JPH0690906B2 - 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 emission characteristics of electrons emitted from the cathode.

[Prior Art] Conventionally, an electron tube cathode used for a picture tube has barium on 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, which is formed by depositing an oxide layer of an alkaline earth metal containing (Ba), 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.

The reason for going through such a procedure is that Ba has an excellent electron emission ability, but is very active, so that it easily reacts with moisture in the air to form barium hydroxide (Ba (OH) ₂ ).
This is because it is difficult to generate free Ba from (OH) ₂ in an electron tube, and therefore, a carbonate that is chemically stable must be used as a starting material.

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. because there is,
In order to facilitate understanding, a unitary carbonate will be described in detail as an example.

FIG. 6 is a schematic cross-sectional view showing an example of a conventional electron tube cathode, in which a heater (3) is provided inside a cathode tube composed of a cathode cap body made of a base metal (1) and a tube (2). The structure is such that the temperature is raised by heating, and the electron-emitting material layer (5) made of barium oxide (BaO) is formed on the surface of the base metal (1).
5) has been formed.

The electron emitting material layer (55) is formed by the following steps. That is, after mixing BaCO _{3 in} a resin solution such as nitrocellulose dissolved in an organic solvent,
It is deposited on the base metal (1) by a method such as spraying, electrodeposition or coating.

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.

However, in this method, during the reaction represented by the formula (I), due to the oxidizing atmosphere such as carbon monoxide (CO) and oxygen (O ₂ ) in the tube, the reducing agent Si which plays an important role in the reduction reaction, In addition to the drawback that Mg is oxidized, Ni on the surface of the base metal (1) is also oxidized.

FIG. 7 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 constituting the electron emitting material layer (5) is formed by crystallizing rod-shaped minute crystals (8) into crystal grains (9) having a size of several μm to several + 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 perform the following reduction reaction near the interface (11).

2BaO + Si → 2Ba + SiO ₂ (II) This free Ba acts as a donor of electron emission.

At this time, the reaction represented by the formula (III): SiO ₂ + 2BaO → Ba ₂ SiO ₄ (III) 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 or disappears by reacting with gases such as CO, CO ₂ , O ₂ and H ₂ O remaining in the electron tube. It is necessary to replenish the donor by carrying out such a reaction, and it is necessary for the cathode to always perform this reduction reaction during operation. To balance this replenishment and extinction, this type of cathode is typically used at elevated temperatures of about 800 ° C.

However, the formula (II) or the formula (II
Reaction products such as SiO ₂ , Ba ₂ , and SiO ₄ shown in I) (12)
Are generated at the interface (11), which is the bonding surface between the electron-emitting substance layer (55) and the base metal (1), the reaction product (12) is gradually advancing to the interface (11) and the grain boundaries (7). It becomes a barrier (generally referred to as an intermediate layer) such as Si that accumulates and moves through the crystal grain boundaries (7), and the reaction gradually slows down, making it difficult to generate Ba as a donor. In addition, 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, JP-A-61-269828
JP-A-61-271732 and other publications form an electron-emitting material layer in which powder of scandium oxide (Sc ₂ O ₃ ) is dispersed to form Sc ₂ O ₃ and an alkaline earth metal oxide. The complex oxide (eg, Ba ₂ Sc ₄ O ₉ ) generated by the reaction causes thermal decomposition during the operation of the cathode to generate free Ba as a donor and supplies it. Free metal scandium (Sc) is the electron emitting material layer. It is disclosed that the reaction products such as Ba ₂ SiO ₄ generated at the interface are dissociated.

[Problems to be Solved by the Invention] As described above, an electron tube cathode capable of operating at a high current density is disclosed by providing an electron emissive material layer in which Sc ₂ O ₃ powder is dispersed. The electron emission characteristics of the cathode may vary, and it is difficult to manufacture an electron tube cathode having a constant electron emission characteristic. Also, Sc ₂ O ₃
Is sufficiently evenly dispersed in the electron-emissive material layer, but some products have a smaller electron emission current than the cathode in which Sc ₂ O ₃ is not dispersed in the electron-emissive material layer, that is, In some cases, the dispersion effect of Sc ₂ O ₃ is not obtained.

The present invention has been made to solve the above problems, by providing an electron emissive material layer in which Sc ₂ O ₃ having a dodecahedral crystal structure is dispersed, stable electron emission characteristics can be obtained over a long period of time. The purpose is to obtain an electron tube cathode.

[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 dodecahedral crystal form.
c ₂ O ₃ and an electron tube cathode in which 0.1 to 20% by weight is dispersed in the electron emitting material layer.

[Operation] Sc ₂ O ₃ having a dodecahedral crystal structure dispersed in the electron-emitting substance layer according to the present invention does not fill the crystal gaps in the electron-emitting substance layer, and the alkaline earth metal carbonate decomposes. When it is converted to an oxide or when this oxide (BaO, etc.) dissociates by a reduction reaction, it prevents the oxidation reaction of the base metal, and the intermediate layer consisting of a composite oxide of a reducing agent causes electron emission with the base metal. It is formed so as to be prevented from being concentratedly formed in the vicinity of the interface with the material layer so that movement of free atoms (such as Ba) in the layer is not hindered.

[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 at least Si, and those conventionally used as a cathode base metal can be used. Specific examples of the cathode base metal include Ni and Nichrome (Ni-Cr) containing Si, and if necessary, containing Mg, W, Zr, Al and the like. 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 the cathode cylinder can be used, and examples thereof include those made of nichrome (Ni-Cr).

The electron emissive material layer is a layer mainly composed of Ba-containing alkaline earth metal oxide, and has a dodecahedral crystalline form of Sc ₂ O _2.
3 (which may be unavoidably crushed, preferably dodecahedral crystals are 50% or more, more preferably 70% or more, particularly preferably 90% or more) is 0.1 to 20 in the layer %, Preferably 3 to 10% dispersed layer. The thickness of the layer is preferably 50 to 200 μm.

Examples of the alkaline earth metal oxide include BaC
Examples include O ₃ , (Ba, Sr) CO ₃ , and (Ba, Sr, Ca) CO ₃ that are thermally decomposed and converted into oxides.

Sc ₂ O ₃ having a dodecahedron crystal form has a crystal structure as shown in FIG. 2, and actually has a crystal structure as shown in FIG. 3 (electron micrograph at 800 times magnification). is there. The average particle size of Sc ₂ O ₃ is preferably 5 to 50 μm. If the average particle size is less than 5 μm, it becomes easier to fill the gaps in the electron emitting material layer, and if it exceeds 50 μm, the electron emitting material layer is formed by the spraying method.
Crystals of Sc ₂ O ₃ tend to precipitate during spraying, and the dispersed state within the layer tends to become poor.

Sc ₂ O ₃ having a dodecahedral crystal form may be produced by any method, but scandium hydroxide is converted into hydrochloric acid (HCl).
It can be produced by dissolving it in water and precipitating it with ammonium oxalate (C ₂ O ₄ (NH ₄ ) ₂ ). On the other hand, the one prepared by dissolving Sc ₂ O ₃ in nitric acid (HNO ₃ ) and precipitating it with ammonium carbonate (NH ₄ ) ₂ CO ₃ is shown in FIG.
It becomes a fine substantially spherical crystal structure as shown in (00 times electron micrograph), which is easily broken and easily fills the gaps in the electron emitting material layer, which is not desirable.

When the content of Sc ₂ O ₃ is less than 0.1% in the electron emitting material layer, the effect of preventing the deterioration of electron emission under high current density operation is not sufficient, and when it exceeds 20%, the cathode It is not practical because a sufficient electron emission current cannot be obtained at the stage (initial characteristic) when the activation 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. Therefore, the spraying method is preferable. For example, it was determined that BaCO ₃ and Sc ₂ O ₃ were mixed in a solution of nitrocellulose dissolved in an organic solvent at a desired ratio (the carbonate of the alkaline earth metal (for example, BaCO ₃ ) becomes an oxide (for example, BaO)). It is preferable that the oxide and Sc ₂ O ₃ are mixed at a ratio) to form a suspension, which is then deposited by a spraying method.

The electron tube cathode manufactured by the above-described structure by the evacuation process and the activation process becomes the electron tube cathode by the same evacuation process and activation process as the conventional process for generating the donor as the electron emission source.

The function and effect of the electron tube cathode manufactured in this manner will be described by taking a single carbonate (BaCO ₃ ) as 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 the roller reaction, BaCO ₃ is converted into BaO which forms the electron emitting material layer (5).

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 (5). Electron emitting material layer (5)
In the BaO constituting, the rod-shaped minute crystals (8) are aggregated to form crystal grains (9) having a size of several μm to several tens of μm. From the viewpoint of electron emission performance, it is desirable that the electron emitting material layer (5) be porous having a proper gap (10) between crystal grains.
Such properties are mostly determined during deposition of BaCO ₃ . Sc ₂ O ₃ (4) having a dodecahedral 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 are generated by the reaction as shown in the formula (I). This BaO
At the interface (11) during the activation step of reducing the hydrogen, a reaction represented by the formula (II): 2BaO + Si → 2Ba + SiO ₂ (II) is performed with the reducing agent diffusing from the base metal (1). The free Ba emits electrons as a donor of electron emission.

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

As described above, the electron donor Ba is the electron-emitting material layer (5).
Is generated at the interface (11) between the base metal (1) and the base metal (1), moves through the gap (10) between the crystal grains (9) of the electron-emitting substance layer (5), and emerges on the surface to play the role of electron emission. , It evaporates or disappears by reacting with the gases such as CO, CO ₂ , O ₂ , etc. remaining in the electron tube, so it is necessary to constantly carry out the above reactions to replenish, and the cathode always operates during operation. This reduction reaction is performed. 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, Sc ₂ O ₃ having a dodecahedral crystal form dispersed in the electron-emitting substance layer (5) rarely fills the gap (10) and rather easily forms the gap (10). have. Further, as can be easily understood from FIGS. 2 and 5, the base metal (1) and the surface (13) of Sc ₂ O ₃ (4) having a dodecahedral crystal form have a crystal structure which is easily in contact with each other. Therefore, there is an advantage that the operation described below is easy to obtain.

That is, the reaction product B represented by the above formula (III)
a ₂ SiO ₄ of the formula _{(IV): Sc 2 O 3} + 10Ni → 2ScNi 5 +30 ScNi 5 and equation produced by the reaction represented by (IV) (V): 9Ba 2 SiO 4 + 16ScNi 5 → 4Ba 3 Sc 4 O ₉ + 6Ba + 9Si + 80Ni (V) Reacts as shown in (V) and is decomposed by Sc ₂ O ₃ and Ni, so that it is hard to be accumulated at the interface (11) between the electron emitting material layer (5) and the base metal (1). .

Therefore, like the conventional cathode, reaction products such as Ba ₂ SiO ₄ accumulate at the interface between the base metal and the electron-emitting material layer, and Si
As a barrier for the reducing agent to pass through, the reduction reaction gradually slows down, and the generation of free Ba 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. Also, unlike the case where an electron emitting material layer in which substantially spherical Sc ₂ O ₃ precipitated by (NH ₄ ) ₂ CO ₃ is dispersed is provided, a porous electron emitting material layer can be formed and Atoms can be easily replenished and a sufficient electron emission current can be obtained. Furthermore, the electron tube cathode of the present invention has the advantage that the steps of decomposing and activating the electron emitting material layer may be the same as the conventional ones, and thus the manufacturing steps of the electron tube may be the same as the conventional ones.

Example 1 and Comparative Example 1 Scandium hydroxide was dissolved in hydrochloric acid (HCl) and Sc ₂ O ₃ was precipitated with ammonium oxalate (C ₂ O ₄ (NH ₄ ) ₂ ) to have a dodecahedral crystal form. Was 90% or more, and Sc ₂ O ₃ having an average particle size of 20 μm was obtained.

In the solvent of nitrocellulose dissolved in an organic solvent, the content of Sc ₂ O ₃ in the electron emitting material layer was adjusted to 5% by BaC.
O ₃ and Sc ₂ O ₃ were mixed to form a suspension, and using this suspension, the thickness of the cathode base metal made of Ni containing 0.03% of Si and 0.05% of Mg was measured. Is formed by the spraying method so that the thickness becomes about 100 μm,
An electron tube cathode as shown in FIG. 1 was produced by an exhausting step and an activating step.

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 usual exhausting step and activating step.

Using the obtained electron tube, we carried out a life test for 6000 hours under the forced acceleration condition of the current density of 3 A / cm ² to investigate the deterioration state of the electron emission current, and as a result, the conventional cathode in which Sc ₂ O ₃ was not dispersed Showed a characteristic of degrading to 50% of the initial value after 6000 hours, but the electron tube cathode of the present invention showed 70% of the initial value at 6000 hours.
%, Which is about 2.5 times as long as the life time.

Also, although tens of thousands of electron tube cathodes of Example 1 were repeatedly manufactured, the yield to reach the desired radiated electron flow rate in the test of the inspection step after the electron tube manufacturing process was always 99% or more, and any electron tube cathode was produced. It had stable electron emission performance.

Examples 2 and 3 An electron tube cathode and an electron tube were produced in the same manner as in Example 1 except that the content of Sc ₂ O ₃ in the electron emitting material layer was changed as shown in Table 1.

Then, in the same manner as in Example 1, a life test was performed for 6000 hours. The results are shown in Table 1.

Further, each electron tube cathode was repeatedly manufactured in the same manner as in Example 1, and all the electron tube cathodes had the same stable electron emission performance as in Example 1.

[Advantages of the Invention] As described above, in the electron tube cathode of the present invention, Sc ₂ O ₃ having a dodecahedral crystal form is dispersed in an alkaline earth metal oxide on the surface of a base metal containing at least Si as a reducing agent. It is possible to obtain stable electron emission characteristics for a long time by forming the electron emission material layer. Further, even if the electron tube cathode of the present invention is repeatedly manufactured, it is possible to obtain an electron tube cathode having stable electron emission performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of an embodiment of an electron tube cathode of the present invention,
FIG. 2 is a schematic diagram showing the dodecahedral crystal structure of scandium oxide used in the electron tube cathode of the present invention, and FIG. 3 is an electron micrograph (magnification of 800 times) showing the crystal structure of scandium oxide used in the electron tube cathode of the present invention. FIG. 4 is an electron micrograph showing the crystal structure of scandium oxide obtained by precipitation with ammonium carbonate (magnification: 800 times), and FIG. 5 shows the base metal and the electron-emitting substance layer in the electron tube cathode of the present invention. 6 is an enlarged schematic view of a part of the cross section of the interface showing the vicinity of the interface, FIG. 6 is a schematic sectional view of the conventional electron tube cathode, and FIG. 7 is the vicinity of the interface between the base metal and the electron emitting material layer in the conventional electron tube cathode. FIG. 4 is an enlarged schematic view of a part of a cross section of the interface showing the above. (Main symbols in the drawings) (1): Base metal (4): Scandium oxide crystal having a dodecahedral crystal structure (5): Electron emitting material layer

Claims (2)

[Claims] 1. An electron tube cathode comprising a cathode base metal containing nickel as a main component and containing at least silicon, and an electron emitting material layer containing barium containing alkaline earth metal oxide and scandium oxide. An electron tube cathode in which the scandium oxide is scandium oxide having a dodecahedral crystal form and is dispersed in an electron emitting material layer in an amount of 0.1 to 20% by weight. 2. An electron tube cathode according to claim 1, wherein scandium oxide having a dodecahedral crystal form is synthesized by precipitation with ammonium oxalate.