US1966211A - Cathode - Google Patents

Cathode Download PDF

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Publication number
US1966211A
US1966211A US600366A US60086632A US1966211A US 1966211 A US1966211 A US 1966211A US 600366 A US600366 A US 600366A US 60086632 A US60086632 A US 60086632A US 1966211 A US1966211 A US 1966211A
Authority
US
United States
Prior art keywords
barium
coating
oxide
cathode
free
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
US600366A
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English (en)
Inventor
Walter T Millis
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.)
Westinghouse Electric Corp
Original Assignee
Westinghouse Electric Corp
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 BE395224D priority Critical patent/BE395224A/xx
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Priority to US600366A priority patent/US1966211A/en
Priority to GB5233/33A priority patent/GB405466A/en
Priority to FR753113D priority patent/FR753113A/fr
Application granted granted Critical
Publication of US1966211A publication Critical patent/US1966211A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01J9/04—Manufacture of electrodes or electrode systems of thermionic cathodes
    • H01J9/042—Manufacture, activation of the emissive part

Definitions

  • My invention relates to cathodes and it has particular relation to oxide coated cathodes of thermionic devices.
  • Anobject of my invention is to increase the 5 thermionically active content of an oxide coated lament.
  • Another object of my invention is to provide additional free alkaline earth metal in the coating of an oxide coated lament.
  • an object of my invention is to increase the thermionically active content of an oxide coated llament by adding barium azide to the coating of the lament in the process of manufacture and to reduce this barium azide to free metallic barium in the coating on the cathode of the completed tube.
  • Fig. 2 is a view in elevation of a lament and its coating with part of the coating removed to show the core
  • Fig. 3 is a series of curves disclosing the superiority of the coating of my invention over the standard coatings.
  • the electron emission from oxide coated cathodes is due to the presence of free alkaline earth metal in such cathodesv.
  • the amount of this free alkaline earth metal, generally barium is usually very small in the stand- 35 ard coating now in use since the decomposition rate is very low.
  • This standard coating is usually applied in the form of carbonates of barium and strontium or of these two in combination with carbonates of 140 calcium.
  • the carbonates are then reduced by heat to the oxide and a small amount of free barium is present upon the reduction of the carbonates.
  • an activation process is necessary to form the free barium.
  • the cathode would become an emitter but owing to the high evaporation rate of the barium, the emission would soon disappear. Accordingly, the oxide is necessary to retard the evapora- 50 tion of the barium.
  • An object of my invention is to supply a morev abundant amount of free barium or other alkaline earth metal in an oxide coating so that the amount of emission, in respect to temperature, is
  • my invention deals with adding a readily decomposable compound of an alkaline earth metal which decomposes by heat to form a free alkaline earth metal plus an inactive residue, preferably in the form of a gas or vapor, to facilitate its removal from the device.
  • My invention specifically deals with adding barium azide (BaNe) to the usual or standard barium oxide and strontium oxide coated cathodes.
  • This barium azide is a compound of barium which is readily decomposed. The decomposition is effected in air at a temperature of 225 C. and is probably less in a high vacuum.
  • the decomposition is of the iorm: BaN+HeatzBa+3Na
  • the barium azide may be mixed with the carbonates of barium and/or strontium, and/or calcium if desired, and with the use of a nitro-cellulose binder, preferably nitro-cellulose with a solvent such as amyl acetate, applied to the conductor, such as a lament or sleeve, in the form of a spray. Other methods such as dipping may be used but the spray method is preferred on account of the low temperature of decomposition of the barium azide.
  • a representative coating may be as follows:
  • the percentage of the barium azide from the coating is not critical but may be varied from .5% up to 85% of the mixture. Ii desired, calcium carbonate may be added to the mixture or may replace the strontium carbonate. The barium azide may also replace the barium carbonate in the coating.
  • the carbonates To ensure a good mixture and to obtain a fine enough emulsion for spraying, it is preferable to grind the carbonates together.
  • the rate of grinding should not be too rapid to cause the barium azide to decompose by friction.
  • Fig. 2 discloses a coating 10 on a lament 11 and thus forming a cathode 12.
  • the coated cathode 12 is then incorporated in a tube such as the tube 13 of Fig. 1 having the grid 14 and the plate 15.
  • the tube, including the coated cathode then undergoes the usual and well known high vacuum treatment. This high vacuum treatment decomposes the carbonates into oxides, and also decomposes this barium azide to free metallic barium in the barium and strontiiun oxide.
  • the filament in Fig. 1 having a coating 1l o1" the oxides of barium and strontium permeated abundantly with free metallic barium.
  • the oxide of calcium may also be included in the coating, if desired, preferably by mixing calcium carbonate with the carbonates oi barium and strontium and combining this with the barium azide, to produce my oxide coating as explained above.
  • the cathode having this increased electron emitting content of free barium has decided advantages over the mere oxide coating and some of these advantages are graphically illustrated by the curves in Fig. 3. It is possible that the en hanced activity is due to the presence of at least twice as much free barium as in the present standard oxide coating.
  • My coating will be reducible at the normal operating temperature of an oxide coating such as 4 watts per square centimeter.
  • the barium azide has a much lower decomposition temperature than the carbonates in the activation of the coating. Accordingly, the presence of a large quantity of barium in the coating permits its normal emission at greatly reduced temperatures or enhanced emission at the usual operating temperature. This means lower operating wattages are required. This operation at lower temperature also means, of course, greater efficiency and longer life for a cathode. It is well known that the operation of lament cathodes at high temperatures is the major cause of short lives of tubes.
  • the oxide part of the coating holds the barium on the lament and prevents it from vaporizing onto the other parts of the tube, such as the grid and anode, which is the cause of the above-mentioned reverse emission.
  • This core may be of nickel, platinum, platinum iridium, platinum rhodium, or platinum nickel, but I pre- Yfer to use an alloy of nickel with cobalt and ferrotitanium such as described in the copending application o Erwin F. Lowry, ASerial No. l44,91l, lod October .28, 1926.
  • the method of increasing the electron emissive content of a cathode coating of the compounds of barium and strontium which comprises mixing barium azide with said barium and strontium compounds, applying said mixture to a conductor, drying said mixture on said conductor at a low temperature, incorporating said conductor in a vacuum tight container and treating said coating to reduce said barium azide to free metallic barium in said coating.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
  • Discharge Lamp (AREA)
US600366A 1932-03-24 1932-03-24 Cathode Expired - Lifetime US1966211A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE395224D BE395224A (enrdf_load_stackoverflow) 1932-03-24
US600366A US1966211A (en) 1932-03-24 1932-03-24 Cathode
GB5233/33A GB405466A (enrdf_load_stackoverflow) 1932-03-24 1933-02-20
FR753113D FR753113A (fr) 1932-03-24 1933-03-24 Perfectionnements aux cathodes

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US600366A US1966211A (en) 1932-03-24 1932-03-24 Cathode

Publications (1)

Publication Number Publication Date
US1966211A true US1966211A (en) 1934-07-10

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ID=32508278

Family Applications (1)

Application Number Title Priority Date Filing Date
US600366A Expired - Lifetime US1966211A (en) 1932-03-24 1932-03-24 Cathode

Country Status (4)

Country Link
US (1) US1966211A (enrdf_load_stackoverflow)
BE (1) BE395224A (enrdf_load_stackoverflow)
FR (1) FR753113A (enrdf_load_stackoverflow)
GB (1) GB405466A (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2464702A (en) * 1944-11-04 1949-03-15 Hartford Nat Bank & Trust Co Process for manufacturing cathodes for electron discharge tubes
US2840751A (en) * 1953-05-28 1958-06-24 Westinghouse Electric Corp Electrode coating composition and electrode for cold cathode gas discharge lamp

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2464702A (en) * 1944-11-04 1949-03-15 Hartford Nat Bank & Trust Co Process for manufacturing cathodes for electron discharge tubes
US2840751A (en) * 1953-05-28 1958-06-24 Westinghouse Electric Corp Electrode coating composition and electrode for cold cathode gas discharge lamp

Also Published As

Publication number Publication date
GB405466A (enrdf_load_stackoverflow) 1934-02-08
FR753113A (fr) 1933-10-07
BE395224A (enrdf_load_stackoverflow)

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