US2798010A - Method of manufacturing indirectly heated cathodes - Google Patents

Method of manufacturing indirectly heated cathodes Download PDF

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US2798010A
US2798010A US510489A US51048955A US2798010A US 2798010 A US2798010 A US 2798010A US 510489 A US510489 A US 510489A US 51048955 A US51048955 A US 51048955A US 2798010 A US2798010 A US 2798010A
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layer
particles
indirectly heated
pores
ceramic layer
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US510489A
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Bender Harry
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GTE Sylvania Inc
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Sylvania Electric Products Inc
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    • 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

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  • Such' a structure comprises a hollow nickel cylinder or sleeve, the outside surface of which is coated with electron emissive material, and a suitably insulated tungsten heater element is mounted within the sleeve. Heat radiated by the element when it is electrically energized impinges on the sleeve; when the sleeve attains a suitable operating temperature (on the order of 800 C.), electrons are emitted. from the surface of the electron emissive coating.
  • Another object is to provide a new process for producing indirectly heated cathode structures simply and inexpensively.
  • Still another object is to' provide a new and improved indirectly heated cathode structure characterized by a short warm-up period and an extended useful life.
  • a refractory metallic heater element formed for example, from tungsten, molybdenum or alloys thereof, is first coated with a layer of ceramic material such as aluminum oxide or other ceramic characterized by low electrical conductivity at elevated temperatures. This layer is sintered to bond the layer to itself and to the heater. A second layer of metallic material such as nickel is then applied over the oxide layer. The composite structure is then heated to sinter and bond the metallic layer to itself and to the first layer. Finally a third layer of electron emissive material such as a mixture of the carbonates of barium, calcium and strontium is then applied over the second layer and sintered to form the completed cathode.
  • ceramic material such as aluminum oxide or other ceramic characterized by low electrical conductivity at elevated temperatures.
  • a second layer of metallic material such as nickel is then applied over the oxide layer.
  • the composite structure is then heated to sinter and bond the metallic layer to itself and to the first layer.
  • a third layer of electron emissive material such as a mixture of the carbonates of barium, calcium
  • the aluminum oxide coating of this structure is somewhat porous; if suitable precautions are not taken, the pores can be filled with metals or other compounds; as a result, undesired electrical conducting paths can be formed between the outer layer and the heater element.
  • a thin protective coating for example a lacquer coating
  • the size of the metallie particles is not critical and again the leakage problem, is solved. In either case an indirectly heated cathode characterized by low heater cathode leakage is produced.
  • coatings can either be applied electrophoretically or by a conventional drag-cup process well known to the art. Either technique results in thin coatings. Consequently, the emission surface is substantially the same size as the heater surface and is in close proximity thereto. Therefore, the warm-up period of the cathode is sharply reduced. Further, the temperature differential between the heater element and the emissive surface is. also-reduced and the useful life of thecathode is correspondingly increased.
  • Fig. 1 shows one form of an indirectly heated structure in accordance with tlie'invention
  • Fig. 2 illustrates diagrammatically a heater element coating process for producing the structure.
  • the indirectly heated cathode of Fig. 1 comprises a heater element, for example a tungsten wire 1, clad with a layer 2 of ceramic material such as aluminum.
  • a second layer 3 of metallic material such as nickel surrounds the first layer and a third layer 4 of electron emissive material such. as a mixture of the carbonates of barium, strontium and calcium covers the second layer.
  • Each of these layers is securely bonded to each other, and the first layer is likewise securely bonded to the heater element;
  • the ends of wire 1 are exposed for suitable electrical connection.
  • a nickel tab 5 is welded or otherwise connected to the nickel layer and serves as a cathode return connection.
  • Fig. 2 illustrates a process for producing the structure of Fig. l.
  • the tungsten wire is unreeled from a supply spool and is passed under pulley 101 and over pulley 1&2 into pulley 103 of drag cup 104.
  • This cup contains a liquid dispersion'of aluminum oxide and suitable binder particles.
  • the wire leaving drag cup 104 is loosely coated with a layer 2 of Alundum particles.
  • the oxide coated wire is then passed through a furnace 105 wherein it is heated to a temperature on the order of 1800" C. in an oxygen free atmosphere containing argon or other inert gas or a reducing agent such as moist hydrogen to sinter the oxide particles to each other and to the wire.
  • This coating is somewhat porous.
  • the Alundum coated wire is then passed over pulleys 106 and 167 onto pulley 108 of drag cup 1&9.
  • This cup contains a conventional lacquer.
  • the lacquered wire is then passed under pulley 110 and over pulley 111 onto pulley 112 of drag cup 113.
  • This cup contains a liquid dispersion of nickel particles and a suitable binder.
  • the wire leaving drag cup 13 then is coated with a sintered layer 2, a thin layer of lacquer, and a loose layer of nickel particles.
  • the wire is then fed through a second furnace 114 where it is heated in an oxygen free atmosphere to a temperature on the order of 1500 C.
  • the lacquer coating is vaporized and a sintered nickel layer is formed and bonded to the oxide layer.
  • the nickel coating seals off but does not penetrate the pores of the oxide layer.
  • the wire leaving furnace 114 is then passed over pulley 115 and under pulley 116 onto pulley 117 of drag cup 118.
  • This cup contains a slurry of alkaline earth carbonates.
  • the wire leaving drag cup 118 then has been coated with a sintered aluminum oxide layer 2, a sintered nickel layer 3, and a loose carbonate layer 4.
  • the wire is then fed through a third furnace 119 wherein it is heated in an atmosphere of carbon dioxide to sinter the particles of layer 4 to each other and to the nickel layer to form the completed structure.
  • the coated wire leaving furnace is then wound over take-up spool 120.
  • Two or more drag cups containing the same dispersion can be arranged in series to build up the thickness of any particular layer to any value desired.
  • successive layers of aluminum oxide can be applied as necessary.
  • the entire layer is sintered in the manner previously indicated.
  • Aqueous-base or lacquer-base dispersions can be used.
  • a typical aqueous base dispersion has the following composition:
  • a typical lacquer base dispersion has the following composition:
  • Lacquer 50 cc Amyl acetate 100 mls. Nickel particles 100 gms.
  • the particle size of the nickel is critical for leakage purposes as indicated previously.
  • nickel flake powder of the type identified as MD75O and manufactured commercially by Metals Disintegrating Co. has the proper particle classification for this purpose; i. e. these powders will pass through a 325 mesh screen.

Description

July 2, 1957 METHOD FURNACE H. BENDER 2,798,010
OF MANUFACTURING INDIRECTLY HEATED CATHODES Filed May 25, 1955 FURNACE INVENTOR. HARRY BENDER BY MQ%\ Unite States Patent Office 2,798,010 Patented July 2, 1957 METHOD Q15 MANUFACTURING INDIRECTLY HEATED CATHODES Harry Bender, Albertson, N. Y., assignor to Syivania Electric Products Inc., a corporation of Massachusetts ApplicationMay 23, 1955, fierialldo; 516,489
4 Claims. (Cl. 117-==-217)' My invention relates to improved electron tubes. and methods for making the same.
Many types of conventional electron tubes employ indirectly heated cathode structures. Typically, such' a structure comprises a hollow nickel cylinder or sleeve, the outside surface of which is coated with electron emissive material, and a suitably insulated tungsten heater element is mounted within the sleeve. Heat radiated by the element when it is electrically energized impinges on the sleeve; when the sleeve attains a suitable operating temperature (on the order of 800 C.), electrons are emitted. from the surface of the electron emissive coating.
This type of structure, due to the number and complexity of the components, is relatively expensive to produce in quantity. Moreover, the efliciency of heat transfer is low. As a result, a relatively longwarmup or heating period is required. Asa further result, the operating temperature of the heater is much higher than that of the, sleeve, since the useful life of the element decreases rapidly as its operating temperature increases, this temperature differential is obviously undesirable.
Accordingly, it is an object of the invention to simplify the construction and improve theheat transfer efficiency of indirectly heated cathode structures.
Another object is to provide a new process for producing indirectly heated cathode structures simply and inexpensively.
Still another object is to' provide a new and improved indirectly heated cathode structure characterized by a short warm-up period and an extended useful life.
These and other objects of my invention will either be explained or" will become apparent hereinafter.
In my invention, a refractory metallic heater element, formed for example, from tungsten, molybdenum or alloys thereof, is first coated with a layer of ceramic material such as aluminum oxide or other ceramic characterized by low electrical conductivity at elevated temperatures. This layer is sintered to bond the layer to itself and to the heater. A second layer of metallic material such as nickel is then applied over the oxide layer. The composite structure is then heated to sinter and bond the metallic layer to itself and to the first layer. Finally a third layer of electron emissive material such as a mixture of the carbonates of barium, calcium and strontium is then applied over the second layer and sintered to form the completed cathode.
The aluminum oxide coating of this structure is somewhat porous; if suitable precautions are not taken, the pores can be filled with metals or other compounds; as a result, undesired electrical conducting paths can be formed between the outer layer and the heater element. However, I have discovered that when the size of the metallic particles is sufiiciently large, these particles will seal off (and not penetrate) the oxide layer, and leakage no longer presents a problem. I have further discovered that when the oxide layer is covered with a thin protective coating, for example a lacquer coating, to seal the pores before the metallic layer is applied, the size of the metallie particles is not critical and again the leakage problem, is solved. In either case an indirectly heated cathode characterized by low heater cathode leakage is produced.
These coatings can either be applied electrophoretically or by a conventional drag-cup process well known to the art. Either technique results in thin coatings. Consequently, the emission surface is substantially the same size as the heater surface and is in close proximity thereto. Therefore, the warm-up period of the cathode is sharply reduced. Further, the temperature differential between the heater element and the emissive surface is. also-reduced and the useful life of thecathode is correspondingly increased.
An illustrative embodiment of my invention will now be described in detail with reference to the accompanying, drawings wherein:
Fig. 1 shows one form of an indirectly heated structure in accordance with tlie'invention; and
Fig. 2 illustrates diagrammatically a heater element coating process for producing the structure.
Referring now to the drawings, the indirectly heated cathode of Fig. 1 comprises a heater element, for example a tungsten wire 1, clad with a layer 2 of ceramic material such as aluminum. A second layer 3 of metallic material such as nickel surrounds the first layer and a third layer 4 of electron emissive material such. as a mixture of the carbonates of barium, strontium and calcium covers the second layer. Each of these layers is securely bonded to each other, and the first layer is likewise securely bonded to the heater element; The ends of wire 1 are exposed for suitable electrical connection. A nickel tab 5 is welded or otherwise connected to the nickel layer and serves as a cathode return connection.
Fig. 2 illustrates a process for producing the structure of Fig. l. The tungsten wire is unreeled from a supply spool and is passed under pulley 101 and over pulley 1&2 into pulley 103 of drag cup 104. This cup contains a liquid dispersion'of aluminum oxide and suitable binder particles. The wire leaving drag cup 104 is loosely coated with a layer 2 of Alundum particles. The oxide coated wire is then passed through a furnace 105 wherein it is heated to a temperature on the order of 1800" C. in an oxygen free atmosphere containing argon or other inert gas or a reducing agent such as moist hydrogen to sinter the oxide particles to each other and to the wire. This coating is somewhat porous. In order to prevent substantial leakage, the Alundum coated wire is then passed over pulleys 106 and 167 onto pulley 108 of drag cup 1&9. This cup contains a conventional lacquer.
The lacquered wire is then passed under pulley 110 and over pulley 111 onto pulley 112 of drag cup 113. This cup contains a liquid dispersion of nickel particles and a suitable binder. The wire leaving drag cup 13 then is coated with a sintered layer 2, a thin layer of lacquer, and a loose layer of nickel particles. The wire is then fed through a second furnace 114 where it is heated in an oxygen free atmosphere to a temperature on the order of 1500 C. As a result, the lacquer coating is vaporized and a sintered nickel layer is formed and bonded to the oxide layer. The nickel coating seals off but does not penetrate the pores of the oxide layer. I do not fully understand why this action occurs, but I believe that the nickel particles will tend to sinter and bond to each other to some extent before the lacquer is completely vaporized, and this initial sintering prevents nickel particles from falling into the pores. Alternatively, when the nickel particles are sufficiently large to seal off the oxide pores, the lacquer application step can be eliminated.
The wire leaving furnace 114 is then passed over pulley 115 and under pulley 116 onto pulley 117 of drag cup 118. This cup contains a slurry of alkaline earth carbonates. The wire leaving drag cup 118 then has been coated with a sintered aluminum oxide layer 2, a sintered nickel layer 3, and a loose carbonate layer 4. The wire is then fed through a third furnace 119 wherein it is heated in an atmosphere of carbon dioxide to sinter the particles of layer 4 to each other and to the nickel layer to form the completed structure. The coated wire leaving furnace is then wound over take-up spool 120.
Two or more drag cups containing the same dispersion can be arranged in series to build up the thickness of any particular layer to any value desired. Thus, for example, successive layers of aluminum oxide can be applied as necessary. However, in order to insure that each Alundum layer has sufiicient adherence to permit the addi tion of a subsequent Alundum layer, it is necessary to interpose heating stations between adjacent aluminum oxide containing cups to dry the binder and thus obtain the desired amount of adherence. After the overall thickness has been increased to the desired value, the entire layer is sintered in the manner previously indicated.
I have found that in order to form an acceptable metallic layer using a single cup, the ratio by weight of liquids to solids in the applicable dispersion must be on the order of 4/5. Either aqueous-base or lacquer-base dispersions can be used. A typical aqueous base dispersion has the following composition:
A typical lacquer base dispersion has the following composition:
Lacquer 50 cc. Amyl acetate 100 mls. Nickel particles 100 gms.
When the preliminary lacquer coating technique is not used, the particle size of the nickel is critical for leakage purposes as indicated previously. I have found that nickel flake powder of the type identified as MD75O and manufactured commercially by Metals Disintegrating Co. has the proper particle classification for this purpose; i. e. these powders will pass through a 325 mesh screen.
While I have shown and pointed out and described my invention in one preferred embodiment, it will be apparent to those skilled in the art that many modifications can be made within the scope and sphere of my invention as defined in the claims which follow.
What is claimed is:
1. In a method of manufacturing an indirectly heated cathode, the steps of depositing ceramic particles having low electrical conductivity out of liquid media onto the surface of a refractory metallic heater element; heating the resultant structure in an oxygen free atmosphere until a sintered somewhat porous ceramic layer well bonded to said surface is formed; coating said ceramic layer with lacquer to seal off the pores thereof; depositing metallic particles out of liquid media onto the ceramic layer; and heating the resulting structure in an oxygen free atmosphere until a sintered metallic sheath is formed, said sheath being well bonded to said ceramic layer and sealing off the pores thereof.
2. In the method as set forth in claim 1, the further steps of depositing particles of electron emissive material out of liquid media onto the metallic sheath; and heating the resultant structure in an oxygen free atmosphere until a sintered electron emissive layer well bonded to' the metallic sheath is formed.
3. In a method for manufacturing an indirectly heated cathode, the steps of depositing ceramic material of low electrical conductivity out of liquid media onto the surface of a refractory metallic heater element; sintering said ceramic coated element to form a porous ceramic layer well bonded to said surface; coating said ceramic layer with lacquer to seal olf said pores; depositing metallic particles out of liquid media-onto the lacquer coated element; and sintering the resultant structure in an oxygen free atmosphere to form a metallic sheath well bonded to said ceramic layer, the pores of said layer being free from said metallic particles.
4. In a method for manufacturing an indirectly heated cathode from a refractory metallic heater element coated with a porous layer of ceramic material characterized by low thermal conductivity at elevated temperatures, the steps of depositing metallic particles out of liquid media onto the surface of said ceramic layer, the size of said particles being related to the size of the pores in said layer in such manner that the particles seal off and do not penetrate said pores; and sintering the resultant structure until a sintered metallic sheath well bonded to said porous layer is formed.
References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN A METHOD OF MANUFACTURING AN INDIRECTLY HEATED CATHODE, THE STEPS OF DEPOSITING CERAMIC PARTICLES HAVING LOW ELECTRICAL CONDUCTIVITY OUT OF LIQUID MEDIA ONTO THE SURFACE OF A REFRACTORY METALLIC HEATER ELEMENT; HEATING THE RESULTANT STRUCTURE IN AN OXYGEN FREE ATMOSPHERE UNTIL A SINTERED SOMEWHAT POROUS CERAMIC LAYER WELL BONDED TO SAID SURFACE IS FORMED; COATING SAID CERAMIC LAYER WITH LACQUER TO SEAL OFF THE PORES THEREOF; DEPOSITING MATALLIC PARTICLES OUT OF LIQUID MEDIA ONTO THE CERAMIC LAYER; AND HEATING THE RESULTING STRUCTURE IN AN OXYGEN FREE ATMOSPHERE UNTIL A SINTERED METALLIC SHEATH IS FORMED, SAID SHEATH BEING WELL BONDED TO SAID CERAMIC LAYER AND SEALING OFF THE PORES THEREOF.
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3041209A (en) * 1955-06-28 1962-06-26 Gen Electric Method of making a thermionic cathode
US3150342A (en) * 1960-02-10 1964-09-22 Morganite Resistors Ltd Non-linear resistors
US3213308A (en) * 1961-11-29 1965-10-19 Westinghouse Electric Corp Ultraviolet radiation detector
US3418164A (en) * 1963-02-06 1968-12-24 Philips Corp Filament wire for use in the cathode of a thermionic valve
US20150266288A1 (en) * 2012-10-25 2015-09-24 Leonhard Kurz Stiftung & Co. Kg Hot Stamping Machine

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2112969A (en) * 1926-12-11 1938-04-05 Rca Corp Cathode
US2711390A (en) * 1952-11-18 1955-06-21 Sylvania Electric Prod Method of making composite thermionically emissive cathode material

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2112969A (en) * 1926-12-11 1938-04-05 Rca Corp Cathode
US2711390A (en) * 1952-11-18 1955-06-21 Sylvania Electric Prod Method of making composite thermionically emissive cathode material

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3041209A (en) * 1955-06-28 1962-06-26 Gen Electric Method of making a thermionic cathode
US3150342A (en) * 1960-02-10 1964-09-22 Morganite Resistors Ltd Non-linear resistors
US3213308A (en) * 1961-11-29 1965-10-19 Westinghouse Electric Corp Ultraviolet radiation detector
US3418164A (en) * 1963-02-06 1968-12-24 Philips Corp Filament wire for use in the cathode of a thermionic valve
US20150266288A1 (en) * 2012-10-25 2015-09-24 Leonhard Kurz Stiftung & Co. Kg Hot Stamping Machine
US9889641B2 (en) * 2012-10-25 2018-02-13 Leonhard Kurz Stiftung & Co. Kg Hot-stamping machine

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