JP2001167689A - Cathode for electron tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode for electron tube. SOLUTION: Fine particle siges of a base metal surface are adjusted from 3 to 50 μm in the cathode for electron tube containing a base metal and a electron-emitting substance layer. Thereby, the fine particle of the base metal surface can be controlled freely by a series of heat-treatment, a dispersion efficiency of an intermediate produced on working is excellent and a diffusion path of a reducing agent can be provided continuously, whereby an excellent long life property can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode for an electron tube, and more particularly, to a cathode for an electron tube having improved life and electron emission characteristics.

[0002]

2. Description of the Related Art As a cathode for an electron tube, an oxide converted from an alkaline earth metal carbonate containing barium as a main component is coated on a base metal containing nickel as a main component and a small amount of silicon or magnesium as a reducing agent. An oxide cathode provided with a layer of an electron-emitting substance is widely used.

[0003] Therefore, the life characteristics of the oxide cathode are mainly affected by the base metal and the oxide, and in particular, the intermediate products formed during the operation of the oxide cathode hinder the diffusion of the reducing agent to prevent the cathode from being diffused. The life is greatly shortened.

FIG. 1 shows a conventional base metal (Si 0.05w).
5 is an optical micrograph of the surface structure of nickel metal (t% and 0.05 wt% of Mg). As shown in the figure, the conventional base metal has a surface texture of about 10 particles.
It reaches about 0 μm.

[0005] Such an oxide cathode is generally manufactured by the following method. First, a carbonate powder mainly composed of barium carbonate is mixed with an organic solvent in which nitrocellulose is dissolved, and the mixture is applied on a base metal by a method such as spraying or electrodeposition, and then attached to an electron gun. And assemble it into an electron tube. In an evacuation process for evacuating the inside of the electron tube, the carbonate is heated to about 1000 ° C. by a heater, and at this time, barium carbonate is converted into barium oxide by a reaction represented by the following formula (1).

BaCO ₃ → BaO + CO ₂ (1) The produced barium oxide is formed by the reducing agent Si, Mg or the like in the base metal at the boundary where the electron emission material layer comes into contact with the base metal during operation of the cathode, as follows: A reduction reaction occurs as in the equations (2) and (3).

BaO + Mg → MgO + Ba (2) 4BaO + Si → Ba ₂ SiO ₄ + 2Ba (3) When the glass barium thus generated emits electrons, it is expressed by the above formulas (2) and (3). Like MgO,
Ba ₂ SiO _{4 is} also generated at the boundary between the electron emitting material layer and the base metal and at the grain boundary of the base metal. This reaction product is called an intermediate product, and serves as a barrier that hinders the diffusion of Mg and Si, making it difficult to generate glass barium that contributes to electron emission. Therefore, this intermediate product results in shortened life of the oxide cathode. In addition, the intermediate product has a problem that the current density is limited because the intermediate product obstructs the flow of the electron emission current due to the high resistance.

In order to solve such a problem, Matsushita Corporation of Japan has proposed a cathode having a metal layer made of tungsten and molybdenum on the surface of a base metal through Japanese Patent Application Laid-Open No. 3-257735. However, this cathode itself generates not only a reducing agent but also an additional intermediate Ba ₃ WO ₃ , so that the initial electron emission is too large, and the electron emission characteristics and the life characteristics of the cathode deteriorate as time passes. is there.

[0009]

Accordingly, the technical problem to be solved by the present invention is to solve the problem of intermediate products generated at the boundary between the base metal and the electron-emitting material layer and the grain boundary of the base metal during the operation of the cathode for an electron tube. It is an object of the present invention to provide a cathode for an electron tube which can solve the problems of shortening the life and increasing the cutoff drift rate induced by an object.

[0010]

According to the present invention, there is provided an electron tube cathode including a base metal and an electron emitting material layer, wherein a fine structure particle size of the base metal surface is 3 to 50 μm. A cathode for an electron tube.

In the present invention, the particle size of the fine structure on the surface of the base metal is preferably formed by heat treatment. This heat treatment includes: a) an oxidizing heat treatment step of heating the base metal to 300 to 1100 ° C. in the air to form a metal oxide film; and b) a dew point temperature of the base metal on which the metal oxide film is formed having a dew point of −50 to -50 ° C. A dry reduction heat treatment step of removing the metal oxide film by heating to a temperature of 500 to 1200 ° C. in a hydrogen atmosphere of −90 ° C., and c) removing the base metal after the step b) to a dew point temperature of −10 to −40 ° C. A wet reduction heat treatment step of heating to 500 to 1200 ° C. in a hydrogen atmosphere.

In the present invention, it is preferable that the oxidizing heat treatment is performed at a maximum temperature for 3 to 60 minutes. The dry reduction heat treatment is performed at a maximum temperature of 3 to 60.
It is desirable to maintain for minutes. Preferably, the wet reduction heat treatment is performed at a maximum temperature for 3 to 60 minutes.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a cathode for an electron tube according to the present invention will be described in more detail with reference to the accompanying drawings.

In order to prevent deterioration of various characteristics such as life characteristics due to the intermediate product formed during the operation of the cathode for an electron tube, a method of suppressing the generation of the intermediate product itself, or a method of suppressing the generated intermediate product A method of dispersing the layer and continuously supplying the reducing agent to the electron-emitting layer can be considered. According to the present invention, as the latter method, the intermediate material generated by controlling the structure of the base metal surface to a very fine structure through the heat treatment is dispersed and the diffusion path of the reducing agent is continuously provided. By doing so, effects such as an increase in service life and a reduction in cutoff drift rate are brought about.

For this reason, the cathode for an electron tube according to the present invention is:
A cathode whose particle size on the base metal surface is controlled by heat treatment is used.

In this heat treatment, first, the oxidation heat treatment of the base metal is performed by heating the base metal at 300 to 1100 ° C. in air.
At a temperature of 3 to 60 minutes, in which Ni, the main component of the base metal, combines with oxygen to form NiO, and the oxide film thus formed stores a large amount of energy. Also, since the growth rate of the oxide film is very high, the grain growth of the base metal is suppressed.

FIG. 2 shows the same base metal (Si) as in FIG.
N in which 0.05 wt% and Mg 0.05 wt% are dissolved
1 is an optical microscope photograph of the surface after the oxidation heat treatment step was completed by heating the metal (i-metal) at a temperature of 800 ° C. for 30 minutes in the atmosphere at a magnification of 500 times.

Here, "particles" means nickel grains, and in a metal sample, Ni atoms gather together in classes having the same atomic arrangement direction to form one grain. A grain boundary means such an interface between grains. In addition, a black line in a portion that looks round in the attached FIGS. 1 to 5 indicates a grain boundary.

Second, in the dry reduction heat treatment step, the base metal is removed in a hydrogen atmosphere having a dew point temperature of about -50 to -90 ° C.
The heat treatment is performed at a temperature of 00 to 1200 ° C. for 3 to 60 minutes, and the oxide film formed in the oxidation heat treatment is removed. FIG. 3 is an optical microscope photograph of the surface of the base metal of FIG. 2 which has been subjected to the dry heat treatment at a temperature of 1000 ° C. for 8 minutes after the oxidation heat treatment is completed.

Finally, the wet reduction heat treatment step is a heat treatment in a hydrogen atmosphere having a dew point of about -10 to -40 ° C. at a temperature of 500 to 1200 ° C. for 3 to 60 minutes. This is a step of appropriately adjusting the concentration gradient of the contained reducing agent and forming precipitates at grain boundaries so that grain growth does not occur.

As described above, the grains are formed by the atomic arrangement of Ni, and the size of the grains is related to the precipitation of the reducing agent. When the Mg and Si reducing agents form oxide precipitates at grain boundaries by wet heat treatment or oxidative heat treatment, the larger the amount, the more the grain growth can be suppressed.

FIG. 4 and FIG. 5 show the surface textures of the base metals, each of which has been subjected to wet reduction heat treatment at 1000 ° C. for 8 minutes, for 200 minutes each.
Optical micrographs at × 200 and × 500, showing that a very fine structure was formed as compared to the surface structure of the conventional base metal shown in FIG. 1, and the particle size was 3 to 50 μm. Having a distribution of

The heating temperature in each of the above-mentioned heat treatment steps is an appropriate temperature for sufficiently causing the oxidation and reduction reactions of the base metal and an appropriate time for controlling the surface microstructure of the base metal to be small.

That is, according to the present invention, the above heat treatment reduces the particle size of the fine structure on the surface of the base metal to 3 to 5 particles.
A cathode for an electron tube adjusted to 0 μm is provided. The cathode has an extended life, a reduced cut-off drift rate, etc. by dispersing intermediate products generated during operation and continuously providing a diffusion path of a reducing agent. Bring the effect.

Further, as a preferred embodiment of the present invention, Si and Mg are each used as a base metal in 0.05% each.
Although the description mainly focuses on Ni metal containing wt%, the content and type of the reducing agent are not limited thereto, and may be changed as necessary.

Electrons used in the cathode for an electron tube according to the present invention
Emissive materials are those used in the industry as electron emitting materials
Anything is fine. Specifically, for example,
Alkaline earth metal carbonate layer containing
Is (Ba, Sr, Ca) CO _ThreeTernary carbonic acid composed of
Salt or (Ba, Sr, Ca) CO_ThreeComposed of
There are oxides converted from binary carbonates, and here
Scanning to improve electron emission characteristics and life characteristics
Oxide, barium-scandate, lantern-ma
Emissive material with added gnesium composite oxide can also be used
Wear. In addition, tungsten or
Is also applicable when molybdenum is coated.

The effect of the cathode for an electron tube according to the present invention on various performances will be described below. The cathode for an electron tube used in the test was manufactured by the following method.

After cleaning the upper surface of the Ni metal body containing 0.05% by weight of Si and 0.05% by weight of Mg, (B)
a, Sr, Ca) CO ₃ ternary carbonate was spray-coated with a nitrocellulose suspension in which 0.07 wt% of a La—Mg composite compound was added, and dried to prepare a carbonate cathode. After inserting the manufactured cathode into the electron gun, a cathode heater was inserted inside the sleeve. After sealing the electron gun in a bulb for an electron tube, an oxide cathode was manufactured through an evacuation process.

The cathode for an electron tube employing the base metal of FIG. 1 described above as a comparative example, and the cathode for an electron tube employing the base metal of FIG. 4 manufactured by the above-described heat treatment method for an electron tube according to an embodiment of the present invention. The life characteristics of each cathode were evaluated.

FIG. 6 shows the results of testing the accelerated lifetime (6.9 V, 3 A / cm ² ) of three 15-inch tubes each using the cathodes of the comparative example and the embodiment. It can be seen that the cathode according to the embodiment of the present invention has excellent electron emission characteristics (half drift rate) and cutoff drift rate. The effect of reducing the cut-off drift rate reaches 20% or more, and usually, the life of the cathode is MTTF (mean) of the elapsed time until the IK residual rate reaches 50%.
The conventional oxide cathode life shown as a comparative example is 10,000 to 15,000 hours, and the cathode life of the present invention is 20,000 to 30,000 hours, which is defined as Time to Failure Mode. hand,
25% more than the conventional oxide cathode life,
It can be seen that the life characteristics can be remarkably improved even in a high current density region following the trend toward higher definition and larger size of television cathode ray tubes and the like recently.

[0031]

As described above, the present invention provides a microstructure of the base metal surface and a reducing agent contained in the base metal through a series of heat treatments leading to an oxidation heat treatment step, a dry reduction heat treatment step, and a wet reduction heat treatment step. Can be freely controlled. As a result, the cathode for an electron tube of the present invention is excellent in the effect of dispersing intermediate products generated during operation, can continuously provide a diffusion path for the reducing agent, and has excellent long-lasting characteristics with a reduced cutoff drift rate. .

[Brief description of the drawings]

FIG. 1 is a 200 × magnification optical microscope photograph showing the surface texture of a conventional base metal.

FIG. 2 is an optical microscope photograph (magnification: 500 times) showing a surface texture of a base metal after an oxidation heat treatment according to one embodiment of the present invention.

FIG. 3 is an optical micrograph (× 1000) showing a surface texture of a base metal after dry reduction heat treatment according to an embodiment of the present invention.

FIG. 4 is an optical microscope photograph (magnification: 200) showing a surface texture of a base metal after a wet reduction heat treatment according to an embodiment of the present invention.

FIG. 5 is an optical micrograph (× 500) showing a surface texture of a base metal after wet reduction heat treatment according to an embodiment of the present invention.

FIG. 6 is a graph showing a result of measuring a half drift rate and a cutoff drift rate of the cathode for an electron tube according to the embodiment of the present invention and a comparative example.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Korea Authority South Korea, Korea

Claims (6)

[Claims] 1. An electron tube cathode including a base metal and an electron emitting material layer, wherein the fine metal particle size on the surface of the base metal is 3 to 50 μm.
m, a cathode for an electron tube. 2. The cathode for an electron tube according to claim 1, wherein the particle size of the microstructure on the surface of the base metal is formed by heat treatment. 3. The heat treatment includes the steps of: a) heating the base metal to 300 to 1100 ° C. in air to form a metal oxide film; and b) dew-pointing the base metal on which the metal oxide film is formed. 500 to 1200 in a hydrogen atmosphere at a temperature of -50 to -90C
(C) a dry reduction heat treatment step of removing the metal oxide film by heating the base metal to a temperature of -10.
The cathode for an electron tube according to claim 2, further comprising a wet reduction heat treatment step of heating to 500 to 1200 ° C in a hydrogen atmosphere of to -40 ° C. 4. The cathode of claim 3, wherein the oxidation heat treatment is performed at a maximum temperature for 3 to 60 minutes. 5. The cathode of claim 3, wherein the dry reduction heat treatment is performed at a maximum temperature for 3 to 60 minutes. 6. The cathode according to claim 3, wherein the wet reduction heat treatment is performed at a maximum temperature for 3 to 60 minutes.