JPH0619942B2 - Method for manufacturing impregnated cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for manufacturing an impregnated cathode, and particularly to a manufacturing method excellent in mass productivity.

(Prior Art) As a structure of an impregnated cathode and a method of manufacturing the same, one of the inventors of the present invention has already proposed a structure disclosed in JP-A-56-86436. In this method, a semi-sintered thin sheet-shaped ruthenium molybdenum brazing material is interposed between the porous cathode substrate and the supporting cup, and the cathode substrate and the supporting cup are joined by resistance welding.

This is highly reliable, but there is a difficulty in automation because it is necessary to insert and sandwich a thin sheet-shaped brazing material processed into a predetermined shape and size between the cathode substrate and the supporting cup. , Not necessarily suitable for mass production.

On the other hand, a method disclosed in Japanese Patent Laid-Open No. 58-44643 has been proposed as a manufacturing method excellent in mass productivity. First, a large diameter and long porous tungsten rod obtained by compression-molding tungsten powder and then sintering in a reducing atmosphere is manufactured. Next, the holes are impregnated with copper. This is sliced by lathing or wire electric discharge machining to obtain a large-diameter copper-impregnated porous tungsten thin plate having a thickness of about 0.5 mm and a diameter of about 30 mm, for example. Next, copper is removed by dissolution of copper with nitric acid and heating in a reducing atmosphere. Then, on the back surface of this large-diameter porous tungsten thin plate, in order to prevent the electron emitting substance from evaporating from the back surface side, the ruthenium molybdenum brazing material is melt-impregnated so as to fill the back surface side pores of this porous substrate. . Therefore, a suspension prepared by adding an organic binder to a mixed powder of ruthenium and molybdenum is dropped and dried, and then heated at, for example, 2000 ° C. in a reducing atmosphere to melt-impregnate the ruthenium molybdenum wax into the porous substrate. . Then, the disk-shaped porous tungsten was converted into BaO, C in a reducing atmosphere.
An electron emitting material consisting of aO and Al ₂ O ₃ is impregnated.
Further, this large-diameter porous tungsten thin plate is cut out into a large number of disk-shaped cathode single substrates having a predetermined shape and size by electric discharge machining or laser machining. Then, such a cathode single substrate is joined to the supporting cup by welding.

According to such a manufacturing method, it is particularly difficult to control the penetration depth of the brazing filler metal from the back surface side of the porous substrate, and if it penetrates too deeply, the electron emission life of the cathode itself may be shortened. Further, the variation in the penetration depth tends to increase.

(Problems to be Solved by the Invention) As described above, according to the conventional manufacturing method, it is not easy to obtain an impregnated-type cathode assembly having stable quality in mass production.

The present invention solves the above inconveniences, reliably prevents the evaporation of the electron emitting substance from the back surface side of the porous cathode substrate, and is stable in mass production, and a method for producing an impregnated cathode excellent in mass productivity. It is intended to be provided.

[Structure of the Invention] (Means for Solving the Problems) The present invention is to apply a ruthenium / molybdenum mixed powder mixed with a solvent to one main surface of a large-diameter thin plate of porous tungsten, and then apply this ruthenium.・ Sintered at a temperature lower than the melting point of the molybdenum mixed coating layer to adhere the ruthenium / molybdenum mixed sintered layer integrally, and then impregnate the holes of the large-diameter thin plate of porous tungsten with an electron emitting substance. After that, a large-diameter thin plate of porous tungsten to which the ruthenium / molybdenum mixed sintered layer is integrally attached is cut out into a single substrate having a predetermined shape and size, and then this single substrate is used as a cup-shaped cathode support. Method for producing impregnated cathode in which a sintered layer is placed in contact with the bottom wall and at least a part of this sintered layer is melted by welding to join the single substrate and the cathode support It is.

(Operation) According to the present invention, since the ruthenium / molybdenum mixed sintered layer is adhered by entering into the recess opening on the back surface of the thin plate of the hole portion of the porous tungsten thin plate, sufficient adhesion strength is obtained and baking is performed. The peeling of the bonding layer is prevented, and the impregnation amount of the electron emitting substance into the pores of the porous tungsten thin plate is prevented. Then, when fixing the single substrate obtained by the cutting process to the cup-shaped cathode support, the ruthenium / molybdenum mixed sintered layer is at least partially melted to function as a brazing material, and a strong bonding state is obtained. Therefore, a cathode impregnated with a sufficient amount of the electron emitting substance can be obtained, and the assembling property is excellent.

(Example) Hereinafter, an example will be described with reference to the drawings. The same parts are represented by the same symbols.

First, the process of manufacturing the impregnated cathode single substrate will be described with reference to FIGS. 1 (a) to 1 (h).

That is, first, as shown in Fig. 1 (a), the particle size is 2-10 μm.
m tungsten powder is compression-molded and then sintered in a reducing atmosphere to obtain a long porous tungsten rod 11 having a large diameter of 50 mm, for example. Then, copper is infiltrated to improve workability.

Next, as shown in FIG. 3B, the copper-impregnated porous tungsten rod 11 is sliced into a thin plate having a thickness of 0.5 mm by wire electric discharge machining or a diamond wire saw. Thus, a large-diameter thin plate 12 of porous tungsten is obtained.

Next, as shown in (c) of the figure, hold each large-diameter thin plate 12
13 are placed on top of each other and heated in an acid melting or reducing atmosphere to evaporate and remove copper.

After that, on the back side of the porous tungsten large-diameter thin plate 12,
A suspension obtained by adding an organic binder to a mixed powder composed of 40.9% ruthenium and 57.1% molybdenum is applied by a printing method or brush coating, and dried to form a coating layer 14a.

Next, this is placed in a reducing atmosphere at the melting point of the ruthenium / molybdenum mixed coating layer (about 194 in the case of the above-mentioned mixed powder).
5 ° C.), for example, by heating at 1900 ° C. for 10 seconds, a ruthenium molybdenum sintered layer 14 is formed on the back surface side of the porous Tangste large-diameter thin plate as shown in FIG. The thickness is formed in the range of ˜50 μm. In this case, since the suspension is applied and then sintered, ruthenium and molybdenum enter into the hollow holes on the back surface of the porous tungsten large-diameter thin plate, but the amount is the total volume of the thin plate holes. It is so small that it can be ignored compared to. Thus, the ruthenium-molybdenum sintered layer adheres to the back surface of the thin plate with almost no impregnation in the pores.

After that, as shown in FIG. 6F, the surface side of the porous tungsten large-diameter thin plate 12 is impregnated with an electron emitting material 15 made of BaO, CaO, and Al ₂ O ₃ in a reducing atmosphere.
The large-diameter substrate is subjected to a surface treatment to remove the surplus electron emitting material.

Then, as shown in (g) and (h) of the same figure, a large number of impregnated-type cathode simple substance substrates 16 having a diameter of 1.45 mm, for example, are obtained by electric discharge machining or laser machining. Each single substrate 16 is obtained with the ruthenium-molybdenum sintered layer 14 integrally attached to the back surface side.

According to the manufacturing process of the impregnated cathode according to the embodiment of the present invention, since the ruthenium-molybdenum suspension is applied to the large-diameter thin plate of porous tungsten, workability and uniformity are improved. And the ruthenium / molybdenum mixed sintered layer is
Since the porous tungsten thin plate enters and is adhered to the recess of the hole that opens on the back surface, sufficient adhesion strength is obtained and peeling of the sintered layer is prevented. The reduction of the impregnated amount of the electron emitting substance is prevented. In other words, since the mixed coating layer of ruthenium / molybdenum is sintered at a temperature lower than its melting point, ruthenium / molybdenum does not melt, and therefore, in this sintering process, ruthenium / molybdenum is not contained in the pores of the porous tungsten thin plate. Therefore, the impregnation amount of the electron emitting substance into the pores of the porous tungsten large-diameter thin plate in the next step is the same as the conventional method of impregnating the pores by melting the above-mentioned ruthenium molybdenum braze. In comparison, it can be increased sufficiently. Moreover, by irradiating the surface of the ruthenium / molybdenum sintered layer with a laser, the diameter of the ruthenium / molybdenum sintered layer does not become larger than the diameter of the impregnated type cathode single substrate, but rather due to the influence of heat during electric discharge machining or laser machining. Since the peripheral portion of the sintered layer is partly scattered or melted, the diameter of the sintered layer is always small. Therefore, since the peripheral portion of the single substrate is tapered or arcuate, it can be smoothly inserted into the supporting cup in the subsequent assembling steps.

The ruthenium-molybdenum sintered layer is a ruthenium,
It is mainly composed of molybdenum, and a slight amount of another metal may be mixed therein.

The individual substrates 16 thus manufactured are assembled as an electron gun cathode assembly for a cathode ray tube as shown in FIG. That is, ruthenium-molybdenum sintered layer 14 on the back side
Impregnated type cathode single substrate 16 in a state of being integrally attached,
It is placed at the bottom of a supporting cup 17 made of tantalum or niobium. And the electrode of the resistance welding machine (not shown)
The back surface of the supporting cup 17 and the upper surface of the single cathode substrate 16 are brought into contact with each other and resistance welding is performed to join them. A part of the ruthenium-molybdenum sintered layer is melted and alloyed by this welding, and acts as a brazing filler metal to bond the single substrate and the supporting cup. In this way, the impregnated-type cathode single substrate 16 is fixed to the bottom of the supporting cup 17.

Next, the cup 17 welded to the single substrate 16 is fitted and fixed to the top of the cathode sleeve 18 made of tantalum or niobium, and the side surface is welded at the melting point 19. Further, a cathode support 20 made of three tantalum or niobium ribbons is fixed to the outer periphery of the bottom of the cathode sleeve 18 at welding points 21.
The other end of the cathode support 20 is fixed to a shoulder 22a of a cathode support cylinder 22 made of a Fe-Ni-Co alloy plate at a welding point 23 to form a cathode assembly.

[Advantages of the Invention] As described above, according to the present invention, the mechanical adhesion strength of the ruthenium-molybdenum mixed sintered layer to the porous tungsten large-diameter thin plate can be sufficiently obtained, and the void of the porous tungsten thin plate can be obtained. There is no impregnation of ruthenium molybdenum into the pores, and a sufficient impregnation amount of the electron emitting material can be obtained. When the single substrate is fixed to the cup-shaped cathode support, the ruthenium / molybdenum mixed sintered layer is at least partially melted to serve as a brazing material, and a strong bonding state is obtained.

Therefore, a cathode impregnated with a sufficient amount of the electron emitting substance is obtained, evaporation of the electron emitting substance from the back surface side of the single substrate is prevented, and the assembling property is excellent.

[Brief description of drawings]

1 (a) to 1 (h) are process drawings showing an embodiment of the present invention, and FIG. 2 is a partially cutaway perspective view showing a cathode assembly using the same. 11 …… Columnar porous tungsten sintered compact, 12 …… Porous tungsten large diameter thin plate, 14 …… Ruthenium molybdenum sintered layer, 15 …… Electron emission material, 16 …… Cathode single substrate, 17 …… Cathode support Cup.

Claims (1)

[Claims] 1. A method for producing an impregnated cathode in which a large-diameter thin plate of porous tungsten is impregnated with an electron-emitting substance, which is cut into a single substrate having a small diameter, and which is then joined to a cup-shaped cathode support. After coating a mixture of ruthenium / molybdenum mixed powder in a solvent on one major surface of a large-diameter thin sheet of high-quality tungsten, sintering it at a temperature lower than the melting point of this ruthenium / molybdenum mixed coating layer, and ruthenium / molybdenum A step of integrally adhering the mixed sintered layer, a step of impregnating the holes of the large-diameter thin plate of porous tungsten with an electron emitting material, and a step of integrally forming the ruthenium / molybdenum mixed sintered layer. The step of cutting out the large-diameter thin plate of porous tungsten attached to the single substrate into a single substrate having a predetermined shape and size, and thereafter, removing this single substrate. Arranging the sintered layer in contact with the bottom wall of the cup-shaped cathode support and melting at least a part of the sintered layer by welding to bond the single substrate and the cathode support. A method for manufacturing an impregnated-type cathode, comprising: