US1838776A - Method of making electron emission devices - Google Patents

Description

METHOD OF MAKING ELECTRON EMISSI ON DEVICES Original Filed Dec. 30, 1924 I INVENTOR J ohvv wMAeDEf-x ATTORNEY Patented Dec. 29, 1931 UNlED STATES PATENT" OFFICE JOHN W. MARDEN, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE LAMP COMIPANY, A CORPORATION OF PENNSYLVANIA METHOD OF MAKING ELECTRON EMISSION DEVICES Original application filed December 30, 1924, Serial No. 758,800. Divided and this application filed December 1, 1927. Serial No. 237,001.

This invention is a division of my copending application Serial No. 758,800 filed December 30, 1924 for electron emission device.

Radio tubes of the type to which the above mentioned copending application relates employ a low pressure vapor of an alkali metal such as caesium and may be termed caesium tubes. The alkali metal under certain condiment or cathode of an adsorbed film which re-- sists evaporation at a temperature far above the vaporizing point of the alkali metal. The formation of the adsorbed 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 adsorbed 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.

In radio tubes of the caesium type, 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 high temperature to remove the impurities from the surface. A little oxygen is let into the tube from any suitable source 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 substance to be activated may be sealed into the tube and an electrode or an extension thereof may support the substance to be activated. For example, on one of the discs of an electrode or on a separate disc may be disposed a quantity of oxygen yielding compound, together with a capsule or other container containing an alkali metal or its compound. In addition, a small quantity of misch metal may be provided as a clean up agent of the character set forth in a copendmg application ofJ. 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 abo e 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 disc or electrode may then be further heated to distill the alkali metal and sealed oil 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 Weredeemed necessary.

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

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 anode elements in section; and F Fig. 2 is a View taken on line II-II in s an example of one type of device with which the present method may be practiced, 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 ma\' be embedded in a pressed portion 16 of a stem 12' integral with the bulb or container 1H. The lilament may be heated electrically from any suitable source, such for example, as a battery 18. The plate electrode may be composed of a plurality of discs or ring-like members 19 having centrally disposed apertures 21.

The rings or discs of the anode which may be termed anode discs, may be connected to a common conductor and support 22 secured in the press l6 and having a suitable conductor 23 connected thereto. The discs may be secured to the conductor 22 in any suitable manner, as by connector members 23 welded thereto and to the connector 22, or the discs may be integral with or secured to a conductor or support without welding, as hereinafter more fully described.

The discs may be spaced a 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 discs may be secured to a common support 26 secured in the press 16 and provided with a conductor 27. The grid discs may be mounted in a manner, similar to that described for the anode discs and may be positioned between the anode discs in such relation to the filament that the same may be concentrically dis posed in the apertures 25 of the grid discs. The spaced relation of the discs 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 discs.

The present arrangement of discs 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 discs or, when desirable, a separate support or platform 28 may be provided. As shown in Fig. lthis platform may be connected to the support 22 and may be slotted, as shownin 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 disposed, as indicated in dotted lines, a quantity ot' oxygen-yielding compound 29, such for example as barium peroxide or manganese dioxide, a quantity of alkali metal or compound 30, such as those of 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 mount by either being welded, pasted or otherwise suitably fastened thereto and a mount having the materials so disposed therein is ready for consolidation with a bulb for the usual commercial exhaust and activation.

When a mount has been provided with the necessary substances positioned as described the same may be sealed to a bulb 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 high- Frequency 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.

In practicing the present method the several substances such as an oxygen-yielding compound, an alkali metal or its compound and a clean-up agent are introduced into the bulb preferably on a portion of the mount of the device which is then sealed to the bulb.

The sealed-in bulb which includes the mount and bulb is then applied to a suitable pump by means of the usual exhaust tube. This sealed-in bulb which as a whole may be called the device, is thoroughly baked out and exhausted.

Inasmuch as the oxygen-yielding compound yields oxygen at a relatively low tem perature of about 400 or 600 C. this action may be brought about without affecting the alkali metal or the clean-up agent.

When the oxygen has been released, the filament may be lighted or flashed in the usual manner as above mentioned, thus causing the desired layer of oxygen to become deposited upon the filament. This step in the method differs from others since whereas the oxygen had heretofore been supplied from a separate or outside source, the present method produces the oxygen Within the device and avoids the disadvantage of an auxiliary communication with another container. After the oxygen has performed its service, it may be pumped out of the device. The compounds may then be subjected to a tempera ture of such degree as, for example, (700 to 900 C.) liberate the alkali metal and distill. Ofl' an alkali vapor within the device to produce a layer of alkali metal upon the filament. The clean-up agent may then be subjected to arelatively high temperature as, for example, 1000 to 1200? C. to clean up any deleterious gas within the device.

The steps above outlined may be varied as for instance, if desirable, after the oxygen has been liberated within the device an amount of oxy en may be retained and an amount of alkali vapor may be produced so that caesium oxide is formed to remove hy drogen, after which the operation of activating the clean-up agent may be performed.

The various steps may be accomplished progressively by a heat gradient effected thru any suitable medium, for example the coil 34.

A 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 discs 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 disc for heating, particularly if caesium is used, the plate or disc 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.

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. The method of manufacturing an electron-emission device which consists in providing the device with an integral electrode, depositing upon said electrode suitable quantities of an oxygen yielding compound, an alkali met-a1 and misch metal and activating 'the compounds successively by inductively heating the electrode.

2. The method of manufacturing an electron-emission device which consists 1n providing the device with an integral electrode, depositing within the device a quantity of barium per-oxide, a quantity of caesium and a quantity of misch metal, heating the electrode to different temperatures to successively activate the several substances.

3. The method of manufacturing an elec- C tron-emission device which comprises inimetal and misch metal, applying the envelope to a vacuum pump, heating the oathode of the device to remove impurities, oxidizing the compound by heating at a relatively low. temperature, heating the alkali metal to a higher temperature to vaporize the same, sealing the bulb from the pump and heating the misch metal to a relatively high temperatureto eflect a final gas clean- 5. The method of manufacturing a multiple electrode electron-emission device including a bulb, which comprises initially depositing on one of the electrodes, a quantity of oxygen-yielding compound, alkali metal and misch metal, heating the electrode to a temperature suflicient to activate the said compound, elevating the temperature to activate the alkali metal, sealing off the bulb and again elevating the temperature of the electrode to activate the misch metal.

6. The method of manufacturing an electron device including a bulb having a cathode and a plurality of electrodes, which comprises depositing on one of said electrodes, a quantity of oxygen-yielding compound, an alkali metal and misch metal, heating the electrodes to a gradually elevated temperature to first produce oxygen, second to distill the alkali metal then evacuating the the temperature of said electrodes to activate the misch metal to effect a final gas clean-up.

7. The method of manufacturing an elec-.

tron device including a bulb having a cathode and a plurality of electrodes, which comprises depositing on one of said electrodes, a quantity of barium peroxide, caesium, and misch metal, heating the electrodes to first produce oxygen, elevating the temperature of the electrodes to distill the caesium, evacuating the bulb, sealing off the same and further elevating the temperature of the electrodes to activate the misch metal.

8. The method of manufacturing an electron device including a bulb having a cathode and a plurality of electrodes, which com prises depositing on one of said electrodes, a quantity of barium peroxide, caesium, and misch metal, applying the bulb to a pump, baking out the bulb, flashing the filament, heating the electrode containingthe oxidbulb, sealing the same and further elevating izing and activating material to first produce oxygen, heating the filament to the required temperature, further heating the electrode to distill the caesium, sealing off the 5 bulb and finally elevating the temperature of the electrode to drive off the misch metal to give the final gas clean-u In testimony whereof, have hereunto subscribed my name this 30th day of Novemm her, 1927.

JOHN W. MARDEN.

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