JPS5826769B2 - Manufacturing method of impregnated cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an impregnated cathode, and more particularly to a method for manufacturing an impregnated cathode for use in electron tubes that require high current density.

Conventionally, impregnated base electrodes are made by sintering powder of high melting point metal such as tungsten or molybdenum, melting and impregnating it with oxygen-free copper, etc., machining it into a predetermined shape, and then heating it in a vacuum or dissolving it with acid. We perform so-called decoppering, which removes copper.
After that, the material is melted and impregnated with an electron radioactive material, and the excess electron radioactive material adhering to the material is removed using a tungsten scrubber or sandpaper.

In other words, in the past, the surface of the cathode was formed into a material 1010 and an original hole 102, as shown in FIG.
The opening 103 of the opening 103 is collapsed, and the opening 103 becomes an elongated groove, and the opening area becomes extremely narrow.

Therefore, when melting and impregnating an electron radioactive substance, the pores originally possessed by the porous high-melting point metal base material cannot be sufficiently melted and impregnated, and furthermore, when the cathode is operated after being impregnated with the electron radioactive substance, the cathode Due to the small openings on the surface, the exposure of the electron radioactive material was poor, and the electron emitting surface was not completely covered with the electron radioactive material, resulting in large variations in current density or insufficient current density. .

The purpose of the present invention is to improve the electron emission characteristics of an impregnated cathode and to improve the current density by polishing the porous high melting point metal substrate in a manner that does not crush the pores originally formed in the porous high melting point metal substrate in order to eliminate the above-mentioned drawbacks. The objective is to manufacture a cathode with less variation.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 2 is a schematic diagram showing the manufacturing process of the method for manufacturing an impregnated cathode according to the present invention.

In step 1, a high melting point metal powder with an appropriate particle size distribution is prepared, and in step 2, the prepared metal powder is molded into an appropriate shape by a method such as mechanical pressing, isostatic pressing, or casting.

The formed material is sintered in step 3 by directly applying electricity to the cathode, in a furnace, hot pressing, or the like.

The sintered material, that is, the sintered body, is immersed in molten copper in step 4 to impregnate the porous sintered body with copper.

When the copper impregnation is completed, in step 5, the cathode is processed into a predetermined cathode shape by ordinary machining such as lathing.

After processing into a cathode shape in Step 5, surface polishing is performed in Step 6 using an appropriate method such as sandpaper, diamond paste, tapping polishing, chemical mechanical polishing, centerless polishing, etc.

After the surface polishing is completed, in step 7, the impregnated copper is heated in a vacuum or dissolved with an acid to remove the copper, so-called decopper removal, to facilitate machining.

After the copper is removed in step 7, the amount of micropores in the sintered body is measured in step 8 by an appropriate method to determine the quality of the sintered body.

If the porosity is determined to be good in step 8, in step 9, an electron-emitting substance made of a mixture of oxides mainly containing barium oxide or a mixture containing carbonate, which is a raw material thereof, is applied to the sintered body to remove the ring element. Melt impregnation in a neutral atmosphere or vacuum.

After the impregnation with the electron radioactive substance is completed, in step 10, if the surface of the cathode that has been impregnated with the electron radioactive substance is flat, sandpaper, diamond paste, tapping polishing, chemical mechanical polishing, centerless polishing, or electric discharge machining is performed. Excess electron radioactive material adhering to the surface of the cathode is removed by polishing, etc., and final polishing is performed.

Therefore, according to this embodiment, since the surface polishing step was added after the machining step of the conventional impregnated cathode manufacturing method, the surface of the porous tungsten substrate was as shown in FIG. A porous tungsten substrate 1100, such as a porous tungsten substrate made by the method
It is possible to obtain a cathode which is sufficiently impregnated with the electron radioactive material without clogging the original pores 120 and which can provide a high current density without any variation in current density.

Figure 5 compares the electron emitting surface of an impregnated monopole produced by the conventional method without polishing with the electron emitting surface of an impregnated cathode polished according to the present invention, taken with an electron microscope at 500x magnification. This is an indication.

FIG. 5a shows the conventional one, and FIG. 5 shows the one of the present invention, where the black parts in the photographs show the holes and the white parts show the base metal.

In addition, in the photograph of the conventional product shown in FIG. 5a, the horizontal black lines indicate marks from machining.

Figure 4 shows the current radiation characteristics.

This is a comparison between the impregnated cathode according to the present invention and the conventional impregnated cathode, with current density plotted on the vertical axis and cathode temperature plotted on the horizontal axis.
FIG. 4A shows a characteristic curve of an impregnated cathode according to an embodiment of the present invention, and FIG. 4B shows a characteristic curve of a conventional impregnated cathode.

As is clear from Fig. 4, at the same cathode temperature,
The impregnated cathode according to the present invention has a higher current density than the conventional impregnated cathode.

In this example, the example of surface polishing before copper removal was explained.
It goes without saying that it is also applicable to a process after copper removal, a process after impregnation with an electron radioactive substance, or an impregnated cathode that is directly formed into a cathode shape without machining.

As explained above, according to the present invention, the electron emission characteristics of the impregnated cathode can be improved by sufficiently impregnating the electron radioactive substance without clogging the pores originally formed in the porous high melting point metal substrate. Moreover, a cathode with less variation in current density can be manufactured.

[Brief explanation of the drawing]

Figure 1 is a partial cross-sectional view of the electron emitting surface of a conventional impregnated cathode.
FIG. 2 is a process diagram showing an example of an impregnated cathode according to the present invention, FIG. 3 is a partial cross-sectional view of the electron emitting surface of the impregnated cathode according to the present invention, and FIG. 4 is a conventional impregnated cathode. and a cathode temperature-current density characteristic curve diagram comparing the impregnated cathode according to the present invention, and FIG. 5 is an electron micrograph of the electron emitting surface of the conventional example and the impregnated cathode according to the present invention at a magnification of 500 times. 5... Machining process 6... Surface polishing process, 7
... Copper removal process, 120 ... hole.

Claims (1)

[Claims] 1. A step of sintering powder of tungsten, molybdenum, etc. to form a high melting point metal porous body, and a step of machining the high melting point metal porous body into a desired cathode shape to form a cathode substrate. A method for producing an impregnated cathode, comprising the steps of polishing the electron emitting surface of the cathode substrate by a stress-free polishing process, and impregnating the cathode substrate after the polishing process with an electron emitting substance. .