US2885334A - Thermionic cathode heaters - Google Patents

Thermionic cathode heaters Download PDF

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Publication number
US2885334A
US2885334A US478028A US47802854A US2885334A US 2885334 A US2885334 A US 2885334A US 478028 A US478028 A US 478028A US 47802854 A US47802854 A US 47802854A US 2885334 A US2885334 A US 2885334A
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US
United States
Prior art keywords
coating
alumina
heaters
heater
cathode
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
US478028A
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English (en)
Inventor
Green Bernard Jeffrey
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.)
International Standard Electric Corp
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International Standard Electric Corp
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Filing date
Publication date
Application filed by International Standard Electric Corp filed Critical International Standard Electric Corp
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Publication of US2885334A publication Critical patent/US2885334A/en
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/02—Electrophoretic coating characterised by the process with inorganic material
    • 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
    • H01J1/22—Heaters
    • 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

Definitions

  • the present invention relates to heaters for thermionic cathodes.
  • Heaters for thermionic cathodes are normally coated with alumina to ensure adequate cathode-heater insulation.
  • a desirable heating coating should be smooth and certainly free from any cracks.
  • a thermionic cathode having a heater coated with alumina, the surface of the alumina being intentionally crazed with small fissures.
  • Cathode heaters of the coil type are usually. coated either by spraying or electrophoretically. Straight or faggot type heaters are usually dipped or dragged.
  • electrophoretic methods of coating have been tried out, for various reasons they have not been entirely successful, and, in consequence, for coiled heaters spraying is more popular, in spite of the great waste of coating material involved.
  • the main fault with electrophoretic coating up to the present time has been its extreme embrittling effect on tungsten. If this eifect could be eliminated, or at least minimised, the electrophoretic method of coating has great advantages, vlz:
  • Alumina exists in three main forms: a-alumina, which has a specific gravity of 3.8 and is characterised by a triagonal crystal structure; B-alumina with a specific gravity of 3.3 and a hexagonal crystal structure; and 'y-alumina having a cubic structure and a specific gravity of 2.8.
  • electrophoretic coatings were based on a suspension consisting mainly of u-alumina in a suitable liquid, the suspension containing little or no binder.
  • the coated wire in the case of continuously coated heaters passed direct into drying and sintering ovens.
  • unit heaters such as double helical coils which were dipped into the electrophoretic bath, an external nitro-cellulose binder was applied, usually after drying, but sometimes the binder was included in the coating suspension. This binder supported the coating until sintering was completed.
  • the three forms of alumina mentioned above are related in that, on heat treatment 'y-alumina can be converted into 19- and on further heating the )8- into aalumina.
  • a view to overcoming the brittleness of heaters coated with tat-alumina we use a less dense alumina as part of the coating, which coating shrinks on processing, producing a network of fine cracks. This allows for free expansion and contraction of the heater core without affecting the electrical properties of the insulator.
  • the present invention further provides the method of manufacture of a heater for a thermionic cathode in which the heater is electrophoretically coated with alumina containing eight parts by weight of 'yalumina for every eight to twelve parts of a-alumina, resulting in the fully processed cathode having a heater with an insulated coating which is crazed with small fissures.
  • the preferred proportion of 'y to on alumina is such as to result in the mean specific gravity of the mixed alumina being 3.5.
  • Fig. 1 is a drawing taken from a photomicrograph of a portion of a heater according to the present invention after electrophoretic coating and before processing
  • Fig. 2 is a drawing taken from a photomicrograph of a portion of heater manufactured according to the present invention after removal from a valve which has been fully processed.
  • the 'y-alumina for use in coatings of the present invention is first treated with hydrochloric acid, as known in the art, to condition the charge carrying properties of the particles.
  • the preparation of the electrophoretic suspension is preferably carried out in the following manner:
  • Fig. 2 shows the change in appearance of heater wire according to the invention on removal from a thermionic valve which has been normally processed and aged.
  • the method of manufacture of a thermionic cathode comprising the steps of electrophoretically coating the cathode heater with alumina from a bath containing eight parts by weight of 'y alumina for each eight to twelve parts of a alumina, drying the coating, heating the coating between 800-1000 C. for conversion of the 'y alumina ultimately into or alumina, whereby the resultant mixture has an increased specific gravity which causes a volume shrinkage of the coating and crazing thereof with small fissures.
  • alumina coating comprises a mixture of substantially like compositions by weight of 'y-alumina as cubic crystals and a-alumina as triagonal crystals with a mean specific gravity range between 2.8 and 3.8.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Solid Thermionic Cathode (AREA)
US478028A 1954-01-01 1954-12-28 Thermionic cathode heaters Expired - Lifetime US2885334A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB47/54A GB739325A (en) 1954-01-01 1954-01-01 Improvements in or relating to thermionic cathode heaters

Publications (1)

Publication Number Publication Date
US2885334A true US2885334A (en) 1959-05-05

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ID=9697439

Family Applications (1)

Application Number Title Priority Date Filing Date
US478028A Expired - Lifetime US2885334A (en) 1954-01-01 1954-12-28 Thermionic cathode heaters

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US (1) US2885334A (en))
GB (1) GB739325A (en))
NL (2) NL193502A (en))

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3137766A (en) * 1957-12-16 1964-06-16 Norton Co Electric wire for use at high temperatures
US3160946A (en) * 1960-03-11 1964-12-15 Sylvania Electric Prod Electrical heaters
US3223607A (en) * 1959-02-24 1965-12-14 Egyesuelt Izzolampa Method of manufacturing electrical heating elements with improved aluminum oxide coating
CN115332026A (zh) * 2022-07-15 2022-11-11 中国电子科技集团公司第十二研究所 一种可快速启动的阴极组件及其制备方法和应用

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0722034B2 (ja) * 1989-07-01 1995-03-08 株式会社日立製作所 無機絶縁ヒータおよびその製法並びにそれを用いた陰極線管

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1942879A (en) * 1931-05-07 1934-01-09 Champion Spark Plug Co Refractory material and batch and method for making the same
US1975870A (en) * 1933-07-07 1934-10-09 Rca Corp Indirectly heated cathode
US2092815A (en) * 1935-11-23 1937-09-14 Rca Corp Cathode heater insulation
US2164913A (en) * 1935-03-06 1939-07-04 Int Standard Electric Corp Indirectly heated cathode
US2442864A (en) * 1944-11-23 1948-06-08 Sylvania Electric Prod Electrophoresis coating of electron tube parts
US2734857A (en) * 1951-10-11 1956-02-14 snyder

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1942879A (en) * 1931-05-07 1934-01-09 Champion Spark Plug Co Refractory material and batch and method for making the same
US1975870A (en) * 1933-07-07 1934-10-09 Rca Corp Indirectly heated cathode
US2164913A (en) * 1935-03-06 1939-07-04 Int Standard Electric Corp Indirectly heated cathode
US2092815A (en) * 1935-11-23 1937-09-14 Rca Corp Cathode heater insulation
US2442864A (en) * 1944-11-23 1948-06-08 Sylvania Electric Prod Electrophoresis coating of electron tube parts
US2734857A (en) * 1951-10-11 1956-02-14 snyder

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3137766A (en) * 1957-12-16 1964-06-16 Norton Co Electric wire for use at high temperatures
US3223607A (en) * 1959-02-24 1965-12-14 Egyesuelt Izzolampa Method of manufacturing electrical heating elements with improved aluminum oxide coating
US3160946A (en) * 1960-03-11 1964-12-15 Sylvania Electric Prod Electrical heaters
CN115332026A (zh) * 2022-07-15 2022-11-11 中国电子科技集团公司第十二研究所 一种可快速启动的阴极组件及其制备方法和应用

Also Published As

Publication number Publication date
NL193502A (en))
GB739325A (en) 1955-10-26
NL84939C (en))

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