JPH04322030A - Impregnated type cathode - Google Patents

Abstract

PURPOSE:To prevent an electron radioactive material from oozing out so as to enhance an electric characteristic by forming, at the back surface of a cathode pellet, a shielding film for preventing the electron radioactive material from oozing out on the surface of the cathode pellet, and inserting a heater into a groove formed on the back surface of the cathode pellet. CONSTITUTION:A copper impregnating tungsten rod, where oxygen free copper is impregnated in a sintering body made of metal powder having a high melting point including mainly tungsten powder, is machined so that an electron emitting surface and heater inserting grooves 2 formed at back surface are machined. The metal material having a high melting point is deposited on the back surface of a cathode base and the inside and side surface of the groove 2, thus obtaining a coated layer. A wax material is applied onto the coated layer in a molten state, thus forming a shielding film 3. A heater 4, which is machined into the same shape as that of the heater inserting groove, is inserted into the groove 2, and a cathode supporting wire 6 is fixed with a wax material. Consequently, the heater 4 can be disposed directly inside a cathode pellet 1, thereby enhancing an electric characteristic without requiring preheating all the time. Since the shielding film 3 is provided, a function can be exhibited even if a wax material having a poor wax flowing characteristic is used.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impregnated cathode used in microwave tubes, cathode ray tubes, etc., and more particularly to a quick-acting impregnated cathode that starts operating quickly after power is turned on.

0002

2. Description of the Related Art Hitherto, impregnated cathodes have been used for cathodes used in magnetrons, which are subject to strong electron reverse impact and ion impact, and cathode ray tubes, which are subject to severe operating conditions. The structure of an example of a conventional impregnated cathode is shown in FIG. 3 or 4. In other words, in FIGS. 3 and 4, 1 is a cathode pellet, and barium oxide, calcium oxide, aluminum oxide, etc. are placed on a cathode base made of sintered high-melting point metal powder mainly composed of tungsten powder and formed into a predetermined shape. It is formed by melting and impregnating an electron emitting substance consisting of a mixture of 4 is a heater for heating the cathode pellet;
A cathode sleeve 8 supports and fixes the cathode pellet 1 and houses the heater 4 inside. 9 is a cap for preventing electron radioactive substances from scattering from the back side of the cathode pellet 1 to the heater 4 side, and the cathode pellet 1, the cap 9,
The cathode sleeve 8 is integrally formed by welding.

In the conventional example shown in FIG. 3, the heater 4 is formed in a spiral shape, and in the example shown in FIG. 4, the heater is formed in the shape of a flat mosquito coil. The length of the heater 4 that satisfies the characteristics can be selected as appropriate, but in any case, the heater 4 is arranged below the cathode pellet 1.

In this case, in order to transfer the heat of the heater 4 to the cathode pellet 1 as quickly as possible, or to withstand harsh operating conditions such as vibration, the heater 4 is made of alumina powder 10.
Another method is to use high melting point insulating powder to fix the material.

[0005]

[Problems to be Solved by the Invention] However, in the conventional configuration in which the heater is placed below the cathode pellet, the cathode pellet and the heater are separated, so it is difficult to raise the temperature of the cathode pellet to the temperature required for electron emission. It takes a long time and a fast-acting cathode cannot be obtained.

Furthermore, even if the heater is fixed to the cathode sleeve using alumina powder or the like, the thermal conductivity of the alumina itself is not very good, and the heat capacity of the entire cathode including the area around the heater increases, causing a rise in the temperature of the cathode pellet. It took a long time, and it was not possible to obtain a fast-acting cathode, and it was necessary to increase the heating power.

Furthermore, since the conventional impregnated cathode requires a cathode sleeve for inserting a heater, there is a problem in that the entire cathode must be large. On the one hand,
An impregnated cathode has a porous cathode substrate impregnated with an electron-radioactive material, so even if the interior was hollowed out and a heater was buried, the electron-radioactive material would seep out and harm the electrical properties, making it impossible.

[0008]

[Means for Solving the Problems] The present invention provides a cathode pellet on the back side in which a cathode substrate made of a high-melting point metal porous body obtained by sintering high-melting point metal powder is impregnated with an electron radioactive substance mainly composed of barium. A first groove for inserting the heater is formed, and a shielding film formed on the surface of the first groove prevents the electron radioactive substance from seeping out, and the heater is inserted into the first groove. The above problem is solved by arranging the above.

Another feature of the present invention is that a second groove for reducing heat capacity is formed between first grooves for inserting a heater formed on the back surface of the cathode pellet.

0010

[Operation] According to the present invention, the first groove for inserting the heater is formed on the back surface of the cathode pellet, and the heater is disposed within the first groove, so that the cathode pellet has a heat source inside. The heat generated from the heater can be effectively used to raise the temperature of the cathode pellet, and the temperature can be raised in a short time.

Moreover, since the shielding film is formed on the surface of the first groove, the electron radioactive substance in the cathode pellet does not scatter toward the heater side, and the electrical characteristics do not deteriorate. In addition, even if the pitch of the heater coil is large and there may be a difference in the temperature of the cathode pellet between the heater insertion part and the part without the heater, the second groove provided on the back of the cathode pellet allows the part without the heater to The heat capacity of the cathode pellet is reduced, and it acts to maintain a uniform temperature distribution on the surface of the cathode pellet.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of an impregnated cathode according to an embodiment of the present invention. In the figure, 1 and 4 represent the same parts as in FIG. 3, 2 is a first groove for inserting a heater, and 3 is a shielding film for preventing seepage of electron radioactive substances. Reference numeral 5 denotes an alumina powder sintered body for fixing the heater, but it may be omitted if the usage conditions of the product incorporating this cathode are not severe and there is no need to fix the heater. Even if the material is fixed, it may be made of an insulating, high-melting-point powder other than alumina powder, as long as it can be sintered. Reference numeral 6 denotes a cathode support wire, which supports and fixes the cathode pellet at a predetermined position within the electron tube.

The method for manufacturing the impregnated cathode of this example will be explained. First, a sintered body of high-melting point metal powder, mainly tungsten powder, is made of oxygen-free copper (plastic etc. is also fine).
A copper-immersed tungsten rod impregnated with is machined into a predetermined shape with an electron emitting surface and a first groove for inserting a heater on the back surface. Then in a vacuum furnace at about 1800℃ for 30 minutes.
By performing a heat treatment for 1 minute, the oxygen-free copper is evaporated and removed to form a cathode substrate.

[0014] Next, sputtering or C
A high melting point metal material such as tungsten, molybdenum, or rhenium is deposited using the VD method to form an adhesion layer, and Mo-Ru brazing material is applied and melted on the adhesion layer to a thickness of 5 to 10 μm. A second shielding film 3 is formed. This adhesion layer is formed by Mo-Ru. If you try to form a shielding film using only the brazing material, the brazing material will flow into the pores of the cathode substrate (the gaps between the powders of the high melting point metal powder sintered body). This is because most of the pores are blocked, and impregnation of the electron radioactive substance that is to be impregnated into the pores later becomes impossible or reduced. In addition, we use materials that have poor wettability and poor wax flow, such as molybdenum bolite (Mo2).
This is because, if B) is used, pinholes will occur in the brazing material and it will not be able to function as a shielding film. From this point of view, the idea of shielding with a metal plate like a conventional cap,
It has not been possible to achieve a technique of inserting or embedding a heater within a porous cathode pellet.

Next, a heater 4 machined into the same shape as the first groove 2 for inserting the heater formed on the back surface of the cathode substrate is inserted into the first groove 2, and alumina powder is poured into the first groove 2. It is embedded and heated at about 1900° C. for 10 minutes in a reducing atmosphere such as a hydrogen furnace to sinter it.

Next, the cathode support wire 6 made of a heat-resistant material with low thermal conductivity, such as rhenium wire, is fixed with Mo--Ru brazing material.

[0017] After that, the surface of the cathode substrate (electron emitting surface)
An electron-radiating substance such as an aluminate compound containing barium as a main component is coated on the surface of the plate, and the mixture is heated to 1800°C in a reducing atmosphere.
The rapid-acting impregnated cathode of this example is obtained by performing a heat treatment for 5 minutes for impregnation, polishing off the excess electron radioactive substance remaining on the surface, and performing surface treatment.

When the heater 4 is not fixed in the cathode substrate, the heater 4 is inserted into the first groove 2 of the cathode pellet 1 in the electron tube.
A cathode can be constructed by fixing the cathode pellet 1 and the heater 4 so that they are inserted into the container.

FIG. 2 is a cross-sectional view of an impregnated cathode showing a further improved embodiment of the present invention. In the figure, 1 to 6 indicate the same parts as in FIG. 1, and 7 is the second groove formed between the first grooves 2 for inserting the heater on the back surface of the cathode pellet 1. This second groove 7 is not necessary when the coil pitch of the heater 4 is small and the interval between the first grooves 2 is narrow, but when the coil pitch is large and the interval between the first grooves 2 is large, Since the heat capacity between the grooves 2 is large, if there is variation in temperature between the electron emission surface above the first groove 2 and the electron emission surface between them, the heat capacity between the first grooves 2 should be reduced. This is to make the temperature of the surface of the cathode pellet 1 uniform. By doing so, a rapid-acting impregnated cathode with a uniform temperature can be obtained even when the heater pitch is large.

[0020]

[Effects of the Invention] As explained above, according to the present invention,
The heater can be placed directly inside the cathode pellet of the impregnated cathode.
Since the heat capacity of the entire cathode can be minimized, the temperature of the cathode can be raised immediately, and the heater can be operated immediately after turning on the power.There is no need for constant preheating, which saves power. It greatly contributes to the utilization of electronic devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an impregnated cathode that is an embodiment of the present invention.

FIG. 2 is a sectional view of an impregnated cathode according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional impregnated cathode.

FIG. 4 is a sectional view of another conventional example of an impregnated cathode.

[Explanation of symbols]

1 Cathode pellet 2 First groove 3 Shielding film 4 Heater 5 Alumina powder sintered body 6 Cathode support line 7 Second groove

Claims (4)

[Claims] Claim 1: A cathode pellet in which a cathode substrate made of a high-melting point metal porous body obtained by sintering a high-melting point metal powder is impregnated with an electron radioactive substance mainly composed of barium, and a heater for heating the cathode pellet. an impregnated cathode comprising: a first groove having a shielding film formed thereon for preventing the electron radioactive substance from seeping out on the back surface of the cathode pellet; An impregnated cathode in which the heater is arranged in a groove of the impregnated cathode. 2. The impregnated cathode according to claim 1, wherein the shielding film is formed of a brazing material with an adhesion layer of a high melting point metal material interposed therebetween. 3. The impregnated cathode according to claim 1, wherein the heater disposed in the first groove is firmly embedded with high melting point insulating powder. 4. The impregnated cathode according to claim 1, wherein a second groove is formed between the first grooves formed on the back surface of the cathode pellet.