JPS62165832A - Cathode for electron tube - Google Patents

Abstract

PURPOSE:To realize a long service life under a high current density operation, by spreading and forming an electron emitting substance layer consisting of an alkaline earth metal oxide including barium as the main component, containing a rare earth metal oxide and nickel powder, cobalt powder, or an alloy powder. CONSTITUTION:An electron emitting substance layer 2 is spread over the upper side of the bottom of a base 1, and it consists of an alkaline earth metal oxide including barium, containing strontium and/or calcium as the main component, and moreover, including 0.1-20wt% of scandium oxide and less than 10wt% of nickel powder. When the carbonate in the alkaline earth metal is dissolved, or the barium oxide is dissociated in the operation as a cathode while the electron emitting substance layer 2 is activated in spreading and forming over the base 1, the rare earth metal oxide controls the diffusion of the reducing element included in the base 1 in the electron emitting substance layer 2, as well as prevents the oxidizing reaction of the base 1, preventing from forming concentrically an intermediate layer consisting of a complex oxide of the reducing element around the interface between the base 1 and the electron emitting substance layer 2, resulting in a dispersion of the intermediate layer in the electron emitting substance layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electron tube cathode used in a TV double-loud tube, and more particularly to an improvement in an electron emissive material layer.

[Conventional technology]

Figure 2 shows a cathode used in a conventional double picture tube for TVs. A bottomed cylindrical base made of nickel,
(2) is deposited on the upper surface of the bottom of this substrate, and includes an electron-emitting material layer made of an alkaline earth metal oxide containing at least barium (Ba) and also strontium (Sre) and/or calcium (Ca3); 3) is a heater (3) disposed within the base (1), which is used to emit thermoelectrons from the electron emitting material layer (2) by heating.

In the electron tube cathode configured in this way, the base (1)
The electron emitting material layer (2) is deposited on the substrate as follows. First, alkaline earth metals (Ba*s
A suspension consisting of a carbonate of r l ca) is applied to the substrate (1) and heated by a heater (3) during the evacuation step. At this time, the alkaline earth metal carbonate turns into an alkaline earth metal oxide. Thereafter, by reducing a part of the alkaline earth metal oxide and activating it to have semiconducting properties, an electron emitting material layer ( 2) is coated.

In this activation process, a part of the alkaline earth metal oxide reacts as follows□In other words, the substrate (
1) Reducing elements such as silicon and magnesium contained in the substrate (1) diffuse into alkaline earth metal oxides and the substrate (1)
) and reacts with alkaline earth metal oxides. For example, barium oxide (Ba
If it is d), the reaction will be as shown in the following formulas (1) and (2).

BaO+ 1/28 i = Ba + 1/28 i
oz −(1)BaO+ Mg = Ba
+ MgO...(2) As a result of this reaction, a part of the alkaline earth metal oxide deposited on the substrate (1) is reduced, becoming an oxygen-deficient semiconductor, and the cathode temperature is 700 to 8
At an operating temperature of 00'O, an electron emission of 0.5-0.8 A/cnl will be obtained. However, in the electron tube cathode formed in this way, the electron emission is 0.5~
o, s It is impossible to obtain a current density higher than A/crIt. The reasons for this are as follows. In other words, when a part of the alkali earth metal oxide is subjected to a reduction reaction, as is clear from the above (1) (2+ equation), the substrate (1
) and the alkaline earth metal oxide layer.
A composite oxide layer (intermediate layer) of MgO or BaO-8i0□ is formed, and this intermediate layer becomes a high resistance layer and obstructs the flow of current. It is thought that barium (Ba) is not sufficiently generated because it prevents barium from diffusing to the surface side of the electron emitting material layer (2).

[Problem that the invention seeks to solve]

In the electron tube cathode constructed in this way, during operation, the nickel crystal grain boundary near the interface between the substrate (1) and the electron emitting material layer (2), especially near the surface of the substrate (1), and the
Since the aforementioned intermediate layer is segregated at a position inside the electron emitting material layer (2) of approximately 0 pm, current flow and diffusion of reducing elements toward the surface of the electron emitting material layer (2) are hindered, resulting in a high current density. There was a problem in that sufficient electron emission characteristics could not be obtained.

This invention has been made in view of the above-mentioned points, and prevents the formation of an intermediate layer made of a composite oxide in a concentrated manner near the interface between the substrate and the electron emitting material layer under high current density. The purpose of this invention is to obtain a cathode for an electron tube that has stable emission characteristics over a long period of time and has high productivity and reliability.

[Means for solving problems]

The cathode for an electron tube according to the present invention has an alkaline earth metal oxide containing at least barium as a main component, and
An electron-emitting material layer containing 20% by weight of rare earth metal oxide and 10% by weight or less of nickel powder, cobalt powder, or alloy powder consisting of nickel and cobalt is placed on a substrate mainly composed of Monokel. It is formed by adhesion.

[Effect]

In this invention, 0 contained in the electron emitting material layer
, 1 to 20% by weight of rare earth metal oxides are oxidized during activation when depositing an electron emissive material layer on a substrate, during decomposition of alkaline earth metal carbonates, or during operation as a cathode. It prevents the oxidation reaction of the substrate when barium undergoes a dissociation reaction, and moderately controls the diffusion of reducing elements contained in the substrate into the electron emitting material layer, and is made of a composite oxide of reducing elements. This prevents the intermediate layer from being formed intensively near the interface between the substrate and the electron emitting material layer, and disperses the intermediate layer within the electron emitting material layer.

Furthermore, in the present invention, by containing 10% by weight or less of nickel powder, cobalt powder, or one or more types of alloy powder consisting of nickel and cobalt, alkaline earth metal oxide formed on the substrate can be formed. This improves the tetraelectricity of the oxide layer and improves the adhesion of this oxide layer to the substrate.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, (2) is deposited on the upper surface of the bottom of the substrate (1), contains at least barium, and also contains strontium or/and calcium as a main component, and has a content of 0.1 to 20% The electron-emitting material layer contains scandium oxide in an amount of % by weight, and nickel powder in an amount of 10% by weight or less.

Next, in the cathode for an electron tube configured in this way, the method of depositing the electron emissive material layer (2) on the substrate (1) will be explained. Powder and nickel powder are added and mixed to a desired weight and weight (% by weight assuming all of the above ternary carbonates become oxides) to prepare a suspension.

This suspension e is applied to a thickness of approximately 80 microns by spraying onto a substrate (1) whose main component is nickel, and then
Similar to the conventional method, the electron emitting material layer (2) is applied to the base (1) through a decomposition process from carbonate to oxide and an activation process to reduce a portion of the oxide.・
Various cathodes for electron tubes were prepared in which the contents of nucandium oxide (Sc, 03.) and nickel powder contained in the electron emitting material layer (2) deposited by this method were varied.
A diode vacuum tube was created using this electron tube cathode, and life tests were conducted at various current densities to examine changes in emission current. Table 1 shows a current density of 0.66 A/crd (2.6 A/cm
) shows the characteristics of the electron tube cathode when operated. In the table, the conventional products are cathodes coated with only ternary oxides of alkaline earth metals (Ba・sr, Ca) 0 used in conventional televisions, and in Examples 1 to 12,
Scρ and Ni were added to this conventional product in the proportions shown in the table. In addition, to evaluate the characteristics of the cathode, the initial emission current was set to 100, and a life test was performed under a current density four times higher than that of the conventional one, and the emission value after 6000 hours was expressed as a relative value (chi). Also. As is clear from Table 1, the device of this example to which scandium oxide and nickel powder were added has less emission deterioration during high current density operation than the device of the conventional example. Also, as seen from the same table, Sc and O5 are 0.
When the addition ratio is from 1% by weight to 20% by weight and Ni is 10% by weight or less, emission deterioration is small.

In order to investigate in detail the effect of containing rare earth metal oxide and Ni powder in the electron emitting material layer (2),
After measuring the emission current for 6000 hours, conventional products and 5% by weight 5c20. As a result of analyzing the cross section of an electron tube cathode with an electron emitting material layer (2) containing 1% by weight of Ni using an electron beam X-ray microanalyzer (EFMA), it was found that the conventional rare earth metal oxide An electron emitting material layer (2) containing no
), the substrate (1) is located near the interface between the nickel substrate (1) and the electron emitting material layer (2).
Si and Mg, which are reducing agents contained within, are segregated, and this segregation state is located at a depth of about 5μ on the substrate (1) side from the interface between the substrate (1) and the electron emitting material layer (2). And the peaks of 8i and Mg, which are reducing agents, were confirmed at the same time at a position of about 3 to 5 μ from the above interface toward the electron emitting material layer (2),
Si further [the maximum peak was observed at a position approximately 18 μm from the above interface toward the electron emitting material layer (2), and these Mg
The presence of a Ba peak was also confirmed at the same location as the peak of , 8i. Since these peaks of Sl+Mg and Ba almost coincide with the peak of oxygen, it is considered that these metals exist as oxides or composite oxides.

Furthermore, the presence of a small amount of SC in the substrate (1) was confirmed. In this way, in the conventional product under high current density operation, near the interface between the base (1) and the electron emitting material layer (2),
At the grain boundaries in the substrate (1), 8i0. , MgO, and their composite oxides are formed, and BaO, MgO, and SiO are formed in the electron emitting material layer (2) from the interface.
It can be seen that a composite oxide layer of , is formed. The above SiO, MgO layer and BaO-S
The iO2 layer suppresses the diffusion rate of Si and Mg, which are reducing agents, from the substrate (1) to the electron emitting material layer (2), and is highly insulating, so it inhibits the flow of current, and finally ¥i
This results in wear and tear due to dielectric breakdown within the electron emitting material.

On the other hand, in the cathode for an electron tube having an electron emitting material layer (2) containing 8c203, which is a rare earth metal oxide, which is the present example, 8i, which is a reducing agent contained in the base (1), Mg is evenly dispersed, and there are no peaks of these reducing agents near the interface between the substrate (1) and the electron emitting material layer (2) as in the conventional example. This is considered to be due to the following reasons. In other words, when an alkaline earth metal carbonate decomposes into an oxide during activation, or when a dissociation reaction such as B, 0 occurs during operation of an electron tube cathode, a rare earth metal oxide forms a base (1). This is thought to be due to the prevention of oxidation.

Therefore, in an electron tube cathode having an electron emissive material layer (2) that does not contain rare earth metal oxides, at the early stage of its life, the electron emissive material layer (2) is already formed at the interface between the substrate (1) and the electron emissive material layer (2). The nickel oxide reacts with the reducing agents Si and Mg in the substrate (8 io, , Mg
O.

is formed in the outermost layer of the interface and in the grain boundaries in its vicinity.

On the other hand, in an electron tube cathode having an electron emitting material layer (2) containing a rare earth metal oxide, which is an embodiment of the present invention, the rare earth metal oxide in the electron emitting material layer (2) is Since the oxidation reaction of nickel is prevented, the reducing elements 8i and Mg do not form an oxide layer at or near the grain boundaries in the substrate (1) and easily diffuse into the electron emitting material. Moreover, since the rare earth metal oxide in the electron emitting material layer (2) moderately controls the rate of diffusion of the reducing element into the electron emitting material, it is stable and good even after long-term operation under high current density. It is possible to maintain good emission characteristics.

Therefore, the addition of less than 0.1 weight of rare earth metal oxide is insufficient to suppress the formation of an oxide layer of Sin, , MgO near the grain boundaries of the substrate (1), resulting in a decrease in emission characteristics. begins to appear. Furthermore, if the amount is more than 20% by weight, the function of suppressing the diffusion of the reducing element within the electron emitting material becomes insufficient, resulting in a decrease in emission characteristics.

Furthermore, in this example, Ni powder is added in addition to 8c and 03. By adding Ni powder, this Ni powder is interposed between the powder particles of the alkaline earth metal oxide,
It functions to increase the electrical conductivity of the oxide layer. The amount of Ni powder added is preferably 10% by weight or less. If the amount added exceeds 10% by weight, sintering progresses between the Ni powder and the alkaline earth metal oxide, resulting in deterioration of the cathode surface.
Electron emission ability decreases. Note that the addition of this Ni powder not only increases the conductivity of the oxide layer but also improves the conductivity of the substrate (
It had the effect of improving the adhesion between 1) and the alkaline earth metal oxide layer, and there was no phenomenon of the electron emitting material layer (2) peeling off from the substrate (1).

In the above example, 5C203 and Ni were used.
Other rare earth metal oxides other than 5c203, such as Y2O
2. A similar effect was obtained with cetOs, and N
Similar effects can be obtained by using co powder or alloy powder made of Ni and co in place of i.

In addition, in the electron tube cathode of the present invention, the electron emitting material layer contains alkaline earth metal oxides, rare earth metal oxides, nickel, cobalt, etc., but in addition to these, 8i0
Of course, it may contain a trace amount of a heat-resistant oxide such as Z, MgQ, ZrO, Atρ, or a trace amount of a metal such as iron, manganese, copper, titanium, or the like.

〔Effect of the invention〕

As described above, the present invention includes the addition of 1 to 20% by weight of a rare earth metal oxide to an electron emitting material layer mainly composed of an alkaline earth metal oxide containing at least barium, which is deposited on a substrate. Since it contains one or more of nickel powder, cobalt powder, or alloy powder consisting of nickel and cobalt in an amount of 10% by weight or less,
Compared to conventional cathodes, this cathode has the advantage of realizing a long life under high current density operation, and providing a highly reliable cathode for electron tubes that is inexpensive and has fewer manufacturing restrictions.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a sectional view showing a conventional cathode for an electron tube. In the figure, (1) is a base body, and (2) is an electron emitting material layer. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] The main component is nickel, the main component is an alkaline earth metal oxide containing at least barium, and the main component is 0.1~
It is characterized by depositing an electron emitting material layer containing 20% by weight of a rare earth metal oxide and 10% by weight or less of nickel powder, cobalt powder, or one or more types of alloy powder consisting of nickel and cobalt. Cathode for electron tubes.