US2418390A - Anode structure - Google Patents

Description

April 1, 1947. z. J. ATLEE ANODE STRUCTURE Filed March 3, 1945 Patented Apr. 1, 1947 ANODE STRUCTURE Zed J. Atlee, Elmhurst, Ill., assignorto General Electric X-Ray Corporation, Chicago, 111., a corporation of New York Application March 3, 1945, Serial No. 580,819

6 Claims.

This invention relates to electronics in general, and particularly to electron flow devices such as electronic rectifiers, X-ray tubes, radio transmitting tubes, and other devices where electron flow is desired.

An important object of the invention is the provision of a new and improved electron flow device embodying an improved anode construction aiTording advantageous voltage distribution in the device.

Another object is to provide an anode for an electron flow device afiording a uniform voltage gradient between the anode and its cooperating cathode.

Another object is to provide novel gettering means in an anode, said gettering means forming a part of the anode; a further object being to form the anode with metallic portions capable of performing a gettering function at the operating temperature of the anode; a still further object being to utilize tantalum, columbium and zirconium for the purpose.

Another object is to provide an anode in the form of a shell having terminal edges and to provide a bead at said edges to control the anodecathode voltage gradient.

Another object is to form the anode as a cylindrical shell and to curl the opposite end edges of the shell to provide beaded edges; a further object being to apply a gettering material to form said beaded edges.

Another object is to form the shell of molybdenum, for its conducting qualities and because of low emissivity. The foregoing and numerous other objects, ad-

vantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken with the accompanying drawings, discloses a selected embodiment for the purpse-of demonstrating the invention.

Referring to the drawings:

Fig. 1 is a sectional view taken longitudinally through an electronic rectifier and embodying the invention;

Fig. 2 is a sectional view on the line 22 of Fig. 1; and

Figs. 3 and 4 are perspective views of parts of the device shown in Fig. 1.

To illustrate the invention, the drawings show an electronic device in the form of a rectifier H, although the several features of the invention are not limited to rectifiers but may be utilized to advantage generally in electronic devices embodying means having an electron emitting source and an anode for receiving the emitted electrons.

The electron flow device, as shown in the drawing, may comprise a sealed envelope l2 of suit able material, such as glass or metal, glass being specifically shown in the drawing. The envelope l2 contains an anode l3 and a cooperating cathode 14. The envelope I2 may bearranged in any convenient or preferred form, but as shown in the drawing comprises a tubular glass shell having re-entrant necks 5 at opposite ends of the shell. are respectively supported on the said necks at the opposite ends of the envelope. The necks l5 define openings, which are closed by seal members it and H of generally cup-shaped configuration. These seal members are preferably made of sheet metal, and each has an annular rim which forms a glass-to-metal seal it with the inwardly facing end of the neck LE on which the seal member is mounted, to thus seal the end of the envelope.

The seal member H, at one end of the envelope, carries the anode is, which preferably comprises a cylindrical shell l9.

The member it, at the other end of the envelope, carries the cathode 14, which, as shown, preferably comprises an electron emission element in the form of a hollow shell.

The cathode it is preferably supported in position within and surrounded by the cylindrical anode i3. The cathode i4 is heated to a proper electron emitting temperature by a filament or heater 2!] which is preferably made of tungsten.

The cathode structure it includes a disc-like head 2;, preferably of metal, which head is mounted on a stud 22 extending in an opening formed in the seal member it, the stud being sealed in said opening and having portions extending outwardly of the envelope. The head 2| carries a tubular skirt 23 secured at one end of the head and extending at the other end in position enclosing the glass-to-metal seal l 8. The skirt thus encloses a space between the seal member 56 and the head 25, which space is in open communication with the interior of the envelope l2 through the annular space defined between the end of the skirt and the glass-to-metal seal l8. Within this space, if desired, means 24 may be provided for performing a gettering operation initially, during the manufacture of the device, and periodically during the life of the device, in order to insure the maintenance of a high degree of vacuum within the envelope, as taught in my United States Patent No. 2,260,927.

The anode l3 and the cathode l4 the head 2!.

One end of the filament is mounted on, electrically connected to, and supported by a conductor stem 25, which may extend through an insulated mounting 26 in the head 2|. The end of the stem may be connected through the seal member it, which may be formed with an opening fitted with a sleeve 2?, sealed in the opening and receiving the stem 25. The stem may be supported in and electrically insulated from the sleeve 27 and the seal member l6 by means of a globule of glass, which supports the stem and seals the sleeve around the stem. Outwardly of the sleeve and seal member l6, the

, connected with a conductor 33, which extends through the seal member I 6, at a sleeve'i-ld therein, the conductor 33 being sealed in the sleeve by means of a glass sealing globule. The filament 20 thus may be electrically connected with the conductors 28 and 33, which extend outwardly of the envelope, such connection'being accomplished by way of the stems 25 and 38, which are electrically insulated from the head 2!.

The tungsten filament 20, which is the heater for the cathode, is enclosed or encased in the cylindrical emitter element M, which preferably comprises columbium. The emitter thus has a columbium surface 38 for emitting electrons, when heated. The emitter is preferably supported on and by the conductor member 38, but may, if desired, be independently supported on The columbium emitter is indirectly heated by the tungsten filament 26, whereby the stream of electrons passes from the cathode M to the anode l3. While the drawings disclose the use of a tubular or cylindrical columbium emitter 36, it is obvious that the columbium emitter may be of any suitable size and shape for the purpose intended.

The invention, however, is not necessarily limited to devices embodying a cathode having a columbium emitter element. The use of indirectly heated columbium for electron emission, however, produces results greatly superior to the other known electron emitting materials, and the operating temperature of a device embodying columbium as an emitter is considerably below that of devices embodying emitting materials, and still produces greater efficiency a d effective ness. Temperatures of 1800 to 1900 Kelvin obtain emission which is more than adequate for various applications, and the temperature of the tungsten heater filament may be held well below the normal operating temperature of tungsten.

An electron flow device functions by the flow of electrons emitted from the cathode and traveling to and impinging upon the anode. When the flow device is constituted as a rectifier, the stream of electrons passing between the cathode and anode form a conduction path along which electrical current may flow in one direction only between the anode and cathode. This unidirectional flow phenomena is utilized for the purpose of rectifying alternating or fluctuating electrical energy in order to provide unidirectional electrical power.

The anode 13 comprises the cylindrical shell 4 l9 preferably comprising a material of high conductivity and low electronic emissivity. To this end, the shell preferably comprises molybdenum and is supported in position surrounding the anode by means of a support bracket 31. This bracket is made of any suitable material, such as molybdenum and comprises a plurality of spaced arms 38 in position to embrace the shell 19. The arms 38 are interconnected on a ring her IT. The member I1 is preferably formed with an opening for receiving a stem 46, which has a portion extending outwardly of the end of the envelope l2 and a portion 4| extending inwardly of the envelope through the opening in the seal, said stem beingsealed in said opening. The ring 39 is secured upon the inner end 4| of the stem in any suitable or preferred fashion, as by means of the holding member 42.

The shell 19 is preferably provided with a pair of spaced apart outwardly pressed circumferential ribs 43, which engage the arms 38 of the support bracket. The shell I9 is secured to said arms in any suitable fashion and preferably by means of rivets 44 extending through the arms and through the shell at the ribs 43.

A jacket collar 45 is applied at each end of the shell I9, said collars comprising cylindrical-rings of tantalum, columbium, zirconium or other metal having the ability to absorb gas when heated and thus to perform a gettering function. These rings are welded 0r riveted, or otherwise attached to the ends of the shell, and preferably have portions extending beyond and snugly curled about the opposed end edges of the shell 19 to provide ribs 46 affording well rounded end edges at the opposite ends of the anode shell.

The foregoing combination of metal gettering members and molybdenum to form an anode structure substantially improves the operating characteristics of electron flow devices embodying the same. Tantalum, columbium and zirconium provide a gettering action when heated above 800 Kelvin. This gettering action comprises the 45 ability to absorb gaseous impurities withinthe envelope, including occluded gases that may be contained or developed in the anode and in the material'of the envelope itself and gradually released within the envelope during the operation 50 of the device. The major portion of such impurities are, of course, removed during the fabrication of the device, as by baking or other heat treatment, and by operation of the gettering means 24, if provided. However, regardless of -such treatment, vestiges of foreign matter may remain and the liberation thereof, during the service life of the device, may impair its operation. By providing gettering members '45 in position to be heated to a gettering temperature 0 during the operation of the device, a gettering operation may be performed continuously during the service life of the device, to the end thatall unwanted gasses liberated within the envelope may be absorbed and thus rendered innocuous as,

and when, liberated.

The elements 45 also can be readily formed in shapes impossible with molybdenum. Tantalum and other gettering materials, however, have poor thermal conductivity as compared with molybdenum and hence do not lend themselves for use in anodes comprising the gettering metal alone.

The employment of the end pieces 65, however,

facilitates the production of the beads 46 atthe end edges of the molybdenum anode for the purpose of controlling and making uniform the volt- 39, which may be mounted on the end seal memage gradient at said edges, and also provides the desirable gettering function continuously during the life of the device.

The present anode structure thus takes advantage of the desirable characteristics of molybdenum and of the gettering members mentioned to produce highly efficient anodes for electron flow devices. The end bands serve not only as a gas gettering material, but also to provide Well rounded anode ends for optimum voltage field conditions, particularly in high voltage devices. The molybdenum anode shell provides high conductivity at an economic cost and has the further advantage that it emits substantially no electrons when heated to operating temperature.

The present invention provides an extremely eflicient electron flow device wherein the use of tantalum, columbium and zirconium in combination with molybdenum provides an extremely effective anode structure. The heating of the anode is uniform and the cost of the device is relatively low, While the operating efiiciency of the flow device is increased by the gettering metals with molybdenum in the manner described.

It is thought that the invention and its numerous attendant advantages Will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the forms herein disclosed being selected embodiments for the purpose of demonstrating the invention.

Having thus described the invention, what I claim as new and desire to secure by United States Letters Patent is:

1. An anode comprising an open ended hollow shell of metal having high conductivity, and a sheet metal band of malleable metallic gettering material fitted within said shell at the open end thereof, said band having edge portions rolled to form a bead embracing and enclosing the end edges of said shell, and body portions extending Within said shell for an appreciable distance from said end edges.

2. An anode comprising an open ended hollow shell of metal having high conductivity, and a sheet metal band of malleable metallic gettering material fitted within said shell at the open end thereof, said band having edge portions rolled to form a bead embracing and enclosing the end edges of said shell, and body portions extending within said shell for an appreciable distance from said end edges, said sheet metal band contain ing a metal from the class comprising tantalum, columbium and zirconium.

3. An anode comprising an open ended hollow shell of metal having high conductivity, and a sheet metal band of malleable metallic gettering material fitted within said shell at the open end thereof, said band having edge portions rolled to form a bead embracing and enclosing the end edges of said shell, and body portions extending within said shell for an appreciable distance from said end edges, said sheet metal band containing a metal from the class comprising tantalum, columbium and Zirconium, and said hollow shell containing molybdenum.

4. An anode comprising a. hollow she'll forming an open ended sleeve of metal having high conductivity, and a sheet metal band of malleable metallic gettering material fitted within each of the open ends of said sleeve, said bands each having edge portions rolled to form a bead embracing and enclosing end edges of said shell, and body portions extending within said shell for an appreciable distance from the end edges thereof, whereby the beads on said bands form well rounded anode end edges at the opposite ends of said sleeve.

5. An anode comprising an open ended hollow shell of metal having high conductivity, and a sheet metal band of malleable metallic gettering material fitted within said shell at the open end thereof, said band having edge portions rolled to form a bead embracing and enclosing the end edges of said shell, and body portions extending within said shell for an appreciable distance from said end edges, said hollow shell having cylindrical configuration, and an electron emitting cathode disposed within and concentrically with respect to said cylindrical shell.

6. An anode comprising an open ended hollow shell of metal having high conductivity, and a sheet metal band of malleable metallic gettering material fitted Within said shell at the open end thereof, said band having edge portions rolled to form a bead embracing and enclosing the end edges of said shell, and body portions extending within said shell for an appreciable distance from said end edges, said shell being formed with an outwardly pressed peripheral rib therein and disposed inwardly of said end edge, and a mounting bracket comprising circumferentially spaced fingers embracing said shell and secured thereto in spaced relation on the outwardly pressed rib.

ZED J. ATLEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date German Sept. 19, 1933 Number Number

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