US3821589A

US3821589A - Storage cathode particularly a mk cathode

Info

Publication number: US3821589A
Application number: US00339325A
Authority: US
Inventors: H Katz; E Huebner
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1972-03-29
Filing date: 1973-03-08
Publication date: 1974-06-28
Anticipated expiration: 1991-06-28
Also published as: IT981639B; FR2177716B1; CA1012600A; DE2215477B2; GB1404473A; DE2215477A1; DE2215477C3; FR2177716A1

Abstract

A dispenser cathode and method of making the same, in which the cathode structure comprises a cylindrical container, open at one side, adapted to form a supply chamber for a charge of emissionpromoting material, with the open side of the container being closed by a porous plate tightly sealed thereto, having a threaded bore therein adapted to mate with a threaded central column extending from one side of a solid disc of refractory metal, which has a similar central column at the opposite side thereof, which carries an insulated heater. The cylindrical container is provided with a wad of tungsten wire disposed adjacent the porous plate, and the heater is adapted to be secured to the second column of said disc by a cement sintered thereon in a high temperature operation. The wad of tungsten is initially disposed in the cylindrical container and the porous plate secured thereto, for example by welding, to form a subassembly, and in like manner the heater is secured to the second column by means of a cement, utilizing a sintering operation, with the two sub-assemblies, following insertion of the charge of emission-promoting material through said bore, into said container the latter is threaded on said threaded column, with an edge of the cylindrical container bearing on said solid disc to form a seal therebetween.

Description

United States Patent Katz et a1.

[ STORAGE CATHODE PARTICULARLY A MK CATHODE [73] Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Germany 221 Filed: Mar. 8, 1973 21 App1.No.:339,325

[30] Foreign Application Priority Data Mar. 29, 1972 Germany 2215477 [52] US. Cl 313/346 R, 29/25.]4, 29/2517, 313/337 [51] Int. Cl HOlj 1/14, HOlj 19/06 [58] Field of Search 313/346, 346 DC, 337; 29/2514, 25.17

[56] References Cited UNITED STATES PATENTS 2,722.626 11/1955 Coppola et a1 313/346 DC 2.975322 3/1961 Cockrill i 313/346 R 3.441.780 4/1969 Hinkeldey 313/346 R 3,676.73] 6/1972 Hofmann et a1. 313/346 DC 3681.641 8/1972 Katz .i 313/346 DC 1 June 28, 1974 Primary E.\'aminer-.lames W. Lawrence Assislant Examiner-Saxfield Chatmon, Jr.

Attorney, Agent, or Firm-Hill, Gross, Simpson. Van Santen, Steadman. Chiara & Simpson [5 1 ABSTRACT A dispenser cathode and method of making the same, in which the cathode structure comprises a cylindrical container, open at one side, adapted to form a supply chamber for a charge of emission-promoting material, with the open side of the container being vclosed by a porous plate tightly sealed thereto, having a threaded bore therein adapted to mate with a threaded central column extending from one side of a solid disc of refractory-metal, which has a similar central column at the opposite side thereof, which carries an insulated heater. The cylindrical container is provided with a wad of tungsten wire disposed adjacent the porous plate, and the heater is adapted to be secured to the second column of said disc by a cement sintered thereon in a high temperature operation. The wad of tungsten is initially disposed in the cylindrical container and the porous plate secured thereto, for example by welding, to form a sub-assembly, and in like manner the heater is secured to the second column by means of a cement, utilizing a sintering operation, with the two sub-assemblies, following insertion of the 5 charge of emission-promoting material through said bore, into said container the latter is threaded on said threaded column, with an edge of the cylindrical container bearing on said solid disc to form a seal therebetween.

16 Claims, 1 Drawing Figure STORAGE CATHODE PARTICULARLY'A MK CATHODE BACKGROUND OF THE INVENTION The invention is directed to dispenser cathodes, and particularly metal-capillary cathodes, in which a charge of emission-promoting material is contained in a storage chamber and enclosed in part, by a porous tungsten plate which constitutes the active emitting surface, the active surface, if desired being provided with an additional metal coating of one or more metals such as rhenium. osmium or the like.

Difficulties arise in the design of such type of dispenser cathodes where the structure must have small dimensions, for example such as employed in cathode ray tubes and particularly in camera and image display tubes. 1

In the great majority of cases, barium oxide is utilized as the primary supply material, in lieu of barium which is conventionally usedas an emission-promoting material, because the advantage offered by its ready action in a convenient temperature change. However, barium oxide has the disadvantage of being hygroscopic and thus subject to reaction with other atmospheric components, which may lead to considerable difficulties during manufacture. For example, the formation of barium hydroxide in the presence of humidity may present a number of problems.

British Patent No. 1,269,028, discloses a dispenser cathode especially designed for electron discharge tubes, which however, is of relatively large dimensions, utilizing a porous carrier plate mounted on a cathode body in which cup-shaped screw-plugs provided with closures contain the supply material and act as storage containers in conjunction with a sealing foil. The construction is such that the foil releases the supply material only when the cathode is initially operated in its discharge tube, as a result of the foil either bursting during evacuation or is held by a paraffin-wax edge seal that is broken. This construction has achieved outstandingly good results in cathodes involving relatively large dimensions, but would be far too expensive for cathodes of significantly smaller dimensions, as are now required, for example, in camera tubes and picture display tubes.

BRIEF SUMMARY OF THE INVENTION The present invention therefor among its objects the production of a dispenser cathode construction comprising, for example, two component sub-assemblies which can be stored indefinitely, and the assembly of which can be effected in a very simple manner without any thermal treatment, immediately prior to complete assembly.

More particularly, the cathode structure of the present invention comprises a cylindrical container which forms the supply chamber, with the container being tightly sealed to a porous plate to form a sub-assembly, while a second sub-assembly comprises a solid disc of refractory metal having a central threaded projection or column extending from one side thereof and a central projection or column extending from the other side thereof, the latter projection having mounted thereon an insulated heater that is secured thereto by means of a cement that has been sintered thereon in a high temperature operation. The cylindrical container is provided with a bore therein at the side opposite to that secured to the porous plate, which bore is of a size to form the receiving opening for the insertion of the charge of emission-promoting material into the container, which bore is provided with internal thread adapted to mate with the thread on the first mentioned central column.

This type of construction provides a closure element which is relatively extremely simple to manufacture and does not require any special precision. Since the sub-assembly, including the solid plate and central column, may be manufactured in the form of an integral structure, difficulties heretofore associated with the provision of small hollow cavities and peripheral threading are avoided.

Likewise, alternatively, a very simple construction can be achieved by the utilization of a single threaded rod or stud, secured in hermetically sealed'relation to the solid disc by means of a conventional hightemperature soldering operation. Advantageously, the perimeter of the solid disc provides a readily available surface for mounting a heat-reflecting and mounting foil cylinder, which may be so secured thereto that the cylinder does not come into thermally conductive contact with the attached heater assembly or with the' cathode body and its porous plate.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like reference characters indicate like or corresponding parts:

The FIGURE illustrates a generally sectional view of a cathode structure embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTION In the embodiment of the invention illustrated, a solid disc 1 of a refractory metal, such as molybdenum, is securely mounted on a central rod or stud having a portion 2 at one side of the disc 1 and an elongated portion forming a central column 3 at the opposite side of the disc. The column 3 has mounted thereon an insulated heater 4, which in the example illustrated is secured thereto by a mass of heater cement 5, adapted to be sintered at high temperature, to unit the parts into a sub-assembly which includes the solid disc 1 and the screw portion 2, and which may be readily manufactured and indefinitely stored.

Cooperable with such sub-assembly is a second subassembly comprising a cylindrical member 6 likewise made of a refractory metal such as molybdenum, which is provided with a central threaded bore 7. Both end faces of such cylindrical members are beveled, with the end face 8 having a concave configuration providing a relatively sharp outer edge, whilethe opposite end face 9 is convex, forming relatively sharp inner edge. Disposed at the concave face 8 and engaged with the relatively sharp outer edge thereof, in sealed relation, is a porous plate 10 of tungsten which can be readily secured to the member 6 by welding. Positioned between the concave end face 8 and the inner face of the tungsten plate 10 is a wad of tungsten wire, and disposed in the threaded bore 7 is a charge of emission material 12, whereby the tungsten wire 1 1 is interposed between the charge 12 and the tungsten plate 10. It will be appreciated that supply chamber formed by the member 6 for the emission material 12, as in the case of the first subassembly described, can be manufactured and stored to a high temperature treatment, for example, in a reducing atmosphere.

Thus, for example, the tungsten plate can be chemically coated with osmium, which involves a reduction process at elevated temperature. In particular, such osmium layer can also be alloyed into the structure of the tungsten plate, e.g., at 1,300C, which greatly enhances the future reliability of the emission properties of the structure. Likewise, if desired, the plate can be suitably sealed with respect to the passage of gas until it is put into operation.

In the assembly of the final, completed structure, the respective and, if desired, additionally treated subassembly respectively consisting of the cylindrical member 6, carrier plate 10 and tungsten wad 11, and the other sub-assembly comprising the disc 1, projections or

columns

2 and 3, as well as the heater 4 and cement 5, may be assembled following insertion of a charge tablet 12 of emission-promoting material into the bore 7. The threaded portion 2 is then inserted in the bore 7 and the container 6 screwed down thereon to provide the necessary sealing action and as a result of engagement of the inner edge of the convex end space 9 with the adjacent face of the solid disc 1, a very effective seal can be achieved. A

A heat reflecting radiation-shield foil cylinder 13, which advantageously may simultaneously serve as the mounting support for the cathode system, may be welded to the outer cylindrical periphery 14 of the solid disc 1. Such radiation shield has no direct thermally conductive contact with either the heater or the porous carrier plate, whereby it can be mounted at an early stage if desired, and in operation, its temperature is substantially lower than that of a conventional assembly. In addition, the utilization of-the column 3 provides a particularly efficient conductive transmission of heat directly from the heater to the upper cathode structure, whereby excellent thermal characteristics are achieved.

Having thus described our invention, it will be obvious that although minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

We claim as our invention:

1. In a dispenser cathode of the type in which emission-promoting material passes from a supply chamber through a porous plate covering the latter to form an active emitting surface, the combination of a cylindrical container, open at one side, and forming a supply chamber for a charge of emission-promoting material, a porous plate closing said open side and tightly sealed to said container, the latter having a bore therein extending to the opposite side thereof, said bore communicating with said chamber and of a size to permit passage of said charge from said opposite end into said chamber, a solid disc of refractory metal having a cenof said chamber, and an insulated heater secured to the column at the opposite side of said disc by a cement sintered thereon.

2. A dispenser cathode according to claim 1, in which said solid disc and said threaded column are separate members united to form an integral assembly.

3. A dispenser cathode according to claim 1, comprising in further combination an outer heat-reflecting and supporting foil cylinder attached to the periphery of said solid disc.

4. A dispenser cathode according to claim 3, in which said foil cylinder is spaced from and does not come into direct thermally conductive contact either with said heater assembly or with said porous plate.

5. A dispenser cathode according to claim 1, in which said porous plate is of tungsten.

6. A dispenser cathode according to claim 1, in which said supply container is in the form of a generally cylindrical body with a central internal threaded bore, and has a concave end surface providing a relatively sharp outer edge to which said porous plate is attached, the other end surface of said container being convex, providing a centrally disposed relatively sharp edge bearing upon said solid plate.

7. A dispenser cathode according to claim 1, in which said active surface of said porous plate is provided with a metallic coating.

8. A dispenser cathode according to claim 7, in which said metallic coating is of rhenium or osmium.

9. A dispenser cathode according to claim 1, in which said supply chamber contains barium oxide.

10. A dispenser cathode according to claim 1, in which a wad of tungsten wire is disposed between said emission material and said porous plate.

11. A dispenser cathode according to claim 1, in which said solid plate is of molybdenum.

12. A dispenser cathode according to claim 6, in which a wad of tungsten wire is disposed between said emission material and said porous plate.

tral column extending from opposite sides of the disc,

the column at one side of the disc having an externally threaded end portion, said bore having internal threads of a size and disposed to mate with the threads of said column, said container being threaded on said column with the latter forming a closure-for the adjacent end 13. A dispenser cathode according to claim 12, in which said porous plate is of tungsten, and said solid disc is of molybdenum.

14. A dispenser cathodeaccording to claim 13, in which said active surface of said porous plate is provided with a coating of rhenium or osmium.

15. A dispenser cathode according to claim 14, com prising in further combination an outer heat-reflecting and supporting foil cylinder attached to the periphery of said solid disc, said cylinder being spaced from and out of direct thermally conductive contact with both said heater assembly and said porous plate.

16. A method of manufacturing a dispenser cathode in the form of a cylindrical container open at one side and forming a supply chamber for a charge of emissionpromoting material, a porous plate adapted to close such open side of said container, the latter having a threaded bore therein at the opposite side thereof communicating with said chamber, and of a size to permit the passage of such a charge therethrough into said chamber, and a wad of tungsten wire adapted to cooperate with said porous plate, with said components adapted to form a first sub-assembly, a solid disc of re-' fractory metal having a central column extending from opposite sides of the disc, the column at one side of said disc having a threaded portion of a size to mate with the thread of said bore, and insulated heater adapted to be secured to the column at the opposite side of said disc,

with said disc, column and heater adapted to form a inserting the charge of emission promoting material into said chamber through said bore, inserting the threaded column of said second sub-assembly into said bore and screwing the container thereon until the convex edge thereof bears on said solid disc to form a seal therebetween.

Claims

1. In a dispenser cathode of the type in which emissionpromoting material passes from a supply chamber through a porous plate covering the latter to form an active emitting surface, the combination of a cylindrical container, open at one side, and forming a supply chamber for a charge of emission-promoting material, a porous plate closing said open side and tightly sealed to said container, the latter having a bore therein extending to the opposite side thereof, said bore communicating witb said chamber and of a size to permit passage of said charge from said opposite end into said chamber, a solid disc of refractory metal having a central column extending from opposite sides of the disc, the column at one side of the disc having an externally threaded end portion, said bore having internal threads of a size and disposed to mate with the threads of said column, said container being threaded on said column with the latter forming a closure for the adjacent end of said chamber, and an insulated heater secured to the column at the opposite side of saiD disc by a cement sintered thereon.

13. A dispenser cathode according to claim 12, in which said porous plate is of tungsten, and said solid disc is of molybdenum.

14. A dispenser cathode according to claim 13, in which said active surface of said porous plate is provided with a coating of rhenium or osmium.

15. A dispenser cathode according to claim 14, comprising in further combination an outer heat-reflecting and supporting foil cylinder attached to the periphery of said solid disc, said cylinder being spaced from and out of direct thermally conductive contact with both said heater assembly and said porous plate.

16. A method of manufacturing a dispenser cathode in the form of a cylindrical container open at one side and forming a supply chamber for a charge of emission-promoting material, a porous plate adapted to close such open side of said container, the latter having a threaded bore therein at the opposite side thereof communicating with said chamber, and of a size to permit the passage of such a charge therethrough into said chamber, and a wad of tungsten wire adapted to cooperate with said porous plate, with said components adapted to form a first sub-assembly, a solid disc of refractory metal having a central column extending from opposite sides of the disc, the column at one side of said disc having a threaded portion of a size to mate with the thread of said bore, and insulated heater adapted to be secured to the column at the opposite side of said disc, with said disc, column and heater adapted to form a second sub-assembly, comprising, the steps of placing said tungsten wire wad into the container adjacent said open side thereof, and welding said porous plate to such open side of said container to close the same, completing said first sub-assembly, securing the heater to the completed column and disc by a cement and sintering the same to complete the second sub-assembly, inserting the charge of emission promoting material into said chamber through said bore, inserting the threaded column of said second sub-assembly into said bore and screwing the container thereon until the convex edge thereof bears on said solid disc to form a seal therebetween.