US3227911A - Indirectly heated cathodes - Google Patents

Indirectly heated cathodes Download PDF

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Publication number
US3227911A
US3227911A US318643A US31864363A US3227911A US 3227911 A US3227911 A US 3227911A US 318643 A US318643 A US 318643A US 31864363 A US31864363 A US 31864363A US 3227911 A US3227911 A US 3227911A
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US
United States
Prior art keywords
metal
metal body
heater
heater assembly
nickel
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
US318643A
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English (en)
Inventor
Heil Oskar
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.)
Varian Medical Systems Inc
Original Assignee
Eitel Mccullough Inc
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
Priority to DENDAT1250013D priority Critical patent/DE1250013B/de
Priority to GB1052995D priority patent/GB1052995A/en
Application filed by Eitel Mccullough Inc filed Critical Eitel Mccullough Inc
Priority to US318643A priority patent/US3227911A/en
Priority to FR992267A priority patent/FR1413363A/fr
Application granted granted Critical
Publication of US3227911A publication Critical patent/US3227911A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01J1/24—Insulating layer or body located between heater and emissive material

Definitions

  • an indirectly heated cathode comprises a metal body having an emissive surface on the exterior thereof.
  • the metal body surrounds a heater which may or may not contain electrical insulation thereon.
  • an electrically insulated heater assembly has been imbedded in a metal powder, such as molybdenum or nickel, and sintered onto the metal cathode body.
  • This type of cathode structure has several disadvantages, such as the metal powder shrinking and cracking due to the sintering.
  • the shrinking also tends to deform the metal cathode body thereby damaging the optical properties of the cathode particularly when the metal cathode body is fabricated from thin material in order to obtain a quick heat up time.
  • the sintered metal powder becomes very rigid and the difference in thermal expansion between the insulated heater assembly and the sintered metal, especially during heat up time, causes friction therebetween which limits the life of the insulation covering the heater wires.
  • an object of this invention is to provide an improved indirectly heated cathode.
  • Another object of this invention is to provide a mechanically rugged indirectly heated cathode having improved heat transfer properties between the heater and emissive surface thereby permitting a reduction of the heater temperature which increases the life of the heater assembly.
  • Still another object of this invention is to provide an indirectly heated cathode wherein the heater assembly is firmly but flexibly retained adjacent an emissive surface.
  • an indirectly heated cathode that includes a metal body having an emissive surface thereon.
  • a heater assembly is located adjacent the emissive surface and in thermal contact with the metal body.
  • a metal material encases the heater assembly and is attached to the metal body. The metal material is capable of following the expanding and contracting motions of the metal body and the heater assembly and still retain the heater assembly firmly adjacent the metal body.
  • the metal material includes 10 to 150 micron size spheres of a first metal, such as nickel, which are bonded together by a second metal, such as molybdenum, and form an alloy therewith. If desired, heater power can be conserved by utilizing a heat insulator in the form of a quantity of alumina powder located adjacent the metal material at a point remote from the emissive surface.
  • FIGURE 1 illustrates a longitudinal cross-section of an indirectly heated cathode made in accordance with one embodiment of this invention
  • FIGURE 2 is a schematic illustration of a metal material utilized in constructing the cathode shown in FIG- URE 1;
  • FIGURE 3 illustrates a longitudinal cross-section of an indirectly heated cathode made in accordance with another embodiment of this invention.
  • FIGURE 1 an indirectly heated cathode in accordance with the present invention that includes a cup shaped metal body 11 of nickel or other suitable material.
  • the bottom or base 12 of the cup 11 is concave and has an electron emissive coating 13 on the exterior surface thereof which may be formed from barium, strontium and calcium oxides together with a suitable activator, such as zirconium, or from any other suitable electron emissive mixture or compound.
  • a suitable activator such as zirconium
  • the bottom or base 12 of the cathode need not be concave for it may be flat, elliptical or any other desired geometric shape.
  • a flat spiral heater assembly Adjacent the emissive coating 13 and within and in intimate thermal contact with the metal body 11 is a flat spiral heater assembly which includes a heater wire 15 of tungsten, or any other suitable material, coated with an insulating material 14, such as aluminum oxide (alumina ceramic).
  • the spacing between the turns of the heater is preferably substantially uniform to aid in even heat transfer to the emissive surface.
  • the metal material 16 firmly retains the heater assembly in thermal contact with the metal body 11 during vibrations and/or shock due to rapid accelerations and decelerations but is flexible enough to follow the expanding and contracting motions of the heater assembly and the metal body 11.
  • the metal material 16 is described in detail hereinbelow.
  • a quantity of heat insulating material 17 such as finely powdered aluminum oxide (alumina), which conserves heater power by acting as a heat dam.
  • the fine powdered aluminum oxide 17 is retained within the metal body 11 by a disk or membrane 18, which is made from any suitable material, such as a ceramic.
  • a jointure or seal of the disk '18 to the metal body 11 not be vacuum tight but yet be tight enough to prevent any of the fine powder 17 from escaping from the metal cup 11.
  • heater leads extend through the disk 18 to permit easy electrical connection to the heater assembly.
  • the metal material 16 is formed by intimately mixing 65 to by volume of 10 to micron size microspheres or particles of a suitable metal, such as nickel, and 35 to 5% by volume of a suitable finely powdered metal, such as molybdenum or palladium.
  • a suitable metal such as nickel
  • a suitable finely powdered metal such as molybdenum or palladium.
  • FIGURE 2 which illustrates in enlarged schematic form the metal material 16, it is shown that the nickel microspheres 19 are permanently bonded together by the molybdenum or palladium powder 20 which forms a nickel-molybedenum or nickel-palladium alloy with at least a portion of the microspheres 19.
  • the spongy metal material 16 is not absolutely rigid, attaches to the walls of the metal body 11, can follow the expanding and contracting motions of the heater assembly and metal body 11 and still firmly retain the heater assembly during vibrations.
  • the nickel microspheres 19 also conduct heat away from the heater and uniformly distribute it to the emissive surface 13.
  • the softness or rigidity of the metal material 16 can be controlled by the amount of metal powder 20 used with the metal microspheres 19 and by the duration and temperature of the heat treatment.
  • the nickel microspheres 19 can be replaced by microspheres of molybdenum in which case the fine powdered metal 20 could be nickel or palladium; or the nickel microspheres 19 can be replaced by palladium microspheres in which case the fine powdered metal 26 could be nickel or molybdenum.
  • Other fine metal powders can also be used as long as they form a lower melting alloy with the metal of the microspheres.
  • the indirectly heated cathode illustrated in FIGURE 1 and fully described hereinabove also has an extended heater life due to the lower operating temperature of the heater for a desired cathode operating temperature. This desirable result is achieved by the excellent thermal conductivity existing between the heater and the emissive surface 13.
  • FIGURE 3 which illustrates another embodiment of the present invention, there is shown a metal body or sleeve 21 formed from any suitable metal. such as nickel.
  • the metal body 21 may assume any cross-sectional shape, such as an oval, circle, rectangle, square, etc.
  • the exterior surface of the metal body 21 contains an electron emissive coating 22 which is formed from any suitable emissive material.
  • Adjacent the emissive coating 22 and within and in thermal contact with the metal body 21 is a heater assembly which includes a heater wire 24 of tungsten, or any other suitable material, coated with an insulating material 23, such as aluminum oxide.
  • the spacing between the turns of the heater is preferably substantially uniform to aid in even heat transfer to the emissive surface.
  • Attached to the interior of the metal body 21 and encasing the heater is the metal material 16 described hereinabove in detail. If desired, a quantity of heat insulating material, such as fine alumina powder (not shown), may be placed at opposite ends of the metal body 21 to act as heat dams.
  • a quantity of heat insulating material such as fine alumina powder (not shown) may be placed at opposite ends of the metal body 21 to act as heat dams.
  • An indirectly heated cathode comprising a metal body having an emissive surface, a heater assembly in thermal contact with said metal body and located adjacent said emissive surface, and a metal material attached to said metal body and encasing said heater assembly, said metal material capable of following the expanding and contracting motions of said metal body and said heater assembly and including to 150 micron size particles of a first metal which are bonded together by a second metal which forms with said first metal particles an alloy having a lower melting temperature than said first metal, and said particles being bonded together along a portion of their peripheries by a eutectic alloy of said second metal and a portion of the metal of said particles.
  • combination according to claim 1 further including a quantity of powdered alumina located within said metal body and adjacent said metal material at an area remote from said emissive surface.
  • An indirectly heated cathode comprising a metal body having an emissive surface, a heater assembly in thermal contact with said metal body and located adjacent said emissive surface, and a metal material attached to said metal body and encasing said heater assembly, said metal material capable of following the expanding and contracting motions of said metal body and said heater assembly and including 65 to by volume of 10 to micron size spheres of a first metal selected from the group consisting of molybdenum, palladium and nickel and which are bonded together by 35 to 5% by volume of a second metal which forms an alloy with said microspheres, and said spheres being bonded together along a portion of their peripheries by a eutectic alloy of said spheres with said second metal.
  • An indirectly heated cathode comprising a metal body having an emissive surface, a heater assembly in thermal contact with said metal body and located adjacent said emissive surface, and a metal material attached to said metal body and encasing said heater assembly, said metal material capa-ble of following the expanding and contracting motions of said metal body and said heater assembly and being formed from a powdered mixture including 65 to 95 by volume of 10 to 150 micron spheres of a metal selected from the group consisting of nickel, molybdenum and palladium and 35 to 5% by volume of an unlike finely powdered metal selected from the group consisting of nickel, molybdenum and palladium, a-nd said spheres being bonded together along a portion of their peripheries by a eutectic alloy of said spheres with said unlike metal.
  • An indirectly heated cathode comprising a metal body having an emissive surface on an outside portion thereof, a heater assembly located within said metal body and adjacent said emissive surface, a firm but flexible spongy metallic material attached to said metal body and encasing said heater assembly, said metal material capable of following the expanding and contracting motions of said metal body and said heater assembly and including 10 to 150 micron spheres of nickel bonded to gether along a portion of their peripheries with a eutectic alloy of molybdenum and a portion of the nickel in said spheres.

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  • Powder Metallurgy (AREA)
  • Resistance Heating (AREA)
US318643A 1963-10-24 1963-10-24 Indirectly heated cathodes Expired - Lifetime US3227911A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
DENDAT1250013D DE1250013B (enrdf_load_stackoverflow) 1963-10-24
GB1052995D GB1052995A (enrdf_load_stackoverflow) 1963-10-24
US318643A US3227911A (en) 1963-10-24 1963-10-24 Indirectly heated cathodes
FR992267A FR1413363A (fr) 1963-10-24 1964-10-22 Cathode émissive à chauffage indirect

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US318643A US3227911A (en) 1963-10-24 1963-10-24 Indirectly heated cathodes

Publications (1)

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US3227911A true US3227911A (en) 1966-01-04

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US318643A Expired - Lifetime US3227911A (en) 1963-10-24 1963-10-24 Indirectly heated cathodes

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US (1) US3227911A (enrdf_load_stackoverflow)
DE (1) DE1250013B (enrdf_load_stackoverflow)
GB (1) GB1052995A (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3323916A (en) * 1964-10-23 1967-06-06 Westinghouse Electric Corp Method of making heater assemblies by wet-settling techniques
US3401297A (en) * 1965-08-23 1968-09-10 Varian Associates Thermionic cathodes for electron discharge devices with improved refractory metal heater wires
US3574910A (en) * 1967-01-25 1971-04-13 Philips Corp Method of manufacturing an indirectly heated disclike cathode and cathode manufactured by said method
US3758876A (en) * 1970-08-04 1973-09-11 Siemens Ag Carbon dioxide laser
FR2681726A1 (fr) * 1991-09-20 1993-03-26 Thomson Tubes Electroniques Potting isolant pour cathodes a chauffage indirect.

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2080284A (en) * 1932-07-30 1937-05-11 Westinghouse Electric & Mfg Co Thermionic rectifier
US2542657A (en) * 1941-01-31 1951-02-20 Hartford Nat Bank & Trust Co Indirectly heated cathode
US2677782A (en) * 1950-10-27 1954-05-04 Sylvania Electric Prod Vacuum tube heater
US2975322A (en) * 1958-12-29 1961-03-14 Raytheon Co Indirectly heated cathodes
US3117249A (en) * 1960-02-16 1964-01-07 Sperry Rand Corp Embedded heater cathode

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2080284A (en) * 1932-07-30 1937-05-11 Westinghouse Electric & Mfg Co Thermionic rectifier
US2542657A (en) * 1941-01-31 1951-02-20 Hartford Nat Bank & Trust Co Indirectly heated cathode
US2677782A (en) * 1950-10-27 1954-05-04 Sylvania Electric Prod Vacuum tube heater
US2975322A (en) * 1958-12-29 1961-03-14 Raytheon Co Indirectly heated cathodes
US3117249A (en) * 1960-02-16 1964-01-07 Sperry Rand Corp Embedded heater cathode

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3323916A (en) * 1964-10-23 1967-06-06 Westinghouse Electric Corp Method of making heater assemblies by wet-settling techniques
US3401297A (en) * 1965-08-23 1968-09-10 Varian Associates Thermionic cathodes for electron discharge devices with improved refractory metal heater wires
US3574910A (en) * 1967-01-25 1971-04-13 Philips Corp Method of manufacturing an indirectly heated disclike cathode and cathode manufactured by said method
US3758876A (en) * 1970-08-04 1973-09-11 Siemens Ag Carbon dioxide laser
FR2681726A1 (fr) * 1991-09-20 1993-03-26 Thomson Tubes Electroniques Potting isolant pour cathodes a chauffage indirect.

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Publication number Publication date
GB1052995A (enrdf_load_stackoverflow)
DE1250013B (enrdf_load_stackoverflow)

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