JPS61216221A - Impregnated type cathode and its manufacture - Google Patents

Abstract

PURPOSE:To prevent evaporation and electron radiation of an electron radioactive substance from portions other than the electron radiating surface so as to acquire an impregnated type cathode with a long service life and a high reliability, by covering the side of the cathode base in an impregnated type cathode formed with a heater container in which a heater is buried. CONSTITUTION:The side of a porous metallic base 21 with a high melting point is processed to seal the pores, combined with a heater container 15, pasted with a brazing material 17a to contact them, then a ring form brazing material 16a is attached to the side of the metallic base 21, and these brazing materials are melted. After that, excessive brazing materials over the side of the metallic base 21 are removed. Then a heater 4 is buried in the heater container 15, and an electron radioactive substance is impregnated to the metallic base 21. In such a way, the side of the cathode base 10 is covered with an elaborate covering layer 16, and, evaporation of the electron radioactive substance from portions other than the electron radiating surface 6 can be reduced broadly, a long service life of the cathode can be maintained, and, at the same time, generation of an inner discharge owing to an attachment of electron radio0active substance can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an impregnated cathode suitable for electron tubes such as traveling wave tubes and klystrons that particularly require high reliability.

[Technical background of the invention and its problems]

High-power traveling wave tubes installed in artificial satellites, etc.

Impregnated cathodes are used in order to achieve high current density characteristics. The first requirement for this impregnated cathode is that it has a long lifespan.In order to guarantee this lifespan, the lifespan of the cathode is mainly determined by the evaporation of the electron emitting material, so unnecessary evaporation must be avoided as much as possible. must be configured.

Second, in order to expect high reliability and long life, the quality of the manufactured cathode must be sufficiently guaranteed. It is necessary to configure the structure so that it does not adhere to the surface and cause discharge phenomena.

However, the conventional impregnated cathode, as shown in FIG. 4, is a porous metal substrate obtained by sintering tungsten powder and is coated with BaO, CaO, AQ, and 0.00%. A heater container ■ made of a high-melting point metal such as molybdenum is bonded to the side surface of a cathode substrate ■ impregnated with an electron-emitting substance made of a metal such as molybdenum with a high-melting point brazing material ■ made of a molybdenum-ruthenium alloy. The heater is embedded in a heat-resistant insulating embedding agent made of sintered alumina powder, and most of the sides of the cathode substrate (υ) are exposed.

Therefore, the electron emitting substance impregnated into the metal base evaporates from the side surface of this cathode base (υ) in addition to the electron emission surface 0 necessary for electron tube operation.Incidentally, in the example of the illustrated shape, the cathode base (1) is The surface is the number of electrons, and the incident surface 0 is 23%,
The side surfaces accounted for 77%, and a large amount of electron-emitting material evaporated from these sides, shortening the life of the cathode. Another disadvantage is that a large amount of electron-emitting material evaporated from this side surface adheres to other electrodes of the electron tube and the inner surface of the envelope, causing discharge within the tube.

Furthermore, if a portion other than the electron emitting surface 0 is exposed as described above, abnormal electrons are emitted from this portion, resulting in an abnormality in the operation of the electron tube. In other words, electrons emitted from the electron emission surface 0 move in a laminar flow and flow into the collector electrode, but electrons emitted from the side face do not move in a laminar flow and become abnormal electrons and flow into the anode electrode. and the helix electrode, causing a decrease in amplification efficiency and the release of abnormal gases, which harm the operation of the electron tube.

[Purpose of the invention]

An object of the present invention is to prevent evaporation of an electron-emitting substance and electron emission from a surface other than the electron-emitting surface, thereby constructing a long-life and highly reliable impregnated cathode.

[Summary of the invention]

The pores of a high melting point porous metal base are impregnated with an electron emitting substance, one end surface is used as an electron emitting surface, and in addition to the cathode base, a heater container is attached to the end surface side, and a heater is embedded in this heater container. In the impregnated cathode structure, the side surfaces of the cathode substrate are coated to prevent evaporation of the electron emitting substance and electron emission from the side surfaces of the cathode substrate.

In addition, when manufacturing this impregnated cathode, after sealing the side surface of the high melting point porous metal substrate, a ring-shaped brazing material made of a high melting point brazing material is attached to the side surface of this metal substrate. After melting and coating the side surfaces of the metal substrate, the excess brazing material is removed to form the desired coating layer, thereby making it possible to easily manufacture the desired impregnated cathode.

[Embodiments of the invention]

Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

FIG. 1 shows the structure of an impregnated cathode which is an embodiment of the present invention. This cathode has a cathode base (10)'' whose one end surface is an electron emitting surface (1), and a heater portion (11) attached to the other end surface of this cathode base (10).

The cathode substrate (10) has BaO, CaO, AQ20, etc.
The electron emitting surface 0 on one end surface is formed into a concave spherical shape, and the other end surface side is formed to have a smaller diameter than the one end surface side. Also,
An annular groove (13) is provided on the side surface near the electron emitting surface 0.

The heater part (11) is formed to have a larger diameter than the cathode base (10), and has a through hole in the center of one end surface that fits into a small diameter part formed on the other end surface of the cathode base (10). A heater container (15) made of molybdenum is provided with a hole and an annular groove (14) concentrically with the through hole and having approximately the same diameter as the large diameter portion of the cathode substrate (10); It consists of a heater (4) and a heat-resistant insulating embedding agent 0 made of alumina powder filled in the heater container (15) so as to embed the heater (4).

However, on the side surface of the cathode substrate (10), there is a coating layer (16) of a high melting point brazing material made of a molybdenum-ruthenium alloy.
), and the cathode base (10) and heater section (11) are brazed to each other with a brazing material (17) made of a molybdenum-ruthenium alloy provided on the other end surface of the cathode base (10).

The thickness of the coating layer (16) is set to 0.01+ to prevent evaporation of electron emitting substances and emission of abnormal electrons from this part.
nm or more, and since the Wehnelt electrode is placed outside the side surface of this cathode substrate (lO), the electron trajectory design requires 0.3 nm or more.
Formed below nwn.

In FIG. 1, (18) is a support for supporting the impregnated cathode on the support cylinder (19) shown by the broken line.

As shown in the flowchart in Figure 2, this impregnated cathode is manufactured by sealing the side surfaces of the high melting point porous metal substrate and combining it with the heater container (15). After applying a ring-shaped brazing filler metal to the side surface of the metal substrate and melting the brazing filler metal, excess brazing filler metal adhering to the side surface of the metal substrate is removed. Thereafter, the heater (a) is embedded in the heater container (15), and the metal base is further impregnated with an electron emitting substance to produce the heater. This manufacturing method will be explained in more detail below.

In order to produce a high melting point porous metal substrate, first, tungsten powder with a particle size of 3 to 10 mm is compression molded into a rod shape, and then this is sintered in a reducing atmosphere. Thereafter, in order to facilitate cutting of this sintered body, copper is impregnated into the pores, and this is cut, as shown in FIG. 3(A).
A concave spherical electron emitting surface 0 on one end surface, a small diameter portion (20) that fits with the heater container (15) on the other end surface, and an annular groove (
13) into a predetermined form. Thereafter, the impregnated copper is removed by heating at a high temperature using nitric acid and a hydrogen furnace.

Next, the side surface of this metal base (21) is
The diameter of the metal substrate is finished to a predetermined size by polishing it with alumina abrasive paper of No. S, and the pores opened on the side surface of the metal substrate are sealed.

The heater container (15) to be combined with the metal base formed as described above is formed by cutting a molybdenum rod, and as shown in FIG. The small diameter portion (
20) to be assembled.

Next, as shown in FIG.
), and as shown in figure (D), coat the metal substrate (
A ring-shaped filler metal (16) made of molybdenum-ruthenium alloy formed by press forming is placed on the side surface of the
Attach a). The ring-shaped brazing filler metal (16a) is arranged so that, when attached to the side surface of the metal base (21), its height is lower than the annular groove (13) formed on the side surface of the metal base (21). The required coating layer (16) can be easily attached to the metal base (21) and can be melted as described below.
In order to easily form a metal substrate (21),
It is formed in such a size that there is a gap of about 0.05 mm around the entire circumference between the side surface and the side surface.

Next, the brazing filler metal (16a), (
17a) in a hydrogen atmosphere at 2100°C for several tens of seconds, each brazing filler metal (16a), (
17a) is melted.

The molten brazing filler metal (16b) flows into the annular groove (13) formed on the side surface of the metal base (21);
3) prevents electrons from flowing into the emission surface 0. A part of this brazing material (16b) also flows into the annular groove (14) formed on one end surface of the heater container (15), but this groove (14) allows the brazing material (16b) to be located inside the groove (14). This prevents the metal from flowing into the surface of the metal substrate. Further, the molten brazing material (17) covers the other end surface of the metal base (21) and flows into the fitting portion between the metal base (21) and the heater container (15) to join them together.

Next, as shown in FIG. layer(
16).

After joining the metal base (21) and the heater container (15) together as described above, in this heater container (15),
A coiled heater (4) is inserted, and further,
For example, alumina powder with an average particle size of 10Im and 30μs is mixed at a weight ratio of 3Nia, an organic binder is added thereto, a kneaded embedding agent is filled, the heater (4) is embedded, and the mixture is vacuum-filled. Heat in a 1800'C for 12 hours to sinter.

After that, BaO, CaO9AQ, 0. The above metal substrate (21
) is melted and impregnated into the pores.

When the impregnated cathode is constructed as described above, the cathode substrate (10
) is covered with a dense coating layer (16), the evaporation of the electron-emitting substance from areas other than the electron-emitting surface 0 can be significantly reduced, and therefore the cathode can have a long life. can. Furthermore, the occurrence of intraluminal discharge due to adhesion of electron emitting substances can be suppressed. Further, since electron emission from surfaces other than the electron emitting surface 0 can be eliminated, amplification efficiency can be increased, and a cathode with a long life and high performance can be obtained.

In addition, during manufacturing, after sealing the side surfaces of the porous metal substrate (20), the brazing material (16a) is melted to form the coating layer (16).
, so that the molten brazing filler metal (16b) is attached to the metal base (2).
Therefore, the electron emitting substance can be sufficiently impregnated to the side surface of the metal base (20), and good electron emission can be obtained even from the periphery of the electron emitting surface 0. It can be a cathode. In addition, when forming the coating layer (16), since a ring-shaped brazing material (16a) that has been press-molded to a predetermined size is used, it is possible to reduce the flow of the brazing material (16b) to areas other than the required areas. Furthermore, an annular groove (13) is formed on the side surface of the metal base (20) to prevent the molten brazing filler metal (16b) from flowing out to the electron emitting surface, resulting in a highly reliable cathode with stable quality. can now be manufactured.

The above description has been made of an impregnated cathode having a cathode substrate whose side surfaces have the same diameter as the electron emitting surface. However, this invention is applicable when the side surface diameter is larger than the diameter of the electron emitting surface or smaller than the diameter of the electron emitting surface. It can be applied to various impregnated cathodes with different structures, such as cathode substrates with side surfaces of different diameters.

〔Effect of the invention〕

A coating layer is formed on the side surface of the cathode substrate, which is made by impregnating a high-melting point porous metal substrate with an electron-emitting substance, to eliminate evaporation of the electron-emitting substance and electron emission from areas other than the electron-emitting surface. It is possible to obtain a high-performance cathode that is less likely to cause intraluminal discharge during its lifetime and can increase amplification efficiency.

In addition, during manufacturing, after sealing the side surfaces of the porous metal substrate, a coating layer made of brazing material was formed on the side surfaces to prevent the brazing material from penetrating into the interior of the metal substrate.
The metal substrate can be sufficiently impregnated with the electron-emitting substance up to the periphery, and the cathode can provide good electron emission even from the periphery of the electron-emitting surface.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of an impregnated cathode according to an embodiment of the present invention, Fig. 2 is a flowchart showing the manufacturing process, and Figs. 3 (A) to F) are for explaining the manufacturing method. FIG. 4 is a sectional view of a conventional impregnated cathode structure. (4)...Heater 0...Electron emission surface (
10)... Cathode base (11)... Heater part (13), (14)... Annular groove (15)...
・Heater container (16)...covering layer (17)
... Brazing filler metal (21) ... Metal base

Claims (7)

[Claims] (1) A cathode substrate in which the pores of a high-melting point porous metal substrate are impregnated with an electron-emitting substance and one end surface serves as an electron-emitting surface, and a heater is installed in a heater container attached to the other end surface of the cathode substrate. An impregnated cathode comprising an embedded heater section and a coating layer covering a side surface of the cathode substrate. (2) The impregnated cathode according to claim 1, wherein the coating layer has a thickness of 0.01 to 0.3 mm. (3) The impregnated cathode according to claim 1, wherein the coating layer is made of a high melting point brazing material. (4) The impregnated cathode according to claim 1, wherein the cathode substrate has an annular groove on a side surface close to the electron emitting surface to prevent a brazing material from flowing into the electron emitting surface. (5) A step of sealing the side surface of a porous metal substrate obtained by sintering a powder containing a high melting point metal as a main component, a step of combining the metal substrate with a heater container, and a step of combining a high melting point metal with a heater container; A step of attaching a ring-shaped brazing material made of brazing material to the side surface of the metal substrate, a step of melting the ring-shaped brazing material to cover the side surface of the metal substrate, and a step of removing the surplus portion of the brazing material after melting. A method for manufacturing an impregnated cathode, comprising the steps of removing and finishing the coating layer to form a desired coating layer, and impregnating the metal substrate with an electron emitting substance. (6) The method for manufacturing an impregnated cathode according to claim 5, wherein the side surface of the metal substrate is sealed by grinding. (7) The method for manufacturing an impregnated cathode according to claim 5, wherein the surplus portion of the brazing material after melting is removed by grinding.