EP0157634A2 - Cathode à réserve contenant du tungstène et de l'iridium - Google Patents

Cathode à réserve contenant du tungstène et de l'iridium Download PDF

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Publication number
EP0157634A2
EP0157634A2 EP85302311A EP85302311A EP0157634A2 EP 0157634 A2 EP0157634 A2 EP 0157634A2 EP 85302311 A EP85302311 A EP 85302311A EP 85302311 A EP85302311 A EP 85302311A EP 0157634 A2 EP0157634 A2 EP 0157634A2
Authority
EP
European Patent Office
Prior art keywords
cathode
agglomerates
tungsten
iridium
porous
Prior art date
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.)
Granted
Application number
EP85302311A
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German (de)
English (en)
Other versions
EP0157634B1 (fr
EP0157634A3 (en
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
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Varian Associates Inc filed Critical Varian Associates Inc
Publication of EP0157634A2 publication Critical patent/EP0157634A2/fr
Publication of EP0157634A3 publication Critical patent/EP0157634A3/en
Application granted granted Critical
Publication of EP0157634B1 publication Critical patent/EP0157634B1/fr
Expired legal-status Critical Current

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Classifications

    • 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 or the 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. If the sintering is held to a minimum, 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.
  • 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 a number of refractory, moderately chemically active metals such as molybdenum.
  • barium as an example of an alkaline earth metal or compound, 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 produce free barium atoms. This barium can then be transported to the active surface to re-activate it as fast as surface material was removed.
  • a surface layer of iridium or other metals of the platinum group produces a significant further lowering of the work function and hence higher emission density.
  • the work function is believed to be affected by the extent to which the surface metal can polarize the barium dipole layer.
  • the iridium provides tighter bonding of the barium atoms, reducing evaporation as well as work function. Iridium, however, has low reducing power.
  • 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.
  • the iridium provides a surface which can be activated to have a low work function. Even when surface material is removed, the surface is regenerated.
  • the pure tungsten islands are porous grains, each formed from many fine tungsten particles sintered together. Their large surface area provides a reducing interface with the impregnant to produce an adequate supply of reactivating barium to the emitting surface. Their size and convolutions is sufficient to prevent alloying with the iridium except on their outer surfaces.
  • 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 A/cm 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, 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.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
  • Powder Metallurgy (AREA)
EP19850302311 1984-04-02 1985-04-02 Cathode à réserve contenant du tungstène et de l'iridium Expired EP0157634B1 (fr)

Applications Claiming Priority (2)

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

Publications (3)

Publication Number Publication Date
EP0157634A2 true EP0157634A2 (fr) 1985-10-09
EP0157634A3 EP0157634A3 (en) 1986-01-08
EP0157634B1 EP0157634B1 (fr) 1988-08-17

Family

ID=24384685

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19850302311 Expired EP0157634B1 (fr) 1984-04-02 1985-04-02 Cathode à réserve contenant du tungstène et de l'iridium

Country Status (3)

Country Link
EP (1) EP0157634B1 (fr)
JP (1) JPH0630214B2 (fr)
DE (1) DE3564511D1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5134343A (en) * 1989-08-22 1992-07-28 Asea Brown Boveri Ltd. Quasi-optical gyrotron having an electron gun with alternating high and low density electron emitting segments
EP0720198A1 (fr) * 1994-12-29 1996-07-03 Samsung Display Devices Co., Ltd. Structure de cathode chauffée directement et son procédé de fabrication
EP0720197A1 (fr) * 1994-12-28 1996-07-03 Samsung Display Devices Co., Ltd. Structure de cathode chauffée directement
EP1193733A1 (fr) * 2000-09-28 2002-04-03 Ushiodenki Kabushiki Kaisha Lampe à décharge à arc court

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

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5134343A (en) * 1989-08-22 1992-07-28 Asea Brown Boveri Ltd. Quasi-optical gyrotron having an electron gun with alternating high and low density electron emitting segments
EP0720197A1 (fr) * 1994-12-28 1996-07-03 Samsung Display Devices Co., Ltd. Structure de cathode chauffée directement
US5703429A (en) * 1994-12-28 1997-12-30 Samsung Display Devices Co., Ltd. Directly heated cathode structure
CN1070636C (zh) * 1994-12-28 2001-09-05 三星电管株式会社 直热式阴极构件
EP0720198A1 (fr) * 1994-12-29 1996-07-03 Samsung Display Devices Co., Ltd. Structure de cathode chauffée directement et son procédé de fabrication
CN1084924C (zh) * 1994-12-29 2002-05-15 三星电管株式会社 直热式阴极构件及其制造方法
EP1193733A1 (fr) * 2000-09-28 2002-04-03 Ushiodenki Kabushiki Kaisha Lampe à décharge à arc court
US6844678B2 (en) 2000-09-28 2005-01-18 Ushiodenki Kabushiki Kaisha Short arc discharge lamp

Also Published As

Publication number Publication date
DE3564511D1 (en) 1988-09-22
EP0157634B1 (fr) 1988-08-17
EP0157634A3 (en) 1986-01-08
JPH0630214B2 (ja) 1994-04-20
JPS60220529A (ja) 1985-11-05

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