US1981620A - Electrode for electron discharge devices - Google Patents

Description

Nov. 20, 1934. E. A. GIARD I ELECTRODE FOR ELECTRON DiSCHARGE DEVICES Filed March 26, 1932 Patented Nov. 20, 1934' PATENT OFFICE ELECTRODE FOR ELECTRON DISCHARGE DEVICES Eugene A. Giard, Shorewood, Wis., assignor to I Cutler-Hammer, Inc., Milwaukee, Wis., a corporation ol. Delaware Application March 26, 1932, Serial No.. 601,404

8 Claims.

This invention relates to an improved material for electrodes and especially control electrodes or gridsof electron tubes.

In my application, Serial No. 557,221, filed on August 15, 1931, it was pointed out that control electrodes of electron tubes, especially when the cathode is coated with an emission increasing material, may produce secondary emission when they become heated from various causes during operation and that such secondary emission can be reduced by the employment of certain metals and subjecting such metals to a superficial oxidizing process. Among the metals heretofore proposed is tantalum, but tantalum is very expensive and in the prior application I have proposed an electrode equipped with an oxidized tantalum surface. I have now found that similar and even more beneficial results can be obtained by alloyv ing nickel with a very small amount of beryllium and oxidizing this alloy superficially.

An object of the invention is to provide an electrode which is inexpensive to manufacture and which yet has the desirable characteristics of electrodes which heretofore have been manufactured of high grade and expensive material.

Another object of the invention is to provide an electrode of rugged construction and of a relatively inexpensive material with a coating which prevents secondary emission.

Another object is to provide an electrode having an oxidized beryllium surface and requiring a minimum of beryllium metal.

The accompanying drawingshows one form of an electron tube with which the present invention may be employed, it being understood, however, that the invention is advantageous in connection with other types of tubes employing a control electrode.

In the drawing, 1 designates a glass or other container which in the present case may be filled with a highly attenuated gas or with mercury vapor, 2 is a heated cathode and 3 an anode, while 4. is a control electrode consisting in the present case of an imperforate metal sheet which completely encloses the cathode except for openings at its'upper end opposite the anode. In the past such control electrodes were made of pure tantalum and were subsequently superficial- 1y oxidized so as to reduce the secondary emission during operation.

According to the present invention, the grid is made of an alloy of nickel and beryllium containing about 2% of beryllium. It should be understood, however, that the amount of beryllium may be higher or less but it has been found that a 2% admixture of beryllium is sufficient to obtain the satisfactory results aimed at. After the grid has been given the desired shape the surface is oxidized by heating it in air. This produces on the surface a layer consisting of a mixture of the oxides of nickel and beryllium. After the tube is completed, it is again heated during the exhausting process by means of a high frequency current induced in the conductlng'elements. This heating either reduces or vaporizes the nickel 05 oxide or does both and leaves a substantially pure beryllium oxide film on the surface of the grid.

It is possible to produce the beryllium oxide layer on the surface of the grid by other methods such as the deposition'and subsequent oxidation of beryllium on a nickel base and I wish it to be understood that I do not'limit myself to the production of the beryllium oxide surface by the method described heretofore,

A tube constructed in the aforedescribed manner and equipped with a coated. cathode was tested when new and showed a cathode emission of approximately .05 micro-amperes. After being in continuous operation for about one month above the rated temperature of the filament and with anode current flowing the tube was tested. again and the cathode-grid current was less than it was initially. A pure nickel grid would have shown an appreciable increase of secondary emission after being operated over such an extended 8 period. I

The conclusion to be drawn is therefore that the oxidized beryllium surface of the grid combines with the compounds vaporized from the cathode and deposited on the grid to form thermionically inactive compounds in a way similar to those formed on oxidized tantalum surfaces.

While the invention has been described in connection with gaseous electron tubes it may also be employed in high vacuum and other types of tubes having a control electrode subject to secondary emission, and with other electrodes capable of yielding undesirable secondary emission under the conditions obtaining in the tfibe.

What I claim as new and desire to secure by Letters Patent is:

1. An electrode for an electron discharge tube comprising a beryllium alloy having an oxidized beryllium surface. 3

2. An electrode for an. electron discharge device comprising a, beryllium alloy having a surface which is substantially composed of beryllium oxide.

3. An ihtrode for an electron discharge tube comprising a beryllium alloy having a substantial 7. In combination with anelectron discharge device; a control electrode having a surface composed of a beryllium compound.

8. The method of surfacingan electrode comprising a beryllium alloy, with a beryllium oxide coating which consists in subjecting the electrode to an oxidizing treatment and reducing the re-,

suiting oxide mixture to remove an oxide but that of beryllium' EUGENE A. GIARD.

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