US2071849A - Electrical discharge device - Google Patents

Description

' Feb. 23, 1937. E. F. LOWRY 2,071,849

ELECTRICAL DI SCHARGE DEVICE Filed July 19, 1934 v 2 Sheets-Shgetl I Op/fqa/ E/ran efe r" WITNESSES: INVENTOR ATTORNEY Patented Feb. 23, 1937 UNIED ATENT OFFICE.

ELECTRICAL DISCHARGE DEVICE Pennsylvania Application July 19, 1934, Serial No. 735,986

4 Claims.

This application is a continuation in part of my copending application Serial No. 407,690, filed November 16, 1929, now Patent No. 1,997,693, for Electrical discharge devices.

My invention relates to electrical discharge devices and particularly to electrical discharge devices which employ electrodes operating at temperatures at which they emit electrons freely.

One object of my invention is to provide an electron emissive cathode, the heating energy required by which is small relative to the magnitude of the electron emission per unit area of surface.

Another object of my invention is to provide an electron emissive cathode in which-the ratio of the electron emission to the heat dissipation per unit area of the cathode is relatively large.

Another object of my invention is to provide an electrical discharge device with an electron emissive cathode in which the rate of heat dissipation per unit area of surface at a given opcrating temperature is minimized.

A further object of my invention is to provide an electron emissive cathode for electrical and discharge devices which shall have a larger surface area than cathodes of the prior art, but which will require supports therefor only at its ends.

Other objects ofrny invention will become apparent upon reading the following specification taken in connection with the drawings, in which:

Figure 1 is a View partly in elevation and partly in section of an electrical discharge device having an electron emissive cathode embodying my invention;

Fig. 2 is a sectional View taken on the line IIII of Fig. 1;

Fig. 3 is a View partly in elevation and partly in section of an arrangement for testing the temperature effects of various sized pleats in the cathode constructed according to my invention;

Fig. 4 is a graph of watts per square inch input in relationship to temperature of three filaments with different spacing between the pleats thereof; and

Fig. 5 is a similar graph of a narrower filament with six different spacings between the pleats thereof.

It is desirable for certain purposes to provide the electrical discharge devices with electron emissive cathodes having relatively large surfaces, and consequently capable of emitting large electron currents. Such cathodes are desirable both for high vacuum electrical discharge tubes and for electrical discharge devices having gaseous atmospheres at appreciable pressures. Devices in which mercury vapor is present as an atmosphere about the cathode are examples of the later devices. Other examples are the devices containing noble gases, such as neon, argon, .5 etc. When it is attempted to insure a large electron current by extending the surface area ofthe cathode tolarge dimensions, the energy dis-- sipated as heat from the cathode surface becomes a serious source of lost and decreased electrical efficiency. One of the principal objects of my invention has been accordingly to devise methods of constructing hot cathodes which shall have relatively extensive surface areas, but which shall require only moderate amounts of power to maintain them at their proper operating temperatures.

The foregoing object I achieve by constructing the cathode of a relatively thin sheet material, which is so bent back and forth or pleated that a large fraction of its surface is so positioned that it faces other portions of its surface. In this way, the heat radiated from the first-mentioned portion of the surface is absorbed by some other portion of the surface and the amount dissipated to the surrounding surfaces and lost entirely is relatively small. Thus the heating current has to supply only the relatively small losses last-mentioned, and the amount of cathode heating power required to maintain the cathode at its operating temperature is minimized.

I have also discovered that the spacing between adjacent pleats very materially affects the heating efficiency and that this spacing should be less than the depth of the pleat. The same consideration requires that the width of the filament be greater than the spacing between the pleats. The pleat will thus take the form of a deep pocket from which the electron current is started with a maximum of heating efiiciency. Due to the neutralization of the space dischargev by the positive ions in the gaseous atmosphere surrounding the cathode, there is no difiiculty in obtaining electrons from these deep pleated pockets.

I also desire to have this cathode structure such that it will maintain its shape during the operation of the device and yet have a minimum amount of support therefor so that the heat from the filament will not be dissipated by contact with a large and relatively cool supporting area. To accomplish this object, I construct my cathode of a thin ribbon of an alloy of cobalt, nickel and ferro-titanium described in my copending application Serial No. 1%,911, filedOctober 28, 1926. 55

As described in this copending application, the alloy constitutes to of cobalt and nickel with the nickel ranging from 5% to 95%, and the cobalt ranging from 5% to 95% of the total percentages of these two materials. The ferro-titanium acts as a deoxidizer in the alloy and comprises from 5% to 20% of the total. This material is commonly known by the trade-mark Konal. Due to the very high hot tensile strength of this alloy, a cathode in its ribbon form can hold its shape under the high operating temperature, and in certain forms this cathode. will only require supports at each end thereof. I prefer to use the Konal alloy as a core material. and to coat the core with a barium and strontium oxide coating to provide the electron source.

In Figs. 1 and 2 is disclosed a preferred form of my cathode in which a metallic ribbon H1 is folded into deep pleats, as disclosed more particularly in Fig. 2. The spacing ll between the pleats is very small and preferably much smaller than the width l2 of the ribbon or the depth 13 of the pleats. As previously mentioned, this cathode is preferably formed of a core of cobalt, nickel and ferro-titanium with a coating of barium and strontium oxides thereover. Due to the Strength of this material at operating temperature, only two supports l4 and I5 are required for this ribbon and these supports also act as lead-in wires for the ends of the cathode structure. Within the container I6 is a gaseous atmosphere which may be of mercury vapor orone of the noble gases. At one end of the container is the anode IT to form the familiar two-electrode rectifier tube. If desired, one or more grids may be inserted between the anode and the cathode to form the familiar grid-controlled glow-discharge tube.

In order to test out the effect of the relative spacing l I of the pleats, I tested out the efficiency of my cathode structure with various distances between .the pleats in the manner illustrated in Fig. 3. A series of pleated or crimped filaments were constructed having the same depth of fold but with varied spacings between the consecutive surfaces thereof. A very small hole 20 of about 55 mils is drilled from one end 2| of the filament through the center portion to the middle 22 of the cathode structure, so that the middle portion of the filament was exposed from one side, of a cathode structure. The filament was then mounted in a glass vacuum tube 23, fitted with a ground glass joint 24 on a standard 25. The tube had a connection 26 to a vacuum pump.

' When a. high vacuum had been attained within the tube, the filament was raised to a red heat by current passing through the connections 2'! and 28. An optical pyrometer 30 was trained upon the central hot portion 22 of the filament, and pyrometer readings were taken of the central portion of the filament because it was least affected by the colder supports and outside radiation. The power was varied, using the current as a measure, while the voltage was taken directly from leads 3| and 32 welded on the. filament near the supports. Readings were taken for each change of current. The visibility or actually the absorption of the glass was measured by first obtaining a temperature reading of the filament 33 in a small bulb 34 placed directly in back of the tube in a line that just skims across the top of the heavier filament within the tube, there fore recording the apparent brightness of the bulb viewed through two walls of glass. The bulb was shifted to one side in such a Way that.

its distance from the pyrometer was unchanged and no intervening medium between them. Half the difference between readings when plotted against the reading temperature gives the correction to be added for absorption.

Readings were first obtained on filaments made of nickel, cobalt, and ferro-titanium ribbon 12 inches long by .75 inch wide and .02 inch thick. The pleats were respectively A; and inch wide, and the results are plotted in Fig. 4, disclosing the watts per square inch input for the; temperature in degrees centigrade. The depth of the fold or pleat was one inch as disclosed on. the side of Fig. 4.

The test was also made with a filament 12 inches long, .5086 inch wide, .0125 inch thick and folded into deep pleats one inch in depth as disclosed in the right-hand portion of Fig. 5. Fig. 5- shows the graphs for spacing A 1%, A., and inch, respectively, between the sides of the pleats.

An examination of the curves in- Figs. 4 and 5 will disclose the increased efficiency produced by my cathode with very deep pleats, whose depth is greater than the width of the ribbon and the spacing between the sides of the pleats. I prefer to make this spacing as small as possible in order to have as great an area of electron emitting surface incorporated in a Very small area because this close spacing of the sides of the pleat pockets therein approaches a black body effect in its heat radiation characteristic.

In accordance with the patent statutes, I have disclosed a particular embodiment of my invention, but it will be recognized that this is intended to be only illustrative and that the broad principle thereof will be capable of alternative embodiments which will be evident to those skilled in the art. I' desire,,accordingly, that the claims shall be given the broadest construction of which their terms are susceptible in view of the prior art.

I claim as my invention:

1. A cathode adapted, to emit electrons freely when heated, comprising a, deeply pleated sheet member of essentially a nickel-cobalt alloy containing ferro-titanium, and supports for said member only at its ends.

2.. A cathode adapted to emit electrons freely when heated comprising a thin metallic ribbon having continuous rectangular folds therein, the maximum distances between opposing surfaces of the same fold being less than the depth of the fold and less than the width of the ribbon, and supports for said. ribbon only at its ends.

3. A cathode adapted to emit electrons freely when heated comprising a thin metallic ribbon composed essentially of a. nickel-cobalt alloy containing ferro-titanium, said ribbon having continuous rectangular folds therein, the maximum distances between opposing surfaces of the same fold being less than the depth of the fold, and supports for said ribbon only at its ends.

4. An electrically heated conductor in, the form of a sheet member of essentially av nickel-cobalt alloy containing titanium, and means, for conducting current to the ends thereof and. for supporting said conductor, the, length of the conductor between the center of gravity of the portion thereof intervening between said points of support and the nearest point of support thereto being large compared with the straight line distance between said center of gravity and said nearest point of support.

ERWIN F; LOWRY.

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