JP7025816B2 - Manufacturing method of cathode for electron tube - Google Patents

Description

The present invention relates to a method for manufacturing a cathode for an electron tube that emits electrons in a vacuum used for a magnetron, a klystron traveling wave tube, or the like.

In recent years, the demand for higher output for microwave electron tubes has been increasing more and more. In particular, magnetrons are widely used in the field of other microwave application equipment such as medical equipment and radar equipment because they efficiently generate microwaves.

FIG. 3 shows a general configuration of the magnetron 7. Normally, the magnetron 7 arranges the cathode 12 in a tube that holds a vacuum. Further, as an anode, a vane 13 arranged radially and an anode shell 14 for joining the vane 13 are provided around the coaxial surface of the cathode 12. Further, by arranging the pole pieces 15a and 15b at the vertical positions of the cathode 12, a magnetic field is applied in the axial direction. A heater 10 is arranged inside the cathode 12.

FIG. 4 shows a general configuration of a cathode for an electron tube. By energizing and heating the heater 10, the thermionic emitting substance 11 provided on the surface of the base metal 9 is heated and thermionic electrons are emitted. By applying a high voltage between the cathode 12 and the vane 13, the thermions emitted from the thermoelectron emitting substance 11 orbit around the electric and magnetic fields in the working space and reach the vane 13. The energy generated by this electron motion is given to the cavity resonator formed in the space surrounded by the adjacent vanes 13 and the anode shell 14 shown in FIG. 3, and the microwave oscillates.

The process of thermionic emission of the cathode for electron tubes shown in FIG. 4 will be described in detail with reference to FIG. As shown in FIG. 4, a base metal 9 is fitted to the outside of the cathode sleeve 8, and the thermionic emission material 11 is provided so that a part of the thermionic emission substance 11 is exposed on the outer surface of the base metal 9. It is embedded. A spiral heater 10 is arranged inside the cathode sleeve 8.

When the heater 10 heats the surface of the hollow portion of the cathode sleeve 8 by passing an electric current through the heater 10, the base metal 9 arranged outside the cathode sleeve 8 and the thermionic emitting substance 11 are heated, and thermionic electrons are generated. Thermions are emitted from the emitting substance 11.

By the way, in order to operate the magnetron stably, it is necessary to efficiently transfer the heat generated by the heater 10 to the thermionic emission substance 11. However, since the surface of the hollow portion of the general cathode sleeve 8 has a structure in which the metal material is exposed, the heat generated by the heater 10 is reflected and the heater 10 is heated. If the temperature of the heater 10 rises, the resistance value rises, and the current decreases, and the calorific value of the heater 10 decreases, heat cannot be efficiently transferred to the thermionic emission substance 11.

On the other hand, a method in which a part of the radiant heat from the heated heater 10 is efficiently absorbed by the cathode sleeve 8 is also being studied. For example, a method has been proposed in which the surface of the hollow portion of the cathode sleeve is made uneven by an etching method using a chemical solution to increase the area receiving radiant heat from the heater 10 and increase the heat absorption rate of the cathode sleeve 8. (Patent Document 1).

Japanese Unexamined Patent Publication No. 2002-343267

However, even if the surface of the hollow portion of the cathode sleeve is made an uneven rough surface by the conventional manufacturing method, the uneven surface has a structure in which the surface of the metal itself constituting the cathode sleeve is exposed, so that the heater No effect was obtained to significantly reduce the reflection of radiant heat from. Even if the conventional manufacturing method is applied as a manufacturing method for the cathode of the magnetron, which is particularly required to have high output, the radiant heat from the heater is reflected on the surface of the hollow portion of the cathode sleeve, and the heat is absorbed on the surface. The rate did not improve as expected, and it could not be adopted as a manufacturing method for cathodes for electron tubes, which requires high output.

Therefore, an object of the present invention is to provide a method for manufacturing a cathode for an electron tube provided with a cathode sleeve that efficiently absorbs radiant heat from the heater 10.

In order to achieve the above object, the method for manufacturing a cathode for an electron tube according to the present invention is to manufacture a cathode for an electron tube provided with a cathode sleeve in which a thermoelectron emitting substance is adhered or impregnated on the surface and a heater is arranged in a hollow portion. In the method, the step of forming the first metal film on the surface of the hollow portion of the cathode sleeve and the second metal film in which the first metal film is changed by heat-treating the first metal film. The method for forming the first metal film includes the step of forming the first metal film by heating and sublimating the metal forming the first metal film in a mixed gas containing an inert gas and oxygen to form a linear shape. Alternatively, it is a step of forming a metal film made of a whisker-like oxide film of the metal, and the method of forming the second metal film is to reduce the oxide of the metal by heating the oxide film of the metal. It is characterized in that it is a step of forming the linear or whisker-shaped metal film .

According to the method for manufacturing a cathode for an electron tube of the present invention, the second metal film having an excellent heat absorption rate is formed in the hollow portion of the cathode sleeve by changing from the first metal film to the second metal film by heat treatment. It can be formed on the surface.

Further, since the cathode sleeve of the cathode for the electron tube formed by the manufacturing method of the present invention can efficiently transfer the heat generated by the heater to the thermionic emission material, the electron tube can be operated stably even if the input power of the heater is lowered. It is possible to make it. In particular, the second metal film formed on the surface of the hollow portion of the cathode sleeve does not expose the surface of the metal itself constituting the cathode sleeve, so that it is possible to prevent abnormal heating of the heater body.

Specifically, when a metal oxide film is attached to the cathode sleeve and then reduced to form a metal film, the metal fine particles formed when the metal oxide film is attached are formed on the surface of the cathode sleeve through the voids. It becomes a layered shape and can efficiently absorb the heat released from the heater. Further, in the metal film formed by removing the binder, the portion from which the binder is removed becomes a void portion, and the heat released from the heater can be efficiently absorbed without being reflected.

It is a figure explaining the manufacturing method of the cathode for electron tubes which concerns on 1st and 2nd Examples of this invention. It is a figure explaining the manufacturing method of the cathode for electron tubes which concerns on 1st and 2nd Examples of this invention. It is a figure explaining a general magnetron. It is a figure explaining the conventional cathode for electron tubes.

The method for manufacturing a cathode for an electron tube of the present invention is a method for forming a metal film having an excellent heat absorption rate on the inner surface of a cathode sleeve with a uniform thickness.
Hereinafter, examples of the present invention will be described in detail.

The first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, a cylindrical cathode sleeve 1 made of molybdenum is prepared. The material of the cathode sleeve 1 may be any melting point metal and is not limited to molybdenum.

First, the cathode sleeve 1 and the tungsten wire are placed in a container that can be sealed and has an exhaust device. Next, after achieving a desired degree of vacuum while exhausting the air in the container, a reduced pressure state is maintained while introducing a mixed gas composed of oxygen gas and, for example, argon gas as an inert gas into the container. At this time, the flow rate of oxygen gas, the flow rate of argon gas, and the degree of vacuum in the container can be appropriately selected.

After the flow rate of each gas and the degree of vacuum in the container are stabilized to the desired conditions, the mixture is heated to about 1200 ° C. while controlling the current flowing through the tungsten wire. The heated tungsten wire reacts with oxygen gas in the vicinity to form an oxide. Since this generated oxide sublimates at about 1000 ° C., it dissociates from the tungsten wire as soon as it is oxidized and is transported upward by the updraft created by the heated tungsten wire.
At this time, by arranging the cathode sleeve 1 above the tungsten wire, the sublimated tungsten oxide is deposited on at least the inner surface of the cathode sleeve 1, and the metal film 5 (corresponding to the first metal film). To form.
Here, when the degree of vacuum in the container is 4 × 10 ⁴ Pa or more, it is deposited as a linear or whisker-shaped metal film 5 made of tungsten oxide on the inner surface of the cathode sleeve 1, and the shape has many voids.

After that, the cathode sleeve 1 having the metal film 5 made of tungsten oxide formed on the surface of the hollow portion is placed in the reducing device, and the metal film 5 made of tungsten oxide is placed at about 400 to 500 ° C. in a dry hydrogen atmosphere. The metal film 5 made of tungsten oxide is reduced by heating or contacting with hydrogen plasma. As a result, oxygen is removed from the metal film 5 made of tungsten oxide, and the metal film 6 made of tungsten (corresponding to the second metal film) is obtained (FIG. 2). The metal film 6 is deposited in a linear or whisker shape, and has a shape with many voids.

The following steps are the same as those for manufacturing a normal cathode for electron tubes.
First, a cylindrical base metal 2 having an inner diameter that can be fitted to the cathode sleeve 1 is prepared. As the material of the base metal 2, generally, high-purity metallic nickel or metallic nickel containing a trace amount of magnesium is used. A cylindrical base metal 2 is fitted to the outside of the cathode sleeve 1 to bring it into close contact with the cathode sleeve 1 to integrate the cathode sleeve 1 and the base metal 2.

Alternatively, the shape in which the cathode sleeve 1 and the base metal 2 are integrated may be formed, for example, by mechanically carving.

Next, a groove is formed on the outer surface of the cylindrical base metal 2. This groove can be formed by mechanical metal processing. As shown in FIG. 2, a plurality of grooves are formed in the circumferential direction of the cylindrical base metal 2. Alternatively, various changes can be made, such as providing a plurality of heaters in a straight line substantially parallel to the insertion direction of the heater 4, providing the grooves in a grid pattern by crossing each other, or forming the grooves in an island shape and providing them in a staggered pattern. ..

The thermionic emission substance 3 is embedded in the groove formed on the outer surface of the base metal 2. As the thermoelectron emitting substance 3, for example, a mixed salt of barium, strontium, calcium or the like is used. As a method for embedding the thermionic emission substance 3, a spray coating, a dipping method, a dropping coating, or the like can be considered, but any method may be used.

Further, the outer surface of the base metal 2 may be sintered with, for example, granular tungsten to form a porous structure, and the thermoelectron emitting substance 3 may be impregnated with, for example, barium, calcium, aluminum or the like.

Next, the cathode for the electron tube is completed by inserting the heater 4 into the cathode sleeve 1 integrated with the base metal 2 (FIG. 2).

When a so-called oxide cathode is selected as the cathode for the electron tube configured in this way, when the heater 4 is energized and heated, the heat from the heater 4 is transferred from the metal film 6 to the cathode sleeve 1 and the base metal 2 in this order. Heats the thermionic emission material 3. Then, by adjusting the input power to the heater 4, when the thermionic emitting substance 3 is heated to about 800 ° C., thermionic electrons are emitted from the surface of the thermionic emitting substance 3. At this time, the presence of the metal film 6 having a large number of voids efficiently absorbs the radiant heat from the heater 4, and the temperature of the heater 4 is 30 to 50 ° C. lower than that of the conventional cathode for electron tubes in which the metal film 6 does not exist. Even if the input power to the heater 4 is reduced by 5.6 to 9.3%, the thermionic emission substance 3 can be reliably heated to a temperature at which thermionic electrons are emitted.

On the other hand, when a so-called impregnated cathode is selected as the cathode for the electron tube, the heat generated by energizing the heater 4 is transmitted in the order of the metal film 6, the cathode sleeve 1, and the base metal 2, and finally the thermoelectron emitting substance 3 is heated. do. At this time, by adjusting the input power to the heater 4, when the thermionic emitting substance 3 is heated to about 1000 ° C., thermionic electrons are emitted from the surface of the thermionic emitting substance 3. Further, since the presence of the metal film 6 having a large number of voids can efficiently absorb the radiant heat from the heater 4, the heater 4 is more than the case of using the conventional cathode for electron tubes in which the metal film 6 does not exist. Even if the temperature of the thermoelectron is lowered by 40 to 70 ° C. or the input power to the heater 4 is reduced by 7.5 to 13.1%, the thermionic emission substance 3 is surely heated to the temperature at which thermionic electrons are emitted. It is possible to do.
In particular, the presence of the metal film 6 is advantageous in the impregnated cathode in which the thermionic emitting substance 3 needs to be heated to a high temperature.

Next, a second embodiment will be described. As a method of forming a metal film on the surface of the hollow portion of the cathode sleeve 1, it is also possible to apply metal particles using a binder. For example, nitrocellulose and butyl acetate are used as a binder, and a desired amount of tungsten particles having a particle size of about 0.2 to 0.8 μm is dispersed and applied to the surface of the hollow portion of the cathode sleeve to form a coating film. (Not shown). The viscosity of the coating liquid may be selected according to the inner diameter of the cathode sleeve. For example, when the inner diameter of the cathode sleeve is small, a binder having increased fluidity by adjusting the mixing ratio of nitrocellulose and butyl acetate may be prepared and poured. If the inner diameter of the cathode sleeve is large, prepare a binder whose fluidity is adjusted to a desired state in the same manner as described above, and apply it directly on the surface of the hollow portion of the cathode sleeve, or use a spray or the like. You may apply it by spraying.

Subsequently, the binder was removed by heat treatment at a temperature of 720 to 980 ° C. for 5 to 20 minutes in a hydrogen atmosphere, and a metal film 5'made of temporarily sintered tungsten was formed on the inner surface of the cathode sleeve 1. (Fig. 1).

Subsequently, the metal film 5'made of tungsten was sintered by treatment under a reduced pressure atmosphere at a temperature of 1200 to 1600 ° C. for 30 to 120 minutes, and the metal film made of tungsten was formed on the inner surface of the cathode sleeve 1 ((FIG. 2). 6)) (corresponding to the second metal film) can be formed.
The metal film 6 thus formed has a shape with many voids from which the binder has been removed.

The following steps are the same as those for manufacturing a normal electron tube cathode, and the cathode sleeve 1 having the second metal film formed by the above method on the surface of the hollow portion and the thermionic emission substance 3 are attached to or attached to the surface. By fitting the impregnated base metal 2 and inserting the heater 4 into the cathode sleeve 1, the cathode for an electron tube can be obtained.

Although the examples of the present invention have been described above, it goes without saying that the present invention is not limited to the above examples. For example, the metal type of the metal film formed on the inner surface of the cathode sleeve may be a metal having a high melting point and a low vapor pressure. Specific examples thereof include molybdenum, nichrome, nickel and the like in addition to the above-mentioned tungsten, and the metal may be used alone or as an alloy containing at least one kind.
Further, the types of the binder and the metal particles can be changed as appropriate.

1,8: Cathode sleeve, 2,9: Base metal, 3,11: Thermoelectron emitting material, 4,10: Heater, 5,5': First metal film, 6: Second metal film, 7: Magnetron, 12: Cathode

Claims (1)

In a method for manufacturing a cathode for an electron tube, which comprises a cathode sleeve in which a thermoelectron emitting substance is adhered or impregnated on the surface and a heater is arranged in a hollow portion.
By the step of forming the first metal film on the surface of the hollow portion of the cathode sleeve and the heat treatment of the first metal film, the second metal film in which the first metal film is changed is formed. Including the process
The method for forming the first metal film is to heat and sublimate the metal forming the first metal film in a mixed gas containing an inert gas and oxygen to oxidize the metal in a linear or whisker shape. This is a step of adhering a metal film made of an object to the surface of the hollow portion of the cathode sleeve.
The method for forming the second metal film is a step of reducing the oxide of the metal by heating the first metal film to form a linear or whisker-shaped metal film made of the metal. A method for manufacturing a cathode for an electron tube, which is characterized by the above.

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