JPS5918539A - Impregnated cathode - Google Patents

Abstract

PURPOSE:To obtain an impregnated cathode that improves electron emission performance and controls the evaporation of barium and barium oxide by providing a scandium oxide coat on the electron emission surface of the impregnated cathod with a specific thickness. CONSTITUTION:For example, a compound obtained by blending 4BaO, Al2O3, and CaO with a porus tungusten substrate is heated and melted under a hydrogen atmosphere and the substrate is impregnated with an electron emission material. Then excessive electron emission material remaining on the substrate is removed. This cathode is contained in a sputtering device that uses scandium oxide, etc. as the target and the electron emission surface of the cathode is coated with scandium. An indirect heat type cathode is created by welding together the cathode coated with the scandium oxide and a cup-type barrier layer consisting of a tantalm sleeve 5 of 25mum thickness and tantalm using laser beams. As a result, electron emission performance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impregnated cathode for use in electron tubes such as cathode ray tubes and image pickup tubes.

The impregnated cathode is seen as a promising cathode for improving the performance of electron tubes. An impregnated cathode is one in which the pores of a porous metal substrate are impregnated with an electron-emitting substance. Most porous metal substrates are manufactured from tungsten, but are not limited to tungsten, and may also contain heat-resistant metals such as molybdenum and tantalum. As the electron-emitting substance, a compound or mixture containing barium oxide and at least one of aluminum oxide, calcium oxide, magnesium oxide, etc. is generally used as a starting material for impregnation. The porous metal substrate is manufactured by press-molding and sintering metal powder.

It is said that the appropriate porosity of the porous metal substrate is about 17 to 30%. In order to uniformly distribute the pores within the substrate, it is necessary to select sintering conditions that will result in poor distribution when the metal powders are diffused together during sintering, and the particles will bond relatively lightly to each other. . The impregnated cathode is manufactured by placing a barium aluminate compound on a porous metal substrate, heating and melting it in a reducing or non-oxidizing atmosphere, and impregnating it into the pores of the substrate. Further, the pores of the substrate can be impregnated by immersing the porous metal substrate in a barium aluminate compound molten bath.

In the operating state of such an impregnated pole, the porous metal substrate and the barium aluminate compound react to generate barium, which reaches the surface of the substrate, that is, the electron emitting surface, and diffuses into the surface to emit electrons. Form a suitable monoatomic layer.

Such an impregnated cathode is seen as a promising cathode that can exhibit high electron emission performance over a long period of time, and is being developed for use in small electron tubes such as cathode ray tubes and image pickup tubes. However, although it has high electron emission ability, the operating temperature is 105
Since the temperature is as high as 0 to 1200c, a large amount of barium and barium oxide evaporates and adheres to other electrodes, which adversely affects the characteristics of the bulb. Additionally, due to the high temperature, it is necessary to change the electrode and sleeve materials used in the oxide cathode. Furthermore, since the heater temperature for heating the impregnated cathode becomes high, it has drawbacks such as being unable to be used for a long time. For this reason, there is active search for an I electrode that can operate at low temperatures, but this has not yet been realized.

On the other hand, as a way to lower the operating temperature,
A method is adopted in which osmium, ruthenium, osmium-ruthenium alloy, iridium, or the like is coated to a thickness of several hundred nanometers. According to this, the operating temperature is 900-1050
It decreases to about 0. The coating is performed by vapor deposition, sputtering, or the like. Inside the porous metal substrate,
Osmium, osmium-ruthenium alloy, ruthenium.

(An impregnated cathode made by dispersing and impregnating an electron-emitting substance such as iridium has also obtained the same results as a coated cathode.)

The object of the present invention is to improve the electron emission ability of barium,
An object of the present invention is to provide an impregnated cathode in which the amount of barium oxide evaporated is suppressed.

In order to achieve the above object, the impregnated cathode according to the present invention is characterized in that scandium oxide is provided on the electron emitting surface of the conventional impregnated cathode.

The impregnated cathode according to the present invention uses a porous metal body produced by press-molding, sintering, etc. from raw material powder of the porous metal body, and fills the pores of the metal body with hydrogen or non-oxidizing material. It is manufactured by depositing scandium oxide by sputtering or the like on the electron emitting surface of an impregnated cathode that is impregnated with an electron emitting material by melting it in an atmosphere, and the method will be explained in more detail below.

The porous metal body is manufactured by press molding into a cathode shape and sintering using raw material powder whose particle size has been adjusted. Moreover, there is no problem even if the cathode shape is processed by cutting or the like after sintering. As the electron-emitting substance to be impregnated into the pores of this porous metal body, in addition to the barium aluminate compound, a mixture of barium carbonate, aluminum oxide, and calcium carbonate may be used as a starting material for impregnation. This 3
The compositions that showed good electron emission characteristics in combination were (barium carbonate): (aluminum oxide): (calcium carbonate) = 4:1:1 to 5:2:3. A scandium oxide film is deposited on the impregnated electrode thus produced by sputtering.

Among the constituent materials of the impregnated pole described above, the porous metal body is typically tungsten, and the electron emitting material is barium.
Select and explain an aluminate compound. First, tungsten powder whose particle size has been adjusted is prepared and press-molded using a cylindrical press jig. For press molding, polyvinyl alcohol, alcohol, etc. are used as a binder as necessary. Then 1000-1200 tons in hydrogen? After heating to remove the binder and pre-sintering to make it easier to handle, heat it to 17oo~2000c in a non-oxidizing atmosphere such as vacuum or hydrogen.
Create a porous tungsten body with 17-30% porosity. The porosity can be selected depending on the particle size of the tungsten powder, press molding pressure, and sintering conditions, but it is usually 3 to 8μ.
Using a particle size of
Sintering is performed under sintering conditions for about 0.5 to 3 hours. Powders are evenly distributed when the particles are dispersed to a different degree.
If diffusion has progressed sufficiently and there is movement of powder particles, even if the porosity is the same, the distribution is uneven and there are many closed pores. When cutting into a cathode shape, strength is required and diffusion must proceed, but when press forming with the cathode shape in mind from the beginning, it is sufficient to have the strength as a cathode. Become. A barium aluminate compound was placed on the substrate thus produced, and the barium aluminate compound was heated to about 170% in hydrogen.
An impregnated cathode is manufactured by heating and melting it to 0C and pouring it into the holes.

A cross-sectional model diagram of the impregnated cathode manufactured as described above is shown in g.
Shown in Figure 1. 1 is a porous tungsten base, 2 is a hole, and 3 is a barium aluminate compound. FIG. 2 shows the saturation current characteristics 10 of the impregnated cathode manufactured in this manner. This impregnated cathode has a high operating temperature, and a large amount of barium and barium oxide evaporates.When a tube is fabricated, this may have an adverse effect on other electrodes, leading to deterioration of the tube characteristics, or the cathode may be damaged. It has drawbacks such as the need to raise the temperature of the heater for heating, resulting in a short lifespan. As a way to lower the operating temperature, the surface of this impregnated cathode is coated with osmium (but still ruthenium).

iridium or alloys thereof) to about 5 Q Qnm
The operating temperature can be increased to 100-150℃ by coating the
We have succeeded in lowering C. The characteristics of the impregnated cathode coated with osmium are shown in 11 in FIG.

It has been found that the operating temperature of the osmium-coated impregnated cathode 11 can be lowered by depositing scandium oxide instead of osmium. The scandium oxide was deposited by high speed sputtering. With scandium oxide, a remarkable effect was seen from 0.1 μm or more. If scandium oxide is too thick, it will behave in the same way as an oxide cathode, and from the viewpoint of work time and cost such as sputtering time,
00 μm or less is desirable. Therefore 0.1-1100
It is desirable to deposit a scandium oxide film of At. Instead of scandium oxide, scandium may be deposited by vapor deposition or the like, and then taken out to the atmosphere and oxidized to form scandium oxide. FIG. 2 shows the saturation current characteristics 12 of the impregnated cathode of the present invention manufactured in this manner. The operating temperature can be lowered by 250 to 300 C compared to the conventional impregnated cathode, and 100 to 150 C lower than that of the osmium-coated impregnated cathode, and the amount of evaporation of electron-emitting substances such as barium and barium oxide is reduced, and the heating time is longer. It was advantageous in that it had a longer lifespan.

According to the present invention, as explained above, by adding scandium oxide to the conventional manufacturing method, the operating temperature can be significantly lowered. By lowering the operating temperature by 100 to 300c, the evaporation rate of barium and barium oxide can be lowered by about 1.5 to 3 orders of magnitude, and at the same time, the service life can be extended. The impregnated cathode according to the present invention can be said to have superior properties to conventional impregnated cathodes and osmium-coated impregnated cathodes.

Hereinafter, the present invention will be explained by examples.

Tungsten powder with a particle size of 5 μm was prepared, and 15 mg of the powder was press-molded using a cylindrical press jig with a diameter of 1.5 mm.

Polyvinyl alcohol was used as a binder for Konofres molding. Molding pressure is 4 ton/cmt
It was carried out in Then, it was pre-sintered in hydrogen for 10,000.1 hours to remove the binder and make it easier to handle. Next, sintering was performed at 1900 C for 1 hour in a vacuum at a pressure of 1×1 O-1 l'porr or less to produce a porous tungsten substrate.

The porosity at this time was 26%. 4BaO・Al2O5
・A compound consisting of a mixture of CaO is heated to 17% in a hydrogen atmosphere.
The material was heated and melted at 40 t:' for 3 minutes to impregnate the electron emitting material. Next, the excess (9) electron-emitting material remaining on the substrate was removed. This cathode was placed in a sputtering device using scandium oxide as a target, and about 30 μm of the material was deposited on the electron emitting surface of the cathode. This impregnated cathode coated with scandium oxide is coated with a tantalum sleeve 5 having a thickness of 25 μm and a cup-shaped barrier layer 6 made of tantalum.
An indirectly heated cathode was made by beam welding, a tungsten heater 7 was installed inside the sleeve, a diode consisting of an anode and a cathode was made, and the saturation current of the cathode was measured using a pulsed power source. It is shown at 12 in FIG.

As described above, according to the present invention, the operating temperature can be lowered by depositing scandium oxide instead of the conventional osmium coating without significantly changing the manufacturing process of conventional impregnated cathodes. The shape of the cathode is also 250~300C,
The osmium-coated impregnated cathode can also be lowered by 100 to 150C, and as a result of the lower operating temperature, barium.

An impregnated cathode can be obtained which has excellent properties such as being able to reduce the evaporation rate of barium oxide by 1.5 to 3 orders of magnitude.

[Brief explanation of the drawing]

(10) FIG. 1 is a cross-sectional model diagram of an impregnated cathode, and FIG. 2 is a diagram comparing an impregnated cathode produced by a conventional method and an impregnated cathode according to the present invention. DESCRIPTION OF SYMBOLS 1... Porous tungsten base body, 2... Hole part, 3
... barium aluminate compound, 4 ... impregnated cathode, 5 ... tantalum sleeve, 6 ... tantalum barrier layer, 7 ... tungsten core wire, 8 ... insulation coating layer, 9 ...・Indirectly heated impregnated cathode, 10...Saturation current characteristics of conventional impregnated cathode, 11...Saturation current characteristics of impregnated cathode whose characteristics have been improved by coating with osmium, 12...Saturation current characteristics of the impregnated cathode according to the present invention (11) Figure 1

Claims (1)

[Scope of Claims] 1. An impregnated cathode comprising a porous metal body and an electron-emitting substance, characterized in that a scandium oxide film is provided on the electron-emitting surface. 2. The impregnated cathode according to claim 1, wherein the thickness of the scandium oxide film is 0.1 to 100 μm.