JPH0197343A - Manufacture of impregnated type cathode - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a method for manufacturing an impregnated cathode.

(Prior Art) In general, an impregnated cathode is constructed as shown in FIG.
and a cathode base 5 which is bonded to one end of the cathode support cylinder 1 by a brazing material 4 in contact with an embedding material 2 and impregnated with an electron emitting substance.

In manufacturing such an impregnated cathode, a porous body made by sintering single or mixed powder of high-melting point metals such as tungsten and molybdenum in a high-temperature vacuum or in hydrogen is mixed with copper or copper in order to improve machining. It is impregnated with plastic and then cut into the desired shape. Furthermore, after removing the copper or plastic impregnated before cutting by a predetermined operation, the porous cathode substrate 5 is filled with an electron emitting material mixed in a desired molar ratio.
It is well known that the above-mentioned material is dissolved and impregnated in a high-frequency hydrogen furnace.

Recently, a cathode containing scandium oxide as an electron emitting material has been developed in order to lower the operating temperature and obtain good electron emission for a long time at a higher current density (Japanese Patent Application Laid-open No. 154131/1983). Public bulletin).

This impregnated cathode is made by pressing a mixture of tungsten powder and scandium oxide, sintering it at a temperature of about 1700°C, and cutting it into the desired shape. .

It can be obtained by impregnating it with an electron emitting substance such as Al2O3.

(Problems to be Solved by the Invention) However, although the impregnated cathode described above has improved electron emission characteristics compared to one that does not contain scandium oxide,
It has the following drawbacks.

(2) Scandium and its compounds are very expensive, and the loss of scandium during cutting after sintering the cathode substrate is economically disadvantageous.

■Since scandium oxide is difficult to crush, it does not have a uniform particle size distribution, resulting in uneven concentration of scandium oxide inside the sintered body. As a result, it is difficult to operate stably over a long period of time.

This invention solves the following disadvantages of conventional impregnated cathodes containing scandium, and provides a low-cost impregnated cathode with stable electron emission characteristics even when operated at high current densities for long periods of time. It is an object of the present invention to provide a method for manufacturing an impregnated cathode that yields a cathode.

[Structure of the Invention] (Means for Solving the Problems) This invention contains scandium in an alkaline earth metal carbonate by coprecipitation, and converts this scandium-containing alkaline earth metal carbonate into a porous high melting point metal. A method for producing an impregnated cathode, which is characterized in that the alkaline earth metal carbonate is a barium single salt or a double salt thereof.

(Function) According to the present invention, the distribution of scandium contained in the cathode substrate becomes very uniform, and it is possible to obtain a method for producing an impregnated cathode that has stable operating characteristics over a long period of time and at high current density.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The impregnated cathode obtained by the manufacturing method of the present invention has a first
The structure is similar to that shown in the figure, but in manufacturing, tungsten powder is first press-molded, then heated and sintered in a hydrogen atmosphere, the porous tungsten body is impregnated with copper, and then a predetermined cathode shape is formed. After that, it is immersed in acid and further heated to completely remove the copper, creating a cathode substrate. This is a well-known and common method.

Next, a method for manufacturing the electron emitting material to be impregnated into the cathode substrate will be described.

First, an alkaline earth metal nitrate such as high purity barium nitrate is dissolved in 96.6% by weight pure water.

3.4% by weight of scandium nitrate is dissolved in this solution with stirring, and the temperature of the solution is maintained at 95° C. or higher.

Next, a predetermined amount of high-purity ammonium carbonate is dissolved in pure water and maintained at 65 to 70°C while stirring.

This ammonium carbonate solution is added to a nitrate solution of barium nitrate and scandium nitrate at a constant addition rate and allowed to react. The shape of the crystals produced can be freely controlled by adjusting the reaction rate, degree of shrinkage, etc., but in this invention, the reaction conditions are such that needle-shaped crystals are obtained.

Even after the addition of ammonium carbonate is completed, stirring is continued for about 30 minutes in order to ripen the formed crystals.

The resulting co-precipitated carbonate of barium carbonate and scandium carbonate is allowed to stand, the supernatant liquid is drained, and washing with hot water is repeated until impurities are removed, dehydrated by methods such as centrifugal dehydration, and dried to form a white product. A coprecipitated carbonate is obtained. The carbonate thus obtained has a composition of 98% by weight of barium and 2.0% by weight of scandium.

Next, the cathode substrate is impregnated with the electron emitting material obtained as described above.

First, the barium carbonate containing scandium obtained above, calcium carbonate, and aluminum oxide are mixed in a molar ratio of 4:1:1, and after heating for pretreatment, the mixture is impregnated into the cathode substrate while heating in a reducing atmosphere. After removing the excess material, the impregnated cathode substrate is completed.

Thereafter, the surface is coated with Ir and heat treated to form an Ir-W alloy layer.

Using the above cathode substrate, a cathode structure is made by a well-known method,
Completed the diode tube. The electron emission characteristics of this diode during long-term operation were measured.

FIG. 2 shows the pulse emission ratio (%) for each time when the device is operated for a long time at a current density of 6 A/cm 2 . The solid line X shown in the figure shows the case when the present invention is used, and the dotted line Y shows the case when a conventional cathode (tungsten powder mixed with 5% by weight scandium oxide, pressed and sintered) is used.

As this characteristic curve diagram shows, the impregnated cathode of the present invention is
It is clear that the deterioration of electron emission characteristics due to long-time operation at high current density is extremely small. Very little deterioration of pulse emission means that high and stable electron emission ability can be maintained for a long time.

In the above example, barium carbonate containing 2.0% by weight of scandium carbonate was explained.
According to the inventor's experiments, similar effects can be obtained within a content range of 0.1 to 5.0% by weight.

If the amount of scandium contained exceeds 5% by weight, it will take a long time to stabilize the initial electron emission characteristics, which will cause problems in mass production, and the amount of scandium used will increase, causing economic disadvantage, making it difficult to put into practical use. It wasn't the range. Further, when the content was less than 0.1% by weight, a problem occurred in stability during long-term operation.

Further, the present invention includes the steps of incorporating scandium into an alkaline earth metal carbonate by coprecipitation as described above, and melting and impregnating this scandium-containing alkaline earth metal carbonate into a cathode substrate made of a porous high melting point metal. Since Keigai employs a well-known manufacturing method, detailed explanation will be omitted.

(Modified example) In the above example, the coprecipitated electron-emitting material of barium carbonate and scandium carbonate was explained, but the coprecipitation of lucium carbonate and scandium carbonate, or the triple coprecipitation of barium carbonate, lucium carbonate, and scandium carbonate is also possible. It goes without saying that even if used, the same effect as in the above embodiment will be obtained. .

[Effects of the Invention] According to the present invention, a mixture of scandium nitrate and alkaline earth metal nitrate is reacted with an alkali carbonate such as ammonium carbonate or sodium carbonate solution, and scandium is reacted with an alkaline earth containing at least barium, which is an electron emitting substance. It is contained inside the metal carbonate crystal, and then impregnated into the cathode substrate.

For this reason, barium scandate, which is effective in improving electron emission characteristics, is reliably and easily generated, and is uniformly and effectively produced within the cathode substrate, and the electron emission characteristics do not deteriorate even during long-term operation at high current densities. few.

Furthermore, since conventional scandium-containing cathodes use scandium oxide powder, the scandium concentration distribution within the cathode substrate is affected by the particle size of the scandium oxide powder. Therefore, the concentration distribution of scandium is very uniform.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a general impregnated cathode, and FIG. 2 is a characteristic curve diagram showing the relationship between operating time and electron emission characteristics in the impregnated cathode. DESCRIPTION OF SYMBOLS 1... Cathode support cylinder, 2... Embedding material, 3... Heater, 4... Brazing material, 5... Cathode base body. = 10-

Claims (2)

[Claims] (1) An impregnated cathode characterized by containing scandium in an alkaline earth metal carbonate by coprecipitation, and melting and impregnating the scandium-containing alkaline earth metal carbonate into a cathode substrate made of a porous high melting point metal. manufacturing method. (2) The method for producing an impregnated cathode according to claim 1, wherein the scandium-containing alkaline earth metal carbonate is a barium single salt or a double salt thereof.