JP3283116B2 - Manufacturing method of oxide cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide cathode used in a thermionic electron tube.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 2, an oxide cathode structure is made of an alloy containing nickel as a main component and a trace amount of a reducing agent such as magnesium or silicon as a cathode base metal 11. The cathode base metal made of this alloy is press-molded to a required shape and thickness, and then joined and fixed to the tip of the cathode sleeve. Then, an alkaline earth metal carbonate powder made of barium, strontium, calcium, or the like to be the electron emitting material layer 12 is applied on the metal surface of the base by a spraying method or the like. The cathode structure is incorporated in an electron tube, and the carbonate is thermally decomposed in an exhaust step to form an alkaline earth metal oxide. The alkaline earth metal carbonate is a double salt or a mixed salt of an alkaline earth metal containing barium as a main component. Generally, barium is 57% by weight, strontium is 39% by weight, and calcium is 4% by weight. Ternary carbonate, which is a double salt of, is widely used. Of the alkaline earth metal oxides, barium oxide contributes to electron emission. This barium oxide is a reducing agent magnesium that diffuses into the base metal during operation of the oxide cathode,
By silicon or the like, reduced at the boundary between the base metal and the oxide,
For example, when magnesium is used as a reducing agent, free barium that contributes to electron emission is formed by the following reaction. BaO + Mg → Ba + MgO Accordingly, in the oxide cathode, the reaction between the reducing agent and the oxide, which is an electron emitting substance, proceeds near the interface between the base metal and the oxide. Is formed.

In such a conventional oxide cathode, it is known that fine crystal grain layers 13 and 14 are formed near both surface portions of the cathode base metal 11, respectively. The formation of the fine crystal grain layer is caused by processing strain caused by press working or the like existing on the surface of the cathode base metal, wet hydrogen treatment for forming a black layer on the surface of the cathode sleeve, or oxidation from the carbonate of the electron emitting substance. It has been found to be related to a heating step for a decomposition reaction into a substance. The fine crystal grain layer 14 which is not in contact with the electron emitting material layer 12 does not cause any problem because it has no particular effect on the electron emission performance, but the fine crystal grain layer 13 which is in contact with the electron emitting material layer 12 is formed of a cathode substrate. The diffusion of the reducing agent in the metal to the surface in contact with the electron emitting material layer is inhibited, and the electron emitting ability is significantly reduced.

As a method of removing the fine crystal grain layer,
A method of removing the fine crystal grain layer by cutting before applying the electron-emitting substance, a method of chemically polishing, and the like have been proposed, but it is difficult to completely remove the layer. In addition, in the conventional oxide cathode, the generation of the fine crystal grain layer increases with the operation time, and in many cases, stable electron emission for a long time cannot be obtained. The reason is that oxygen dissociated from barium oxide in the electron emitting material during the operation of the cathode dissolves into the metal of the cathode base and reaches the fine grain layer, thereby promoting the growth of the fine grain layer that is not yet stable. Conceivable.

[0005]

The electron emission characteristics, especially the life characteristics, of the conventional oxide cathode as described above greatly depend on the amount of the fine crystal grain layer formed near the surface of the cathode base metal. ing. That is, the diffusion of the reducing agent in the base metal to the surface is hindered by the increase in the formation amount of the fine crystal grain layer and does not reach the base metal surface, so that the reaction between the reducing agent and barium oxide at the interface decreases. However, the production of free barium is significantly reduced. The increase in the formation amount of the fine crystal grain layer depends on the operation time and the emission current density, so that it is impossible to maintain the electron emission ability at a high current density for a long time.

The present invention solves the above-mentioned disadvantages of the conventional method for manufacturing an oxide cathode, and provides a method for manufacturing an oxide cathode with less deterioration in electron emission characteristics even when operated at a high current density for a long time. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION This invention fixedly joined to the cathode sleeve of the cathode base metal with a reducing agent thereto to mainly nickel slightly added after having press-molded, the negative
The method for producing an oxide cathode structure in which an electrode sleeve is blackened by heat treatment in humidified hydrogen and an electron emission material layer of an alkaline earth metal carbonate is adhered onto the metal surface of the cathode substrate , wherein the blackened cathode is A first step of heat-treating the cathode base metal fixed to the sleeve in a non-oxidizing atmosphere, and a second step of subsequently heat-treating the cathode base metal in an oxidizing atmosphere. A third step of heat-treating the cathode base metal in a non-oxidizing atmosphere, and a fourth step of adhering the electron-emitting substance on the cathode base metal surface.
And a process for producing an oxide cathode.

[0008]

According to the present invention, the fine crystal grain layer near the surface of the cathode base metal can be made stable and strong, and as a result, the operation time as seen in the conventional oxide cathode and the fine crystal grain layer can be reduced. It is possible to stably obtain a high current density for a long time without increasing the formation amount. Also, in the step of heating the cathode base metal in an oxidizing atmosphere, ultrafine irregularities are formed on the surface of the cathode base metal, the adhesion strength to the electron emitting material layer is increased, and the electron emitting material layer can be operated for a long time. There is almost no risk of peeling.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. The oxide cathode structure according to the present invention is shown in FIG.
It is configured as shown in FIG. That is, the cathode base metal 11 made of a nickel alloy containing a small amount of a reducing agent obtained by rolling is compressed from the upper and lower surfaces by press working so that it can be closely fitted to the inner diameter of the cathode sleeve 15 made of a nichrome alloy. It is press fit into this cathode sleeve with a diameter dimension and fixed by laser welding. Then, heat treatment is performed on the cathode sleeve 15 in humidified hydrogen to selectively oxidize the cathode sleeve 15 and blacken the surface. Next, three strip-shaped supports 16 are welded to the cathode sleeve, and these are welded to the openings of the cylindrical cathode holder 17 to assemble the cathode assembly.

Then, in order to alleviate the processing distortion of the cathode base metal 12, in a non-oxidizing atmosphere such as a hydrogen furnace,
Heat treatment is performed at a temperature in the range of 0 to 900 ° C., for example, 800 ° C. for about 10 minutes. Next, a heat treatment is performed in an oxidizing atmosphere such as air at a temperature in the range of 700 to 850 ° C., for example, 780 ° C. for about 10 minutes. In this step, an oxide layer is formed on the surface of the cathode base metal, but a fine crystal grain layer (corresponding to 13 and 14 in FIG. 2) near the surface is somewhat internally oxidized. Further, in a non-oxidizing atmosphere such as a hydrogen furnace, 700 to 90
A heat treatment is performed at a temperature in the range of 0 ° C., for example, 800 ° C. for about 10 minutes to reduce the surface oxide layer of the cathode base metal. Finally, the electron emitter layer 12 is applied on the metal surface of the cathode substrate to complete the oxide cathode structure.

[0011] For comparison, the oxide cathode assembly assembled in this manner and, for comparison, a cathode assembly according to a conventional manufacturing method in which a heat treatment is performed at 700 ° C. for 10 minutes in a hydrogen atmosphere and the electron emission material is applied after cleaning. Was assembled in a color cathode ray tube, and the cathode was heated in the exhaust process to decompose the electron-emitting substance from carbonate to oxide.After the exhaust tube was chipped off, the cathode was activated in the aging process to complete the process. . Then, the electron emission characteristics associated with the long-term operation of each cathode ray tube were measured.

FIG. 3 shows the results of a life test when operating at a current density of 2.0 A / cm ² for a long time. The curve X shown in the figure is for the oxide cathode of the present invention, and the curve Y is for the conventional oxide cathode. As is clear from this characteristic comparison, the oxide cathode of the present invention has much less deterioration in electron emission characteristics due to long-term operation than the conventional oxide cathode, and the effect is more remarkable as the operation time becomes longer. Is evident.

After the operation test for 10,000 hours, the cathode of the present invention was taken out from the cathode ray tube, and the fine crystal grain layer near the surface of the cathode base metal was observed. Was hardly observed.

In the above-described embodiment, in order to ease the processing strain of the metal of the cathode base, 800 ° C., 10 ° C.
Although the case where the heat treatment is performed for a minute is described, when the treatment temperature is lower than 700 ° C., the processing strain of the cathode base metal is not sufficiently relaxed, a fine crystal grain layer is generated frequently, and the initial characteristics are problematic. there were. Further, when the treatment temperature is higher than 900 ° C., the generation of the fine crystal grain layer is reduced,
Decolorization of the selective oxidation layer of the cathode sleeve and other problems such as a decrease in the mechanical strength of the cathode constituent material have been problems. From these, the optimum temperature range was 700 ° C. to 900 ° C. as described above.

If the heat treatment temperature in an oxidizing atmosphere for forming a stable and strong fine crystal grain layer is lower than 700 ° C., the stabilization of the fine crystal grain layer is insufficient. Met. On the other hand, when the treatment temperature was higher than 850 ° C., the formation position of the fine crystal grain layer became deep, and the generation of vertical grain boundaries became remarkable. Further, there is a problem in that oxidation of a cathode constituting material other than the cathode base metal, for example, a strip-shaped support becomes remarkable and mechanical strength is reduced. From these, the heat treatment temperature in an oxidizing atmosphere is 700
The range from ℃ to 850 ° C was optimal.

Further, if the heat treatment temperature in a hydrogen atmosphere for reducing the surface oxide layer of the cathode base metal and other cathode constituent materials is lower than 700 ° C., the reduction is insufficient and the oxide remains. On the other hand, if the heat treatment temperature is higher than 900 ° C., there is a problem that the selective oxidation layer of the cathode sleeve is decolorized and the mechanical strength of the cathode constituting material is reduced. Therefore, this heat treatment temperature ranges from 700 ° C. to 9 ° C. as described above.
The range of 00 ° C. was optimal.

The oxide cathode of the present invention can be widely used not only for cathode ray tubes but also for other thermionic tubes. Further, the electron emitter layer may contain a small amount of scandium oxide, other oxides, or the like.

[0018]

As described above, according to the present invention,
It is possible to obtain a stable and highly reliable oxide cathode which is excellent in long-time operation at a high current density.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cathode assembly according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of a general cathode base metal part.

FIG. 3 is a life comparison characteristic diagram of the present invention and a conventional one.

[Explanation of symbols]

 11: cathode base metal 12: electron emitting layer 15: cathode sleeve

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 9/04

Claims (3)

(57) [Claims] 1. A cathode base metal mainly composed of nickel and to which a small amount of a reducing agent is added is press-molded and fixed to a cathode sleeve, and the cathode sleeve is heat-treated in humidified hydrogen.
A method for producing an oxide cathode assembly, wherein the cathode sleeve is blackened by applying an electron emission material layer of an alkaline earth metal carbonate on the metal surface of the cathode substrate.
A first step of heat-treating the cathode base metal fixed in a non-oxidizing atmosphere, a second step of subsequently heating the cathode base metal in an oxidizing atmosphere, and thereafter the cathode base metal A heat treatment in a non-oxidizing atmosphere, and a fourth step of thereafter depositing the electron-emitting substance on the metal surface of the cathode substrate. . 2. The method for producing an oxide cathode according to claim 1, wherein the processing temperature in the first and third steps of performing the heat treatment in a non-oxidizing atmosphere is in a range of 700 to 900 ° C. 3. The process temperature in the second step of heat treatment in an oxidizing atmosphere is in the range of 700 to 850 ° C.
2. The method for producing an oxide cathode according to 1.