US3590242A - Making fused thorium carbide-tungsten cathodes for electron guns - Google Patents

Making fused thorium carbide-tungsten cathodes for electron guns Download PDF

Info

Publication number
US3590242A
US3590242A US832758A US3590242DA US3590242A US 3590242 A US3590242 A US 3590242A US 832758 A US832758 A US 832758A US 3590242D A US3590242D A US 3590242DA US 3590242 A US3590242 A US 3590242A
Authority
US
United States
Prior art keywords
tube
mixture
cathode
thorium
cathodes
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
Application number
US832758A
Other languages
English (en)
Inventor
Homer H Glascock Jr
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.)
General Electric Co
Original Assignee
General Electric 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 General Electric Co filed Critical General Electric Co
Application granted granted Critical
Publication of US3590242A publication Critical patent/US3590242A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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
    • 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
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/1266—O, S, or organic compound in metal component
    • 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
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component

Definitions

  • My invention relates to thorium compound cathodes and, in particular, to new and improved methods of making fused thorium compound cathodes and the resultant cathodes.
  • Thermionic cathodes composed of an aggregate of particles of thorium carbide, or thorium carbide and tungsten, have been used in a variety of electron gun applications. These cathodes conventionally are fabricated by compressing mixed thorium and carbon, or thorium and tungsten carbide powder into a refractory metal cup at a pressure of several tons per square inch. With subsequent heating in vacuum to operating temperatures, a chemical reaction converts the mixture to a sintered thorium carbide or thorium carbide plus tungsten.
  • Thorium carbide cathodes possess a higher work function than do other conventional cathodes, such as barium oxide or barium dispenser cathodes, and also operate at much higher temperatures. As a consequence, thorium carbide cathodes consume more power and exhibit greater emission cooling for the same level of emission than do barium cathodes. On the other hand, thorium carbides do possess the outstanding ability to yield high emission current density in a rather poor vacuum for long periods of time. Moreover, thorium carbide has a rather high electrical conductivity so that cathodes formed from it suffer from none of the problems associated with insulating or semiconducting emitters.
  • my invention consists in making a fused thorium compound cathode by melting a mixture of the desired thorium and other metal powders, suspending a tube of a refractory metal in the molten mixture so that its lower end is immersed in the molten mixture, and allowing the'mixture to ascend the tube by capillary attraction, the resultant filled tube, upon cooling, being divided into cathode bodies of desired length.
  • Another feature of my invention consists in bombarding such a cathode body with an electron beam to produce melting of the end of the body and thereby form a smooth hemispherical surface which when used in an electron optical device maximizes the density of the current emitted by the cathode in a small beam spot.
  • FIG. 1 illustrates a starting step in my method of making a thorium compound cathode
  • FIG. 2 illustrates an intermediate step in the making of such a cathode
  • FIG. 3 illustrates a variation in my improved method of making a thorium compound cathode
  • FIG. 4 is a schematic drawing of the principal elements of an electron discharge device employing my improved thorium compound cathode
  • FIG. 5 illustrates a modification of my method and apparatus for making a thorium compound cathode
  • FIG. 6 illustrates a modified thorium compound cathode embodying additional features of my invention.
  • a sample of a chosen emission mixture 1 is placed in a container or boat 2 and a refractory metal tube 3 is inserted in the mixture.
  • the mixture 1 may comprise any chosen mixture of emission powders, for example, thorium carbide powder or a mixture of thorium and tungsten carbide powders.
  • the boat or container 2 may comprise any suitable refractory metal, such as, for example, a tungsten container.
  • Refractory metal tube 3 may, likewise, comprise any satisfactory refractory metal such as, for example, a tube formed of an alloy of tungsten and rhenium, a conventional alloy consisting of approximately 75 percent tungsten and 25 percent rhenium. Tube 3 is supported by conventional means (not shown) so that its lower end remains immersed in the powders during subsequent manufacture of the thorium compound cathode.
  • refractory metal tube 3 After refractory metal tube 3 is supported in position in container 2, the entire assembly is heated until the emission mixture melts.
  • the entire assembly may be placed in a refractory container and heated by radiofrequency currents in vacuum until the emission mixture melts.
  • I employ the surface energy of the liquid phase of the thorium compound to form a dense, fused cathode structure.
  • capillary attraction draws the liquid up into the refractory metal tube 3.
  • the height, h, to which the liquid will rise in metal tube 3 may be expressed approximately by the equation where:
  • S is the liquid-vapor surface tension 6 is the angle of contact of the liquid with the tube p is the liquid density r is the inside tube radius and g the local gravitational acceleration term.
  • FIG. 2 illustrates the assembly of FIG. 1 after the powder mixture has been melted and the surface energy of the liquid phase of the melted powder has caused it to rise by capillary attraction in tube 3.
  • FIG. 3 illustrates how the length of the filled tube can be increased by inclining the tube at an angle D with the vertical.
  • the tube 3 After the tube 3 has been filled with liquid emission mixture, it is allowed to cool. It is then cut into cathodebodies of the desired length, typically 0i'050 inch long for 0.030- to 0.040 inh'e'xt'erhal diameter of tube 3.
  • FIG. 4 is a schematic drawing of the essential portions of an electron discharge device embodying the cathode of my invention.
  • the cathode body 5 formed by utilizing capillary attraction to fill the refractory metal tube with a liquid emission mixture, is supported by a pair of legs 6, 7 which provide externally accessible terminals for the cathode body.
  • anode 6 Opposed to the emissive surface of cathode 5 is an anode 6 having a narrowed neck portion 8, the outer end of which is spaced a desired distance from the surface of cathode 9.
  • Anode 8 is surrounded by an insulating cylinder 10 of any suitable material such as, for example, alumina, which in turn is supported in a rigid supporting member 11 for maintaining the surface of anode 9 in fixed spaced relation with respect to the opposed surface of cathode 5.
  • alumina any suitable material such as, for example, alumina
  • a cathode formed by capillary attraction is superior in a number of respects to a cathode formed by packing emissive powders in a supporting cylinder.
  • it is found to be more resistant to hydrolysis and, likewise, is mechanically stronger than prior cathodes and hence easier to handle.
  • the cost of producing the cathode by the capillary attraction method of my invention is much less than the cost of producing a cathode by packing powders in a refractory tube and thereafter sinter ing the packed powders.
  • the cathode of my invention possesses a more mechanically stable emitting surface and has a lower evaporation rate than does the packed powder cathode.
  • the mechanical stability of the cathode emission surface is particularly desirable for use in electron tubes where it is desired to avoid changes in the electron optical properties of the tubes.
  • FIG. illustrates a modification of the apparatus and method used in manufacturing cathodes in accordance with my invention which is particularly useful where an emission mixture is used which does not possess a fixed melting point.
  • a near eutectic liquid may be drawn off where the refractory metal tube is immersed in the emission mixture powder prior to melting.
  • the resulting tube fill has quite different composition from that of the original powder mixture.
  • the mixture of powders 1 is placed in a boat or container 15 and suspended by means of legs 16 from the inturned lower edges 17 of a U-shaped support 18.
  • Contained within support 18 are a plurality of tungsten guides 19 having one end attached to the wall of support 18 and their other end 20 partially encircling tube 3.
  • l likewise, provide a fusible support 21, the ends of which are attached to the walls of support 18 and which is attached to tube 23 to maintain it in a position where it is supported above the top of the mixture of powders i.
  • supporting strip 21 is formed of a material which has a melting point higher than the melting point of the powders of mixture 1. Accordingly, after the powders in boat 15 are melted, the entire assembly is heated to slightly above the melting point of strip 21. Tube 3 then drops into a completely molten emission mixture which flows up the tube and invariably yields the desired composition of the material for the cathode body.
  • fusible strip 21 may be formed of niobium. Accordingly, when the assembly is heated to a temperature slightly above 2468 C., the melting point of niobium, tube 3 will drop into the molten mixture.
  • a weight 22 formed of a suitable high-melting material such as, for example, molybdenum, may be placed on top of the tube to assure that the tube drops into the molten mixture.
  • an equal molar mixture of I thorium carbide and tungsten is desired since this mixture results in a fixed interlocking tungsten dendritic structure with the interstices filled with the thorium carbide-tungsten eutectic COEIPOSIIIOI].
  • Use of the apparatus of FIG. 5 is particularly desirable in this case since the eutectic composition of the thorium carbide-tungsten alloy system is on the thorium-carbide-rich side of the phase diagram. If the refractory metal tube is immersed in the emission powder rise prior to the melting of the mixture powder, there is a tendency to draw off the eutectic composition into the tube leaving tungsten in the boat.
  • the tube will drop upon the melting of the fusible strip 21 into a completely molten emission mixture which then flows up the tube and invariably yields the desired tungsten dendritic structure when quenched which results in cathodes with very mechanically stable surfaces.
  • a recurring problem is maximizing the current density of a cathode in a small beam spot. Since maximum spot brightness is directly limited by the cathode brightness, it is desirable to maximize cathode emission density by effectively focusing the cathode emission into a beam or small spot corresponding to a virtual point source.
  • FIG. 6 Such a structure is illustrated in FIG. 6 in which the cathode body 5, after being mounted in heater legs 6, 7, is bombarded by an electron beam by a conventional means (not shown) so that the tip 30 melts and surface tension forms it into a spherical surface after which it is allowed to cool.
  • the tip of the solid rod 3 formed in accordance with the methods illustrated in FIGS. 1 and 5 may be melted by electron beam bombardment and thereafter the spherical tip and a small portion of the rod cut from the remainder of the rod and mounted on refractory metal supports 6, 7.
  • the cathode body 5 may be mounted in the supports prior to electron beam bombardment.
  • the formation of the spherical tip by surface tension in a molten state results in a very smooth, dense surface of accurate sphericity when a single solid phase or eutectic composition is used.
  • the electric field is accurately radial and of high intensity. Electrons emitted from the surface tend to follow the field lines makirg them appear to come from the center of the sphere. Electron lenses, therefore, using such cathodes have a small virtual ob ject with which to form an image.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
  • Manufacture And Refinement Of Metals (AREA)
US832758A 1969-06-12 1969-06-12 Making fused thorium carbide-tungsten cathodes for electron guns Expired - Lifetime US3590242A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US83275869A 1969-06-12 1969-06-12

Publications (1)

Publication Number Publication Date
US3590242A true US3590242A (en) 1971-06-29

Family

ID=25262550

Family Applications (1)

Application Number Title Priority Date Filing Date
US832758A Expired - Lifetime US3590242A (en) 1969-06-12 1969-06-12 Making fused thorium carbide-tungsten cathodes for electron guns

Country Status (5)

Country Link
US (1) US3590242A (enrdf_load_stackoverflow)
DE (1) DE2028481A1 (enrdf_load_stackoverflow)
FR (1) FR2051157A5 (enrdf_load_stackoverflow)
GB (1) GB1304744A (enrdf_load_stackoverflow)
NL (1) NL7008505A (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930139A (en) * 1974-05-28 1975-12-30 David Grigorievich Bykhovsky Nonconsumable electrode for oxygen arc working
US4002940A (en) * 1974-06-12 1977-01-11 U.S. Philips Corporation Electrode for a discharge lamp

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3160780A (en) * 1961-01-17 1964-12-08 Philips Corp Indirectly heated cathode
US3258636A (en) * 1961-09-01 1966-06-28 Electron emitter with activator of sill cide, boride or carbide of solid solu- tion of barium and at least one other alkaline earth metal
US3269804A (en) * 1963-11-01 1966-08-30 Gen Electric Dispenser cathode and method for the production thereof
GB1046639A (en) * 1964-08-17 1966-10-26 Gen Electric Improvements in dispenser cathode
US3307241A (en) * 1963-10-14 1967-03-07 Litton Prec Products Inc Process for making cathodes
US3338988A (en) * 1963-04-04 1967-08-29 Commissariat Energie Atomique Method of making bars of an uranium compound and in particular uranium carbide
US3405044A (en) * 1964-08-19 1968-10-08 Rca Corp Method of making high purity metal zeolite and product thereof
US3434812A (en) * 1964-04-16 1969-03-25 Gen Electric Thermionic cathode
US3474281A (en) * 1965-12-23 1969-10-21 Siemens Ag Electron beam production system for electronic discharge
US3488549A (en) * 1968-01-15 1970-01-06 Gen Electric Dispenser cathode material and method of manufacture

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3160780A (en) * 1961-01-17 1964-12-08 Philips Corp Indirectly heated cathode
US3258636A (en) * 1961-09-01 1966-06-28 Electron emitter with activator of sill cide, boride or carbide of solid solu- tion of barium and at least one other alkaline earth metal
US3338988A (en) * 1963-04-04 1967-08-29 Commissariat Energie Atomique Method of making bars of an uranium compound and in particular uranium carbide
US3307241A (en) * 1963-10-14 1967-03-07 Litton Prec Products Inc Process for making cathodes
US3269804A (en) * 1963-11-01 1966-08-30 Gen Electric Dispenser cathode and method for the production thereof
US3434812A (en) * 1964-04-16 1969-03-25 Gen Electric Thermionic cathode
GB1046639A (en) * 1964-08-17 1966-10-26 Gen Electric Improvements in dispenser cathode
US3405044A (en) * 1964-08-19 1968-10-08 Rca Corp Method of making high purity metal zeolite and product thereof
US3474281A (en) * 1965-12-23 1969-10-21 Siemens Ag Electron beam production system for electronic discharge
US3488549A (en) * 1968-01-15 1970-01-06 Gen Electric Dispenser cathode material and method of manufacture

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930139A (en) * 1974-05-28 1975-12-30 David Grigorievich Bykhovsky Nonconsumable electrode for oxygen arc working
US4002940A (en) * 1974-06-12 1977-01-11 U.S. Philips Corporation Electrode for a discharge lamp

Also Published As

Publication number Publication date
FR2051157A5 (enrdf_load_stackoverflow) 1971-04-02
GB1304744A (enrdf_load_stackoverflow) 1973-01-31
NL7008505A (enrdf_load_stackoverflow) 1970-12-15
DE2028481A1 (enrdf_load_stackoverflow) 1970-12-17

Similar Documents

Publication Publication Date Title
US4165473A (en) Electron tube with dispenser cathode
US4002940A (en) Electrode for a discharge lamp
US3911309A (en) Electrode comprising a porous sintered body
US2339392A (en) Cathode
US3766423A (en) Integral emissive electrode
US3373307A (en) Dispenser cathode
US3590242A (en) Making fused thorium carbide-tungsten cathodes for electron guns
US3159461A (en) Thermionic cathode
US5407633A (en) Method of manufacturing a dispenser cathode
JPH0355739A (ja) 含浸型陰極の製造方法
US4982133A (en) Dispenser cathode and manufacturing method therefor
US3758809A (en) Emissive fused pellet electrode
KR100189035B1 (ko) 스캔데이트 음극
KR100315123B1 (ko) 전자빔 장치용 음극 물질
US3656020A (en) Thermionic cathode comprising mixture of barium oxide, calcium oxide and lithium oxide
US3760218A (en) Thermionic cathode
US3697798A (en) Rotating x-ray target
JP2001006521A (ja) カソード構体およびカラーブラウン管
KR890002949A (ko) 디스펜서 캐소드 제조방법
EP0157634B1 (en) Tungsten-iridium impregnated cathode
KR20030030686A (ko) 전자관용 금속 음극
CN113584437B (zh) 钨铜合金的制备方法及制备设备
JPS62237634A (ja) デイスペンサ陰極およびその構成方法
US1954189A (en) Electric discharge tube
GB2109157A (en) Electron tube and dispenser cathode with high emission impregnant