JPH05250981A - Impregnation type cathode and its manufacturing thereof - Google Patents

Abstract

PURPOSE:To provide an impregnation type cathode which can withstand oxidation in a sealing process of manufacturing an electronic tube and in which a barium-scandium-oxygen complex layer having a high electron emitting characteristic and a low work function is formed. CONSTITUTION:An electron emitting material part 4 is composed of a compound 2 containing barium and oxygen and a compound 3 containing tungsten, scandium and oxygen, and after press forming is carried out, it is sintered, so that a barium-scandium-oxygen complex layer 9 can be formed. Thereby, a practical level/low temperature operating impregnation type cathode having a high electron emitting characteristic can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode used in a cathode ray tube such as a cathode ray tube, an image pickup tube or a traveling wave tube, and in particular, an impregnated cathode capable of operating at a low temperature and obtaining a high current density and its manufacture. Regarding the method.

[0002]

2. Description of the Related Art An impregnated cathode of this type is tungsten W.
It is based on a structure in which a heat resistant porous substrate made of, for example, is impregnated with an electron emitting substance made of a barium Ba compound. Generally, the cathode is used in a state of being heated to a high temperature. However, the higher the operating temperature is, the shorter its life is. Therefore, it is desirable that the cathode can emit a high-density electron stream at the low operating temperature.

As a method of lowering the operating temperature of the cathode, for example, as disclosed in Japanese Patent Publication No. 47-21343, osmium-ruthenium (Os-R) is formed on the surface of the cathode.
u) Generally, it is coated with an alloy or the like. However, in this method, the operating temperature of the cathode is still high at about 1000 ° C., which is a major obstacle to putting a low temperature and high current density cathode into practical use.

Similarly, as another method for lowering the operating temperature of the cathode, as disclosed in Japanese Patent Laid-Open No. 61-13526, tungsten W and an oxide are used instead of the osmium-ruthenium (Os-Ru) alloy. Scandium (Sc ₂
A method of depositing a thin film of O ₃ ) by a vacuum sputtering method or a method of baking a raw material powder to form a sintered thin film has been proposed.

During operation of the latter cathode, the cathode has a low work function (Ba, S) of about a monomolecular layer to several molecular layers on the surface of the cathode.
c, O) composite layer can be formed to lower the operating temperature by 150 ° C to 200 ° C than the former cathode. However, the tungsten W in the tungsten-scandium oxide (W—Sc ₂ O ₃ ) mixed thin film is oxidized in the step of sealing the cathode in the electron tube, and has a low work function (Ba, Sc, O) suitable for electron emission. The formation of the composite layer becomes difficult, the electron emission characteristics peculiar to the cathode largely fluctuate, and the electron emission characteristics are poor in reproducibility, which makes it difficult to use under low temperature conditions.

[0006]

As described above, the impregnated cathode according to the prior art has a tungsten-scandium oxide (W-Sc ₂ O ₃ ) content in the sealing process in manufacturing an electron tube.
By oxidizing the tungsten W in the mixed thin film,
There is a problem in that the electron emission characteristics inherent in the cathode cannot be obtained. The reason for this is that due to the oxidation of tungsten W in the above tungsten-scandium oxide (W—Sc ₂ O ₃ ) mixed thin film, (Ba, Sc, O) having a low work function on the cathode surface.
This is because the composite layer cannot be easily formed.

FIG. 6 is a cross-sectional view for explaining a schematic structure of a conventional impregnated cathode, which is an impregnated cathode pellet 05 made of a heat-resistant metal portion 01 made of a heat-resistant porous substrate and an electron emitting substance 04, and a barrier layer 06. , A sleeve 07, a heater 08, a mixed thin film 03 containing tungsten W and tungsten oxide (WO ₃ ) and scandium oxide (Sc ₂ O ₃ ).

By heating the cathode by energizing the heater 08, WO ₃ and Sc ₂ O are mixed in the mixed thin film 03.
₃ reacts to produce Sc ₂ W ₃ O according to the following reaction formula (1).
₁₂ is generated. 3WO ₃ + Sc ₂ O ₃ → Sc ₂ W ₃ O ₁₂ (1) Further, in the impregnated cathode pellet 05, the refractory metal part 01 and the electron emitting substance 04 react with each other to produce barium Ba. For example, as the electron emitting substance 04, Ba ₃ Al ₂
When O ₆ is used and W is used as the refractory metal part 01, barium Ba is produced by the following reaction formula (2). (2/3) Ba ₃ Al ₂ O ₆ + (1/3) W → (1/3) BaWO ₄ + (2/3) BaAl ₂ O ₄ + Ba (2) A part of the generated barium Ba is on the cathode surface. At the same time as other barium Ba is diffused into the
c ₂ W ₃ O ₁₂ reacts with Ba to produce scandium Sc according to the following reaction formula (3). Sc ₂ W ₃ O ₁₂ + 3Ba → 3Ba WO ₄ + 2Sc (3) Barium Ba and scandium Sc diffused on the cathode surface
Is combined with oxygen generated by thermal decomposition of the electron-emitting substance 04 and oxygen in the atmosphere to form an extremely thin (Ba, Sc, O) composite layer 0 of about a single molecular layer to a few molecular layers on the mixed thin film 03.
9 is formed.

This composite layer 09 has a small electron emission work function of 1.2 eV, which is a factor for obtaining a high electron emission ability. However, the conventional impregnated cathode is
The formation rate of the (a, Sc, O) composite layer 09 did not have stable reproducibility, and the electron emission characteristics varied greatly from cathode to cathode.
In order to improve the reproducibility of the (Ba, Sc, O) composite layer 09 and to obtain a stable coverage, W, WO in the thin film
_3, and Sc ₂ but the amount of O ₃ it is necessary to be able to freely controlled, in the prior art, WO ₃ adopts a method of reacting with the gas in the atmosphere during sputtering of W, gas in the atmosphere Since the partial pressure fluctuates greatly, the amount of WO ₃ produced cannot be controlled. As a result, a reproducible thin film composition cannot be obtained.

Further, Sc ₂ W ₃ O ₁₂ is used instead of Sc ₂ O _3.
However, since the evaporation rates of scandium Sc and tungsten W are different, the thin film composition gradually changes, and it is necessary to constantly review the same thin film forming conditions. If this problem is not solved, it will be difficult to put the impregnated cathode of low temperature operation into practical use. An object of the present invention is to provide an impregnated cathode that can withstand oxidation in the sealing process of manufacturing an electron tube and can easily form a barium-scandium-oxygen composite layer having a low work function suitable for electron emission on the cathode surface. is there.

[0011]

In order to achieve the above object, the present invention provides tungsten W or molybdenum Mo.
Refractory metal part containing at least barium Ba and oxygen O
And a cathode structure composed of a compound containing at least tungsten W, and an electron emission material part made of a compound containing at least tungsten W, scandium Sc and oxygen O.

The cathode is manufactured by mixing the heat-resistant metal powder and the electron-emitting substance powder, press-molding them into a desired cathode pellet shape, and sintering them in a non-oxidizing atmosphere. That is, the impregnated cathode according to the present invention contains a refractory metal part 1 containing tungsten W and / or molybdenum Mo, a compound 2 containing at least barium Ba and oxygen O, at least tungsten W, scandium Sc and oxygen O. And an electron emission material portion 4 made of a compound 3.

The impregnated cathode according to the present invention comprises a sleeve 7, a refractory metal part 1 containing tungsten W and / or molybdenum Mo or both of which is attached to one end of the sleeve 7, a compound containing at least barium Ba and oxygen O. 2 and an electron emission material part 4 composed of at least tungsten W and a compound 3 containing scandium Sc and oxygen O, and barium B formed on the electron emission surface of this impregnation type cathode pellet 5.
a, scandium Sc and oxygen O composite layer 9, and a heater is attached to the other end of the sleeve.

In the impregnated cathode according to the present invention, the first granulation step 21 for granulating tungsten W powder, molybdenum Mo powder or both with a binder and the second granulation step for granulating a compound of barium Ba and oxygen O. In the granulating step 22, the third granulating step 23 for granulating the compound of tungsten W, scandium Sc and oxygen O, and the first granulating step 21, the second granulating step 22 and the third granulating step 23. In a weighing / mixing step 25 of weighing and mixing the granulated granules, a pelletizing step 26 of press-molding the mixture mixed in the weighing / mixing step 25 into a desired shape and pelletizing, and a pelletizing step 26. The pellet obtained by molding is heated in a hydrogen atmosphere to decompose the binder,
Sintering tungsten W powder or molybdenum Mo powder,
It is characterized in that it is manufactured by a manufacturing method including a sintering / fixing step 27 for fixing the electron emission material powder and an assembling step 28 for assembling the same with the barrier layer 6 into the sleeve 7 to assemble the cathode for an electron tube.

[0015]

With the above-mentioned constitution, under the same thin film forming condition, the reproducibility is good, and the thin film having the same composition is always formed, and the (Ba, Sc, O) composite layer 9 has good reproducibility, Moreover, a stable coverage can be obtained. That is, the heater 8 is provided with a cathode including a refractory metal part containing tungsten W or molybdenum Mo, an electron emitting material part containing at least barium Ba and a compound containing oxygen O, and at least a compound containing tungsten W, scandium Sc and oxygen O. An extremely thin (Ba, Sc, O) composite layer 9 having a thickness of from a single molecular layer to a few molecular layers is formed on the surface of the cathode by heating the cathode by heating.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a schematic structure of an embodiment of an impregnated cathode according to the present invention, in which 1 is a refractory metal part, 2 is a first compound containing at least Ba and O,
3 is a second compound containing at least W, Sc and O, 4 is an electron emitting material part composed of the first compound 2 and the second compound 3, and 5 is a refractory metal part 1 and an electron emitting material part 4. Impregnated cathode pellets, 6 is a barrier layer, 7 is a sleeve, 8 is a heater, and 9 is a (Ba, Sc, O) composite layer.

In the impregnated cathode of this embodiment, an impregnated cathode pellet 5 consisting of a heat-resistant metal portion 1 and an electron-emitting substance portion 4 is assembled in a sleeve 7 and a heater 8 is energized,
A first compound 2 containing at least Ba, O and (W, S
(c, O) at least the electron-emitting substance part 4 made of the second compound 3 is thermally decomposed, and the extremely thin (Ba, Sc, O) composite layer 9 of about several molecular layers is formed on the cathode surface. Formed in.

The (Ba, Sc, O) composite layer 9 has a small electron emission work function of 1.2 eV, and a high electron emission capability can be obtained. Next, the above (Ba, Sc, O) composite layer 9
The formation process of Al is performed by using tungsten W as the refractory metal 1, barium Ba, and Ba ₃ Al ₂ as the second compound 2 containing oxygen O.
The case where Sc ₂ W ₃ O ₁₂ is used as the compound 3 containing O ₆ , tungsten W, scandium Sc, and oxygen O will be described.

As described above, when the cathode pellet 5 is heated, W reacts with Ba ₃ Al ₂ O ₆ to produce barium Ba according to the following equation. (2/3) Ba ₃ Al ₂ O ₆ + (1/3) W → (1/3) BaWO ₄ + (2/3) BaAl ₂ O ₄ + Ba (4) A part of the generated barium Ba is the cathode surface. At the same time, the other barium Ba reacts with Sc ₂ W ₃ O _12, and scandium Sc is produced according to the following equation.

Sc ₂ W ₃ O ₁₂ + 3Ba → 3Ba WO ₄ + 2Sc (5) Barium Ba and scandium S diffused on the cathode surface
c is combined with oxygen generated by thermal decomposition of the electron-emitting substance 4 and oxygen in the atmosphere to form an extremely thin (Ba, Sc, O) composite layer 9 of about one to several molecular layers on the cathode surface. .. In this way, the tungsten W on the cathode surface
(Or molybdenum Mo) composite layer 9 formed on
Has a small electron emission work function of 1.2 eV, and high electron emission capability can be obtained.

In the conventional impregnated cathode, the tungsten W in the thin film containing tungsten W and Sc ₂ O ₃ is oxidized in the sealing process of manufacturing the electron tube, so that the metal tungsten W does not exist in the thin film. , Part of the oxidized tungsten W disappears, and part of it reacts with other oxides, so that the composition and the amount of oxygen in the thin film vary from the desired composition and the desired characteristics, and scandium Sc is easily produced. In addition, since no metallic tungsten W is present on the cathode surface, the low work function (Ba, Sc, O) composite layer 9 is formed.
Are difficult to form, and there is no reproducibility, excellent electron emission characteristics cannot be obtained, and the characteristics vary greatly from cathode to cathode.

On the other hand, according to the embodiment of the present invention,
It is the heat-resistant metal substrate tungsten W or molybdenum Mo that is exposed on the cathode surface that oxidizes even during the sealing process of manufacturing the electron tube. Since the oxide of tungsten W or molybdenum Mo has a high vapor pressure, it evaporates and disappears during the activation process of the cathode. After that, unoxidized tungsten W and molybdenum Mo are exposed again on the cathode surface. Further, barium Ba and scandium Sc forming the composite layer 9 having a low work function are generated inside the cathode, so that they are not affected in the sealing process of manufacturing the electron tube.

Compounds containing barium Ba and oxygen O include BaO, (Ba, Sr, Ca) O, and Ba ₃ Al ₂ O.
₆ , Ba ₂ Sc ₅ O ₅ , Ba ₃ Sc ₄ O ₉ , Ba ₅ Ca
Al ₄ O _{12 and the} like are preferable. The compound containing tungsten W, scandium Sc, and oxygen O is Sc _{2
W 3 O 12, Sc 6 WO} 12, Sc 2 (WO 4) 12 any equivalent effect such as can be obtained.

Sc ₂ Mo instead of tungsten W
The same effect as above can be obtained with ₃ O ₁₂ and Sc ₂ Mo ₂ O ₁₂ . As described above, by using the cathode structure of this embodiment, it is possible to constantly form the (Ba, Sc, O) composite layer 9 having a low work function even through the sealing process of manufacturing the electron tube, and thus the high electron emission is achieved. The characteristics are obtained, and low temperature operation is possible. Further, the formation of a thin film containing W and Sc ₂ O ₃ can be omitted, and the cost can be reduced.

FIG. 2 is a schematic process diagram for explaining a manufacturing method of an embodiment of the impregnated cathode according to the present invention shown in FIG. 1, in which 21 is a first granulation step, 22 is a second granulation step, Two
3 is a third granulating step, 24 is a weighing / mixing step, 25 is a pelletizing step, 26 is a sintering / fixing step, and 27 is an assembling step. The first granulation step 21 is to granulate tungsten W which becomes the refractory metal part 1, in an acetone solution in which powder of tungsten W having an average particle size of 5 μm is added with 1.25% polymethylmethacrylic as a binder. The tungsten W powder is granulated by gradually evaporating acetone with stirring. The granules are sized with a 200-mesh sieve to obtain tungsten granules for producing a cathode.

In the second granulation step 22, Ba which becomes compound 2 is obtained.
A granulation step of -O compounds, BaCO _3, CaCO
₃ , Al ₂ O ₃ powder was weighed at a molar ratio of 4: 1: 1, mixed, and then mixed in a hydrogen atmosphere at 1100 ° C. → 16.
BaCO ₃ , CaCO by two-step heat treatment at 00 ° C
Decomposition of ₃ carbonates into oxides (1100 ° C) and 4
Ba-Ca having a composition of BaO / CaO / Al ₂ O ₃
Compound 2 is obtained by synthesizing an aluminate compound (1600 ° C.).

In the third granulating step 23, tungsten W,
In the manufacturing process of compound 3 containing scandium Sc and oxygen O, WO ₃ and Sc ₂ O ₃ powders are weighed and mixed at a molar ratio of 3: 1, and the mixture is mixed in an oxygen atmosphere. Sc ₂ W ₃ O ₁₂ was synthesized at 1100 ° C, and this was crushed and granulated in the same manner as tungsten W powder,
Sieve through a 400 mesh screen.

In the weighing and mixing step 24, the tungsten W granules obtained in the first granulation step, the Ba-Ca aluminate compound granules obtained in the second granulation step, and the third step
The Sc ₂ W ₃ O ₁₂ compound granules obtained in the granulation step are weighed in a volume ratio of 7: 2: 1 and then mixed. The tungsten W granules serving as the refractory metal substrate are usually selected in the range of 60 to 80% of the cathode pellets. The ratio of the Ba—Ca aluminate compound 2 to the Sc ₂ W ₃ O ₁₂ compound 3 is preferably selected so that the former is more than 1: 1 considering the life characteristics of electron emission.

In the pelletizing step 25, the diameter is 1.25 m.
Using a cylindrical press die of m, the tungsten W granules 1 and Ba-Ca are placed in the press die so that the height becomes 0.5 mm.
A mixture of aluminate compound granules 2 and Sc ₂ W ₃ O ₁₂ compound granules 3 is automatically supplied in a fixed amount, and a press-molded body (pellet) having a desired shape in anticipation of the final shape is prepared by a press-molding pressure of 5 t / cm ^2. ..

Next, in the sintering / fixing step 26, the above pellets are subjected to a two-step heat treatment in a hydrogen atmosphere at 1000 ° C. → 1700 ° C. to obtain impregnated cathode pellets 5. Of these heat treatments, the treatment at 1000 ° C. is performed using tungsten W powder, B
a-Ca aluminate compound powder, and Sc ₂ W ₃ O
_{12 The} purpose is to decompose and evaporate polymethylmethacrylic, which is a binder used in the step of granulating ₁₂ compound powder. It is necessary that no carbon is left behind after the decomposition of this binder. Therefore, this process is 600 ° C to 120 ° C.
You may choose from 0 ° C.

The second heat treatment at 1700 ° C. is aimed at sintering the tungsten W powders and fixing the electron emitting substance powders or the tungsten W powders. It is necessary to carry out this treatment at a temperature not higher than the melting point of the electron-emitting substance (the melting point differs depending on the compound, but 2,000 ° C. or lower is a standard). The impregnated cathode pellet 5 thus obtained is
In the assembling step 27, after inserting into the cup-shaped barrier layer 6 made of molybdenum Mo and further into the sleeve 7 for enclosing the heater 8, these are fixed and the cathode main body for electron tube is manufactured.

With respect to the impregnated cathode manufactured as described above, the sealing process for manufacturing an electron tube was simulated, and
The following results were obtained when the electron emission characteristics were measured by applying 0 min oxidation treatment. That is, this electron emission characteristic is that two electrodes of a parallel plate composed of an anode and a cathode are placed in a high vacuum container of a vacuum degree of 10 ⁻⁷ Pascal class, and the cathode temperature is heated to 1150 ° C. to activate the cathode. After the operation, the cathode temperature was lowered to 850 ° C., a positive pulse voltage was applied to the anode, and the emission current from the cathode was measured.

FIG. 3 is an explanatory view of the change in current density with the activation time of the oxidized cathode, and shows the relationship between the activation time of the cathode and the emission current density at the operating temperature of 850 ° C. In the figure, 31 is the characteristic when the oxidation treatment is not carried out, 32 and 33 are the cases where the oxidation treatment is carried out.
2 is the characteristic of the impregnated cathode of this embodiment, 33 is W on the cathode surface
It is a conventional characteristic of a cathode having a -sc ₂ O ₃ thin film.

As can be seen from the figure, the characteristic 33 of the conventional cathode does not recover (increase) the emission current density even after repeated activation. The characteristic 32 of the cathode of this example has an activation time showing the maximum emission current density which is slightly longer than that of the characteristic 31 of the untreated cathode, but there is no problem in practical use, and a decrease in the emission current density is observed. I can't. FIG. 4 is an explanatory diagram of the Auger spectrum of the activated cathode surface of an embodiment of the impregnated cathode according to the present invention (cathode having the characteristic 32 of FIG. 3) that has been subjected to an oxidation treatment. It is analyzed under the operating condition of 850 ° C.

From the figure, it is shown that an extremely thin low-work function (Ba, Sc, O) composite layer 9 is formed on the surface of the tungsten W on the cathode surface, which is suitable for electron emission, from a single molecular layer to several molecular layers. Is shown. From this, it can be seen that the impregnated cathode of this example is an impregnated cathode that can withstand oxidation in the sealing step during manufacturing of the electron tube and that operates at low temperature.

FIG. 5 is a sectional view showing an example of a color cathode ray tube using an electron gun having an impregnated cathode according to the present invention, where 51 is a face panel, 52 is a funnel, and 53.
Is a neck, 54 is an electron gun, 55 is a shadow mask, 56
Is a fluorescent layer, and 57 is a deflecting device. In the figure, the impregnated cathodes described above are mounted on the three cathodes constituting the electron gun 54, and the electron beams R, G, B emitted from the respective cathodes are made horizontal and vertical by the deflecting device 57. The light is deflected and projected onto the fluorescent layer applied to the inner surface of the face panel 51 to reproduce a desired image.

According to this color cathode ray tube, a bright image can be reproduced with low power, and a highly reliable and long-life image reproducing apparatus can be constructed.

[0038]

As described above, according to the impregnated cathode according to the present invention, the impregnated cathode having a low work function (B
(a, Sc, O) composite layer can be easily formed, and a low-temperature impregnated cathode of a practical level can be obtained.

When the electron gun using the impregnated cathode according to the present invention is mounted on an electron tube, the operating temperature is 150 ° C. to 20 ° C. as compared with the conventional Os-Ru coated impregnated cathode.
It is possible to lower the temperature by 0 ° C., the evaporation temperature of Ba and BaO from the cathode surface can be reduced by one digit, and the deterioration of the tube characteristics due to grid emission or the like can be prevented.

Further, since the impregnated cathode according to the present invention operates at a low temperature, the reliability of the heater for heating the cathode can be greatly improved, and the conventional Os-Ru thin film or W-Sc ₂ O ₃ thin film can be used. Can be omitted, the manufacturing process can be simplified, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating a schematic structure of an embodiment of an impregnated cathode according to the present invention.

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

FIG. 3 is an explanatory diagram of a change in current density depending on activation time of an oxidized cathode.

FIG. 4 is an explanatory diagram of an Auger spectrum of a cathode surface activated for an example of the impregnated cathode according to the present invention which has been subjected to an oxidation treatment.

FIG. 5 is a cross-sectional view showing an example of a color cathode ray tube using an electron gun mounted with an impregnated cathode according to the present invention.

FIG. 6 is a sectional view illustrating a schematic structure of a conventional impregnated cathode.

[Explanation of symbols]

1 Heat-Resistant Metal Part 2 First Compound 3 Containing At least Ba, O 3 Second Compound At least Containing W, Sc, O 4 Electron Emitting Material Part Consisting of First Compound 2 and Second Compound 3 5 Heat-Resistant Metal Part Impregnated cathode pellet 6 composed of 1 and electron emission material portion 6 Barrier layer 7 Sleeve 8 Heater 9 Ba, Sc, O composite layer

Claims (3)

[Claims] 1. A heat-resistant metal portion containing tungsten or molybdenum or both, a compound containing at least barium and oxygen, and an electron emitting material portion containing at least a compound containing tungsten, scandium and oxygen. Impregnated cathode. 2. A sleeve, a refractory metal portion containing tungsten and / or molybdenum or both attached to one end of the sleeve, a compound containing at least barium and oxygen, and a compound containing at least tungsten, scandium and oxygen. An impregnated cathode pellet comprising an electron emission material portion and a composite layer of barium, scandium and oxygen formed on the electron emission surface of the impregnated cathode pellet, and a heater is attached to the other end of the sleeve. An impregnated cathode characterized in that 3. A first granulation step of granulating tungsten powder or molybdenum powder or both together with a binder, a second granulation step of granulating a compound of barium and oxygen, and a compound of tungsten, scandium and oxygen. A third granulating step of granulating, the first granulating step,
A weighing / mixing step of weighing and mixing the granules granulated in the second granulating step and the third granulating step, and a pellet for pelletizing the mixture mixed in the weighing / mixing step by pressing into a desired shape Sintering / fixing step of heating the pellets obtained by the pelletizing step and the pelletizing step in a hydrogen atmosphere to decompose the binder and sinter the tungsten powder or molybdenum powder to fix the electron emission material powder. And a step of assembling the same with a barrier layer into a sleeve to assemble an electron tube cathode.