US3497757A - Tungsten dispenser cathode having emission enhancing coating of osmium-iridium or osmium-ruthenium alloy for use in electron tube - Google Patents

Tungsten dispenser cathode having emission enhancing coating of osmium-iridium or osmium-ruthenium alloy for use in electron tube Download PDF

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Publication number
US3497757A
US3497757A US732985A US3497757DA US3497757A US 3497757 A US3497757 A US 3497757A US 732985 A US732985 A US 732985A US 3497757D A US3497757D A US 3497757DA US 3497757 A US3497757 A US 3497757A
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Prior art keywords
osmium
cathode
tungsten
alloy
iridium
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US732985A
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English (en)
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Pieter Zalm
Antonius Johannes Albe Stratum
Henricus Hubertus Peeters
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US Philips Corp
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US Philips Corp
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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
    • 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
    • H01J1/14—Solid thermionic cathodes characterised by the material

Definitions

  • the matrix emitting surface is coated with a thin porous layer of an alloy of osmium and iridium or osmium and ruthenium to provide longer cathode lifetime and less danger during the manufacture of the cathode in comparison with prior art coated cathodes.
  • This application is a continuation of application Ser. No. 704,032 filed Feb. 8, 1968, which is now abandoned.
  • This invention relates to a dispenser cathode, and in particular to a thermionic dispenser cathode in which the emitting surface is contituted by a surface of a porous refractory metal matrix or body of tungsten or tungstenmolybdenum alloy in the pores of which or behind which a barium-containing alkaline earth metal compound or compounds which will react upon heating with the tungsten to generate free barium metal and/or barium oxide is provided.
  • the present invention is an improved high work function metal coated dispenser cathode in which the two mentioned drawbacks of the prior art coated cathode are minimized or eliminated.
  • a coated cathode results which has practically all of the favorable characteristics of the osmium coated cathode while the aforementioned drawbacks are minimized or eliminated.
  • the coating is constituted by an osmium-iridium alloy containng 3070 atomic percent of osmium, or an osmium-ruthenium alloy containing 20-80 atomic percent of osmium.
  • FIG. 3 illustrates diagrammatically a suitable apparatus for providing the coating on the cathode.
  • the drawing is essentially the same as the drawing of our aforementioned patent, as the present invention is basically the same as that of our previous invention as described in the patent except for the substitution of the alloy coating described above for thecoating described in said patent.
  • the invention is applicable to dispenser cathodes of the type comprising a porous tungsten or molybdenum-tungsten alloy body in the pores of which or behind the pores of which is provided a barium-containing activating compound which upon the cathode being heated to its emission temperature reacts with the tungsten of the porous body to generate free barium metal and/ or barium oxide which migrates as a vapor through the pores of the porous body to form on its emitting surface what is consideered to be a substantially monatomic layer of barium, or of barium on oxygen, on tungsten or the tungsten-molybdenum alloy or the coating which reduces to a low level the work function of that surface enabling electrons to be emitted in co'pius amounts.
  • the barium compounds or compositions can be chosen from among a large group which are well known in the prior art, reference to which has been made in the patent.
  • the barium compound chosen is a barium aluminate or a barium calcium aluminate, which is formed by fusing a mixture of the constituents or their corresponding carbonates to produce the desired aluminates, which is also Well known in the art.
  • a preferred mole ratio of the constituents is between 23:1 of the barium oxide to the aluminum oxide with 1-3 of the calcium oxide.
  • other suitable compositions are described in detail in our patent.
  • FIG. 1 illustrates a typical cavity-type dispenser cathode. It comprises an H- shaped cylindrical body 1, preferably of molybdenum, defining a lower cavity containing a heating filment 2 and an upper cavity 3 in which is provided a pellet 3 which may for example consist of by weight of fine tungsten powder and 40% by Weight of a barium calcium aluminate having a mole ratio of BaO:Al O :CaO of 5:213.
  • the upper cavity 3 is sealed off by means of a suitable weld by a porous tungsten wall 4 which is usually of densely sintered tungsten having a density of approximately of solid tungsten.
  • the upper surface of the tungsten wall 4 which constitutes the emitting surface of the cathode, which is a planar type intended to generate a cylindrical beam of electrons, is coated with a thin layer 5 of the alloy previously described, details of which will be later provided.
  • FIG. 2 illustrates a typical impregnated type dispenser cathode which comprises a cylindrical molybdenum body 6 provided with a molybdenum plate 9 to isolate a heating filament 2 from the active emitter part 7 of the cathode.
  • Aluminum oxide 10 may be employed to seal the plate 9 to the molybdenum body 6.
  • the emitting body 7 comprises a porous tungsten body 7, which is usually a densely sintered tungsten body having a porosity of about 80%, whose pores which are interconnected have been filled or impregnated from the melt with barium calcium aluminate, for example of the 5:2:3 mole ratio composition previously described.
  • the impregnated body 7 can also be formed by compressing and sintering a mixture of tungsten powder and aluminate powder of the composition described, the sintering taking place at a temperature at which the aluminate melts, though to obtain best results we prefer to use the impregnated version in which the tungsten is preformed as a completely sintered body and later impregnated from the melt with the barium calcium aluminate.
  • the impregnated cathode illustrated in FIG. 2 also has on its emitting surface a coating 8 of the alloy previously mentioned.
  • FIG. 3 illustrates a suitable apparatus for sputtering the alloy coating 5 of FIG. 1 and 8 of FIG. 2 onto the surfaces of the cathode bodies 4 and 7.
  • the cathode bodies to be coated are supported on a lower plate 14 connected to one side-of a voltage source, the other side of which is connected to an upper plate which in this case is composed of an alloy of osmium and iridium or osmium and ruthenium in the proportions previously stated.
  • the plate 14 preferably is of the same alloy.
  • the plates may have a diameter of 3 cm. and are spaced apart by a distance of about 6 mm.
  • the apparatus includes a base plate 11 and a bell jar 12, and the interior can be evacuated by means of an exhaust tube 13 and the usual pumping system not shown. After evacuation, the interior of the bell jar is filled with, for example, argon, at a pressure of approximately 1 mm. Hg and then the upper plate 15 which is connected as a cathode is sputtered by establishing a discharge of about milliamperes between the two plates at a voltage of about 600 volts. The sputtered material of course deposits on the cathode bodies 4 and 7. In about 15 minutes under the conditions above mentioned, an alloy layer is formed on the cathode bodies with a thickness of about 1000 A.
  • the gas discharge may be confined to the center by means of an axial magnetic field.
  • the cathode bodies are preferably sintered in hydrogen of about one atmosphere pressure and at a temperature of approximately 1350 C. in order to improve the adhesion of the alloy coating to the bodies.
  • the emission properties obtained of the two alloy coatings mentioned as the high work function metal coating of a dispenser cathode are .substantially the same as those of a pure osmium coated cathode.
  • the tungsten diffuses less rapidly through the alloy coating than if it were constituted of pure osmium, which prolongs its lifetime in comparison with the osmium coated cathode.
  • the alloys are applied as easily by cathode sputtering as the pure high work function metals alone, and other known application teachniques should also prove equally satisfactory.
  • the thickness range for the alloy coating is preferably from a few hundred, e.g. 200 to 10,000 A.
  • the alloy coated cathodes offer the advantage over the single high work function metal coated cathodes that they can be operated at higher temperatures with reasonable lifetime more satisfactorily, up to, for instance, a pyrometrically obtained temperature of 1050 C.
  • Both named alloys offer the important advantage that toxic OsO is not formed. They not only exhibit a higher resistance to reaction with oxygen, in comparison with osmium alone, but they also exhibit a higher resistance to other residual gases in the tube.
  • the osmium-ruthenium alloy is readily pressed and sintered from powder to form plates or rods which can be employed in the apparatus illustrated in FIG. 3 as a sputtering source for coating the cathode bodies.
  • cathodes will prove useful in all applications where high electron emission densities at relatively low cathode temperatures are required, examples of which are camera tubes, cathode ray picture tubes, and various microwave tube applications.
  • a dispenser cathode comprising a porous body of a refractory metal selected from the group consisting of tungsten and tungsten-molybdenum alloys, an alkaline earth metal compound in relative relationship with the body and capable when heated of releasing free barium metal which is capable of flowing through the pores to form a layer of barium on a surface of the body intended to serve as an emissive source of electrons, a thin layer of a refractory metal alloy having a work function higher than that of pure tungsten and selected from the group consisting of osmium-iridium containing 3070 atomic percent of osmium, and osmium-ruthenium containing 2080 atomic percent of osmium on the surface of said body from which electron emission is desired, said layer being porous to the barium flowing through the pores of the body, and means for heating said body at an elevated temperature whereby said cathode exhibits substantially the same emission level as a comparable cathode without the higher work function layer but
  • a dispenser cathode comprising a densely-sintered porous body of a refractory metal selected from the group consisting of tungsten and tungsten-molybdenum alloy, an alkaline earth metal compound in reactive relationship with the body and capable when heated of releasing free barium metal which is capable of flowing through the pores to form a layer of barium on a surface of the body intended to serve as an emissive source of electrons, a thin layer of a refractory metal alloy having a work function higher than that of pure tungsten and selected from the group consisting of osmium-iridium containing 30-70 atomic percent of osmium, and osmium-ruthenium containing 2080 atomic percent of osmium on only the surface of said body from which electron emission is desired, said layer being porous to the barium flowing through the pores and having a thickness between about 200 and 10,000 A., and means for heating said body at an elevated temperature whereby said cathode exhibits substantially the same emission level

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US732985A 1968-01-09 1968-05-29 Tungsten dispenser cathode having emission enhancing coating of osmium-iridium or osmium-ruthenium alloy for use in electron tube Expired - Lifetime US3497757A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL686800278A NL154047B (nl) 1968-01-09 1968-01-09 Elektrische ontladingsbuis met een kathode die in het inwendige activeringsmateriaal bevat, en kathode bestemd voor een dergelijke ontladingsbuis.

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AT (1) AT287128B (de)
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3842309A (en) * 1970-11-12 1974-10-15 Philips Corp Method of manufacturing a storage cathode and cathode manufactured by said method
US4007393A (en) * 1975-02-21 1977-02-08 U.S. Philips Corporation Barium-aluminum-scandate dispenser cathode
US4019081A (en) * 1974-10-25 1977-04-19 Bbc Brown Boveri & Company Limited Reaction cathode
US4165473A (en) * 1976-06-21 1979-08-21 Varian Associates, Inc. Electron tube with dispenser cathode
EP0004424A1 (de) * 1978-03-23 1979-10-03 Thorn Emi-Varian Limited Thermionische Kathode
EP0019992A1 (de) * 1979-05-29 1980-12-10 Thorn Emi-Varian Limited Glühkathode und Verfahren zu ihrer Herstellung
US4274030A (en) * 1978-05-05 1981-06-16 Bbc Brown, Boveri & Company, Limited Thermionic cathode
GB2127617A (en) * 1981-12-11 1984-04-11 Tokyo Shibaura Electric Co Cathode structure for electron tube
EP0055146B1 (de) * 1980-12-12 1985-08-14 Societe Pour L'etude Et La Fabrication De Circuits Integres Speciaux - E.F.C.I.S. Frequenzabhängiger numerischer Regelkreis

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2469792A1 (fr) * 1979-11-09 1981-05-22 Thomson Csf Cathode thermo-ionique, son procede de fabrication et tube electronique incorporant une telle cathode

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3155864A (en) * 1960-03-21 1964-11-03 Gen Electric Dispenser cathode
US3243637A (en) * 1962-10-31 1966-03-29 Gen Electric Dispenser cathode
US3373307A (en) * 1963-11-21 1968-03-12 Philips Corp Dispenser cathode

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3155864A (en) * 1960-03-21 1964-11-03 Gen Electric Dispenser cathode
US3243637A (en) * 1962-10-31 1966-03-29 Gen Electric Dispenser cathode
US3243638A (en) * 1962-10-31 1966-03-29 Gen Electric Dispenser cathode
US3373307A (en) * 1963-11-21 1968-03-12 Philips Corp Dispenser cathode

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3842309A (en) * 1970-11-12 1974-10-15 Philips Corp Method of manufacturing a storage cathode and cathode manufactured by said method
US4019081A (en) * 1974-10-25 1977-04-19 Bbc Brown Boveri & Company Limited Reaction cathode
US4007393A (en) * 1975-02-21 1977-02-08 U.S. Philips Corporation Barium-aluminum-scandate dispenser cathode
US4165473A (en) * 1976-06-21 1979-08-21 Varian Associates, Inc. Electron tube with dispenser cathode
EP0004424A1 (de) * 1978-03-23 1979-10-03 Thorn Emi-Varian Limited Thermionische Kathode
US4274030A (en) * 1978-05-05 1981-06-16 Bbc Brown, Boveri & Company, Limited Thermionic cathode
EP0019992A1 (de) * 1979-05-29 1980-12-10 Thorn Emi-Varian Limited Glühkathode und Verfahren zu ihrer Herstellung
US4570099A (en) * 1979-05-29 1986-02-11 E M I-Varian Limited Thermionic electron emitters
EP0055146B1 (de) * 1980-12-12 1985-08-14 Societe Pour L'etude Et La Fabrication De Circuits Integres Speciaux - E.F.C.I.S. Frequenzabhängiger numerischer Regelkreis
GB2127617A (en) * 1981-12-11 1984-04-11 Tokyo Shibaura Electric Co Cathode structure for electron tube
US4524296A (en) * 1981-12-11 1985-06-18 Tokyo Shibaura Denki Kabushiki Kaisha Cathode structure for electron tube

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NL154047B (nl) 1977-07-15
AT287128B (de) 1971-01-11
NL6800278A (de) 1969-07-11

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