JP3205638B2 - 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 an impregnated cathode used for an electron tube requiring a high current density.

[0002]

2. Description of the Related Art Conventionally, an impregnated cathode sinters particles of a high melting point metal such as tungsten (W) or molybdenum (Mo), melts and impregnates it with oxygen-free copper, etc., and machine-processes it into a predetermined shape. The so-called copper removal is performed to remove copper by heating in a vacuum or dissolving with an acid, etc., and then melt-impregnating with an electron-emitting substance, polishing with a tungsten wire brush, alumina polishing cloth, etc. It was manufactured by a process that removes electron-emitting materials. The flowchart is shown in FIG. However, in this flowchart, the inspection step and other steps of the end-of-leaf branch not related to the present invention are omitted. In the figure, tungsten (W) is used as a high melting point metal, BaCO ₃ is used as an electron-emitting substance,
Each of CaCO ₃ and Al ₂ O ₃ is employed.

[0003]

As described above, in the conventional method, a sintered body of a refractory metal such as tungsten or molybdenum is melt-impregnated with an electron-emitting substance. The sintering of the part is not uniform, the pores required for impregnation are crushed, and the penetration of the electron-emitting substance is deteriorated. Oxygen-free copper does not necessarily have to be impregnated for machining, but there are also methods of temporary sintering and machining, and polishing after main sintering. This is a factor that raises manufacturing costs.

However, it is not easy to make the porosity of the sintered body constant even with such a step, and the variation can be eliminated even by strict control of the particle size of the refractory metal such as tungsten. It is difficult. Therefore, there has been a problem that the concentration distribution of the electron-emitting substance impregnated in the sintered body also varies, which affects the electron emission characteristics.

The present invention has been made in view of the above problems, and has as its object to provide an impregnated cathode in which the manufacturing process can be simplified and the electron emission material has a good concentration distribution.

[0006]

To achieve the above object, according to an aspect of the invention, the mixture coating or披着 of binary or more carbonate particles containing at least barium tungsten particles
After forming the formed particles, compression molding to form a compact having a predetermined shape, and decomposing the binary or more carbonates containing at least barium in the compact into oxides and melting the oxides And a heat treatment step of sintering tungsten. Alternatively, the step of after forming the mixture coated or披着is allowed particles of binary or more oxide particles comprising <br/> least barium tungsten particles were compression molded to form a compacted body having a predetermined shape, A heat treatment step of melting at least binary oxide containing barium in the compact and sintering tungsten.

[0007]

[Function] Coating high-melting metal particles with particles of electron-emitting substance
Alternatively, by forming and sintering the deposited particles , good dispersibility of the electron-emitting substance in the high-melting metal can be secured in advance, and the electron-emitting substance is injected into the cathode by the sintered state of the high-melting metal particles. It does not cause poor distribution or variations in density distribution. These particles were compression molded.
Thereafter, when the electron-emitting material is melted by heat treatment, the high melting point metal is sintered at a lower temperature than ever before. The present inventors have knowledge of these facts and have led to the present invention.

[0008]

Embodiments of the present invention will be described below. First, the average particle size of 10 [mu] m or less of BaCO _3, CaCO _3, A
The particles mixed with particles of l ₂ O ₃ at a predetermined molar ratio, polyvinyl
Mix with a binder such as Neil alcohol (PVA)
Tungsten having an average particle size of 1 to 20 μm
(W) Particles are coated or covered with a powder surface modification device, etc.
After the formed particles are formed, they are compressed and molded with a compression molding machine such as a mechanical press or a hydrostatic press at a pressure of 1.0 to 4.0 t / cm ² to produce a compact having a predetermined shape. At this time, at the time of completion of sintering performed later, in order to obtain a cathode having a final shape, the degree of shrinkage or deformation due to sintering is grasped by experiments,
It is important to determine the shape of the compression molding machine.

Next, the compact is placed in a hydrogen furnace,
Set to 1300 ° C, carbonate (BaCO ₃ , CaCO ₃ )
Is heated until it is completely decomposed into oxides (BaO, CaO). Subsequently, the hydrogen furnace was set at 1600 to 1800 ° C,
Oxide (BaO, CaO) and Al ₂ O ₃ are melted. By maintaining this state, the tungsten is sintered to become porous tungsten, and then cooled and excessive electron emission positive substances (BaO, Ca) adhered to the porous tungsten.
O, Al ₂ O ₃ ) is polished and removed with a tungsten wire brush, an alumina polishing cloth, or the like, and as a result, an impregnated cathode in which porous tungsten is impregnated with an electron-emitting substance can be obtained. .

Conventionally, 220 is used for sintering tungsten alone.
Although heating at 0 to 2400 ° C. was required, the present invention required heating at 1700 to 2000 ° C., and therefore, even if sintering and impregnation, which were conventionally performed in separate steps, were performed substantially simultaneously according to the present invention, the emissivity of the electron-emitting material could be reduced. Dissipation by evaporation can be avoided. FIG. 1 shows a flowchart of a series of steps in the embodiment described above. Note that, also in FIG. 1, the step of the branch and leaf end node is omitted as in FIG. 2. By comparing this figure with FIG. 2 showing a conventional example, it can be understood that the conventional process is remarkably omitted according to the present invention.

In the embodiment described above, the electron emission
BaCO ₃ , which is a carbonate , and CaC
O ₃ and Al ₂ O ₃ were used, but the oxide Ba
Obviously , O, CaO and Al ₂ O ₃ may be used.
You. At this time, there is no process of decomposing the carbonate into oxide.
You. In the above embodiment, the carbonate containing Ba or
Is a carbonate or acid of Ca as long as it contains oxides
Compound, Al ₂ O _3, or the not included a cathode even not formed child
Can be.

[0012]

As described above, according to the present invention,
The process can be significantly simplified, and the amount of electron-emitting substances can be reduced.
An impregnated cathode having good dispersibility can be manufactured. Also,
To provide an inexpensive impregnated cathode with improved electron emission characteristics
Can be.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an outline of a series of steps in one embodiment of the present invention.

FIG. 2 is a flowchart showing an outline of a series of steps in a conventional example.

Claims (2)

(57) [Claims] 1. A coating of a mixture of binary or more carbonate particles containing at least barium tungsten particles or
After forming the deposited particles, compression molding to form a compact having a predetermined shape, and decomposing a binary or more carbonate containing at least barium in the compact into an oxide, And a heat treatment step of sintering tungsten. 2. A coating of a mixture of binary or more oxide particles containing at least barium tungsten particles or
After forming the披着is allowed particles, compression molding, melt forming a compacted body having a predetermined shape, the upper Symbol binary or more oxide containing at least barium compacted body during the sintering tungsten A method for producing an impregnated cathode, comprising a heat treatment step.