US3614514A

US3614514A - Dispenser cathode structure

Info

Publication number: US3614514A
Application number: US51891A
Authority: US
Inventors: Helmut Katz; Erwin Hubner
Original assignee: Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 1969-07-04
Filing date: 1970-07-02
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: DE1934067A1; GB1269028A; DE1934067B2; FR2054137A5

Abstract

A dispenser MK-type cathode structure adapted for storage and/or handling with subsequent activation and a method of producing the same whereby a supply source substance for an emission-promoting substance (i.e., barium oxide) is positioned in an open end storage chamber of a pluglike insert member (composed of tantalum), and the supply source substance is surrounded with an inert atmosphere at ambient pressure and sealed by a gas impermeable foil member (composed of tantalum). A plurality of such insert members are mechanically mated with a ring-shaped cathode body member (composed of molybdenum) so that the foil member separates the supply source substance from the cathode body member. A suitably porous tungsten disk is mounted on the cathode member body in communication with the foil member so that by evacuating the area around the cathode structure the foil ruptures and the emission-promoting substance (released by heat from the supply source substance) is free to come into contact with the adjacent underside portions of the porous disk. Each of the insert members is provided with shaped contact surfaces to positively seal the foil members between the insert member and the body member.

Description

United States Patent [45] Patented [72] Inventors HelmutKatz;

Erwin Hubner, both of Munich, Germany [21] Appl. No. 51,891 [22] Filed July 2, 1970 Oct. 19, 1971 Siemens Aktiengesellschait Berlin and Munich, Germany [73] Assignee [32] Priority July 4, 1969 [33] Germany [31] Pl934067.1

[54] DISPENSER CATHODE STRUCTURE 5 Claims, 2 Drawing Figs.

Primary Examiner- David Schonberg Assistant ExaminerPaul A. Sacher Att0rneyHill, Sherman, Meroni, Gross & Simpson ABSTRACT: A dispenser MK-type cathode structure adapted for storage and/or handling with subsequent activation and a method of producing the same whereby a supply source substance for an emission-promoting substance (i.e., barium oxide) is positioned in an open end storage chamber of a pluglike insert member (composed of tantalum), and the supply source substance is surrounded with an inert atmosphere at ambient pressure and sealed by a gas impermeable foil member (composed of tantalum). A plurality of such insert members are mechanically mated with a ring-shaped cathode body member (composed of molybdenum) so that the foil member separates the supply source substance from the cathode body member. A suitably porous tungsten disk is mounted on the cathode member body in communication with the foil member so that by evacuating the area around the cathode structure the foil ruptures and the emission-promoting substance (released by heat from the supply source substance) is free to come into contact with the adjacent underside portions of the porous disk. Each of the insert members is provided with shaped contact surfaces to positively seal the foil members between the insert member and the body member.

BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to dispenser cathodes and more particularly to MK-type cathode structures having a relatively large emission surface and a method of producing the same.

2. Prior Art Metalcapillary cathodes (i.e., MK cathodes) are known. Generally, such cathodes comprise a confining metal cup member having a supply source substance for an emissionpromoting material therein (i.e., one yielding barium at a high temperature) and a porous disk welded to the rim of the cup member, the upper surface of which defines an emission surface. A heating means heats both the cup member and the disk causing the supply source substance to release the emissionpromoting material to evaporate and migrate by capillary action through the porous disk. The emission-promoting material forms a film on the free surface of the disk and acts to reduce the work function of the material forming the disk.

In certain more recent developments relating to this type of dispenser cathode, suggestions have been made to utilize barium-strontium-carbonate as a supplysource substance for an emission-promoting substance. Improved results have been noted with the use of this material, especially when utilized in relatively small dimension cathodes; However, when cathodes having relatively emission surfaces, such as ring surfaces, are desired, use of barium-strontium-carbonate leads to opera tional difficulties and even to nonoperability. Such difficulties appear to be the result of the relatively larger amounts of gas generated during the transformation of the carbonate into an oxide. These difficulties are particularly prevalent in bombardment-heating cathodes, since emission of the respective auxiliary cathodes are needed to heat up the main cathode. With such bombardment-heating cathodes, the emission is greatly impaired due to the gas collection from the main cathode and/or even destroyed due to the careless operation. A possible solution to this problem is to replace the gas generating supply source substance with a nongassing supply source substance. However, practical considerations such as operating temperatures, availability of materials, and effectiveness of such nongassing supply source substance materially reduce the practical use of such a solution.

The instant invention provides a cathode structure and a method of producing the same which avoids the aforesaid difficulties and is particularly adapted for cathodes having relatively large dimensions, such as a ring-shaped cathode with bombardment heating, and does not require the utilization of nongassing supply source substance for an emission-promoting substances, such as aluminate.

SUMMARY OF THE INVENTION The invention provides a novel dispenser cathode structure of the MK-type and a method of producing the same wherein a supply source substance for an emission-promoting substance is stored in an open end storage chamber of a pluglike insert member and sealed in an inert atmosphere and from the surrounding environment by gas impermeable foil member. A plurality of such insert members are spaced about a ringshaped cathode body and each member mechanically mates or locks with a suitably shaped portion of the cathode body member so that each of the foil members is tightly secured between an inner surface area of the body member and an outer surface area of the insert member. The insert members have shaped surfaces for contact with portions of the body member, such as lower side ring-shaped sealing edges or upper frontal ring-shaped sealing edges, so that mechanical mating between the shaped surfaces and the body member portions positively seal the foil member against the insert member and prevent the emission-promoting substance from coming in contact with the emission surface until activation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an overall diagrammatic sectional view of an embodiment of a ring-shaped cathode structure constructed in accordance with the principles of the present invention and includes a cross-sectional Viewthroughan embodiment of one; insert member; and

FIG. 2 is a somewhat enlarged cross-sectional view of another embodiment of an insert member constructed in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED'EMBODIMENTS The invention generally provides an indirectly heated structures generally include ring-shaped emission surfaces,

supported on a ring-shaped cathode body member wherein supply source substance for an emission-promoting substance, such as an alkaline earth metal oxide, is spaced within and distributed around the perimeter of the ring-shaped cathode body member. Theemission-promoting substance communicates (after release, as by heat, from the supply source substance) with the emission surface by traveling from a storage chamber and through a porous tungsten disk coveringrthe storage member. The outer free surface of the porous tungsten disk defines the emission surface. Preferably, a porously sintered tungsten disk is utilized and the emission-promoting substance is selected from the group consisting of barium oxide and alkaline earth metal oxides.

A cathode body member is provided with a large emission surface composed of porously sintered tungsten or other emission base material and with a plurality of apertures in communication with the emission surface and generally uniformly spaced around the cathode body member. One or more pluglike insert members are provided for insertion into the apertures. Each insert member is formed to define an open end storage chamber for containing an amount of a supply source substance for an emission-promoting substance. The outer sidewalls of the insertmembers mechanically mate or lock with the peripheral sidewalls of the apertures, as by a suitably provided screw thread surface on the respective adjacent walls. Preferably, the insert members are composed of a high melting metal such as tantalum, and the-cathode body member is also composed of a high melting metal such as molybdenum.

In one embodiment of the insert member, the outer lower side surfaces adjacent the end which in assembly faces away from the emission surface, are provided with a. slightly enlarged lower portion that defines a ring-shaped sealing edge. This sealing edge. contacts the lower end surfaces of the cathode body member so as to tightly secure the foil member at end surfaces opposite those adjacent the sealing edges (such end surfaces sometimes are referred to herein as securing surfaces), against the cathode body member. The securing surfaces are provided with sealing portions that are forced into an overlapping relation with the foil member. Such sealing portions may be intricately formed with the insert member or may be separate units in the form of gasket means, i.e., wires or wadding or the like.

In another embodiment of the insert member, the end surfaces that contact the foil member in assembly (i.e., the securing surfaces) are shaped so as to present relatively small areas of contact that pinch or squeeze the foil member against appropriately shaped surface portions of the cathode body member.

The supply source substance for an emission-promoting substance can be formed into tablets or the like for ease of usage and insertion into the open ended storage chamber of the insert members. Preferably, the supply source substance is placed in the storage chamber and a dry inert gas is pumped or injected at about ambient pressure into the storage chamber so as to completely fill and blanket the supply source substance. The storage chamber is then tightly sealed by a foil member composed of, for example, tantalum. The foil member can be pressed on between sealing portions at securing surfaces of the insert member whereby the sealing portions overlap or are pinioned onto the foil member so that the protective insert atmosphere cannot escape. As will be appreciated, the foil member is gas impermeable. In this form, the insert member can be stored or handled for as long as desired without any danger of a chemical reaction occurring with the supply source substance. Of course, such insert members may also be assembled into a cathode body member and stored in this manner until activation.

Activation is simply achieved by positioning an assembled cathode body member, i.e., one having the filled (with a supply source substance for an emission-promoting substance) insert member locked in place, into a suitable envelope or tube device or other device utilizing a cathode, and evacuating the tube device whereby the pressure of the inert gas within the insert member will burst and/or destroy the relatively thin foil member and the emission-promoting substance can then substantially uniformly migrate upon heating, to the emission surface carrying disk member.

Referring now to the drawings, it will be noted that FIG. 1 is an overall diagrammatic sectional view of a cathode structure which has a relatively large diameter ring shape, and those elements thereof which do not materially aid to a better understanding of the principles of the invention are left out or are merely not given a reference numeral.

As shown, a ring-shaped cathode body member 1 supports and carries a ring-shaped disk member 2 at least partially composed of an emission base material. Preferably, such emission base material is tungsten which has been formed into a suitably sized porously sintered disk member. The cathode body member 1 is provided with a plurality, and as least three, axial apertures or bores 3, generally uniformly spaced about the periphery of the body member 1. The bores 3 extend generally through a major portion of the body member 1 and are open at the surface away from the disk member 2 so as to receive an insert member 4 at such open end. The inner peripheral walls of the bores 3 are provided with a screw thread along the length thereof for mechanically mating with similar surfaces of the insert members. A passage means 11 is provided along the upper surface of the bores 3 so as to communicate with the exposed underside of disk member 2.

The pluglike insert member 4 is formed somewhat in the shape of a hollow setscrew or the like and has an open ended storage chamber 5 for receiving a supply source substance for an emission-promoting substance 6, which is preformed into tablets as shown. The storage chamber 5 is open toward the disk member 2 and is spaced therefrom. As indicated before, the preferred supply source substance is selected from the group consisting essentially of barium oxide and alkaline earth metal oxides, and of these barium oxide is the most preferred. The emission-promoting substance tablets 6 are positioned within the storage chamber 5 and an absolutely dry inert atmosphere is injected within the remaining hollow space of the chamber 5. The inert atmosphere is maintained at about ambient pressure although a slightly positive pressure can be utilized if desired. The storage chamber 5, containing the supply source substance 6 and the dry inert atmosphere is then tightly sealed from the surrounding environment by a foil member 8.

Preferably, the foil member 8 is relatively thin and is comosed of a relatively high melting metal such as tantalum. If necessary, gasket means in the form of tungsten wire, wadding or the like can be used in conjunction with the foil member 8 to insure the formation of a gas impermeable seal so that the inert protective gas within the chamber 5 cannot escape or diffuse away.

Such assembled insert member can then be inserted, as by screwing, into the bores 3 of the cathode body member 1 and stored or handled as desired without any danger of a chemical reaction occurring with the supply source substance for an emission-promoting substance. When an assembled cathode is inserted into an envelope or tube device (not shown) which is then evacuated, the gas pressure within the chamber 5 will burst the foil member 8 and a path of communication between the supply source substance and the adjacently spaced disk member 2 is opened. A ring-channel or passage means 11 provides communication around the entire periphery of migrating body member 1 so that the emission-promoting substance can uniformly contact the entire underside of the disk member 2.

In the embodiment of the insert member shown at FIG. 1, the foil member 8 is sealed or rolled under a blanket of inert gas at the upper front ring surface of the hollow insert member 2 with securing surfaces or sealing portions 9 by means of a special device or tool. The insert member itself, as opposed to the storage chamber, is sealed or locked in place by means of it rolled back or undercut ring surface 10 adjacent the lower end surface of member 4. As shown, the undercut surface 10 separates the insert member 2 in a lower headlike portion, which is somewhat larger in diameter than the main body portion of member 2. The edges of this headlike portion are forced against adjacent portions of the cathode body member.

FIG. 2 illustrates another embodiment of the insert member constructed in accordance with the principles of the invention. This embodiment is particularly useful with disk-shaped cathodes of normal shape and having a mushroomlike porous disk member 2. In this embodiment, the cathode .body member la is generally formed into a similarly shaped member as body member 1 of FIG. 1, in that it is provided with an open ended storage chamber 5a for containing a supply source substance an emission-promoting substance 6a therein. Body member la differs from body member 1 in that it is provided with a ring-shaped groove 21 along a surface thereof which upon assembly contacts the foil member.

The pluglike insert member 4a is also generally similar to insert member 4 except that insert member 40 has generally straight peripheral walls and is without a special head portion or undercut sealing edge 10. Instead, the insert member 4a is provided with a securing end surface or edge 20 which is aligned to generally mate and register with the groove 21 on the body member la. Thus, when a foil member 8a is positioned on the securing edges 20 and forced against the opposed surfaces of the body member la, as by the turning or the screwing of the insert member 4a, a portion of the foil member 8 is pinched or squeezed into the groove 21 and a gastight seal is formed so that the inert atmosphere within the chamber 5a cannot escape. If necessary, tungsten wire or wadding may be provided along the boundaries of groove 21 and along the securing surfaces 20 to further insure the formation of a gastight seal so as to prevent escape of the protective inert gas within chamber 5a.

When utilizing the insert member embodiment shown at FIG. 2, the assembly of the insert member 4a filled with a supply source substance for an emission-promoting substance with the body member la must be performed in an inert atmosphere at, for example, normal ambient (i.e., atmospheric) pressures. As will be appreciated, in carrying out the mechanical locking or securing of the insert member with the cathode body member in an inert atmosphere, the foil member may be sealed in a number of different ways.

As previously indicated the

axial bores

3, 3a are evenly dis tributed on the circumference of the ring-shaped cathode body member 1, la and each

bore

3, 3a is provided with an insert member 4, 4a. The axial bores 3, 3a are interconnected with each other by a formed ring channel or passage means 11, 11a so that the emission-promoting substance can travel uniformly to all of the underside of disk member 2, 2a when the foil member 8, 8a has been destroyed.

Thus, the invention provides a novel indirectly heated dispenser cathode structure comprising a shaped porous disk member having an emission surface with a cathode body member supporting and carrying the disk member along a surface thereof opposite the emission surface. The cathode body member has a plurality of axial bores distributed about the a periphery of the body member and extending toward the emission surface. A plurality of insert members are provided which are adapted to mechanically lock with the walls of the bores and each insert member has an open ended storage chamber opening toward the disk member with a supply source substance for an emission-promoting substance sealed within the chamber and surrounded by an inert atmosphere.

A gas impermeable foil member is positioned between the storage chamber and a passage means within the body member that provides communication between the storage chamber and the disk member to block travel of the emissionpromoting substance to the disk member. The mechanical locking between the insert members and the cathode body member is augmented by specially shaped wall portions, which also serve to maintain the foil member in a gastight sealing relation with the storage chamber.

Various other modifications, other than those discussed, can, of course, be effected without departing from the novel concepts of the invention.

We claim as our invention:

1. An indirectly heated dispenser cathode structure comprising: a shaped porous disk member having an emission surface, a cathode body member supporting and carrying said disk member along a surface thereof opposite said emission surface, said body member having a plurality of axial bores distributed about the periphery of said body member and extending toward said emission surface, a plurality of insert members mechanically locking with peripheral walls of said axial bores, each of said plurality of insert members having an open ended storage chamber, said chamber opening toward said disk member, a passage means positioned within said body member providing communication between said storage chamber with said disk member, a supply source substance for an emission-promoting substance positioned in said storage chamber and surrounded by an inert atmosphere, and a gas impermeable foil member positioned between said storage chamber and said passage means blocking travel of said emission-promoting substance to said disk member.

2. An indirectly heated dispenser cathode structure as defined in claim 1 wherein said insert members each have shaped peripheral wall portions for positively locking one of said insert members into one of said axial bores of the cathode body member and to positively seal said gas impermeable foil member against said storage chamber.

3. An indirectly heated dispenser cathode structure as definedin claim 2 wherein said shaped peripheral wall portions are undercut protruding edges along the lower side portions of each of the insert members, which edges contact adjacent portions of said cathode body member.

4. An indirectly heated dispenser cathode structure as defined in claim 2 wherein said shaped peripheral wall portions are tapered securing edges at the upper end portions of the insert member and the cathode body member is provided with a groove in registry with said securing edges whereby the foil member is pinched between the tapered securing edges and the groove.

5. An indirectly heated dispenser MK cathode structure comprising a ring-shaped porously sintered tungsten disk member defining an emission surface, a molybdenum cathode body member positioned to support and carry said disk member along a portion of an underside surface thereof so that the upper surface of the disk is free and the lower surface is partially free, said body member having at least three axial bores substantially uniformly spaced about the periphery of the body member extending toward said disk member, said bores having a passage means along their upper boundaries providing communication with each other and with the entire free lower surface of said disk member, at least three insert members composed of tantalum and each adapted to mate and mechanically lock with walls of one of the axial bores, each of the insert members having an open ended storage chamber directed toward said disk member, a supply source substance for an emission-promoting substance selected from the group consisting essentially of barium oxide and alkaline earth metal oxides positioned in the storage chamber and surrounded by an inert dry atmos here at substantially ambient pressures, a gas impermeable re atlvely thin foll member composed of tantalum positioned on each of the storage chambers so as to seal the same and prevent the supply source substance from participating in a chemical reaction, and a tungsten gasket means positioned in working relation with each of the foil members to positively seal each of the storage chambers and prevent the inert atmosphere from escaping.

Claims

3. An indirectly heated dispenser cathode structure as defined in claim 2 wherein said shaped peripheral wall portions are undercut protruding edges along the lower side portions of each of the insert members, which edges contact adjacent portions of said cathode body member.

5. An indirectly heated dispenser MK cathode structure comprising a ring-shaped porously sintered tungsten disk member defining an emission surface, a molybdenum cathode body member positioned to support and carry said disk member along a portion of an underside surface thereof so that the upper surface of the disk is free and the lower surface is partially free, said body member having at least three axial bores substantially uniformly spaced about the periphery of the body member extending toward said disk member, said bores having a passage means along their upper boundaries providing communication with each other and with the entire free lower surface of said disk member, at least three insert members composed of tantalum and each adapted to mate and mechanically lock with walls of one of the axial bores, each of the insert members having an open ended storage chamber directed toward said disk member, a supply source substance for an emission-promoting substance selected from the group consisting essentially of barium oxide and alkaline earth metal oxides positioned in the storage chamber and surrounded by an inert dry atmosphere at substantially ambient pressures, a gas impermeable relatively thin foil member composed of tantalum positioned on each of the storage chambers so as to seal the same and prevent the supply source substance from participating in a chemical reaction, and a tungsten gasket means positioned in working relation with each of the foil members to positively seal each of the storage chambers and prevent the inert atmosphere from escaping.