US1871343A - Heater element for electron emission devices - Google Patents

Heater element for electron emission devices Download PDF

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Publication number
US1871343A
US1871343A US276340A US27634028A US1871343A US 1871343 A US1871343 A US 1871343A US 276340 A US276340 A US 276340A US 27634028 A US27634028 A US 27634028A US 1871343 A US1871343 A US 1871343A
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US
United States
Prior art keywords
filament
insulator
gases
chromium
heater element
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
US276340A
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English (en)
Inventor
Ramage John Humphreys
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 Lamp Co
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Westinghouse Lamp Co
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 BE360639D priority Critical patent/BE360639A/xx
Priority to NL30977D priority patent/NL30977C/xx
Application filed by Westinghouse Lamp Co filed Critical Westinghouse Lamp Co
Priority to US276340A priority patent/US1871343A/en
Application granted granted Critical
Publication of US1871343A publication Critical patent/US1871343A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01J1/24—Insulating layer or body located between heater and emissive material

Definitions

  • This invention relates to heater units for rectly transferred to an electron emission matcriahto permit an electron flow between electrodes in the device.
  • aradio tube designed to operate on alternating current such as that known in the trade as the ⁇ TY-227, may be considered.
  • This tube comprises the usual bulb and base and its internal structure includes a glass press upon which the several electrodes are mounted.
  • Tubes of this type may'einploy a plate or anode, agrid or control element'a'nd a cathode assembly.
  • the cathode assembly usually consists of a heater element as a length of re l fractory wire, enclosed in a suitable insulator,
  • the heater element and the surrounding insulator may betermed aheater unit.
  • the msulator of the heater unit is surrounded'by a metallic sleeve coated with a suitable electron emitting material, as a carbonate coating which is heated by conduction throughithe insulator from the heater element, which may be in the form of a filament wire, preferably of tungsten, molybdenum, but which may be of other suitablematerial as tantalum, or the like.
  • t ytap'ere f urmut wasting away of the ,filamentat the hotter portions may be paused bypresence of gas 7 released from the porous insulator, which gas may be water vapor, carbon monoxide or dioxide.
  • Figure 1 is a longltudinal sectional View of accordance with” the present. invention and an insulator 'with a filament therein.
  • Figure 2 is a transverse sectional view of the insulator member and filament
  • Figure 3 is an enlarged transverse sectional view showing the protective coating about the filament.
  • Figure 4 shows a radio tube constructed in I applied to an exhaust of a'vacuum pump.
  • a cathode assembly 4 is shown in section and, as will be noted, the said assembly 1ncludes a filament 5 bent to provide sections 6 and 7 which are disposed in apertures 8 and 9 provided in an insulator member10.
  • the insulator maybe made circular, as shown 1n the transverse cross section ( Figure 2), or it may be non-circular in transverse crossssec-
  • The. cathode assembly shown is given as an example of one practical embodiment of. theinvention and it willbe seen from the draw-' ing that'the outer surface of an insulator 10 iii ' tite, around the filament.
  • apertures IQand 13 which receive the filament are about 6.5 mils to 7 .5
  • the wire is about 5 mils diameter. This gives a closespaced' relation between theinsulator and the filament and when using an'insulator such as isolantite the walls thereof often. fuse about and bind the filament. With the present method, the lIlSll".
  • the filament after use indicated that the eroding agent was water vapor. This conclusion was supported by further investigation when the filament was heated during the operation ofexhausting the device and also upon a fus ing of the insulator, as for example, isolan-
  • the present invention therefore, provides the filamentwith a protective medium capable' of fixing oxygen and thus breaking the Water cycle.
  • Materialsfor this purpose may be chromium, thorium, zirconium, uranium, tantalum, boron, silicon, vanadium, ti-
  • tanium any other elements capable of forming compounds with and 'holding indefi- 7 nitely any gases detrimental to the life of the filament or capable of causing an erosion of thefilament.
  • chromium has been found to be preferable and chromium plated wire may be used. Ordinarily a plated wire may be brittle, although devices using chromium plated wire were successful and showed no.
  • chromium may be applied by mixing chro mium powder with abinder as amyl acetate.
  • the method of applyingthe chromium'in'the binder may be the same as that practiced for I the' gettering of filament wire, viz., the wire may be passed through a mixture of chromium powder and binder or the wire may be dipped or sprayed. I It has been found that good results are obtained by mixing 10 grams of chromium powder, passed through a 200 mesh screen, with 15 cc. of a 3% solution offilm dope in amyl acetate. These ingredients may be thor oughly mixed in a ball mill. Thewire may then bepassed through the mixture at aspeed of about 6 meters per minute.
  • the filament will then'be coated and maybe formed in V or hairpin shaped sections. These sections are then threaded through the bores 8 and-9 or apertures in the insulator 11.
  • the insulator may then beassembled in what has been termed the catho'de'assembly 4 and mounted in abulb 14: withthe other elements as the. grid 15 and anode 16, thus making theinterior structure of the device complete and ready for the exhausting operation,.where upon it is appliedto a vacuum pump i(not shown) by inserting exhaust tube 17 into an exhaustport 18.
  • v p In practice, the exhausting operation is per.-
  • the filament being moved through sixpositions 7 unlighted, eight positions while lighted with apotentlal of 5.5.volts and twelve positions at 4.5 volts;
  • This voltage is relatively high is primarily to break down the carbonates of the cathode to the oxide, but in the present invention the heating is utilized as an aid to lnasmuch as the normal voltage of the fila- W mentis 2.5 volts.
  • the heating of the filament 7 heat the chromium so that oxides or compounds will be produced around the hotter portions of the filament by reason of the gases released from the insulator or otherwise dur ing the heating.
  • an insulator element such as :lSO? lantite
  • the isolantite being fusible at a relatively low temperature will fuse about the filament along its length except at cooler portions adjacent to the ends of the insulator.
  • non fusible insulators as porcelain, quartz, etc, in the event that gases are evolved the chromium powder will be precipitated to the wall of the insulator around the hot portions of the filament.
  • the filament will be free from any erosive action, as would otherwise occur from gases liberated from the insulator, and at the same time the filament will be free to move relative to the insulator under vary-' ing temperature conditions.
  • the filament to apply the coating to the wall of the insulator prior to the heat treatment to produce the protective layer.
  • the protective medium employed serves to guard the filament against erosion caused by the attack of the gases which are released.
  • the coating provides a protective agent which is neutral to the filament and does not alloy with it, thus the voltage of the filament remains unchanged.
  • the protective agent is of such a character, particularly when used with an isolantite insulator which fuses about the filament, that the filament remains free for relative movement with respect to theinsu:
  • the binding action of the insulator is notas important.
  • the advantage of the protective agent remains, since it is necessary in any case to protect the filament against erosion due to released gases, which causes a disintegration of the filament at the hotter portions and destroys its usefulness.
  • Any insulator be employed with a metal that is not readily volatilizedbut is chemically active, such as chromium, and it has been foundthat porcelain "or isolantite,
  • slag formed is the result of a reaction" between the chromium and the silica "of the insulating material and presents a hard greenish e' to the filament and bondswith 1- the insulator.
  • glazed surfac n will he-seen item the Me an; that the inventive idea contemplates'theuse of a filament incombination with a material which, acts as'a keeper' or fixer which neutralizes device to which the invention maybe'appliedQ
  • the injurious element is water vapor, it is to be understood that erosion of the filament may be due to carbonaceous gases in which the material employed will form permanent carbides with the same beneficial results.
  • the present invention therefore, provides a heater unit for a thermionic device, such as a radio tube, in which the heater element, which ispreferably in the form of a tungsten filament, is protected against the erosive action caused by the attack of gases.
  • a thermionic device such as a radio tube
  • the heater element which is preferably in the form of a tungsten filament
  • the present invention contemplates a simple and effective prevention of filament erosion and that the same may be accomplished in various ways without departing from the spirit and scope of the invention as set forth in the V appended claims.
  • a heater unit for an electron emission device comprising an insulative sleeve enclosing a refractory wire and a layer of chromium oxide-on the wall of the insulator and r between the insulator and the refractory wire.
  • a heater element for an electron emis- I sion device comprising a refractory wire, a tubular insulator surrounding said wire, the inner wall of said insulator being permeated with a medium to protect the filament against erosion caused by the release of gases.
  • An electrical device comprising a sealed envelope, aninsulator within said envelope having an electron emission material thereon, I r
  • a heater element for elevating the temperature of said insulator and a material disposed on the wall of said insulator adjacent to said element for neutralizing gases detrimental to the life of said element.
  • a thermionic device having an indirect- 1y, heated cathode comprising a heater elev ment, a porous insulator surrounding, said I element and a stable compound on the inner I surface of the insulator to prevent gases from I attacking the. filament. Y l In testimony whereof, I have hereunto sub.-

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  • Electron Sources, Ion Sources (AREA)
US276340A 1928-05-09 1928-05-09 Heater element for electron emission devices Expired - Lifetime US1871343A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
BE360639D BE360639A (zh) 1928-05-09
NL30977D NL30977C (zh) 1928-05-09
US276340A US1871343A (en) 1928-05-09 1928-05-09 Heater element for electron emission devices

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US276340A US1871343A (en) 1928-05-09 1928-05-09 Heater element for electron emission devices

Publications (1)

Publication Number Publication Date
US1871343A true US1871343A (en) 1932-08-09

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ID=23056255

Family Applications (1)

Application Number Title Priority Date Filing Date
US276340A Expired - Lifetime US1871343A (en) 1928-05-09 1928-05-09 Heater element for electron emission devices

Country Status (3)

Country Link
US (1) US1871343A (zh)
BE (1) BE360639A (zh)
NL (1) NL30977C (zh)

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Publication number Publication date
NL30977C (zh)
BE360639A (zh)

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