US3262814A - Method for coating an indirectly heated cathode - Google Patents

Method for coating an indirectly heated cathode Download PDF

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Publication number
US3262814A
US3262814A US159255A US15925561A US3262814A US 3262814 A US3262814 A US 3262814A US 159255 A US159255 A US 159255A US 15925561 A US15925561 A US 15925561A US 3262814 A US3262814 A US 3262814A
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United States
Prior art keywords
cathode
layer
filament
aluminum
nickel
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Expired - Lifetime
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US159255A
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English (en)
Inventor
Provisor Henri
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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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
    • H01J1/26—Supports for the emissive material
    • 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

Definitions

  • This invention has .for its object to provide improved indirectly heated cathodes, of which the electron-emissive surface is formed by an alkaline-earth oxide layer or by a layer containing such oxides.
  • the improvement obtained by this invention relates to furthering the heat transfer from the filament, which constitutes the source of heat, to the cathode proper, i.e. to the part serving as a carrier for the emissive layer across the space separating and insulating these two ele ments.
  • the invention relates mainly to the application of a black layer to the surface of the said carrier body, exposed to the direct heat radiation from the said filament, in order to raise the absorption power of this surface for the said radiation.
  • the invention furthermore relates to a method of applying this black layer and, moreover, to electron tubes comprising cathodes provided with such a black layer.
  • the temperature of the filament must be kept as low as possible for maintaining a predetermined temperature of the emissive layer. Use must therefore be made of means for transferring to the cathode proper a maximum quantity of the heat produced by the filament.
  • Such means therefore consist in blackening the insulating coating of the filament and the inner surface of the cathode to the maximum extent.
  • the object of the invention is attained, when the filament has a minimum temperature with a given tempera ture of the emissive layer, so that the temperature difference between the filament and the emissive layer is at a minimum.
  • the present invention has for its object to apply a black layer to the surface of the cathode proper, i.e. the supporting body of the emissive layer, exposed directly to the radiation from the filament.
  • this layer on the said surface is formed by the reaction of aluminum in extremely fine state with the cathode metal at a temperature of about 600 C. in a reducing or a neutral atmosphere or in vacuo. The reaction yields a grey-black intermetallic layer.
  • the metal of the supporting body of the emissive layer may consist of Patented July 26, 1966 nickel, molybdenum, iron or an alloy having one of these metals as a base.
  • this cathode may be tubular (for example a hollow cylinder) or flat (for example a strip).
  • the invention therefore relates to two shapes of the black layer on the cathode metal.
  • the aluminum required for the reaction is provided in the form of a fine powder suspended in a fluid.
  • the suspension is applied to the surface of the carrier body to be blackened. By drying in air an aluminum powder layer with an adhesive formed by the suspension agent, is formed on the body. If the carrier body is tubular, the suspension is introduced into the tube, for example by sucking. If the body is strip-shaped, the suspension may be applied by atomizing.
  • An example of a suspension which yields satisfactory results is a solution of 2.50 gms. of nitrocellulose in gms. of ethylene-glycol, and 22.5 gms. of butanol; in mls. of this solution 20 gms. of fine aluminum powder is suspended.
  • nickel oxide an addition of nickel oxide to this suspension may provide a considerable improvement in the uniformity of the black layer; 5 to 15 gms. of nickel oxide is a suitable quantity with 20 gms. of aluminum powder.
  • suspension composition is, of course, only stated by way of example; the ratio between the suspension liquid and the aluminum powder and the nickel oxide may be varied within Wide limits. Even the suspension agent may be differently composed. A solution of methacrylate, for example methylmethacrylate, may replace the solution of nitro-cellulose.
  • the suspension agent need serve only as a medium for the aluminum and as a provisional adhesive for sticking the aluminum particles to each other and to the metal surface. After the reaction of the aluminum with the metal of the surface no residues should be left which are likely to change the electronic properties of the cathode.
  • the aluminum required for the reaction is applied by condensing aluminum vapour, which is obtained in vacuo.
  • This method is particularly suitable for a strip-shaped metal carrier body.
  • the surface of the strip is covered with an aluminum layer of a thickness of a fraction of a micron; the layer is produced by the thermal evaporation of aluminum in vacuo.
  • the further treatment according to the invention is the same in the two methods described above.
  • the coated metal supporting body is sintered in vacuo, in a neutral or in a reducing atmosphere. Satisfactory results are obtained with a temperature lying between 610 C. and 650 C. during 15 to 30 minutes.
  • the sintering temperature should not be lower than 590 C.; it may, 'however, exceed 650 C.
  • the sintering period may vary between a few minutes and a few hours, if it is found to be necessary.
  • the aluminum blackening of the inner surface of the cathode is not advisable for tubes having a long lifetime.
  • the undesirable diffusion of aluminum may, however, be avoided to a considerable extent by oxidizing part of this metal subsequent to sintering.
  • a second sintering treatment between 550 C. and 600 C. for 30 minutes in a humid, reducing atmosphere does not change considerably the rigidity of the parts and converts the aluminum not yet bound into a comparatively stable compound.
  • the coating thus formed maintains the absorption power for the radiation heat obtained in the first layer of the intermetallic compound.
  • FIG. 1 shows, by way of example, a longitudinal sectional view of a cylindrical cathode according to the invention.
  • FIG. 2 shows the process of manufacturing a cathode according to the invention.
  • the cathode shown in FIG. 1 comprises a filament body 1, which is accommodated in a central, refractory body 4 shaped in the form of a rod, hereinafter termed heating body.
  • the heating body 4 serves at the same time as a support and an insulator for the filament 1.
  • the heating body 4 is coated on the outer side with a grey-black layer, obtained by the aforesaid reaction of aluminum and nickel.
  • a tubular envelope 5 of nickel is arranged concentrically around the heating body 4.
  • the inner surface of this envelope is coated with a black layer 6 of the inter-metallic aluminum-nickel compound obtained by carrying out one of the aforesaid methods.
  • the said envelope is provided on the outer surface with an emissive layer of suitable thickness 7, which contains mainly barium oxide and strontium oxide.
  • the efficiency of the grey-black layer obtained in the manner described above with respect to the heat exchange between the filament and the cathode can be easily checked by measuring the temperature of these two elements, after they have been arranged in an exhausted bulb.
  • a filament voltage of 6.3 v. at the filament arranged in a blackened cathode envelope a temperature drop of about 100 C. is measured with respect to a conventional filament in a conventional cathode envelope.
  • the blackened envelope is, moreover, considerably hotter than the conventional cathode.
  • cathode envelopes are blackened for use in a diode, which is extremely sensitive to break-down between the cathode and the filament; the diodes are subjected to an endurance test in a test arrangement.
  • a sequence of ten tubes, comprising these cathode envelopes and a comparison sequence with the conventional cathode envelopes were used.
  • the tubes were driven for a long time under the following operational conditions: the voltage V at the filament 1 was 6.3 v.; the voltage V between the filament 1 and the cathode was v.
  • the voltage V between the cathode and the anode was w
  • the last two voltages were fed via a resistor of 15.000 ohms, connected in series with the cathode; this resistor served as a current limiter in the event of a break-down.
  • This resistor was shunted by a capacitor C of 10 ,uf. None of the comparison diodes ope-rated for a longer period than 500 hours, since a break-down occurred between the cathode and the filament body. However, even after 2500 hours no shortcircuit and no abnormal phenomena occurred in the said tubes comprising the blackened cathode envelopes.
  • a method of manufacturing an indirectly heated cathode including a heating element, a nickel supporting body in heat-transfer relationship to the heating element the surface of which facing the heating element being covered with a black layer, and an emissive layer on a surface of the supporting body on a side thereof remote from the heating element, which comprises the steps, forming on the surface of said supporting body facing the heating element a layer of finely divided aluminum and nickel oxide, heating the so-covered supporting body to a temperature of at least 590 C. in a vacuum to form a grey-black intermetallic layer, and heating the body with the grey-black layer in a humid, reducing atmosphere to a temperature between 550 C. and 600 C. for 30 minutes to convert unbound aluminum into a stable compound.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
  • Powder Metallurgy (AREA)
US159255A 1960-12-15 1961-12-14 Method for coating an indirectly heated cathode Expired - Lifetime US3262814A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR847062A FR1282691A (fr) 1960-12-15 1960-12-15 Perfectionnement aux cathodes à oxydes à chauffage indirect pour tubes électroniques

Publications (1)

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US3262814A true US3262814A (en) 1966-07-26

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US159255A Expired - Lifetime US3262814A (en) 1960-12-15 1961-12-14 Method for coating an indirectly heated cathode

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US (1) US3262814A (en。)
DE (1) DE1146207B (en。)
FR (1) FR1282691A (en。)
GB (1) GB994471A (en。)
LU (1) LU40949A1 (en。)
NL (1) NL272248A (en。)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3500454A (en) * 1967-11-16 1970-03-10 Sylvania Electric Prod Insulator heater coating for heater-cathode assembly
US3958146A (en) * 1974-02-08 1976-05-18 Gte Sylvania Incorporated Fast warm up picture tube cathode cap having high heat emissivity surface on the interior thereof
US4009409A (en) * 1975-09-02 1977-02-22 Gte Sylvania Incorporated Fast warmup cathode and method of making same

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL8002665A (nl) * 1980-05-09 1981-12-01 Philips Nv Werkwijze voor het van een thermisch zwart oppervlak voorzien van een metalen onderdeel.
JPH0677435B2 (ja) * 1985-03-18 1994-09-28 株式会社日立製作所 傍熱形陰極の製造方法

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2723363A (en) * 1952-04-01 1955-11-08 Gen Electric Cathode and method of producing same
US2740726A (en) * 1947-02-15 1956-04-03 Gen Electric Bulb coating method
US2817572A (en) * 1954-04-06 1957-12-24 Telefunken Ges Fur Drahtlase T Electrodes for electron discharge tubes
US2891879A (en) * 1957-07-26 1959-06-23 Westinghouse Electric Corp Black coating of high thermal emissivity and process for applying the same
US2949557A (en) * 1957-10-04 1960-08-16 Philips Corp Equipotential cathode for electric discharge tubes
US2987423A (en) * 1958-09-26 1961-06-06 Rca Corp Heat radiating coatings
US3056061A (en) * 1959-03-06 1962-09-25 Philips Corp Method of manufacturing nickel supports for oxide cathodes and cathodes provided with such supports
US3068337A (en) * 1958-12-05 1962-12-11 Gen Electric Vaporizer and method for making the same

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1090774B (de) * 1959-03-20 1960-10-13 Siemens Ag Heizelement fuer mittelbar geheizte Kathoden und Verfahren zur Herstellung eines Isolierueberzuges

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2740726A (en) * 1947-02-15 1956-04-03 Gen Electric Bulb coating method
US2723363A (en) * 1952-04-01 1955-11-08 Gen Electric Cathode and method of producing same
US2817572A (en) * 1954-04-06 1957-12-24 Telefunken Ges Fur Drahtlase T Electrodes for electron discharge tubes
US2891879A (en) * 1957-07-26 1959-06-23 Westinghouse Electric Corp Black coating of high thermal emissivity and process for applying the same
US2949557A (en) * 1957-10-04 1960-08-16 Philips Corp Equipotential cathode for electric discharge tubes
US2987423A (en) * 1958-09-26 1961-06-06 Rca Corp Heat radiating coatings
US3068337A (en) * 1958-12-05 1962-12-11 Gen Electric Vaporizer and method for making the same
US3056061A (en) * 1959-03-06 1962-09-25 Philips Corp Method of manufacturing nickel supports for oxide cathodes and cathodes provided with such supports

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3500454A (en) * 1967-11-16 1970-03-10 Sylvania Electric Prod Insulator heater coating for heater-cathode assembly
US3958146A (en) * 1974-02-08 1976-05-18 Gte Sylvania Incorporated Fast warm up picture tube cathode cap having high heat emissivity surface on the interior thereof
US4009409A (en) * 1975-09-02 1977-02-22 Gte Sylvania Incorporated Fast warmup cathode and method of making same

Also Published As

Publication number Publication date
FR1282691A (fr) 1962-01-27
GB994471A (en) 1965-06-10
LU40949A1 (en。) 1962-02-12
DE1146207B (de) 1963-03-28
NL272248A (en。)

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