US3441781A - Microwave tube cathode of the bariumcalcium aluminate type - Google Patents

Microwave tube cathode of the bariumcalcium aluminate type Download PDF

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Publication number
US3441781A
US3441781A US695804A US3441781DA US3441781A US 3441781 A US3441781 A US 3441781A US 695804 A US695804 A US 695804A US 3441781D A US3441781D A US 3441781DA US 3441781 A US3441781 A US 3441781A
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United States
Prior art keywords
aluminate
cathode
tungsten
members
barium
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Expired - Lifetime
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US695804A
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English (en)
Inventor
Brian Frederick Cooper
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Teledyne UK Ltd
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English Electric Valve Co Ltd
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Publication date
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02—Electrodes; Magnetic control means; Screens
    • H01J23/04—Cathodes
    • H01J23/05—Cathodes having a cylindrical emissive surface, e.g. cathodes for magnetrons
    • 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

  • a microwave tube of the barium-calcium aluminate type comprises a stack of members of a metal selected from the group consisting of tungsten and molybdenum, assembled to leave narrow spaces between parts of adjacent members in the stack, and a filling comprising at least mainly aluminate in the spaces, the working surface of the cathode comprising areas which are at least mainly of aluminate separated by areas of the selected metal.
  • the members may be annular with central holes fitted over a central support member, and may be separated by interspersed spacers of smaller diameter than the members so as to form gaps between the outer portions of the members which are filled with the aluminate material which may comprise a mixture of 40% by weight of barium-calcium aluminate mixture and 60% by weigh-t of molybdenum or tungsten powder.
  • a magnetron is essentially a diode vacuum tube in which the fiow of electrons is controlled by an externally applied magnetic field to generate power at microwave frequencies.
  • cathode One of the most satisfactory types of cathode yet produced for pulsed magnetrons is the so-called impregnated barium-calcium aluminate cathode.
  • the usual known form of this cathode consists of a dense sintered, porous tungsten matrix which is impregnated with bariumcalcium aluminate by bringing it into contact with this material in the molten state.
  • This type of cathode has the advantages, over the earlier conventional nickel matrix oxide type of cathode, of longer operational life, and capability of use at longer pulse lengths with improved performance as respects sparking.
  • the secondary emission coetficient of a known impregnated barium-calcium aluminate cathode is so low as, practically speaking, to preclude its use in some pulsed magnetrons, especially some of those designed for operation at low anode voltages.
  • the present invention seeks to provide improved barium-calcium aluminate cathodes in which the above mentioned defects of high cost of manufacture and relatively low secondary emission coefiicient are substantially reduced.
  • a barium-calcium aluminate cathode comprises a stack of tungsten or molybdenum members assembled to leave narrow spaces between parts of adjacent members in the stack, and a filling consisting at least mainly of aluminate in said spaces so that the working surface of the cathode consists of areas which are at least mainly of aluminate separated by areas of tungsten or molybdenum, as the case may be.
  • the expression mainly of aluminate just employed, and similar statements in this specification indicating that the filling is mainly of aluminate are used to mean that the filling is mainly aluminate by volume.
  • the filling is not necessarily mainly aluminate by weight and, indeed, in the preferred embodiments of the invention it is not so.
  • the ratio of at least mainly aluminate filling to tungsten or molybdenum in the working surface area of the cathode is approximately unity or more.
  • a preferred construction of cathode in accordance with the invention comprises a central support member, a stack of annular tungsten or molybdenum members with their central holes fitted over the central support member and alternating along said member with annular spacerrings of the same material so as to leave annular gaps between adjacent members, and a filling consisting at least mainly of barium-calcium aluminate mixture in said gaps.
  • a preferred method of making a cathode in accordance with this invention comprises the steps of making a plurality of tungsten or molybdenum members and a plurality of space-rs of the same material, forming a stack of said members and spacers with the members and spacers alternating so as to leave thin gaps outwardly of the spacers and between adjacent members, and substantially filling the gaps with a mixture consisting at least mainly of barium-calcium aluminates by bringing the assembled stack into contact with said mixture when in the molten state so that the gaps substantially fill with said mixture as a result of surface tension forces,
  • a quantity of tungsten or molybdenum powder is mixed in with the aluminate material.
  • the addition of such powder considerably improves the final cathode not only by increasing the area of contact between aluminate and metal, thus increasing the rate of liberation of free barium but also by militating against the accumulation of surface charges on the surface of the aluminate, which is, of course, an insulating material.
  • the result is a cathode of longer useful life and considerably improved performance as regards sparking.
  • the quantity of tungsten or molybdenum powder mixed in with the aluminate is not critical but a mixture of approximately 60% tungsten or molybdenum powder with 40% aluminate (by weight) gives excellent results. Owing to the much greater specific gravity of tungsten or molybdenum as compared with aluminate, such a mixture (60% metal and 40% aluminate by weight) is still mainly of aluminate by volume.
  • the cathode structure therein shown comprises a central tube 1 on which is a stack of tungsten or molybdenum annular members 2 which alternate with and are spaced by ring spacers 3 of the same material.
  • the ring spacers 3 and members 2 are centralised by the central tube 1 so that they are concentric with one another and with the tube and, after assembly, the parts comprising the stack are clamped or brazed together.
  • annular gaps or spaces are left outside the ring spacers 3 between adjacent annular members 2.
  • gaps or spaces are then substantially filled with a mixture of barium-calcium aluminates with tungsten or molybdenum powder (a suitable mixture is approximately 60% metal and approximately 40% aluminate by weight) by bringing the assembled stack into contact with the mixture in a molten state so that the available volume is substantially filled as a result of surface tension forces, the gaps or spaces being then enough for this to happen.
  • a suitable mixture is approximately 60% metal and approximately 40% aluminate by weight
  • the illustrated construction is comparatively inexpensive to make because it dispenses with expensive machining operations necessary in known impregnated bariumcalcium aluminate cathodes. Also a large part of the cost of producing a conventional known barium aluminate cathode is incurred in filling a tungsten or molybdenum matrix with copper before machining it and then removing the copper afterwards. This costly process is unnecessary with a construction in accordance with this invention. Moreover the ratio of aluminate to tungsten (or molybdenum) in the surface area of the cathode-the external cylindrical area-can readily be made 1:1 or higher so that a better secondary emission coeflicient is readily obtainable than with the known impregnated cathodes.
  • Molybdenum is preferred .to tungsten because it gives faster rates of the chemical action necessary to this type of cathode and compensates better for the reduced area of contact (as compared to the known impregnated cathodes) between aluminates and metal.
  • a microwave tube cathode of the barium-calcium aluminate type comprising a stack of members formed of a metal selected from the group consisting of tungsten and molybdenum assembled to leave narrow spaces between parts of adjacent members in the stack; and fillings comprising, by volume, at least mainly aluminate in said spaces, said fillings extending substantially to the outer surface of the stack and the peripheries of said fillings being substantially coincident with the peripheries of said members, the working surface of the cathode comprising areas which are at least mainly of aluminate separated by areas of the selected metal,
  • a cathode as claimed in claim 1 and comprising a central support and annular spacer rings of said selected metal fitted over said central support, said members alternating along said central support with said annular spacer rings so as to leave annular gaps between adjacent members, and said fillings comprising, by volume, at least mainly barium-calcium aluminate mixture in said gaps.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
  • Powder Metallurgy (AREA)
  • Microwave Tubes (AREA)
US695804A 1964-05-11 1968-01-04 Microwave tube cathode of the bariumcalcium aluminate type Expired - Lifetime US3441781A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB19505/64A GB1023598A (en) 1964-05-11 1964-05-11 Improvements in or relating to magnetron cathodes

Publications (1)

Publication Number Publication Date
US3441781A true US3441781A (en) 1969-04-29

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Application Number Title Priority Date Filing Date
US695804A Expired - Lifetime US3441781A (en) 1964-05-11 1968-01-04 Microwave tube cathode of the bariumcalcium aluminate type

Country Status (6)

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US (1) US3441781A (ko)
CH (1) CH421312A (ko)
DE (1) DE1491342B1 (ko)
GB (1) GB1023598A (ko)
NL (1) NL6505936A (ko)
SE (1) SE320437B (ko)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0593768A1 (en) * 1992-04-15 1994-04-27 Proizvodstvennoe Obiedinenie "Pluton" Magnetron

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3501617A (en) * 1967-11-24 1970-03-17 Chicago Bridge & Iron Co Apparatus for sublimating and evaporating metals
GB2214704B (en) * 1988-01-20 1992-05-06 English Electric Valve Co Ltd Magnetrons

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1891074A (en) * 1931-02-19 1932-12-13 Gen Electric Cathode for electric discharge devices
US3160780A (en) * 1961-01-17 1964-12-08 Philips Corp Indirectly heated cathode
US3201639A (en) * 1955-02-09 1965-08-17 Philips Corp Thermionic dispenser cathode
US3210575A (en) * 1961-03-07 1965-10-05 Podolsky Leon Thermoelectron engine having composite emitter

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1307503A (fr) * 1961-01-23 1962-10-26 S F D Lab Procédé pour interrompre le fonctionnement d'un dispositif électronique à champs croisés

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1891074A (en) * 1931-02-19 1932-12-13 Gen Electric Cathode for electric discharge devices
US3201639A (en) * 1955-02-09 1965-08-17 Philips Corp Thermionic dispenser cathode
US3160780A (en) * 1961-01-17 1964-12-08 Philips Corp Indirectly heated cathode
US3210575A (en) * 1961-03-07 1965-10-05 Podolsky Leon Thermoelectron engine having composite emitter

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0593768A1 (en) * 1992-04-15 1994-04-27 Proizvodstvennoe Obiedinenie "Pluton" Magnetron
EP0593768A4 (en) * 1992-04-15 1994-12-28 Proizv Ob Pluton MAGNETRON.

Also Published As

Publication number Publication date
NL6505936A (ko) 1965-11-12
CH421312A (fr) 1966-09-30
SE320437B (ko) 1970-02-09
GB1023598A (en) 1966-03-23
DE1491342B1 (de) 1969-11-13

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