US1707002A - Electrode material - Google Patents

Description

March 20, 1929. w, RO 1,707,002

ELECTRODE MATERIAL Filed July 26, 1926 ATTORNEY Patented Mar. 26, 1929.

UNITED STATES H 1,707,002 PATENT OFFICE.

WILLIAM BENJAMIN GERO, OF BLOOMFIELD, NEW JERSEY,' ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

ELECTRODE MATERIAL.

Application filed July 26,

This invention relates to an electrode for an electrical discharge device and more partieularly to an electrode for such devices composed at least in part of a rare earth metal or mixture or alloy of such metals.

In a copending application Serial No. 59,986 of Harvey O. Rentschler, filed Oct. 2, 1925, entitled Electric discharge device, and

assigned to Westinghouse Lamp Company, there is described and claimed a gaseous discharge device of the point-to-plate discharge 1 voltage in radio receiving circuits when the plate curent is obtained from rectified alternating current, through the use of so-called battery eliminators Other applications of the device are in connection with protective devices, such as overload circuit breakers,-

point-to-plate rectifiers, neon lamps, etc.

The cerium group metal anode apparently serves a double purpose. Residual impurities in the gas which come from the elements of the tube, such as insufficiently treated electrodes orwhich exist in the gas as impurities, will be cleaned up by the misch metal during the seasoning process. Also, during the operation of the tube, the impurities which may be liberated from the parts ot the tube will be cleaned up and thus the operating characteristics of the device maintained uniform during the life thereof. At the sam'e time some of the misch metal will be volatilized and condensed on the plate, thus giving a lower start ing and operating potential than would be obtained if the metal of the plate were composed solely of one of the common metals used for purposes of this kind, such as nickel, iron, etc.

In accordance with the invention set forth in the application of Dr. Rentschler, mentioned above, the anode is composed of a wire of nickle or other suitable metal sealed through the press of the device and having a suitably secured to the outer end thereof.

Heretofore the misch metal employed in the formation of such anode has been obtained by extruding the misch metal at a red heat into wire or rodais set forth'in patent of strip of misch metal clamped or otherwise.

1926. Serial. No. 124,927.

John W. Marden and Malcolm N. Rich, #1,653,367, granted December 20, 1927, entitled Miseh metal wire, and assigned to the Westinghouse Lamp Company. I

One of the objects of the present invention is to provide the cerium group metal employed as the anode, in a more active form.

Another object is to provide, in a gaseous discharge device of the point-to-plate type, an anode which serves more maintain the gas in a ure eondition and which is conducive to quiet operation of the device.

Other objects and advantages Will hereinafter appear. 1 I a In accordance with the present invention I employ as the anode material, cerium or other rare earth metal or an alloy of such metals, as misch metal in a .porous form as distinguished from the dense condition of the extruded metal. In the porous condition I have discovered that the metal is much more active as indicated by the greater tendency of the metals to spark when scraped with a knife or other instrument. Due to this increased activity it serves more efficiently to clean-up the residual impurities during the initial exhaust and throughout the life of thedevice and by maintaining the gaseous filling in a pure condition more quiet operation of the device is obtained. This ellnnnation of noise during operation is of particular importance when the anode is employed in a device for the regulation of plate voltage for radio receiving apparatus since any noise developed in the voltage regulator tube may be reproduced in the speaker.

While it is difficult, at the present time, to state definitely what the beneficial action of the porous metal over the extruded metal is due to, it is thought that the greater exposed surface of the porous material accounts for the greater efliciency which is obtained in tubes employing the same.

,Misch metal or other cerium group metal can be produced in a sufficiently porous condition to render the same effective for the purpose explained, by casting the metal into molds. Due to the extreme activity of the rare earth metals it is necessary to protect the same from oxidation during melting. This is conveniently accomplished in the case of misch metal by melting-the metal under a fused salt such as sodium chloride. The molten metal isthen run into molds preferably in the form of thin brass tubing set in an iron body. The cast metal'shrmks on cooling and is readily removed from molds.

However, this process for the casting of the misch metal forms no part of the present invention.

The cast metal is straighter than the eX truded metal under the usual condition of manufacture and lends itself better to being fabricated into anodes. It is also more readily produced in uniform sizes since with the extruded metal the size varies as the extrusion progresses due to clogging of the dies, etc. Aside from its porosity, its chief physical diiierence between the extruded and cast metal appears to be in the crystal structure. The extruded metal has been drawn out to a fibrous nature, while the cast metal has not. Whether this alters the action of the misch metal either in its gaspurifying action or in lowering the starting and operating potential of the device is not known.

In order that the invention will be better appreciated reference is made to the accompanying drawing in which Fig. 1 illustrates a protective tube adapted to serve as a rectifier or to control the voltage supplied to the plate of a radio receiving tube.

Fig. 2 illustrates a system employing the device of Fig. 1.

The device shown in Fig. 1 comprises an envelope 1 containing an anode 2, a cathode 3 and a filling of monatomic gas or mixture of such gases.

The anode 2 consists of a wire 4 of nickel. or other suitable metal sealed through the press 5 of the device and has secured thereto a tip of misch metal or other metal of the cerium group of rare earth metals in a porous form. The metal tip is preferably of cast metal although it may be otherwise formed providing it is of a less dense nature than extruded metal. The tip is drilled from one end as at -7 and the end-of the wire 4 is inserted therein. If desired, the anode may be posed entirely of misch metal.

The cathode 3 consists ofa cylindrical plate concentric with the anode and supported from the press 5 by support wires 8. The cathode may be composed of nickel, iron, molybdenum or other suitable metal.

The-anode and 'cathode'are provided with. current conducting leads 9 and 10 joined to the wire; 4 and cathode support 8, respectively, and to the terminals 11 and 12 of the base 13. i

To assist in starting the discharge, a projection in the form of a wire 14. extends from the cathode 3 into proximity to the anode 2.

The envelope is preferably filled with argon at a pressure of from about 3 to 7 mm. of mercury, although other monatomic gases or mixtures of gases may be employed depending on the starting and operating potentials desired. After filling with gas and sealing off it is necessary to subject the device to a treating schedule to develop the starting and operating characteristics thereof. Preferably such treatment consists in operating the device on 220 volt alternating current with a protective resistance in series therewith for-a short time and then seasoning the device at 110 Volts alternating current for a period of hours. The seasoningtimc required differs with the manufacturing and operating conditions and is continued until the electrical characteristics of the tube become stable. This stable condition is much more readily obtained when employing a cast or porous misch metal anode than when employing the extruded metal.

The seasoning treatment ionizes the gas and heats the anode to a sufficiently high temperature to render the misch metal active so that it is effective to thoroughly purify the gaseous filling. It also renders the cathode ,more sensitive or active and thus effective to initiate a discharge therethrough and maintain it at a low potential. The misch metal or some constituent thereof appears to be sputtered, (vaporized or otherwise deposited on the cathode from the anode.

Devices of the nature described have a starting potential of from to 125 volts and a minimum operating potential of from 80 to 100 volts, depending somewhat on gas content, its pressure, the current drawn by the device, etc.

The misch metal serves throughout the life of the device to maintain the gas in a'pure 1 condition and due to the large exposed area of the cast and porous material it is extremely efficacious for preserving the purity of the While only a single embodiment of the invention has been described it is obvious that the cast and porous electrode of rare earth metal may be employed either as a clean-up and gas purifying agent or as an electrode in evacuated or gas-filled devices of various kinds and may be produced in various manners, without departing from the invention.

In Fig. 2 I have shown a system employing the device of Fig. 1 in which direct current obtained from a suitablenectifier 15 from an alternating current source 16 is smoothed out and rendered uniform in value by the capacities 17 and inductance 18. The rectified current is employed to supply the plate current for a number of radio receivmg tubes or other suitable apparatus 19. In order to maintain the voltage supplied the apparatus 19 constant, the device of Fig. 1 is placed across the line as at 20. Other adaptations of the device will be apparent to those skilled in the art.

What is claimedis: Y

1. A gaseous conduction device of the point-to-plate discharge type having a cathode of extended surface and an anode of 0 small surface area, said anode being composed at least in part of a metal' of the cerium group of rare earth metals in a porous condition.

2. A gaseous conduction device of the,

point-to-plate discharge type having a cathode of extended surface and an anode of small surface area, said anode being comcathode of extended surface and an anode of small surface area, said anode being composed at least in part of cast misch metal.

4. A gaseous conduction device of the point-to-plate discharge type having a cathode of extended surface and an anode of small surface area, said anode being composed at least in part of a metal of the cerium group of rare earth metals in cast condition.

In testimony whereof, I have hereunto subscribed my name this 24th day of July, 1926.

WILLIAM BENJAMIN GERO.

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