JPS6017831A - Impregnated cathode - Google Patents

Abstract

PURPOSE:To obtain the impregnated cathode having a little amount of evaporation together with a stable quality by forming a gap while removing by the thickness of a few mum. an electron emissive substance located inside an empty hole and exposed on the cathode surface. CONSTITUTION:The high melting point metal powder such as tungsten powder is sintered into a desired cathode form for forming a cathode base 1 having porosity of 20-25% while being heated up to 1,600-1,700 deg.C after being coated with an electron emissive substance or the like formed in advance for being melted and impregnated. Thereafter, a surplus electron emissive substance attached to the cathode surface except the empty hole of the cathode base is removed by polishing. Further, the electron emissive substance 6 located on the cathode surface part 7 of the empty hole 5 and exposed on the cathode surface is removed by the thickness from a few mum to scores of mum for forming the gap 8. Thereby, the cathode extreamly hard to be evaporated can be obtained, while the free barium formed by reducing reaction with the base metal is liquefied and disporsed on the cathode surface so as not to badly influence the electron emissive properties at all.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impregnated cathode, and more particularly to an impregnated cathode with an improved cathode surface and improved electrical characteristics.

For example, an impregnated cathode is a cathode substrate made of a porous high melting point metal having pores with a porosity of 20 to 25%, and is coated with barium oxide (Bad), oxidizing lucium (Cab), aluminum oxide (A1203), etc. A material of an electron radioactive substance consisting of a mixture is heated to 1600 to 1700°C in a non-oxidizing atmosphere in vacuum or hydrogen to melt and impregnate it to form a cathode pellet.9For example, as shown in FIG. (2) is fixed to the tip of the cathode sleeve 3 together with the isolation plate 2, and the heater 4 is inserted into the cathode sleeve 3 to cause a reduction reaction with the structural metal to generate free barium, which diffuses onto the cathode surface to form barium monomers. Electron emission occurs by creating an atomic layer and lowering the work function of the cathode surface.

This impregnated cathode has an operating temperature of 950°C to 1050°C, which is about 2 times higher than the oxide cathode widely used in electron tubes.
Although the current density is higher than 00°C, it has the characteristic that it can obtain a current density more than 20 times that of 10AA, and is used in electron tubes that require high current density or have severe usage conditions. . However, this impregnated cathode has the disadvantage that the amount of evaporation from the cathode is about two orders of magnitude higher than that of an oxide cathode due to the high operating temperature. In other words, if the amount of evaporation from the cathode is large, 2. For example, in electron tubes equipped with a grid, such as traveling wave tubes and image pickup tubes, the evaporated electron radioactive material will land on the grid, causing grid emission, which will affect the characteristics. cause deterioration.

In addition, in high-definition image pickup tubes and video tubes, the small holes provided in the electron beam control holes are buried in electron radioactive materials due to grids having very small holes, making them inoperable. Furthermore, if the amount of evaporation is large, there is also the drawback that the degree of vacuum decreases, which adversely affects the electrical characteristics of the electron tube, even if it does not cause the tube to become inoperable.

On the other hand, an impregnated cathode involves many intermediate steps such as impregnating the cathode substrate made of porous high-melting point metal with an electron radioactive substance and then joining it with a cathode sleeve or enclosing it into an electron tube. It takes a considerable amount of time to create a vacuum, and during that time there are many opportunities for the impregnated cathode to be exposed to air containing moisture. Generally, many electron radioactive substances easily react with moisture, and once they react with moisture, they no longer function as electron radioactive substances, which adversely affects the electron emission characteristics. Therefore, the electron emission characteristics fluctuate due to the intermediate steps of electron tube manufacturing.The present invention was made in view of this situation, and an object of the present invention is to provide an impregnated cathode for an electron tube that does not deteriorate the electrical characteristics of the electron tube and has good reliability. The purpose is to
Specifically, after melting and impregnating an electron radioactive substance into the pores of a cathode substrate made of a porous high-melting point metal having a large number of pores, at least a number of the electron radioactive substances in the pores exposed on the cathode surface are melted and impregnated. This structure is such that the electron emissive material is not exposed on the cathode surface by removing it to a thickness of μm to form a void. This will be explained in detail below with reference to the drawings.

First, a method for manufacturing an impregnated cathode, which is an embodiment of the present invention, will be described. First, high-melting point metal powder such as tungsten powder with an average particle size of 5 μm is sintered into a desired cathode shape, or the voids of a sintered body sintered into a large shape are impregnated with copper or the like. Electron radioactive materials such as Bad, Cab produced by impregnation after machining into the cathode shape.

A compound consisting of A720a or a mixture of raw materials for electron radioactive substances such as BaCO3, CaC0a, and AlzOa in an appropriate molar ratio is applied to
Heat to 0°C to melt and impregnate. When this raw material is used, the generation and impregnation of the electron radioactive substance are performed at the same time. Thereafter, excess electron emitting material adhering to the surface of the cathode other than the pores of the cathode base is removed by polishing to form cathode pellets.

If this cathode pellet is fixed to a cathode sleeve to form a cathode, it becomes a conventional impregnated cathode.

In the present invention, the electron radioactive material in the pores exposed on the surface of the cathode pellet is further removed to a thickness of several micrometers to several tens of micrometers from the cathode pellet state with excess electron radioactive material removed. It is distinctive in that it has voids formed on its surface. This state is enlarged and exaggerated in FIG. 2, and a cross-sectional view is shown in comparison with a conventional cathode pellet. That is, FIG. 2 ta+ shows a conventional cathode pellet l in which the electron radioactive substance 6 is filled throughout the holes 5, and FIG. 2 fbl shows the cathode surface portion 7 of the holes 5 exposed to the cathode surface of the present invention. A void 8 is formed by removing the electron radioactive substance 6.

You can remove it mechanically by brushing it with something.

Chemical removal using a treatment solution or the like, or thermal removal by heating in a high vacuum for a long time, etc., can be applied. The cathode Pel knot thus formed is fixed to a cathode sleeve or the like, a heater is inserted, and the impregnated cathode is sealed in an electron tube and evacuated to function as a cathode.

6- According to the impregnated cathode of the present invention, the electron radioactive substance is not directly near the cathode surface, so the distance between the electron radioactive substance and the anode or grid becomes large, and the surface of the cathode pellet absorbs moisture from the outside air. A cathode that is extremely difficult to evaporate can be obtained because the electron-emitting material on the surface that is easily absorbed and evaporated has been removed.

A comparison with the poles is shown in FIG. That is, as shown in FIG. 3 (al is the evaporation characteristic of the conventional impregnated cathode, and FIG. 3 (bl is the evaporation characteristic of the impregnated cathode of the present invention), as is clear from FIG. However, the amount of evaporation is very low from the beginning of use.

In the conventional impregnated cathode, there is a very large amount of evaporation at the beginning of use (half-life of about 20 hours), and as the cathode is used, the amount of evaporation decreases and after about 100 hours it reaches the same level as the impregnated cathode of the present invention.

This is thought to be because the easily evaporated electron radioactive material on the surface of the hole had completely evaporated. In addition, the impregnated cathode according to the present invention absorbs moisture on the surface of the cathode during the cathode manufacturing process and removes electron-emitting substances that adversely affect the electron emission characteristics, so the quality is stable without variations in the electron emission characteristics. It becomes what it is. For this reason, a method for removing electron radioactive substances on the surface has been obtained, and even high-definition electron tubes can be used without trouble.2 Electron tubes using the impregnated cathode according to the present invention are reliable and do not deteriorate in vacuum or electrical characteristics. This has the effect of making an electron tube with good performance.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing an example of a conventional impregnated cathode, and Fig. 2 is a partially enlarged cross-sectional view of a cathode pellet impregnated with an electron radioactive substance (aJ is the conventional one, (bJ is the one of the present invention, Fig. 3 shows the amount of evaporation of the impregnated cathode against the operating time, with A being the conventional cathode and B being the one according to the present invention.1 Cathode pellet, 5...Void, 6... Electron radioactive substance, 7... cathode surface portion, 8... void. Patent applicant: New Japan Radio Co., Ltd. 9- Figure 2 (a) Figure 3

Claims (1)

[Claims] a cathode substrate formed of a high melting point metal and having a large number of pores; an electron radioactive substance impregnated into the pores of the cathode substrate;
consisting of a heating heater disposed near the cathode substrate,
A negative type cathode of the cathode substrate.