JPH02288041A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To extend the life under the operation by high current density by overlaying a scadium metallic powder layer and an electron emitter layer on a substrate. CONSTITUTION:The topside of the bottom of a substrate 1 whose main ingredient consists of nickel is covered with a scandium metallic powder layer 4, and this is covered with an electron emitter layer 5. Many irregularities are made at the surface of this scandium metal. As a result, the bonding strength of the substance layer 5 overlayed through this layer increases, and the use in a long time becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a cathode for an electron tube used in a di-braun tube for TV.

[Conventional technology]

Figure 2 shows a cathode used in a conventional di-cathode-ray cathode ray tube for TVs. A bottomed cylindrical base 2 made of nickel is coated on the bottom upper surface of the base 1, and contains at least barium (Ba) and an alkaline earth metal containing strontium (Sr) and/or calcium (Ca). The electron emitting material layer 3 made of oxide is a heater disposed within the base 1, and is for emitting thermoelectrons from the electron emitting material layer 2 by heating.

In the cathode for an electron tube having such a structure, the electron emitting material layer 2 is deposited on the substrate 1 in the following manner. First, a suspension consisting of a ternary carbonate of alkaline earth metals (Ba, Sr, Ca) is applied to the bottom upper surface of the substrate 1, and heated by the heater 3 during the evacuation process. At this time, the alkaline earth metal carbonate changes to an alkaline earth metal oxide. Thereafter, a part of the alkaline earth metal oxide is reduced and activated to have semiconductor properties, thereby obtaining an electron emitting material layer 2 made of the alkaline earth metal oxide on the substrate 1.

In the activation step, a portion of the alkaline earth metal oxide reacts as follows. That is, reducing elements such as silicon and magnesium in the substrate 1 move to the interface between the alkaline earth metal oxide and the substrate 1 by diffusion, and react with the alkaline earth metal oxide. If the metal oxide is barium oxide (Bad), the following formula (1
), reacts as shown in (2).

BaO+ '/2Si=Ba+3sio, ・
++ ・・-o) BaO10Mg =Ba+ MgO
--(2) Through this reaction, a part of the alkaline earth metal oxide on the substrate 1 is reduced and becomes an oxygen-deficient semiconductor,
The cathode temperature is 0.5-0.0 at an operating temperature of 700-800°C.
An electron emission of 8 A/cd will be obtained.

However, in the above cathode for an electron tube, the electron emission is 0.5~
A current density of 0.8 A/c- or higher cannot be obtained.

The reason for this is that when a part of the alkaline earth metal oxide is subjected to a reduction reaction, as is clear from the above equations (1) and (2), the interface between the substrate 1 and the alkaline earth metal oxide layer has a ,, A composite oxide layer (intermediate layer) such as MgO or BaO・SiO It is thought that a sufficient amount of barium (Ba) is not generated because it prevents the elements (Si, Mg) from diffusing to the surface side of the electron emitting material layer 2. In other words, during electron tube operation, the intermediate layer segregates near the interface between the substrate 1 and the electron emitting material layer 2, particularly at the nickel grain boundary near the surface of the substrate 1 and at a position about 10 mm inside the electron emitting material layer 2 from the interface. Therefore, the flow of current and the diffusion of the reducing element toward the surface of the electron emitting material layer 2 are hindered, resulting in a problem that sufficient electron emission characteristics under high current density cannot be obtained.

On the other hand, Japanese Patent Application No. 60-229303 discloses a method of incorporating 0.01 to 0.5% by weight of rare earth metal into the substrate. This is caused by oxidation of the substrate when alkaline earth metal carbonate decomposes during the activation described above when depositing an electron emitting material layer on the substrate, or when barium oxide undergoes a dissociation reaction during operation as a cathode. This is an attempt to prevent a reaction. In addition, the diffusion of the reducing element contained in the substrate into the electron emitting material layer is moderately controlled,
It is intended to prevent the intermediate layer made of a composite oxide of the reducing element from being formed intensively near the interface between the substrate and the electron emitting material layer, and to disperse the intermediate layer within the electron emitting material layer. In other words, the electron tube cathode of this second conventional example has excellent characteristics in that emission deterioration is reduced during high current density operation of about 1 to 2^/C- due to the dispersion of the intermediate layer. However, even in this cathode for an electron tube, there is a problem that emission deterioration is large when operating at a high current density exceeding 2 A/c+1, for example, 2.5 A/cJ.

Next, in Japanese Patent Application No. 60-160851, oxidation of the substrate is prevented by containing 0.1 to 20 MM% of rare earth metal oxide in the electron emitting material layer, as in the second conventional example mentioned above. A technique has been proposed in which the intermediate layer is dispersed. In this case, similarly to the above, the deterioration of emissions can be reduced by operating at a high current density of 2 A/c-. However, 2
In operation at a high current density of A/c+a or higher, evaporation of barium becomes significant due to Joule heat caused by the current flowing through the electron emitting material layer, and the electron emission characteristics may deteriorate.

In order to solve the above problems, the inventors
First, on a substrate whose main component is nickel, the main component is an alkaline earth metal oxide containing at least barium, which also contains a compound of scandium and one type of oxide of aluminum, silicon, titanium, etc. An electron tube cathode tube coated with an electron emissive material layer was proposed.

As a result, it was possible to provide a cathode for an electron tube that exhibits long-term stable emission characteristics even in high current density operation exceeding the above-mentioned 2A/c+a.

[Problem to be solved by the invention]

However, in the electron tube cathode previously proposed by the above inventors, peeling occurs, although very rarely, at the adhesion interface between the electron tube cathode base and the electron emitting material layer, especially after long-term use. This is a serious cause of deterioration of the emission characteristics of the cathode, which poses a problem of deteriorating the reliability of the product.

This invention has been made to solve these problems.

[Means for Solving the Problems] The present invention involves depositing scandium metal powder on a substrate whose main component is nickel, and further forming an electron-emitting material layer of an alkaline earth metal oxide containing at least barium thereon. This is a cathode for an electron tube, characterized in that it is formed by depositing.

[For production]

In this invention, scandium metal powder is first deposited on the substrate, this makes the surface rough, specifically, it has many irregularities, and an electron emitting material layer is deposited and formed on the surface. .

Therefore, the electron emitting material layer is embedded between the irregularities, and the peeling resistance at the interface is significantly increased.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In this figure, reference numeral 1 denotes a substrate whose main component is nickel, and this substrate 1 contains a reducing agent such as St or Mg.

Next, 4 is a scandium metal powder layer deposited on the bottom upper surface of the base 1. The average particle size of the scandium metal powder is desirably about 2 microns, but preferably in the range of 1 to 5 microns. Below this lower limit, the interfacial adhesion strength with the electron emitting material layer, which is the object of the present invention, will be insufficient, and above the upper limit, the film strength will be reduced, both of which are not preferred.

The binder used is not particularly limited, but for example, butyl acetate lacquer containing nitrocellulose is desirable. The above-mentioned scandium metal powder is dispersed in an amount of about 3% by weight, applied by a spray method, and dried. The dry film thickness is 5 to 20. The thickness is desirably about 10 microns.

Then, sintering is further performed at 1000° C. for about 5 minutes in a hydrogen atmosphere.

Next, 5 is an electron emitting material layer deposited on the scandium metal powder layer 4, and specifically, it is mainly composed of ternary oxides of barium, strontium, and calcium. Alkaline earth metal oxides such as barium mentioned above are
As described above, carbonate is first mixed, and as in the conventional method, it is formed through a process of decomposing the carbonate into an oxide and an activation process of reducing a part of the oxide.

Figure 3 shows a specific example of the present invention, in which scandium metal powder with an average particle size of 2 microns is sintered to a thickness of 10 microns on a substrate mainly composed of nickel, and then barium and strontium 5 calcium oxides are coated. What I wore (a)
Furthermore, as conventional examples, barium 5 strontium and calcium oxides containing 4% by weight of scandium oxide (b), and those containing no scandium oxide (C
) are respectively formed on the above-mentioned substrates by a method similar to the method described above to produce an electron tube cathode, and this electron tube cathode is used to produce a diode vacuum tube; 2.
This figure shows the results of investigating changes in emission current when a life test was performed by operating at a current H degree of 5^/c4.

According to the results shown in Fig. 3, compared to the electron emitting material layer (C) which does not contain scandium oxide, the embodiment of the present invention (a) exhibits significantly less emission deterioration over time and has a longer lifespan. Met.

Moreover, compared to (b) in which barium, strontium, and calcium oxides contain scandium oxide and are formed as a single layer on a substrate, the
After long-term use of up to 8,000 hours, the difference in emission deterioration was obvious.

The reason why the cathode for electron tubes of the present invention is able to maintain the above-mentioned excellent characteristics, which are higher than those of conventional products, is considered to be as follows.

(1) The scandium metal on the substrate creates many irregularities on its surface, which increases the adhesion strength of the electron emitting material layer deposited through this layer and maintains this for long periods of use. It turns out.

(11) The presence of the scandium metal layer between the substrate and the electron emitting material layer improves the current density, which also contributes to the improvement of the above characteristics.

〔Effect of the invention〕

As described above, the cathode for an electron tube of the present invention is made by depositing scandium metal powder on a substrate mainly composed of nickel, and depositing an alkaline earth metal oxide containing at least barium thereon. Due to the presence of the scandium metal powder layer, the adhesion interface between the substrate and the electron emitting material layer is maintained stably, and the current density is also improved. It has the effect of achieving a long lifespan in the fruit.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a cathode for an electron tube according to an embodiment of the present invention, Fig. 2 is a sectional view showing a conventional cathode for an electron tube, and Fig. 3 is a life test time of a diode vacuum tube using the cathode for an electron tube. FIG. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A cathode for an electron tube, characterized in that scandium metal powder is deposited on a substrate mainly composed of nickel, and an electron emitting material layer of an alkaline earth metal oxide containing at least barium is further deposited thereon. .