KR920004552B1 - Dispenser cathode - Google Patents

Abstract

The dispenser cathode is produced by storing a molded material of with sea Ba-Ca-aluminate powder and W powder as an electron emitting material in the U-type cup, putting a porous tungsten substrate on the cup and the molded material, inserting them into the sleeve, and forming a thin film on the substrate. The thin film of 5-6000 nm thickness is composed of (Ba, Sr or Ca) CO3 powder, butyl acetate and nitrocellulose. The substrate is obtained by mixing W powder of 3-8 μm particle diameter with 5 wt.% Sc2O3, molding the mixt., and sintering the molded material. The cathode for CRT has a high current density.

Description

Dispenser cathode

1 is a longitudinal cross-sectional view of a dispenser cathode manufactured by one embodiment of the present invention.

2 is a longitudinal sectional view of the dispenser cathode according to another embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

1: thin film layer 2: porous tungsten gas

2 ': composite porous tungsten base 3: molded body

4: reservoir 5: sleeve

6: heater

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dispenser cathodes used in cathode ray tubes, such as CRTs, and more particularly to dispenser cathodes having long life and high current density characteristics capable of low temperature operation.

Conventional dispenser negative electrode or impregnated negative electrode impregnates the electron emitting material containing Ba as a main component in the pores of porous high melting point metal gas such as W, Mo, or a molded article impregnated with the electron emitting material in a storage tank made of Mo or the like. And a porous metal cover made of W, Mo, etc. on the upper part of the molded body, which is called a dispenser cathode by the operation principle that Ba is diffused and distributed from the surface of the porous metal cover during operation of the cathode. have.

Such a dispenser cathode is a cathode having a long life and high current density characteristics, which is promising as a cathode for improving the performance of a CRT or an electron tube, for example, high quality and high brightness. In this case, the electrode material must be changed, and also the reliability of the heater cannot be guaranteed. In order to solve the shortcomings of high temperature operation, there are so-called M-type or MM (mixed matrix) type cathodes in which metals such as Os, Ru, Ir, and Re are coated on the surface of the impregnated cathode, but the operating temperature is 950-1050. The impregnated cathode prepared by coating a surface of the impregnated cathode with Sc or Sc ₂ O ₃ or using a porous metal gas containing these materials has a low operating temperature of 850 to 900 ° C. However, such an improved negative electrode requires a long activation time of 10 hours or longer at a temperature of, for example, about 1250 ° C. in order to have high current density at its operating temperature.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a dispenser cathode capable of shortening an activation time and high current density in low temperature operation.

Another object of the present invention is to provide a novel dispenser cathode, which shortens the manufacturing time of the cathode, improves productivity and enables low temperature operation, thereby requiring no change of the electrode component and the change of the heater.

Still another object of the present invention is to provide a dispenser cathode which can be applied to any of the negative electrode of the impregnation type and the storage type.

In order to achieve the above object, the dispenser cathode according to the present invention comprises a u-shaped storage tank formed of Mo, a molded body for compressing and storing an electron-emitting material in the storage tank, a heater and a sleeve for heating the cathode to release hot electrons. In the present invention, the porous tungsten gas formed by compressing and uniformly mixing Sc oxide with W powder is laminated on the upper part of the storage tank in which the molded body is stored, and BaO or BaCO ₃ is mainly contained on the upper surface of the porous tungsten gas. It is characterized by consisting of a thin film layer coated with a material.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a longitudinal cross-sectional view of a dispenser cathode prepared according to one embodiment of the present invention.

The dispenser cathode according to the figure is compression-molded by forming a u-shaped Mo reservoir 4 by press or the like, and then mixing barium-calcium-aluminate powder and W powder therein. One molded body 3 is mounted.

After disposing the porous tungsten gas 2 mixed with W and Sc ₂ O ₃ at the upper end of the reservoir 4 and the molded body 3, it is inserted into the sleeve 5 formed of Mo and welded thereto.

In the above, the porous tungsten gas 2 is press-molded by uniformly mixing 5 wt% of Sc ₂ O ₃ powder with W powder having a particle diameter of 3 to 8 μm, and then sintered in a reducing (hydrogen) atmosphere, and finally sintered in vacuum. Thus, the porosity is 15 to 30% of the porous gas.

And a porous tungsten gas (2) inserted into the sleeve (5) and welded to form a thin film layer (1) on the upper surface of the cathode, which (Ba, Sr, Ca) CO ₃ powder is transferred to butyl acetate and nitrocellulose. The dispersed dispersion is applied by spraying so as to have a thickness of 5 to 6000 nm.

The thin film layer 1 may be deposited or coated with an oxide containing BaO as a main component by sputtering or other thin film formation coating method. Nitrocellulose as a binder used to form the thin film layer 1 starts to evaporate when heated to about 300 ° C., and when heated to about 1000 ° C., carbonate is decomposed to become an oxide.

The relationship in which hot electrons are emitted from the dispenser cathode having the structure as described above will be described.

First, when the heater 6 is heated, barium-calcium-aluminate, W (tungsten), which is an electron-emitting material in the molded body 3 mounted on the storage tank 4, is reacted to generate free Ba (barium) by the heat. , a glass Ba is spread on the surface of the processing unit through a porous tungsten body (2) mixed in a W and Sc ₂ O _3. As such, when Ba is diffused from the surface of the porous tungsten gas 2, Ba, Sc, and O are combined to form a monomolecular layer composed of Ba-Sc-O, and the monomolecular layer serves to lower the work function. Also emits hot electrons.

In the present invention, in order to shorten the activation time of the cathode, a thin film layer 1 containing Ba as a main component is formed, which ensures hot electron emission until a monomolecular layer of Ba-Sc-O is formed. That is, since the thin film layer 1 mainly containing Ba easily emits hot electrons at a relatively low temperature, for example, 850 ° C. or lower, sufficient hot electrons can be emitted even during low temperature operation, while Ba-Sc-O is used. Since the formed monomolecular layer is sufficiently formed, activation is performed in a short time, thereby obtaining a high current density (10 A / cm 2).

As another method of forming the porous tungsten gas 2 composed of W and Sc ₂ O ₃ in the dispenser cathode as described above, a porous tungsten gas having a suitable porosity is first produced, and then a Sc ₂ O ₃ layer is formed on the surface thereof. You may form the oxide thin film layer 1 which has Ba as a main component.

Meanwhile, the dispenser negative electrode shown in FIG. 2 illustrates another embodiment of the present invention.

In FIG. 2, the composite porous tungsten base 2 'is stored in a storage tank 4 made of heat-resistant high melting point metal, and the composite porous tungsten base 2' is barium-calcium in the pores of the compression molded body made of W. In FIG. After melt-impregnating the mixed powder of aluminate and Sc ₂ O ₃ at a temperature of about 1450 ° C., BaO or BaCO ₃ is mainly used on the top of the sleeve 5 and the reservoir 4 as shown in FIG. The thin film layer 1 is formed.

As such, when the mixed powder of barium-calcium-aluminate and Sc ₂ O ₃ is melted and impregnated, Sc ₂ O ₃ does not melt at 1450 ° C., so it penetrates into the pores with the melt, but is distributed in a larger amount on the surface. Therefore, there is an effect that it greatly contributes to the formation of a single molecule layer of Ba-Sc-O on the surface. Another application example in this embodiment is a thin film layer containing BaO or BaCO ₃ as a main component by melting and impregnating barium-calcium-aluminate in the pores of a composite porous tungsten gas composed of W and Sc ₂ O ₃ . It goes without saying that the same effect can be obtained even when forming (1).

As described above, according to the dispenser cathode of the present invention, the time required for the activation process is greatly shortened, thereby contributing to the improvement of productivity, and at the same time, a high current density can be obtained for a long time even at low temperature.

In addition, when the dispenser cathode according to the present invention is employed in an electron tube such as a cathode ray tube, it is possible to operate at a low temperature, thereby preventing deformation of the electrode component and the heater due to heat, and thus have stable electron emission characteristics for a long time. There is an excellent effect to provide a long-life dispenser cathode.

Claims (5)

In the storage tank 4 formed of Mo (molybdenum), the molded body 3 is formed by compression-molding the electron-emitting material, and the heater 6 and the sleeve 5 for heating the cathode are provided. The tungsten gas 2 formed by compressing and uniformly mixing Sc oxide with W powder is laminated on the upper portion of the storage tank 4 equipped with the _c ), and BaO or BaCO ₃ is deposited on the upper surface of the porous tungsten gas 2. A dispenser cathode, which is formed by forming a thin film layer (1) coated with a main material. The dispenser cathode according to claim 1, wherein the thin film layer (1) has a thickness of 5 to 6000 nm. The dispenser negative electrode according to claim 1, wherein the molded body (3) is compression molded by mixing barium-calcium-aluminate and W powder. A dispenser cathode comprising a sleeve (5) for receiving and supporting a U-shaped reservoir (4) composed of Mo, and a heater (6) for heating a cathode to emit hot electrons, wherein the reservoir (4) is formed of W. The porous porous tungsten gas 2 ', in which the mixed powder of barium-calcium-aluminate and Sc ₂ O ₃ is melt-impregnated at a temperature of about 1450 ° C, is stored in the pores of the molded body 3, and the composite porous tungsten gas A dispenser cathode characterized in that a thin film layer (1) formed by coating a material containing BaO or BaCO ₃ as a main component is laminated on an upper surface of a storage tank (4) in which (2 ') is stored. The dispenser cathode according to claim 4, wherein the thin film layer (1) has a thickness of 5 to 6000 nm.

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