US1795730A - Electron-emission device - Google Patents

Description

March 10, 1931. j w MARDEN 1,795,730

ELECTRON EMISSION DEVICE Filed Dec. 30 924 FIGJ INVENTOR JOHN W. MARDE N ATTORNEY Patented Mar. 10, 1931 UNITED STATES PATENT OFFICE JOHN WESLEY MARDEN, OF EAST ORANGE, NEW JERSEY, ASSIGNOB TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA ELECTRON-EMISSION DEVICE Application filed December 30, 1924. Serial No. 758,800.

-to increase electron-emission.

An object of the present invention is to provide a device of the above character which may be manufactured in an expeditious and practical manner without the sacrifice of any of the essential characteristics required to make the device useful and desirable.

Another object of the invention is to provide a practical construction of tube in which the use of oxidizing and activating materials may be facilitated.

Another object of the invention is to provide a practical and expeditious method of treating oxidizing and activating materials in electron-emission devices.

Another object of the invention is to provide an electron-emission device of the above character so constructed that the grids and plates thereof may be treated by inductionheating.

Another object of the invention is to pro-. vide an electron-emission device of such construction, as to protect the device from detrimental eifects which may attend the use of oxidizing and activating materials.

A further object of the invention is to provide a device of the above character in which certain of the electrodes may be conveniently produced at a miniumm cost.

A still further object of the invention is to provide a device of the above character with electrodes which may readily be treated by induction heating and which will prevent the detrimental effect of positive ions upon a filament during operation of the device.

Other objects and advantages of the invention will be apparent as the description proceeds.

The present invention aims to provide an improved structure for an electron-emission device, such for example, as a radio tube in which a cathode is employed operable at low temperature and to further provide a more practical method of manufacture than that heretofore suggested.

Radio tubesof the foregoing type, employ a low pressure vapor of an alkali metal such as caesium and may be termed caesium tubes. The alkali metal under certain conditions, greatly increases the electron-emission of the heated cathode, particularl at cathode temperatures so low, that in t e absence of the vapor, no substantial electron-emission would occur. The life of tubes operating under these conditions is greatly increased and at the same time a greater electron-emission is possible. The desirable results obtained are believed to be due to the continuous formation on the tungsten filament or cathode of an absorbed film which resists evaporation at a temperature far above the vaporizing point of the alkali metal. It is believed that the formation of the absorbed film is greatly facilitated by the introduction of certain gases having suitable properties, the action being, that if the atoms of certain gases strike the heated electrodes, they form an absorbed film thereon of substantially atomic thickness which is capable of holding on the atoms of the alkali metal more strongly than does the surface of the heated electrode.

It has been found that desirable results have been obtained by the introduction of small quantities of electro-negative gases incapable of reacting with the alkali metal but which react with the material of the cathode. These electro-negative gases have the effect of greatly increasing emission of a tungsten surface in the presence of a suitable alkali metal.

In radio tubes of the above character, it has been the practice to use a vane arrangement of grid and anode elements which consist of strips of metal supported perpendicularly and parallel to each other in the tube. This arrangement of the elements is not only difficult to make but presents diificulties when the operation of removing occluded gases from the elements is to be performed, since the plates and grids have heretofore not been supported in any fashion in which induction heating could advantageously be employed.

In the present invention an electron-emission device of the above character is .provided,in which the grid and plate elements are composed of a plurality of members electrically connected and each element may readily be degasified by the apparatus now in general use in the factory for other types of devices.

The plates and grids of the present device may consist of disks or connected metal plates of nickel, iron, molybdenum, or the like, and may be supported by suitable connector mem bers. The plates or disks may be positioned in spaced relation along the longitudinal axis of the device, having their sides opposite and may be provided with apertures or perforations centrally located with respect to each disk. The disks may be so arranged that a filament may be positioned concentrically within the apertures and substantially coincident with the longitudinal axis of the device.

It has been found preferable to provide the grid plates with apertures of smaller perimeter than the apertures of the anodes. Thus the grid or control electrode is disposed in closer relation to the filament than are the plates. It will be understood that the size of the holes in the disks, the spacing of the disks with respect to each other and their relative position with respect to a filament are governed by the constants desired cf the tube.

By reason of the present construction it is possible to manufacture the grid and anode in a practical and economical manner. The parts may be readily formed either on a plate bending machine or may be stamped from a suitable strip of metal and secured in position. When stamped or bent to shape, the usual welding operation may be eliminated, thus removing certain disadvantages which may occur during the operation of the tube, particularly where a poor weld results in oxides which subsequently release oxygen to the detriment of the life of the tube. The present horizontal spaced and connected arrangement of the component parts of the grid and plate electrodes permits them to be readily heated for the removal of gases therefrom and this arrangement with the proper grid bias prevents damage to the filament from gas ionization.

In radio tubes manufactured according to other methods the plates are positioned vertically and a long time interval is necessary to bake the tube for the removal of gas, after which the tungsten filament is heated to a very high temperature to remove the impurities from the surface. A little oxygen is let into the tube and the filament is again heated to give a layer of oxygen on the tungsten filament. It is then necessary to distill some of the alkali metal into the tube and again let in oxygen to form a little caesium oxide which ultimately removes hydrogen and finally, after thorough treatment, it is necessary to activate the filament in the alkali metal vapor.

In the manufacture of a tube constructed in accordance with the present invention, the electrodes may be employed to support sub stances to be activated. On one of the disks of an electrode or on a separate disk may be disposed a quantity of oxygenyielding compound, together with a capsule or other container containing an alkali metal. addition, a small quantity of misch metal may be provided as a clean-up agent of the character set forth in a copending applica tion of J. W. Marden and H. C. Rentschler,

Serial No. 679,489, filed December 8, 1923,

and assigned to the same assignee as is the present application.

The tube will then be ready for a commercial exhaust and activation. The device having the above contents may then be applied to a pump, gently warmed by the usual inductive heating to produce the oxygen and the filament heated to the proper temperature.

The separate disk or electrode may then be further heated to distill the alkali metal and sealed off and finally the misch metal may be driven from the plate to give the final gas clean-up.

All these operations may, according to the present invention, be accomplished in the factory within a relatively short time period as in contradistinction to the hours of baking heretofore required with the great number of steps as were deemed necessary.

The present invention provides a practical structure for electron-emisson devices of the above type which will prevent detrimental effects to a filament by reason of ionization of the gases within the device. The plates which form the electrodes are so spaced with relation to each other that ionization occurs between the plates and the ions are directed thereto rather than to the cathode.

By reason of the present structure, therefore, practical and effective electrodes may be provided which will serve to avoid the detrimental effect of the ions upon the filament and, at the same time, answer the requirements of expeditious produc'lion as is necessary in commercial manufacture.

The applicant is aware that electrical devices have been constructed with perforated disks positioned with a filament in the apertures thereof. These disks, however, have been in the form of condenser plates and so spaced as to provide a dielectric either by reason of the vacuum within a container or by interposed pieces of mica. Such construction would not meet the requirements of a device to which the present invention is applied since the plates are not positioned in the desired relation, as in the applicants invention, to effectively prevent positive ions from passing between the plates and reaching the filaments.

- The advantages above enumerated are, to a great extent, derived by using the improved form of grid and plate and by the arrangement of these element with the addition of r m 1 but withcoil removed; r a

the use of misch metal or other agent to attain a quick and satisfactory clean-up of residual hydrogen or other gases.

The invention will be more fully understood by reference to the accompanying drawing, in which Fig. 1 is an elevational view of a radio tube showing the control electrode and anode elements in section;

Fig. 2 is a view taken on line II--II in Fig.

Fig. 3 is a view taken on line III-III in Fig. 1;

Fig. 4 is a side view of a modification in the structure of the grid and plate;

Fig. 5 is a perspective view of the electrodes substantially the same as shown in Fig. 4 but applied to a press or stem;

Fig. 6 is a side view of an electrode composed of disks but shows another form of connector member;

Fig. 7 is a plan viewof the electrode shown in Fig. 6; v

Fig. 8.is a sectional view of the electrodes shown in Fig. 1 but applied to a V-shaped filament, and

Fig. 9 is a sectional view of the type of plate and grid electrode adapted to accommodate a plurality of filaments.

An electron discharge device of the threeelectrode type is illustrated in Fig. 1 and comprises an evacuated container or bulb 10,

a cathode or coiled filament 11, an anode or plate electrode 12 and a grid or control electrode 13. The filament 11 may be connected at its terminals to conductors 14 and 15, which conductors may serve as supports and may be embedded in a pressed portlon 16 of a stem 17 integral with the bulb or container 10. The filament may be heated electrically from any suitable source, such for example, as a battery 18. The plate electrode may be com posed of a plurality of disks or ring-like members 19 having centrally disposed apertures 21.

The rings or disks of the anode which may be termed anode disks, may be connected to a common conductor and support 22 secured in the press 16 and having a suitable conductor 23 connected thereto. The disks may be secured to the conductor 22 in any suitable manner,asby connectormembers 23' welded thereto and to the connector 22, or the disks may be integral with or secured to a conductor or support without welding, as hereinafter more fully described.

The disks may be spaced at suitable distance apart and so arranged with respect to the filament 11, that the filament will be disposed concentrically within the ring-like members.

The grid electrode may be constructed of ring members 24 having apertures 25 therein of a lesser diameter than the apertures 21 of the plate element, thus bringing the effective surface of the grid in the proper relation to the filament. The grid disks may be secured to a common support 26 secured in the press 16 and provided with a conductor 27. The grid disks may be mounted in a manner, similar to that described for the anode disks and may be positioned between the anode disks in such relation to the filament that the same may be concentrically disposed in the apertures 25 of the grid disks. The spaced relation'of the disks of the two electrodes may be changed in accordance with any desired constants of the tube, which is also true with respect to the apertures in the disks.

By reason of the arrangement of the component parts or disks of the several electrodes certain disadvantages, due to the release of oxygen from poor welded joints during the life of the tube, are avoided. This arrangement of disks provides an electrostatic field as a substantial barrier about the filament to deflect any gases escaping from the component parts of the device and which would otherwise attack the filament. By reason of the integral or connected component parts constituting each of the grid and anode electrodes, it is possible in the present invention to employ one of the electrodes as a support or heating agent for the several substances to be activated or oxidized within the bulb.

The material to be treated may be disposed upon one of the disks or, when desirable, a separate support or platform 28 may be provided. As shown in Fig. 1 this platform may be connected to the support 26 and may be slotted, as shown in Fig. 3, to embrace the electrode supporting members and substantially cover and protect the upper end of the press 16. Upon this platform may be dis-, posed, as indicated in dotted lines, a quantity of oxygen-yielding compound 29, such for example as bZIIlHlIlPGIOXlClB or manganese dioxide, a quantity of alkali metal 30, such as caesium or rubidium, or a compound of caesium and magnesium and a quantity of a clean-up agent 31, such for example as misch metal. These various substances may be deposited on the platform of a lamp mount by either being welded, pasted or otherwise suitably fastened thereto and a mount having the materials so disposed therein, is ready for ,the usual commercial exhaust and activation.

When a device has beenprovided with the necessary substances positioned as described the same may be scaled to a mount and put thru the usual factory operations. That is, the bulb may be applied to a pump 32 (indicated in dotted lines in Fig. 1) which may be connected to the exhaust tube 33 of the bulb in the usual manner. The bulb may then be disposed within the confines of a coil 34 suitably connected to a high-frequency or other generator 35 or other suitable source of highfrequency current controlled by a switch 36. Upon closing the switch 36, high-frequency current in the coil 34 will induce the corresponding current in the plate, which induced current heats the plate and other conducting parts of the device. Thus, in the manufacture of a device of the present character, the same may be put in communication with the pump and first gently baked out by heating, which heating may be continued in steps of different degrees, and inasmuch as the oxygen-yielding compound selected, yields its oxygen at a relatively low temperature and r the alkali metal produces a vapor at a higher temperature and the misch metal is activated at a still higher temperature, the various steps may be accomplished progressively by a heat gradient eflfected thru any suitable medium, for example the coil 34.

The practical and expeditious manner of treating the various materials is readily accomplished in the present invention by reason of the cooperating structure of the elements, such as the grid and plate electrodes. The novel arrangement of the disks constituting the electrodes has a further advantage in connection with the oxidizing and activation steps.

When the material to be treated is placed upon a disk for heating, particularly if caesium is used, the plate or disk prevents a deposit in the form of a layer across the top of the press 16 which may have a tendency to electrically connect the supports and thus short circuit the device.

If desirable, each of the disk electrodes may be made of a single strip of suitable material. For example, as shown in Fig. 4, the grid electrode 38 is bent from a sheet of material 39 to produce a plurality of spaced plates or disks 41 consisting of folded sections of the plate pressed into intimate contact and provided with a central aperture 42. The anode 43 may be formed in a similar manner and provided with central apertures 44.

Fig. 5 shows in perspective, the grid and plate electrodes formed in a manner similar to that described for the ones shown in Fig. 4, except that portions of the plate have been removed to provide relatively narrow supporting strips 45 and 46 for the grid and anode respectively.

It will further be observed that these supporting strips may be bent at 47 and clamped to support members 48 and 49, thus avoiding any welding operation. Further welding operations may be avoided by clamping the filament 11 to supports 51 and 52. With this construction, a tube may be provided which avoids the effect of gases released from welded joints, thus eliminating the detrimental effect thereof during the operation of the device. The present construction of electrodes is also applicable to other forms of filament.

It will be appreciated that the apertures in the disk may be of oblong or of suitable configuration to accommodate filaments havmg one or more sections, such for example, as

the V-shaped filament 55 which is shown in Fig.8 as disposed in operative relation to a grid electrode 56 and a plate electrode 57. The disks of various electrodes may be provided with other novel connector members or supports, one of which is shown in Fig. 6 and comprises a strip 58 of suitable material bent to provide a plurality of spaced slots 59, the walls of these slots being formed of folded material which may be readily pressed more tightly against disks 61 disposed therein to hold the same in the proper relation, thus providing a non-welded structure.

The present construction of grid and plate electrodes is particularly adapted for use in an electron discharge device employing a plurality of filaments. As illustrated in Fig. 9, each of the disk members 63 of a grid electrode 64 may be provided with a plurality of apertures 65 and each of the disk members 66 of a plate electrode 67 may be provided with a plurality of apertures 68. The filaments may be supported by suitable support members 69 and 71, thus the advantages of a double or multiple grid and plate are at tainable with but slight modification from the structure shown in Fig. 1. It will thus be noted that the present invention includes a structure that is not only simple and relaively low in manufacturing costs, but one which lends itself to various modifications for the production of electron devices of different desirable characteristics.

The present invention, further provides for the more practical and commercial produc tion of a device, in which an electron-emission is possible by reason of the presence of a vapor of certain alkali metals and in which the eflect of such vapor is facilitated by the introduction of electro-negative gas and in which it is desirable to clean-up the residual gases within the tube. The structure is of course equally as applicable for other types of devices, such as the radiotrons of the more well known types.

Although a preferred structure and method have been shown and described as illustrating an embodiment of the present invention, it is to be understood that the same is not limited to the use of the particularly specified substances recited herein for the production of oxygen or vapors, but that other equivalent substances are applicable as will occur to those skilled in the art, as well as modifications of the present structure, all of which it is to be understood come within the spirit and scope of the present invention as set forth in the appended claims.

What is claimed is:

1. An electron-emission device, comprising a sealed envelope containing an alkali metal, a filament, a grid element and an anode element, each of said elements comprising a plurality of perforated plates supported in spaced relation by an electrical conmetal, a cathode, an anode and a grid electrode, said grid and anode being comprised of a plurality of ring-like members, each member positioned to encompass said filament, and means for holding said members in substantially parallel relation to each other as to prevent detrimental effect on the filament of gas ionization caused by said alkali metal.

3. An electron-emission device comprising a sealed envelope containing an alkali metal, a cathode an anode and a control electrode, said anode comprising a plurality of integral ring-like members disposed in spaced relation, said control electrode comprising a plurality of integral ring-like members disposed in spaced relation to and between the members of said anode, said filament being surrounded by each of said ring members, said members being disposed in such spaced relation as to prevent gas ionization by reason of said metal from affecting said filament.

4:. An electron discharge device comprising an electrode formed from a continuous strip of material having upon each other to provide a plurality of spaced sections having apertures therein and a filament disposed in said apertures.

5. An electron discharge device comprising a plurality of electrodes, each of said electro es being formed from a continuous strip of material having portions folded upon each other to provide a plurality of flat sections, the sides of the sections of one electrode being spaced from and opposed to sections of the other electrode, apertures in said sections and a filament disposed in said apertures.

6. An electron-emission device comprising an envelope containin an alkali metal, a lament, a grid electro e consisting of a plurality of disks, a conductive su port connecting said disks, relatively sma apertures disposed centrally with respect to each of said disks to receive a filament, an anode comprising'disks of similar construction to said grid electrode but having apertures of 7. An electron device comprising a sealed envelope containing an alkali metal, a filament, a grid electrode consistingof a plurality of members disposed in spaced relation, each of said members surrounding said filament, a plate electrode comprising a plural ity of members disposed in spaced relation and alternately disposed between the members of said grid electrode and surroundim said filament, said electrodes being so spaced with relation to each other that gas ionization by reason of the alkali metal occurs between the members of said electrodes andthe ions are diverted from said filament.

In testimony whereof, I have hereunto subscribed my name this 27th day of December,

JOHN WESLEY MARDEN.

portions folded greater perimeters to receive the filament,

said grid disksand said anode disks being so arran ed as to avoid gas ionization b reason 0 said metal from. aflecting sai filnmant.

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