JPH05182580A - Oxide cathode for electron tube - Google Patents

Abstract

PURPOSE:To stabilize the radiation characteristic of an electron tube by constituting a cathode of a base metal composed mainly of nickel and containing silicon and a plurality of electron emitting material layers composed of alkaline earth metal oxides containing scandium, and making the density of application of the material layer in contact with the base metal smaller than that of the other layer. CONSTITUTION:A cathode comprises a cathode tube 2, a base metal 3, a heater 4 and an electron emitting material layer 5, the heater 4 being located within the cathode tube 2 to heat the cathode to raise its temperature. The material layer 5 consists of two layers; the first material layer 51 in contact with the base metal 3 contains scandium oxide 58 while the density of application of the scandium oxide 58 is made small. The same material as the first material layer 51 is applied as the second material layer 51 to be laid over the first layer while the density of application of the second layer is made larger than that of the first material layer 51 since the surface of the second layer is flattened. More specifically, nickel containing 0.05% silicon and 0.04% Mg is employed as the base metal and the amount of the scandium oxide contained in the first and second material layer is 3%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to oxide cathodes for electron tubes. More specifically, it relates to an oxide cathode provided in an electron tube such as a picture tube having improved reliability.

[0002]

2. Description of the Related Art Conventionally, a cathode provided in an electron tube such as a picture tube has a base metal containing nickel (Ni) as a main component and a trace amount of a reducing metal 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 barium (Ba), is often used.

The oxide cathode thermally decomposes a carbonate of an alkaline earth metal to convert it into an oxide, and then reacts the reducing metal with the oxide to generate free atoms from the oxide to generate an electron emission donor. It is designed to emit electrons as a (source). The reason for going through such a complicated procedure is that barium (Ba) has an excellent electron emission ability but is very active, so that it reacts with moisture in the air to form barium hydroxide (Ba (OH) ₂ ). However, since it is difficult to generate free barium (Ba) from the barium hydroxide in the electron tube, it is necessary to use a chemically stable carbonate as a starting material.

Carbonates include those of BaCO ₃ unit (Ba, S
r, Ca) CO _3, etc., but the basic mechanism of activation that forms the donor is the same, so in order to facilitate understanding, let's take the unit carbonate as an example. Explained.

FIG. 4 is an explanatory view showing a schematic structure of an example of a conventional oxide cathode for an electron tube.

The oxide cathode 1 for an electron tube comprises a cathode tube 2, a base metal 3, a heater 4 and an electron emitting material layer 7. A heater 4 is provided inside the cathode cylinder 2 to have a structure for heating and heating, and an electron emitting material layer 7 made of barium carbonate (BaCO ₃ ) is formed on the surface of the base metal 3. The electron emitting material layer 7 is formed by adding barium carbonate (BaC) to a resin solution such as nitrocellulose dissolved in an organic solvent.
O ₃ ) is mixed and generally deposited by a spraying method to a thickness of about 80 μm, but in a special case, it is also deposited by an electrodeposition method.

In general, the cathode 1 used in a picture tube has a very small distance of about 0.1 mm from the first grid 6 arranged oppositely, so that the surface of the electron emitting material layer 7 is formed as flat as possible. It is desirable to be done. As means for achieving this, for example, there is a method of reducing the spraying amount per unit time and lengthening the spraying time as much as possible during spraying.

The oxide cathode 1 thus constructed is incorporated in an electron tube and heated to about 1000 ° C. by a heater 4 in an evacuation process for evacuating the electron tube to remove barium carbonate (BaCO ₃ ). It is thermally decomposed as shown in the following formula.

BaCO ₃ → BaO + CO ₂ (1) Carbon dioxide gas (CO ₂ ) generated by the above 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 out of the tube together with carbon dioxide. By the reaction of the formula (1), barium carbonate (BaCO ₃ ) in the electron emitting material layer 7 is converted into barium oxide (BaO).

The BaO is a base metal 3 as shown in FIG.
At the interface 8 in contact with, it reacts with the reducing metal such as silicon (Si) or magnesium (Mg) to generate free barium (Ba). These reducing metals diffuse and move in the crystal grain boundaries 11 between the nickel (Ni) crystal grains 10 of the base metal 3 and carry out the reduction reaction in the vicinity of the interface 8.

A reaction example is shown below.

4BaO + Si → 2Ba + Ba ₂ SiO ₄ (2) 2BaO + Si → 2Ba + SiO ₂ (3) BaO + Mg → Ba + MgO (4) As described above, the donor is the electron emitting material layer 7. The electron emitting material layer 7 is generated at the bonding surface of the metal substrate (cathode cap body) 3.
The gap 12 to move the, but the role of the electron emission exit on a surface thereof, the evaporation or, in the residual gas of the electronic tube CO, CO _2, H ₂ O
Since it disappears by reacting with the above, 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.

During use of the cathode, the formulas (2) and (3)
Reaction products 9 such as Ba ₂ SiO ₄ and SiO ₂ are generated at the interface 8 which is the bonding surface between the electron emitting material layer 7 and the base metal 3, and are accumulated in the interface 8 and the crystal grain boundaries 11. The reaction product 9 has a function of joining the electron emitting material layer 7 and the base metal 3. On the other hand, the reaction product 9 (hereinafter, also referred to as an intermediate layer) becomes a barrier through which Si or the like passes, and the reaction formulas (2), (3),
The reaction such as (4) is gradually delayed, and there is a problem that it becomes difficult to generate Ba as a donor. In addition, the reaction product 9
The (intermediate layer) has a problem that it has a high resistance value and hinders the flow of radiated electron current.

To solve such a problem, there has been proposed a scandium oxide-dispersed cathode in which scandium oxide (Sc ₂ O ₃ ) is dispersed in the electron emitting material layer 7 (Japanese Patent Publication No. 64-5417).

This is Ba ₂ SiO _{4 from} scandium (Sc).
Although the above problem is solved by using the dissociation action of the reaction product 9 such as the above, when the cathode is actually used, the electron emitting material layer 7 is an interface at the center of the base metal 3. There is a problem in that the cut-off voltage fluctuates greatly during the operation of the picture tube due to the fact that it locally floats up from No. 8 in a blister form or, in severe cases, peels off.

The reason why the cutoff voltage is abnormal in the scandium oxide-dispersed cathode will be examined in more detail as follows. That is, during the operation of the cathode 1, the reaction represented by the above formula (2) occurs, and the intermediate layer material barium silicate (Ba ₂ SiO ₄ ) has the formula (5) and the formula (6).
Is decomposed via scandium oxide (Sc ₂ O ₃ ) and nickel (Ni).

Sc ₂ O ₃ + 10Ni → 2ScNi ₅ + 30 (5) 9Ba ₂ SiO ₄ + 16ScNi ₅ → 4Ba ₃ Sc ₄ O ₉ + 6Ba + 9Si + 8ONi (6) Further, SiO ₂ is decomposed similarly.

However, as a result, the reaction product at the interface 8 between the electron emitting material layer 7 and the base metal (cathode cap body) 3 disappears, and the bonding action between the electron emitting material layer 7 and the base metal 3 becomes weak. Furthermore, when the operation of the picture tube is turned on and off, the stress received from the difference in the coefficient of thermal expansion between the electron-emitting substance layer 7 and the base metal 3 is large, and it is presumed that the surface gradually rises. As a result of detailed experiments and investigations regarding the floating and the cutoff fluctuation which are considered to be caused by this stress, it was found that these phenomena were more likely to occur as the coating density of the electron emitting material layer was higher.

[0019]

As described above, the scandium oxide-dispersed cathode can suppress the formation of the intermediate layer and endure long-term operation. If the surface of the material layer is formed smoothly and the coating density of the electron emitting material layer is high, the electron emitting material layer locally rises like a blister from the interface at the center of the base metal, which is the base, or in severe cases. However, there is a problem in that the cut-off voltage fluctuates greatly during long-time operation, such as peeling off.

The present invention has been made to solve the above problems, and is an oxide for an electron tube having a smooth electron emitting material layer, excellent adhesion to a base metal, and stable electron emitting characteristics for a long time. The purpose is to obtain a cathode.

[0021]

The present invention comprises a base metal containing nickel as a main component and at least silicon.
A cathode comprising a plurality of electron-emissive material layers formed of an alkaline earth metal oxide containing at least barium deposited on the surface of the base metal, the electron emission being at least on the side in contact with the base metal. The present invention relates to an oxide cathode for an electron tube, wherein the coating density of the material layer is made smaller than the coating density of the other electron-emitting material layers.

[0022]

In the present invention, since the coating density of the first electron emitting material layer in contact with the base metal is reduced, the peeling from the base metal is eliminated. Further, since the electron-emitting substance layer formed as the surface layer has a high coating density, the surface smoothness can be maintained.

Further, when scandium oxide is contained in the first electron emitting material layer, generation of the intermediate layer is suppressed and long-time operation is enabled.

[0024]

【Example】

Example 1 and Comparative Example 1 First, an example of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view showing the schematic structure of an embodiment of the oxide cathode for an electron tube of the present invention.

The cathode 1 is composed of a cathode tube 2, a base metal 3, a heater 4 and an electron emitting material layer 5, and a heater 4 is arranged inside the cathode tube 2 to heat and raise the temperature.

The base metal 3 is nickel (Ni) containing silicon (Si) as a reducing metal. The cathode tube 2 is made of nichrome (Ni-Cr).

On the upper surface of the base metal 3, an electron emitting material layer 5 is deposited and formed. The electron emitting material 5 has two layers,
First electron emitting material layer 51 in contact with the base metal 3 of the cathode 1
Contains scandium oxide 58 and has a low coating density. A second layer is formed on the first electron emitting material layer 51.
As the electron emitting material layer 52, the same electron emitting material as that of the first electron emitting material layer 51 is applied. However, this coating density is made higher than the coating density of the first electron-emitting substance layer 51 as described above in order to flatten the surface.

The electron emitting material layer 5 of the oxide cathode 1 thus constructed may be formed in the same manner as in the conventional method. As an example, 1500 cc of a solution of nitrocellulose dissolved in an organic solvent is added to an alkaline earth metal carbonate. Salt ((Ba, Sr, Cu) CO ₃ ) 9
Scandium oxide (Sc ₂ O ₃ ) was mixed with 00 g and the alkaline earth metal carbonate in an amount of 3% (wt%, the same applies hereinafter) to form a suspension, and the particle size was adjusted by a method such as a bowl mill. The method of depositing by spraying was used in this example.

The specific coating method was as follows.

That is, the first electron-emitting substance 51 was sprayed four times so that the spray amount per spray was 10 μm after drying, and was deposited and formed to a thickness of 40 μm. The coating density after drying was 0.8 mg / mm ³ . The second electron emitting material layer 52 was sprayed 40 times by adjusting the nozzle diameter of the spraying machine so that the spraying amount per time was 1 μm after drying, and the thickness was 40 μm. The coating density after drying is
It became 2.5 mg / mm ³ .

In this example, a base metal containing nickel as the main component, 0.05% silicon and 0.04% Mg was used.

Further, in the obtained electron-emitting substance layer after drying, the content of cadmium oxide contained in the first electron-emitting substance layer on the side in contact with the base metal is 3% with respect to the alkaline earth metal carbonate. And a second layer formed as a surface layer
The composition of the electron-emitting material layer was the same as that of the first electron-emitting material.

An operation test was carried out by incorporating the oxide cathode 1 thus formed into a picture tube. After 6000 hours, when the cutoff voltage defined by the interval between the oxide cathode 1 and the first grid 6 was measured, no abnormal cutoff voltage was observed. After the test, the picture tube was destroyed, the cathode 1 was taken out, and the electron emitting material layer 5 was observed. As a result, no abnormality such as peeling was observed. on the other hand,
80 times spraying was performed with one spray amount of 1 μm 8
With a thickness of 0 μm (conventional method), the electron-emitting material layer 3 was deposited, and the coating density of all layers after drying was 2.5 mg / mm ³
(Comparative Example 1) showed an abnormal value of the cutoff voltage which was considered to be a sign that the electron emitting material layer was lifted up when the cutoff voltage was measured after 6000 hours had elapsed. After the test for 6000 hours, the picture tube was destroyed, the oxide cathode 1 was taken out, and the electron emission material layer was observed. That is, the portion where the emission electron current was taken out, that is, the minute portion of the electron emission material layer in the center of the base metal. There was such a rise.

[Embodiment 2] FIG. 2 is an explanatory view showing a schematic structure of an embodiment of the oxide cathode 1 for an electron tube according to the present invention. The basic structure is the same as that of FIG. Indicates the same site.

The different points are as follows. The electron emitting material layer 5 was composed of two layers, and the first electron emitting material layer 53 in contact with the base metal 3 of the oxide cathode 1 contained scandium oxide 58, and its coating density was made small. On the first electron emitting material layer 53, an electron emitting material composed of only an alkaline earth metal carbonate containing no scandium oxide 58 is applied as the second electron emitting material layer 54. However, this coating density was made higher than the coating density of the first electron emitting material layer 51. The coating liquid was manufactured by the same method as in Example 1.

The specific coating method was as follows.

That is, the first electron-emitting substance layer 53 was sprayed four times so that the spray amount per spray was 10 μm after drying, and was deposited to a thickness of 40 μm. The coating density after drying was 0.8 mg / mm ³ . Second electron-emitting material layer 5
For No. 4, spraying was performed 40 times by adjusting the nozzle diameter of the spraying machine so that the spraying amount per drying was 1 μm after drying.
The thickness was μm. The coating density after drying was 2.5 mg / mm ³ .

In this embodiment, a base metal containing nickel as a main component and containing 0.05% of silicon and 0.04% of magnesium was used.

In the obtained electron emitting material layer after drying, the first electron emitting material layer on the side in contact with the base metal had a casdium oxide content of 3% with respect to the alkaline earth metal carbonate, The second electron emitting material layer formed as a layer did not contain scandium oxide.

In the case of the present embodiment, the cost can be reduced because the expensive scandium oxide 58 is not included in the second electron emitting material layer 54.

[Embodiment 3] FIG. 3 is an explanatory view showing a schematic structure of one embodiment of the oxide cathode for an electron tube of the present invention. In the case of this embodiment, the electron emitting material layer has a three-layer structure. .. Then, 3% of scandium oxide 58 was dispersed in the first electron emitting material layer 55, and the coating density of the electron emitting material layer of each layer was made different. Further, the coating density of the electron emitting material layer 5 on the side in contact with the base metal 3 was increased successively. That is, the coating density of the first electron emitting material layer 55 after drying is 0.8 mg / mm ³ ,
The coating density of the second electron emitting material layer 56 after drying is 1.5 mg / mm.
³ , the coating density after drying the third electron-emitting material layer 57 is 2.5 mg
/ mm ³

In this example, a base metal containing nickel as a main component, containing 0.05% of silicon and 0.04% of magnesium was used.

Further, in the obtained electron-emitting substance layer after drying, the content of cassium oxide in the first electron-emitting substance layer in contact with the base metal is 3 with respect to the alkaline earth metal carbonate.
%, The thickness after coating and drying was 30 μm, the second electron-emitting material layer 56 formed as an intermediate layer did not contain scandium oxide, the thickness was 30 μm, and it was formed as a surface layer. Similarly, the third electron emitting material layer did not contain scandium oxide, and the thickness after coating and drying was 20 μm.

Thus, by gradually increasing the coating density from the base metal 3 toward the surface, the smoothness of the outermost surface layer portion of the electron emitting material layer 5 can be further increased.

The oxide cathode for an electron tube of the present invention has been described above with reference to the examples. The base metal containing nickel as the main component used in the present invention preferably has a silicon content of 0.02 to 0.06%. The base metal may further contain magnesium or the like in an amount of 0.01 to 0.1%.

Of the plurality of electron emitting material layers, the electron emitting material layer on the side in contact with the base metal is a layer made of an alkaline earth metal oxide containing at least barium, but the barium oxide content is 50 to 50%. It is preferably 70%.
Examples of alkaline earth metals other than barium include strontium and calcium. Further, the electron emitting material on the side in contact with the base metal preferably contains 1 to 5% of a rare earth metal oxide such as scandium oxide or yttrium oxide in order to suppress the formation of a reaction product called an intermediate layer. In particular, scandium oxide is preferably contained. The electron emitting material layer on the side in contact with the base metal needs to have a lower density than other electron emitting material layers, but the density is preferably 0.5 to 1.1 mg / mm ³ , and the thickness is preferably 20 to 50 μm. ..

The electron emitting material layer formed as the surface layer does not necessarily need to contain a rare earth metal oxide such as scandium oxide, and its density is preferably 2 to ³ mg / mm ³ , and its thickness is 20 to. 50 μm is preferred.

[0049]

INDUSTRIAL APPLICABILITY The oxide cathode for an electron tube of the present invention can smooth the surface layer of the electron emitting material layer, prevent the electron emitting material layer from rising and peeling off, and have stable electron emitting characteristics for a long time. You can get it.

The electron tube cathode of the present invention was repeatedly manufactured, but stable electron emission performance was always obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an oxide cathode for an electron tube of the present invention.

FIG. 2 is an explanatory view showing an example of an oxide cathode for an electron tube of the present invention.

FIG. 3 is an explanatory diagram showing an example of an oxide cathode for an electron tube of the present invention.

FIG. 4 is an explanatory diagram showing an example of a conventional oxide cathode for an electron tube.

FIG. 5 is an enlarged cross-sectional view in the vicinity of a base metal and an electron emitting material layer of a conventional oxide cathode for an electron tube.

[Explanation of symbols]

 1 Electron Tube Oxide Cathode 3 Base Metal 5 Electron Emissive Layer 58 Scandium Oxide

Claims (3)

[Claims] 1. A plurality of layers of an electron emitting material composed of a base metal containing nickel as a main component and containing at least silicon, and an alkaline earth metal oxide containing at least barium deposited on the surface of the base metal. An oxide cathode for an electron tube, characterized in that the coating density of at least the electron emitting material layer on the side in contact with the base metal is smaller than the coating density of the other electron emitting material layers. .. 2. The oxide cathode for an electron tube according to claim 1, wherein the electron emitting material layer on the side in contact with the base metal contains at least a rare earth oxide in addition to the alkaline earth metal oxide. 3. The oxide cathode for an electron tube according to claim 2, wherein the rare earth metal oxide is scandium oxide.