US2972078A - Carburization of dispenser cathodes - Google Patents

Carburization of dispenser cathodes Download PDF

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Publication number
US2972078A
US2972078A US78860359A US2972078A US 2972078 A US2972078 A US 2972078A US 78860359 A US78860359 A US 78860359A US 2972078 A US2972078 A US 2972078A
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US
United States
Prior art keywords
cathode
barium
type
emission
dispenser
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 - Lifetime
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English (en)
Inventor
Levi Roberto
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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Filing date
Publication date
Priority to NL108689D priority Critical patent/NL108689C/xx
Application filed by US Philips Corp filed Critical US Philips Corp
Priority to US78860359 priority patent/US2972078A/en
Priority to DEN17772A priority patent/DE1094887B/de
Priority to CH60660A priority patent/CH402197A/de
Priority to GB208260A priority patent/GB919419A/en
Priority to DK20760A priority patent/DK93307C/da
Priority to AT40760A priority patent/AT219166B/de
Priority to BE586842A priority patent/BE586842A/fr
Priority to FR816505A priority patent/FR1245997A/fr
Application granted granted Critical
Publication of US2972078A publication Critical patent/US2972078A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • H01J9/042—Manufacture, activation of the emissive part
    • H01J9/047—Cathodes having impregnated bodies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/249921—Web or sheet containing structurally defined element or component
    • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
    • Y10T428/249955—Void-containing component partially impregnated with adjacent component

Definitions

  • barium-containing dispenser cathodes there are three main types of barium-containing dispenser cathodes available in the art.
  • the earliest developed type is known as the L-type cathode, and is described in United States Patent No. 2,543,728.
  • a barium-containing emissive or activating material is located in a cavity behind a porous .refractory inetal wall portion. Heating such a structure by a suitably arranged filament causes a chemical reaction to bccurbetween the emissive material and the refractory r'netal of the ,wall resulting in. the generation offree barium metal; which. then diffuses through the porggof the wall to form ,a monatomic layer. on anexternal surface of'that wall.
  • the resultant heated barium on refractory metal surface constitutes an excellent primary source of electrons, which is found especially useful in microwave tubes because of its high emission densities, its extreme resistance to ion or electron bombardment, and its inherent accuracy of shape and dimensions as well as-fiatness of the emissive surface.
  • a later modification o'f this cathode-has been termed the impregnated? cathode' and the main structural difference between it and the Ii-typecathode is the placing-of the emissive material inside the pores of the porous refractory metal wall portion ⁇ which is-de'scribed in United States Patent No. 2,700,000. This is done by melting the emissive.
  • the first which is termed the type A impregnated cathode, uses a fused mixture ofbarium oxide and aluminum oxide, which forms, a barium'aluminate mixture, as the emissive material impregnant.
  • a later-developed impregnated cathode has been'termed the type B cathode, and uses a fused rated from the emissive surface, and this vapor deposits on cathode surfaces that should not emit and adjacent electrode elements in the tube, such as a control-grid member or accelerating anode or cathode support member.
  • cathode surfaces that should not emit and adjacent electrode elements in the tube, such as a control-grid member or accelerating anode or cathode support member.
  • these other surfaces or electrode or support members are generally at an elevated temperature by virtue of their close proximity to the heated cathode, and because of deposition thereon of barium and barium oxide, they in turn generate primary electrons. This is quite disadvantageous for various reasons.
  • the main advantage of the type Bimpregnated cathode over the type A impregnated cathode is the increase in emission by a factor of four.
  • the type B cathode does have some limitations relative to the type A, which include lower resistance to poisoning, and an operating temperature range whose upper limit is somewhat below that of the type A cathode, and there are applications for such cathodes where the dispenser cathode requires a higher poisoning resistance, or attains 'a'high elevated temperature by reason of back bombardment of the cathode by returning electrons or ions which has required the employment of a type A cathode because of its somewhat higher permissible operating temperature.
  • a dispenser cathode having some of the advantages of the type A impregnated cathode as well as the higher emission densities associated with a type B cathode.
  • the main advantage'pfthetyPe B impregnated cathode over the type A impregnated-cathode is an increase of emission at the same-temperature by a factor of four, accompanied by a'jreduction" in activation-time.
  • the third type of dispenser cathode isjknown as the pressed cathode, and comprisescompacting and sintering together a mixture of tungsten and barium aluminate particles to form the refractory metal-emissive"material combination required to. -func tion;as a dispenser type cathode. This is described in United States Patent No. 2,769,708.
  • the resultant impregnated dispenser cathode has the higher emission densities associated with these dispenser cathodes and at the same time possesses higher poisoning resistance, and may be operated; at higher temperatures.
  • Fig. 1 is across-sectional yiew of anwassembly of eies merits illustrating the first step in one way of making an impregnated-type dispenser cathode producing a hollow beam of electrons;
  • Fig.2 is a cross-sectional view illustrating the second step in the manufacture of a hollow beam source
  • Fig. 3 is a cross-sectional view of the completed cathode made in the manner illustrated in Figs. 1 and 2.
  • the invention will first be described in detail in connection with the making of a hollow cathode source using both the enhancing and inhibiting techniques above-described.
  • microwave tube applications such as the traveling-wave tube, in which a beam of electrons of generally cylindrical form traverses an extended beam path within a delay line, along which is passed an electromagnetic wave. Operation results from interaction of the electrons and the electromagnetic wave.
  • it is primarily the electrons on the periphery of the beam that participate in this phenomenon, it is desirable to remove the center core of electrons. This can be done by providing a hollow beam source.
  • a porous tungsten pellet or disc 10 as shown in Fig. 1.
  • tungsten is preferred, other refractory metalsor combinations, such as molybdenum-tungsten, or tantalurn-molybdenum may also be employed.
  • the method for making a porous tungsten disc with about 83% density is described in detail in my United States Patent No. 2,721,372.
  • a short hollow cylinder 11 of refractory metal is placed on the top or emitting surface of the pellet 10.
  • This cylinder 11 whichpreferably has aflat enjd surface, acts as a mask for a contacted annular surface portion 12 of the disc.
  • the assembly of disc and hollow cylinder is surrounded and contacted on all its exposed surfaces with fine carbon or graphite powder 13. Thereafter, the assembly is heated hydrogen to a n elevated temperature of about 1500 Q, brightness and maintained at that temperature for about 5 minutes.
  • the carbon-contacted tungsten surfaces react to form a tungstencarbide skin on the disc with a depth of about, 10-40 microns.
  • the annular surface 12 masked off by the hollow cylinder 11 remains substantially unaffected by this process, although it does become slightly smaller due to carbon diffusion from the sides. For this reason, the cylinder 12 should be-slightly oversize so that the final dimensions of the annular surface portion 12 will hav'ethe required valueJ
  • the -resultant structure of the disc includes, except for this annular surface 12 on its top, a tungsten carbide skin 15 around all the remaining surfaces of the disc. This is shown in Fig.2.
  • a type A impregnant comprising a fused mix-ture of barium oxide and aluminum oxidejn a 5:2 mole ratio-see United States Patent No. 2,700,000 for a description of other suitable barium compositions-- is provided as a thin layer ona surface and the disc placed on top of the layer 16 as shown in Fig. 2.
  • the aluminate powder can be suspended in an amyl acetate carrier and painted as a thin layer on the support. The combination is now reheated to an elevated temperature of about l750 C.
  • phere such as hydrogen
  • phere such as hydrogen
  • the pr'efuse'd barium aluminate material melts and is drawn into the "pores of the tungsten disc by capillary action, in iheprdcesser which the molten alumin'a'te traverses the tungsten fearbide skin 1'5 on the disc 10.
  • the resultant impregnated disc 10 is "then mioun'ted in a suitable support 17 containing a heating filament --18, "and is then ready for assembly into an electron tube in the usual by reference numeral 19, whereas the other carburized disc surface portions 15 are essentially non-emitting and thus, as illustrated in Fig.
  • emission from such a structure is in the form of a hollow cylinder, as required.
  • the emission density from the emitting portions of such a cathode is of the same order as that from a type B impregnated cathode, although the" tYP A impregnant has been employed and although the emission densities of such impregnants in the usual im pregnate'd cathode have been below that of the type B impregnated cathode by a factor of-four. More'ov'er, because the type A impregnant is employed, the cathode will possess a higher resistance to ion bombardment and poisoning, and operate at higher temperatures where this is required.
  • the emission-inhibiting mechanism is operable only when the carburized surface is maintainedat an elevated temperature.
  • This temperature will generally be in excess of 950 C., and will depend upon the arrival rate of the barium metal and barium oxide contaminants to the carburized surface. With high arrival rates, the temperature of 950* C. or higher is required. At lower arrival rates, lower temperatures, e.g., 900 -or 800 C., are permissable. It is believed that the explanation for this phenomenon is con;-
  • the non-emitting area can be painted with a suspension of tungsten or molybdenum carbide, which islater heated to sinter the carbide coating'in position.
  • Carburization can also be obtained in other ways.
  • the tungsten pellet or electrode element'to be carburized can be heated in a hydrocarbon gas atmosphere of such a nature that the hydrocarbon disassociate l on contact with the heated pellet and the resultant carbon then can react with the tungsten to form the carbidedesired.
  • the element tobe carburized be heated in a naphthalene atmosphere. Insofar-as the impregnated-type cathode is concerned, it will be hppa'rent'that carburization of a surface portion to prevent emission can 'alsobe done after it has been impregnated with its activatiiig material. v 7
  • an ordinary planar impregnated cathode it is not necessary first to carburize the surface as described earlier.
  • a cathode can be simply made by providing an organic compound that when decomposed by heat will furnish a porous carbon matrix on the tungsten disc or pellet, and then melting the barium aluminate through this carbon mask formed prior to or while attaining the melting temperature into the tungsten interior.
  • Grdinary household sugar has worked well in this technique. Thereafter, the carbon mask may be brushed off or otherwise mechanically removed from the cathode surface together with the excess aluminate to leave a surface of impregnated tungsten from which high emission can be obtained.
  • a thin layer of tungsten powder may be painted on the pellet before applying thereto the carbon-forming compound, which thus prevents contact of the carbon with the surface of the disc.
  • machining can be employed for removing any slight carbide layer that results or other mechanical material-removing treatments.
  • Another technique that may be used involves oxidizing the surface of the cathode by heating it in air after which it is heated in a reduc- Such successive oxidation-reduction treatments cause material removal by sublimation and can be employed for removing any thin carbide layers present.
  • a method of making an improved dispenser-type cathode comprising providing a porous refractory-metal body, providing surface portions of the body with-a layer of a substance selected from the group consisting 'of tungsten carbide and molybdenum carbide-and impregmating the "pores of said body withactivating material by passing molten'barium-containing activating material through the said carbide surface layer into the pores, the carbide surface portions of said body when heated at an elevated temperature possessing substantially. no emissive capabilities, surface portions of said body free of the carbide layer and when heated at an-elevated temperature possessing improved emission-capabilities.
  • An electron device comprising a dispenser-type cathode generating a barium-containing contaminant, a surface receiving said contaminant and tending to emit electrons, and a substance selected from the group consisting of tungsten carbide and molybdenum carbide on said surface and inhibiting its emission, said surface being maintained at an elevated temperature.
  • An electron tube comprising a dispenser-type cathode containing a barium-type activating material, means for heating the cathode at an elevated temperature at which the cathode generates barium andbarium oxide, an element having a surface receiving said barium and barium oxide and tending to emit electrons, and a surface layer of a substance selected from the group consisting of tungsten carbide and molybdenum carbide on said surface and inhibiting its emission, said surface being maintained at an elevated temperature above about 950 C.
  • a dispenser-type cathode comprising a refractorymetal-containing body associated with a barium-containing activating material and generating a barium-containing contaminant, an emissive surface on said body and also a non-emissive surface receiving said contaminant and tending to emit electrons, a surface layer of a substance selected from the group consisting of tungsten carbide and molybdenum carbide on said non-emissive surface and inhibiting its emission, and means for heating the cathode at a temperature in excess of 950 C.
  • a dispenser-type cathode comprising a tungsten matrix impregnated with barium aluminate and generating a barium-containing contaminant, emissive and non emissive surface portions on said matrix, a tungsten carbide surface at said non-emissive surface portion and inhibiting its emission, and means for heating the cathode at an elevated temperature in excess of 950 C.
  • a method of inhibiting the emission from a surface exposed to barium and barium oxide evaporated from a dispenser-type cathode comprising providing the said surface with a surface layer of a substance selected from awarm the, group consisting of tungsten carbide and molybdenum carbide, and maintaining the said surface at an elevated temperature above about 950" C.
  • a method ofgmaking an improved impregnatedtype' dispenser cathode comprising the steps of providing a porous refractory-metal body, and impregnating the pores of said body with molten barium-containing activating material through a carbonrcgnta ing element.
  • a method of reducing the secondary emission from a dispenser cathode'of the type comprising a porous refract or yimetal body Whose pores are filled with a bariumcontaining activating material; comprising leaching-out the activating lm at eria l from the surface pores of the emissive surface of'the body.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
US78860359 1959-01-23 1959-01-23 Carburization of dispenser cathodes Expired - Lifetime US2972078A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
NL108689D NL108689C (enrdf_load_stackoverflow) 1959-01-23
US78860359 US2972078A (en) 1959-01-23 1959-01-23 Carburization of dispenser cathodes
DEN17772A DE1094887B (de) 1959-01-23 1960-01-19 Verfahren zur Herstellung einer impraegnierten Kathode fuer elektrische Entladungsroehren
GB208260A GB919419A (en) 1959-01-23 1960-01-20 Improvements in or relating to impregnated cathodes suitable for use in electric discharge tubes
CH60660A CH402197A (de) 1959-01-23 1960-01-20 Verfahren zur Herstellung einer imprägnierten Kathode für elektrische Entladungsröhren und eine nach diesem Verfahren hergestellte Kathode
DK20760A DK93307C (da) 1959-01-23 1960-01-20 Fremgangsmåde til fremstilling af katoder til elektriske udladningsrør.
AT40760A AT219166B (de) 1959-01-23 1960-01-20 Verfahren zur Herstellung einer imprägnierten Kathode für elektrische Entladungsröhren
BE586842A BE586842A (fr) 1959-01-23 1960-01-22 Cathode imprégnée pour tube à décharge et son procédé de fabrication.
FR816505A FR1245997A (fr) 1959-01-23 1960-01-23 Cathode imprégnée pour tube électronique et son procédé de fabrication

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US78860359 US2972078A (en) 1959-01-23 1959-01-23 Carburization of dispenser cathodes

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US2972078A true US2972078A (en) 1961-02-14

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US (1) US2972078A (enrdf_load_stackoverflow)
AT (1) AT219166B (enrdf_load_stackoverflow)
BE (1) BE586842A (enrdf_load_stackoverflow)
CH (1) CH402197A (enrdf_load_stackoverflow)
DE (1) DE1094887B (enrdf_load_stackoverflow)
DK (1) DK93307C (enrdf_load_stackoverflow)
FR (1) FR1245997A (enrdf_load_stackoverflow)
GB (1) GB919419A (enrdf_load_stackoverflow)
NL (1) NL108689C (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3869632A (en) * 1972-09-01 1975-03-04 Kernforschung Gmbh Ges Fuer Glow cathode
EP0009261A1 (de) * 1978-09-27 1980-04-02 Siemens Aktiengesellschaft Vorratskathode, insbesondere Metall-Kapillar-Kathode
US5173633A (en) * 1990-01-31 1992-12-22 Samsung Electron Devices Co., Ltd. Dispenser cathode
US20020187712A1 (en) * 1999-12-22 2002-12-12 Jean-Luc Ricaud Process for assembling a cathode-ray tube

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2043991B (en) * 1978-11-30 1983-05-11 Varian Associates Method of fabricating a dispenser cathode
DE3334971A1 (de) * 1983-09-27 1985-04-18 Siemens AG, 1000 Berlin und 8000 München Vorratskathode, insbesondere metall-kapillar-kathode
KR910006044B1 (ko) * 1988-11-12 1991-08-12 삼성전관 주식회사 디스펜서 캐소오드의 제조방법

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1922244A (en) * 1930-09-13 1933-08-15 Fansteel Prod Co Inc Electrode and method of making the same
GB701871A (en) * 1951-02-08 1954-01-06 Philips Electrical Ind Ltd Improvements in or relating to cathodes for electric discharge tubes and methods of producing such cathodes
GB705126A (en) * 1951-02-16 1954-03-10 Siemens Ag Improvements in or relating to cathodes for electric discharge tubes

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1922244A (en) * 1930-09-13 1933-08-15 Fansteel Prod Co Inc Electrode and method of making the same
GB701871A (en) * 1951-02-08 1954-01-06 Philips Electrical Ind Ltd Improvements in or relating to cathodes for electric discharge tubes and methods of producing such cathodes
GB705126A (en) * 1951-02-16 1954-03-10 Siemens Ag Improvements in or relating to cathodes for electric discharge tubes

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3869632A (en) * 1972-09-01 1975-03-04 Kernforschung Gmbh Ges Fuer Glow cathode
EP0009261A1 (de) * 1978-09-27 1980-04-02 Siemens Aktiengesellschaft Vorratskathode, insbesondere Metall-Kapillar-Kathode
US4310775A (en) * 1978-09-27 1982-01-12 Siemens Aktiengesellschaft Dispenser cathode, particularly a metal capillary cathode
US5173633A (en) * 1990-01-31 1992-12-22 Samsung Electron Devices Co., Ltd. Dispenser cathode
US20020187712A1 (en) * 1999-12-22 2002-12-12 Jean-Luc Ricaud Process for assembling a cathode-ray tube
US6705915B2 (en) * 1999-12-22 2004-03-16 Thomson Licensing S.A. Method of assembling an emissive cathode for electron gun

Also Published As

Publication number Publication date
DE1094887B (de) 1960-12-15
AT219166B (de) 1962-01-10
FR1245997A (fr) 1960-11-10
BE586842A (fr) 1960-07-22
DK93307C (da) 1962-04-30
NL108689C (enrdf_load_stackoverflow) 1900-01-01
GB919419A (en) 1963-02-27
CH402197A (de) 1965-11-15

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