JPH06168660A - Impregnation type cathode and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve an electron emitting characteristic in a space charge limited current area, and reduce grid emission by containing scandium or scandium oxide by specific weight % in the first layer on a surface of an electron emitting material impregnated layer and the second layer on the first layer. CONSTITUTION:About 25% pores of a porous W base body 3 formed of W powder are impregnated with Sc2O3 contained and uncontained electron emitting materials 1 and 2, and a cathode pellet 5 is formed. This pellet 5 is soaked into pure water 7, and water 10 is filled in a container 9 housing an ultrasonic vibrator 8, and ultrasonic vibration is added, and an excess material 2 is removed, and a pore (b) layer is formed. A material 1 formed by adding Sc 0 by 1 to 30 weight % is applied to this (b) layer, and it is heated and melted in a vacuum, and thickness of an (a) layer is adjusted. This pellet 5 is put in a Ta cup 12, and is welded to a Ta sleeve 13, and a W core 14 is heated by an alumina covering heater 15. Thereby, an electron emitting characteristic is improved in a space charge limited current area, and grid emission is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impregnated cathode and a method for manufacturing the same, and more particularly to an impregnated cathode having a porous tungsten substrate having a two-layer structure on the upper part thereof and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a scandium (Sc) -based impregnated cathode has a heat-resistant porous structure in which scandium oxide (Sc ₂ O ₃ ) particles are dispersed in the upper portion thereof, as disclosed in JP-A-59-79934. Layer, and an electron-emitting substance (B
aO, CaO, Al ₂ O ₃ etc.) and a structure impregnated with the structure described in JP-A-59-203343.
Fine tungsten (W) powder, Sc ₂ O ₃ , on the cathode surface,
And structures with uniform layers of electron-emissive materials have been proposed.

Further, while such an impregnated cathode can operate at a high current density, its operating temperature is about 200 ° C. higher than that of a commonly used oxide cathode. for that reason,
From the cathode, barium (Ba) or barium oxide (Ba)
A large amount of O) evaporates and adheres to the grid electrode, resulting in grid emission, which adversely affects the characteristics of the electron tube.

As a method for improving the evaporation of Ba and BaO from the cathode, as described in Japanese Patent Publication No. 4-21977, an electron emitting material impregnated in the pores of a porous W substrate is disclosed. It has been proposed to remove a few μm from the surface of the substrate.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The Sc-impregnated cathodes disclosed in Japanese Patent No. 934 and Japanese Patent Laid-Open No. 59-203343 each have a high electric field,
That is, although the electron emission characteristic is excellent in the temperature control current region, the electron emission characteristic is significantly deteriorated in a low electric field, that is, in the space charge limited region, and an electron tube for operating the cathode mainly in the space charge control current region, for example, In electron tubes such as cathode ray tubes and image pickup tubes, it has not been possible to endure practical use.

[0006] Further, as disclosed in Japanese Patent Publication No. 4-21977, Ba, BaO by removing a part of the electron-emitting substance is disclosed.
The large amount evaporation preventing method of (1) causes a problem that the electron emission characteristic is deteriorated if the removing method is not appropriate. For example, in the method of heating in a vacuum or the like, not only the electron-emitting substance near the surface but also required BaO inside the substrate is evaporated. Further, it is not possible to remove BaO within several μm by a mechanical method (polishing, brush, etc.), but rather dust such as an abrasive adheres. Further, a chemical method such as dissolution with an acid causes the entire electron-emitting substance to be melted out, which has a problem that the electron-emitting characteristics are adversely affected.

In view of the above problems, the present invention improves the electron emission characteristics in the space charge limited current region,
Moreover, it is an object of the present invention to provide an impregnated cathode and a method for manufacturing the same, in which grid emission due to a large amount of evaporation of Ba and BaO is reduced.

[0008]

According to the present invention, there is provided an impregnated cathode comprising a heat-resistant porous metal substrate impregnated with an electron-emitting substance, the first layer on the surface of the electron-emitting substance-impregnated layer. And a second layer on the first layer containing scandium or scandium oxide.

In the present invention, it is preferable that scandium or scandium oxide contained in the first layer and the second layer is contained in the electron emitting material in an amount of 1 to 30% by weight.

Further, in the present invention, the thickness of the first layer is 5 μm.
m-0.3 mm, while the second layer has a thickness of 50 n
It is preferably m to 5 μm.

Further, according to the present invention, the above object is to impregnate a heat-resistant porous metal substrate with an electron-emitting substance containing no scandium or scandium oxide, and a heat-resistant porous metal substrate impregnated with the electron-emitting substance. Of the heat-resistant porous metal substrate from which the electron-emitting substance has been removed, and a step of incorporating scandium or scandium oxide into the surface layer and the upper layer thereof. And a method of manufacturing an impregnated cathode.

Further, according to the present invention, according to the present invention, a heat-resistant porous metal substrate is impregnated with an electron-emitting substance containing barium oxide, and a part of the electron-emitting substance containing barium oxide is part of the heat-resistant porous metal substrate. A method for producing an impregnated cathode, comprising a step of removing from the surface, wherein the electron-emitting substance is removed in pure water by ultrasonic vibration.

[0013]

According to the present invention, a sufficient amount of scandium (Sc) is contained in the upper layer (second layer) of the surface of the heat resistant porous metal substrate.
In addition, since a sufficient amount of Ba (barium) is replenished from the ordinary electron emitting substance in the lower layer portion (first layer) thereof, the electron emission characteristic is improved in the space charge limited current region. It Further, in the present invention, a part of the electron emitting substance such as BaO in the manufacturing process is removed in pure water,
Moreover, since the removal is performed by using ultrasonic vibration, the removal amount can be controlled cleanly and finely, the evaporation of BaO can be suppressed well while maintaining the electron emission characteristics, and the grid emission can be prevented.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of an impregnated cathode according to the present invention. As shown in FIG. 1, the impregnated cathode of the present invention has an electron emission material 1 containing Sc ₂ O _3.
Is provided on the upper layer b layer of the porous W (tungsten) substrate 3 and further on the heat-resistant porous metal substrate upper surface a layer. Therefore, the lower layer portion of the porous W substrate 3 is made of the electron emitting material 2 that does not contain Sc ₂ O ₃ .

The porous W substrate has a diameter of 1.5 mm, a thickness of 0.6 mm, and a porosity of 20 to 40%. In addition to W, Mo,
You may use Ir, Pt, Re, etc. and these alloys.

FIG. 2 is a flow chart showing the manufacturing process of the impregnated cathode according to the present invention. In the impregnated cathode according to the present invention, first, a W powder having a particle size of about 5 μm is used to form a porous W substrate 3 having a porosity of about 25%, and Sc _{2 is} added to the pores.
An electron emitting material 1 containing O ₃ and an electron emitting material ₂ not containing Sc ₂ O ₃ are impregnated to prepare a cathode pellet having the structure of the present invention. First of all, how to make it is BaO, CaO,
AlO ₂ O ₃ was mixed in a molar ratio of 4: 1: 1, S
The electron emitting material 2 containing no c ₂ O ₃ was placed on the upper and lower parts of the porous W substrate 3, heated to about 1700 ° C. in a vacuum or hydrogen atmosphere, and impregnated to form cathode pellets.

It is also possible to use a material having a molar ratio different from the above molar ratio as the electron emitting substance.

Then, as shown in FIG. 3, the impregnated cathode pellets 5 were placed in a 500 ml beaker 6 for 10 pieces (5 pieces).
4) with a specific resistance of 2 × 10 ⁶ Ωcm
Immerse in 100 ml of pure water 7. The number of cathode pellets 5 and the amount of pure water 7 are preferably smaller in the former case and larger in the latter case in consideration of the fact that the electron emission material is removed and discharged into the pure water 7. It may be allowed to overflow at all times.

After that, water 10 is poured into a container 9 containing an ultrasonic oscillator 8 and the above beaker 6 in which the cathode pellet 5 is immersed is placed in the container 9. Ultrasonic vibration is applied under the conditions of 200 W and 75 KHz to remove excess electrons. The released material was removed. As a result, holes (in the layer b in FIG. 1) for impregnating the electron emitting substance 2 containing Sc ₂ O ₃ are formed. The thickness of layer b can be adjusted by the temperature of pure water 7, the power of ultrasonic vibration, the frequency, the time, and the like.

BaO, C was added to the region (b layer) of the thus obtained porous W substrate from which the electron emitting substance was removed.
An electron-emitting substance prepared by blending aO and Al ₂ O ₃ in the same molar ratio of 4: 1: 1 as described above and adding Sc ₂ O ₃ at 10% by weight was placed and heated to 1700 ° C. in vacuum. Melted
Note Sc ₂ O ₃ may be used Sc ₂ O ₃ of the electron-emitting BaO above with different molar ratios as the substance 1, CaO and Al ₂ O ₃ material or different amount including, yet depending on the material It can be heated and melted at 1700 to 2000 ° C. In this process, by adjusting the weight of the electron emissive material 1 containing Sc ₂ O ₃ placed on top of the W substrate suitably comprises Sc ₂ O ₃ formed on the electron emission surface of the porous W base 3 The thickness of the electron emission material layer (FIG. 1-a layer) can be adjusted.

The cathode pellet thus produced is put into the Ta cup 12, and then the Ta cup 12 is resistance-welded or laser-welded to the Ta sleeve 13. Brazing may be used instead of welding. Cathode heating is W
This is performed using a heater 15 in which the core wire 14 is coated with alumina.

Using the impregnated cathode of the present invention thus produced, a DC voltage of 200 V is applied to the G2 electrode in a triode method, and the operating temperature of the cathode, that is, the heater voltage is continuously increased to 1 to 7 V. It was changed and the electron emission capability was measured. The results are shown in Fig. 4. The electron emission characteristic according to the present invention is a space charge limited current from an operating temperature of the cathode of about 750 ° C. _B, and about 800 ° C. in an electron tube such as a picture tube.
_{With B,} it is ready for practical use. However, conventional S
electron emission characteristic of c-based impregnated cathode has appeared deterioration of the electron emission characteristics during the so-called low voltage, unpractical also in the cathode operating temperature 900 ° C. _B. The conventional S
Japanese Patent Laid-Open No. 59-79934 discloses a c-type impregnated cathode.
As described in Japanese Patent Publication No. JP-A-2003-242, a composite porous substrate composed of a heat-resistant porous layer in which Sc ₂ O ₃ particles are dispersed and a heat-resistant porous body in which Sc ₂ O ₃ is not dispersed has a molar ratio of 4: 1: 1. BaO, C
A cathode impregnated with an electron emitting material composed of aO and Al ₂ O ₃ was used.

Further, the porous W of the impregnated cathode of the present invention
FIG. 5 shows the electron emission characteristics when the addition amount of Sc ₂ O ₃ among the electron emission substances occupying the upper layer of the substrate is changed. The base electron emitting material was BaO, CaO, and Al ₂ O ₃ in a molar ratio of 4: 1: 1, and the addition amount of Sc ₂ O ₃ was changed to 0 to 50% by weight. PC voltage 200 on G2 electrode by triode method
V was applied, the cathode temperature was fixed at 850 ° C. _B , and the emission current was measured. As a result, the added amount of Sc ₂ O ₃ is 1 to 30.
It was effective in the weight% range.

Further, the addition amount of Sc ₂ O ₃ is set to 5% by weight so that the thickness of 0.1 mm (FIG. 1b layer) becomes an electron emitting substance containing Sc from the surface to the inside of the porous tungsten substrate. FIG. 6 shows the characteristics when the thickness (FIG. 1a layer) formed on the surface of the porous tungsten substrate is changed. It was found that the thickness of part a is effective in the range of 50 nm to 5 μm.

Further, the characteristics when the thickness of the layer a is set to 1 μm and the thickness (layer of FIG. 1b) in which the electron emitting substance containing Sc is impregnated from the surface to the inside of the porous tungsten substrate is changed. It shows in FIG. The thickness of layer b is 5 μm to 0.3
It has been found to be effective in mm.

Further, a porous W substrate having a porosity of about 25%, which was produced by using W powder having a particle size of about 5 μm as in the above example, had a molar ratio of BaO, CaO and Al ₂ O ₃ of 4: The electron emitting substance mixed in a ratio of 1: 1 is heated to 1700 ° C. to be melted, and then ultrasonic vibration (200 W, 75 KHz) is applied for 5 minutes using the same device as in FIG. 30 μm was removed from the surface of the substrate. As described above, the cathode pellet from which the electron emission material has been removed is immersed in an organic solvent such as alcohol or acetone, and then 500 to 8 in vacuum.
Drying was performed by heating at 00 ° C. The reason why this drying is necessary is that if the electron emitting substance is removed and then left in the air as it is, the electron emitting substance is transformed into a hydroxide and the electron emitting characteristic is deteriorated.

The cathode pellets thus formed were coated with Ir by a sputtering method, and the electron emission characteristics were evaluated by a triode method as usual.

As a result, as shown in FIG. 8, the electron emission characteristics of the cathode from which the electron emission material is removed by the conventional method are deteriorated as compared with the characteristics of the cathode without the electron emission material, but according to the present invention. The characteristics of the cathode were as good as those of the cathode that did not remove the electron emitting material.

Further, since Ba or BaO has the largest amount of evaporation during the activation process of the cathode, the amount of evaporation when activated (heated in the electron tube) at 1200 ° C. for 1 hour was examined. 5 if not removed
-10 μg evaporated, 1-3 μ for cathode according to the invention
Therefore, it was found that it was also effective in reducing the evaporation of Ba / BaO.

[0031]

As described above, according to the present invention, the electron emission characteristics can be improved in the space charge limited current region and the grid emission can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of an impregnated cathode according to the present invention.

FIG. 2 is a flowchart showing a manufacturing process of an impregnated cathode.

FIG. 3 is a schematic diagram of an electron emission substance removing apparatus of the present invention.

FIG. 4 is a comparison diagram of electron emission characteristics of the present invention and a conventional Sc-based impregnated cathode.

FIG. 5 is a diagram showing the relationship between the amount of Sc ₂ O ₃ added and the electron emission characteristics in the electron emission material of the upper layer of the porous tungsten substrate of the present invention.

FIG. 6 is a diagram showing the relationship between the thickness of the layer “a” in the schematic diagram of the present invention and electron emission characteristics.

FIG. 7 is a diagram showing the relationship between the thickness of a schematic layer b of the present invention and electron emission characteristics.

FIG. 8 is a comparison diagram of electron emission characteristics of the cathode of the present invention, a cathode in which an electron emitting substance is not removed, and a cathode in which an electron emitting substance is removed by vacuum heating as a conventional example.

[Explanation of symbols]

Electron emission material 2 Sc ₂ O ₃ does not contain an electron emission material 3 porous W base 5 cathode pellet 6 beakers 7 Pure water 8 ultrasonic oscillator 9 container 10 water 12 Ta cup 13 Ta sleeve 14 containing 1 Sc ₂ O ₃ W core 15 Alumina coated heater

Claims (6)

[Claims] 1. An impregnated cathode obtained by impregnating a heat-resistant porous metal substrate with an electron-emitting substance, comprising: a first layer on the surface of the electron-emitting substance-impregnated layer; and a second layer on the first layer. An impregnated cathode comprising scandium or scandium oxide. 2. The electron-emitting substance contains scandium or scandium oxide contained in the first and second layers in an amount of 1 to 30% by weight.
The impregnated cathode described. 3. The thickness of the first layer is 5 μm to 0.3 mm.
2. The impregnated cathode according to claim 1, wherein the second layer has a thickness of 50 nm to 5 μm. 4. A step of impregnating a heat-resistant porous metal substrate with an electron-emitting substance containing no scandium or scandium oxide, the electron-emitting substance from the surface layer of the heat-resistant porous metal substrate impregnated with the electron-emitting substance. And a step of allowing scandium or scandium oxide to be contained in the surface layer portion of the heat-resistant porous metal substrate from which the electron-emitting substance has been removed and in the upper layer thereof. . 5. The method for producing an impregnated cathode according to claim 4, wherein the electron emission material is removed in pure water by ultrasonic vibration. 6. An impregnation step of impregnating a heat-resistant porous metal substrate with an electron-emitting substance containing barium oxide, and removing a part of the electron-emitting substance containing barium oxide from the surface of the heat-resistant porous metal substrate. A method of manufacturing an impregnated cathode, comprising removing the electron-emitting substance in pure water by ultrasonic vibration.