydes selon la revendication 3, caractérisée en ce que les couches successives contiennent un taux pondéral d'oxyde de scandium décroissant plus on s'éloigne du support. 5 - Oxide cathode according to claim 3, characterized in that the successive layers contain a decreasing rate by weight of scandium oxide the further one moves away from the support. 6 - Cathode à oxydes selon la revendication 3, caractérisée en ce que la succession de couches comporte au moins une couche paire contenant un premier taux pondéral d'oxyde de scandium et au moins une couche impaire contenant un second taux pondéral d'oxyde de scandium, le premier taux d'oxyde de scandium étant relativement éloigné du second taux d'oxyde de scandium. 6 - Oxide cathode according to claim 3, characterized in that the succession of layers comprises at least one even layer containing a first weight ratio of scandium oxide and at least one odd layer containing a second level by weight of scandium oxide, the first level of scandium oxide being relatively distant from the second level of scandium oxide. 7 - Cathode à oxydes selon l'une des revendications 1 à 6, caractérisée en ce que les oxydes de métaux alcalino-terreux sont des oxydes doubles tels que les oxydes de barium et de calcium. 7 - Oxide cathode according to one of claims 1 to 6, characterized in that the alkaline earth metal oxides are double oxides such as barium and calcium oxides. 8 - Cathode à oxydes selon l'une des revendication 1 à 7, caractérisée en ce que les oxydes de métaux alcalino terreux sont des oxydes triples tels les oxydes de barium, de calcium et de strontium. 8 - Oxide cathode according to one of claims 1 to 7, characterized in that the oxides of alkaline earth metals are triple oxides such as barium, calcium and strontium oxides. 9 - Cathode à oxydes selon l'une des revendications 1 à 8, caractérisée en ce que le support est en nickel. 9 - Oxide cathode according to one of claims 1 to 8, characterized in that the support is made of nickel. 10 - Cathode à oxydes selon l'une des revendications 1 à 9, caractérisée en ce que l'épaisseur de la couche d'oxydes de métaux alcalino-terreux est sensiblement égale à l'épaisseur du mélange d'oxydes de métaux alcalino-terreux et d'oxyde de scandium. 10 - Oxide cathode according to one of claims 1 to 9, characterized in that the thickness of the layer of alkaline earth metal oxides is substantially equal to the thickness of the mixture of alkaline earth metal oxides and scandium oxide. 11 - Procédé de réalisation d'une cathode selon l'une des revendications 1 à 10, caractérisé en ce qu'il comporte au moins les étapes suivantes : - dépôt, sur le support, à partir d'un premier dispositif de projection, d'une suspension d'un ou plusieurs carbonates de métaux alcalino-terreux dans un liant organique, - projection immédiatement après, à partir d'au moins un autre dispositif de projection, d'une suspension d'un ou plusieurs carbonates de métaux alcalino-terreux et de carbonate de scandium, dans un liant organique. - activation de la cathode sous vide en la chauffant pour transformer les carbonates en oxydes. 11 - Method for producing a cathode according to one of claims 1 to 10, characterized in that it comprises at least the following steps: - depositing, on the support, from a first projection device, a suspension of one or more carbonates of alkaline earth metals in an organic binder, - spraying immediately afterwards, from at least one other spraying device, of a suspension of one or more carbonates of alkaline earth metals and of scandium carbonate, in an organic binder. - activation of the cathode under vacuum by heating it to transform the carbonates into oxides. 12 - Procédé de réalisation d'une cathode selon la revendication 11, caractérisé en ce que la suspension de carbonates de métaux alcalino-terreux et de carbonate de scandium dans le liant organique est déposée en plusieurs étapes, à partir de plusieurs dispositifs de projection, de manière à former une succession de couches. 12 - Process for producing a cathode according to claim 11, characterized in that the suspension of carbonates of alkaline earth metals and of scandium carbonate in the organic binder is deposited in several stages, from several projection devices, so as to form a succession of layers. 13 - Procédé de réalisation d'une cathode selon la revendication 11, caractérisé en ce que le liant organique est du collodion dissous dans de l'acétate de butyle. 13 - Process for producing a cathode according to claim 11, characterized in that the organic binder is collodion dissolved in butyl acetate.
EP92401339A 1991-05-31 1992-05-15 Oxide cathode and method of its manufacture Ceased EP0516503A1 (en)

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FR9106575A FR2677169A1 (en) 1991-05-31 1991-05-31 OXIDE CATHODE AND METHOD OF MANUFACTURE.

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Cited By (3)

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Publication number Priority date Publication date Assignee Title
EP0641006A1 (en) * 1993-08-24 1995-03-01 Samsung Display Devices Co., Ltd. Cathode for an electron tube
EP1061543A2 (en) * 1999-06-14 2000-12-20 Hitachi, Ltd. Cathode ray tube having an improved cathode
RU2462781C1 (en) * 2011-03-14 2012-09-27 Государственное образовательное учреждение высшего профессионального образования "Мордовский государственный университет им. Н.П. Огарева" Material of emission coating of cathodes of electronic-ionic instruments

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EP0091161A1 (en) * 1982-04-01 1983-10-12 Koninklijke Philips Electronics N.V. Methods of manufacturing a dispenser cathode and dispenser cathode manufactured according to the method
EP0210805A2 (en) * 1985-07-19 1987-02-04 Mitsubishi Denki Kabushiki Kaisha Cathode for electron tube

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JPS6010539A (en) * 1983-06-30 1985-01-19 Toshiba Corp Cathode structure

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EP0091161A1 (en) * 1982-04-01 1983-10-12 Koninklijke Philips Electronics N.V. Methods of manufacturing a dispenser cathode and dispenser cathode manufactured according to the method
EP0210805A2 (en) * 1985-07-19 1987-02-04 Mitsubishi Denki Kabushiki Kaisha Cathode for electron tube

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0641006A1 (en) * 1993-08-24 1995-03-01 Samsung Display Devices Co., Ltd. Cathode for an electron tube
EP1061543A2 (en) * 1999-06-14 2000-12-20 Hitachi, Ltd. Cathode ray tube having an improved cathode
EP1061543A3 (en) * 1999-06-14 2003-08-13 Hitachi, Ltd. Cathode ray tube having an improved cathode
RU2462781C1 (en) * 2011-03-14 2012-09-27 Государственное образовательное учреждение высшего профессионального образования "Мордовский государственный университет им. Н.П. Огарева" Material of emission coating of cathodes of electronic-ionic instruments

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