JPH07107824B2 - Electron tube 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 cathode for an electron tube used in a cathode ray tube or the like.

[0002]

2. Description of the Related Art FIG. 4 shows, for example, Japanese Examined Patent Publication No.
FIG. 3 is a partially enlarged cross-sectional view of a cathode for an electron tube used in a conventional cathode ray tube for a television receiver and an image pickup tube disclosed in Japanese Patent Laid-Open Publication No. H11-242242. In FIG. 4, (1) is silicon (S
i), a cap-like base metal containing a trace amount of reducing elements such as magnesium (Mg), the main component of which is nickel (Ni) closed at one end, and welded to one end of a substantially cylindrical sleeve (4) It is fixed. (2) is an electron-emitting material layer formed by coating on the upper surface of the top of the base metal (1), which is closed at one end. The electron emitting material layer (2) contains barium (Ba), and also contains strontium (Sr) and calcium (C).
This is a structure in which a rare earth metal oxide (22) such as scandium oxide is dispersed in a ternary alkaline earth metal oxide (21) containing a). (3) is a heater arranged in the sleeve (4), the base metal (1) is heated by heating the heater (3), and thermoelectrons are emitted from the electron-emitting substance layer (2). Be punished.

Next, a method of depositing and forming the electron-emitting substance layer (2) on the base metal (1) in the electron tube cathode thus constructed will be described.

First, a ternary carbonate of barium, strontium and calcium and a predetermined amount of scandium oxide are mixed with nitrocellulose which is a binder and butyl acetate which is an organic solvent to prepare a suspension, and this suspension is prepared. Is applied to the top of the base metal (1) by a spray method or the like to form a film which becomes the electron emitting material layer (2). Then, this cathode is incorporated into an electron gun and heated by a heater (3) during the cathode ray tube evacuation process. At this time, the ternary carbonate is converted to the alkaline earth metal oxide (21) by thermal decomposition. After the exhausting step, activation is performed by heating at a higher temperature. At this time, a part of the alkaline earth metal oxide (21) is reduced so that the electron emitting material layer (2) has a semiconducting property, and the alkaline earth metal oxide (2) is formed on the base metal (1). Electron emitting material layer consisting of a mixture of 21) and a rare earth metal oxide (22)
(2) is formed.

In this activation step, a part of the alkaline earth metal oxide (21) reacts as follows. That is, reducing elements such as silicon and magnesium contained in the base metal (1) move to the interface between the alkaline earth metal oxide (21) and the base metal (1) by diffusion, and Reacts with (21). For example, when barium oxide (BaO) is taken as an example of the alkaline earth metal oxide (21), it reacts as in the following formulas (I) and (II).

4BaO + Si → 2Ba + Ba₂SiO_Four (I) BaO + Mg → Ba + MgO (II) As a result of this reaction, it is deposited on the base metal (1).
Part of the alkaline earth metal oxide (21) is reduced to oxygen.
It becomes a depletion type semiconductor, and electron emission becomes easy. Electronic release
If the rare earth metal oxide (22) is not contained in the material layer (2)
Or 0.5-0.8A at operating temperature of cathode temperature 700-800 ℃
/cm² Current density operation is possible. On the other hand, electron emitter
Rare earth metal oxides such as scandium oxide (2
2) included, 1.32 to 2.64 A at the same operating temperature
/cm²It enables high current density operation.

In general, in the case of an oxide cathode, the operable current density is small when the rare earth metal oxide is not contained, and the electron emission capability depends on the amount of excess Ba present in the oxide. Therefore, if the rare earth metal oxide (22) is not contained, the sufficient excess Ba required for high current density operation is not supplied, and the maximum operable current density is restricted. That is, it is a by-product generated during the above reaction and is called barium silicate (Ba ₂ Si) called an intermediate layer.
O ₂ ) and magnesium oxide (MgO) are nickel crystal grain boundaries of the base metal (1) or the base metal (1) and the electron emitting material layer (2)
Since it is formed intensively at the interface with the, the diffusion rate of magnesium and silicon is suppressed by the influence of this intermediate layer, and as a result, the supply of excess Ba is insufficient. On the other hand, a rare earth metal oxide (22) is formed on the electron emitting material layer (2).
In the case of scandium oxide as an example, the base metal (1) and the electron-emitting material layer (2) during cathode operation are included.
At the interface with and, a part of the reducing agent that has diffused and moved in the base metal (1) and suncadium oxide react as in the following formula (III) to generate a small amount of metallic scandium, and the metallic scandium Is partially dissolved in nickel of the base metal (1), and a part thereof is present at the interface.

1 / 2Sc ₂ O ₃ + 3 / 2Mg → Sc + 3 / 2MgO (III) This metallic scandium is formed on the base metal (1) or at the nickel crystal grain boundary of the base metal (1). Since it has the action of decomposing B as shown in the following formula (IV), the excess B
It is believed that the supply of a will be improved and that higher current density operation will be possible than if the rare earth metal oxide (22) were not included.

1 / 2Ba ₂ SiO ₄ + 4 / 3Sc → Ba + 1 / 2Si + 2 / 3Sc ₂ O ₃ (IV)

[0010]

In the cathode for an electron tube having such a structure, the rare earth metal oxide is excessive in Ba.
However, the supply rate of excess Ba is limited by the diffusion rate of a small amount of reducing agent present in nickel, which is the base metal, and the life characteristics deteriorate at high current density operation of 2 A / cm ² or more. I have a problem.

Further, since the rare earth metal oxide has a function of decomposing the intermediate layer as described above, it has an effect of suppressing the formation of the intermediate layer substance such as barium silicate on the surface of the base metal, but Since the adhesion of the electron emitting material layer to the base metal is weakened during operation for a long time, there is also a problem that the electron emitting material layer separates from the base metal and floats up during operation. Therefore, since the distance from the first grid arranged facing the cathode varies,
There are problems that the cutoff voltage fluctuates and the screen brightness gradually fluctuates, and in the case of a color CRT, the color tone fluctuates during long-time operation.

[0012]

According to the present invention, a tungsten powder layer is provided on a base metal containing nickel as a main component and containing at least one reducing agent, and an alkaline earth metal containing at least barium is provided thereon. The present invention relates to a cathode for an electron tube, which is formed by depositing an electron emitting material layer made of an oxide and a rare earth metal oxide.

[0013]

[Function] In the present invention, the tungsten powder layer provides excess Ba.
2A / cm to contribute to salary² For high current density operation above
It is possible to improve the life characteristics.

Further, the tungsten powder layer can solve the drawback that the electron emitting material layer is easily separated from the base metal during long-term operation, and the reliability of the cathode is greatly improved.

[0015]

EXAMPLES In the present invention, a base metal containing nickel as a main component and containing at least one kind, usually 2 to 4 kinds of reducing agents is used.

Examples of the reducing agent include silicon,
Examples include magnesium, zirconium, and tungsten.

In the base metal, the ratio of the reducing agent is usually 0.01 to 3
% (Weight%, the same applies hereinafter) is used.

A tungsten powder layer is provided on the base metal.

From the standpoint of workability, the particle size of the tungsten powder is preferably 0.5 to 1.0 μm. The thickness of the tungsten powder layer is preferably 0.5-5 μm, and 2-3 μm
Is more preferable. If the thickness is less than 0.5 μm, the coating tends to be difficult to be uniform, and the thickness is 5 μm.
If it exceeds, the reaction between the base metal and the electron emitting substance tends to be slow.

In the cathode for an electron tube of the present invention, an electron emitting material layer made of an alkaline earth metal oxide containing at least barium and a rare earth metal oxide is deposited on the tungsten powder layer.

The alkaline earth metal oxide contains strontium, calcium and the like in addition to barium.

The rare earth metal oxide is a component dispersed in the alkaline earth metal oxide, and specific examples thereof include scandium oxide and yttrium oxide.

The proportion of the alkaline earth metal oxide in the electron emitting material layer is preferably 90 to 99%, and the proportion of the rare earth metal oxide is preferably 1 to 10%.

The thickness of the electron emitting material layer is preferably about 60 to 100 μm.

Next, an example of a method for producing the cathode for an electron tube of the present invention will be described.

First, after welding the base metal to the sleeve,
Heat treatment such as cleaning and hydrogen treatment is performed to remove surface dirt and oxide layer.

Next, the tungsten powder, a binder such as nitrification cotton, and an organic solvent such as butyl acetate are uniformly mixed in a ball mill or the like for about 24 to 48 hours, coated on a base metal by a spray method or the like, and then heat treated. Is performed to form a tungsten powder layer on the base metal. The ratio of the binder and the organic solvent used is not particularly limited. The heat treatment is preferably performed in a hydrogen atmosphere or a vacuum atmosphere of about 10 ⁻⁵ Torr or less from the viewpoint of removing the oxide layer on the surface layer of the tungsten powder and decomposing the binder. Processing temperature is 800-1000 ℃, processing time is 10
It is preferably -30 minutes.

Next, a suspension prepared by mixing the powder of alkaline earth metal carbonate and the powder of rare earth metal oxide with butyl acetate, nitrification cotton, etc. on the tungsten powder layer by a spray method or the like. By coating, the cathode for an electron tube of the present invention is manufactured. The cathode for an electron tube of the present invention as described above is a cathode ray tube for a display that takes out a narrow electron beam in order to achieve high resolution, a projection type cathode ray tube or a large cathode ray tube for flowing a large current to achieve high brightness, and further a large current. It is also suitable for power tubes such as traveling wave tubes required.

Next, one embodiment of the present invention will be described more specifically with reference to FIG.

In FIG. 1, (1) is a cap-shaped base metal whose one end is closed, and is fixed to one end of a substantially cylindrical sleeve (4). (5) is a tungsten powder layer deposited on the top surface of the base metal (1) closed at one end,
Further, an electron-emitting substance layer (2) is formed on it. In the electron emitting material layer (2), the alkaline earth metal oxide (2
Rare earth metal oxide (22) is dispersed in 1). (3) is inserted and disposed in the sleeve (4) and is a base metal (1)
Is a heater for heating the, and by heating the heater (3), thermoelectrons are emitted from the electron-emitting substance layer (2). Example 1 and Comparative Example 1 First, the main component was nickel, and a trace amount of magnesium (0.05%), silicon (0.
After welding the base metal (1) consisting of 05%) to the sleeve (4), cleaning and hydrogen treatment at 1000 ° C. for 5 minutes were performed to remove surface stains and oxide layers.

Next, 100 g of tungsten powder having a particle size of 0.5 to 1.0 μm was mixed with 5 g of nitrification cotton as a binder and 500 ml of butyl acetate solution as an organic solvent and mixed in a ball mill for 24 hours. The obtained mixture was applied onto the base metal (1) by a usual spraying method so that the thickness after drying was about 2 μm, and then naturally dried to form a tungsten powder layer (5).

Next, scandium oxide and an alkaline earth metal carbonate were mixed with butyl acetate and nitrification cotton. The thickness of the resulting mixed solution after spraying is about 80.
It was coated on the tungsten powder layer (5) so as to have a thickness of μm and dried. In this way, an electron emitting material layer (2) in which scandium oxide was dispersed in an alkaline earth metal oxide in a weight ratio of about 3% was formed.

The obtained cathode for an electron tube was incorporated into an electron gun for a cathode ray tube, a heater voltage was set to 6.3 V, and a current drawn from the cathode was set to 2 A / cm ² , and a life test was conducted on a 14-inch cathode ray tube for a display. The results are shown in Figure 2. In FIG. 2, the horizontal axis represents the life test time and the vertical axis represents the cathode current value, which is shown as a relative value with the initial value being 100.

As a comparative example, a conventional cathode for an electron tube having no tungsten powder layer was similarly evaluated.

From FIG. 2, it can be seen that the cathode current of the cathode for an electron tube of the present invention is less deteriorated as compared with the conventional one.

The reason why the life characteristics of the cathode for an electron tube of the present invention are good is presumed as follows.

The excess Ba is produced as shown in the above formulas (I) and (II) by the action of the reducing impurities contained in the base metal (1). In addition to this, the tungsten powder layer (5) reacts as in the formula (V): 2BaO + 1 / 3W → Ba + 1 / 3Ba ₃ WO ₆ (V) to contribute to the production of excess Ba. As described above, since the excess Ba is generated more than the conventional one, it is considered that the load is reduced even in the high current density operation and the life characteristics are favorably changed.

Further, since the cathode powder for an electron tube of Example 1 is provided with the tungsten powder layer, the adhesion of the electron emitting material layer to the base metal is improved, and even if the electron emitting material layer is operated for a long period of time, the electron emitting material layer is locally localized. It was possible to prevent the floating. FIG. 3 is a graph showing the variation of the cutoff voltage,
It can be seen that the rise of the electron emitting material layer (2) is reduced and the cutoff voltage is more stable than the conventional one.

[0039]

As described above, in the cathode for an electron tube of the present invention, since the tungsten powder layer is formed between the electron emitting material layer containing the rare earth metal oxide and the base metal, excess Ba is not produced. Facilitates high current density operation. Furthermore, since the tungsten powder layer improves the bondability between the electron emitting material layer and the base metal, stable high current density operation is possible for a long time. Therefore, it can be applied to a high-luminance and high-definition cathode ray tube, which has a problem with the conventional cathode for an electron tube.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional view of a cathode for an electron tube of the present invention.

FIG. 2 is a graph showing changes in cathode current with time.

FIG. 3 is a graph showing changes in cutoff voltage.

FIG. 4 is a partially enlarged cross-sectional view of a conventional cathode for an electron tube.

[Explanation of symbols]

 1 Base Metal 2 Electron Emitting Material Layer 3 Heater 4 Sleeve 5 Tungsten Powder Layer 21 Alkaline Earth Metal Oxide 22 Rare Earth Metal Oxide

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiji Watanabe 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Corporation Life Systems Research Institute (72) Masato Saito 2-14, Ofuna, Kamakura, Kanagawa Prefecture No. 40 Mitsubishi Electric Corporation Living Systems Laboratory (72) Inventor Akira Suzuki 2-14-20 Ofuna, Kamakura-shi, Kanagawa Prefecture Mitsubishi Electric Corporation Living Systems Laboratory (72) Inventor Keiji Fukuyama 2-chome Ofuna, Kamakura-shi, Kanagawa 14-40 Mitsubishi Electric Co., Ltd. Living Systems Research Laboratory (72) Inventor Takuya Ohira 2-14-40 Ofuna, Kamakura-shi, Kanagawa Mitsubishi Electric Corporation Living Systems Research Laboratory (56) Reference JP-A-3-163724 ( JP, A)

Claims (1)

[Claims] 1. The main component is nickel, and at least 1.
A cathode for an electron tube, in which a tungsten powder layer is provided on a base metal containing a reducing agent of some kind, and an electron emitting material layer made of an alkaline earth metal oxide containing at least barium and a rare earth metal oxide is formed thereon. .