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
  • H01J9/08—Manufacture of heaters for indirectly-heated 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
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core
  • Y10T428/294—Coated or with bond, impregnation or core including metal or compound thereof [excluding glass, ceramic and asbestos]
  • Y10T428/2942—Plural coatings
  • Y10T428/2944—Free metal in coating
• • 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
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core
  • Y10T428/294—Coated or with bond, impregnation or core including metal or compound thereof [excluding glass, ceramic and asbestos]
  • Y10T428/2942—Plural coatings
  • Y10T428/2949—Glass, ceramic or metal oxide in coating

Definitions

• This invention relates to electron discharge tubes, and particularly to a method of fabricating dark insulated heaters for such tubes.
• Such heaters comprise a core wire of a refractory metal, such as tungsten, a first wire covering layer of an insulating material, such as aluminum oxide, and an outer dark coating such as a particulate mixture of tungsten and aluminum oxide.
• a purpose of the first coating is to provide insulation between the heater wire and the cathode, and a purpose of the outer coating is to increase the thermal emissivity of the heater, thereby lowering the temperature at which the heater need operate to heat the cathode to'its operating temperature. The greater the proportion of tungsten in the outer coating, the darker the heater.
• the technique comprises using a coating bath for the outer coating which isrheologically stable, i.e., which has a low settling rate of the particles therein. This results in a high viscosity bath whereby penetration of the bath into the undercoating is prevented.
• dip coating One methodgenerally known for applying various coatings to heater structures is known as dip" coating. This method involves dipping the heater to be coated into and out of a bath containing an organic solvent and a suspension of the particles to be coated on the heater, the particles adhering to the heater as the emerging heater breaks through the surface of the bath. If the heater structure is in the form of a continuous wire or the like which is drawn through the bath, the process is known as a drag coating process. The thickness of the coating is a function of the specific gravity and viscosity of the bath.
• the undercoating be rendered relatively hard and impervious prior to the overcoating process, by a high temperature firing operation, for minimizing penetration of the overcoating bath into the undercoating, we have discovered that such a high temperature process is not necessary, and that penetration can be avoided even if the undercoating is in a non-sintered, relatively soft and porous condition during the overcoating process.
• the undercoating be substantially completely dry and free of all solvents used both in the undercoating process and in the usual rinsing step performed thereafter. That is, we discovered that the prevention of penetration of the overcoating bath into the undercoating is not so much a function of the hardness and imperviousness of the undercoating, as previously thought, but primarily a function of the degree of removal of the solvents from the undercoating. While not known for sure, it appears that the presence of such solvents in the undercoating tends to dilute and reduce the viscosity of the overcoating bath which contacts the undercoating, thus promoting penetration.
• a heater wire of usual configuration is first coated by a conventional means with a layer of aluminum oxide having a thickness in the order of 5 mils.
• the coating operation can comprise the known dipping, spraying, or cataphoretic processes.
• an organic solvent or vehicle for the aluminum oxide is used which tends to remain with the aluminum oxide coating on the heater wire.
• the aluminum oxide layer is somewhat soft and porous.
• the coated heater is rinsed in a suitable solvent, such as methanol or acetone, to remove loosely adhered particles.
• a suitable solvent such as methanol or acetone
• the heater is air dried at a temperature as high as possible for rapidly drying the heater without causing significant oxidation of the heater wire.
• the temperature used, and the time required to thoroughly dry the heater are functions of the configuration of the heater and the size and mass of the heater. In general, however, to avoid oxidation of the heater wire and thus avoid the need to use a protective atmosphere during the drying operation, temperatures below 400 C are preferred.
• heaters can be placed in a conventional air oven and heated.
• a jet of hot dry air can be blown over the heaters.
• a source of radiations such as infrared radiations from a conventional source, can be directed onto the heaters.
• the latter heating means is preferred since it is simple, noiseless, and the radiations can be accurately focused onto the desired portions of the heaters, thereby avoiding heating of fixtures used to carry the heaters.
• an infrared source is used to heat the heater coating to a temperature of about 300 C for a time of l2 seconds.
• the coated heaters are provided with the outer coating of tungsten.
• a coating bath is used in accordance with the process described in the above-described co pending application.
• a coating bath comprising (by weight) 40 percent tungsten and 60 percent liquid vehicle, the tungsten having a particle size of 0.5 to microns, with the average particle size being about 2 microns, the vehicle comprising 1.68 percent lQQQ second nitrocellulose wet 30 percent by weight by alcohol and 98.5 percent butyl acetate
• the bath is ball milled for about 6 hours. This provides a rheologically stable bath suitable for coating the tungsten particles onto the heater without bath penetration into the undercoating.
• overcoating techniques such as spraying or cataphoretic processes, can be used.
• the heater is again rinsed, in a suitable organic solvent, to remove loosely adherent particles, and the heater is fired at an elevated temperature, in the order of l,600 C to complete the heater.
• the heater wire can be any refractory wire, such as molybdenum, normally used in heaters.
• the undercoating can be various known insulating refractory materials normally used in heaters, such as zirconium oxide, beryllium oxide, and the mixture of chrome oxide and titanium oxide. These materials, and others known to workers skilled in these arts, tend to be relatively soft and porous when initially applied, and are normally later fired at high temperatures. Thus, the above-described problems of the prior art processes exist with the use of such materials, and advantages are obtained using the inventive process described herein.
• the darkening outer coating can comprise various refractory, high thermal emissivity materials such as carbon, titanium, chromium, and molybdenum. Again, avoidance of penetration of these materials into the underlying coating is generally to be desired.
• a method of fabricating a dark heater comprising:
• a method of fabricating a dark heater comprising:

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Resistance Heating (AREA)
• Solid Thermionic Cathode (AREA)

Priority Applications (8)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22977050

Family Applications (1)

Country Status (8)

Cited By (3)

Families Citing this family (3)

Citations (2)

Family Cites Families (5)

• 1972
  • 1972-05-30 US US00257625A patent/US3808043A/en not_active Expired - Lifetime
• 1973
  • 1973-05-02 IT IT23628/73A patent/IT987598B/it active
  • 1973-05-14 CA CA171,257A patent/CA1017208A/en not_active Expired
  • 1973-05-23 GB GB2452973A patent/GB1431571A/en not_active Expired
  • 1973-05-23 DE DE2326202A patent/DE2326202B2/de not_active Ceased
  • 1973-05-29 FR FR7319522A patent/FR2186802B1/fr not_active Expired
  • 1973-05-29 NL NL7307463A patent/NL7307463A/xx not_active Application Discontinuation
  • 1973-05-30 JP JP6071673A patent/JPS5331592B2/ja not_active Expired

Patent Citations (2)

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