US1716159A - Electron-discharge device - Google Patents

Description

June 4, 1929. E. a. WIDELL ELECTRON DISCHARGE DEVICE Filed May 16, 1925 INVENTOR EMIL. a. WIDELL BY fl %TTORNEY Patented June 4, 1929.

UNITED STATES EMIL GIDEON WIDELL, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE PATENT OFFECE'.

LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

ELECTRON-DISCHARGE DEVICE.

Application filed May 16, 1925. Serial No. 30,662.

This invention relates to an electron discharge device and more particularly to a device of this nature containing an alkali 'metal.

The alkali metals are employed in discharge devices, such as photo-electric cells, rectifiers, radio tubes, etc., for many purposes as, for instance, to reduce the potential drop between the electrodes, to serve as a getter, to increase the electron emission from the filament, to increase the current carrying capacity of the device or to increase the sensitivity of the device as a detector of radio signals, etc. The alkali metal, however,

tends to cause conductive paths along the Wall of the envelope between the leading-in conductors, particularly where the current conducting leads are spaced relatively close together resulting in leakage between the electrodes and deleteriously affecting the operation of the device.

One form of discharge device described in British Patent 208,729, to which the present invention is especially adapted, is

for radio detectors and amplifiers employ-f ing an alkali metal such as caesium, rubidium, or the like. The alkali metals under proper conditions, greatly increase the electron emission of the cathode of a thermionic device at a temperature so low that in the absence of the vapor, no substantial electron emission would occur. These results are explained on the theory that an absorbed film of the alkali metal is continuously formed on the cathode which resists evaporation at a temperature far above the vaporization point of the alkali metal. The cathode of such a device consists of a metal having a high electron afiinity such as tungsten, molybdenum or nickel, whereas, the caesium has a low electron affinity. The caesium atoms are therefore, held to the surface of the electrode by electrostatic force.

The formation of the absorbed film ap pears to be greatly facilitated by the presence of an electro-negative gas such as nitrogen or carbon monoxide which on coming into contact with the filament, forms a film of atomic thickness which is capable of holding on to the atom of the alkali metal more strongly thandoes thesurface of the heated electrode.

Another form of alkali metal tube adapted for the detection of high frequency signals depends for its increased detector action on the.;presen'ce of the alkali metal vapor.

In devices of this nature, considerable difliculty has been experienced in eliminat ing the leakage between the lead wires to-a sufficient extent to render the tubes practical and heretofore it has been proposed, in order to reduce the leakage as much as possible, to employ a very tedious and involved method of exhaust and treatment of the various parts of the tube. Such treatment, however, has not'proven to be commercially successful. Although the exact cause of leakage between the leads is not fully understood, it is due to the formation of a conducting film of some sort caused by the presence of the alkali metal in the tube. Possibly the metal or a compound thereof, wets the glass press thus forming a continuous film, or again,

it may be due to a chemical reaction of the vapor with the glass.

One of the objects of this invention is to provide a thermionic device employing alkali'metals in which there will be no leakage between the leads.

Another object is to provide a thermionic device containing an alkali metal in which the leads are spaced relatively close v together and in which the formation of conductive paths between the leads is precluded. Another object is to provide a method of treating the glass of a discharge device containing an alkali metal so as to prevent leakage of current between the leading-in wires.

Another object is to provide a simplified method of producing an alkali metal discharge device.

Another object is to provide a coating material which when applied to glass will prevent the formation of conductive paths by condensation or deposition of alkali metals thereon.

Other objects and advantages will hereinafter appear.

I have found that when the glasson which conductive films of the alkali metals or metallic compounds are apt to form are coated with certain substances, that the formation.

of such conductive filmis entirely prevented.

may be varied to render it proof against leakage due to the action of the alkali metal thereon.

The novelfeatures of the present invention will be set forth particularly in the appended claims but the invention itself will be best understood b reference to the following description ta en in connection with the accompanying drawing which shows an electron discharge device for use for the detection or amplification of high frequency signals.

The device illustrated comprises a glass envelope 1 containing the usual filamentary cathode 2, plate electrode or anode 3 and control electrode or grid 4. -These electrodes ,are supported from the stem 5 of the tube by means of support wires 6 sealed into the press 7. In view of the relatively large number of wires which are sealed in the press, it is necessary that they be spaced relatively close together, thus enhancing the probability of leakage between the wires.

The terminals of thefilament are joined to leading-in wires 8 and 9 connected respectively to the terminal plugs 10 and 11 carried by the base 12. v The control electrode 4 and the anode 3 are similarly connected to leading-in wires 13 and 14 respectively, also joined to terminals on the base.

The alkali metal may be introduced into the device in any suitable manner such as distillation from a side tube or as shown in the drawing, in a capsule 15 welded, soldered or otherwise suitably secured to the anode or other metal part of the device from which it may. be liberated by heat. a In the case of sodium and some of the less active alkali metals, the metal may be introduced in the capsule in metallic form as set forth in copending application of John ,Wesley Marden,.'Serial 'No. 745,071, filed October 22, 1924, entitled Introduction of vaporizable material into exhausted containers and assigned to the Westinghouse Lamp Company. However, the more active metals, such as caesium, may be introduced into the capsule as a compound such as caesium chloride together with a reducing agent as calcium and the compound decomposed by heat to liberate the metal. The method of introducing an alkali metal formsno part of the present invention, however, and need not be described in greater detail herein."

I The caesium, upon being vaporized into the envelope, condenses on various parts of the device causing, in the absence of special precautions, the formation of a conductive layer or coating on the press 7, short-circuiting the leading-in wires where they pass through the lass and causing sufficient leakage to ren er the device inoperative.

I have found that this leakage may be overcome byicoating the press with various organic materlals 17 such as shellac or rosm' I adhering thereto.

and that when so coated, a simplified method -of.exhaust and treatment of the electrodes may be employed. The coating material should, ofcourse, have good insulating properties and must be stable and substantially non-volatile at the operating temperature of the device or the temperature to which is not limited to such materials, as this property of preventing leakage is exhibited by various other natural orartificial resins or esters, such as nitrocellulose.

In the manufacture of alkali metal tubes in accordance with my invention, a thin coating of the protective material is applied to the press between and around the leading-in wires as by paintin spraying or any other suitable manner. terial used for this purpose may be mixed with a suitable solvent orvehicle such as 111-,

cohol, to the proper consistency for applying to the glass. After coating the press with the protective material, the press should be baked at a temperature slightly above that to which it will be subjected during manufacture or operation of the device in order lhe shellac or other ma to remove the more volatile constituents therefrom. Care should be taken, however, to prevent carbonization of the coating during baking thereof or during sealing of the mount into the tube. The mount may be sealed in the envelope in the usual manner a and the envelope baked out during exhaust, preferably at a temperature of about 275 C. to remove any occluded gases or water vapor plate and the capsule carried thereby may be heated by high frequency induction to drive out occluded gases therefrom and liberate the caesium. If desired a small piece of magnesium or other metallic clean-up agent 16 may be attached to-the plateand vaporized by the high frequency heating to assist the caesium in cleaning up the gases and vapors in the tube. The tube may then be tipped off and based.

The glass between the leading-in conductors is .thus completely protected against the v Thereafter and while the I device is still on the exhaust pumps, the

action of the alkali metal and since the alkali metal does not attack the shellac or rosin or form a conductive layer thereon, short-circuiting of the lead wires and leakage therebetween is effectively prevented.

While the invention has been described with particular reference to the production of caesium tubes it is to be understood that it is not so limited, butmay be applied to the manufacture of electrical-devices of any nature employing alkali metals and obvious ly, many changes and modifications may be made in the manner of applying material and various equivalent materials other than those specified, may be used without departing from this invention.

What is claimed is:

1. The method of manufacturing electron dischargedevices employing an alkali metal which consists in sealing electrodes into said device, coating the glass adjacent the leading-in wires of said electrodes with a nonconducting resinous material resistant to the formation of conducting films by the action of the alkali metal thereon, evacuating said device and introducing an alkali metal there- 1n.

2. An electron discharge device comprising an envelope containing an alkali metal, a plurality of leading-in wires sealed into said envelope, the portion of said envelope adjacent said wires having a coating of a nonconducting organic material capable of preventing leakage between said leading-in wires.

3. An electron discharge device comprising an envelope containing an alkali metal, a mount sealed therein, a plurality of current conductors sealedthrough said mount and a coating of a resinous material on said 30 mount between said current conductors for preventing the formation of a conducting film by the action of the alkali metal and consequent leakage between the current conductors.

4. An electron discharge device comprising an envelope containing caesium, electrodes therein, a press, leading-in wires connected to said electrodes and sealed through the press, said press having a coating of a resinous material to render it proof against the leakage of current between said leading-in wires by the action of the caesium thereon.

5. An electron discharge device comprising an envelope containing an alkali metal, a plurality of leading-in wires sealed into said envelope, the portion of said envelope adjacent said wires having a coating of a. non-conducting material capable of preventing leakage between said leading-in wires.

In testimony whereof, I have hereunto subscribed my name this 15th day of May, 1925.

EMIL GIDEON WIDE LL.

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