JPS6032232A - Impregnated cathode - Google Patents

Abstract

PURPOSE:To obtain an impregnated cathode capable of being put in practical use while checking evaporation speed of barium and barium oxide by impregnating the thin hole parts of a heat-resisting porous substrate, in which particles of hafunium oxide, zirconium oxide and titanium oxide are dispersed, with an electron emissive substance. CONSTITUTION:The thin hole parts 3 inside a porous substrate 4 made of material powder 1 of a heat-resisting porous substrate of tungsten, molybdenum, tantalum, rhenium and hafunium oxide, zirconium oxide, titanium oxide or oxide powder 2 containing these are impregnated with an electron emissive substance while, for instance, the electron emissive surface is coated with osmium, iridium, rhenium, ruthenium or an alloy selected from a group thereof. Thereby, the former manufacturing process can be applied to and also the evaporation amount of barium and barium oxide can be lowered by 0.5-3 figures than the impregnated cathode of the former type with no change of the tublar bulb manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an impregnated cathode used in electron tubes such as cathode ray tubes and image pickup tubes.

[Background of the invention]

The impregnated cathode is a high current density cathode and is seen as a promising cathode for improving the commercial performance of electron tubes.

An impregnated electrode is one in which the pores of a porous substrate are impregnated with an electron-emitting substance. Porous substrates are most often made from tungsten, but also molybdenum, tantalum,
It may also contain metals such as osmium, ruthenium, iridium, and rhenium.

Barium oxide and aluminum oxide as electron-emitting materials,
Generally, a compound or mixture containing at least one of calcium oxide, magnesium oxide, etc. is used as a raw material. The porosity of the porous substrate is 17-30
It is selected in the range of %. The porous substrate is manufactured by sintering a particulate material.

The electron-emitting substance is infiltrated into the pores of the porous substrate by heating, melting, impregnation, or other methods.

In an impregnated cathode, during operation, the porous substrate and the electron-emitting substance react to generate barium, which reaches the substrate surface, that is, the electron-emitting surface, and diffuses on the surface to form a barium monoatomic layer suitable for electron emission. Form.

Since such an impregnated cathode maintains high electron emission ability over a long period of time, it is being developed as a cathode for cathode ray tubes, image pickup tubes, and the like. However, although it has a high electron emission ability, the operating temperature is as high as 1000-1200℃, which increases the evaporation of nitric acid and barium oxide.
It adheres to other electrodes and adversely affects the characteristics of the tube, which is an obstacle to its practical application.
The purpose is to provide an impregnated type with a full rate of % firing rate that can withstand practical use.

[Summary of the invention]

There are two ways to think about achieving the above objective. The first method is to increase the electron emission ability of the impregnated cathode and lower its operating temperature. Currently, metals such as osmium, iridium, and ruthenium are coated on the electron-emitting surface to improve the electron-emitting ability. However, it is still incomplete. The second point is to suppress the production and evaporation rate of nocurium and barium oxide.

For this purpose, it is necessary to add some innovation to the porous substrate or the electron-emitting material. Furthermore, the porosity of the porous substrate may be reduced, but there is a limit.

In the impregnated cathode of the present invention, the second point is that the porous substrate is devised, and the production method suppresses barium and barium oxide without changing the conventional method. Specifically, the impregnated cathode of the present invention comprises a porous substrate and pores in which hafnium oxide, zirconium oxide, titanium oxide, or oxide particles containing these particles are dispersed in a 1Ii-1 thermally porous substrate. consists of emitted electron-emitting materials.

Furthermore, a groove in which osmium/iridium, ruthenium/rhenium, or an alloy containing these is coated on the electron emitting surface is preferable. Hafnium oxide (Hf02) -1'l
Zirconium oxide (ZrO2), titanium oxide (Ti
Examples of oxides containing rare earth elements (Hf02)
゜zrO□, Tj02) or alkaline earth metal' (Hf02. Zr02
.

(including at least one layer of TI02).

Two or more of these substances may be used as a mixture, or a mixture with HfO2, ZrO2, and Tj02 may be used.

The impregnated cathode according to the present invention has a porous structure made by weighing, mixing, press-molding, sintering, etc. raw material powder of a heat-resistant porous substrate and rhenium oxide, zirconium oxide, titanium oxide, or oxide powder containing these. It is manufactured by impregnating the pores in the solid substrate with an electron-emitting substance, and then coating the electron-emitting surface with osmium, iridium, rhenium/ruthenium, or an alloy selected from these groups.

The method will be explained in more detail below. The porous substrate is
Using two or more powders, mix, press mold into cathode shape,
Manufactured by sintering. A conventionally used element is used for at least one of the two or more powders. In other words, tungsten, molybdenum, tantalum, rhenium or alloys containing these, or on the electron emitting surface,
A mixed powder containing an element (osmium, iridium, ruthenium, or an alloy containing these) whose properties can be improved by coating is used. The other type is rhenium oxide, zirconium oxide, titanium oxide, or oxide particles containing these. From the two groups mentioned above, tungsten and rhenium oxide are selected as representatives, and osmium is selected as the element deposited on the electron emitting surface for explanation. First, prepare tungsten powder and hafnium oxide. It is desirable that the particle size of any powder be adjusted. It is desirable that both particle sizes be the same or smaller for the rhenium oxide powder. When the amount of rhenium oxide to be dispersed in the substrate is small, it is better to make it smaller than the tungsten powder particles which are the poisonous component of the substrate. Oxidize the prepared tungsten powder...
After mixing the appropriate amount of rhenium powder in a mortar etc., press forming using a cylindrical press jig.
For press molding, polyvinyl alcohol, alcohol, etc. are used as a binder as necessary. Then, in hydrogen
After heating to 1,700 to 1,200'C to remove the binder and pre-sintering to make it easier to handle, the material is heated to 1,700 to 2,000'C in vacuum and sintered to reduce the binder to 15 to 30%. A porous substrate having porosity, that is, a substrate having a structure in which hafnium oxide is dispersed in tungsten, can be manufactured. The above sintering may be performed in a non-oxidizing atmosphere such as an inert gas atmosphere or a reducing atmosphere other than in a vacuum. The porosity can be selected depending on the particle size of the tungsten powder, press molding pressure, and sintering conditions, but usually 3 to 8 μm particle size is used, and 1 to 10 to
Molding is performed at a pressure of n/cm2, and sintering is performed at a pressure of 1700~2
Sintering is carried out under conditions of approximately 000'c and 0.5 to 3 hours. If the powders are sufficiently diffused and the powder particles move, the distribution will be uneven and there will be many closed pores even if the porosity is the same. When making a cathode shape by cutting, strength is required, so 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. It turns out. The amount of hafnium oxide dispersed is desirably 40% or less of the volume of the porous substrate due to the characteristics or the strength of the porous substrate. Also, due to its characteristics,
In order to obtain remarkable results, it is desirable that the content be 3% or more.

From the viewpoint of characteristics or cathode strength characteristics, approximately 20 inches is usually good. In the manner described above, a substrate in which hafnium oxide is dispersed in porous tungsten can be manufactured. Fig. 1 shows a cross-sectional model diagram thereof. 1 is tungsten grain, 2 is hafnium oxide.

3 indicates a pore portion and a 4id porous substrate.

An impregnated cathode can be produced by impregnating the thus produced porous substrate with a barium aluminate compound by heating and melting it in hydrogen at about 1700'C. In addition to barium and aluminate compounds, a mixture of barium carbonate, aluminum oxide, and calcium carbonate in appropriate amounts may be used as the lightning bolt emitting substance. The saturated foz flow characteristics of the impregnated cathode manufactured in this way are the same as those when using a porous tungsten substrate, and no change is observed, but the amount of evaporation of barium and barium oxide changes depending on the amount of hafnium oxide added. It decreased proportionally by 0.5 to 3 orders of magnitude.

FIG. 2 shows the relationship between barium evaporation rate and hafnium oxide in a porous substrate at an operating temperature of 1050'c. The barium evaporation rate was measured using a mass spectrometer @ As shown in FIG.
Furthermore, a heater 10 in which a tungsten core wire 8 is provided with an insulating coating layer 9 such as alumina is combined into an electron tube 1.
When the mounting test was repeated at 000 to 1200''C, the change in electron emission ability over time was almost the same as that of the conventional one.However.

There were no problems with grid emissions even after 20,000 hours. Further, even when the impregnated cathode was coated with osmium, the above tendency did not change, but the temperature at which the same electron emission ability was obtained was lowered by about 150°C. In addition to osmium, it is also possible to use iridium, ruthenium, rhenium, or an alloy containing at least 10 or more selected from these groups.
Alternatively, considering the lifespan, the thickness is preferably 0.02 to 1 μm.

This may be the same condition as applied to the conventional type.

According to the present invention, as explained above, the conventional manufacturing process can be applied, and without changing the tube manufacturing process, the barium and barium oxide The impregnated cathode according to the present invention can reduce the amount of evaporation and can be said to have better characteristics than conventional impregnated cathodes.

[Embodiments of the invention]

The present invention will be explained below by way of examples.

Example 1 Tungsten powder with a particle size of 5 μm and hafnium oxide powder with a particle size of 2 to 3 μm were prepared, and the ratio of hafnium oxide was 3.
They were weighed to give a volume percentage of 6, 12, 20, 35, and 50 vOt% and thoroughly mixed in a mortar cape. The actual door volume value is ±
It was 0.1 voz%. Then 1.511111
Press molding was performed using a 1φ cylindrical press jig.

In this press molding, polypinyl alcohol was used as a binder. The molding pressure was 4 tons/sub 2. Then, 1000'G in hydrogen.

Temporary sintering was performed for 1 hour to remove the binder and make it easier to handle. Then lXl0−'':l'o
Sintering was carried out at 1900'C for 2 hours in a vacuum at a pressure below rr to produce a porous body in which hafnium oxide was dispersed within the base. The porosity of the porous substrate thus produced was in the range of 15 to 25 inches. After weighing and mixing the thus produced porous substrate 41C barium carbonate: aluminum oxide: calcium carbonate in a molar ratio of 4:1:1, heating and melting in hydrogen at 1700 to 1730'C for 3 minutes, An impregnated cathode containing hafnium oxide dispersed therein was fabricated. Hold at 1000-1100'c for 30 seconds before heating to 1700-1730'c,
Barium carbonate and calcium carbonate were decomposed into barium oxide and calcium oxide. A tantalum sleeve 6 with a thickness of 25 μm and a cup-shaped barrier layer 7 made of tantalum are welded with a laser beam to the impregnated cathode 5 manufactured in this way to form an indirectly heated cathode, and a tungsten core wire is placed inside the sleeve. A diode tube consisting of an anode was prepared by providing a heater 10 with an insulating coating layer 9 on 8, and using a pulse power source,
As a result of measuring the saturation current characteristics of the cathode, it was found that there was no difference in saturation current characteristics from that of an impregnated cathode using a porous tungsten substrate. Furthermore, the results of measuring the barium evaporation rate using a mass spectrometer are shown in FIG. Figure 2 shows operating temperature 105
Initial evaporation rate at 0'C is shown.

The vertical axis shows the barium evaporation rate, and the horizontal axis shows the amount of depleted...funium added. It can be seen that as the proportion of hunium oxide in the porous body increases, the barium evaporation rate decreases. By dispersing 3 to 40 VO 1% (volume fraction) of hunium oxide in a porous substrate, the reduction could be suppressed by 0.5 to 3 orders of magnitude compared to an impregnated cathode using a porous tungsten substrate. Furthermore, when looking at the evaporation energy, it was approximately 3.1 e■ in all cases. Therefore, reducing the barium evaporation rate by an order of magnitude reduces the operating temperature by approximately 100
'c is equivalent to lowering. Changes in barium evaporation rate over time are the same as with conventional impregnated cathodes, minus 1 of the heating time.
It was proportional to /2. In order to investigate changes in electron emission ability over time, we mounted it in a tube and subjected it to a life test, but no deterioration in electron emission ability was observed even after approximately 20,000 hours, and grid emission was also a problem. did not become.

Example 2 A cathode was manufactured in which the surface of the impregnated cathode manufactured in Example 1 was coated with osmium ff to a thickness of 0.5 μm by electron beam evaporation. The saturation current characteristics of this osmium-coated impregnated @electrode were also the same as those of the conventional one. That is, in order to obtain the same electron emission ability, the operating temperature should be adjusted to about 150°C.
I was able to lower the temperature. The barium evaporation rate was measured using a mass spectrometer in the same manner as in Example 1, and the same results as in Example 1 were obtained within the range of variation. therefore. The lower operating temperature reduces the barium evaporation rate, which has a significant effect on grid emissions. It was possible to obtain an impregnated cathode that can avoid the problem of grid emission even if the operating temperature is raised to obtain high electron emission performance.

Note that similar excellent effects were obtained when zirconium oxide or titanium oxide were used in place of hafnium oxide.

〔Effect of the invention〕

As described in detail above, according to the impregnated cathode of the present invention, a porous substrate in which hafnium oxide is dispersed is made from tungsten powder and hafnium oxide powder, and this is used to form an impregnated cathode. With this method, the barium evaporation rate can be suppressed by 0.5 to 3 orders of magnitude in conventional impregnated cathodes without changing the conventional manufacturing process or tube manufacturing process, and as a result, grid emissions are eliminated. An impregnated cathode was obtained that had excellent properties such as:

[Brief explanation of the drawing]

FIG. 3 is a diagram showing an assembly diagram of an impregnated cathode, a sleeve, a barrier layer, and a heater. 1... Tungsten grains, 2... Hafnium oxide grains,
3... Pore portion, 4... Porous substrate in which hunium oxide is dispersed, 5... Impregnated pole, 6... Sleeve,
7...Kat agent, patent attorney, bone mother example

Claims (1)

[Scope of Claims] 1. A porous substrate in which at least one hafnium oxide particle, zirconium oxide particle, titanium oxide particle, or an alloy oxide particle containing these particles is dispersed in the heat-resistant porous substrate; An impregnated cathode comprising an electron-emitting substance impregnated into the pores of a solid substrate. 2. The impregnated cathode according to claim 1, wherein the amount of the particles is 3 to 40 times the volume of the porous substrate. 3. The electron emitting surface of the impregnated cathode is further coated with osmium, iridium, Made of at least one alloy selected from the group consisting of ruthenium and rhenium, thickness 0.02
An impregnated cathode according to claim 1 or 2, characterized in that a coating film of ~1 μm is provided.