JPH0750586B2 - Electron tube cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cathode for an electron tube used in a cathode ray tube for TV and the like, and more particularly to improvement of an electron emissive material layer.

[Conventional technology]

FIG. 2 shows a cathode used in a conventional TV cathode ray tube or image pickup tube. In FIG. 2, (1) is a main component containing a trace amount of a reducing element such as silicon (Si) and magnesium (Mg). A cylindrical base with a bottom made of nickel, (2) is deposited on the top surface of the bottom of the base and contains at least barium (Ba), and also contains strontium (Sr) and / or calcium (Ca) in an alkaline earth. An electron emissive material layer (3) made of a metal oxide is a heater (3) arranged in the substrate (1) for emitting thermoelectrons from the electron emissive material layer (2) by heating. Is.

In the cathode for an electron tube having such a structure, the substrate (1)
The electron emitting material layer (2) is deposited on the substrate as follows. First, a suspension composed of a carbonate of an alkaline earth metal (Ba, Sr, Ca) is applied to the substrate (1) and heated by the heater (3) during the vacuum exhaust process. At this time, the alkaline earth metal carbonate is converted into an alkaline earth metal oxide. Then, a part of the alkaline earth metal oxide is reduced and activated so as to have semiconductor properties, so that the electron emitting material layer (made of the alkaline earth metal oxide is formed on the substrate (1) ( 2) is attached.

In this activation step, a part of the alkaline earth metal oxide reacts as follows. That is, the reducing elements such as silicon and magnesium contained 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. For example, if barium oxide (BaO) is used as the alkaline earth oxide, it will react as in the following equations (1) and (2).

BaO + 1 / 2Si = Ba + 1 / 2SiO ₂ (1) VaO + 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 and oxygen deficiency is caused. Type semiconductor, 0.5-0.8A / at the operating temperature of cathode temperature 700-800 ℃
An electron emission of cm ² will be obtained. However, in the electron tube cathode thus formed, the electron emission is
Current densities higher than 0.5 to 0.8 A / cm ² cannot be taken out. The reason is as follows. That is,
When part of the alkaline earth metal oxide is reduced,
As is clear from the above formulas (1) and (2), SiO ₂ , MgO or Ba is formed at the interface between the substrate (1) and the alkaline earth metal oxide layer.
A complex oxide layer (intermediate layer) composed of O and SiO ₂ is formed, and this intermediate layer serves as a high resistance layer to impede the flow of current, and the above intermediate layer causes the reducing element in the substrate (1) to emit an electron. Sufficient barium (B) to prevent diffusion to the surface side of the material layer (2)
It is considered that a) is not generated.

A conventional cathode for an electron tube has the same structure as that shown in FIG. 2 described in Japanese Patent Laid-Open No. 20941/1984, and the plate of the substrate (1) is provided to obtain the fast motion of the cathode. In order to reduce the thickness, prevent the reducing agent from becoming turbid during the life, and prevent the strength of the substrate (1) from decreasing, lanthanum is added to the substrate (1) as LaNi ₅
And La ₂ O _{3 in} the form of dispersed inclusion.

[Problems to be solved by the invention]

In the electron tube cathode thus constructed, the nickel crystal grain boundary near the interface between the substrate (1) and the electron-emitting substance layer (2), particularly near the surface of the substrate (1) and the above interface during operation.
Since the above-mentioned intermediate layer is segregated to a position inside the electron-emitting substance layer (2) by about μm, current flow and diffusion of the reducing element to the surface side of the electron-emitting substance layer (2) are hindered, resulting in high current density. However, there is a problem in that the sufficient electron emission characteristics cannot be obtained.

Further, in those shown in the latter, in order to contain LaNi ₅ and La ₂ O ₃ at the time of manufacture of the base body (1) composed mainly of nickel, containing the LaNi ₅ and La ₂ O ₃ in the base body (1) It was easy for the condition to vary.

The present invention has been made in view of the above points, and prevents the intermediate layer made of a complex oxide from being concentratedly formed in the vicinity of the interface between the substrate and the male emitting material layer under a high current density, It is an object of the present invention to obtain a highly reliable cathode for an electron tube which has stable emission characteristics over a long period of time and which does not cause peeling of an electron emitting material.

[Means for solving problems]

The cathode for an electron tube according to the present invention contains, as a main component, an alkaline earth metal oxide containing at least barium,
An electron emitting material layer containing a rare earth metal oxide having an average particle size of 4.5 μm or less in weight% is formed on a substrate containing nickel as a main component, and a solid solution of a rare earth metal and nickel or an intermetallic compound is used as a basic surface. Was formed.

[Action]

In the present invention, it is contained in the electron emitting material layer.
Rare earth metal oxides with an average particle size of 4.5 μm or less at 1 to 20% by weight are decomposed when the alkaline earth metal carbonate is decomposed during activation when the electron emitting material layer is formed on the substrate, or at the cathode. While preventing the reaction that the base body oxidizes when barium oxide undergoes a dissociation reaction during the operation as a Since it is formed, it is possible to prevent the intermediate layer made of the complex oxide of the reducing element from being intensively formed in the vicinity of the interface between the substrate and the electron-emitting substance layer, and to disperse the intermediate layer in the electron-spreading substance layer. It is a thing. Furthermore, the effect of preventing the phenomenon of peeling of the electron emitting material layer from the base metal under a high current density is further improved.

〔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 alkaline earth metal oxide (11) containing at least barium, and further containing strontium and / or calcium, as a main component, Average particle size 4.5% by weight
It is an electron emitting material layer containing the following rare earth metal oxides (12) such as scandium oxide and yttrium oxide.

Next, in the electron tube cathode thus constructed, a method of depositing the electron emitting material layer (2) on the substrate (1) will be described. First, ternary carbonate of barium, strontium, and calcium and scandium oxide. Powder to desired weight%
(Weight% when all the above ternary carbonates become oxides)
Add and mix to make a suspension. This suspension was applied by spraying to a substrate (1) containing nickel as a main component in a thickness of about 80 μm, and then the decomposition process from carbonate to oxide and oxidation of oxide were carried out in the same manner as the conventional one. After the activation process of reducing the part, the electron emitting material layer (2) is attached to the substrate (1).
It is something to be attached to.

Here, in order to investigate the effect of the particle size of scandium oxide powder, first, Sc ₂ O ₃ powder purchased (Research Chemical Corp.
Without adjusting the particle size of purity 99.9%), a Sc ₂ O ₃ mixed suspension Sc ₂ O ₃ 10% by weight) was prepared as described above to complete a cathode for an electron tube. This cathode for an electron tube was subjected to a life test at various current densities, and the peeling of the electron emitting substance from the Ni substrate after 6000 hours of operation was examined. The results are shown in FIG. Here, the horizontal axis represents the operating current density 0.66A / cm ² of a conventional color television as the relative current density when the 1. In addition, at this time
The average particle size of Sc ₂ O ₃ powder (particle size when the particle size distribution reached 50%) was 8.0 μm. When the relative current density exceeds 3.1, the frequency of the above-mentioned peeling phenomenon tends to increase.

Next, the Sc ₂ O ₃ powder purchase product described above is adjusted with an ultrafine pulverizer such as a fine micromill pulverizer to adjust the average particle size of the Sc ₂ O ₃ powder to similarly mix Sc ₂ O ₃ 10% by weight. A suspension was prepared, and the occurrence frequency of the peeling phenomenon of the electron emitting material and the relative value of the emission current (operation 0
Fig. 4 shows the results of the examination of the value of time as 100%). When the average particle size of the Sc ₂ O ₃ powder is 4.5 μm or less, peeling does not occur, and the emission current maintaining characteristics are greatly improved. Particularly, when the average particle diameter is 3.0 μm or less, excellent characteristics are exhibited.

The cause of such excellent characteristics is considered as follows.
Sc ₂ O ₃ in the electron emitting substance dissociates during operation to form a Ni-Sc solid solution or intermetallic compound layer on the surface of the Ni substrate metal, and this Ni-Sc layer is near the interface between the Ni substrate metal and the electron emitting substance. Formation of an intermediate layer of BaSiO ₃ and MgOSiO ₂ is suppressed, a sufficient emission current is maintained, and the adhesion of the electron emitting material to the Ni base metal is improved. However, the Ni base metal has a large Ni grain size of 10 μm, but many Ni crystal grains have
Therefore, when the average particle size of Sc ₂ O ₃ powder becomes 4.5μ or less,
The Ni-Sc layer is formed on the surface of most of the Ni crystal grains, and the above effect becomes remarkable.

In the above examples, as rare earth metal oxide
Although the one using Sc ₂ O ₃ has been described, other rare earth metal oxides have similar effects, but especially SC ₂ O ₃ , Y ₂ O ₃ , C
The effect was remarkable in e ₂ O ₃ .

〔The invention's effect〕

As described above, the present invention, the main component is made of nickel on the substrate containing a reducing element, the alkaline earth metal oxide containing at least barium as the main component, the average particle size 4.
Since an electron emitting material layer containing 0.1 to 20% by weight of a rare earth metal oxide of 5 μm or less is deposited and formed to form a solid solution or an intermetallic compound of a rare earth metal and nickel on the surface of a substrate, the rare earth metal is formed. A cathode for an electron tube which realizes a long life under high current density operation which is 2 to 5 times higher than that of a conventional one in which an oxide is not contained in the electron emitting material layer, is inexpensive, and has few restrictions on production and high reliability. Is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing a conventional cathode for an electron tube, and FIG. 3 is a view showing a relationship between relative current density and electron emission material separation frequency. 4 is Sc
FIG. 3 is a graph showing the relationship between the average particle diameter of ₂ O ₃ and the frequency of electron emission material separation and emission current ratio. In the figure, (1) is a substrate and (2) is an electron emitting material layer. In each drawing, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiji Watanabe 2-14-40 Ofuna, Kamakura-shi, Kanagawa Mitsubishi Electric Corp. Product Research Laboratory (72) Inventor Toyoichi Kamata 1st place, Nagaokakyo Baba Institute, Kyoto Prefecture Mitsubishi Electric Co., Ltd. Kyoto Works (72) Inventor Kinjiro Sano No. 1 Baba Institute, Nagaokakyo-shi, Kyoto Mitsubishi Electric Co., Ltd. Kyoto Works (56) References JP-A-49-12758 (JP, A)

Claims (1)

[Claims] 1. A rare earth metal oxide containing an alkaline earth metal oxide containing at least barium as a main component and having an average particle size of 4.5 μm or less in an amount of 0.1 to 5 on a substrate containing nickel as a main component and containing a reducing element. A cathode for an electron tube, wherein an electron emitting material layer containing 20% by weight is formed by depositing, and a solid solution of rare earth metal and nickel or an intermetallic compound is formed on a surface of a substrate. (2) The cathode for an electron tube according to claim 1, wherein the substrate contains at least one of silicon and magnesium.