JPH0734345B2 - Method of manufacturing cathode for electron tube - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cathode provided in an electron tube such as a picture tube, and more particularly to a method for producing an electron emissive material.

[Conventional technology]

 FIG. 3 is a sectional view showing a conventional cathode for an electron tube.

In the figure, (1) is nickel (Ni) containing a trace amount of reducing metal such as magnesium (Mg) and silicon (Si).
The main component is a base metal, which is composed of a cathode cylinder (1a) and a cathode cap (1b) fitted to one end of the cathode cylinder. (2) is a heater incorporated in the base metal (1), (3) is an electron emission material layer deposited on the surface of the cathode cap body (1b), and this electron emission material layer (3)
Is barium carbonate (BaCO ₃ ) and scandium oxide (Sc ₂ O ₃ ) in a resin solution such as nitrocellulose dissolved in an organic solvent.
Is mixed at a predetermined weight% to obtain a suspension, which is crushed and adjusted in particle size, and then sprayed, and then deposited on the surface of the cathode cap body (1b) by a method such as electrodeposition or coating.

As described above, a so-called oxide cathode in which an oxide layer of an alkaline earth metal containing barium (Ba) is adhered and formed on a cathode cap body is widely used as a conventional cathode for an electron tube of this type. This oxide cathode thermally decomposes an alkaline earth carbonate to convert it into an oxide, and then reacts the reducing metal with the oxide to generate free atoms from the oxide, which is a donor (source) of electron emission. It is designed to emit electrons as. The reason why you need such a complicated procedure is
Since barium (Ba) has an excellent electron emission ability but is very active, it reacts with moisture in the air to form barium hydroxide (Ba (OH) ₂ ), and this barium hydroxide (Ba (OH) ₂ This is because it is difficult to generate free barium (Ba) in the electron tube from (1), and therefore a carbonate that is chemically stable must be used as a starting material. Some of these carbonates are barium carbonate (BaCO ₃ ) and others are alkaline earth metal carbonates (Ba, Sr, Ca) CO ₃ ). It goes without saying that the basic mechanism is the same.

The cathode constructed as described above is incorporated into an electron tube and heated to about 1000 ° C. by a heater (2) in an evacuation process for evacuating the inside of the electron tube, so that the barium carbonate (BaCO ₃ ) Is thermally decomposed as in the following equation.

BaCO ₂ → BaO + CO ₂ ... [1] Carbon dioxide gas (CO ₂ ) generated by this reaction is discharged outside the electron tube. At the same time, the resin such as nitrocellulose is also thermally decomposed into a gas, which is discharged outside the tube together with carbon dioxide. Further, by the reaction of the above formula [1], barium carbonate (BaCO ₃ ) in the electron emitting material layer (3) is converted into barium oxide (BaO). During the reaction of the formula [1], in the conventional cathode, under the oxidizing atmosphere of carbon dioxide (CO ₂ ) and oxygen (O ₂ ) in the tube, nickel ( Reducing metals such as silicon (Si) and magnesium (Mg), which play an important role in the reduction reaction, are also oxidized together with Ni).

FIG. 4 shows the base metal (1) and the electron emitting material layer (3).
FIG. 6 is a partially enlarged cross-sectional view for explaining in detail the vicinity of a joint surface with and. In general, barium oxide (BaO) converted from barium carbonate (BaCO ₃ ) aggregates into rod-shaped minute crystals (8) to form crystal grains (9) having a size of several microns to several tens of microns. Care is taken to form a porous electron-emitting substance layer (3) in which a suitable gap (10) is formed between the crystal grains. This barium oxide (BaO) is a base metal (1)
At the interface (11) in contact with, it reacts with the reducing metal silicon (Si) or magnesium (Mg) to generate free barium (Ba). These reducing metals diffuse and move in the crystal grain boundaries (7) between the crystal grains (6) of nickel (Ni) of the base metal (1), and carry out a reduction reaction in the vicinity of the interface (11).

An example of the reaction is shown below.

2BaO + Si → 2Ba + SiO ₂ [2] BaO + Mg → Ba + MgO ... [3] This free barium (Ba) plays a role of electron emission donor. At this time, the reaction of the following equation also occurs at the same time.

SiO ₂ + 2BaO → Ba ₂ SiO ₄ ... [4] The donor is generated at the bonding surface between the electron emitting material layer (3) and the base metal (1), and the gap between the electron emitting material layer (3) is generated. It moves through (10) and emerges on the surface to play the role of electron emission, but evaporates, and CO, CO ₂ , and O of the residual gas in the electron tube.
Since it disappears by reacting with ₂ , H ₂ O, etc., it is necessary to constantly carry out the above reaction to replenish it, and the cathode always carries out this reduction reaction during use. To balance this replenishment and extinction, this type of cathode is commonly used at elevated temperatures of about 800 ° C. Also, during use of the cathode, the above [2], [4]
As is clear from the equation, reaction products (12) such as SiO ₂ and Ba ₂ SiO ₄ are generated at the interface (11) which is the bonding surface between the electron emitting material layer (3) and the base metal (1). , The interface (11) and the grain boundaries (7) are accumulated more and more, and become a barrier (hereinafter referred to as an intermediate layer) through which silicon (Si) and the like pass, and the reaction is gradually delayed, and it becomes difficult to generate barium (Ba) as a donor. . This intermediate layer has a high resistance value and impedes the flow of emitted electron current.
As a means for solving such problems, Japanese Patent Application No. 60-1126
As disclosed in Japanese Patent Publication No. 02-002, the scandium oxide (Sc ₂ O ₃ ) is dispersed in the electron emitting material layer (3), and the reaction product (such as Ba ₂ SiO ₄ ) is formed by the scandium (Sc) ( 12)
However, such a scandium-dispersed cathode does not always have a stable effect.

[Problems to be solved by the invention]

As described above, in the conventional cathode for an electron tube, the oxidation of the reducing metal and the accumulation of the reaction product occur during the reaction action of the decomposition and reduction of the carbonate to form the donor of the electron emission source. During operation, reaction products accumulate in the vicinity of the interface (11) between the base metal (1) and the electron-emitting substance layer (3), particularly in the nickel crystal grain boundaries (7) near the surface of the base metal (1). Therefore, the emission electron current and the diffusion and replenishment of the reducing metal to the electron emission material layer (3) are gradually hindered, and sufficient electron emission characteristics under a high current density cannot be obtained for a long time. .

[Means for solving problems]

The method for producing a cathode for an electron tube according to the present invention comprises a step of activating a cathode, which reacts with silicon (Si), which is a reducing agent contained in the base metal (1) in advance, to reduce the emission current from the cathode region. At least the electron current is taken out for activation.

[Action]

According to this invention, in the activation step of the cathode, the activation is performed while taking at least the electron current from the region of the cathode from which the emission current is taken out. The layer material is not concentrated and formed in the vicinity of the interface between the base metal and the electron emitting material layer.

Example of Invention

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

FIG. 1 is a sectional view showing an embodiment of the present invention. In the figure, (1) is a base metal, and the cathode cylinder (1a)
The cathode cylinder body (1b) is fitted to one end of the cathode cylinder body, and the cathode cylinder body (1a) and the cathode cap body (1b) are the same as the conventional ones. Nickel (Ni) containing a small amount of reducing metal such as nickel, magnesium (Mg), and silicon (Si) may be used as the main component, and one cathode cylinder (1a) is nickel-chromium. (Ni
-Cr) may be used. (2) is the base metal (1)
It is a heater built in.

(30) is an electron-emitting material layer deposited on the surface of the cathode cap body (1b). The material of the electron-emitting material layer (30) contains at least barium (Ba), and strontium ( Sr) or an alkaline earth ternary metal oxide containing calcium (Ca) is used as the main component, and 0.1 to 20 weight percent of scandium oxide (Sc ₂ O ₃ ) is dispersed in it. The method of forming on the surface of the cathode layer (1b) of the electron emitting material layer (30) is similar to that of the conventional one, and a solution of nitrocellulose dissolved in an organic solvent is added to barium carbonate (BaCO ₃ ) and scandium oxide. (Sc ₂ O ₃ ) was mixed with a predetermined weight percentage (the weight percentage calculated as the above ternary carbonate became an oxide) to form a suspension, which was crushed using a bowl mill or the like to adjust the particle size. By the spraying method The film is formed to have a film thickness of about 100 μm, but it may be formed by deposition by a method such as electrodeposition or coating, and although it is not limited by this forming method, it is preferable to form a porous layer film. It is important for obtaining electron emission performance, and the above spraying method is desirable.

Next, an activation process for generating a donor, which is an electron emission source, with respect to the electron tube cathode manufactured as described above will be described.

The cathode for an electron tube, in which the electron-emitting substance layer (30) is formed on the surface of the cathode cap body (1b), is incorporated in the electron tube, and the base metal (1 The temperature is raised to about 1000 ° C. by the heater (2) in (), and barium carbonate (BaCO ₃ ) is thermally decomposed according to the following equation.

BaCO ₃ → BaO + CO ₂ ··· [1] Carbon dioxide gas (CO ₂ ) generated during this reaction is discharged to the outside of the electron tube, and at the same time, nitrocellulose is also thermally decomposed into a gas, and carbon dioxide gas (CO 2 ₂ ) and discharged outside the pipe. By this reaction, barium carbonate (BaCO ₂ ) in the electron emitting material layer (30) is converted into barium oxide (BaO).

Next, the cathode for an electron tube is maintained at a high temperature of about 800 ° C. to 900 ° C., and the activity of reducing barium oxide (BaO) over about 1 hour while taking out an electron current at a current density of about 2 A / cm ² To convert. During the activation process, the above [1]
The product of the formula, barium oxide (BaO), is a reducing metal silicon (Si) that diffuses from the base metal (1).
It produces free barium (Ba) by reacting with magnesium or magnesium (Mg). At this time, it is important to take out the electron current from the cathode region where the emission current is taken out at least when the cathode for the electron tube is used. . Furthermore, the barium oxide (BaO), which is a product of the above formula [1],
Generates free barium (Ba) by reacting with reducing metal such as silicon (Si) or magnesium (Mg) diffused from the base metal (1) during the activation step of reducing the same. These reducing metals diffuse and move in the crystal grain boundaries (7) between the nickel (Ni) crystal grains (6) of the base metal (1), and at the interface (11) with the electron emitting substance (30). Performs a reduction reaction in the vicinity.

An example of the reaction is shown below.

2BaO + Si → 2Ba + SiO ₂ [2] This free barium (Ba) plays a role as a donor of electron emission. At this time, the reaction of the following equation also occurs at the same time.

SiO ₂ + 2BaO → Ba ₂ SiO ₄ ... [4] The cathode activated by the method described above could always obtain stable cathode performance. The reason is considered as follows. That is, in the activation process of the cathode, when activation is performed while taking out an electron current, the intermediate layer material barium silicate (Ba ₂ SiO ₄ ) reacts according to the following equation, that is, Sc ₂ O ₃ + 10Ni → 2ScNi ₅ +30 ... [5] 9Ba ₂ SiO ₄ ＋ 16ScNi ₅ → 4Ba ₃ Sc ₄ O ₉ ＋ 6Ba ＋ 9Si ＋ 80Ni ・ ・
.... By [6], scandium oxide (Sc ₂ O ₃ ) and nickel (Ni)
As a result, the intermediate layer material barium silicate (Ba ₂ S) is formed at the interface between the electron emitting material layer (30) and the base metal (1).
This is because iO ₄ ) is not accumulated.

FIG. 2 schematically shows the surface of the cathode cap body (1b) of the base metal (1) from which the electron emitting material layer (30) of the cathode for an electron tube which has been activated by the above-described activation process is peeled off. In the front view shown in FIG. 1, (1b) is a cathode cap body, its peripheral portion (A) shows the barium silicate (Ba ₂ SiO ₄ ) portion of the intermediate layer substance, and its central portion (B) is a cathode for an electron tube. Nickel (N) extracted from the electron current at a current density of about 2 A / cm ² in the activation process of
i) part is shown. The nickel (Ni) portion and the barium silicate (Ba ₂ SiO ₄ ) portion could also be confirmed by X-ray analysis.

Therefore, the reaction product of barium silicate (Ba ₂ SiO ₄ ) is accumulated in the interface (11) or the grain boundary (7) which is the bonding surface of the base metal (1) like the conventional cathode for electron tubes. It serves as a barrier for reducing metals such as silicon (Si) to pass through, which not only eliminates the disadvantage that the reduction reaction is not stable, but also prevents the electron emission current because there is no high-resistance intermediate layer. It was possible to use it with a high current density.

〔The invention's effect〕

As described above, according to the present invention, in the cathode activation step of reacting with the reducing agent silicon (Si) previously contained in the base metal to reduce it, at least the electron current is extracted from the region of the cathode where the emission current is taken out. Since the activation is carried out while taking out, the reaction product of barium silicate (Ba ₂ SiO ₄ ) is formed at the base metal interface like the conventional cathode, and the reducing metal such as silicon (Si) passes through. Since it becomes a barrier, the reduction reaction is not sufficiently performed, and free barium (B
There is an effect that the generation of a) does not become difficult.
In addition, since the intermediate layer material having a high resistance value is not concentrated and formed at the interface between the base metal and the electron emitting material layer, an electron having a stable electron emitting performance at a high current density without disturbing the electron emission current is obtained. There is an effect that a cathode for a tube can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a front view schematically showing the surface of a cathode cap body from which an electron emitting material layer is peeled, and FIG. 3 is a conventional cathode for an electron tube. A sectional view and FIG. 4 are enlarged sectional views schematically showing the vicinity of the bonding surface between the base metal and the electron emitting material. (1) ... Base metal, (1a) ... Cathode cylinder, (1b) ... Cathode cap, (11) ... Interface, (30) ... Electron emitting material layer. In the drawings, 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 Corporation Product Research Laboratory (72) Masato Saito 2-14-40 Ofuna, Kamakura-shi, Kanagawa No. Mitsubishi Electric Corporation Product Research Center (72) Inventor Akira Suzuki 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Corporation Product Research Center (72) Inventor Keiji Fukuyama 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture No. Mitsubishi Electric Co., Ltd. Product Research Laboratory (72) Inventor Seiko Ishida 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Co., Ltd. Product Research Laboratory (56) Reference JP-A-61-269828 (JP, A) Kaihei 1-76638 (JP, A)

Claims (5)

[Claims] 1. A step of depositing and forming an electron-emitting material layer comprising a substrate metal whose main component is nickel and a predetermined amount of an alkaline earth oxide containing at least barium and scandium oxide dispersed on the surface thereof. A cathode for an electron tube comprising an activation step of reducing the barium oxide while taking out the electron current at a given current density from the region of the cathode where the substrate metal is kept at a given high temperature together with the electron emitting material layer and the emitted current is taken out. Production method. 2. The method for producing a cathode for an electron tube according to claim 1, wherein the amount of dispersion of the alkaline earth metal and scandium oxide is 0.1 to 20% by weight. 3. The method for producing a cathode for an electron tube according to claim 1, wherein the thickness of the electron emitting material layer is 100 μm. 4. The method for producing a cathode for an electron tube according to claim 1, wherein the deposition of the electron emitting material layer is performed by a spraying method. 5. The activation of the electron-emitting material layer is carried out by using a base metal of 80
A method of reducing barium oxide for 1 hour while keeping a high temperature of 0 ° C. to 900 ° C. and taking out an electron current at a current density of ² A / cm ² from a region of a cathode where a radiation current is taken out. The method for producing a cathode for an electron tube according to item 1.