JPS62193031A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To enable the use of a cathode at a high current density, by providing a sintered nickel powder layer and an electron emission substance layer made by dispersing scandium oxide powder in an alkaline earth metal oxide containing barium on the surface of a base metal. CONSTITUTION:When an indirectly heated cathode for an electron tube is formed, a sintered nickel power layer 4 is first provided with a thickness of 10-50mu on the surface of a base metal 1 of nickel in which a heater 3 is housed. A suspension made by dispersing scandium oxide powder 2b in alkaline earth metal oxide 2a containing barium is applied to the surface of the sintered layer 4 and then subjected to and evacuation and heating process so that an electron emission substance layer 2 is made on the sintered layer. Since the sintered layer 4 is interposed, the reduction of electric conductivity due to the formation of an intermediate layer is prevented. The reaction between the scandium oxide and the alkaline earth metal oxide creates free barium to increase the electric conductivity. As a result, the cathode can thus be used at a higher current density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an indirectly heated cathode used in an electron tube such as a cathode ray tube for a display, and is particularly directed to improving the electron emission characteristics thereof.

[Conventional technology]

Conventionally, this type of cathode has been made by depositing an alkaline earth metal oxide layer containing Ba on a base metal mainly composed of nickel. With the high-definition ablation of tubes, there is an increasing demand for using +m current density.

However, with conventional cathodes, the sail 5~0.8A/am2
There is a limit to its use at a current density of 1,000,000,000 yen, and if it is used at a current density higher than this, the problem arises that the life of the cathode will be shortened.

Figure 2 is a longitudinal cross-sectional view showing the structure of a conventional cathode used in display cathode ray tubes and image pickup tubes, where fl+ is S
i, a base metal made of nickel containing a small amount of reducing elements such as Mg; (2) is an electron emitting material layer deposited and formed on the surface of the base metal (11);

Free Ba formed in ternary alkaline earth metal oxides of Ca
It is included. (This is a heater that heats the electron emitting material layer (21) through the base metal (11). The suspended coating liquid is applied onto the surface of the base metal +l+ by a method such as spraying, and in the vacuum evacuation step, it is heated by a heater (31) to convert the carbonate into an oxide, and then the decomposition step is performed at 900~
Electron emissivity is obtained by heating to 1100° C. to reduce part of the oxide, remove oxygen, and make it have semiconductor properties. The reason why a trace amount of reducing elements such as Si and Mg is contained in the base metal (11) is to cause a reduction reaction to occur during the activation process. moves to the interface between the alkaline earth metal oxide and the base metal fi+ by diffusion and reacts with the alkaline earth metal oxide.For example, BaO reacts as follows.

2 BaO+Si = 2Ba+5iOzBaO+Mg
= Ba + MgO As a result, a part of the alkaline earth metal oxide is reduced to become an oxygen-deficient semiconductor, and the cathode temperature increases from '700 to Boo.
An electron-emissive material layer (2) is obtained which can be used at a current density of 0.5-0.8 A/am'' at an operating temperature of .degree.

Although the conventional cathode cannot extract a current higher than the above, ■ As a result of the reduction reaction in the activation process, the base metal + I
5i02. at the interface between + and the electron emitting material layer (2). Mg
An oxide layer (intermediate layer) such as O is formed, and this intermediate layer becomes a high resistance layer and prevents the flow of current.

(2) This is thought to be due to the fact that the presence of the intermediate layer prevents the reaction between the alkaline earth metal oxide and the reducing element from being suppressed, preventing sufficient Ba from being produced.

[Problem to be Solved by the Invention 1] As described above, in the conventional cathode, an intermediate layer is not formed at the interface of the fully curved substrate [II hepta-alkaline earth metal intoxicate layer (2)] in the activation process. However, there was a problem in that it could not be used at high current densities.

This invention was made to solve the above problems, and provides a cathode that can be used at high current densities by reducing the effects of suppressing high current electron emission and suppressing the generation of free Ba due to the presence of the intermediate layer. The purpose is to

[Means for solving problems]

The cathode according to this invention has a nickel powder sintered layer on the nickel A/substrate metal, and an electron emitting layer on which scandium oxide (S0203) powder is dispersed in an alkaline earth sulfide. The material layers are numbered.

[Effect]

The nickel powder sintered layer on the nickel substrate forms the middle layer,
In addition, the scandium oxide powder dispersed in the alkaline earth metal oxide increases the conductivity of the electron emitting material layer, and also prevents the scandium oxide from interacting with the alkaline earth metal oxide. The junction oxide produced by the reaction, for example Ba5Sc409, undergoes thermal decomposition during operation of the cathode to produce free Ba, which acts to increase thermionic emission.

〔Example〕

An embodiment of the present invention will be explained below using diagram vJ1.

Mix nickel metal powder with a particle size of 3 to 5 microns with cellulose lacquer, butyl acetate, etc. to create a suspension, and spray the nickel base metal powder to a thickness of about 30 microns. The sintered layer (41) of the above nickel metal powder was prepared by applying heat treatment on the nickel metal powder for 10 minutes at 100'C in a hydrogen atmosphere. 5.0 weight percent of scandium oxide powder was added and mixed, and nitrocellulose lacquer and butyl acetate were added to the mixture and mixed by rolling to prepare a suspension.This suspension was poured onto the sintered layer (4). The cathode was fabricated by applying the coating to a thickness of approximately 80 microns by a spray method and performing an exhaust heating process and an activation process under the same conditions as before. (21 is the electron emitting material layer, (2a)/f'i Alkaline earth metal oxide produced by thermal decomposition of alkaline earth metal carbonate, (2b)t
It is scandium powder.

When a diode vacuum tube was made and tested using the cathode manufactured in this way, the operating temperature of the cathode was found to be between '700 and '80.
It was confirmed that an electron emission characteristic of 1 to 2 A/cm2 was obtained at 0°C, and that it could be used for a long period of time at a higher current density than conventional products.

The reason why good electron emission was obtained in the above practical example VC is considered to be due to the following reasons.

■ The scandium oxide powder (2b) added and mixed in the electron emitting material layer (21) is an alkaline earth metal oxide (2a).
For example, a complex oxide (Bas
Sc<09) is dispersed in the electron emitting material layer (2), and this composite oxide prevents thermal decomposition from occurring during operation of the cathode to generate free Ba. Free B in conventional cathode
aO raw W contains a trace amount of Sl in the base metal (1).
However, in this example, free Ba generated by thermal decomposition of the composite oxide is added, so even if the intermediate layer suppresses the reduction reaction. Even if the amount of free Ba is increased, the amount of free Ba will not be insufficient.

(2) A part of Sc in the composite oxide is liberated and becomes metallic scandium, which is distributed throughout the electron emitting material layer (2).

Due to the presence of this metal scandium, the electron emitting material FT+
The conductivity of the electron emitting material layer (2) increases, compensating for the decrease in conductivity due to the intermediate layer, and improves the conductivity of the electron emitting material layer (2).

■ A sintered layer (41) made of nickel powder is porous, and a part of the electron emitting material layer (2) coated on top of this sintered layer (41) penetrates into the nickel-based gold layer (41). IU
[In contact with +1, the intermediate layer absorbs live in this part, but most of the electron emitting material layer (21 is in contact with the sintered layer (41), so the conductivity decreases due to the formation of the intermediate layer. can be prevented.

The thickness of the nickel powder sintered layer (41) formed on the nickel base metal (11) is preferably 10 to 50 microns. If the thickness is 10 microns or less, the intermediate layer In addition, if the thickness exceeds 50 microns, the alkaline earth metal oxide may not penetrate sufficiently into the sintered layer (41).
, the proportion of contact with the nickel-based metal (11) is small (
This means that the cathode is sufficiently activated.

Furthermore, regarding the scandium oxide powder added to the electron emitting material layer (21), an example was explained in which a 5.0 weight ratio was mixed, but if the amount of scandium oxide mixed is less than 0.1 weight ratio, the effect is small and it is not practical. On the other hand, when the amount of the mixture exceeds 20% by weight, the initial properties become poor and it is not practical.

〔Effect of the invention〕

As described above, the present invention involves depositing a uniformly dispersed mixture of alkaline earth metal carbonate powder and scandium oxide powder on the surface of a base metal provided with a sintered layer of nickel metal powder. Since it is a formed cathode, the action of generating free Ba by the composite oxide produced by scandium oxide dispersed in the electron emitting material layer, the action of increasing the conductivity of the electron emitting material layer, and the action of increasing the conductivity of the sintered layer. The interposition prevents a decrease in conductivity due to the formation of an intermediate layer, resulting in an electron tube cathode that can be used at a higher current density than conventional cathodes.

[Brief explanation of drawings]

FIG. 11 is a longitudinal sectional view showing an example of the electron tube cathode of the present invention;
FIG. 2 is a longitudinal sectional view showing a conventional electron tube cathode. (11...Base metal, (2)...Electron emitting material layer,
(2a)...alkaline earth oxide, (2b)...
- Scandium oxide powder, (4)...sintered layer. In addition, in FIG. 1, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A sintered layer of nickel powder with a thickness of 10 to 50 microns on the surface of a nickel base metal, and scandium oxide powder dispersed in an alkaline earth metal oxide containing barium. and an electron emissive material layer deposited on the sintered layer.