JP3378275B2 - Porous sintered substrate, method for producing the same, and impregnated cathode using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous sintered substrate for an impregnated cathode used in electron tubes such as cathode ray tubes and image pickup tubes, a method for producing the same, and an impregnated cathode formed by using the porous sintered substrate.

[0002]

2. Description of the Related Art Impregnated cathodes have been attracting attention as cathodes for improving the performance of electron tubes. Impregnated cathodes have a porous sintered substrate of a refractory metal and an electron emissive material (hereinafter also referred to as an emitter). ) Is melt-impregnated, and thermions are emitted from the cathode surface.

Conventionally, a porous sintered substrate used for an impregnated cathode is generally manufactured by press-molding a raw material metal powder and then sintering it. The porous sintered substrate thus obtained is subjected to cutting or electric discharge machining to have a predetermined shape, or as it is as a sintered body, the emitter is melt-impregnated into the pores of the porous sintered substrate to obtain an impregnation type. Manufactures the cathode. However, in such a conventional method, the plate thickness of the cathode is apt to become non-uniform, and the surface forming the cathode surface is rough (for example, the surface roughness Rmax is 10 μm in the state of a sintered body, and the surface is cut). Therefore, the electron emitting substance remains on the cathode surface after being impregnated with the electron emitting substance. FIG. 7 is a cross-sectional view of the vicinity of the cathode surface impregnated with the emitter after sintering, showing a state where the emitter remains on the cathode surface. This electron-emitting substance is easily soluble in water and reacts with a small amount of water immediately to form a hydroxide, which significantly reduces the electron emission property. Also,
There is a problem in that a large amount of the emitter remaining on the surface easily evaporates.

In order to obtain the optimum porosity of the porous sintered body, for example, according to JP-A-59-18539,
Polyvinyl alcohol was added as a binder to W powder having a particle size of 5 μm, and after molding, pre-sintering was performed in a hydrogen stream at 1000 ° C. for 1 hour, and further, it was baked at 1900 ° C. for 1 hour under a reduced pressure of 1 × 10 ⁻⁵ Torr or less. I'm tied. However, in such a conventional method, the sintering conditions change due to changes in the particle size distribution of the raw material powder and changes in the average particle size. Therefore, in order to obtain a constant porosity, the sintering time and the like are finely controlled. There is a need. There is also a problem that it is difficult to uniformly disperse the pores due to segregation of the powder.

Conventionally, the average particle size of the powder used as the metal powder raw material is about 2.5 to 3.4 μm, but the secondary particles and skeletal particles generated during the manufacturing process are around 125 μm at the maximum. It may become large, and such 2
When powder containing secondary particles and skeletal particles is press-molded and sintered, pores having a size several times larger than usual are generated inside the sintered body. FIG. 8 shows a state (cross-sectional view) of such a unique pore portion. For example, since tungsten powder originally has poor grain kinematics, pores do not collapse even when pressed and sintered in a portion where secondary particles and skeleton particles are aggregated. With such large pores, when impregnated with the electron emitting substance, a large amount of the electron emitting substance is impregnated into the large pores, and the thermal expansion thereof tends to spread the tungsten sintered body. For this reason, the grain boundary strength at this portion is weak, and problems such as crack generation and swelling of the surface of the sintered body occur. FIG. 9 shows a state (cross-sectional view) of a swollen portion on the surface. When this happens, not only the life of the impregnated cathode is shortened, but also the characteristics as a cathode are deteriorated. In the conventional manufacturing method, even if the pressing method or the pressing conditions are changed, the raw material powder itself has a problem, so that the large pores cannot be closed.

W is usually used as the material of the porous sintered substrate for the impregnated cathode as described above, and the density measurement is generally used to evaluate the porosity of the porous sintered substrate.
In the case of W, it is used with a density of 15.5 to 16.5 g / cm ³ (theoretical porosity of 19.7 to 14.5%). However, the final required property is the impregnation ratio of the emitter, and in the case of evaluation by density, the amount of closed pores is also included, so it is difficult to correlate the density with the impregnation ratio of the emitter. It was

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a porous sintered substrate whose surface roughness is controlled, a method for producing the same, and this porous sintered substrate. The purpose is to provide an impregnated cathode used, and more specifically, as follows.

According to the present invention, stable characteristics can be obtained by making the thickness of the cathode uniform, and the electron emission material can be prevented from remaining on the surface of the cathode after impregnation with the electron emission material to reduce the electron emission property. An object of the present invention is to provide a porous sintered substrate having a controlled surface roughness and a method for producing the same, which can prevent the evaporation of the electron emitting substance and suppress the evaporation amount of the electron emitting substance.

Further, according to the present invention, a porous sintered substrate having a small variation in sintering conditions and a uniform distribution of pores regardless of a slight variation in the average particle size or particle size distribution of the powder used. The purpose is to provide a manufacturing method.

Further, according to the present invention, by crushing the secondary particles and skeletal particles in the raw material powder, it is possible to prevent the generation of large pores in the obtained porous sintered substrate. It aims at providing the manufacturing method of.

[0011]

[0012]

In order to solve the above-mentioned problems of the prior art, the porous sintered substrate of the present invention is a porous sintered substrate for an impregnated cathode, wherein the surface roughness of the cathode surface is (Rmax) is 5 μm or less, and the impregnating rate of the impregnating material for evaluation measured by impregnating and removing the impregnating material made of Cu into the porous sintered substrate is 6 to
It is characterized by being 10% by weight.

The porous sintered substrate is characterized in that the cathode surface of the porous sintered substrate is polished and finished.

The porous sintered substrate is preferably made of tungsten or molybdenum.

In the method for producing a porous sintered substrate of the present invention, the surface roughness (Rmax) of the cathode surface is set to 5 μm or less, and the porous sintered substrate is impregnated with the impregnating material for evaluation and removed. In the method for producing a porous sintered substrate for an impregnated-type cathode, wherein the impregnation rate of the evaluation impregnating material made of Cu is 6 to 10% by weight, the metal granulated powder or a pre-classified metal. After producing a porous sintered body by press molding and sintering the raw material powder,
The surface roughness (Rmax) is controlled to 5 μm or less by the step of polishing the surface of the obtained porous sintered body.

In the polishing step, it is preferable that the pores of the porous sintered substrate are impregnated with the sealing material in advance and then the polishing is performed.

[0017]

[0018]

Further, in the porosity evaluation method of the porous material of the present invention, the impregnating material for evaluation made of Cu is impregnated into the porous material and removed, and the impregnation rate of the impregnating material is measured to measure the porosity of the porous material. It is characterized by evaluating the porosity.

The porous sintered substrate for the impregnated-type cathode preferably has an impregnation rate of 6 to 10% by weight of the impregnating material for evaluation made of Cu measured by the above-mentioned evaluation method.

Detailed Description of the Invention Although W is generally used as a constituent material of the porous sintered substrate, it is not limited to this and may be a refractory metal such as Mo or Ta, or an alloy thereof. .

The surface roughness Rmax of the cathode surface of the porous sintered substrate for impregnated cathode of the present invention is 5 μm or less, preferably 0.01 to 5 μm, and more preferably 0.01.
It is controlled to about 2.5 μm. Here, the surface roughness Rmax means that when the extracted portion is sandwiched by two straight lines which are parallel to the average line of the portion extracted by the reference length from the sectional curve, the interval between these two straight lines is the direction of the longitudinal magnification of the sectional curve. It is the value measured in accordance with (JIS B0601). Since the surface roughness is controlled in this way, when the porous sintered substrate is impregnated with the emitter, the surface area of the emitter exposed on the cathode surface can be reduced, and the evaporation amount of the emitter can be suppressed. In addition, since it is possible to prevent the emitter from remaining on the cathode surface, it is possible to prevent the deterioration of the electron emission characteristics due to the deterioration of the characteristics of the emitter that remains on the cathode surface in a large amount as in the conventional case. As the emitter with which the porous sintered substrate is impregnated, for example, a mixture of barium oxide and aluminum oxide, calcium oxide, magnesium oxide or the like is preferably used.

The control of the surface roughness of the cathode surface of the porous sintered substrate can be preferably carried out by polishing the cathode surface of the porous sintered substrate. Since the plate thickness of the porous sintered substrate can be made uniform by such a polishing step, the characteristics can be stabilized in this respect as well.

This polishing step is carried out by previously impregnating the pores of the porous sintered substrate with a sealing material and then polishing. Since the porous sintered substrate is porous, if it is polished as it is, the metal that is a constituent material of the sintered substrate is clogged, and the electron emitting substance cannot be impregnated. In order to prevent this, a sealing material for protecting the pores of the porous sintered substrate is impregnated before the polishing step. Since this sealing material becomes unnecessary after the polishing treatment, it is dissolved in a solvent after the polishing treatment or removed by a heat treatment.

Therefore, as a sealing material to be impregnated during polishing, 1) easy removal after polishing treatment,
2) When removing the sealing material by heat treatment, it is necessary to satisfy the requirement that it does not react with the porous sintered substrate even at high temperatures. As a substance satisfying such requirements, C
Examples of the material include u, plastics, various resins, and the like. When using, for example, W as the porous sintered substrate, Cu that does not react with W and has a relatively low melting point is preferable.

By the way, when the sealing material is removed by heat treatment, a heating furnace is used, but the sealing material diffuses and adheres to the furnace core by the heat treatment. When the sealing material adheres to the furnace core in this manner, it becomes difficult to uniformly heat the furnace core, and it becomes difficult to keep the atmosphere constant, which deteriorates the thermal efficiency of the furnace. Therefore, it is necessary to remove the sealing material attached to the furnace core,
In the conventional heating furnace, since the furnace core tube is fixed to the furnace, it is difficult to remove the sealing material adhering to the inside of the tube. Therefore, it is preferable that the furnace core tube has a double structure so that the inner tube can be removed. In this way, the sealing material can be easily removed, and the heat treatment can always be performed using a good furnace core.

The above-mentioned porous sintered substrate is manufactured by press-molding a metal raw material powder and then sintering it. In the present invention, in order to obtain a homogeneous porous sintered substrate,
Make the following improvements. The following improvements can be applied not only to the production of the porous sintered substrate for the impregnated cathode, but also to the general production method of the porous sintered body.

As the raw material powder, a metal granulated powder or a powder classified beforehand is used. By using the metal granulated powder or pre-classified powder in this way, it is possible to obtain a homogeneous porous calcinated material in which pores are uniformly dispersed under constant sintering conditions, regardless of the difference in the particle size and particle size distribution of the raw material powder. A bonded substrate can be obtained. Granulation or classification may be appropriately performed by a conventionally used method. The particle size of the granulated powder is preferably about 35 to 70 μm. Further, it is preferable to remove about 5 to 10% by volume of each of the large particle size side and the small particle size side by classification.

Further, before the press forming step of the metal raw material powder, a step of previously pulverizing the metal raw material powder is provided.
By this step, secondary particles and skeletal particles existing in the raw material powder, which cause generation of large pores, are crushed,
It is possible to obtain a porous sintered substrate without large pores.

A porous sintered substrate is obtained by press-molding and sintering the above-mentioned granulated or classified or pulverized raw material powder in the same manner as in the conventional method. In this case, the press molding is carried out by mixing the raw material powder with or without a binder such as PVA or paraffin, and molding pressure of 2 to 5 ton /
Perform in cm ² . 145 The obtained compact for example in H ₂
Preliminary sintering is performed at 0 to 1600 ° C. for about 250 to 400 minutes, and then, for example, in H ₂ at 1700 to 1900 ° C. until a predetermined porosity is obtained to obtain a porous sintered substrate.

When a porous sintered body is used as a porous sintered substrate for an impregnated cathode, the impregnation ratio of the emitter to the porous sintered substrate has conventionally been evaluated by measuring the density. In the invention, instead of this, the impregnation material for impregnation rate evaluation can be impregnated into the porous sintered substrate and removed, and the impregnation rate of the emitter can be determined from the impregnation rate of the impregnation material.

The porous sintered substrate has closed pores in addition to open pores, and the emitter is impregnated only in the open pores and cannot enter the closed pores. Since the density corresponds to the total porosity without distinguishing between open and closed pores, the conventional density evaluation does not correspond to the accurate emitter impregnation rate. According to the present invention, since the impregnating material for evaluation is impregnated only in the open pores like the emitter, the impregnation ratio of the emitter can be accurately estimated from the impregnation ratio of the impregnating material for evaluation.

The evaluation of the impregnation rate of the emitter can be applied not only to the emitter but also as a method of evaluating the porosity of the porous material. That is, for example, by impregnating the porous material with an impregnating material for evaluation such as Cu or plastic and then removing it, the porosity of the porous material can be evaluated.

In this case, if the same substance as the sealing material required for the above-mentioned polishing is used as the impregnating material for evaluating the impregnation rate, both effects can be obtained, which is beneficial.

In the porous sintered substrate for the impregnated cathode of the present invention, the impregnation rate of the impregnating material for evaluation made of Cu measured by the above method is 6 to 10% by weight, preferably 7 to
It is in the range of 9% by weight. When the impregnation rate of the impregnating material for evaluation is too large, the amount of evaporation of the impregnated emitter increases, while when it is too small, the effect of the emitter cannot be fully exhibited.

[0036]

Example 1 Tungsten powder having a polishing particle size of about 3 μm is mixed with paraffin, and 5 g of powder is used to press-mold about 30 g of powder.
Obtain a molded body of mmφ. 800 in H ₂
After degreasing at ℃ × 275 minutes, in H ₂ at 1500 ℃ × 33
Sinter for 0 minutes. Further, it is sintered in H ₂ at 1700 ° C. until the porosity becomes 15 to 18%.

The resulting sintered body was placed in H ₂ at 1100 ° C. × 1.
The sample is impregnated with copper for 20 minutes, and the obtained sample is subjected to parallel grinding and lapping to a target plate thickness. This sample is immersed in a mixed solution of nitric acid and water at a ratio of 1: 1 and heat-treated to completely remove copper.

As described above, a porous sintered substrate whose surface is polished is obtained. This porous sintered substrate was impregnated with an emitter to obtain a base of an impregnated cathode.

On the other hand, for comparison, a porous sintered substrate was obtained by molding and sintering under the same conditions as in the above-mentioned example except for the steps of impregnating copper, polishing and removing copper. The base was impregnated with the emitter to obtain a base of an impregnated cathode (comparative example).

Regarding these Example 1 and Comparative Example,
Table 1 shows the results of comparing the disk surface roughness Rmax of the cathode and the residual amount of the emitter on the disk surface.

Table 1 Examples Comparative Examples Surface Roughness Rmax 0.2-0.5 μm 5-10 μm Small amount of residual emitters on the surface Large In addition, the state near the disk surface of the cathode obtained in this Example 1 is schematically shown in a sectional view. Are shown in FIG. As is clear from FIG. 1 and Table 1, it can be understood that the amount of residual emitter on the disk surface can be suppressed to a low level by performing a polishing treatment to control the surface roughness. Therefore, according to the present embodiment, it is possible to prevent the electron emission characteristic from deteriorating and suppress the evaporation amount of the emitter.

Example 2 Pelletization W powder having an average particle size of 3 μm was doped with PVA, and the mixture was granulated with a spray dryer using pure water as a solvent to have a particle size of 60 μm. 7.65 g of this was press-molded (molding pressure ² ton / cm ² ) using a 28 mmφ cylindrical pressing jig. Then, after degreasing in H ₂ at 800 ° C. for 275 minutes, temporary sintering was performed in H ₂ at 1700 ° C. for 330 minutes.
Next, these pre-sintered bodies were subjected to a specific gravity (1
6 ± 0.15) was sintered.

For comparison, a porous sintered body was also manufactured by the conventional method without granulation. That is, W powder having an average particle size of 3 μm was doped with PVA, and 7.65 g was
A 28 mmφ cylindrical press jig was used for press molding (molding pressure ² ton / cm ² ). Then, in H ₂ , 80
After degreasing at 0 ° C x 275 minutes, in H ₂ at 1700 ° C x 3
Temporary sintering was performed for 30 minutes. Next, these temporary sintered bodies are
Sintering was performed at 800 ° C. until the target specific gravity (16 ± 0.15) was reached.

FIG. 2 shows the result of obtaining the pass rate at each set time for this example and the comparative example. As is clear from FIG. 2, according to the present embodiment, the variation in the set time, which is the target specific gravity, is extremely small, which is 1/5 or less of that in the comparative example. Therefore, according to this embodiment, the sintering process can be easily controlled.

Example 3 W powder having an average particle size of 3 μm was removed by a dry classifier at a volume ratio of 30% on each of the small particle size side and the large particle size side. The obtained W powder was doped with PVA, and 7.65 g was used as one portion for 28
Press forming using a cylindrical press jig of mmφ (forming pressure 2
ton / cm ² ). Then, after degreasing in H ₂ at 800 ° C. for 275 minutes, temporary sintering was performed in H ₂ at 1700 ° C. for 330 minutes. Next, these pre-sintered bodies were sintered at 1800 ° C. so as to have a desired specific gravity (16 ± 0.15).

For comparison, a porous sintered body was also manufactured by a conventional method without classification treatment. This comparative example is the same as the method for manufacturing the porous sintered body of the comparative example described in the above-mentioned Example 2.

FIG. 3 shows the result of obtaining the pass rate at each set time for this example and the comparative example. As is clear from FIG. 3, according to the present embodiment, the variation in the set time, which is the target specific gravity, is extremely small, which is 1/6 or less of that in the comparative example. Therefore, according to this embodiment, the sintering process can be easily controlled.

Example 4 10 kg of raw material powder of raw material crushed W, 100 balls (carbide or alumina), a magnetic pot were prepared, and the raw material powder and the ball were put in the magnetic pot and placed on a pot roller. 48-96
After H treatment, take out the powder from the magnetic pot, press-mold under the same conditions as before (molding pressure ² ton / cm ² ), sinter (in H ₂ after temporary sintering at 1700 ° C. for 330 minutes, H
Sintering is performed at 1800 ° C. in ₂ until the desired specific gravity (16 ± 0.15) is reached.

According to the method of this embodiment, since the secondary particles and skeletal particles in the raw material powder are crushed, it is possible to obtain a W porous sintered substrate without large pores. The cross-sectional appearance of the porous sintered substrate thus obtained is schematically shown in FIG. It can be seen that the pores are uniformly dispersed in the sintered substrate.

Since the W porous sintered substrate obtained by the method of the present example does not have large pores, the grain boundary strength is high and the cathode surface swells or cracks even when impregnated with the electron emitting material. There is nothing. Therefore, it becomes difficult for the life and characteristics of the cathode to decrease.

Example 5 Emitter Impregnation Rate Evaluation Method Several kinds of porous sintered bodies having different specific gravities were prepared, and Cu was melt-impregnated in each sample, and then the impregnated Cu was removed. The impregnation rate was measured. Next, the emitter was impregnated and the impregnation ratio of the emitter was measured. FIG. 5 shows the correlation between the Cu impregnation ratio and the emitter impregnation ratio thus obtained.

On the other hand, for comparison, the correspondence between the density of the porous sintered body and the impregnation ratio of the emitter was also examined.

As is clear from FIG. 5, in the evaluation method of this embodiment, the Cu impregnation rate and the emitter impregnation rate correspond well. Therefore, according to the evaluation method of this example, the emitter impregnation ratio can be accurately controlled from the Cu impregnation ratio.

It was also found that a good emitter impregnation rate was obtained when the Cu impregnation rate was in the range of 6 to 10%.

[0055]

According to the present invention, since the cathode surface of the porous sintered substrate is polished and the surface roughness Rmax is controlled to 5 μm or less, the residual amount of the emitter on the cathode surface is suppressed. As a result, a decrease in electron emission can be prevented and the amount of evaporation of the emitter can be suppressed. In addition, since the raw material powder that has been granulated or classified is used, there is little fluctuation in the sintering conditions, regardless of the slight fluctuations in the average particle size and particle size distribution of the powder used, and the porous calcination in which the pores are uniformly dispersed. A bonded substrate can be obtained. In addition, since the raw material powder is crushed and used in advance, secondary particles and skeletal particles in the raw material powder are crushed,
It is possible to obtain a porous sintered substrate in which uniform pores are dispersed without large pores. Furthermore, since the impregnating material for evaluation is impregnated into the porous material and the impregnation rate of the porous material is measured by measuring the impregnation rate, it is necessary to take an accurate correlation with the emitter impregnation rate of the porous sintered substrate. You can

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the vicinity of a disk surface impregnated with an emitter after surface polishing in an example.

FIG. 2 is a graph showing the results of determining the pass rate at each set time of heat treatment for Example 2 and Comparative Example.

FIG. 3 is a graph showing the results of obtaining the pass rate at each set time of heat treatment for Example 3 and Comparative Example.

FIG. 4 is a cross-sectional view of a porous sintered substrate obtained by crushing raw material powder, followed by press molding and sintering.

FIG. 5 is a diagram showing a correlation between a Cu impregnation rate and an emitter impregnation rate.

FIG. 6 is a cross-sectional view of the vicinity of a cathode surface which is impregnated with an emitter after sintering.

FIG. 7 is a cross-sectional view showing a state of a unique pore portion.

FIG. 8 is a cross-sectional view showing a state of a swollen portion on the surface.

Front page continuation (72) Inventor Junji Hatakeyama 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Yokohama Works, Ltd. (72) Inventor Toshiaki Nakajima 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Toshiba Yokohama Works (72) Inventor Shin Nakamura Shinya Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa 8 Yokohama-shi Works (56) Reference JP-A-5-114352 (JP, A) Japanese Patent Publication 58- 26769 (JP, B1) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01J 1/28 H01J 9/04

Claims (7)

(57) [Claims] 1. A porous sintered substrate for an impregnated cathode, comprising:
The surface roughness (Rmax) of the cathode surface was set to 5 μm or less, and the impregnation material for evaluation, which was measured by impregnating and removing the impregnation material for evaluation made of Cu into the porous sintered substrate, was 6%. A porous sintered substrate, characterized in that it is 10% by weight . 2. The porous sintered substrate according to claim 1, which is obtained by polishing the cathode surface of the porous sintered substrate. 3. The surface roughness (Rmax) of the cathode surface is 5 μm.
The impregnation rate of the evaluation impregnating material made of Cu is 6 to 10% by weight, which is not more than m and is measured by impregnating and removing the evaluation impregnating material made of Cu into the porous sintered substrate. In the method for producing a porous sintered substrate for a die cathode, a porous sintered body is produced by press-molding and sintering metal granulated powder or pre-classified metal raw material powder, A method for producing a porous sintered substrate, wherein the surface roughness (Rmax) is controlled to 5 μm or less in the step of polishing the surface of the sintered body. 4. The method for producing a porous sintered substrate according to claim 3, wherein in the polishing step, the pores of the porous sintered substrate are impregnated with a sealing material in advance and then polished. . 5. The method for producing a porous sintered substrate according to claim 3, further comprising the step of pulverizing the metal raw material powder before press molding. 6. An impregnated cathode, which comprises the porous sintered substrate according to claim 1 or 2 and is impregnated with an electron emissive substance. 7. The impregnated cathode according to claim 6, which is used for an electron tube.