US2445257A - Thermionic emitting device - Google Patents

Description

July'13, 1948. z. J. ATLEE THERMINIC EMITTING DEVICE Filed July 3, 1944 I Zea/JL/QZ/f@ uw 21% 904mg Patented July 13, 1948 THERMIONIC EMITTING DEVICE.

Zed J. Atlee, Elmhurst, Ill., assigner to General Electric X-Ray Corporation, Chicago, Ill., a corporation of New York Application July 3, 1944, Serial No. 543,369*

This `invention'relates to electronics in general, and particularly to electron-flow devices, such as electronic rectiers, X-ray tubes, radio tubes, and suchother devices as employ electron emitting elements. f

An important object of 'theinvention'is'the provision of a new and improved electron emission element adapted to `beheated for electron emission at a relatively low temperature; a further object'being` to use columbium for electron emission. 1

Another'object of the invention is the provision, in an `electron ilow' device, of an electron emission element 'comprising columbium` supported on a suitable structure such as tungsten, molybdenum, or Otherhighfmelting ypoint material.

Anotherobject of the invention is the provision of a columbium emitter indirectly heated, as bymeans of a suitable electrically energized filament, whereby 'electron emission is obtained at low operating temperaturesA well below the normal operating-temperature of =a conventional tungsten electron emitting filament, thereby rendering indeiinite life to the tube;` also, the heating 'of the anode is more uniform and' the'emciency 'of the devicevis `greatly enhanced.

Another object of the invention is 'the' provision of an electron emitter'made of columbium,v either in the form of a strip, coil, tube or other wire;' a further object being toform the-emitter as asupport member of material having a high meltingpoint and having a' coating `of columbium vforming an emitting surface.V

A further object is to provide an electron flow device including an anode and a columbium electronemittingelement 'so' constructed and arranged that it will'shield a co-operating heater filamentlto thus protect `the filamentr from the electrostatic force between it and theanodewithout creating an undue space charge with respect toithe anodegto make possible a relatively large uniform emitting -srface of the cathode, to per mit the proper and ideal'design of the cathode fromthe standpoint of high voltage stresses, to make possible greater' electronic emission for a given amount ofheater or filament wattage, Aas well `as to provide for greater eiliciency in general andmore rugged construction.

A still further object is ythe provision'of an improved electron emitting element in the form of a cylindrical `member having a columbium emitting surface. e v Still another object ofthe invention is to form an electron emitting element lofcolumbium,and

`1 claim. (C1. 25o-27.5)

further that the thermionic emitting temperature of columbium is substantially,1'700 to 190 Kelvin, being considerably lower than tungsten and tantalum, the two pure metallic thermionic emitters heretofore generally employed.

Numerous other objects'and advantages will be apparent throughout the following specification. I

The :accompanying drawing illustrates a selected embodiment of the invention,I andthe views therein are as follows: I

Fig. 1 is a sectional view taken longitudinally through an electronic rectifier embodying'the invention; f Y i Fig. 2 is a sectional view on Fig. l;

Fig. 3 is a fragmentary sectional View showing a modified arrangement of 4filament mounting; and f Fig. cathode structure ter is substantially elongated tering or gas absorbing eflect.

To illustrate the invention, the drawings show an electronv flow'device I embodying an anode 3 and 'a cathode 4 enclosed in a sealed envelope 2, suitable conductor ymeans being provided for connecting the `anode and cathode in electrical operating circuits externally of the envelope. While the invention is not limited to the shape of the anode, the same is shown as a hollow cupshaped element enclosing the electron emitting portions of the cathode.

The electron emitting portion of the cathode comprises columbium which functions to emit electrons ata temperature of 1700 yto 1900Kel vin. This is'substantially below thel temperature at which tungsten and tantalum emit electrons so that devices embodying my present invention avoid the disadvantages inherent to devices embodying conventional emitters.

' The columbium emitter element of my present invention may comprise an element of pure metal, 0r the element may comprisea support of metal, suchv as tungsten or molybdenum, having a high melting point, the support being coated with columbium to form the electron' emitting surface thereof.

The emitting element, however formed, may be heated for electron emission either by direct application of electric power to the element or by mounting the element in position to be' the liner 2-2 of 4 is `a detail sectional view of a modified in which the columbium emitto provide a getheated indirectly by suitable heating means.'

Where itis desired to heat the emitting element by direct electrical action, the same maybe formed either as a coil, wire or strip of pure columbium, or of other metal coated with columbum, and means may be provided to connect the element with a suitable electrical power source. Where the element is heated by indirect action, it may be operatively associated with a suitable heater. To this end, the emitting element may comprise a coil inductively associated with an induction coil or may be formed as a plate, strip or shell in heat exchange relation with respect to a heater, preferably an electrically energized coil or filament of metal such as tungsten.

The particular structure herein shown for the purpose of illustrating the invention comprises an electronic device in the form of a rectifier tube I, although the several features of the invention are not limited to rectifiers but may be utilized to advantage generally in electron flow devices, including X-ray tubes, radio tubes, and such other devices Where therrnionic emission is desired from a pure metallic source.

The rectifier tube I, as shown in the drawing, comprises a sealed envelope 2 of suitable material, such as glass or metal, glass being specically shown in the drawing. The envelope 2 contains the anode 3 and the co-operating cathode 4. The envelope 2 may be arranged in any convenient or preferred form, but is shown in the drawing as being a tubular glass shell having re-entrant necks 5 at opposite `ends of the shell. The anode 3 and the cathode 4 are respectively supported on the said necks at the opposite ends of the envelope in any suitable fashion, although I prefer to employ supporting and sealing means of the sort 'shown in my previous U. S. Patents Nos. 2,250,323 and 2,336,769, respectively issued July 22, 1941:and December 14,1943. In .this connection, the necks 5 denne `openings which are closed by seal members 6 and I of generally cupshaped cong-uration. These seal members 5 and 1 are preferably made of sheet metal, Each of said members '6 and 'I has an annular rim which forms a glass-to-metal seal 8 with the inwardly facing end of the neck V5 on which the seal member is mounted, to thus seal the end of the envelope. y

The seal member l, at one end of the envelope, carries the anode 3., which preferably comprises a. ytmp-'shaped element formed with a stem :9 which projects outwardly of the end of the envelope through .an opening formed in the seal member l, -the stem 9 being sealed in said opening and carrying a bracket 9a, within the envelope, on 'the lcup-shaped anode element is mounted, as by rivets :or other fastening.

The :seal `member ll5, at the other end of the envelope, I'carries the cathode 4 which, as shown, preferably comprises an electron emission lelement suitably mounted on support means carried by the seal .member AIi.

According to the present invention, the electron emission velement `comprises fcolumbium and is preferably supported in position within and surrounded by the cup-shaped yanode 3. The columbium emission element may be formed as a llament for direct connection in an electrical heating circuit or may be formed as a 'separate element and heated to a proper electron emitting temperature by 'a heater element I0 which -is preferably made of tungsten.

The rcathode structure 4, as shown in Fig. 1, maybe ,mounted and sealed on the envelope by means -of Aa support and sealing structure of :the sort shown in my U. S. Patent No. 2,250,323, such structure comprising a disk-like `head Il., :preferably of metal, which head is mounted on a stud I2 extending in an opening formed in the seal member 6, the stud being sealed in said opening and having portions extending outwardly of the envelope. The hea-d II ycarries a tubular skirt I3 secured at one end on the head and extending at the other end in position enclosing the glassto-metal seal 8. The skirt thus encloses a space I4 between the seal member E and the head II, which space is in open communication with the interior of the envelope 2 through the annular space deiined between the end of the skirt I3 and the glass-to-metal seal 8. Within this space, means may be provided for performing a gettering operation during the fabrication of the tube in order to insure the maintenance of -a high 4degree of vacuum within the envelope. This operation is accomplished by means of a loop of gettering wire I9 in the space I4, said wire being connected at one end to the stud I2 and at the other end to a conductor 20 which lextends outwardly of the envelope through a suitable Vseal in the member t. By applying electric potential between the wire 20 and an extension of the stud I2, outwardly of the envelope, the gettering wire may be'energized to perform its gettering function within the envelope.

The opposite ends of the ilament I0 may he mounted on, electrically connected to, and supported by .conductor stems I5 and 2I which extend through openings I 6 formed in the head =I I. The ends of the stems may be mounted yon and insulated from the head by fitting the openings IG with grommets .I FI which receive the .stems I5 and 2| and which, in turn, are sealed in the openings as by welding or brazing. 'The lstems are `supported in and electrically insulated from the grommets and the head II by means of :globules of glass I'B; which support the ste-ms in the grommet and seal the gramme-t opening :around the stems. Within the space I 4, the ends of the stems I5 .and .21 are electrically connected, as tby clamps 22, with conductors .23 which extend through openings in .the sea-l member f6, said openings lbeing provided with grommets 24., like the groirimets I 1, rin which the conductors 23 .are lsealed by means of glass globules simil-ar to the globules I8,` all as taught in my aforesaid U. S. Paten-t'No. 2,250,323. lThe filament iI'Il thus is electrically connected with the conductors :23 which extend outwardly -offthe envelope, such #connection being accomplished by way of fthe stems =I 5 and 2:I which are electrically insulated from the head II.

The filament I0, Whichfis l,the heater for the cathode II, may be made of columbium :and thus form an Ielectron emitter in :accordance with :the present invention, yor fthe lament may comprise tungsten coated -with columb-ium as .an emitter. However, the ilament vmay be used merely :as a heater element :en-closed .o1-'encased within a oylindrical tube r25 made of columbiumf-or Aof other metal coated with columbium. vIn ceither case, the tube `2li Wil-l 4have a columbium surface T26 lfor emitting electrons. 'The :columbium cathode emitter .25 vis thus v:arranged to be indirectly heated by the heater which, in such case, may be made fof tungsten or other suitable material. While the drawings disclose .the use of a tubular or cylindrical columbium .emitter 25, itis of course understood that the emitter =`may be of any 'suitable size and shape for the purpose intended; and the emitter may be supported on fthe head I'I in any suitable or convenient fashion, as 'by-mounting it 'on support l'brackets 21 carried 7by one for other of thefstems I 5 and 2i..

25cm-asv The use vof columbiumffor electronA emission in'- dire'ctlylieated bythe tungstenl lament IIJ produces'results greatly'superiorto-any conventional electron' emission material; and the operating temperature of a device embodying 'tlieinvention' is' considerably below rthat of'like devices employing other emission materials. and still'v produces greater efficiency and effectiveness. IIlemperatures of'1700`t`o 1900 Kelvin obtain emission which is more 4than adequate for various applications, and the temperature of the tungsten heaterfiilament is well below the normal operating temperature of tungsten. Theuseof columbium as a cathode emitter does not produce high space charges in the tube itself and still protects the lamentto prevent the formation of any substantiali electrostatic force between the. lament and the anode. The. heating of theI anode isL uniform whereby localized. melting of the anodeis overcome. In addition', low lamentcurrent eliminates the burning outoi' the filament. Moreover,the cathode emission per watt of filament consumption is very great. Irr addition, the thermionic emitting device, as herein disclosed and comprising the columbiumtube or equivalent columbium structure, makes possible a large uniform emitting surface of the cathode, as well as making it possible for the proper design of a cathode from the standpoint of high voltage stresses. Also, the use of columbium has the further advantage in that it can be formed more easily than tungsten, tantalum, or other emission materials. The thei'mionic emitting temperature is approximately 600 Kelvin lower than tungsten, and thereby prolongs the life of the filament and the cathode emitter itself. Columbium makes possible more emission for a given heater or filament wattage.

The tubular emitter 25 is preferably arranged concentrically about the tungsten filament I and may be supported in position by molybdenum ribbons 21 welded or otherwise secured to the outside of the tube 25 and to the upstanding support stem 2l. The filament I0 is connected at its upper end to the stem 2|, and at its lower end to the stem I5, preferably by wrappings of 5 mil (.005 inch) molybdenum wire, as indicatedat 28 in the drawing. The construction is such that the columbium tube is rigidly supported and is so arranged with respect to the filament that there will be no obstruction to the emission oi electrons. It will be seen that the cathode emitter is electrically connected with one of the conductors 23, outwardly of the envelope, through the support stem and the molybdenum ribbons 21.

An electron flow device functions by the flow of electrons emitted from the cathode and traveling to and impinging upon the anode. When the flow device is constituted as a rectifier, the stream of electrons passing between the cathode and anode form a conduction path along which electrical current may iiow in one direction only between the anode and cathode. This uni-directional flow phenomena is utilized for the purpose of rectifying alternating or uctuating electrical energy in order to provide uni-directional electrical power.

The columbium emitter 25, regardless of its shape or where its operative position may be, is capable of electron emission by indirect heat radiation or by electron bombardment through a diierence in potential between the filament and the columbium. Also, the emission from the columbium may occur by the electronic bombardment `plus radiant heatA from the lament tothe columbium emitter.' f

' Fortungsten filament filament or heater' made oi columbium iil'amnt may be in the form of ,a helix, as shown, with respect to the tungsten, or the columbium filament may be a vtube or a strip orI it' may assume any shape? proper toperform the functionintend'edy The-columbium emitter asgherein disclosed may be indirectly heated by co-operation-with a separate heating filament, or may bei heated directly by making the heater or fiifament itself of columbium. i

In somev applications, as indicated in Fig. 3, it may'bed'esirable to ground one or other vof the stems' I5 or2l o n the head l I instead of mounting them both in insulating grommets. This may be accomplishedby press-tting the stem to be groundediinv an opening or socket la, in the head II-,` as' taught'inmy U-L S. Patent No.'2',250,323,"in whiel'i'case one of the connection conductors 23 may be eliminated and connection with the grounded stem accomplished through the support stem I2,'outwardl'y of theenvelope;`rv` At leastone stemfhowev'er, must bein'sulated from the head and end seal. Where one of the stems is grounded, the emitter 25 may be connected either to the grounded or to the insulated stem, but if connected to the insulated stem, the emitter also must be insulated from the head I I.

As shown in Fig. 4, the columbium emitter 25 Ill'may be substituted a' v may be provided with an integral elongated lower end 3l extending considerably below the bottom end of the filament I0. The part of the emitter above the projection or elongation may attain a temperature range of between 1700 and 1900 Kelvin during operation. However, the temperature range of the projection or elongation may vary from 1700" Kelvin at the upper end 32 of the elongation 3l to about 600 Kelvin at the lower end 33 thereof. The elongation 3I acts continuously as a getter preventing the formation of gaseous matter within the envelope. The use of columbium, therefore, not only acts as a greatll7 improved emission element, but when extended, as shown in Fig.4, the elongation 3| acts as a gas absorber, eliminating gaseous material within the envelope. In this embodiment, the lower end of the tube may be supported on the head II and thus electrically connected thereto, in which case electrical connection with the emitter may be had outwardly of the envelope through the stem I2 and its extension. To this end, it is desirable to employ a modified cathode support structure of the sort shown in my U. S. Patent No. 2,336,769, in which the head I I is supported on and electrically connected with the seal member 6 by the skirt I3 instead of by the extension of the stem I2 inwardly of the seal member. Elimination of the inwardly extending portion of the stem I2 allows for supporting the stems I5 and 2l centrally on the head II. Alternately, the tube 25 may be supported on the head by suitable insulating means, in which case electrical connection of the emitter may be had outwardly of the envelope by connecting the tube 25 with one or other of the stems I5 or 20.

The tube 25 also may be formed with a closed top 34 whereby the filament is entirely enclosed within the tube and thus completely shielded from electrostatic forces that otherwise might prevail between the anode and filament when the device is in operation.

The invention provides an extremely efiicient thermionic emitting device for use in connection columbium, and suchwith rectifying tubes, X-ray tubes, radio transmitting tubes, and other vacuum tubes where pure thermionic emission is desired. The construction is such that the lament ls properly located and supported Without any obstructions, as is the case where a spiral support is provided for the filament. Moreover, the use of a columbium cathode emitter, indirectly heated by a tungsten filament, or by making the lament of columbium for direct emission, permits lower operating temperatures well below the normal operating temperature of tungsten, thereby rendering indefinite life to the tube. The heating of the anode is uniform, and the efficiency of the device is greatly enhanced. The use of the columbium as herein disclosed also acts as a getter in that gases within the envelope are absorbed or eliminated.

Changes may be made in the form, construction and arrangement of the parts without departing from the spirit of the invention, and the right is hereby reserved to make all such changes as fairly fall within the scope of the following claim.

The invention is hereby claimed as follows:

An electron flow device comprising an enclosing envelope, a .cathode emitter having a columbium surface arranged inside of said envelope, a. llamentheater arranged adjacent said surface and indirectly heating said surface, a conductor stem for the filament, and getter means of columbium on the emitter extending below the end of the filament a predetermined distance and acting as a getter.

ZED J. ATLEE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS

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