JPH0696661A - Electronic tube cathode - Google Patents

Abstract

PURPOSE:To increase bonding strength between the base body metal of a cathode and an alkaline earth metal oxide layer deposited thereon, and enable stable electron emission characteristics to be provided for a long time, even in high current density state. CONSTITUTION:Regarding an electron tube having a cathode made of a base body metal 2 and an alkaline earth metal oxide layer 4 formed thereon, an upper layer 5 containing the predetermined amount of rare earth metal oxide dispersed in an alkaline earth metal oxide is formed on the layer 4. In this case, the rare earth metal oxide in the upper layer 5 is made spherical, and the mean grain size thereof is between 0.01mum and 2.0mum, thereby constituting the cathode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron tube cathode having an alkaline earth metal oxide layer provided on the surface of a base metal, and particularly to an alkaline earth metal oxide layer which is usually used as an electron emitting material. The present invention relates to an electron tube cathode in which an upper layer in which a predetermined amount of rare earth metal oxide is dispersed in an alkaline earth metal oxide layer is formed to form an electron emitting material in a double layer.

[0002]

2. Description of the Related Art Generally, in electron tubes such as cathode ray tubes for color TVs and display tubes for data display terminals, there is a demand for higher definition of displayed images. The cathode of the above-mentioned type of electron tube is required to have a stable electron emission characteristic for a long time even in a high current density state.

Conventionally, several proposals have been made for the cathode of the electron tube of the above-mentioned type to meet the above-mentioned needs, and one of them is the technical means disclosed in Japanese Patent Laid-Open No. 1-213935. There is.

FIG. 3 is a sectional view showing the cathode of the electron tube disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 1-213935.

In FIG. 3, reference numeral 11 denotes a cathode base metal, and 12
Is an electron emitting material layer, 13 is a heater, and 14 is a composite oxide layer of an alkaline earth metal oxide and a rare earth metal oxide.

The cathode of the electron tube is mainly composed of nickel and contains a small amount of silicon (S) which is a reducing element.
On the cathode base metal 11 containing i) or magnesium (Mg), first, a composite oxide layer 14 of an alkaline earth metal oxide and a rare earth metal oxide is deposited, and then the layer 1 is formed.
4 is formed by depositing an electron-emitting material layer 12 containing at least barium (Ba) and other than alkaline earth metal oxide containing strontium (Sr) and / or calcium (Ca) as a main component. It is configured.

If the above structure is adopted, the cathode base metal 11
The mixed oxide layer 14 of alkaline earth metal oxide and rare earth metal oxide deposited on the upper side of the is partially dissociated during heating during the activation process or during heating during normal operation of the electron tube. The rare earth metal therein becomes an atom, for example, a scandium (Sc) atom and is released. At this time, the reducing element composed of silicon (Si) or magnesium (Mg) in the cathode base metal 11 is converted into the cathode base metal 11.
While diffusing to the surface and reacting with barium oxide (BaO) in the electron emitting material layer 12 to generate barium (Ba) atoms, so-called intermediate material barium silicate (Ba).
SiO ₃ ) is formed, and this intermediate substance is decomposed by the rare earth metal atom, for example, scandium (Sc) atom. Also, when this cathode is operated in a high current density state, the barium (B
Although the evaporation of a) tends to increase, this barium (B
Since a) atoms are attached to the complex oxide layer 14, the evaporation of barium (Ba) is suppressed. As described above, the cathode of the electron tube according to the above-described structure operates in a high current density state, for example, a current state of 4 A / cm ³ or more, because the intermediate substance is less formed and barium (Ba) is less evaporated. Even in the case where it is caused, the emission current does not decrease so much and a long-life cathode can be surely realized.

In addition to this, in the cathode of the electron tube of the above-mentioned type, the one which meets the above-mentioned need is disclosed in Japanese Patent Laid-Open No.
There are technical means disclosed in JP-A-3-310535 and JP-A-63-310536.

FIG. 4 shows the above-mentioned Japanese Patent Laid-Open No. 63-310535.
FIG. 3 is a sectional configuration diagram showing a cathode of an electron tube disclosed in Japanese Patent Laid-Open No. 63-310536.

In FIG. 4, 21 is a base metal, 22 is an electron emitting material layer, 23 is scandium oxide (Sc ₂ O ₃ ) in the electron emitting material layer 22, and 24 is a heater.

The cathode of the electron tube is mainly composed of nickel (Ni) and contains the base metal 21 of the cathode containing a small amount of silicon (Si) and barium (Ba).
Alkaline earth metal oxides and scandium oxide (Sc ₂
O ₃ ) 23 and the electron emitting material layer 22. The scandium oxide (Sc ₂ O ₃ ) 2
3 has a crystal form of dodecahedron (JP-A-63-310535) or a columnar polyhedron (JP-A-63-310536), which is dispersed in the electron-emitting substance layer 22 in an amount of 0.1 to 20% by weight. It is a thing.

According to the above structure, the scandium oxide (Sc ₂ O ₃ ) 23 in the crystalline form of the dodecahedron or the columnar polyhedron is used.
However, it does not extinguish free atoms such as barium (Ba) atoms and donors, and an intermediate substance composed of a complex oxide is formed near the interface between the cathode base metal and the electron-emitting substance layer. As a result, stable electron emission characteristics can be obtained for a long time.

[0013]

However, although the conventional cathode of the electron tube according to the above-mentioned disclosure is capable of obtaining stable electron emission characteristics for a long time, in any case, the cathode metal and the base metal No consideration is given to the bonding strength with the deposited alkaline earth metal oxide layer and the cost of the additive.

Generally speaking, when an electron emissive material layer is deposited on the base metal of the cathode, the bonding force between the base metal and the electron emissive material layer is usually contained in the base metal. It is promoted by a silicon-based intermediate substance generated from a trace amount of silicon. However, in contact with the base metal of the cathode, scandium oxide (Sc ₂
When O ₃ ) is present, it is specifically described in the above-mentioned JP-A-63-
As in the cathode of the electron tube disclosed in JP-A-310535 and JP-A-63-310536, an alkaline earth metal oxide layer (electron emission) in which the base metal and scandium oxide (Sc ₂ O ₃ ) powder are dispersed (A material layer), and a composite oxide containing the base metal and scandium oxide (Sc ₂ O ₃ ) powder, as in the cathode of the electron tube disclosed in JP-A-1-213935. When it is in contact with the layer (electron emitting material layer), scandium (S
c) The atoms suppress the formation of the silicon-based intermediate material, and thus the bonding force cannot be sufficiently obtained, and the coefficient of thermal expansion between the base metal and the electron-emitting material layer during the operation of the cathode. There is a problem that the electron emitting material layer comes to be peeled off from the base metal due to the difference in electric field and electrostatic force. In addition, rare earth metal oxides are expensive, and dispersing a few% of them increases the cost of the cathode.

In this regard, the present inventors directly coated an alkaline earth metal oxide layer (electron emitting material layer) in which a powder of scandium oxide (Sc ₂ O ₃ ) was dispersed on the base metal of the cathode. An experiment was conducted on its durability using a cathode, and it was found that the bonding force between the base metal and the alkaline earth metal oxide layer (electron emitting material layer) was lowered during the operation of the cathode. In extreme cases, a phenomenon occurs in which the alkaline earth metal oxide layer (electron emitting material layer) is separated from the base metal, and this phenomenon occurs in the alkaline earth metal oxide layer. It was confirmed that the higher the content of the scandium compound, the more prominent it appeared.

The present invention eliminates such problems, and an object thereof is to increase the bonding strength between the base metal of the cathode and the alkaline earth metal oxide layer deposited thereon at low cost. Another object of the present invention is to provide an electron tube cathode capable of obtaining stable electron emission characteristics for a long time even in a high current density state.

[0017]

To achieve the above object, the present invention provides an electron tube cathode in which an alkaline earth metal oxide layer is provided on the surface of a base metal, and the alkaline earth metal oxide layer is formed on the alkaline earth metal oxide layer. Forming an upper layer in which a predetermined amount of a rare earth metal oxide is dispersed in an alkaline earth metal oxide, and the rare earth metal oxide in the upper layer has a spherical shape and has an average particle diameter of 0.01 To 2.0 μm. As a result of various experiments, it was found that the dispersed amount of the rare earth metal oxide was proportional to the surface area of the particle. Therefore, the particle size was made smaller than that of the alkaline earth metal oxide, and The range of the amount of the metal oxide dispersed was 0.01 to 0.3% by weight.

[0018]

In the present invention, an upper layer in which a predetermined amount of rare earth metal oxide, for example, scandium oxide is dispersed in the alkaline earth metal oxide layer, is formed on the alkaline earth metal oxide layer. Since it was formed so that scandium oxide (Sc ₂ O ₃ ) did not come into direct contact with the base metal of the cathode, the action of the silicon-based intermediate substance generated from the trace amount of silicon contained in the base metal As a result, the bond between the base metal and the alkaline earth metal oxide layer deposited thereon is promoted, and the alkaline earth metal oxide layer is removed from the base metal even during the operation of the cathode. An electron tube cathode that does not peel off is obtained.

In the present invention, since the surface area of the powdery scandium (Sc) crystal can be made large by making it spherical, the grain size of the scandium (Sc) is set to 0.01 to 2.0 μm. ) Is uniformly dispersed in the alkaline earth metal carbonate, the content of scandium (Sc) in each cathode can be minimized and the electron emission characteristics can be improved.

[0020]

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

FIG. 1 is an enlarged sectional view showing an embodiment of the structure of the cathode portion of the electron tube according to the present invention.

In FIG. 1, 1 is a cathode sleeve, 2 is a cathode base metal, 3 is an electron emitting material layer consisting of the following first and second layers, and 4 is an alkaline earth metal oxide layer (first
Layer), 5 is an upper layer (second layer), and 6 is a heater.

The base metal 2 of the cathode is composed of a material containing nickel as a main component, and the alkaline earth metal oxide layer (first layer) 4 is a carbonate (Ba, barium, strontium, calcium, etc.). It is composed of Sr, Ca) CO ₃ . The upper layer (second layer) 5 is a carbonate (Ba, Sr, C) such as barium, strontium, or calcium.
a) 0.05 for alkaline earth metal oxides composed of CO _3.
Wt% (per cathode) scandium oxide (Sc
₂ O ₃ ) dispersed therein, and in this case, the scandium oxide is a spherical crystal having a particle size of about 0.5 μm, and 80% by weight or more of pure scandium oxide is contained in the component. Is included. Furthermore, the crystal shape (spherical shape) of scandium oxide (Sc ₂ O ₃ ) is barium, strontium, calcium carbonate (Ba,
Sr, Ca) is different from the shape of CO ₃ (acicular), and the crystal grain size of scandium oxide (Sc ₂ O ₃ ) is a carbonate (Ba, Sr, Ca) such as barium, strontium, or calcium. The particle size of 1/10 of the particle size of CO ₃ is selected. In the electron emitting material layer 3, scandium oxide (Sc) contained in the electron emitting material layer 3 is included.
_It is preferred to choose so that the total amount of ₂ O ₃ ) is in the range of 0.01 to 0.3% by weight.

The cathode having the above structure is manufactured by the following procedure.

First, nitrocellulose lacquer and butyl acetate are added to powders of carbonates (Ba, Sr, Ca) CO ₃ of barium, strontium, calcium, etc., respectively, and rolling-mixed to prepare a suspension (hereinafter, referred to as "here"). The solution obtained in step A is referred to as solution A). In addition, carbonates such as barium, strontium and calcium (Ba, Sr, Ca) CO ₃
Nitrocellulose lacquer and butyl acetate were also added to a powder prepared by dispersing 0.05% by weight (per cathode) of scandium oxide (Sc ₂ O ₃ ) in the powder of 1. to prepare a suspension ( Hereinafter, the liquid obtained here is referred to as liquid B).

Next, about 10 parts of the solution A is sprayed on the base metal 2 of the cathode containing nickel (Ni) as a main component.
The alkaline earth metal oxide layer (first layer) 4 is formed by applying the alkaline earth metal oxide layer (first layer) 4 on the alkaline earth metal oxide layer 4 by the same spraying method. The solution B is applied to a thickness of about 60 μm to form the upper layer (second
Layer) 5 to form the electron emitting material layer 3 consisting of two layers.

Subsequently, in the vacuum evacuation step, the electron emitting material layer 3 is heated by the heater 6 to decompose the carbonate in the electron emitting material layer 3 into an oxide, and then 900 to 11
It is heated in an atmosphere of 00 ° C. for activation to form a cathode.

FIG. 2 is an operating characteristic diagram showing the variation of the maximum anode current relative ratio with respect to the operating time of the cathode ray tube in which the cathode manufactured as described above is internally mounted.

Further, in FIG. 2, a is the first layer and the second layer.
Operating characteristics of a cathode ray tube in which the cathode of this embodiment having an electron emitting material layer formed thereon is internally mounted, b is the conventional cathode having an electron emitting material layer formed only of the second layer The operating characteristics of the mounted cathode ray tube and c are the operating characteristics of the cathode ray tube in which the conventional cathode internally coated with the electron emitting material layer not containing scandium oxide (Sc ₂ O ₃ ) is mounted.

As is apparent from the characteristics shown in FIG. 2, when the operating characteristics a of the cathode of this embodiment and the operating characteristics c of the conventional cathode are compared, the operating characteristics a of the cathode of this embodiment is the conventional cathode. It is clear that it has a long life characteristic that is far superior to the operating characteristic c of 1. Further, when comparing the operating characteristic a of the cathode of this embodiment with the operating characteristic b of the conventional cathode, the operating characteristic b of the conventional cathode is superior to the operating characteristic a of the cathode of this embodiment at the beginning. 2 shows that the characteristics of the conventional cathode deteriorate rapidly when the time exceeds about 20000 hours in FIG. The operating characteristic a does not cause such a rapid deterioration.

In this embodiment, the total amount of scandium oxide contained in the electron emitting material layer 3 is 0.01.
The reason for selecting the range of 0.3 to 0.3% by weight is that the rare earth metal oxide such as scandium oxide has a spherical shape and the average particle size is 0.01 to 2.0.
When the total amount is 0.01% by weight or less, the effect due to the two-layer structure of the electron-emitting substance layer 3 cannot be obtained in the case of being composed of fine particles of μm.
This is because if the total amount exceeds 0.3% by weight, the rapid deterioration as seen in the operating characteristic b of the conventional cathode will occur during operation. In this case, when the total amount is 0.3% by weight or more, the cause of such rapid deterioration is considered to be that the electron emitting material layer 3 is separated from the base metal 2 of the cathode.

As described above, the cathode of the electron tube according to the present embodiment is produced from the trace amount of silicon contained in the base metal 2 because the scandium oxide is not arranged in contact with the base metal 2 of the cathode. Silicon-based intermediate material,
For example, by the action of barium silicate (BaSiO ₃ ),
The bond between the base metal 2 and the alkaline earth metal oxide layer (first layer) 4 deposited on the base metal 2 is promoted, and the alkaline earth metal oxide layer (first layer) is operated even during operation of the cathode. )
It is possible to obtain the cathode of the long-life electron tube which does not peel off from the base metal 2 and operates stably even in the high current density state.

In the above-mentioned embodiments, scandium oxide (Sc ₂ O ₃ ) is used as the rare earth metal oxide, but other rare earth metal oxides, especially yttrium oxide (Y ₂ O ₃ ) are used. ), Cerium oxide (Ce ₂ O ₅ ), barium scandate (Ba ₂ Sc ₂ O ₅ , Ba ₃ Sc ₄ O ₉ ,
Even when BaSc ₂ O ₄ ) is used, the same effect as when scandium oxide (Sc ₂ O ₃ ) is used can be obtained. Further, other rare earth metal oxides such as BaY ₂ O ₄ , Sr ₂ Sc ₄ O ₈ , Ba ₃ Y ₄ O ₉ , and Ca.
It is also possible to use a composite oxide containing an alkaline earth metal having a composition such as Sc ₄ O ₉ or Ba ₃ Ce ₄ O ₉ .

Subsequently, the liquid B used for forming the upper layer (second layer) 5 is selected such that the crystal shape of scandium oxide is spherical, and the crystal grain size of scandium oxide is 0. Since we chose the one with 0.5 μm,
For example, the dispersion stability in the liquid B can be measured by adding the liquid B into a tank having a capacity of 20 liters (l) at the start of the spraying work and the end of the work about 8 hours after the spraying work. The difference in the amount of scandium oxide dispersed in the liquid was only 0.01% by weight, and the dispersion characteristics were extremely stable.

As described above, the cathode of the electron tube according to the present embodiment has a large surface area when the scandium oxide (Sc ₂ O ₃ ) crystal is formed into a spherical shape, so that it has a grain size of 0.01 to 2.0 μm. By uniformly dispersing the scandium (Sc) in the alkaline earth metal carbonate, the content of scandium (Sc) in each cathode can be minimized to improve the electron emission characteristics. Can be planned.

[0036]

As described above, according to the present invention, a two-layer structure is adopted as the electron emitting material layer 3 and the base metal 2 of the cathode is used.
Rare earth metal oxides such as scandium oxide (Sc
₂ O ₃ ) are arranged so that they do not come into contact with each other, so that a silicon-based intermediate substance generated from a minute amount of silicon contained in the base metal 2 such as barium silicate (Ba).
The action of SiO ₃ ) promotes the bonding between the base metal 2 and the alkaline earth metal oxide layer (first layer) 4 deposited thereon, and the alkaline earth metal is maintained even during the operation of the cathode. The oxide layer (first layer) 4 does not peel off from the base metal 2, and it is possible to obtain a long-life cathode of the electron tube that operates stably even in a high current density state.

According to the present invention, the crystal form of a rare earth metal oxide such as scandium oxide (Sc ₂ O ₃ ) is converted to a carbonate of an alkaline earth metal oxide such as barium, strontium or calcium carbonate. Salt (Ba, S
r, Ca) Since it has a spherical shape different from that of CO ₃ and has a particle diameter of about 0.01 to 2.0 μm, the scandium oxide (Sc ₂ O ₃ ) is used.
Not only can be uniformly dispersed in the alkaline earth metal carbonate, but the effect of being able to improve the electron emission characteristics by minimizing the content ratio of scandium (Sc) in each cathode. is there.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an embodiment of the configuration of a cathode portion of an electron tube according to the present invention.

FIG. 2 is an operating characteristic diagram showing a change in a maximum anode current relative ratio with respect to an operating time of a cathode ray tube in which a cathode is internally mounted.

FIG. 3 is an enlarged cross-sectional view showing an example of the configuration of a cathode portion of a conventional electron tube.

FIG. 4 is an enlarged cross-sectional view showing another example of the configuration of the cathode portion of the conventional electron tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cathode sleeve 2 ... Cathode base metal 3 ... Electron emitting material layer consisting of first and second layers 4 ... Alkaline earth metal oxide layer (first layer) 5 ... Upper layer (second layer) 6 ... Heater.

Claims (3)

[Claims] 1. An electron tube cathode having an alkaline earth metal oxide layer provided on a surface of a base metal, wherein a predetermined amount of a rare earth metal oxide in the alkaline earth metal oxide is provided on the alkaline earth metal oxide layer. An electron tube in which an upper layer in which is dispersed is formed, and the rare earth metal oxide in the upper layer has a spherical shape and has an average particle diameter of 0.01 to 2.0 μm. cathode. 2. The electron tube cathode according to claim 1, wherein a dispersion amount of the rare earth metal oxide in the alkaline earth metal oxide layer is 0.01 to 0.3% by weight. 3. The rare earth metal oxide in the upper layer is scandium oxide (Sc ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), cerium oxide (Ce ₂ O ₅ ), barium scandate (Ba ₂ Sc _2). O ₅ , Ba ₃ Sc ₄ O ₉ , BaSc ₂
The electron tube cathode according to claim 1, which is at least one of O _{4 and the} like.