JPH0821309B2 - Impregnated type cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to an impregnated cathode suitable for use in electron tubes such as image pickup tubes and cathode ray tubes.

[Conventional technology]

As the performance of electron tubes has improved, high current density cathodes have become necessary, and impregnated cathodes composed of a porous metal body and an electron emitting material have been actively developed. As a porous metal body,
It is necessary that the holes have a desired porosity, that the size and distribution of the holes are uniform, and that all of the holes are connecting holes. In order to make such a porous metal body, it is made by sintering powder. In order to form the cathode shape, the powder is press-molded using a method of cutting from a large sintered body and using a cathode-shaped press jig from the beginning.
It can be made by sintering. Thus, the impregnated cathode substrate is manufactured by impregnating the electron-emitting substance into the cathode-shaped porous metal body by a method such as heating and melting in a reducing or non-oxidizing atmosphere. The cathode substrate thus prepared generally has a barrier layer 2 on the back surface (heater side) of the cathode substrate 1 as shown in FIG.
Is fixed to the sleeve 3 and further assembled with the heater 4 having a tungsten wire provided with an insulating layer and combined with the electrode to form an electron tube.

The cathode base 1 and the barrier layer 2 and the sleeve 3 are fixed to each other by a method such as brazing or welding. In the case of brazing, the brazing metal penetrates into the fine holes of the cathode base and the space between the cathode base and the barrier layer. Voids are generated, and when a large amount of brazing material is used, the brazing material penetrates deep into the cathode substrate, or the brazing material flows to the surface of the cathode, that is, the electron emission surface.

In addition, when fixed by welding, the small cathode parts such as the barrier layer and sleeve have a small thickness and cracks occur during welding, and the electron emission material easily evaporates from the gap at the high temperature when the cathode is in operation and the heater side There was the inconvenience of getting around.

To solve these problems, the barrier layer and the sleeve are brazed as shown in JP-A-60-74229,
A method of fixing the cathode substrate by welding has been proposed. However, when the cathode substrate impregnated with the electron emitting substance is welded, there is a problem that the electron emitting substance is melted at a high temperature at the time of welding and the blown electron emitting characteristics are adversely affected.

On the other hand, as the performance of the electron tube is improved, a cathode having a high current density is required for the cathode, while the hole diameter of the electrode facing the cathode, that is, the first grid, is becoming smaller and smaller. Therefore, the cathode can be small. However, the impregnated cathode has an operating temperature higher than 300 ° C as compared with the oxide cathode. As described above, it is difficult to design a heater for an impregnated cathode that requires a high operating temperature. In particular, in order to guarantee reliability, it is necessary to thicken the tungsten wire of the heater, and the minimum coil outer diameter of the heater made at that time is about 1.5 mm in the current technology. Therefore, even if the impregnated cathode is made smaller according to the hole diameter of the first grid, there is a problem that there is no applicable heater. Therefore, it is necessary to use the current heater, and an improved impregnated cathode structure as shown in FIG. 3 is considered. In the impregnated cathode of this improved structure, a convex portion 1A is provided on the end surface of the cathode substrate 1 on the electron emission side, and the zenith surface of the convex portion 1A is used as the actual electron emission surface. Since the end surface area on the electron emission side other than the above is large, there is a disadvantage that unnecessary Ba vaporization is large, and it is likely to cause grid emission. Therefore, the current heater is used, and the impregnated cathode needs to have a minimum required area other than the electron emission surface to reduce the Ba evaporation amount.

[Problems to be solved by the invention]

As described above, in a small impregnated cathode for a cathode ray tube or the like, the sticking of the cathode substrate to the barrier layer or sleeve adversely affects the electron emission characteristics, and the excess Ba from the electron emission surface and its periphery is also affected. There is a drawback that the grid emission occurs due to evaporation.

Therefore, an object of the present invention is to provide an impregnated cathode having a structure that does not adversely affect the electron emission characteristics, can firmly fix the cathode substrate, the barrier layer, and the sleeve, and has little Ba evaporation from other than the electron emission surface. To do.

[Means for solving problems]

According to the present invention, the above object is to provide a convex portion on the electron emission surface side of the cathode substrate, use the zenith surface of the convex portion as an electron emission surface, and cover the portion other than the electron emission surface with a metal lid made of a refractory metal. This is achieved by sandwiching the cathode substrate with the body and the metal supporting plate and by welding or brazing the metal lid and the metal supporting plate.

[Action]

In the impregnated cathode according to the present invention, since the cathode base is fixed by fixing the metal supporting plate and the metal lid, there is no influence such as welding or brazing on the electron emitting surface side of the cathode base. In addition, since the periphery other than the electron emission surface is covered with a metal lid, a small impregnated cathode with high reliability with little Ba evaporation can be obtained.

〔Example〕

FIG. 1 shows a sectional structure of an impregnated cathode according to an embodiment of the present invention. A convex portion having a diameter of 0.5 mm and a height of 0.1 mm is formed on the end surface of the cathode substrate 1 having a diameter of 1.45 mm and a height of 0.45 mm, and a thickness of 0.1 mm, a diameter of 1.65 mm, and a height of 0.55 mm.
A metal cover 6 made of molybdenum having a circular hole with a diameter of 0.5 mm and a metal support plate 5 made of molybdenum with a diameter of 1.65 mm and a thickness of 0.1 mm were prepared. Mo-41.6Ru eutectic fine powder and butyl carbitol acetate as a binder were added to the joining surface of the metal lid 6 and the metal supporting plate 5 and a paste-like brazing material was applied thereto, and then the cathode substrate 1 was attached to the metal lid 6 After pushing it in, combine the metal support plates 5, and then the inner diameter 1.65mm, the outer diameter
A brazing material in the form of paste is applied to the upper inner peripheral surface of the sleeve 3 having a length of 1.71 mm and a length of 5.3 mm, and it is heated in a vacuum for about 1950 ° C. for 1 to 2 seconds by a tungsten coil heater.
Integrating the metal lid 6, the metal support plate 5, and the sleeve 3,
Further, a heater 4 having an outer diameter of 1.48 mm, which is obtained by insulatingly coating alumina on the surface of the tungsten wire, was inserted into the sleeve 3 to produce the impregnated cathode of the present invention.

By covering other than the zenith surface of the convex portion 1a of the cathode substrate 1 with the metal lid 6, the evaporation amount of Ba is reduced by almost an order of magnitude as compared with the conventional impregnated cathode having a diameter of 1.45 mm. I was able to eliminate the concern about the emission. Further, the adverse effect of the brazing material / welding on the cathode substrate was eliminated, stable operation was performed for a long time, and the reliability of the impregnated cathode could be greatly improved.

〔The invention's effect〕

According to the present invention, the amount of Ba vaporized from other than the electron emission surface can be reduced without changing the specifications of the conventional heater and sleeve, which is very advantageous as a countermeasure against grid emission. Further, since the cathode substrate is fixed by being sandwiched between the metal lid body and the metal supporting plate by being fixed, it is not necessary to fix the cathode substrate to the metal lid body or the metal supporting plate by welding or brazing. Therefore, the adverse effect of the brazing material or welding on the cathode substrate can be eliminated, which is extremely advantageous for improving the reliability of the impregnated cathode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of an impregnated cathode according to an embodiment of the present invention, and FIGS. 2 and 3 are schematic sectional views showing respective constitutional examples of a conventional impregnated cathode. Is. 1 ... Cathode substrate, 1B ... Convex portion of cathode substrate, 3 ...
... Sleeve, 4 ... Heater, 5 ... Metal support plate made of refractory metal, 6 ... Metal lid made of refractory metal.

Claims (1)

[Claims] 1. An impregnated type comprising at least a cathode base made of a refractory metal impregnated with an electron emitting substance, and a cathode sleeve made of a refractory metal inserted and fixed to an inner peripheral surface of the upper part of the cathode base. In the cathode, a convex portion is provided on the electron emission surface side of the cathode substrate, and the zenith surface of the convex portion serves as an electron emission surface, and is a metal lid body and a barrier layer made of a refractory metal that covers other than the electron emission surface. An impregnated cathode characterized in that the cathode substrate is sandwiched by a metal supporting plate, and the joint surface between the metal lid and the metal supporting plate is fixed by welding or brazing.