US1922254A - Thermionic tube electrode - Google Patents

Description

Patented 15, I

WestingliouseElectric & Manufacturing Company, a Corporation of Pennsylvania ribjfnmwing. Application May 2 0; 1926 f 'SerialNo. 119,545

. 6 Claims. (Cl. 250- 2 7.5)

invention relates-to the manufacture of thermionic tubes and has particular reference to makingcathodes or other electrodes therefor. In the: manufacture of electrodes for use in through if the electrode is to be used as a cathode,

and'to coat this carrier with jafmetallic conduct- 10 ing surface. Such electrodes are particularly de sirable for use in'the so-called A. C. tubesin Whichthe thermal lagoi the' insulating carrier prevents to a large extent the fluctuations in its surface temperature.

aspecial grade ofhighly vitrified porcelain, and

it has beenthe custom to formzthe metallic coating either by the Schoopprocess of spraying the nickel thereon or by bending a thin nickel sheet around a porcelain tube. Neitherof these methods have provedsatis factory, mainlyon account of the difficultyv of obtaining good thermal conductivity between the insulating support and the metallic coating. When this coating is applied apply it uniformly andit'is'also noted that it does not adhere as firmly to the porcelain as is desir-- able. Obviously, when. the cathodes are formed by bending a sheet around a porcelain tube contact between the sheet andtube is far from perfect.,'

It is accordingly, an objectof my invention to provide a thermionic cathode or other electrode having a metallic coating in intimategandper- 35. manent contact with an insulating support;

Another object of myinvention is to provide a method whereby electrodes designed primarily foruse in thermionic'tubes maybe easily and economically manufactured. I a

A further. object of my invention is to provide a more efficient cathode for use in thermionic tubes. w f

Still another object of Imy invention is to vprovide a method'whereby'an insulating support 5. may be coated with alfirm, adherent coating of metal which will not fiakeofi in use.

, .The porcelain'tubing', or other objectof which 7 it is desired to form an, electrode,- is first'painted witha mixture of finely divided metallic parti- 5,., cles suspended in a volatilizable vehicle. The

coated electrode isthen given such further treatment as will drive off' the vehicle and cause the adhering particles to change their characteristics. Mypreferred 'method comprises the following 5' steps:

1 prising .finely divided particles of metal such as 5 thermionic tubes, it has beenfound desirable many instances toemploy an insulating. carrier, which may be'he'ated by'a filament passing therecontemplate using, .ina.this mixture if desirable,

These cathodes have. in general beenmade of by Schoops process of spraying, it is difiicult to ,The porcelain tubing a other object, metallic or. insulating,-of which it is desired to make an electrode, is'firstpainted with a mixture comnickel or a metallic oxide such as nickel oxide in water 0" in some other. liquid such-Ias glycerine, alcohol orturpentine hichJmay be later driven off by heat without any deleterious residue. '1 r a temporary bindingmaterial such as agar-agar,

it being obvious that this bindingmaterial should b I I be such that subsequent heat or other treatment 'will entirely removeit from the cathode. ,-I may aisouse as a hinder or soluble compound of nickel,

such as the formats or nitrate, which'when heated 9 shall decompose to liberate metallic nickel As an alternative method of obtaining the coating, the porcelain tubingmay be'coated with the binder and slightly moistened, and the finely divided particlesof metal or metallic oxide may 75 be'placed thereon. either by means of an air blast or by being lightly dustedfrom a camels hair brush;

If a liquid vehicle or binderis used in the process .of applying the particles to the porcelain sup- 3? porn-the coated cathode'is then thoroughly dried. 7 ,After drying, if metallic particles have been used; the-coated electrode is then fired in a vacuum or in a'neutral or a reducing atmosphere at a temperature below the melting point of the metal 5 but high enough to cause the metallic particlesto sinter together into an adherent conducting layer over the porcelain. During this heating, any residue of the binder 'is driven off. l

If particles of metallic oxide such 'as nickel5 91f oxide have been used in the coating material, the

heat treatment above referred tois given, not in a vacuum, but in a reducing atmosphere, in order to reduce the oxide particles to themetallic state. The temperature is then raised to a point 5 below the melting point of the particles, which areaccordingly caused to sinter together into a coherentrconducting. layer as is the case when the metallicparticles are employed directly; In

the case or nickel, this temperature WOllld'flP-l proximate1200 C. '7 Y The porcelain used, although it may be-highly vitrified, has microscopic openings in its surface and the liquid will to a certain extent penetrate into these openings-and carry along the finely divided particles. It willthus, be seen that-upon drying, the coated electrode the-surface coating is keyed to the porcelain by innumerable small extensions, very much in the same way that plaster is keyed to a wire-netting or lath-covered 10 waufi When'the metallic particles are later tered together, .these microscopic extensions of sin- ' tendency to flake oft, even though the support be is firm and coherent and inexcellent thermal raisedto a temperature of "1000 C. The coating contact with the porcelain so that the heat from the porcelain is very readily conveyed thereto.

' My process is also capable of being carried out by the most unskilled laborer, it being only necessary to carefully superintend the last step of the firing process in order to make sure'that all ofthe vehicle or binder is eliminated and ticles are entirely sintered together.

Although I have described herein certain specific forms of my inventionj'I. am fullyaware that many other modifications are possible and my'inventio'n is not tobe limited except insofar as is necessitated by the prior art and as indicated by the. following claims. v

. Iclaim asmy inventionz. .-1.'-.The process. for manufacturing thermionic tube: cathodes which includes applying to a surl face a coating comprisingfinely divided nickel 30 suspended in a volatilizable' vehicle, eliminating the major portion of the vehicle, placing the coated: surface in a non-oxidizing environment, eliminating the residuum of the vehicle, and then heating: the nickel to .a sintering temperature. 1 2.:The process of manufacturing av cathode which'comprises applying: to the surfaceof an in sulating refractory material a coating of finely divided metal suspended in a volatilizable vehicle,

that the pareliminating the-vehicle, and then sintering the metal particles. v

3. The method of making metal filmsupon porous, electrically non-conducting bodies, which comprises mixing a highly comminuted metal with. a sufiiciently viscous liquid Whichdoes not react with the body at ordinary temperatures, to form a paste, spreading the paste upon the body, and-then heating the coated body to a sintering temperature. l 7. v 4. The method of making metal films upon porous electrically non-conducting oxide bodies, which comprises forming a paste by mixing a highly comminuted metal with a sufficiently viscous liquid Which'reacts with the metal at high temperatures to form a conducting compound, spreading the paste upon the oxide body, and then heating the coated oxide body to a sintering tem-' perature; I

' 5. The method of making metal films upon porous electrically non-conducting oxide bodies, which'comprises forming a paste by mixing a highly comminuted 'metal with a' sufficiently viscous liquid which reacts with the oxide at high temperatures to form a conducting compound, spreading 'thepaste-upon the oxidebody, and then heating the coated oxide body to'a sintering-temperature. 4

'6. The method of making metal films upon porous electrically non-conducting oxide bodies, which comprises forming a paste by mixing a highly comminuted metal with viscous liquid which reacts with both the metal and the oxide body at high temperatures to-form a conducting compound, spreadingthe paste upon the'oxide body, and then heatingthe coated oxide body'to'a sintering temperature.

1 H LEON MCCULLOCH;

a 'sufliciently