JPH0626096B2 - Electron tube cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cathode for an electron tube used in a TV Braun tube or the like, and more particularly to improvement of electron emission characteristics.

[Conventional technology]

FIG. 2 shows the cathode used in the conventional TV Braun tube or image pickup tube of FIG. 2, where (1) is silicon.
(Si), magnesium (Mg) and the like, the main component that contains a trace amount of reducing elements such as nickel is a bottomed cylindrical substrate, (2) is adhered to the bottom upper surface of this substrate and contains at least barium (Ba) , Other strontium (Sr) and / or calcium
An electron emitting material layer made of an alkaline earth metal oxide containing (Ca), (3) is a heater (3) arranged in the substrate (1),
It is for emitting thermoelectrons from the electron emitting material layer (2) by heating.

In the electron tube cathode thus constructed, the electron emitting material layer (2) is deposited on the substrate (1) as follows. First, a suspension composed of a carbonate of an alkaline earth metal (Ba, Sr, Ca) is applied to the substrate (1) and heated by the heater (3) during the vacuum evacuation process. At this time, the alkaline earth metal carbonate is converted into an alkaline earth metal oxide.
After that, a part of the oxide of the alkaline earth metal is reduced and activated so as to have semiconductor properties,
An electron emitting layer (2) made of an alkaline earth metal oxide is deposited on a substrate (1).

In this activation step, a part of the alkaline earth metal oxide reacts as follows. That is, the substrate
(1) Reducing elements such as silicon and magnesium contained in the alkaline earth metal oxide and substrate by diffusion (1)
Of the alkaline earth metal oxide.
For example, if barium oxide (BaO) is used as the alkaline earth oxide, it will react as in the following formulas (1) and (2).

BaO + 1 / 2Si = Ba + 1 / 2SiO ₂ (1) BaO + Mg = Ba + MgO (2) As a result of this reaction, a portion of the alkaline earth metal oxide deposited on the substrate (1) is reduced to generate oxygen. It becomes a deficiency type semiconductor, 0.5-0.8A / at the operating temperature of cathode temperature 700-800 ℃
An electron emission of cm ² will be obtained. However, in the electron tube cathode thus formed, the electron emission is
A current density of 0.5 to 0.8 A / cm ² or more cannot be taken out. The reason is as follows. That is, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, SiO _{2 at} the interface between the substrate (1) and the alkaline earth metal oxide layer, as is clear from the above equations (1) and (2), A complex oxide layer (intermediate layer) composed of MgO or BaO.SiO ₂ is formed, and this intermediate layer acts as a high resistance layer to prevent current flow, and the intermediate layer prevents the reducing element in the substrate (1) from It is considered that it prevents diffusion to the surface side of the electron emitting material layer (2) and sufficient barium (Ba) is not generated.

A conventional cathode for an electron tube has the same structure as that shown in FIG. 2 described in Japanese Patent Laid-Open No. 20941/1984, and the plate of the substrate (1) is used to obtain the fast motion of the cathode. For the purpose of reducing the thickness, preventing suspension of the reducing agent during the life, and preventing the strength of the substrate (1) from decreasing, lanthanum was added to the substrate (1) with LaNi ₅ and
Dispersed inclusions in the form of L _a2 O ₃ are shown.

[Problems to be solved by the invention]

In the electron tube cathode thus configured, during operation, near the interface between the substrate (1) and the electron-emitting substance layer (2), particularly the substrate (1)
Since the intermediate layer segregates at a position near the nickel crystal grain boundary near the surface and the electron emitting material layer (2) within about 10 μm from the above interface, current flow and reducing property to the electron emitting material layer (2) surface side There is a problem that diffusion of elements is hindered and sufficient electron emission characteristics under high current density cannot be obtained.

In the latter case, the inclusion of LaNi ₅ and La ₂ O ₃ in the substrate (1) is included because LaNi ₅ and La ₂ O ₃ are contained in the substrate (1) containing nickel as a main component. It was easy for the condition to vary.

The present invention has been made in view of the above points, and prevents the intermediate layer made of a complex oxide from being concentratedly formed in the vicinity of the interface between the substrate and the electron-emitting substance layer under a high current density, It is an object of the present invention to obtain a cathode for an electron tube which has stable emission characteristics over a long period of time and has high productivity and reliability.

[Means for solving problems]

The cathode for an electron tube according to the present invention is mainly composed of nickel, which is an electron emitting material layer containing an alkaline earth metal oxide containing at least barium, and a reducing element such as Si and Mg. It was deposited on a substrate containing 100% scandium.

[Action]

In the present invention, 0.01 to 0.5% by weight of scandium contained in the substrate is activated during the deposition of the electron-emitting substance layer on the substrate, when the alkaline earth metal carbonate decomposes, or It prevents the oxidation of the substrate when barium oxide undergoes a dissociation reaction during operation as a cathode, and controls the diffusion of the reducing element contained in the substrate into the electron-emitting substance layer appropriately to reduce the reducing property. It is intended to prevent the intermediate layer composed of the element composite oxide from being intensively formed in the vicinity of the interface between the substrate and the electron emitting material layer, and to disperse the intermediate layer in the electron emitting material layer.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. In the figure, (13) is scandium contained in the substrate (1) in an amount of 0.01 to 0.5 wt%, (2) is deposited on the upper surface of the bottom of the substrate (1), contains at least barium, and contains strontium or / and Alkaline earth metal oxides containing calcium
This is an electron emitting material layer containing (11) as a main component.

Next, in the electron tube cathode thus configured, first, a ternary carbonate of barium, strontium and calcium, a binder and a solvent are added and mixed to form a suspension. This suspension contains nickel as a main component, and is made to contain 0.03 to 0.1 wt% of reducing elements such as Si and Mg beforehand.
It is applied by spraying to a substrate (1) containing 1 to 0.5 wt% of scandium to a thickness of about 80 μm, and then, like the conventional one, the decomposition process of carbonate to oxide and the oxide The electron emissive material layer (2) is deposited on the substrate (1) through an activation process of reducing a part thereof.

In this way, various cathodes for electron tubes with various contents of scandium contained in the substrate (1) were prepared, and bipolar cathode tubes were prepared using the cathodes for electron tubes, and life tests were conducted at various current densities. As a result of investigating the change of the emission current,
The results shown in FIG. 8 were obtained. Figure 3 shows the scandium content and life characteristics of the substrate (1) when operated at 3.1 times (2.05 A / cm ² ) the current density of 0.66 A / cm ³ as a conventional TV cathode. It shows the relationship of. As is apparent from FIG. 3, the substrate of the present embodiment in which scandium is contained in the substrate (1) has less emission deterioration in high current density operation than the conventional one.

Thus, in order to investigate in detail the effect of containing scandium in the substrate (1), in the experimental result of FIG.
Conventional product and substrate after measuring emission current over time (1)
The cross section of the cathode for an electron tube containing 0.05 wt% Sc was analyzed by an electron beam X-ray microanalyzer (EPMA). As a result, in the conventional product under the operation of high current density, the base material (1) and the electron emitting material layer (2) were
SiO ₂ , MgO and their complex oxide layers are formed at the grain boundaries in (1), and the electron emitting material layer (2) from the above interface.
It can be seen that the composite oxide layer of BaO and SiO ₂ is formed at the position of 10 μm on the side. The above-mentioned SiO ₂ MgO layer and BaO, SiO ₂ layer suppress the diffusion rate of Si and Mg, which are reducing agents, from the inside of the substrate (1) into the electron-emitting substance layer (2) and have high insulation, so Of the electron emission material and eventually causes wear due to dielectric breakdown in the electron-emitting material layer.

On the other hand, in the electron tube cathode of this embodiment, the substrate
The reducing agents Si and Mg contained in (1) are dispersed evenly, and these reducing agents are added in the vicinity of the interface between the substrate (1) and the electron-emitting substance layer (2) as in the conventional one. The peak of the agent does not exist at all. This is considered to be due to the following reasons. That is, when the alkaline earth metal carbonate decomposes into an oxide during activation, or when BaO or the like undergoes a dissociation reaction during the operation of the cathode for an electron tube, in the substrate (1) near the interface with the electron-emitting substance. It is considered that this scandium is caused by preventing the oxidation of the substrate (1).

That is, the scandium reaction is represented by the following equations (4) and (6).

BaCO ₃ → BaO + CO 2 (in electron emitting material) Conventional example (Ni surface) Ni + 1 / 2CO 2 → NiO + 1 / 2C …… (3) The present invention (Ni surface) 2Sc ＋ 3CO ₂ → Sc ₂ O ₃ ＋ 3CO …… (4) BaO → Ba + O ( Electron emitting material) Conventional example (Ni surface) Ni + O → NiO …… (5) The present invention (Ni surface) 2Sc + 3O → Sc ₂ O ₃ …… (6) Therefore, it is clear from the above formulas (3) (5). As described above, in the electron tube cathode having the electron-emitting substance layer (2) containing no scandium in the substrate (1), the substrate was already formed at the beginning of its life.
The nickel oxide formed at the interface between (1) and the electron emitting material layer (2) reacts with the reducing agents Si and Mg of the substrate (1) to form SiO.
₂ , MgO2 will be formed in the outermost layer of the interface and in the grain boundaries near it. Therefore, the diffusion of the reducing agents Si and Mg into the electron emitting material layer (2) is controlled by the oxide layer of SiO ₂ and MgO, and the sites of the reactions (1) and (2) are affected by the oxidation. It is formed in the vicinity of the object layer.

Therefore, particularly when operating at a high current density, the reactions (1) and (2) are actively carried out, and oxides SiO ₂ and MgO due to the reducing agent are concentrated and generated near the above oxide layer. ) As the reaction of (2) progresses, the diffusion of reducing elements Si and Mg into the electron-emitting material is further suppressed, and the reduction in emission becomes remarkable.

On the other hand, in the electron tube cathode containing scadium in the substrate (1) which is an example of the present invention, scandium in the substrate (1) prevents oxidation reaction of nickel of the substrate (1),
The reducing elements Si and Mg do not form an oxide layer at or near the crystal grain boundaries in the substrate (1), but diffuse easily into the electron-emitting substance, and the reaction of (1) and (2) occurs. Site is an electron emitting material layer
The reaction sites are formed at the grain boundaries in (2) and are more dispersed than in the conventional example. Further, scandium in the substrate (1) functions to decompose the intermediate layer formed at the interface between the substrate and the electron emitting material layer during the lifetime. The intermediate layer is BaO and Si
The reaction formula is shown below by taking a case of a compound compound of O _{2 as} an example.

SiO ₂ + 4 / 3Sc → Si + 2 / 3Sc ₂ O ₃ (7) Ba ₂ SiO ₄ + 8 / 3Sc → 2Ba + Si + 4 / 3Sc ₂ O ₃ (8) Therefore, the conventional As described above, the concentrated formation of the intermediate layer made of the Mg and Si compounds is suppressed at the interface between the substrate and the electron emitting material layer during the lifetime, and the reaction between the reducing agent and the electron emitting material layer is more difficult than the conventional one. This is performed on the layer side, and the intermediate layer is more dispersed on the electron emitting material layer side, and good life characteristics at high current density operation can be obtained. Therefore, the addition of less than 0.01% by weight of scandium is insufficient in suppressing the formation of an oxide layer of SiO ₂ or MgO in the vicinity of the grain boundaries of the substrate (1), and the reaction (4), (6 ) Compared to the reaction rate, the diffusion of scandium from the inside of the substrate (1) is insufficient and the antioxidant effect of Ni is insufficient,
The deterioration of the emission characteristic appears.

Further, within the addition range of 0.01 to 0.5% by weight of scandium, there is no peeling phenomenon of the electron emitting material layer (2) from the substrate (1) after 6000 hours of operation (current density 2.05 A / cm ² ). It was. By the way, the occurrence frequency of the chestnut phenomenon was 30% in the cathode for an electron tube having the electron emitting material layer (2) on the conventional substrate not containing scandium.

Next, a comparison was made of the initial emission characteristics depending on the presence or absence of scandium in the substrate. 0.04 nickel base
Made by vacuum melting method to contain 0.05 wt% scandium with a reducing agent of wt% silicon and 0.07 wt% magnesium, and a scaffold-free nickel substrate (0.04 wt% silicon and 0.07 wt% magnesium). Content) was prepared separately and applied to the cathode of each cathode ray tube, and the initial maximum emission current was measured.

In the case of the conventional example in which the nickel substrate does not contain scandium,
The average value of the initial emission current of 12 cathode ray tubes is 2
813 μA (minimum value: 2660 μA to maximum value: 2980
μA), the average value of the initial emission currents of the six Braun tubes is 2945 μA (minimum value: 2890).
μA to maximum value: 3000 μA), the average value of the initial emission current of the cathode ray tube according to the present invention is high, and the variation of the emission current value is small. The excellent characteristics of the electron tube cathode obtained by carrying out the present invention are considered as follows. That is, scandium has extremely high chemical activity as compared with rare earth elements such as yttrium and lanthanum, and has a characteristic of forming a certain amount of solid solution in nickel. Therefore, during the cathode ray tube manufacturing process or the operation of the electron tube cathode, scandium preferentially reacts with the dispersion gas of the alkaline earth metal carbonate or reacts with the electron emitting material to cause the interface between the electron emitting material layer and the nickel substrate. A scandium oxide layer is formed. The scandium oxide layer has a function of dispersing the intermediate layer, and thus increases the initial emission and improves the life characteristics under high current density operation.

As described above, according to the present invention, the cathode can be manufactured under substantially the same manufacturing conditions as the conventional one, and the dispersion state of the rare earth metal can be controlled relatively easily.

〔The invention's effect〕

As described above, according to the present invention, an electron emitter layer containing an alkaline earth metal oxide containing at least barium as a main component is coated on a substrate containing 0.01 to 0.5 wt% scandium together with a reducing element in advance. Since it is supposed to be worn, compared to the conventional one that does not contain scadium, 2
The effect is that a long life under high current density operation of up to 4 times is realized, and an inexpensive and highly reliable cathode for an electron tube can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional cathode for an electron tube, and FIG. 3 is a diagram showing a relationship between a scandium content rate in a substrate and an emission characteristic. . In the figure, (1) is a substrate and (2) is an electron emitting material layer. In each drawing, the same reference numerals indicate the same or corresponding parts.

Front Page Continuation (72) Inventor Seiko Ishida 2-14-40 Ofuna, Kamakura City, Kanagawa Mitsubishi Electric Corp. Product Research Laboratory (56) Reference JP 58-40731 (JP, A) JP 58- 225528 (JP, A) JP 61-7536 (JP, A)

Claims (1)

[Claims] 1. An alkali containing at least barium on the surface of a substrate whose main component is nickel and 0.01 to 0.5% by weight of scandium together with one or more reducing agents containing one or both of silicon and magnesium. A cathode for an electron tube, comprising an electron emitting material layer containing an earth metal oxide as a main component.