EP0121564B1 - Procede de fabrication du reservoir d'une cathode a reserve - Google Patents

Procede de fabrication du reservoir d'une cathode a reserve Download PDF

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Publication number
EP0121564B1
EP0121564B1 EP83903655A EP83903655A EP0121564B1 EP 0121564 B1 EP0121564 B1 EP 0121564B1 EP 83903655 A EP83903655 A EP 83903655A EP 83903655 A EP83903655 A EP 83903655A EP 0121564 B1 EP0121564 B1 EP 0121564B1
Authority
EP
European Patent Office
Prior art keywords
mandrel
coating
dispenser
reservoir
housing
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.)
Expired
Application number
EP83903655A
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German (de)
English (en)
Other versions
EP0121564A1 (fr
Inventor
Louis R. Falce
Glenn S. Breeze
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.)
Raytheon Co
Original Assignee
Hughes Aircraft Co
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 Hughes Aircraft Co filed Critical Hughes Aircraft Co
Publication of EP0121564A1 publication Critical patent/EP0121564A1/fr
Application granted granted Critical
Publication of EP0121564B1 publication Critical patent/EP0121564B1/fr
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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

Definitions

  • This invention relates to control porosity dispenser cathodes and methods for making the same.
  • This invention is a further advance pertaining to the structure of and the method for fabricating controlled porosity dispenser cathodes.
  • Thermionic emission cathodes of the type that can be used in microwave tubes such as traveling wave tubes are, in many applications, required to have high reliability and long life. It is also desirable that all areas of the cathode surface be operated in a space charge limited mode for more stable operation.
  • cathodes such as the "B”, the "S” and the “M” types, are made of random porosity structures impregnated with barium calcium aluminate compounds and generally tend to provide a non-uniform emission over the surface of the cathode. The result is that excessive temperatures are required to assure that space charge limited emission is achieved in less active areas of the cathode surface. Consequently, the more active areas become excessively hot resulting in decreased reliability and shortened life. The end result is that emission is gradually reduced as the pores become depleted of the impregnant. Examples of these types of cathodes are disclosed in U.S. Patent No. 2,700,000, issued on January 18, 1955 to R. Levi et al. and U.S. Patent No. 2,722,626, issued on November 1, 1955 to P. P. Coppola et al.
  • a method for fabricating a dispenser-reservoir housing for a controlled porosity dispenser cathode characterised by the steps of:
  • the step of coating is by chemical vapor deposition and the coating material is tungsten.
  • the mandrel is removed such as by etching it away, thereby leaving the hollow housing of tungsten which will serve as a reservoir for an activating material.
  • This housing then has an array of apertures drilled in the top surface such as by a pulsed laser thereby creating a controlled porosity emitter-dispenser surface.
  • the reservoir of the structure can be filled from the open end with a barium calcium aluminate compound or other barium bearing compound that will decompose when heated, thereby supplying activating material to the emitter-dispenser surface through the array of apertures.
  • the filled housing can then be attached to a heater structure to make a complete dispenser cathode.
  • This housing is featured in that it is constructed of a single material wherein the crystalline-atomic bonding of the top surface and the side walls of the housing forms an essentially monolithic or single piece.
  • Several advantages include control over the crystalline orientation in the top surface member which becomes the emitter-dispenser surface and the fact that there is little likelihood of contaminates forming on the emission-dispenser surface during fabrication. Consequently, the work function of the surface is generally uniform whereupon there is a high degree of emission uniformity across this surface.
  • the dispenser cathode can be operated at a lower temperature than other dispenser cathodes of the controlled porosity type as a result of the feature of the support-thermal cross members which tend to distribute the heat more deeply and uniformly into the activating material and to the emitter-dispenser surface. As a consequence, it is able to produce a higher emission density for a given temperature than was heretofore obtained and a more stable emission at these lower temperatures. Moreover, at these lower temperatures there is a lower evaporation rate thereby resulting in a reduced loss of the activating material barium and barium oxide (Ba + BO).
  • Still another advantage is that the structure is not likely to delaminate or fail during thermal cycling as a result of its unitary and single material construction.
  • the process and structure has the added manufacturing advantages that it: reduces the number of manufacturing steps; reduces the hand work required; is suitable for large scale production; allows very thin wall structures to be readily fabricated; and results in an easily replicated, precision structure.
  • FIG. 1 is illustrative of a first step of fabrication in which a mandrel is formed having a configuration generally similar to the configuration of the final emitter-reservoir housing.
  • the mandrel 20 is cylindrical and is made of molybdenum. It should be understood that the mandrel could be made of other materials which are capable of withstanding the temperatures at which the subsequent fabrication steps take place and which are otherwise compatible with these steps.
  • the end face 22 of the mandrel 20 is slotted with two intersecting slots 24 and 26 which extend into the body of the material at right angles to each other and are preferably both in a plane coextensive with or collateral with the axis of the mandrel.
  • the slots 24 and 26 extend across the diameter of the mandrel.
  • These strips are of the same material that the remainder of the emitter-reservoir housing will be made from. While tungsten is used in the preferred embodiment, it could be of any other material which has an attractive work function and which is capable of withstanding the operating temperature of the control porosity dispenser cathode over extended periods of time.
  • These strips 28 and 30 are brazed together and in place by copper brazing material 32.
  • the mandrel 20 is machined down to remove the surplus brazing material 32 and the edges of the strips 28 and 30 which protrude beyond the side and end surfaces of the mandrel 20 so that the strip edges are flush with the surface of the mandrel.
  • a shoulder 34 is formed.
  • the mandrel 20 is subjected to chemical vapor deposition process in which a tungsten coating 36 (not drawn to scale) 0.1016 mm (0.004 of an inch) thick is formed on the mandrel surface. During this chemical vapor deposition step, the edges of the strips 28 and 30 atomically bond to the tungsten coating 36.
  • This vapor deposition step can be accomplished in a quartz reaction chamber in which reactive gases of the tungsten metal compound will flow across the heated mandrel to form the deposited layer.
  • the heat for the mandrel can be supplied by an inductive type power supply and the flow rate of the gases can be controlled.
  • end surface 22 of the mandrel is machined into a spherical- radius concave surface 38 such as by electrical discharge machining.
  • This surface 38 is dependent upon the end application of the cathode and the type of beam focusing to be used. Thus, this surface 38 could have been left flat or have other configurations for certain types of applications and beam focusing.
  • tungsten 40 is formed upon the exposed surface of the first tungsten coating 36 and the exposed mandrel concave surface 38 by means of the chemical vapor deposition process.
  • the term "thin” as used herein is about 0.0254 mm (0.001 of an inch) thick in the preferred embodiment. However, it could also be somewhat less or somewhat greater depending upon the structural integrity of the layer or upon the ease at which the electron emitting material is to migrate to the emitting surface. For example, the range could be between about 0.0127 mm (0.0005 of an inch) and 0.127 mm (0.005 of an inch) or, in some cases, more. Care must be taken to be sure that this layer is not so thin that the activating material will readily evaporate or so thick that the activating material will not readily migrate to the emitter surface through the pores to be formed.
  • the two layers of tungsten 36 and 40 bond together by atomic crystalline growth to form a monolithic or single piece of a single material with a somewhat thickened side wall.
  • the tungsten coating which forms the concave emitter-dispenser 42 atomically bonds to the exposed edges of the strips 28 and 30 which form the mechanical- thermal supports. These strips serve to hold the thin wall emitter-dispenser 42 in its precise configuration and will subsequently serve to distribute heat into an activating material as well as to the emitter surface.
  • the end segment of the mandrel 20 holding the configured tungsten coating is cut off at about a plane coextensive with the lower edges of strips 28 and 30, and the molybdenum mandrel 20 is removed such as by a differential solvent thereby forming a hollow housing with a reservoir 44 formed therein.
  • a differential solvent which has been found to be effective is nitric acid which etches the molybdenum and any remaining copper brazing material 32 but does not significantly affect the tungsten.
  • mandrel 20 is used for the mandrel 20, or the housing 48, it may be necessary to use another differential solvent.
  • an array of apertures 46 is formed through the emitter-dispenser 42 in open communication with the reservoir 44. It is preferable that these apertures be of small diameter, closely spaced and in a precise pattern. Accordingly, one way that these apertures have been formed is by laser drilling in which apertures 5.0 microns in diameter on centers spaced 15.0 microns apart have been formed. This results in a controlled porosity emitter-dispenser 42.
  • the reservoir 44 of the hollow emitter-dispenser housing 48 is filled with an activating material 50 through the open end thereof.
  • activating material 50 which has been found to be particularly useful is a mixture of 80% by weight of barium calcium aluminate having a 5:3:2 mole ratio and 20% by weight of tungsten powder.
  • barium bearing compounds that will decompose when heated to supply activating material to the emitter surface of the emitter-dispenser 42 can be used.
  • a controlled ' porosity dispenser cathode is formed by attaching the filled emitter-dispenser housing 48 to a heater assembly 54.
  • the heater assembly 54 includes a hollow support member 56 made of a high temperature resistant material such as tungsten which encloses a heater coil 58 potted in a thermally conductive material 60 such as aluminum oxide AI 2 0 3 .
  • the emitter-reservoir housing 48 is affixed to the end thereof such as by brazing. Thereafter, heat from the heater coil 58 is conducted to the activating material 50 thereby causing barium and barium oxide to migrate both along the interspace between the emitter-dispenser 42 and the activating material 50 and directly through the apertures 46 to the emitter surface of the emitter-dispenser 42 thereby continuously replenishing the activating material on the surface as it is used up during electron emission.
  • the strips 28 and 30 also provide thermal conductivity into the activating material 50 and to the emitter surface thereby providing for efficient operation of the overall device.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Vapour Deposition (AREA)
  • Cold Cathode And The Manufacture (AREA)

Abstract

Boîtier émetteur-distributeur (48) pour une cathode distributrice de porosité contrôlée fabriquée dans un matériau simple en tant que pièce unitaire selon un procédé de déposition de la phase de vapeur chimique au cours duquel un mandrin configuré (20) est enduit d'une couche de matériau (36 et 40) comme le tungstène, par exemple, de façon que, lorsque le mandrin (20) est retiré du revêtement de matériau (36), soit formé un boîtier creux (48) possédant une paroi latérale (36 et 40) et une paroi terminale (42) délimitant un réservoir (44). En outre, des bandes s'entrecoupant (28 et 30) de même matériau que le revêtement, qui a été placé dans le mandrin (20), s'étendent transversalement à travers le réservoir (44) dont les bords sont liés par croissance atomique et cristalline au revêtement (36 et 40) lors de la déposition de la phase de vapeur chimique pour former une pièce unitaire. Ensuite est formée une rangée d'ouvertures (46) dans la paroi terminale (42) du boîtier par perforations au laser afin de créer un émetteur-distributeur (42).

Claims (9)

1. Procédé de fabrication d'un boîtier (48) de réservoir pour une cathode à réserve (52) de porosité contrôlée, caractérisé par les étapes qui consistent:
à revêtir la surface latérale et la surface extrême adjacente (22) d'un mandrin (20) d'une couche (36) d'une matière pour former un revêtement monolithique de ladite matière par croissance cristalline;
à retirer le mandrin (20) pour obtenir un boîtier (48) de ladite matière, ayant une paroi latérale (36, 40) et une paroi extrême (42) qui définissent un réservoir (44); et
à former un réseau d'ouvertures (46) à travers la paroi extrême (42) en communication ouverte avec le réservoir (44) pour former une surface de réserve émissive.
2. Procédé selon la revendication 1, dans lequel l'étape de revêtement du mandrin (20) consiste:
à revêtir le mandrin (20) d'une première couche (36) de ladite matière;
à retirer la première couche (36) de ladite matière de ladite surface extrême (22) du mandrin (20);
à configurer la surface extrême (38) du mandrin en une forme souhaitée; et
à revêtir ladite surface latérale et ladite surface extrême du mandrin (20) d'une seconde couche (40) de ladite matière qui se lie à la première couche (36) de ladite matière par croissance atomique-cristalline.
3. Procédé selon la revendication 1 ou 2, dans lequel l'étape de revêtement s'effectue par dépôt chimique en phase vapeur.
4. Procédé selon les revendications 1, 2 ou 3, dans lequel la matière de revêtement est du tungstène.
5. Procédé selon l'une quelconque des revendications précédentes, dans lequel la matière (40) de revêtement sur la surface extrême (38) du mandrin (20) possède une orientation cristalline qui favorise une émission électronique uniforme.
6. Procédé selon l'une quelconque des revendications précédents comprenant l'étape qui consiste à positionner au moins deux lamelles croisées (28, 30) d'une matière qui est la même que la matière de revêtement dans des rainures de la surface du mandrin configuré (20) afin que leurs bords, qui sont à découvert mais qui ne dépassent pas des surfaces latérale et extrême, se lient atomiquement à la matière de revêtement pour former une seule pièce avec elle, s'étendant transversalement au réservoir (44).
7. Procédé selon l'une quelconque des revendications précédentes, dans lequel la surface extrême du mandrin (20) est configurée en une surface concave sphérique (38).
8. Procédé selon l'une quelconque des revendications précédentes, dans lequel le réseau d'ouvertures (46) est foré au laser.
9. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'étape consistant à enlever le mandrin (20) s'effectue par attaque chimique différentielle qui dissout la matière du mandrin (20), mais n'attaque pas notablement la matière du boîtier (48).
EP83903655A 1982-10-12 1983-10-06 Procede de fabrication du reservoir d'une cathode a reserve Expired EP0121564B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US43358682A 1982-10-12 1982-10-12
US433586 1995-05-03

Publications (2)

Publication Number Publication Date
EP0121564A1 EP0121564A1 (fr) 1984-10-17
EP0121564B1 true EP0121564B1 (fr) 1987-11-25

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EP83903655A Expired EP0121564B1 (fr) 1982-10-12 1983-10-06 Procede de fabrication du reservoir d'une cathode a reserve

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EP (1) EP0121564B1 (fr)
JP (1) JPS59501887A (fr)
DE (1) DE3374738D1 (fr)
IL (1) IL69936A (fr)
IT (1) IT1172332B (fr)
WO (1) WO1984001664A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR920004900B1 (ko) * 1990-03-13 1992-06-22 삼성전관 주식회사 함침형 음극구조체와 그 제조방법
ATE552607T1 (de) * 2003-02-14 2012-04-15 Mapper Lithography Ip Bv Vorratskathode
US9056432B2 (en) * 2012-04-25 2015-06-16 Johnson & Johnson Vision Care, Inc. High-density mask for three-dimensional substrates and methods for making the same

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1078606A (fr) * 1953-04-02 1954-11-19 Csf Perfectionnements aux cathodes émissives
US2931934A (en) * 1955-02-05 1960-04-05 Egyesuelt Izzolampa Indirectly heated supply cathode
BE550302A (fr) * 1955-08-15
JPS50150357A (fr) * 1974-05-21 1975-12-02
GB2043991B (en) * 1978-11-30 1983-05-11 Varian Associates Method of fabricating a dispenser cathode
US4310603A (en) * 1978-11-30 1982-01-12 Varian Associates, Inc. Dispenser cathode
US4379979A (en) * 1981-02-06 1983-04-12 The United States Of America As Represented By The Secretary Of The Navy Controlled porosity sheet for thermionic dispenser cathode and method of manufacture

Also Published As

Publication number Publication date
IL69936A (en) 1988-02-29
IT1172332B (it) 1987-06-18
WO1984001664A1 (fr) 1984-04-26
DE3374738D1 (en) 1988-01-07
EP0121564A1 (fr) 1984-10-17
JPS59501887A (ja) 1984-11-08
IT8349128A0 (it) 1983-10-10

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