EP0157634B1 - Wolfram und Iridium enthaltende Vorratskathode - Google Patents

Wolfram und Iridium enthaltende Vorratskathode Download PDF

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Publication number
EP0157634B1
EP0157634B1 EP19850302311 EP85302311A EP0157634B1 EP 0157634 B1 EP0157634 B1 EP 0157634B1 EP 19850302311 EP19850302311 EP 19850302311 EP 85302311 A EP85302311 A EP 85302311A EP 0157634 B1 EP0157634 B1 EP 0157634B1
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EP
European Patent Office
Prior art keywords
cathode
agglomerates
tungsten
particles
porous
Prior art date
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Expired
Application number
EP19850302311
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English (en)
French (fr)
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EP0157634A3 (en
EP0157634A2 (de
Inventor
Michael Curzon Green
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Varian Medical Systems Inc
Original Assignee
Varian Associates Inc
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Publication of EP0157634A2 publication Critical patent/EP0157634A2/de
Publication of EP0157634A3 publication Critical patent/EP0157634A3/en
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Publication of EP0157634B1 publication Critical patent/EP0157634B1/de
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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
    • 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

Definitions

  • the invention pertains to thermionic cathodes in which a porous body of refractory metal is impregnated with a molten oxide containing an alkali- earth.
  • U.S. Patent No. 3,373,307 issued November 12, 1964 describes an improved impregnated cathode in which the emissive surface is coated with iridium or other metals of its group.
  • the coating improves the electron emission, but it has been found that the improvement is often short-lived.
  • a principal problem seems to be that, in an electron tube where high current density is drawn from the cathode at high voltage, ions are formed from the residual gas. They are accelerated back to the cathode and sputter away a thin layer from its surface, removing the iridium.
  • U.S. Patent No. 4,165,473 issued August 21,1979 to Louis R. Falce and assigned to the assignee of the present invention discloses a cathode in which particles of iridium orthe like are dispersed among the tungsten particles of the matrix. During sintering the iridium partially alloys with the tungsten. This dispersed cathode solved the problem of surface sputtering. It has been found, however, that the sintering is a very delicate process. If the time and temperature are enough to get a lot of alloying, the emission is often poor.
  • the emission is initially good, but interdiffusion of iridium and tungsten occurs at operating temperature to form unreactive alloy. This in turn causes the barium supply to the surface to fall off with a resultant decay in emission. Also, shrinkage of the cathode button can take place with the distortion of the emitting surface, which impacts adversely on the electron optics of the gun.
  • An object of the invention is to provide a cathode with improved emission over a long life span.
  • Another object is to provide a cathode which is tolerant of the exact parameters of manufacture and operation.
  • thermoionic cathode comprising:
  • an emitting surface which has a low work-function. This is provided by a thin (sometimes monatomic) layer of an alkaline earth metal such as barium, strontium, calcium or mixtures thereof and often containing oxygen as well.
  • an alkaline earth metal such as barium, strontium, calcium or mixtures thereof and often containing oxygen as well.
  • the second requirement is a means for replenishing the active layer as it is removed in operation by evaporation or sputtering.
  • tungsten to include molybdenum.
  • barium as an example of an alkaline earth metal, which may additionally include calcium, strontium, and alloys thereof as well.
  • the emitting layer is on the surface of the porous tungsten. It has a moderately low work function and thus give emission capability of a few amperes per square centimeter. The life is very good however, because the surfaces of the tungsten matrix in contact with the barium aluminate impregnant are chemically reducing at the operating temperature of around 1000°C, sufficient to react with the oxide and product free barium atoms. This barium can then be transported to the active surface to re-activate it as fast as surface material was removed.
  • the iridium provides tighter bonding of the barium atoms, reducing evaporation as well as work function. Iridium, however, has low reducing power. When it is added to the matrix as taught by U.S. Patent No. 4,165,473 it alloys with the tungsten, perhaps more as a surface coating than a bulk alloy. This will decrease the reducing power of the tungsten and slow the replenishment of lost barium.
  • This embodiment of the invention has been found to provide emission current densities equal or superior to, and lives exceeding those of, the best examples of the prior art.
  • this cathode can be reproducibly manufactured. Cathodes capable of 8 amperes per square centimeter below 1050°C brightness have been produced with greater than 90% yield. Running temperatures for a given current density were within 10°C of each other. The performance was very stable with operating time. Cathodes have passed 4,000 hours at 8 Alcm 2 with practically no change.
  • Fig. 2 illustrates the incorporation of the emitting element (the "cathode” proper) in a cathode structure as used in a linear-beam microwave tube.
  • Cathode 10' is machined to have a smooth concave emitting surface 20' (usually spherical). Its base is fitted onto a cylindrical support 22, as of molybdenum or tantalum and attached thereto as by welding at junction 23.
  • a radiant heater 24, as of tungsten wire in a bifilar spiral is supported by its legs 25 by the support means (not shown) of cylinder 22.
  • the proportions of the various components can cover a wide range. For example, we believe the ratio of iridium to tungsten may vary from about 20% to about 80%.
  • the "barium” may also include calcium, and/or strontium, or mixtures thereof.
  • the "tungsten” may be molybdenum, tungsten, or their alloys.
  • the "iridium” may be osmium, ruthenium, rhenium, iridium or alloys thereof.

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

Claims (15)

1. Glühkathode (10'), die folgendes umfasst:
eine poröse Grundmasse (10) aus Teilchen (12) einer Legierung aus (a) mindestens einem Edelmetall der Platingruppe und (b) mindestens einem hochschmelzenden Metall, das aus Wolfram und Molybdän ausgewählt wird,
poröse Agglomeraten (13), die aus einem der besagten, hochschmelzenden Metalle zusammengestellt werden, die in besagter Grundmasse dispergiert werden, wobei die porösen Agglomerate so gross sind wie vergleichsweise die besagten Teilchen der Legierung, sodass Legierung mit dem Edelmetall ausser auf der äusseren Fläche der Agglomerate verhindert wird, und
die Poren der besagten Grundmasse und der besagten Agglomerate mit einem aktiven Material (18) gefüllt werden, das mindestens ein alkalines Erdoxid enthält.
2. Kathode (10') nach Anspruch 1, bei der besagtes aktives Material ferner Aluminiumoxid enthält.
3. Kathode (10') nach Anspruch 1 oder 2, bei der besagtes Metall der Platingruppe Iridium ist.
4. Kathode (10') nach einem der vorangehenden Ansprüche, bei der das hochschmelzende Metall Wolfram ist.
5. Kathode (10') nach einem der vorangehenden Ansprüche, die ferner eine glatte Oberfläche (20') umfasst, die zur Elektronenemission angepasst ist.
6. Kathode (10') nach Anspruch 5, die ferner eine ebenmässige, homogene Schicht aus besagter glatter Oberfläche umfasst, wobei besagte Schicht besagtes Metall der Platingruppe und besagtes hochschmelzendes Metall umfasst.
7. Kathode (10') nach Anspruch 6, bei der die Zusammensetzung der besagten Schicht ungefähr der durchschnittlichen Zusammensetzung der Grundmasse entspricht.
8. Kathode (10') nach einem der vorangehenden Ansprüche, die ferner Mittel (22) zum Stützen der besagten Kathode umfasst.
9. Kathode (10') nach einem der vorangehenden Ansprüche, die ferner Mittel (24) zum Heizen der besagten Kathode auf eine Temperatur zwischen ungefähr 1000°C und 1100°C umfasst.
10. Verfahren zur Herstellung einer Glühkathode (10'), das folgende Stufen umfasst:
Bildung eines porösen Körpers durch Zusammensintern von mindestens einem hochschmelzenden Metall, das aus Wolfram und Molybdän ausgewählt wird,
mechanisches Zerlegen des besagten, porösen Körpers in Feinanteile und Agglomerate (14) des hochschmelzenden Metalls,
Mischen der besagten Feinanteils und Agglomerate (14) mit Teilchen (12), die mindestens ein Edelmetall enthalten, das aus Iridium, Rhenium, Ruthenium und Osmium ausgewählt wird, deren Teilchen im Vergleich zu besagten Agglomeraten so klein sind, dass das Legieren mit dem Edelmetall nur an der äusseren Oberfläche der Agglomerate und mit den Feinanteilen stattfindet,
Kompression besagter Mischung,
Zusammensintern besagter Mischung, um besagte Teilchen und besagte Agglomerate in einer porösen Masse (10) zu binden,
Impregnieren besagter Masse mit einem geschmolzenen Oxid (18), der ein alkalines Erdoxid enthält.
11. Verfahren nach Anspruch 10, das ferner nach dem Sintern der besagten Mischung die folgenden Stufen umfasst:
Impregnieren der besagten, porösen Masse mit einer Flüssigkeit,
Umwandeln besagter Flüssigkeit in einen Feststoff, um besagte, poröse Masse zu stützen, Formen der besagten Masse in die Form der gewünschten Kathode,
Entnahme des Feststoffes.
12. Verfahren nach Anspruch 11, das ferner folgende Stufen umfasst:
Formen einer glatten zur Elektronenemission angepassten Oberfläche (20') auf besagter Kathodenform,
Ablagern auf besagter, glatten Oberfläche einer ebenmässigen, homogenen Schicht, die besagtes Edelmetall und besagtes hochschmelzendes Metall umfasst.
13. Verfahren nach Anspruch 12, bei dem die Zusammensetzung der besagten Schicht ungefähr der durchschnittlichen Zusammensetzung der besagten, das Edelmetall enthaltenden Teilchen entspricht.
14. Verfahren nach einem der vorangehenden Ansprüche 11 bis 13, das ferner die Stufe des Befestigens der besagten Kathode.(10) auf die Stützmittel (22) umfasst.
15. Verfahren nach Anspruch 14, das ferner die Stufe des Anbringens eines Heizers (24) an besagte Stützmittel in der Nähe der besagten Kathode (10) umfasst, wobei er in der Lage ist, besagte Kathode auf ungefähr 1000 bis 1100 Grad Celsius aufzuheizen.
EP19850302311 1984-04-02 1985-04-02 Wolfram und Iridium enthaltende Vorratskathode Expired EP0157634B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US59578984A 1984-04-02 1984-04-02
US595789 1984-04-02

Publications (3)

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EP0157634A2 EP0157634A2 (de) 1985-10-09
EP0157634A3 EP0157634A3 (en) 1986-01-08
EP0157634B1 true EP0157634B1 (de) 1988-08-17

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EP19850302311 Expired EP0157634B1 (de) 1984-04-02 1985-04-02 Wolfram und Iridium enthaltende Vorratskathode

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EP (1) EP0157634B1 (de)
JP (1) JPH0630214B2 (de)
DE (1) DE3564511D1 (de)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH678671A5 (de) * 1989-08-22 1991-10-15 Asea Brown Boveri
KR0161381B1 (ko) * 1994-12-28 1998-12-01 윤종용 직열형 음극 구조체
KR100195167B1 (ko) * 1994-12-29 1999-06-15 손욱 직열형 음극 구조체 및 그 제조방법
JP3596453B2 (ja) 2000-09-28 2004-12-02 ウシオ電機株式会社 ショートアーク放電ランプ

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4165473A (en) * 1976-06-21 1979-08-21 Varian Associates, Inc. Electron tube with dispenser cathode
DE2909958A1 (de) * 1979-03-14 1980-09-25 Licentia Gmbh Sinterwerkstoff
FR2469792A1 (fr) * 1979-11-09 1981-05-22 Thomson Csf Cathode thermo-ionique, son procede de fabrication et tube electronique incorporant une telle cathode

Also Published As

Publication number Publication date
EP0157634A3 (en) 1986-01-08
EP0157634A2 (de) 1985-10-09
DE3564511D1 (en) 1988-09-22
JPH0630214B2 (ja) 1994-04-20
JPS60220529A (ja) 1985-11-05

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