US2711390A - Method of making composite thermionically emissive cathode material - Google Patents

Description

June 21. 1955 A. H. cHlLnERs l-:rAL METHOD OF' MAKING COMPOSITE THERMIONICALLY EMIssIvE cATHoDE MATERIAL Filed Nov. 1s, 1952 .W Y' "a,

jV l'r Pateteddune 271'.;

' The heaterfof this inventi'onis in many respects. simi'- 2,711,s90- METHOD F COMPOSITETHERMIONI- CALLY Alida H. Cliild'ers,'New York, and Daniel Gold, Brooklyn, N. Y., assignors to Sylvania Electric' Products, luci, a corporation. of Massachusetts components i the most important distinctionr being 5 in sulating coating of Alundum 12u which is. in turni-directsrciaims. (ci. .204--1815 1y Coated with a nickei s111114. `This. spin tumcoated with a normalroxide lcoating'usuallyfused foricathodesrf n which is vshown in the drawings .at 16". lrrtheV er'nbodi-` This invention relatesto a quick heating cathode and 1;) ment Shown hlrs 'matlerlfial its k'eplkfd` ffm a tflplleV Caftheir method of manufacture.k It particularly relates to bOIIae a quick heating catho-de ofthe type suitable for use in electron discharge devices.` I The cathode assemblies ofthe prior lartconsistof a cathode sleeve usually nickel withl an insulated heater centrally located inside the sleeve. The cathode becomes effective and emits electrons` whenV the oxide Y coated sleeve is heated toa temperature in. the neighborhood of 850 C. This Ais accomplished in the 'prior c Y n Y* l v y art cathode sleeves by passing current through the 'heatg5 @rating emPefal-ek Wlu -bsubstantlauyf IQWeF- 'Fuf' er wire and bringing it' up to a high temperature whereupon heat waves radiate outwardly from the heating filament and heat up the surrounding cathode sleevef The assembly is, therefore, often called an indirectly .ffac'e whichis in contact withthe,Alundurncoating'the t, iilamentary wire`10.v ,It isyalso.readilyapparent .that a theindirectly heated'cathodesof therpriorY art inasmuch that the cathode is firmly-supported byrthe'vinner core since it is attached directlythereto. f Thiscathode may, ofV c,0,urse,obe produced iny many heated cathode. Althoughcathodes of this utype have 3i) WaYS-"Some Steps in' the Production '0f-V' thiscathofle Y 3; are, Vof course, the Asame as those used. innthe normal of construction ofthe prior Vart-cathode as,fforfexample`,

Y the heater wire may becoated with jthejAlundum Y electrophoreticallyzas is- HOWbeing done in the prior'art;V

Secondly, their eiciency is not as goodv as it might be However# fonce this; has been VaCCOmPlShednt fisrfthn i i given satisfactory servicekandare still .doing so they have obvious disadvantages in that they are fnot dif rectly heated and depend for their sourceof heatonthe radiated heatoenergy emitted from a secondary source.

as considerable energy is lost during this transmission of heat by radiation which is one of the least eicient l heating methods. Thirdly, the construction-is not as rugged as it' might be in view of the fact that the cathn necessary to applya metaliilm'over thecoating., This 1y from the heating filament and fixedly from the grid 31? resulte' This' relatively. difficult in view of the fact that a' sudden i shock or jar could disturb the; relative positions ofthe CCSSfZYKb deposited 011.11116 POIQUS .Alllrldllmtogfom filament and cathode sleeve as well as the sleeve and aODnUOUS me/tal .lmWhCh doe-Sinin Penetr the, Y porousv Alundumusing vapor deposition techniques. o One Vtechnique ofthis type is` illustratedpin Figure, 210i'V It is, therefore, an object of this invention to prov ith-e'flrawingsfinWhichfth Alundumofefdheae 'is i 4 continuously coated with 'mckel from nickel carbonyl .1,- The heater to be formed and'themethodV tofbeused.'y ferred dlrectly to the cathode surfacerby conduction. need notbe limited, to .they use, of* nickelkr fmmnickel y *Y carbonyl." A metal Vfilm may be made from any metal l' Vwhichforms volatile compounds that .can berdecomposed l below the melting point ofthe heater'compone'nts or of f 1. themetal,itselfygflfhedecomposition may berentirelyfn It 1s a further object of th1s invention to `provide a 55 thesrmariorr aided. r reducing atmospheresuch *aS-i .o

hydrogen;V [Forexamplathe nietalmight befa'tantalumll metal sheath which'has been vapo'r'deposited, fromdanother tube elements even when these elements are prop'- erly mounted during the assembly period..

vide a quick heating cathode in whichthe heat is translt is a further object of this invention to provide a quick heating cathode in which the -power required t0 bring the cathode up to operatingV temperature will be substantially lower.

rugged cathode construction wherein the cathode is rmly supported by the inner heating core. Y

It is a still further object of this invention to improve "mmmi pfentachlorida Y* A y or the Cathodes reliability by Controlling the '31.105' ele 60 ln accordance with the method shown inrlig'ure 2 of ments Present in the Cathode itselfthe drawings aL carrier gassuch as helium or-nitrogen In accordance with this invention it has been found that these objects and other advantages incidental thereto can be obtained byv directly coatinga metal film on an insulated heater. Y Y

In the drawings which illustrate features of this Vinvention Figure l is an elevation partly in section of'a quick heating cathode of'thisinvention. fr Figure 2 is a schematic drawing illustrating a meththis. system` is added* nickel carbonyl in gaseous `form nickel carbonyl Aenters theV supply'1ine122wl'1erein it'is od of coating the insulated heater wirejrwith 'a metal transported bythe carrierogas to 'thecoating' area'whichV o consists .essentially of a water cooled condenser 32. -Inlm in order to produce the quick heating cathode of this invention. sulated heater wirefwhiclr-is ypresent on supply spool 40 lar toY an. indirectly heated type heater ofthe prior art, that isto,` say, it .has'substantia'llyithe same number `of Y their .relative` position. ;to on'evanother theyl.

differ fonly in that Vthefnietal forming the cathode sleevefk Y itself insteadV of beinglf'spac'edfrom the insulatedrii'lan -mentary heater yis directly applied thereto.-.:-'Ifhiscan1be4` seen quitel clearly. in Figure il,ofjthe-fdrawingsw ereid/ Application Novemtier 18,'19'sz,seria1 No. 321,186` 1 0 the mammary We heatefls ShOW f1-L Wth *its im' Y `VWith, aheaterr of this Atype .itoisreadily'apparentjthat v. l thecath'ode isfn'ecesrsarily quick Vheated in'view Y, of the fract that heat. is' transferred directly l toithe cathode surf` cathode, of this type'will haverg'reater yetlciency than i" as the kpowerk required to bringdthe cathode :u'pto op-f- *i thermore, this cathode has a1 ruggedizedY construction-in is more Vofa prohlemlsince the metal iilm must'bepcon-r i ktinuous and since the jmetal must not be allowed tofpenefr f trate.' into the porous Alundum otherwisefelectricabi i ode is not firmly supported and must bespaced coaxial# 4^() 163mg?V btwilfhe heater. and the cat hQde -Sul'faCQWL o ould rtaturallyleadk to the production' v, j

and plate if the best results are to be obtained. This is Y fof" an/aunsasftory Cathod@ In accordance VW11-5-`.

' invention itl has vbeen T 'found1that this'fmetalmay, suer,

isadmitted toV the'` system from" `tank 20, perfnr'littedto'vr 4;. ilow into supply-line ZZ''at `a constant ytlow.V rate. VTo

which is obtained by vaporizing lthenickel carbonyl from its liquid form which is'keptin reservoir 3ti. This can Y be heated to ay suitableV temperature toggivexthe desiredfj v vapor pressure by Vmeans'of a heat-er.r 31.` The vaporized E Q is caused to pass centrally through the condenser 32 and is positioned therein by means of pulleys 34- anrl 36. As the insulated wire is passing through the condenser 32 it is heated to a temperature in the neighborhood of 200 C. by means of an induction heating element as shown at 38 in theV drawing. The resultant hot insulated heated wire decomposes the nickel carbonyl as itpasses through the coating area. As the nickel coated wire leaves the coating area it passes over pulley 35 and into a reducing or inert atmosphere furnace 50 wherein the nickel coating is sintered. T he sintered nickel coated wire then passes over pulley 52 and is spooled on reel S4. The Alundum insulation is quite porous therefore the surface deposition conditions have to be controlled in order to maintain the proper insulation conditions between the heater and the cathode. These deposition conditions can be controlled by carrier gas flow rate and the wire temperature as it passes through the coating area. The nickel film thickness deposited can if desired be adjusted by regulating the rate of nickel carbonyl evaporation. For example, continuous nickel coating of a 0.001 tungsten wire insulated with aluminum oxide to a thickness of .003 can be successfully accomplished by using a helium iow rate of 7 cubic feet per hour and a surface temperature on the wire of approximately 200 C. By this method a nickel coating can be placed on the wire having a thickness of approximately 0.0001 to 0.0002. The resulting nickel coated wire can then be electrophoretically coated with triple carbonates to form a completed cathode assembly. In some cases it has been found advantageous to tire the nickel coated units in hydrogen at a temperature of about 950 C. This increases the conductivity along the film and thus makes it possible to use an even thinner film of nickel. n

By using these vapor deposition techniques both in the case of nickel and tantalum it has been found that no substantial diffusion of the metal will take place into the Alundum and high electrical resistance between the tungsten core and the metal film has been noted while excellent conductivity along the kmetal film is achieved.

While the above description and drawings submitted herewith disclose a preferred and practical embodiment of the quick heating cathode of this invention it will be understood by the speciiic details of construction and arrangement of parts as shown and described are by way of illustration and are not to be construed as limiting the scope of the invention.

What is claimed is:

suitable for use as a thermionically emissive cathode in an electron discharge device which comprises electrophoretically coating a heater wire with Alundum, continuously passing the cooled wire through a chamber containing nickel carbonyl while maintaining the wire in the chamber at 200 C. to obtain a nickel sheath thereon, passing the Wire so treated through a chamber maintained at about 950 C. cooling the treated wire and continuously coating it with a thermionically emissive material.

2. The method of manufacturing a composite material suitable for use as a thermionically emissive cathode in ari-electron discharge device which comprises electrophoretically coating a tungsten wire with Alundum, continuously depositing nickel on said Alundum coating by passing the coated tungsten wire through a chamber containing nickel carbonyl while maintaining the wire in said chamber at approximately 200 C., passing the nickel coated wire through a sintering furnace maintained at a temperature in excess of 900 C. and continuously coating the sintered material with a thermionically emissive material.

3. The method of manufacturing a composite material suitable for use as a thermionically emissive cathode in an electron discharge device which comprises electrophoretically coating a tungsten Wire with Alundum, continuously depositing nickel on said Alundum coating by passing the coated tungsten wire through a chamber containing nickel carbonyl while maintaining the Wire in said chamber at approximately 200 C., passing the nickel coated wire through a sintering furnace maintained at a temperature in excess of 900 C. and continuously coating the sintered material with a triple carbonate.

References Cited in the tile of this patent UNITED STATES PATENTS 1,818,909 Reerink Aug. 11, 1931 2,075,910 Robinson Apr. 6, 1937 2,118,186 Farnsworth May 24, 1938 2,442,863 Schneider June 8, 1948 OTHER REFERENCES y Cline et al.: Journal of the Electrochemical Society,

October 1951, pp. 385 to 387.

Claims (1)

1. THE METHOD OF MANUFACTURING A COMPOSITE MATERIAL SUITABLE FOR USE AS A THERMIONICALLY EMISSIVE CATHODE IN AN ELECTRON DISCHARGE DEVICE WHICH COMPRISES ELECTROPHORETICALLY COATING A HEATER WIRE WITH ALUNDUM, CONTINUOUSLY PASSING THE COOLED WIRE THROUGH A CHAMBER CONTAINING NICKEL CARBONYL WHILE MAINTAINING THE WIRE IN THE CHAMBER AT 200* C. TO OBTAIN A NICKEL SHEATH THEREON, PASSING THE WIRE SO TREATED THROUGH A CHAMBER MAINTAINED AT ABOUT 950*. C. COOLING THE TREATED WIRE

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