JPS63175313A - Impregnated cathode and its manufacture - Google Patents

Abstract

PURPOSE:To secure effective pores and to obtain a metallic porous matter with good reproducibility by impregnating a prescribed metallic oxide into pores of the metallic porous matter which is composed of W particles and W particles coated with a specific metallic oxide. CONSTITUTION:An impregnated cathode is composed of the following ingredients: W particles 1, W particles 2 coated with an intermetallic compound comprising W and one of Os, Ir, Lu, Re, and Se, and an oxide 3 which consists of Al and at least one of alkaline metals and which is impregnated into pores of a metallic porous matter consisting of particles 1 and 2. In order to manufacture this cathode, firstly W particles are mixed with one of Os, Ir, Lu, Re, Sc, for example, Ir powder (a content of Ir is 45% or less), and this mixed material is fired so as to obtain W particles 2 coated with an intermetallic compound (oxide) consisting of W and Ir. These particles 2 and W particles 1 are mixed (1:4) and they are molded by heating and then they are sintered. A metallic porous matter obtained is impregnated, at high temperature, with an oxide consisting of Ba and Al and Ca (4:1:1).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cathode for an electron tube such as a traveling wave tube, a cloistron, or a magnetron, and a method for manufacturing the same.

[Conventional technology]

Impregnated cathodes consisting of porous metal substrates containing active oxidants, in particular barium oxide, have long been known. As a result of many years of research and development, this cathode has been put into practical use as a porous tungsten metal impregnated with barium oxide, aluminum oxide, and calcium oxide. This cathode is capable of emitting more than IA of electrons per 112 ICl, and development of cathodes capable of emitting even more electrons is currently underway. For example, experiments at the U.S. Navy's research laboratory have shown that a cathode based on a mixed metal of tungsten and iridium has shown promising results. is formed. When this intermetallic compound is used alone, the amount of thermionic electrons produced by the reaction with barium is much smaller than that produced by tungsten and barium. However, it is generally known that when an intermetallic compound exists together with tungsten and barium, the amount of thermionic electrons produced is several times higher than the amount produced by tungsten and barium. The optimum value is when the tungsten to iridium ratio is 4=1. However, in the actual prototype, sintering progressed due to heating during the formation of the porous metal body, as shown in Figure 6, and the space in the porous metal body for barium etc. was reduced, and good results could not be obtained. . In experiments, even in the best case, when the ratio of tungsten to iridium was 20:1, the increase was only several tens of percent compared to the case of using only tungsten. Therefore, it is essential to control the amount and area of intermetallic compounds formed.For example, in the process of forming a porous metal body, a method has been announced in which an aggregate of tungsten particles is first formed and iridium is mixed with the aggregate. (Unexamined Japanese Patent Publication No. 5
3-13348).

[Problem that the invention seeks to solve]

Since the conventional impregnated cathode described above requires an effective metal porous body, it was not possible to heat the cathode to a sufficiently high temperature in the process of forming the metal porous body.

Moreover, as a result, each mixed substance could not be sufficiently diffused as shown in FIG. 5, and the original performance of the thermionic cathode could not be fully exhibited.

In order for an impregnated cathode to exhibit sufficient properties, osmium,
It requires a surface in which iridium, ruthenium, etc. are diffused into tungsten, and a surface in which tungsten remains. However, if osmium, iridium, ruthenium, etc. are heated until they are sufficiently diffused, sintering will proceed too much as shown in Figure 6, and the space in which aluminum, barium, and calcium oxides can be impregnated will decrease. was there. In addition, the degree of diffusion of mixed substances such as osmium, iridium, and ruthenium is controlled by heating temperature and time, but it is difficult to obtain good reproducibility due to variations in particle shape and oxidation and contamination state on the particle surface. It had the disadvantage of being.

[Means for solving problems]

The present invention comprises a porous metal body containing at least one of osmium, iridium, ruthenium, rhenium, and scandium oxides and tungsten as constituent elements, and the pores of the porous metal body contain aluminum and at least one alkaline earth element. In an impregnated cathode that is almost filled with an oxide having or tungsten particles, tungsten and osmium1. It is characterized by comprising particles made of an intermetallic compound with at least one substance of iridium, ruthenium, rhenium, and scandium oxide. Also according to the invention, tungsten particles and osmium.

mixing and sintering at least one substance of iridium, ruthenium, rhenium and scandium oxide;
A method for manufacturing an impregnated cathode is obtained, which includes a step of pulverizing a sintered body, and a step of mixing and sintering the pulverized powder and tungsten powder.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a sectional view of an impregnated cathode according to an embodiment of the present invention. 1 is a tungsten particle, 2 is a particle coated with an intermetallic compound, and 3 is an oxide. In the manufacturing method, first, tungsten and iridium having a particle size of 5 to 20 microns are mixed. The proportion of iridium is 45% or less, substantially about 20% of the total. This was heated to about 1900℃ for 10
The particle size to be fired and crushed for more than a minute is 10 to 20 microns. As a result, tungsten particles coated with an intermetallic compound of tungsten and iridium are obtained. After mixing the iridium-coated tungsten particles 2 and tungsten particles 1 at a mixing ratio of 1:4 and press-molding the mixture, the mixture was heated to 1750°C.
Sinter for 10 minutes. In the metal porous body made in this way, 4
It is impregnated with oxides 3 of barium, aluminum, and calcium mixed in a 1:1 ratio at 1750°C. A longitudinal cross-sectional view of a surface-treated impregnated cathode is shown in FIG. 1, and an enlarged view thereof is shown in FIG.

Next, another example will be shown. Tungsten and iridium are mixed at a weight ratio of 55:45 and melted at 3000°C. The ingot thus produced is ground into a powder of 10 to 20 microns. The pulverized intermetallic compound powder 6 and tungsten powder 1 were mixed in a ratio of 1:4, pressure-molded, and then fired at 1750° C. for 10 minutes. The metal porous body thus produced is impregnated with an oxide 3 such as barium and subjected to surface treatment to obtain an impregnated cathode. FIG. 3 is a longitudinal sectional view of this cathode. In addition, FIG. 4 shows an enlarged view of FIG. 3. Although the above embodiment describes the case where tungsten and iridium are mixed, the invention is not limited to this. A porous metal body with a similar structure can be obtained by mixing the two.

〔Effect of the invention〕

As is clear from a comparison between Figures 2 and 3 showing the present invention and Figures 5 and 6 showing the conventional example, the present invention allows osmium, iridium, etc. to diffuse into tungsten while ensuring effective pores. This method has the effect of obtaining an ideal porous metal body with a desired proportion of the exposed surface and the surface of only tungsten with good reproducibility.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of one embodiment of the impregnated cathode of the present invention, Fig.
The figure is an enlarged view of Fig. 1, Fig. 3 is a sectional view of another embodiment of the present invention, Fig. 4 is an enlarged view of Fig. 3, and Figs. 5 and 6 are cross sections of a conventional impregnated cathode. It is an enlarged view. 1... Tungsten particles, 2... Particles whose surfaces are coated with an intermetallic compound with iridium, 3
... Oxides of aluminum, barium, calcium, etc., 4,6... Intermetallic compounds of tungsten and iridium, 5... Tungsten, 7... Iridium particles,
8...Iridium.

Claims (3)

[Claims] (1) A porous metal body containing at least one substance of osmium, iridium, ruthenium, rhenium, and scandium oxide and tungsten as constituent elements, and the pores of this metal porous body are composed of aluminum and at least one substance of scandium oxide.
In an impregnated cathode that is almost filled with an oxide containing two alkaline earth elements, the particles constituting the metal porous body are tungsten particles, and at least one substance of osmium, iridium, ruthenium, rhenium, and scandium oxide is present on the surface of the tungsten particles. An impregnated cathode characterized by comprising particles coated with. (2) The first claim in which the particles constituting the metal porous body are composed of tungsten particles and particles made of an intermetallic compound of tungsten and at least one substance of osmium, iridium, ruthenium, rhenium, and scandium oxide. Impregnated cathode as described in section. (3) Tungsten particles, osmium, iridium,
It is characterized by comprising the steps of mixing and sintering at least one substance of ruthenium, rhenium and scandium oxides, pulverizing the sintered body, and mixing and sintering the pulverized powder and tungsten powder. Method for manufacturing an impregnated cathode.