JPH0787069B2 - Electron tube cathode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electron tube cathode used in an electron tube such as a picture tube, and has an improved emission characteristic of electrons emitted from the cathode. .

[Prior Art] Conventionally, an electron tube cathode used in a picture tube or the like has barium on a base metal containing nickel (Ni) as a main component and a small amount of magnesium (Mg), silicon (Si), etc. as a reducing agent. 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. It is designed to emit electrons from.

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

There are two types of carbonates, one such as barium carbonate (BaCO ₃ ) and the other such as (Ba, Sr, Ca) CO ₃ , but the basic mechanism of activation to form a donor is Since they are the same, a unitary carbonate will be described in detail for ease of understanding.

FIG. 4 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 (12) and a tube (2). It has a structure in which it is placed and heated and heated. On the surface of the base metal (12), an electron emitting material layer (1) made of barium oxide (BaO) is formed.
3) has been formed.

The electron emitting material layer (13) 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 (12) 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, the reactions represented by the following formulas (II), (III) and (IV) occur at the same time during the reaction represented by the formula (I), and the reducing agent which plays an important role in the reduction reaction Si and
In addition to the drawback that Mg is oxidized, Ni on the surface of the base metal (12) is also oxidized.

CO ₂ + 2Ni → 2Ni0 + C (II) CO ₂ + Si → SiO ₂ + C (III) CO ₂ + 2Mg → 2Mg0 + C (IV) Figure 5 shows the vicinity of the interface (11) between the base metal (12) and the electron emitting material layer (13). FIG. 3 is an enlarged schematic view of a part of a cross section near the interface for explaining in detail. In general, BaO forming the electron emitting material layer (13) 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 a proper gap (10) between the crystal grains (9) forming the electron-emitting substance layer (13), and it is porous. this
At the interface (11) where BaO contacts the base metal (12),
It reacts with the reducing agent Si or Mg to generate free Ba. These reducing agents diffuse and move in the crystal grain boundaries (7) between the Ni crystal grains (14) of the base metal (12), and the following reduction reaction occurs near the interface (11).

2BaO + Si → 2Ba + Si0 ₂ (V) BaO + Ni → Ba + Ni0 (VI) This free Ba acts as a donor of electron emission, and at the same time Si
Is also exhausted.

At this time, a reaction represented by the formula (VII): Si0 ₂ + 2BaO → Ba ₂ SiO ₄ (VII) also occurs.

As described above, free Ba acting as a donor is generated at the interface (11) between the electron-emitting substance layer (13) and the base metal (12),
It moves through the gap (10) of the electron-emitting substance layer (13), and plays a role of emitting to the surface and emitting electrons, but the donor evaporates, and CO, CO ₂ , O ₂ , which remain in the electron tube, Since it reacts with gas such as H ₂ O and disappears, it is necessary to constantly perform the above reaction to replenish the donor, and at the cathode, this reduction reaction must be performed at all times. . To balance this replenishment and extinction, this type of cathode is typically used at elevated temperatures of about 800 ° C.

However, the formula (V) or formula (VI
Since reaction products (15) such as SiO ₂ and Ba ₂ SiO ₄ shown in I) are generated at the interface (11) which is the bonding surface between the electron emitting material layer (13) and the base metal (12), Barriers such as Si that the reaction products (15) accumulate in the vicinity of the interface and move through the grain boundaries (7) (generally referred to as the intermediate layer)
Then, the reaction becomes slower and it becomes difficult to produce 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.

[Problems to be Solved by the Invention] Thus, in the conventional electron tube cathode, oxidation of the reducing agent and accumulation of reaction products during decomposition or reduction reaction of the carbonate to form the donor of the electron emission source. And the interface (11) between the base metal (12) and the electron emitting material layer (13) during operation.
Since the reaction product (15) accumulates in the vicinity, especially in the Ni crystal grain boundaries (7) near the surface of the base metal (12), the content of Si, which is the reducing agent, is limited, and it is sufficient under high current density. There is a problem that excellent electron emission characteristics cannot be obtained for a long time.

The present invention has been made in order to solve the above problems, and provides a mixed electron emitting material layer composed of an alkaline earth metal oxide and scandium trioxide (Sc ₂ O ₃ ) to form a base metal and In the vicinity of the interface with the mixed electron emitting material layer, it is possible to prevent the reaction product composed of a complex oxide due to the oxidation reaction or the reduction reaction from being concentrated, and further increase the Si content in the base metal, The purpose is to obtain an electron tube cathode which can obtain stable electron emission characteristics for a long time.

[Means for Solving Problems] The present invention contains Ni as a main component and contains at least 0.1 to 10.0% of Si.
(Wt%, the same applies below) On the surface of the contained cathode substrate metal,
The present invention relates to an electron tube cathode having a mixed electron emitting material layer formed of an alkaline earth metal oxide and Sc ₂ O ₃ .

[Operation] When Sc ₂ O ₃ in the present invention decomposes an alkaline earth metal carbonate and converts it into an oxide, or this oxide (BaO
Prevents the oxidation reaction of the base metal when it dissociates by a reduction reaction, and an intermediate layer composed of a complex oxide of a reducing agent is formed in the vicinity of the interface between the base metal and the mixed electron emission material layer. In addition, since the base metal contains a high concentration of Si and has a sufficient supply source, the electron tube cathode has a long life.

[Embodiment] An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

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. A mixed electron emitting material layer (5) is deposited on the surface of the cathode cap body.

As the base metal used in the present invention, a metal containing Ni as a main component and containing at least 0.1 to 10.0% of Si, which can be used as a cathode base metal, can be used. Specific examples of the cathode base metal include Ni containing Si and Mg and, if necessary, W and Zr. The Si content in the base metal is 0.1 to 10.0%, preferably 0.1 to 5.0%, and more preferably 0.1 to 1.0%. When the content is less than 0.1, the reaction represented by the formula (V) is continuously performed during the operation of the cathode, so that Si is consumed in a short time, and the operation is performed at a particularly high current density. In the case of a cigarette, it will be consumed in a shorter time. On the other hand, if it exceeds 10.0%, the ductility of the base metal material is impaired, and the press workability of the cathode cap becomes poor, which is not practical. In the conventional electron tube cathode, a material having a Si content in the base metal of 0.02 to 0.06% is usually used.

In the electron tube cathode of the present invention, Sc ₂ O ₃ in the mixed electron emitting material layer (5) reacts with Ni at the interface (11) to produce ScNi ₅ , and accumulation of reaction products such as Ba ₂ SiO ₄ is accumulated. As described above, a high concentration of Si can be contained 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 mixed electron emitting material layer is a layer composed of an oxide of an alkaline earth metal and Sc ₂ O _3, and is, for example, BaCO ₃ , (Ba, S
r) A layer composed of CO ₂ and (Ba, Sr, Ca) CO ₃ which are thermally decomposed and converted into oxides, and Sc ₂ O ₃ .

Sc ₂ O ₃ is preferably dispersed in the mixed electron emitting material layer at a ratio of 0.3 to 15.0%, more preferably 1 to 5%. When the ratio is less than 0.3%, ScNi ₅ that suppresses the accumulation of Ba ₂ SiO ₄ produced as shown in the above formula (VII) is generated.
Is not sufficiently generated, long-life operation cannot be expected, and 1
If it exceeds 5.0%, sufficient electron emission ability cannot be obtained in the conventional manufacturing process, and the variation tends to increase. Further, the thickness of the layer is preferably 50 to 130 μm.

The method for forming the layer is not particularly limited and may be a method such as electrodeposition, coating, and spraying, but spraying is important because it is important to form a porous layer film in order to obtain good electron emission performance. Method is preferred. For example, it is preferable that Sc ₂ O ₃ and BaCO ₃ are mixed with a solution of nitrocellulose dissolved in an organic solvent to form a suspension, which is then formed by spraying.

What is converted into an electron tube cathode by the exhausting process and the activating process manufactured as described above is an electron tube cathode by the same exhausting process and activating process that are performed to generate a donor as an electron emission source. Is converted to.

The electron tube cathode manufactured as described above has a different action and effect from the conventional electron tube cathode, as described in detail below.

Next, a case where a unitary carbonate (BaCO ₃ ) is used as a starting material for the mixed electron emitting material layer will be described as an example.

The electron tube cathode that is constructed by the evacuation and activation steps configured as described above is incorporated into the electron tube, and is heated up to about 1000 ° C. by the heater (3) in the evacuation step for evacuating the electron tube. BaCO ₃ is pyrolyzed by 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 in the formation of the mixed 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 is converted into BaO forming the mixed electron emitting material layer (5).

In the electron tube cathode of the present invention, CO ₂ generated during the reaction of the formula (I) is mixed with Sc ₂ O ₃ in the mixed electron emitting material layer (5) and the formula (VI
II): 3CO ₂ + Sc ₂ O ₃ → Sc ₂ (CO ₂ ) ₃ (VIII) reacts as shown in the formula (II), (III), (IV) ) Etc., such as Ni, Si, and Mg are hard to oxidize.

FIG. 2 shows a base metal (1) and a mixed electron emitting material layer (5).
FIG. 6 is an enlarged schematic view of a part of a cross section in the vicinity of the interface for explaining in detail the vicinity of the interface. The BaO forming the mixed electron emitting material layer (5) is aggregated into rod-shaped fine crystals (8) 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 mixed electron emission material layer (5) be porous having an appropriate gap (10) between crystal grains. Such properties are mostly determined during deposition of BaCO ₃ .

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
Formed with the base metal (1) during the activation process to reduce the
At the interface with the mixed electron emitting material layer (5) made of BaO, the reducing agent diffusing from the base metal (1) is reacted with, for example, the formula (V): 2BaO + Si → 2Ba + SiO ₂ (V). The free Ba emits electrons as a donor of electron emission. At this time, a reaction represented by the formula (VII): SiO ₂ + 2BaO → Ba ₂ SiO ₄ (VII) also occurs.

As described above, Ba serving as a donor is generated at the interface between the mixed electron emitting material layer (5) and the base metal (1), and the gap (10) between the crystal grains (9) of the mixed electron emitting material layer (5). Move to the surface and play a role of electron emission, but they evaporate or disappear by reacting with gases such as CO, CO ₂ and O ₂ remaining in the electron tube. It is necessary to carry out a reaction to replenish, and it is desirable that the Si content in the base metal (1) is high. At the cathode, this reduction reaction is always performed 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 reaction represented by the above formula (VII) is also performed, but the formed Ba ₂ SiO ₄ is the reaction represented by the formula (IX): Sc ₂ O ₃ + 10Ni → 2ScNi ₅ +30 (IX). SCNi ₅ and expressions generated by _{(X): 9Ba 2 SiO 4} + 16ScNi 5 → 4Ba 3 Sc 4 O 9 + 6Ba + 9Si + 80Ni reacts as shown in (X), in the mixing electron emitting material layer (5) Sc ₂ O ₃ Since it is decomposed by Ni and Ni, it is less likely to be accumulated at the interface between the mixed 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, the generation of free Ba serving as a donor is not difficult, and the Si content can be increased. Further, since there is no intermediate layer having a high resistance value, the electron emission cathode can be operated at a high current density without disturbing the electron emission current. Further, the electron tube cathode according to the present invention has the advantage that the manufacturing process of the electron tube can be the same as the conventional one because the separation activation process of the electron emitting material can be the same as the conventional one.

And mixture of Example 1 and Comparative Example 1 Sc ₂ O ₃ a 3.0% Sc ₂ O ₃ and BaCO ₃ containing, by mixing a solution of nitrocellulose dissolved in an organic solvent and suspension, a Si 0.3 % Of Mg and 0.05% of Mg, the surface of the cathode substrate metal made of Ni is formed into a layer to be a mixed electron emission material layer by a spraying method so as to have a thickness of about 100 μm. Thus, an electron tube cathode as shown in FIG. 1 was produced.

The obtained electron tube cathode is used as a conventional electron tube cathode in three cathodes of a color cathode ray tube having three primary colors (Comparative Example 1: Si content of the base metal is 0.03%, and an electron emitting substance is used. An electron tube was produced by the usual evacuation and activation steps in combination with the same as in Example 1, except that the layer did not contain Sc ₂ O ₃ .

Using the obtained electron tube, a life test of 6000 hours was carried out to examine the deterioration state of the electron emission current. In this test, a forced acceleration condition with a current density of 3 A / cm ² was adopted. The result is the third
Shown in the figure.

As is apparent from FIG. 3, the conventional cathode (17) shows a characteristic of degrading to 50% of the initial value after 6000 hours, but the electron tube cathode (16) of the present invention shows a characteristic of degrading to 70% of the initial value after 6000 hours. That is, the life is about 2.5 times longer when expressed in terms of life time.

Comparative Example 2 An electron tube cathode was produced in the same manner as in Example 1 except that the same cathode substrate metal as in Example 1 was used except that the Si content was 0.03%.

The thus obtained electron tube cathode was assembled in combination with the three cathodes of the color cathode ray tube together with the electron tube cathodes obtained in Example 1 and Comparative Example 1, under the same conditions as in Example 1. An electron tube was manufactured.

A life test was performed in the same manner as in Example 1 using the obtained electron tube. The results are shown in FIG.

As is apparent from FIG. 3, the conventional cathode (18) of this comparative example (corresponding to the example of Japanese Patent Application Laid-Open No. 62-22347) showed 60% of the initial value after 6000 hours. While the electron tube cathode (16) of the present invention was maintained at 70% of its initial value after 6000 hours, the electron emission current at 6000 hours was improved by 10%.

[Advantages of the Invention] As described above, the electron tube cathode of the present invention is a mixed electron emission consisting of an alkaline earth metal oxide containing Sc ₂ O ₃ on the surface of a base metal containing Si as a reducing agent in a high concentration. Since the material layer is formed, there is an effect that stable electron emission characteristics can be obtained for a long time.

[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 enlarged schematic view of a part of the cross section near the interface showing the vicinity of the interface between the base metal and the mixed electron emitting material layer in the present invention, and FIG. 3 is the life of the electron tube cathode of the present invention and the conventional electron tube cathode. Fig. 4 is a graph showing the results of the test, Fig. 4 is a schematic cross-sectional view of a conventional electron tube cathode, and Fig. 5 shows a part of the cross section near the interface between the base metal and the electron-emitting substance layer in the conventional electron tube cathode. It is an enlarged schematic diagram. (Main symbols in the drawing) (1): Base metal (4): Scandium trioxide (5): Mixed electron emitting material layer

Claims (3)

[Claims] 1. A mixed electron-emitting material layer comprising an alkaline earth metal oxide and scandium trioxide is formed on the surface of a cathode base metal containing nickel as a main component and containing at least 0.1 to 10% by weight of silicon. Become an electron tube cathode. 2. An electron tube cathode according to claim 1, wherein scandium trioxide is dispersed in the mixed electron emitting material layer in an amount of 0.3 to 15.0% by weight. 3. An electron tube cathode according to claim 1, wherein silicon is contained in the cathode base metal in an amount of 0.1 to 1.0% by weight.