EP0282040A1 - Dispenser cathode, especially metal capillary cathode, for electric discharge vessels - Google Patents

Dispenser cathode, especially metal capillary cathode, for electric discharge vessels Download PDF

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Publication number
EP0282040A1
EP0282040A1 EP88103733A EP88103733A EP0282040A1 EP 0282040 A1 EP0282040 A1 EP 0282040A1 EP 88103733 A EP88103733 A EP 88103733A EP 88103733 A EP88103733 A EP 88103733A EP 0282040 A1 EP0282040 A1 EP 0282040A1
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EP
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Prior art keywords
emission
tungsten
cathode
dispenser
barium
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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.)
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EP88103733A
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German (de)
French (fr)
Inventor
Hinrich Dr. Heynisch
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Siemens AG
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Siemens AG
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Publication of EP0282040A1 publication Critical patent/EP0282040A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H01J1/28—Dispenser-type cathodes, e.g. L-cathode
    • 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

Definitions

  • the invention relates to a supply cathode according to the preamble of claim 1.
  • Such a supply cathode is known from DE-PS 20 10 479.
  • the problem with these cathodes in particular is that the barium oxide supply, for example in the form of tablets, has a relatively high sensitivity to moisture. This sensitivity to moisture inter alia affects the shelf life of such cathodes is negative.
  • the cathode quality is reduced by the sensitivity to moisture of the barium oxide formed, in particular with regard to the lowering of the electron work function and thus the current density.
  • the invention has for its object to provide a storage cathode, in particular MK cathode, for a high current density and to give its emission stock such a nature that it is largely sensitive to atmospheric humidity by preventing and remaining the formation of barium hydroxide.
  • the advantages achieved by the invention are, in particular, that the emission inventory of the cathode is largely insensitive to atmospheric moisture by avoiding the formation of barium hydroxide and the porous tungsten body filled with the storage mass also acts as a reducing agent.
  • the supply according to the invention consists of a barium oxide-tungsten matrix body, preferably barium oxide-tungsten-osmium or. Rhenium or. Iridium matrix body in easy-to-use tablet form.
  • the production process is preferably carried out in the following manner: Tungsten powder with a particle size of approximately 2 to 50 ⁇ m, osmium powder with the corresponding particle size and barium carbonate are mixed uniformly, preferably in a volume ratio of approximately 4: 1: 5. This mixture is then pressed in an appropriate form, preferably tablet form, under high pressure to give a shaped body. Thereupon the pressed molded body is annealed in a high vacuum, a conversion of the BaCO3 into BaO taking place and a sintering taking place.
  • the storage tablet obtained in this way is practically largely insensitive to atmospheric moisture, so that the handling of the cathode during the manufacture of electrical discharge vessels (for example electron tubes) is significantly better and thus leads to a more uniform cathode quality.
  • Another advantage is that there is no tungsten wadding in the cathode storage space, which is used as a reducing agent in known designs, because the pressed storage body itself now guarantees the reduction of BaO to Ba because of its tungsten content.
  • the storage body is also achieved if a porous tungsten compact is produced, which is subsequently impregnated with conventional processes using BaO or Ba-Ca aluminate.
  • the matrix storage body is distinguished by a reduced evaporation rate of the cathode.
  • the metal capillary cathode shown in the figure consists essentially of a metal sleeve 4, expediently made of molybdenum, which preferably encloses a metal pot composed of two parts, namely an inner part 6 and an outer part 5, advantageously consisting of molybdenum.
  • a heater 7 is preferably cemented into the hollow cylindrical space formed by the inner part 6 and the outer part 5 of the metal pot, the connections 8 of which lead to the outside on the cathode bottom. With the heater 7, the interior, which is formed by the inner part 6 of the metal pot, can be heated.
  • the emission-promoting supply 1 is accommodated in this interior, preferably in the form of a tablet-shaped sintered barium oxide-tungsten or barium oxide-tungsten-osmium matrix body.
  • the emission-promoting supply 1 is covered by the emission carrier 2, which consists of tungsten and is attached to the end face of the metal sleeve 4.
  • the emission carrier 2, which expediently has the shape of a biconcave disk, is provided with a coating 3 of osmium on its active surface in order to keep the electron work function as low as possible.

Abstract

The invention relates to a dispenser cathode, especially a metal capillary cathode, for electrical discharge vessels, in which the dispenser (1) providing the emission consists of alkaline earth compounds such as barium oxide or barium carbonate and the porous, sintered, tungsten emission material carrier (2), covering the dispenser (1), has, in particular, an additional coating (3) of osmium on its active surface. This dispenser cathode is intended to have a high current density and its emission dispenser is intended to be produced such that it is largely insensitive to air humidity, in that barium hydroxide formation is, and remains, eliminated. For this purpose, the invention provides that the dispenser (1) providing the emission consists of a sintered barium oxide-tungsten matrix body. The dispenser cathode according to the invention is used especially as a metal capillary cathode for high current densities in travelling wave tubes. <IMAGE>

Description

Die Erfindung bezieht sich auf eine Vorratskathode gemäß dem Oberbegriff des Anspruchs 1.The invention relates to a supply cathode according to the preamble of claim 1.

Eine derartige Vorratskathode geht aus der DE-PS 20 10 479 als bekannt hervor. Bei diesen Kathoden tritt insbesondere das Prob­lem auf, daß der beispielsweise in Form von Tabletten vorliegen-­de Vorrat aus Bariumoxid eine relativ hohe Feuchtigkeitsempfind­lichkeit besitzt. Diese Feuchtigkeitsempfindlichkeit beeinträch­tigt u.a. die Lagerbeständigkeit derartiger Kathoden negativ. Allgemein wird auch bei der Verwendung von anderen Erdalkaliver­bindungen, beispielsweise von Bariumkarbonat, die Kathodenquali­tät durch die Feuchtigkeitsempfindlichkeit des gebildeten Ba­riumoxids verringt, insbesondere hinsichtlich der Erniedrigung der Elektronenaustrittsarbeit und damit der Stromdichte. Bestrebungen zur Beseitigung dieser Nachteile führten bei der aus der DE-PS 20 10 479 bekannten Vorratskathode zu der bedingt tauglichen Maßnahme der Verwendung eines dichten, für Feuchtig­keit undurchlässigen Schutzüberzuges aus einer in einem orga­nischen Lösungsmittel löslichen hydrophoben Substanz, mit dem der scheibenförmige Wolfram-Emissionsstoffträger versehen ist.Such a supply cathode is known from DE-PS 20 10 479. The problem with these cathodes in particular is that the barium oxide supply, for example in the form of tablets, has a relatively high sensitivity to moisture. This sensitivity to moisture inter alia affects the shelf life of such cathodes is negative. In general, even when using other alkaline earth compounds, for example barium carbonate, the cathode quality is reduced by the sensitivity to moisture of the barium oxide formed, in particular with regard to the lowering of the electron work function and thus the current density. Efforts to eliminate these disadvantages led to the conditionally suitable measure of using a dense, moisture-impermeable protective coating made of a hydrophobic substance soluble in an organic solvent with which the disk-shaped tungsten emission carrier is provided in the storage cathode known from DE-PS 20 10 479 is.

Der Erfindung liegt die Aufgabe zugrunde, eine Vorratskathode, insbesondere MK-Kathode, für eine hohe Stromdichte zu schaffen und deren Emissionsvorrat eine solche Beschaffenheit zu verlei­hen, daß er für Luftfeuchtigkeit weitgehend umempfindlich ist, indem eine Bariumhydroxidbildung unterbunden wird und bleibt.The invention has for its object to provide a storage cathode, in particular MK cathode, for a high current density and to give its emission stock such a nature that it is largely sensitive to atmospheric humidity by preventing and remaining the formation of barium hydroxide.

Diese Aufgabe wird erfindungsgemäß durch eine Vorratskathode mit den Merkmalen des Anspruchs 1 gelöst.This object is achieved according to the invention by a supply cathode with the features of claim 1.

Vorteilhafte Ausgestaltungen bzw. Weiterbildungen der Erfindung sind Gegenstand zusätzlicher Ansprüche.Advantageous refinements or developments of the invention are the subject of additional claims.

Die mit der Erfindung erzielten Vorteile bestehen insbesondere darin, daß der Emissionsvorrat der Kathode für Luftfeuchtigkeit weitgehend unempfindlich ist, indem eine Bariumhydroxidbildung vermieden wird und der mit Vorratsmasse gefüllte, poröse Wolfram-­Körper gleichzeitig als Reduktonsmittel wirkt. Anstatt der als Vorrat für die Kathoden bekannten Bariumoxid-Vorratstabletten besteht der Vorrat erfindungsgemäß aus einem Bariumoxid-Wolfram-­Matrixkörper, vorzugsweise Bariumoxid-Wolfram-Osmium-bzw. Rhenium-bzw. Iridium-Matrixkörper in leicht zu handhabender Tablettenform. Vorzugsweise wird bei dessen Herstellung in fol­gender Weise vorgegangen: Es werden Wolframpulver mit einer Korn­größe von etwa 2 bis 50 µm, Osmiumpulver mit entsprechender Korn­größe und Bariumkarbonat gleichmäßig vermischt, vorzugsweise in einem Volumenverhältnis von ca. 4:1:5. Anschließend wird diese Mischung in einer entsprechenden Form, vorzugsweise Tabletten­form unter hohem Druck zu einem Formkörper gepreßt. Daraufhin wird der gepreßte Formkörper im Hochvakuum geglüht, wobei eine Umsetzung des BaCO₃ in BaO stattfindet sowie eine Sinterung er­folgt.
Die so gewonnene Vorratstablette ist praktisch weitgehend un­empfindlich gegen Luftfeuchtigkeit, so daß die Handhabung der Kathode während der Fertigung von elektrischen Entladungsge­fäßen (z. B. Elektronenröhren) wesentlich besser ist und somit zu einer gleichmäßigeren Kathodenqualität führt.The advantages achieved by the invention are, in particular, that the emission inventory of the cathode is largely insensitive to atmospheric moisture by avoiding the formation of barium hydroxide and the porous tungsten body filled with the storage mass also acts as a reducing agent. Instead of the barium oxide storage tablets known as a supply for the cathodes, the supply according to the invention consists of a barium oxide-tungsten matrix body, preferably barium oxide-tungsten-osmium or. Rhenium or. Iridium matrix body in easy-to-use tablet form. The production process is preferably carried out in the following manner: Tungsten powder with a particle size of approximately 2 to 50 μm, osmium powder with the corresponding particle size and barium carbonate are mixed uniformly, preferably in a volume ratio of approximately 4: 1: 5. This mixture is then pressed in an appropriate form, preferably tablet form, under high pressure to give a shaped body. Thereupon the pressed molded body is annealed in a high vacuum, a conversion of the BaCO₃ into BaO taking place and a sintering taking place.
The storage tablet obtained in this way is practically largely insensitive to atmospheric moisture, so that the handling of the cathode during the manufacture of electrical discharge vessels (for example electron tubes) is significantly better and thus leads to a more uniform cathode quality.

Ein weiterer Vorteil besteht darin, daß Wolfram-Watte im Vor­ratsraum der Kathode, die bei bekannten Ausführungen als Reduk­tionsmittel verwendet wird, entfällt, weil der Preß-Vorrats-­Körper jetzt wegen seines Wolframgehaltes selbst die Reduktion von BaO zu Ba gewährleistet.Another advantage is that there is no tungsten wadding in the cathode storage space, which is used as a reducing agent in known designs, because the pressed storage body itself now guarantees the reduction of BaO to Ba because of its tungsten content.

Noch bessere Ergebnisse bezüglich der Reduktion lassen sich mit einem geringen Zusatz von Zirkon zum Wolframpulver im Vorrats­korper erzielen.Even better results regarding the reduction can be achieved with a small addition of zirconium to the tungsten powder in the storage body.

Die Realisierung des Vorratskörpers erreicht man gemäß einer Weiterbildung der Erfindung auch, wenn ein poröser Wolfram-­Preßkörper hergestellt wird, den man anschließend mit üblichen Verfahren mit BaO oder Ba-Ca-Aluminat imprägniert.According to a further development of the invention, the storage body is also achieved if a porous tungsten compact is produced, which is subsequently impregnated with conventional processes using BaO or Ba-Ca aluminate.

Neben der Verringerung der Gefahr der Bariumhydroxidbildung zeichnet sich der Matrix-Vorratskörper durch eine verringerte Abdampfrate der Kathode aus. Hinzu kommt der Vorteil der Unter­stützung der niedrigen Austrittsarbeit der Kathode auch durch einen Osmium-Anteil im Vorratskörper, und zwar zusätzlich zu der gegebenenfalls vorgesehenen Osmiumbeschichtung der Emis­sionsfläche des aus Wolfram bestehenden Emissionsstoffträgers.In addition to reducing the risk of barium hydroxide formation, the matrix storage body is distinguished by a reduced evaporation rate of the cathode. In addition, there is the advantage of supporting the low work function of the cathode by an osmium content in the storage body, in addition to the optionally provided osmium coating on the emission surface of the emission carrier made of tungsten.

Anhand eines in der Figur der Zeichnung dargestellten, bevorzug­ten Ausführungsbeispiels wird die Erfindung weiter erläutert.The invention is further explained on the basis of a preferred exemplary embodiment shown in the figure of the drawing.

Die in der Figur dargestellte Metall-Kapillar-Kathode besteht im wesentlichen aus einer Metallhülse 4, zweckmäßig aus Molybdän, die einen vorzugsweise aus zwei Teilen, nämlich einem Innenteil 6 und einem Außenteil 5, zusammengesetzten, zweckmäßig aus Molybdän bestehenden Metalltopf umschließt. In den von dem In­nenteil 6 und dem Außenteil 5 des Metalltopfes gebildeten hohl­zylinderförmigen Zwischenraum ist ein Heizer 7 vorzugsweise ein­gekittet, dessen Anschlüsse 8 am Kathodenboden nach außen füh­ren. Mit dem Heizer 7 ist der Innenraum, der von dem Innenteil 6 des Metalltopfes gebildet wird, beheizbar. In diesem Innen­raum ist der emissionsfördernde Vorrat 1 untergebracht, und zwar vorzugsweise in Gestalt eines tablettenförmigen gesinter­ten Bariumoxid-Wolfram- bzw. Bariumoxid-Wolfram-Osmium-Matrix­körpers. Der emissionsfördernde Vorrat 1 ist von dem Emissions­stoffträger 2 überdeckt, der aus Wolfram besteht und an der Stirnseite der Metallhülse 4 befestigt ist. Der Emissionsstoff­träger 2, der zweckmäßig die Form einer bikonkaven Scheibe hat, ist in diesem Ausführungsbeispiel auf seiner aktiven Oberfläche mit einem Überzug 3 aus Osmium versehen, um die Elektronenaus­trittsarbeit möglichst niedrig zu halten.The metal capillary cathode shown in the figure consists essentially of a metal sleeve 4, expediently made of molybdenum, which preferably encloses a metal pot composed of two parts, namely an inner part 6 and an outer part 5, advantageously consisting of molybdenum. A heater 7 is preferably cemented into the hollow cylindrical space formed by the inner part 6 and the outer part 5 of the metal pot, the connections 8 of which lead to the outside on the cathode bottom. With the heater 7, the interior, which is formed by the inner part 6 of the metal pot, can be heated. The emission-promoting supply 1 is accommodated in this interior, preferably in the form of a tablet-shaped sintered barium oxide-tungsten or barium oxide-tungsten-osmium matrix body. The emission-promoting supply 1 is covered by the emission carrier 2, which consists of tungsten and is attached to the end face of the metal sleeve 4. In this exemplary embodiment, the emission carrier 2, which expediently has the shape of a biconcave disk, is provided with a coating 3 of osmium on its active surface in order to keep the electron work function as low as possible.

Claims (6)

1. Vorratskathode, insbesondere Metall-Kapillar-Kathode, für elektrische Entladungsgefäße, bei der der emisionsfördernde Vorrat aus Erdalkaliverbindungen wie Bariumoxid oder Bariumkar­bonat besteht und der den Vorrat überdeckende, porös gesinterte Emissionsstoffträger aus Wolfram insbesondere einen zusätzlichen Überzug aus Osmium auf seiner aktiven Oberfläche aufweist,
dadurch gekennzeichnet,
daß der emissions fördernde Vorrat (1) aus einem gesinterten Ba­riumoxid-Wolfram-Matrixkörper besteht.1. supply cathode, in particular metal-capillary cathode, for electrical discharge vessels in which the emission-promoting supply consists of alkaline earth compounds such as barium oxide or barium carbonate and the porous sintered emission carrier made of tungsten covering the supply has in particular an additional coating of osmium on its active surface,
characterized by
that the emission-promoting stock (1) consists of a sintered barium oxide-tungsten matrix body. 2 Vorratskathode nach Anspruch 1,
dadurch gekennzeichnet,
daß der emissionsfördernde Vorrat (1) aus einem gesinterten Ba­riumoxid-Wolfram-Osmium, Rhenium oder Iridium-Matrixkörper be­steht.2 supply cathode according to claim 1,
characterized by
that the emission-promoting stock (1) consists of a sintered barium oxide tungsten osmium, rhenium or iridium matrix body. 3. Vorratskathode nach Anspruch 1,
dadurch gekennzeichnet,
daß der emissionsfördernde Vorrat (1) aus einem gesinterten Bariumoxid-Wolfram-Osmium, Rhenium und Iridium-Matrixkörper besteht.3. supply cathode according to claim 1,
characterized by
that the emission-promoting stock (1) consists of a sintered barium oxide tungsten osmium, rhenium and iridium matrix body. 4. Vorratskathode nach Anspruch 1,
dadurch gekennzeichnet,
daß der emissionsfördernde Vorrat (1) aus einem mit Bariumoxid oder Barium-Kalzium-Aluminat imprägnierten Wolfram-Preßkörper besteht.4. supply cathode according to claim 1,
characterized by
that the emission-promoting stock (1) consists of a tungsten compact impregnated with barium oxide or barium calcium aluminate. 5. Verfahren zum Herstellen einer Vorratskathode nach Anspruch 1 oder 2,
dadurch gekennzeichnet,
daß als emissionsfördernder Vorrat (1) Wolframpulver und Osmium­pulver mit einer Korngröße bis zu 50 µm sowie Bariumkarbonat gleichmäßig vermischt und anschließend in einer entsprechenden Form unter hohem Druck zu einem Formkörper gepreßt werden, und daß danach der Formkörper im Hochvakuum geglüht wird, wobei eine Umsetzung des Bariumkarbonats in Bariumoxid erfolgt und der Formkörper zu einem Matrixkörper (1) gesintert wird.5. A method for producing a supply cathode according to claim 1 or 2,
characterized by
that as emission-promoting stock (1) tungsten powder and osmium powder with a grain size up to 50 microns and barium carbonate evenly mixed and then in a corresponding Mold are pressed under high pressure to a shaped body, and that the shaped body is then annealed in a high vacuum, the barium carbonate being converted into barium oxide and the shaped body being sintered into a matrix body (1). 6. Verfahren nach Anspruch 5,
dadurch gekennzeichnet,
daß das Verhältnis der Mischungsanteile von Wolframpulver, Osmiumpulver und Bariumkarbonat 4:1:5 beträgt.6. The method according to claim 5,
characterized by
that the ratio of the mixture proportions of tungsten powder, osmium powder and barium carbonate is 4: 1: 5.
EP88103733A 1987-03-10 1988-03-09 Dispenser cathode, especially metal capillary cathode, for electric discharge vessels Withdrawn EP0282040A1 (en)

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DE3707681 1987-03-10
DE3707681 1987-03-10

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0496008A1 (en) * 1991-01-21 1992-07-29 Thomson Elektronenröhren AG Controllable high-power electron tube
EP0673051A1 (en) * 1994-03-16 1995-09-20 Licentia Patent-Verwaltungs-GmbH Dispenser cathode

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2010479B2 (en) * 1970-03-05 1973-04-12 Siemens AG, 1000 Berlin u 8000 München METAL CAPILLARY CATHODE WITH POROUS EMISSION CARRIER PROTECTED AGAINST HUMIDITY
US3842309A (en) * 1970-11-12 1974-10-15 Philips Corp Method of manufacturing a storage cathode and cathode manufactured by said method
DE2808134A1 (en) * 1978-02-25 1979-08-30 Licentia Gmbh Long-life cathode with porous two layer emitter - has emitting layer thinner and of lower porosity than supporting layer
EP0019992A1 (en) * 1979-05-29 1980-12-10 Thorn Emi-Varian Limited Thermionic electron emitters and methods of making them
GB1586664A (en) * 1976-06-21 1981-03-25 Varian Associates Electron tube
EP0052047A1 (en) * 1980-11-07 1982-05-19 Thomson-Csf Thermoelectronic cathode
JPS6188421A (en) * 1984-10-05 1986-05-06 Hitachi Ltd Impregnated cathode

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2010479B2 (en) * 1970-03-05 1973-04-12 Siemens AG, 1000 Berlin u 8000 München METAL CAPILLARY CATHODE WITH POROUS EMISSION CARRIER PROTECTED AGAINST HUMIDITY
US3842309A (en) * 1970-11-12 1974-10-15 Philips Corp Method of manufacturing a storage cathode and cathode manufactured by said method
GB1586664A (en) * 1976-06-21 1981-03-25 Varian Associates Electron tube
DE2808134A1 (en) * 1978-02-25 1979-08-30 Licentia Gmbh Long-life cathode with porous two layer emitter - has emitting layer thinner and of lower porosity than supporting layer
EP0019992A1 (en) * 1979-05-29 1980-12-10 Thorn Emi-Varian Limited Thermionic electron emitters and methods of making them
EP0052047A1 (en) * 1980-11-07 1982-05-19 Thomson-Csf Thermoelectronic cathode
JPS6188421A (en) * 1984-10-05 1986-05-06 Hitachi Ltd Impregnated cathode

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, Unexamined Applications, E Field, Band 10, Nr. 263, 9. September 1986 The Patent Office Japanese Government seite 24 E 435 & JP-A-61 088 421 (Hitachi) 6. May 1986 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0496008A1 (en) * 1991-01-21 1992-07-29 Thomson Elektronenröhren AG Controllable high-power electron tube
US5206565A (en) * 1991-01-21 1993-04-27 Asea Brown Boveri Ltd. High-power low-voltage tetrode having a full walled matrix cathode and a control grid spacing of less than 1 mm
EP0673051A1 (en) * 1994-03-16 1995-09-20 Licentia Patent-Verwaltungs-GmbH Dispenser cathode
US5594299A (en) * 1994-03-16 1997-01-14 Licentia Patent-Verwaltungs-Gmbh Dispenser cathode with porous sintered compacted metal dispenser body containing chromium oxide

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