JPH0821308B2 - Electron tube cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electron tube cathode used in a picture tube or the like, and is intended to improve the emission characteristics of electrons emitted from the cathode.

[Prior Art] Conventionally, an electron tube cathode used for a picture tube or the like has a base metal containing nickel (Ni) as a main component and a small amount of a reducing agent such as magnesium (Mg) and silicon (Si).
A so-called oxide cathode in which an oxide layer of an alkaline earth metal containing barium (Ba) is deposited is often used.

This oxide cathode is obtained by thermally decomposing an alkaline earth metal carbonate and converting it into an oxide.After that, a reducing agent is reacted with an oxide to generate a free atom from the oxide. Is used as an electron emission donor (source) to emit electrons. There are two types of carbonates, one is barium carbonate (BaCO ₃ ) and the other is (Ba, Sr, Ca) CO ₃ , but the basic mechanism of activation to form donors is the same. Therefore, in order to facilitate understanding, a unitary carbonate will be described in detail as an example.

FIG. 4 is a schematic cross-sectional view showing an example of a conventional oxide cathode, in which a heater (3) is provided inside the cathode cylinder composed of a cathode cap body made of a base metal (1) and a cylinder (2). It has a structure that is deployed and heated and heated. Base metal (1)
An electron emitting material layer (55) made of barium oxide (BaO) is formed on the surface of the.

The electron emitting material layer (55) is formed by the following steps. That is, BaCO ₃ is mixed with a resin solution such as nitrocellulose dissolved in an organic solvent, and then the base metal (1) is applied by a method such as spraying, electrodeposition or coating.
Deposit on top.

The cathode thus formed is then incorporated into an electron tube and heated to about 1000 ° C. by a heater (3) in an evacuation process for evacuating the inside of the electron tube.
₃ is pyrolyzed as shown by the following equation and converted to BaO.

BaCO ₃ → BaO + CO ₂ (I) Carbon dioxide gas (CO ₂ ) generated by this reaction is discharged outside the electron tube together with the gas generated by the thermal decomposition of nitrocellulose.

FIG. 5 is an enlarged schematic view of a part of the cross section in the vicinity of the interface for detailed description of the vicinity of the interface between the base metal (1) and the electron emitting material layer (55). In general, BaO forming the electron emitting material layer (55) is formed by agglomeration of rod-shaped minute crystals (8) to form crystal grains (9) having a size of several μm to several tens of μm.
There is an appropriate gap (10) between the crystal grains (9) forming the electron-emitting substance layer (55), which is porous. This BaO
Reacts with the reducing agent Si or Mg at the interface (11) in contact with the base metal (1) to generate free Ba. These reducing agents diffuse and move in the crystal grain boundaries (7) between the Ni crystal grains (6) of the base metal (1), and the following reduction reaction occurs near the interface (11).

2BaO + Si → 2Ba + SiO ₂ (II) BaO + Mg → Ba + MgO (III) This free Ba acts as a donor of electron emission. At this time, the reaction represented by the formula (IV): SiO ₂ + 2BaO → Ba ₂ SiO ₄ (IV) also occurs at the same time.

As described above, free Ba that acts as a donor is generated at the interface between the electron-emitting substance layer (55) and the base metal (1), moves in the gap (10) of the electron-emitting substance layer (55), and then reaches the surface. Although it plays a role of emitting electrons and emitting electrons, the donor constantly evaporates and disappears by reacting with gases such as CO, CO ₂ , O ₂ and H ₂ O that remain in the electron tube. It is necessary to replenish the donor by carrying out the reaction as described above, and it is necessary for the cathode to carry out this reduction reaction at all times during operation. To balance this replenishment and extinction, this type of cathode is generally used at high temperatures of about 800 ° C.

However, during operation of the cathode, the formula (II) or (I
Since reaction products (12) such as SiO ₂ and Ba ₂ SiO ₄ shown in V) are generated at the interface (11) which is the bonding surface between the electron emitting material layer (55) and the base metal (1), The reaction product (12) accumulates at the interface (11) and the grain boundaries (7) and becomes a barrier (generally referred to as an intermediate layer) such as Si that moves through the grain boundaries (7), and the reaction gradually proceeds. It becomes slow and it becomes difficult to generate Ba as a donor. Further, there is a problem that this intermediate layer has a high resistance value and hinders the flow of the emitted electron current.

In order to solve such a problem, Japanese Patent Laid-Open No. 61-2698
No. 28 and Japanese Patent Laid-Open No. 61-271732 disclose that Sc ₂ O ₃ and alkaline earth metal oxides are formed by forming an electron emitting material layer in which a powder of scandium oxide (Sc ₂ O ₃ ) is dispersed. The complex oxide (for example, Ba ₃ Sc ₄ O ₉ ) generated in the reaction of (1) causes thermal decomposition during the operation of the cathode to generate free Ba that is a donor and replenish it.

It is disclosed that the released metal scandium (Sc) enhances the conductivity of the electron-emitting substance layer and dissociates reaction products such as Ba ₂ SiO ₄ generated at the interface.

[Problems to be Solved by the Invention] As described above, an electron tube cathode that can be operated at a high current density is disclosed by providing an electron emissive material layer in which Sc ₂ O ₃ powder is dispersed. As Sc ₂ O ₃ , when using a conventional method, that is, Sc ₂ O ₃ produced by roasting to prepare scandium oxalate by precipitating from a hydrochloric acid solution containing Sc with oxalic acid, such Sc ₂ O ₃ tends to contain chlorine as an impurity, and there is a problem that the reaction represented by the formula (V): Ba + 2Cl → BaCl ₂ (V) occurs and the donor is eliminated. When the annihilation of the donor is large, the slump phenomenon in which the electric emission current is greatly reduced is brought about.

The present invention has been made to solve the above problems, and has a columnar polyhedral crystal structure, and by providing an electron emitting material layer containing Sc ₂ O ₃ containing no chlorine atom, long The purpose is to obtain an electron tube cathode that can obtain stable electron emission characteristics over time.

[Means for Solving the Problems] The present invention relates to an electron emitting material comprising a cathode base metal containing Ni as a main component and containing at least Si, an alkaline earth metal oxide containing Ba and Sc ₂ O _3. An electron tube cathode composed of a layer, wherein the Sc ₂ O ₃ has a columnar polyhedron crystal form, the content of chlorine atoms does not exceed 100 ppm, 0.1 to 20 in the electron emitting material layer. It relates to an electron tube cathode which is dispersed by weight%.

[Operation] Sc ₂ O ₃ having a columnar polyhedral crystal structure dispersed in the electron emitting material layer in the electron tube cathode of the present invention has a chlorine atom content of impurities not exceeding 100 ppm.
It is possible to obtain a stable electron emission current without erasing the donor such as. Further, it is possible to prevent the intermediate layer made of the composite oxide of the reducing agent from being concentrated and formed in the vicinity of the interface between the base metal and the electron emitting material layer.

[Embodiment] An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the electron tube cathode of the present invention, in which a heater is provided inside a cathode tube composed of a cathode cap body made of a base metal (1) and a tube (2). (3)
Is installed and is configured to heat and raise the temperature. An electron emitting material layer (5) is formed on the surface of the cathode cap body.

The base metal used in the present invention may be any as long as it contains Ni as a main component and contains at least Si, and those conventionally used as the cathode base metal are used. sell. Specific examples of the cathode base metal include, for example, Si, and if necessary Mg, W, Zr, Al
Ni, Nichrome (Ni-Cr), etc., containing the above are listed. The Si content is preferably 0.01 to 1.0% (weight%, the same applies hereinafter) in the base metal.

The cylinder used in the present invention is not particularly limited, and those conventionally used for cathode cylinders can be used, and examples thereof include those made of nichrome (Ni-Cr).

The electron emitting material layer is a layer mainly composed of Ba-containing alkaline earth metal oxide, has a columnar polyhedral crystal form, and does not contain an impurity chlorine atom Sc ₂ O ₃
0.1% to 20% in the layer (may include unavoidably crushed particles, preferably 50% or more of columnar polyhedral crystals, more preferably 70% or more, particularly preferably 90% or more) , Preferably 3 to 10% dispersed. The thickness of the layer is preferably 50 to 200 μm.

In the present specification, the content of chlorine atoms in which Sc ₂ O ₃ does not exceed 100 ppm means that chlorine atoms are contained in an amount that does not adversely affect the electron emission performance of the electron tube cathode. However, this amount usually means that the content of chlorine atoms with respect to Sc ₂ O ₃ does not exceed 100 ppm.

Examples of the alkaline earth metal oxide include BaCO
₃ and (Ba, Sr) CO ₃ and (Ba, Sr, Ca) CO ₃ are thermally decomposed and converted into oxides. Further, the Ba content is preferably 40% or more in the layer.

Sc ₂ O ₃ having a columnar polyhedral crystal form is shown in Fig. 2 (magnification 800
It is a crystal as shown in a double electron micrograph). The average particle size of Sc ₂ O ₃ is preferably 5 to 50 μm.
When the average particle size is less than 5 μm, it becomes easy to fill the space in the electron emitting material layer, and when it exceeds 50 μm, when the electron emitting material layer is formed by the spraying method, Sc ₂ O ₃ crystals precipitate during spraying. It is easy and the dispersed state in the layer is likely to become poor.

Further, when the Sc ₂ O ₃ contains chlorine atoms in an amount that adversely affects the electron emission performance of the electron tube cathode, the donor is easily extinguished, which causes a slump phenomenon.

Sc ₂ O ₃ having a columnar polyhedron crystal form and containing no chlorine atom is produced by precipitating Sc ₂ O ₃ from a solution of nitric acid (HNO ₃ ) containing Sc with oxalic acid (C ₂ O ₄ H ₂ ). You can The Sc ₂ O ₃ which has been conventionally used in general, the Sc ₂ O ₃ was dissolved in hydrochloric acid (HCl), although produced precipitated by oxalic acid _{(C 2 O 4 H 2)} , Erareru Sc ₂ It was found that O ₃ tends to contain chlorine as an impurity, and special treatment such as cleaning and baking is required to remove this impurity.

If the content of Sc ₂ O ₃ is less than 0.1% in the electron emitting material, the effect of preventing the deterioration of electron emission under high current operation is not sufficient, and if it exceeds 20%, the activity of the electron tube cathode is deteriorated. It is not practical because a sufficient electron emission current cannot be obtained at the stage (initial characteristics) when the conversion process is completed.

The method for forming the electron-emitting substance layer is not particularly limited and may be a method such as electrodeposition, coating or spraying, but it is important to form a porous layer film in order to obtain good electron emission performance. The spraying method is preferred because it exists. For example, in a solution of nitrocellulose dissolved in an organic solvent, BaCO ₃ and S
It is preferable that c ₂ O ₃ is mixed in a desired ratio to form a suspension, and the suspension is formed by spraying.

The electron tube cathode manufactured by the above-described exhausting and activating steps becomes the electron tube cathode by the same exhausting and activating steps as the conventional one for producing the donor as the electron emission source.

The action and effect of the electron tube cathode manufactured in this manner will be described by taking BaCO ₃ as an example of a starting material of a donor.

The electron tube cathode produced by the evacuation process / activation process manufactured as described above is incorporated into the electron tube, and heated to about 1000 ° C. by the heater (3) in the evacuation process for evacuating the electron tube. Then BaCO ₃ is pyrolyzed as shown in the following equation.

BaCO ₃ → BaO + CO ₂ (I) CO ₂ produced during this reaction is discharged outside the electron tube. When a suspension of nitrocellulose is used during the formation of the electron-emitting substance layer, the nitrocellulose is also thermally decomposed into a gas at the same time and is discharged out of the tube together with CO ₂ . By this reaction, BaCO ₃ forms an electron-emitting substance layer (5), BaO 3.
Convert to.

FIG. 3 is an enlarged schematic view of a part of the cross section near the interface between the base metal (1) and the electron-emitting substance layer (5) in detail. The BaO forming the electron emitting material layer (5) is agglomerated with rod-shaped minute crystals (8) to form crystal grains (9) having a size of several μm to several tens of μm.
The electron emitting material layer (5) has an appropriate gap (10) between crystal grains.
From the viewpoint of electron emission performance, it is preferable that the porous material has a porous structure. Such properties are mostly determined during deposition of BaCO ₃ . Sc ₂ O ₃ (4) having a columnar polyhedral crystal form is dispersed in the electron emitting material layer (5).

The reducing agents Si and Mg diffuse and move in the crystal grain boundaries (7) between the crystal grains (6) containing Ni as the main component of the base metal (1), and undergo a reaction as shown in formula (I). The generated BaO is this BaO
At the interface (11) during the activation step of reducing the oxidizable metal, an oxidizing metal such as the formula (I
I): The reaction shown in 2BaO + Si → 2Ba + SiO ₂ (II) is performed. The free Ba emits electrons as a donor of electron emission.

At this time, the reaction represented by the formula (IV): SiO ₂ + 2BaO → Ba ₂ SiO ₄ (IV) also occurs.

As described above, Ba that serves as a donor is generated at the interface (11) between the electron-emitting substance layer (5) and the base metal (1), and becomes a gap (10) between the crystal grains (9) of the electron-emitting substance layer (5). ), And is emitted to the surface to play a role of electron emission, but it evaporates or disappears by reacting with gases such as CO, CO ₂ and O ₂ remaining in the electron tube. It is necessary to replenish it by carrying out various reactions, and the reduction reaction is always carried out at the cathode during operation. To balance this replenishment and extinction, it is desirable to keep the cathode at about 800 ° C during operation.

In the electron tube cathode of the present invention, the dispersed Sc ₂ O ₃ has a columnar polyhedral crystal form, and therefore has a characteristic that it is easily dispersed in the electron emitting material layer (5) because it is similar to the BaO crystal form. are doing. Therefore, Ba ₂ SiO ₄ which is a reaction product represented by the formula (IV) has the formula _{(VI): Sc 2 O 3} + 10Ni → 2ScNi 5 +30 (VI) and SCNi ₅ produced by the reaction of the formula ( VII): 9Ba ₂ SiO ₄ ＋ 16ScNi ₅ → 4Ba ₃ Sc ₄ O ₉ ＋ 6Ba ＋ 9Si ＋ 80Ni (VI
Since it reacts as shown in I) and is decomposed by Sc ₂ O ₃ and Ni, it is hard to be accumulated at the interface (11) between the electron-emitting substance layer (5) and the base metal (1).

Therefore, reaction products such as Ba ₂ SiO ₄ accumulate at the interface between the base metal and the electron-emitting material layer as in the conventional cathode.
It becomes a barrier through which a reducing agent such as Si passes, the reduction reaction gradually slows down, and the generation of free Ba serving as a donor does not become difficult. Moreover, since there is no high resistance intermediate layer, the electron tube cathode can be operated at a high current density without disturbing the electron emission current. Further, unlike the case of dispersing Sc ₂ O ₃ which can be obtained by precipitation of oxalic acid from a hydrochloric acid solution, the halogen in the electron emitting substance layer (5) due to the halogen contained in the Sc ₂ O ₃ Since there is no annihilation of free atoms, a sufficient electron emission current can be obtained. Further, the electron tube cathode of the present invention has the same advantage that the manufacturing process of the electron tube can be the same as the conventional one because the decomposition activation process of the electron emitting material can be the same as the conventional one.

Example 1 Scandium hydroxide dissolved in nitric acid (HNO ₃ ) and Sc ₂ O ₃ was precipitated with oxalic acid (C ₂ O ₄ H ₂ ) to have a columnar polyhedral crystal form containing no chlorine atom. Was 90% or more, and Sc ₂ O ₃ having an average particle size of 10 μm was obtained.

The solution of nitrocellulose dissolved in organic solvent was mixed with BaCO ₃ so that the content of Sc ₂ O ₃ in the electron emitting material layer became 5%.
Sc ₂ O ₃ was mixed into a suspension.

This suspension contained 0.03% Si and 0.05% Mg.
On the surface of the cathode base metal made of Ni, a layer to be an electron discharge material layer is formed by spraying by a spraying method so as to have a thickness of about 100 μm.
An electron tube cathode as shown in the figure was produced.

The obtained electron tube cathode was used as a conventional electron tube cathode in three cathodes of a color cathode ray tube having three primary colors (Comparative Example 1: one not containing Sc ₂ O ₃ as an electron emitting material layer. (Except for being provided, it is the same as that of Example 1) and incorporated, and an electron tube was manufactured by a normal exhausting step and an activating step.

In the inspection process, the yield of the color cathode ray tube that reached the prescribed radiated electron flow rate was 98% or more. In addition, as a result of conducting a life test for 6000 hours under a forced acceleration condition of a current density of 3 A / cm ² , in order to investigate the state of electron emission current deterioration during use of a color cathode ray tube, it was found that Sc ₂ O ₃ was not dispersed. The cathode is 6
Although it showed a characteristic of deteriorating to 50% or less of the initial value at 000 hours, it was maintained at 70% of the initial value at 6000 hours in the electron tube cathode of the present invention, and a long life of about 2.5 times was obtained in terms of life time. It was

[Advantages of the Invention] As described above, the electron tube cathode of the present invention has a columnar polyhedral crystal form on the surface of the base metal containing at least Si as a reducing agent, and the content of chlorine atoms does not exceed 100 ppm Sc ₂ The electron emitting material layer is formed of an alkaline earth metal oxide in which O ₃ is dispersed, and has an effect that stable electron emitting characteristics can be obtained for a long time. Further, it is possible to obtain an electron tube cathode which can always obtain a stable electron emission current.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of an electron tube cathode of the present invention,
FIG. 2 is an electron micrograph showing the crystal structure of scandium oxide used in the electron tube cathode of the present invention (magnification is 800 times), and FIG. 3 shows the vicinity of the interface between the base metal and the electron-emitting substance layer in the electron tube cathode of the present invention. FIG. 4 is a schematic enlarged view of a part of the cross section near the interface shown in FIG. 4, FIG. 4 is a schematic cross sectional view of a conventional electron tube cathode, and FIG. 5 shows the vicinity of the interface between a base metal and an electron emitting material layer in the conventional electron tube cathode. It is the schematic diagram which expanded a part of cross section near the interface. (Main symbols in the drawings) (1): Base metal (4): Scandium oxide crystal having columnar polyhedral crystal structure (5): Electron emitting material layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-22347 (JP, A) Actual development 55-60648 (JP, U) Actual public 47-16994 (JP, Y1)

Claims (2)

[Claims] 1. An electron tube cathode comprising nickel as a main component, a cathode base metal containing at least silicon, and an electron emitting material layer containing scandium oxide and an alkaline earth metal oxide containing barium. An electron tube cathode in which the scandium oxide has a columnar polyhedral crystal form and a chlorine atom content of not more than 100 ppm and is dispersed in the electron emitting material layer in an amount of 0.1 to 20% by weight. 2. The electron tube cathode according to claim 1, wherein scandium oxide having a columnar polyhedral crystal form is synthesized by dissolving scandium hydroxide in nitric acid and precipitating with oxalic acid.