US1758710A - Electron-discharge device - Google Patents

Description

May 13, 1930. L. K. MARSHALL 1,758,710

ELECTRON DISCHARGE DEVICE Filed Jan. 51, 1929 Patented -May 1-3, 1930 UNITED STATES PATENT; OFFICE LAURENCE K. MARSHALL, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO OLD COLONY TRUST COMPANY, A CORPORATION OF MASSACHU- SETTS ELECTRON-DISCHARGE DEVICE v Application filed. January 31, 1929. Serial No. 336,463.

This invention relates to electron discharge devices and particularly to cathodes therefor. In such devices, the function of the cathode is to emit electrons and the greater 5 the emission, the more desirable such a cathode becomes. As a rule, both the cold and thermionic cathodes have their electron emitting surfaces so treated that a low work function is imparted thereto. Such coatings in general comprise a mixture of the oxides of alkaline earth metals or alkali metals or certain of the rare earth metals.

In order to obtain increased electron emission from the cathode, at least one of two things must be done. If the cathode is to remain the same, it is necessary to increase the temperature of the thermionic cathode to obtain increased emission. This reacts deleteriously on the life of the cathode. Another way which is applicable to both the cold and thermionic cathodes is to .reduce the work functioii at that surface.

- It is also possible to combine these two methods into a third one in which both the Work function is lower and in which the afiinity of the coating for the cathode surface is such that a higher than'ordinary operating temperature Wlll in general be harmless to the coating.

My invention involves this latter procedure. In general'my invention is based upon the fact that certain. of the noble metals such as palladium, platinum, ruthenium or rho-' dium, have the property of absorbing hydrogen. By providing a cathode surface of any nature whatsoever with a coating of one or more of the above noble metals, I am enabled to obtain an active cathode surface which is more eflicient and more tenacious than ordinary coatings. active layer of such noble metal is exposed to hydrogen with a resultant absorption of some of the gas. Thereafter the vapor of an alkali metal is allowed to react on this surface.

As'is well known, alkaline metals form a very efiicient electron emit-tingcathode sur- I face. They labor, however, under the dis-' advantage of being very easily driven off by the heat. By my invention, the alkaline vapm penetrating into the pores of th noble A cathode surface having an metal is fixed therein, probably in the form of a hydride.

A cathode surface thus formed has been found to be very useful and eflicient, both as a cold or thermionic cathode.

Referring to the drawings, Figure 1 is a sectional view of a photo-electric cell having my improved cathode.

, Figure 2 is a section of a vacuum tube provided with a similar cathode.

Referring to Figure 1, 1 is a glass tube Within which is disposed a copper member 2. Upon this copper member is deposited or plated, platinum, palladium, ruthenium or rhodium. Of these metals, I prefer palladium since it absorbs hydrogen with the greatest ease. A ring anode 3 within the tube is supported by lead wire 4 in a press 5. The tube has a base 10 having prongs 12 for connection to an ordinary vacuum tube type socket. Lead wire 4 is connected to one of the prongs. Sealed in press 5 is a wire 14 supporting a metal capsule 15. Within this capsule are chemicals which upon suitable heating, evolve caesium, rubidium or any other of the alkali metals. If desired, a mixture of two or more of the alkaline metals or with any other metal may be used. The chemical for the release of such metals, as a rule, consists of the chloride of the alkali metal mixed metallic calcium. Wire 19 supporting cathode 2 serves as a lead to one of the prongs in base 10.

The tube is thoroughly exhausted and freed of occluded gases in accordance with customary practice. Thereafter a quantity of pure hydrogen is admitted so that there is a pres- ,sure of about .1 mm. A glow discharge betemperature is raised so that the chemicals therein .become heated. Chemical interaction results in the evolution of caesium or oth er alkali metal or mixture of metals which may be used. This metal settles upon the surface of the palladium to form an active layer thereon. The. tube may now be seal-e71 and be ready for use if desired.

However, I prefer to admit a small quantity of helium so that the gas is at a pressure of .1 mm. A discharge is then initiated between the electrodes in the helium. The bombardment of the helium ions formed by the discharge removes any excess alkali metal from the surface of the palladium plated copper member 2 and leaves a very thin active layer of alkali metal. The cell may be exhausted after the discharge has run for a short time and the tube sealedofi'.

Such a tube is sensitive to light variations and makes a very desirable photo-electric cell in every way. I

Referring to Figure 2, an anode 20 is shown supported on wires 21 and 22, the latter being extended through-press 5 to a suitable base for outside connection. A grid 23 disposed within the anode, is supported by two wires 24 and 25 in a similar manner. Within these two electrodes is supported a cathode 28 by wires 29 and 30. This cathode consists of a central core upon which is supported the layer of noble metal 31. This central core may be either of -metal, if the cathode is to be directly energized, or may consist of the well knownheater type of cathode. In either case, the electron emitting surface comprises a layer of one or more of the noble metals on a suit-able metal base if desired and having absorbed a certain quantity of h drogen in combination with one or more 0 the alkali metals. The preparation of the cathode for this tube is exactly the same as for the photoelectric cell above. Either one or both of the tubes may be exhausted to a high vacuum or, if desired, may have a gas at any desired pressure.

I claim: 7

1. In an electron discharge device, a cathode comprising a layer ofmetal having hydrogen absorbed therein and a layer of alkali metal thereon.

2. In an electron discharge device, a cathode comprising a layer of palladium having hydrogen in solution therein and a layer of alkali metal formed thereon.

3. In an electron discharge device, a cathode comprising a layer of palladium having hydrogen in solution therein and a layer of caesium thereon.

4. An electron discharge device comprising an anode ,andiQthode, said. cathode com-'' prising a ineltal meiiiber. havin its surface coveredwitl ij a layer of palla ium. .,ha'ving hydrogen absorbed therein and a liiyer of caesium formed thereon.

5. The method of making an active cathode surface for an electron discharge device, which consists in haying a palladium surface as one electrode of a discharge in a hydrogen atmosphere whereby hydrogen is absorbed by said palladium and thereupon condensing a layer of caesium thereon.

6. The method of making a discharge device, which consists in initiating a discharge in a hydrogen atmosphere between an anode and a cathode, said cathode having a palladium surface whereby hydrogen is absorbed by said palladium, exhausting said device to a high vacuum and thereupon condensing a film of alkali metal thereon.

7. The method of making an electron discharge device which consists in initiating a discharge in a hydrogen atmosphere between an anode and a cathode, said cathode having a palladium surface whereby hydrogen is absorbed by said palladium, exhausting said device to a high vacuum and condensing a film of caesium thereon.

8. The method of making an electron dis charge device which consists in initiating a discharge in a hydrogen atmosphere between an anode and cathode, said cathode having a palladium surface whereby hydrogen is absorbed byv said palladium, exhausting said device to a high vacuum, condensing a layer of alkali metal thereon, then introducing a rare gas in said device, initiating an electrical discharge between said electrodes in said rare gas and then exhausting to a high vacuum.

9. The method of making an electron discharge device which consists in initiating a discharge in a hydrogen atmosphere between an anode and a cathode, said cathode having a palladium surface whereby hydrogen is absorbed by said palladium, exhausting said device to a high vacuum, condensing a layer of caesium thereon, introducing a rare gas,

initiating an electrical discharge between said electrodes in said gas and then exhausting to a high vacuum.

10. The method of making an electron discharge device which consists in initiating a discharge in a hydrogen atmosphere between an anode and a cathode, said cathode hav-- ing a palladium surface whereby hydrogen is absorbed by said palladium, exhausting said device to a high vacuum, condensing a layer of caesium thereon, introducing helium in said device, initiating an electrical discharge between said electrodes in said helium atmosphere, and then exhausting to a high vacuum.

In testimony whereof, I have signed my name to thisspecification.

- LAURENCE K. MARSHALL.

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