JP2625610B2 - Manufacturing method of impregnated cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high emission current density type impregnated cathode for an electron tube, and more particularly to a process for mixing, enclosing and sintering materials.

[0002]

2. Description of the Related Art Impregnated cathodes have been devised to further improve the electron emission characteristics of oxide cathodes.

At present, the impregnated dispenser cathode in which a tungsten (hereinafter referred to as W) porous substrate is impregnated with an electron-emitting substance has become the mainstream of the impregnated cathode. For example, US Pat. No. 473 and US Pat. No. 3,358,178.

[0004] A process for manufacturing a conventional impregnated cathode will be described with reference to FIG. 6 which is a flowchart.

First, in step 1, W powder having an average particle size of several μm is formed into a rod and press-formed, and in step 2, this compact is fired at 2500 ° C. in a hydrogen atmosphere. In step 1 and step 2, the particle size of the W powder, pressing pressure, sintering temperature and the like are adjusted to produce a porous sintered body having a controlled property in step 3 using copper (C).
u) After being buried in the powder and heated, the Cu is melt-impregnated to give strength, and then machined (pelletized) into a predetermined shape in step 4. In step 5, the pellet is heated in vacuum to elute the impregnated Cu. In step 6, BaCO ₃ , CaCO ₃ , Al ₂ O ₃
An electron emitting material (hereinafter referred to as an emitter) in which H ₂ is mixed at an appropriate molar ratio is heated to 1600 to 1800 ° C. in H ₂ ,
Impregnate the pellet holes. Finally, brushing, polishing, and surface cleaning are performed in order to remove the excess emitter sealed on the pellet surface in step 7, and the resultant is sent to the next assembling step 8.

[0006] However, such a method for producing an impregnated cathode has the disadvantage that each step is complicated and the process time is long, resulting in a very high cost. Further, when the emitter is melted at a high temperature of 1600 to 1800 ° C. and impregnated in the porous W pellet, there is a problem that the reduction reaction by W may excessively proceed.

As a method for solving these drawbacks, recently, hot isostatic pressing (hereinafter referred to as H
(Japanese Patent Application Laid-Open No. 3-55739) and US Pat.
No. 6,450 is disclosed.

[0008]

By the way, the above HI
The impregnated cathode of the powder sintering type by the P method is prepared by dry-mixing and press-molding a high melting point heat-resistant metal powder and an emitter, vacuum-encapsulating the molded body in a capsule, and finally placing the capsule in H
It is characterized by being manufactured by IP processing and sintering.

According to this manufacturing method, complicated and time-consuming steps such as a step of manufacturing a porous W sintered body, a step of impregnating and eluting copper, and a step of impregnating an emitter while heating it at a high temperature for a long time are performed. Although it has the advantage of not having it, when a barium (Ba) compound used as an emitter is added in the form of BaO (barium oxide) and subjected to HIP processing,
BaO easily reacts with the W powder to change into BaWO ₄ , which causes a problem that a monoatomic layer of Ba required for emission generation is consumed later.

Also, when HIP treatment is performed by adding a barium compound in the form of BaCO ₃ (barium carbonate), carbon in the carbonate reacts with W during the treatment to cause WC.
(Tungsten carbide), and a reduction reaction by W necessary for emission generation becomes difficult.

[0011]

Accordingly, the impregnated cathode of the present invention comprises a step of dry-mixing the high melting point heat-resistant metal powder and the emitter, a step of press-molding the mixed powder, a step of encapsulating the compact, Finally, in a method for producing an impregnated cathode comprising a step of sintering the mixed powder by subjecting the capsule to hot isostatic pressure, (m ₁ BaO · m ₂ CaO) · nBaAl is used as an emitter.
₂ O ₄ [n is an integer of 1 or more; m ₁ and m ₂ are integers of 0 or more;
[m ₁ + m ₂ ≧ 1] barium aluminate compound in a range of more than 5.7 wt% and 13.8 wt% or less, mixed with the high melting point heat-resistant metal powder and used at 900 ° C. to 1400 ° C.
It is characterized in that it is subjected to a HIP treatment at a temperature of ° C.

Although the above-mentioned barium aluminate compound must be the main raw material of the emitter of the present invention, there is no problem even if it contains a small amount of BaO, BaCO ₃ , calcium oxide or the like.

[0013]

According to the present invention, (m ₁ BaO.
m ₂ CaO) · nBaAl ₂ O ₄ [n is an integer of 1 or more; m ₁ , m
₂ is an integer of 0 or more; m ₁ + m ₂ ≧ 1], a barium aluminate compound exceeding 5.7 wt% and 13.8 wt%
% Or less and mixed with high melting point heat-resistant metal powder for use 900
C. to 1400.degree. C., and according to this configuration, during the HIP process, the emitter in the form of a carbonate becomes W
And barium aluminate is less likely to react with W than BaO 2, can significantly suppress the change to tungstate such as BaWO ₄ and pelletize. A good cathode sintered body can be produced easily.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a flow chart of the manufacturing process of the impregnated cathode of the present invention.

First, a mixed powder prepared by mixing barium carbonate (BaCO ₃ ), calcium carbonate (CaCO ₃ ), and aluminum oxide (Al ₂ O ₃ ), which are the raw materials of the emitter agent, in a molar ratio of 4: 1: 1, It was heated to 1100 ° C. in the atmosphere to convert it to a barium aluminate compound.

At this time, the barium aluminate compounds mainly include Ba ₅ CaAl ₄ O ₁₂ , Ba ₃ Al ₂ O ₆ , Ba ₅ Al ₂ O ₈ , Ba ₇ Al ₂
O ₁₀ , Ba ₁₀ Al ₂ O ₁₃ , BaCa ₂ Al ₈ O _15, etc., and (m ₁ BaO · m ₂ CaO) · nBaAl ₂ O ₄ [n is an integer of 1 or more; m ₁ and m ₂ are An integer of 0 or more; m ₁ + m ₂ ≧ 1].

Next, 6 g (5.7 wt%) of the emitter agent adjusted in form of aluminate and 100 g of W powder, which is a refractory metal having a high melting point, are dry-mixed in step 10 of FIG. Rubber press molding is performed at a pressure of about ² ton / cm ² to form a column.

Next, as shown in FIG. 2, after the molded body 21 is housed in a Pyrex glass container 22, Al ₂ O ₃ powder 23 is filled in the Pyrex glass container 22, and the inside is evacuated. The encapsulation step 12 ends.

Next, as shown in FIG. 3, the vacuum-sealed Pyrex glass container 24 is housed in an HIP processing furnace 25, and subjected to HIP processing according to the heating and pressurizing schedule shown in FIG. Was. The final HIP processing conditions are 1000 ° C,
An argon gas atmosphere at 1500 atm for 20 minutes. This step is the HIP processing step 13.

Further, the sintered body was pressed into a predetermined shape in a machining (pelleting) step 14.

Finally, as step 15, the surface of the pellet was cleaned and sent to the next assembling step. Similarly, 4 g (3.8 wt%) and 8 g (7.4 wt%)
%), 10 g (9.1 wt%), 12 g (10.7 wt%)
%), 14 g (12.3 wt%), 16 g (13.8 w
t%) and 18 g (15.3 wt%) of W powder 1 respectively.
After mixing with 00 g, an impregnated cathode was prepared in the above-described manufacturing process and sent to the next assembling process.

The electron emission characteristics of the impregnated cathodes having different emitter agent contents were measured.

FIG. 5 shows the impregnated cathode of this embodiment.
Emitter content when HIP processing temperature is used as a parameter and emission current density at operating temperature of 1000 ° C (arbitrary unit)
Shows the relationship.

FIG. 5 shows that the emission current density increases remarkably as the content of the emitter agent increases, to about 7 wt%.
It can be seen that the emission current density is maximum at 12 wt%, and the emission current sharply decreases as the content further increases.

It is effective to exceed 5.7% by weight and obtain 13.8% by weight or less at which emission current density higher than the conventional level can be obtained.

The HIP processing temperature is optimally 1300 ° C., but 900 ° C. to 1400 ° C. is effective.

According to this embodiment, (m ₁ Ba) such as Ba ₅ CaAl ₄ O ₁₂ , Ba ₃ Al ₂ O ₆ , Ba ₅ Al ₂ O ₈ contained in the emitter agent is used.
_{O · m 2 CaO) · nBaAl} 2 O 4 [n is an integer of 1 or more; m
₁ , m ₂ is an integer of 0 or more; m ₁ + m ₂ ≧ 1], the barium aluminate compound hardly reacts with W as compared with BaO 2, so that the change to tungstate is significant even after HIP treatment. Is confirmed to be suppressed.

Further, these barium aluminate compounds do not contain a carbonate, so that carbon in the carbonate does not react with W to form WC.

In the present embodiment, in order to convert the mixed powder of BaCO ₃ , CaCO ₃ , and Al ₂ O _{3 as} the raw material of the emitter agent into a barium aluminate compound, it was manufactured under the above-mentioned conditions of the present embodiment. This is an example, and the mixing ratio of the raw material powder, the heat treatment temperature, the treatment atmosphere, and the like are appropriately set, and (m ₁ Ba
_{O · m 2 CaO) · nBaAl} 2 O 4 [n is an integer of 1 or more; m
₁ , m ₂ is an integer of 0 or more; m ₁ + m ₂ ≧ 1], so that the barium aluminate compound in the form of a large amount may be contained in the emitter agent.

HIP processing conditions (temperature, time, pressure)
Is not limited to the conditions of the examples, but when the HIP processing temperature is lower than 900 ° C., the strength of the sintered body is reduced at any content of the emitter agent, and the pelletizing process 1
4 can not stand.

On the other hand, at a temperature higher than 1400 ° C., the strength of the sintered body increases, but the barium aluminate compound in the emitter reacts remarkably with W at any content of the emitter, and Convert to an invalid tongue state.

For this reason, the HIP processing temperature needs to be 900 ° C. or higher and 1400 ° C. or lower.

[0033]

As described above, as an emitter agent,
(M ₁ BaO · m ₂ CaO) · nBaAl ₂ O ₄ [n is an integer of 1 or more; m ₁ and m ₂ are integers of 0 or more; m ₁ + m ₂ ≧ 1]. Over 7wt%,
The emitter is reacted with W during HIP processing to generate WC by mixing and using the high melting point heat-resistant metal powder in the range of 13.8% by weight or less and by setting the HIP processing temperature to 900 ° C to 1400 ° C. it no to, also barium aluminate compound can be remarkably suppressed even for changes to the tungstate is not valid, such as BaWO _4, and can be pelletized to produce a readily cathode sintered body.

[Brief description of the drawings]

FIG. 1 is a flowchart of a manufacturing process of an impregnated cathode according to the present invention.

FIG. 2 is a sectional view for explaining an encapsulation step in the present invention.

FIG. 3 is a cross-sectional view for explaining a HIP processing step of the present invention.

FIG. 4 is a program showing an example of HIP processing conditions of the present invention.

FIG. 5 is a diagram showing the electron emission characteristics of the impregnated cathode according to the present invention.

FIG. 6 is a flowchart of a manufacturing process of a conventional impregnated cathode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 Dry mixing step 11 Press forming step 12 Encapsulation step 13 HIP processing step 21 Molded body 22 Pyrex glass container 23 Alumina powder 24 Vacuumed Pyrex glass container 25 HIP processing furnace

Claims (3)

(57) [Claims] At least a step of dry-mixing a high-melting-point heat-resistant metal powder and an electron-emitting substance, a step of press-molding a mixed powder, and encapsulating a molded body; In the method for producing an impregnated cathode comprising a step of sintering the mixed powder and, as the electron emitting material,
(M ₁ BaO · m ₂ CaO) · nBaAl ₂ O ₄ [n is an integer of 1 or more;
m ₁ and m ₂ are integers of 0 or more; m ₁ + m ₂ ≧ 1], wherein a barium aluminate compound is used. 2. A method for producing an impregnated cathode, wherein the treatment temperature of the hot isostatic pressure treatment according to claim 1 is a temperature of 900 ° C. or more and 1400 ° C. or less. 3. The barium aluminate compound to be mixed with the high melting point heat-resistant metal powder according to claim 1 has a mixing ratio of 5.7% by weight.
, And not more than 13.8 wt%.