JPH0760632B2 - 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 the figure, (1) shows silicon (S
i), a bottomed cylindrical base body whose main component is nickel containing a trace amount of reducing elements such as magnesium (Mg), (2) is deposited on the bottom top surface of this base body, and at least barium (Ba)
And an electron-emitting material layer containing an alkaline earth metal oxide (11) containing strontium (Sr) and / or calcium (Ca), and (3) a heater disposed in the substrate (1). In (3), thermionic electrons are emitted from the electron-emitting substance layer (2) by heating.

In the electron tube cathode thus constructed, the electron emitting material layer (2) is deposited on the substrate (1) 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 a heater (3) during a vacuum exhaust process. At this time, the alkaline earth metal carbonate is converted into an alkaline earth metal oxide. After that, a part of the oxide of the alkaline earth metal is reduced to activate the oxide so that it has semiconducting properties.
An electron emitting material layer (2) made of an oxide of an alkaline earth metal is deposited on (1).

In this activation step, a part of the alkaline earth metal oxide reacts as follows. That is, the substrate
(1) Reducing elements such as silicon and magnesium contained in the oxide and alkaline earth metal oxides and the substrate by diffusion (1)
Of the alkaline earth metal oxide.
For example, barium oxide (BaO) as alkaline earth oxide
In that case, the reaction is as in the following equations (1) and (2).

BaO + 1 / 2Si = Ba + 1 / 2SiO ₂ (1) BaO + Mg = Ba + MgO (2) As a result of this reaction, part of the alkaline earth metal oxide deposited on the substrate (1) is reduced and oxygen deficiency occurs. Type semiconductor, 0.5-0.8A / cm at operating temperature of cathode temperature 700-800 ℃
² electron emission will be obtained. However, the electron emission of the electron tube cathode thus formed is 0.
A current density of 5 to 0.8 A / cm ² or more cannot be taken out. However, this current density is a value considering the actual cathode area. The reason is as follows. That is, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, SiO _{2 at} the interface between the substrate (1) and the alkaline earth metal oxide layer, as is clear from the above equations (1) and (2), MgO or BaO, Si
A complex oxide layer of O ₂ (intermediate layer) is formed, and this intermediate layer functions as a high resistance layer to prevent current flow, and the intermediate layer is a reducing element in the substrate (1), and the reducing element is an electron emitting material layer. It is considered that the barium (Ba) is not generated enough to prevent the diffusion to the surface side of (2).

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 used to obtain the fast motion of the cathode. In order to reduce the thickness, to prevent the reducing agent from becoming turbid during the life, and to 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 configured, during operation, near the interface between the substrate (1) and the electron-emitting substance layer (2), particularly the substrate (1)
Since the above intermediate layer segregates at a position inside the electron emitting material layer (2) about 10 μm from the nickel crystal grain boundary near the surface and the above interface, current flow and reduction property to the surface side of the electron emitting material layer (2) There are problems that the diffusion of elements is hindered, sufficient electron emission characteristics cannot be obtained under high current density, and the phenomenon of delamination of the electron emitting material layer from the Ni base metal occurs.

The present invention has been made in order to solve the above problems, and an intermediate layer made of a complex oxide is concentrated in the vicinity of the interface between a substrate and an electron emitting material layer under the operation of a high current density. And to prevent the electron emitting material layer from peeling off from the substrate, to obtain a cathode for an electron tube which 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 comprises, as a main component, a substrate containing a reducing element containing at least one of silicon and magnesium made of nickel, and an oxide or hydroxide of an alkaline earth metal containing at least barium. A coprecipitate obtained by coprecipitating an oxide or hydroxide of scandium metal is deposited and formed as an electron emitting material layer.

[Action]

In this invention, since the alkaline earth metal oxide and the rare earth metal oxide are formed from the mixed salt powder of the coprecipitated alkaline earth metal salt and the scandium metal oxide or hydroxide, a fine uniform mixture is obtained. An oxide is obtained. As a result, a complex oxide such as BaSc ₄ O ₇ formed by the reaction of barium oxide and scandium oxide during the operation of the cathode realizes the reduction of the work function, and even under the high current operation of high thermal load, the substrate The phenomenon of peeling between the electron emission material and the electron emission material is prevented.

〔Example〕

 An embodiment of the present invention will be described below.

First, the method of forming the electron emitting material layer (2) will be described. 54.0% by weight of barium isopropoxide [Ba (OC
₃ H ₇ ) ₂ ], 37.0 wt% strontium isopropoxide (Sr (OC ₃ H ₇ ) ₂ ), 4.0 wt% calcium isopropoxide (Ca (OC ₃ H ₇ ) ₂ ), and 5.0 wt% of scandium isopropoxide [SC (OC ₃ H _{7) 2]} were thoroughly mixed in n- hexane, and hydrolyzing dropwise little by little water, barium,
A coprecipitated mixed oxide (12) of strontium, calcium and scandium is obtained. The resulting mixed oxide is mixed with nitrocellulose rata and butyl acidate to form a suspension.

The electron-emitting substance suspension produced by the above method was sprayed onto the substrate (1) containing nickel as a main component to a thickness of about 80 microns. Then, in the electron tube manufacturing process, the electron emitting material layer (2) was deposited on the substrate (1) through a high temperature treatment process of the quaternary oxide and an activation process of reducing a part of the oxide. A cathode vacuum tube was created using the cathode thus created and tested.
It was confirmed that an electron emission of 3.5 A / cm ² was obtained, and a higher current was obtained than the conventional one.

FIG. 3 shows a conventional cathode for an electron tube having an electron emitting material layer (2) containing no rare earth and an electron emitting material obtained by simply mixing 5% by weight of scandium oxide with an alkaline earth metal oxide. Electron tube cathode having layer (2) and 5% by weight
The current density of 0.66 A / cm ² (assumed to be 1) was obtained for three types of cathodes for electron tubes having an electron-emitting material layer (2) consisting of a mixed oxide of scandium oxide and an alkaline earth metal oxide On the other hand, the life test was conducted under the conditions that the current density was 2, 3.1 times and 4 times, and the relationship between the current density and the ratio of the emission current at 6000 hours to the initial emission current was shown. As can be seen from FIG. 3, the present example in which an oxide or hydroxide of scandium metal and an oxide or hydroxide of alkaline earth metal were co-precipitated was a conventional product and 5% by weight of scandium oxide. It was confirmed that the effect of further preventing the reduction of the emission under the operation of high current density was more than that of the cathode having the electron emitting material layer mixed with the above.

FIG. 4 shows the above three types of electron tube cathodes,
Similarly, a life test was performed under current density conditions of 0.66 A / cm ² and current density conditions of 2 times, 3.1 times, and 4 times, and the relationship between the current density at 6000 hours and the peeling frequency of the electron-emitting material layer (2) was compared. It is shown. As is clear from FIG. 4, in the conventional cathode, when the current density is quadrupled, a peeling phenomenon of about 40% occurs. A cathode for inter-electron in which 5% by weight of scandium oxide is mixed with the electron emitting material layer also causes a peeling phenomenon although the amount is about 10%. However, in the case of the present example in which the oxide or hydroxide of scandium metal and the oxide or hydroxide of alkaline earth metal were co-precipitated, peeling under high current density operation was not recognized.

In the cathode using the conventional electron emitting material layer (2), near the interface between the substrate (1) and the electron emitting material layer (2), BaSiO ₃ and MgO, SiO
A complex oxide layer (intermediate layer) such as ₂ is formed, which suppresses the diffusion rate of silicon and magnesium that are reducing agents, and also impedes the flow of current due to its high insulating property. As a result, under high current density operation, the above reactions (1), (2)
Is insufficient, the emission is largely lowered, and the heat load is increased due to the heat of the Juule heat of these intermediate layers, so that the above-mentioned peeling phenomenon occurs. On the other hand, by adding scandium oxide to the electron emitting material layer, scandium oxide dissociates to form a solid solution or intermetallic compound of Ni substrate and Ni-Sc,
Since it suppresses the formation reaction of the intermediate layer at the Ni grain boundary, the above reactions (1) and (2) sufficiently occur in the electron emitting material layer even in the case of increasing the current density, and the emission maintaining property is excellent. Become. In addition, the heat load due to the juule heat of the intermediate layer can be suppressed, and the peeling phenomenon can be reduced.

Further, in this invention, because of the use of co-precipitated mixed oxides of scandium and alkali earth metals, formation of BASC ₄ O ₇ is sufficiently performed by the reaction of the scandium oxide barium oxide, BASC ₄ O The emission effect from ₇ is added, and the emission characteristics at high current density become more excellent. Furthermore, since the above mixed oxide is uniform and in the form of fine particles, the above Ni-Sc layer is formed uniformly over the entire surface of the Ni base metal, so that the effect of suppressing the formation of the intermediate layer is extremely large. It is considered that the chestnut phenomenon does not occur.

In the above examples, as a coprecipitation method, a mixed oxide obtained by hydrolyzing an alkoxide salt of an alkaline earth metal and a rare earth metal with n-hexane as a solvent was used. A similar effect was confirmed in the method of dissolving nitrates of earth metals and rare earth metals in mixed water, obtaining mixed hydroxides from ammonium carbonate and ethyl alcohol, and obtaining mixed oxides by heat treatment during electron gun production. It was

〔The invention's effect〕

As described above, according to the present invention, an oxide or hydroxide of alkaline earth metal containing at least barium and scandium are provided on a substrate containing a reducing element containing nickel as a main component and containing at least one of silicon and magnesium. Since a coprecipitate obtained by coprecipitating a metal oxide or hydroxide is formed as an electron emitting material layer by deposition, a conventional rare earth metal oxide is not contained in the electron emitting material layer. On the other hand, it has the effect of achieving a long life in high current density operation of 3 to 6 times, or obtaining a highly reliable cathode for an electron tube that is resistant to peeling.

[Brief description of drawings]

FIG. 1 is a sectional view showing 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 diagram showing a relation between current density and emission current value ratio. The figure shows the relationship between the current density and the peeling frequency of the electron-emitting substance layer (2). In the figure, (1) is a substrate and (2) is an electron emitting material layer. In the drawings, the same reference numerals indicate the same or corresponding parts.

Front page continuation (72) Inventor Keiji Watanabe 2-14-40 Ofuna, Kamakura-shi, Kanagawa Mitsubishi Electric Corp. Product Research Laboratory (72) Inventor Toyoichi Kamata 1st Baba Institute, Nagaokakyo, Kyoto Mitsubishi Electric Corporation Company Kyoto Works (72) Inventor Kinjiro Sano No. 1 Baba Institute, Nagaokakyo City, Kyoto Prefecture Mitsubishi Electric Corporation Kyoto Works (56) Reference JP-A-49-12758 (JP, A)

Claims (2)

[Claims] 1. An oxidation of an alkaline earth metal oxide or hydroxide containing at least barium and scandium metal on a substrate containing a reducing element containing nickel and at least one of silicon and magnesium as a main component. A cathode for an electron tube, wherein a coprecipitate obtained by coprecipitating a substance or a hydroxide is deposited and formed as an electron emitting material layer. ^2. The cathode for an electron tube according to claim 1, which operates under a current density of ² A / cm ^{2 to} 3.5 A / cm ² .