US2899592A - coppola - Google Patents

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US2899592A
US2899592A US2899592DA US2899592A US 2899592 A US2899592 A US 2899592A US 2899592D A US2899592D A US 2899592DA US 2899592 A US2899592 A US 2899592A
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barium
refractory metal
cathode
metal
alloy
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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

Definitions

  • My invention relates to a thermionic dispenser cathode.
  • a supply of alkalne earth material is disposed within a body of refractory metal, eg., tungsten, molybdenum, tantalum, hafnium, or niobium, having a porous wall portion through which alkalne earth metal producedby a reaction between the alkalne earth material and the refractory metal can pass and form an emissive layer on a surface of the body.
  • refractory metal eg., tungsten, molybdenum, tantalum, hafnium, or niobium
  • the reaction between the refractory metal and the alkalne earth compound usually proceeds quite rapidly, and in many cases an excessive amount of alkalne earth metal is supplied to the emissive surface and is evaporated which is a disadvantage of the cathode for certain applications.
  • A'princpal object of my invention is to provide a thermionic dispenser cathode having a reduced rate of evaporation of alkalne earth metal.
  • a still further object of my invention is to provide a cathode in which the porosity of the porous wall is not the controlling factor in determining the rate at which free alkalne earth metal is furnished to the emissive surface of the cathode.
  • a further object'of my invention is to provide a thermionic dispenser cathode in which the initial rate of evaporation of alkalne earth metal duringfabrication and activation is reduced.
  • Another object of my invention is to facilitate the fabrication of a thermionic dispenser cathode by employing a refractory metal alloy which can be sintered into a body at lower temperatures.
  • a further object of my invention is to provide a dispenser cathode employing a more readily machinable refractory metal whereby the cathode can be machined to close tolerances.
  • a further object of my invention is to employ a refractory metal alloy in which one of the constituents of the alloy will serve to bind some undesirable gaseous products which may be produced during the operation of the cathode.
  • the rate of evaporation of alkalne earth metal in a dispenser cathode can be reduced by substituting for the refractory metal, such as tungsten, in the porous wall of the cathode structure an alloy of at least two refractory metals one of which is active in reducing the alkalne earth material disposed in a cavity within the body and the other of which is more passive during the reaction.
  • the refractory metal such as tungsten
  • active refractory metal I mean a refractory metal which will react with certain alkalne earth compounds to furnish a supply of free alkalne earth metal in excess of that required to form a satisfactory emitter.
  • passive refractory metal I mean a re fractory metal which does not react or only reacts with those alkalne earth compounds to such an extent as to form an insufficient amount of free alkalne earth metal.
  • the refractory metals may be either passive or active depending upon which alkalne earth compounds are employed.
  • the passive refractory metal serves to limit the amount of active refractory metal'available for reaction with the alkalne earth material in the cavity and also serves to limit the rate at which the active refractory metal is brought into contact with the alkalne earth material because the active refractory metal must diffuse through the passive refractory metal before Contacting the alkalne earth material. Consequently, the alloy must con tain the active and passive refractory metals in amounts suflicient to form the emissive surface while preventing excessive evaporation of alkalne earth metal.
  • the refractory metals are more or less active in reducng certain alkalne earth compounds or compositions to' free alkalne earth metal. More particularly, I have found that molybdenum is the least active of the refractory metals in its ability to reduce alkalne earth compounds or compositions to the free alkalne earth metal.
  • I mix the alkalne earth material with powdered refractory metal alloy and press the mixture into a body which is sintered to produce a coherent body.
  • this reduction I have found, is materially less than if tungsten alone is used as a refractory metal.
  • the alloys according to my invention substantially reduce the rate of evaporation of the alkaline earth metal by inhibiting the rate of reduction of the alkaline earth material.
  • Fig. 1 is a sectional View of one embodiment of a dispenser cathode according to the invention.
  • Fig. 2 is a sectional view of another embodiment of a dispenser cathode according to the invention.
  • the dispenser cathode shown in Fig. l comprises a tube 1 composed of refractory metal such as molybdenum having an internal partition 2 for separating the tube into two chambers.
  • the lower chamber houses a conventional heater 3 while the upper chamber houses a supply of alkaline earth compounds 4 such as a mixture of barium and strontum carbonates.
  • the upper chamber is closed by a porous disc 5 sealed to the end of the tube fl by welding so that the pores in the wall constitute the only passageways connecting the cavity in which the alkaline earth compounds are disposed to the emissive surface 6.
  • the porous disc 5 is made of an alloy composed of 25% of tungsten and 75% of molybdenum made by pressing the powdered alloy into a disc and sintering the same at a temperature of about l600 to 1900 C Since the resulting disc is porous, the alkaline earth metal obtained by reaction between the alkaline earth compounds in the cavity passes through the pores of the disc and forms an emissive layer on the surface of the cathode.
  • tungsten is the active refractory metal which reacts with the barium and strontum oxides formed by thermal decomposition of the carbonates in the cavity to supply free barium to the emissive surface of the cathode. Since the tungsten is alloyed with molybdenum, not only is the amount of tungsten available for the reaction diminshed but the rate at which it is made available for reaction is limited by its diffusion rate through the molybdenum.
  • alkaline earth compounds or mixtures or solid solutions thereof are substituted in the cavity for the barium and strontum carbonates, other refractory alloys may be used.
  • the following table lists the most suitable refractory metal that should be used for various alkaline earth compositions in the cavity in order to obtain a suflicient but not excessive supply of barium for the ernissive surface.
  • Mo-W up to about 90% of W BaO.
  • Mo-Ta up to about Ta,...
  • W-Ta up to about 10% MO-rNb, up to about 10% Nb Refractory Metal Alloy Passive Ref. Metal-Active Ref. Metal Alkaliue Earth Materialin cavity W-Nb, up to about 10% Nb Basic and normal barium beyl- ⁇ Basic barium aluminates.
  • Mo-Zr less than about 5% Hf Basic barium aluminates. Normal and basic barium hei-yll'atcs.
  • the alkaline earth compounds are homogeneously distributed within the porous disc itself.
  • the disc 5 in which the alkaline earth compounds are disposed is sealed in one end of a tube 1 of refractory metal such as molybdenum and separated from the heater 3 by a partition 2 of refractory metal.
  • the porous disc in which the alkaline earth compounds are disposed can be fabricated as follows.
  • the disc may be made by mixing the refractory metal in powdered form with the alkaline earth material, eg., a 5 to 2 mole ratio of a prefired mixture of BaO and Al O This mixture is then pressed and sintered at a temperature of about 1650 to l750 C. for about 30 seconds.
  • the resulting body is mechanically coherent and relatively free of entrapped gases.
  • a porous disc obtained by pressing and sintering a powdered refractory metal alloy at relatively high temperatures, e.g., l600-1900 C. but in any event no higher than a temperature slightly below the lowest melting point of either the alloy or any of its constituents.
  • the porous disc thus obtained which may be machined, if desircd, is then impregnated with a suitable alkaline earth material as described in U.S. application Serial No. 273,607, filed February 27, 1952, now Patent 2,700,000 by R. Levi et al.
  • the alkaline earth material to be used must have a meltng point below the temperature at which the porous disc was sintered in order to avoid further sintering thereof during impregnation.
  • the alkaline earth material In the cathodes in which the alkaline earth material is homogeneously distributed throughout the porous disc, the alkaline earth material must be selected so that t is readily reducible by the active refractory metal without deleteriously reacting therewith.
  • Suitable alkaline earth materials and the criteria governing their selection for that type of cathode are disclosed in U.S. applications Serial Nos. 258,89l, now Patent No. 2,716,716 and 258,892, now Patent 2,700,112 filed November 29, 1951, by R. C. Hughes et al. All of the compositions and mixtures of alkaline earth compounds disclosed therein may be used in the cathode according to my invention and the foregoing advantages erumerated hereinabove will be realized.
  • the selection of the particular alkaline earth material will to some extent determine the particular refractory metal alloy that should be used and I have listed in the table below the best combinations of refractory metal alloys and alkaline earth materials.
  • the terms pressed powder" and “impreguated” refer, respectively, to cathodes made by mixing the alkaline earth material with the powdered metal alloy and forming a body therefrom, and to a cathode obtained by ntroducing the alkaline earth material into a porous disc by impregratio.
  • Normal barium berylliate Mono-barium aluminates.
  • Basic barium berylliates ⁇ Barium ortho-silicate.
  • the cathode was assembled in an evacuated envelope in which an anode was arranged. All emisson measurements were taken at a cathode Operating temperature of 950 C. brightness pulse-wise with 100 microsecond pulses at the rate of 20 per second at a 1000 volts on the anode. The cathode was held at 1050 C. brightness with 100 volts D.C. on the anode during life.
  • said refractory metal alloy consisting of 75% by weight of molybdenum and 25% by weight of tungsten.
  • a thermionic cathode comprising a tubular structure consisting of .Iefractory metal, &portion of the wall of said -structure constituting the emissive surface thereof consisting of a sintered body composcd of 90% by weight of an alloy consisting of 75% by weight of molybdenum
  • the time required OH the P P for those cathodes was 10 and 25% by weight of tungsten, and 10% by weight of a fraction of that required when pure tungsten or pure molybdenum instead of the alloy was used.
  • This invention is not limited to cathodes having the shape shown but is applicable to dispenser cathodes of more complex Construction.
  • the cathode for example, could have a cylindrical shape, or it could be a concave or planar type of cathode.
  • a thermionic cathode comprisng a structure con sisting of refractory metal, a portion of the wall of said structure constituting the emissive surface thereof consistng of a homogeneously-porous sintered refractory metal alloy, and a supply of a fused mixture of 5 moles of barium oxide and 2 moles of aluminum oxide distributed within and only within the pores of said wall a fused miXture of 5 moles of barium oxide and 2 moles of aluminum oxide, the fused mixture of barium and aluminum oxide being contained within and only within said sintered body.

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  • Solid Thermionic Cathode (AREA)
  • Powder Metallurgy (AREA)
  • Discharge Lamp (AREA)
US2899592D 1953-11-18 coppola Expired - Lifetime US2899592A (en)

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US345392XA 1953-11-18 1953-11-18

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US (1) US2899592A (is")
BE (1) BE533455A (is")
CH (1) CH345392A (is")
DE (1) DE1043519B (is")
FR (1) FR1113555A (is")
GB (1) GB777142A (is")
NL (1) NL97571C (is")

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3127537A (en) * 1960-02-25 1964-03-31 Rca Corp Cathode mount and alloy therefor
US3558966A (en) * 1967-03-01 1971-01-26 Semicon Associates Inc Directly heated dispenser cathode
US3693007A (en) * 1970-05-25 1972-09-19 Egyesuelt Izzolampa Oxide cathode for an electric discharge device
US4417173A (en) * 1980-12-09 1983-11-22 E M I-Varian Limited Thermionic electron emitters and methods of making them

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1954474A (en) * 1927-05-20 1934-04-10 Espe Werner Glow cathode
US2085605A (en) * 1934-05-11 1937-06-29 Gen Electric Thermionic cathode for electric discharge devices
US2121589A (en) * 1934-06-28 1938-06-21 Westinghouse Electric & Mfg Co Emissive incandescent cathode
US2147447A (en) * 1936-09-21 1939-02-14 Siemens Ag Glow cathode
US2180988A (en) * 1937-06-16 1939-11-21 Gen Electric Electrode for electric discharge devices
US2389060A (en) * 1943-08-13 1945-11-13 Callite Tungsten Corp Refractory body of high electronic emission
US2473550A (en) * 1947-08-19 1949-06-21 Raytheon Mfg Co Directly heated cathode
US2543728A (en) * 1947-11-26 1951-02-27 Hartford Nat Bank & Trust Co Incandescible cathode
US2700118A (en) * 1951-11-29 1955-01-18 Philips Corp Incandescible cathode
US2700000A (en) * 1952-02-27 1955-01-18 Philips Corp Thermionic cathode and method of manufacturing same
US2716716A (en) * 1951-11-29 1955-08-30 Philips Corp Cathode containing a supply of an electron-emissive material
US2741717A (en) * 1951-06-14 1956-04-10 Siemens Ag Dispenser type cathode having gettercoated parts

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE707255C (de) * 1936-09-21 1941-06-17 Siemens Schuckertwerke Akt Ges Gluehkathode hoher Leistung, insbesondere fuer gas- oder dampfgefuellte Entladungsgefaese
BE498869A (is") * 1949-10-25
DE895479C (de) * 1951-11-20 1953-11-02 Siemens Ag Kathode fuer elektrische Entladungsgefaesse

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1954474A (en) * 1927-05-20 1934-04-10 Espe Werner Glow cathode
US2085605A (en) * 1934-05-11 1937-06-29 Gen Electric Thermionic cathode for electric discharge devices
US2121589A (en) * 1934-06-28 1938-06-21 Westinghouse Electric & Mfg Co Emissive incandescent cathode
US2147447A (en) * 1936-09-21 1939-02-14 Siemens Ag Glow cathode
US2180988A (en) * 1937-06-16 1939-11-21 Gen Electric Electrode for electric discharge devices
US2389060A (en) * 1943-08-13 1945-11-13 Callite Tungsten Corp Refractory body of high electronic emission
US2473550A (en) * 1947-08-19 1949-06-21 Raytheon Mfg Co Directly heated cathode
US2543728A (en) * 1947-11-26 1951-02-27 Hartford Nat Bank & Trust Co Incandescible cathode
US2741717A (en) * 1951-06-14 1956-04-10 Siemens Ag Dispenser type cathode having gettercoated parts
US2700118A (en) * 1951-11-29 1955-01-18 Philips Corp Incandescible cathode
US2716716A (en) * 1951-11-29 1955-08-30 Philips Corp Cathode containing a supply of an electron-emissive material
US2700000A (en) * 1952-02-27 1955-01-18 Philips Corp Thermionic cathode and method of manufacturing same

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3127537A (en) * 1960-02-25 1964-03-31 Rca Corp Cathode mount and alloy therefor
US3558966A (en) * 1967-03-01 1971-01-26 Semicon Associates Inc Directly heated dispenser cathode
US3693007A (en) * 1970-05-25 1972-09-19 Egyesuelt Izzolampa Oxide cathode for an electric discharge device
US4417173A (en) * 1980-12-09 1983-11-22 E M I-Varian Limited Thermionic electron emitters and methods of making them

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Publication number Publication date
FR1113555A (fr) 1956-03-30
BE533455A (is")
NL97571C (is")
DE1043519B (de) 1958-11-13
GB777142A (en) 1957-06-19
CH345392A (de) 1960-03-31

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