JPH06124648A - Impregnated type cathode and electron tube using this - Google Patents

Abstract

PURPOSE:To provide an impregnated type cathode taking large current operation and low temperature operation, and a highly reliable electron tube using this. CONSTITUTION:In a Sc-coated impregnated type cathode having a porous base 1 of tungsten impregnated with an oxide 2 mainly containing barium, and a coat film 3 mainly consisting of tungsten and containing scandium formed on the upper surface, fine network cracks 4 are formed on the porous tungsten base. Since the barium is supplied to the coat film not only from the pore part of the porous body but also from the crack parts of the porous body, thus, the electron releasing characteristic of the Sc-coated impregnated type cathode is improved. Consequently, this cathode can be operated at a temperature lower than in a conventional Sc-coated impregnated type cathode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron tube such as a cathode ray tube or an image pickup tube, and more particularly to an impregnated cathode which operates at a large current and a low temperature.

[0002]

2. Description of the Related Art A cathode capable of operating with a large current is required to increase the output of an electron tube, for example, to increase the brightness and definition of a cathode ray tube. Impregnated cathodes are generally used for this purpose. The basic structure of the impregnated cathode is a porous substrate made of tungsten, which is mainly composed of BaO, and also Al ₂ O ₃ and CaO which are heated and melted in a hydrogen atmosphere or in a vacuum and impregnated as a composite oxide. . This impregnated material is commonly referred to as the impregnant. The porous tungsten substrate is formed by press-molding tungsten powder having a particle size of 1 μm to 10 μm into a size suitable for the application, and the temperature is 1500 ° C. to 200 ° C.
It was sintered at 0 ° C.

During operation, the impregnated cathode is constantly heated to about 1000 ° C., the tungsten reacts with the impregnating agent,
Release the barium atom. Barium atoms are supplied to the surface of the impregnated cathode by diffusion, and are adsorbed on the tungsten surface, which is the cathode surface, together with oxygen atoms supplied from the inside of the cathode or the atmosphere inside the electron tube. In this way, when the adsorption layer composed of barium atoms and oxygen atoms is formed on the metal surface, the work function of the metal surface is lowered, and the electron emission is facilitated. This is the principle of operation of the impregnated cathode, and detailed consideration therefor can be found in, for example, Journal of Physics D: Applied Physics, Volume 15 (1982), pages 1519 to 1519 (J. Phys.
D: Appl. Phys., 15 (1982) 1519-152.
9).

The impregnated cathode has a low electric resistance because the electron emitting portion is basically made of metal. Therefore, the impregnated cathode does not cause cathode deterioration due to decomposition of the cathode material itself due to Joule heat generation, unlike a so-called high-resistance oxide cathode which is an oxide of alkaline earth metal mainly containing barium.

However, while the impregnated cathode can operate at a high current density, its operating temperature is about 7 times that of an oxide cathode.
It is necessary to operate at a high temperature as compared to 50 ° C. In the case of the impregnated cathode having the above-mentioned basic structure, 1 in the space charge limited state.
Heating to approximately 1100 ° C. is necessary to obtain a current density of 0 A / cm ² .

Therefore, the improvement of the impregnated cathode has been made mainly for the purpose of lowering the operating temperature. For example,
An impregnated cathode in which the surface of the impregnated cathode having the above-mentioned basic structure is coated with osmium, iridium or the like has been developed, and its operating temperature has been lowered to about 1000 ° C. In this regard, IEE Proceedings, Volume 128, Part 1, Number 1 (1981), pages 19 to 32 (IEE Proc., 128, Pt1, No1 (1981) 19-3
2).

Similarly, a coated impregnated cathode (hereinafter abbreviated as Sc-coated impregnated cathode) coated with a thin film containing mainly tungsten and scandium in a Sc / W atomic ratio of about 0.05 to 0.30 is 900 It is possible to operate at the aforementioned current density at ° C. In this regard, SID 91
Digest of Technical Papers 70th
Pages 7 to 710 (SID91 Digest of technical pape
rs 707-710).

[0008]

As described above, the impregnated cathode can operate at a high current density, but the Sc-coated impregnated cathode which can operate at the lowest temperature is 900 ° C.,
The operating temperature is 150 ° C. higher than that of the oxide cathode. Such a high operating temperature causes a temperature rise of the electrodes in the vicinity of the cathode, causing a change between electrodes due to thermal expansion and unnecessary electron emission from electrodes other than the cathode. Therefore, the electron gun of the cathode ray tube using the impregnated cathode is apt to cause a decrease in reliability as compared with the electron gun using the oxide cathode.

By the way, the electron emission from the Sc-coated impregnated cathode is non-uniform, and the high electron emission region corresponds to the region in which the supply amount of barium is large. In this regard as well, SID 91 Digest of Technical Papers, pages 707 to 710 (SID91 Digest
of technical papers 707-710). Therefore, if the supply of barium to the cathode coating film can be increased more than in the conventional case, it is expected that better electron emission characteristics will be obtained, and the operating temperature can be reduced.

It is an object of the present invention to provide an impregnated cathode capable of operating at a low temperature with a high current density and a highly reliable electron tube using the same.

[0011]

In order to achieve the above object, the impregnated cathode of the present invention comprises a surface coating film containing scandium mainly of tungsten and an impregnating agent for supplying barium atoms to the coating film. A porous tungsten substrate incorporated therein, wherein the porous tungsten substrate has three-dimensional mesh-like cracks at intervals of several times to several tens times the tungsten particle size, or at intervals of 10 μm to 100 μm. did.

Here, the impregnated cathode of the present invention is basically the same as the conventional Sc-coated impregnated cathode except that the porous tungsten substrate has network-like cracks. It contains scandium in an atomic ratio of Sc / W of 0.05 to 0.30 and a coating film thickness of 0.1 μm.
m to 0.5 μm is desirable. Similarly, the impregnating agent is the same as that for a general impregnated cathode, and includes BaO, Al ₂ O ₃ and CaO.
The molar ratio may be 4: 1: 1 or 5: 2: 3. further,
The tungsten powder, which is a raw material for the porous body, is the same as that for a general impregnated cathode, and 1 μm to 10 μm is used.

[0013]

In the conventional impregnated cathode, the barium atom generated by the reaction between the tungsten and the impregnating agent inside the cathode diffuses through the pores of the porous body and is supplied to the cathode surface and the coating film layer. On the other hand, in the impregnated cathode of the present invention, in addition to the supply by diffusion of barium atoms through the void portion, the supply by diffusion through the cracked portion is added. Therefore, in the impregnated cathode of the present invention, the amount of barium supplied to the cathode surface and the coating film layer increases. As a result, good electron emission characteristics can be obtained, and operation at a lower temperature can be performed than ever before. Also,
The electron tube using the impregnated cathode of the present invention can suppress the temperature rise in the vicinity of the cathode, and can achieve higher reliability than the electron tube using the conventional impregnated cathode.

[0014]

EXAMPLE FIG. 1 is a sectional view of a porous tungsten substrate 1 containing an impregnating agent 2 and a coating film 3 formed on the surface thereof for explaining an example of an impregnated cathode according to the present invention. . The porous tungsten substrate has mesh-like cracks 4. FIG. 2 is a SEM microstructure photograph of the surface of the impregnated cathode of this example. Tungsten powder, which is a raw material for the porous body, has a particle size of 5 μm. It can be seen that the mesh-like cracks 4'exist with a size several times to several tens of times the particle size, that is, a size of about 20 μm to 100 μm. FIG. 3 is a SEM photograph of a conventional impregnated cathode surface shown for comparison. In the conventional impregnated cathode, there are no network cracks.

In the embodiment shown in the SEM photograph of FIG. 2, tungsten powder having a particle size of 5 μm is sintered in vacuum at 1600 ° C. and then impregnated with hydrogen in an impregnating agent. Impregnating agent is B
A mixture of aO, Al ₂ O ₃ and CaO at a molar ratio of 4: 1: 1 was used. However, BaCO ₃ and CaCO ₃ were used as raw materials for BaO and CaO. Before impregnation, these are preheated at about 1000 ° C. and decomposed to form oxides. Then, it was heated to 1900 ° C. in a hydrogen atmosphere and melt-impregnated.

After the impregnation, the surface of the porous substrate was polished and a coating film of about 0.2 μm was formed with a sputtering film forming apparatus. As the sputtering target, tungsten and Sc ₂ W ₃ O ₁₂ were used. The shape of the cathode is a cylinder, and its diameter is 1.2 mm. This was integrated with a support component consisting of a molybdenum cup and a sleeve, and a heater was inserted into the sleeve so that heating could be performed.

In this example, the cathode which was not heated at all was rapidly heated to about 800 ° C., and cracks were formed by the degassing pressure of the gas contained in the impregnated cathode. Then, it heated at 1150 degreeC for 4 hours. Figure 3
The conventional example of No. 1 is the same as the impregnated cathode of the present invention, except that the temperature is raised relatively slowly.

After heating at 1150 ° C. for 4 hours, 9
The emission current was measured at 00 ° C. In the measurement, the anode was opposed to the impregnated cathode by 7 mm, and a pulse voltage of 4 kV was applied to the anode. The temperature of the cathode is the brightness temperature measured by an optical thermometer. As a result, an emission current of 390 mA was obtained in this example, while it was 280 mA in the conventional example. The cathode temperature at which the same current of 280 mA as in the conventional example was obtained was about 800 ° C. Therefore, the impregnated cathode of the present invention has an additional 1% more than the conventional Sc-coated impregnated cathode.
The operating temperature can be reduced to about 00 ° C.

In the examples, as the impregnating agent, BaO, Al
_A mixture of ₂ O ₃ and CaO in a molar ratio of 4: 1: 1 was used, but this may be a mixture of 5: 2: 3 and other compositions generally used for impregnated cathodes. Similar effects are shown. The electron emission mechanism of the impregnated cathode of the present invention is
Since it is the same as the Sc-coated impregnated cathode, the composition and manufacturing method of the coating film 3 may be the same as that of the Sc-coated impregnated cathode. Therefore, the preferred composition is in the range of 0.05 to 0.30 in terms of Sc / W atomic ratio. In the examples, tungsten and Sc ₂ W ₃ O ₁₂ were used as the sputtering target, but tungsten, Sc ₂ O ₃ or Sc ₆ WO ₁₂ may be used, or tungsten oxide may be added. The film forming method is not limited to the sputter film forming method. The tungsten powder used as the raw material of the porous tungsten substrate of this example had a particle size of 5 μm, but the particle size of tungsten may be 1 μm to 10 μm used in a general impregnated cathode. The particle size does not have to be uniform, and a mixture of these may be used.

Although the embodiment has been described with reference to the impregnated cathode, the impregnated cathode of the present invention is used for an electron tube, and an electron tube using the impregnated cathode of the present invention is a conventional impregnated cathode. It is clear that it has a higher reliability for thermal factors from the cathode than the one used. Therefore, the present invention includes an electron tube using the impregnated cathode of the present invention.

[0021]

According to the structure of the impregnated cathode of the present invention, it is possible to supply more barium to the coating film layer mainly composed of tungsten and containing scandium than in the conventional structure. as a result,
The large current density operation required for the electron tube can be performed at a temperature about 100 ° C. lower than that of the conventional Sc-coated impregnated cathode.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating the configuration of an embodiment of an impregnated cathode according to the present invention.

FIG. 2 is a microstructure photograph of a surface of an impregnated cathode showing an example of the present invention.

FIG. 3 is a microstructure photograph of the surface of an impregnated cathode showing a conventional example.

[Explanation of symbols]

1 ... Porous tungsten substrate, 2 ... Impregnating agent, 3 ... Coating film, 4, 4 '... Network-like cracks.

Front page continuation (72) Inventor Emiko Yamada 1-280 Higashi-Kengokubo, Kokubunji-shi, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Tadashi Seisei 1-280 Higashi-Kengikubo, Kokubunji-shi, Tokyo Hitachi Research Center Co., Ltd. In-house

Claims (3)

[Claims] 1. A surface of an impregnated cathode obtained by impregnating a barium-containing oxide with a porous tungsten substrate sintered with tungsten powder, and at least one of scandium, scandium oxide, and scandium tungstate, or tungsten. In a coated impregnated cathode formed with a coating film including a plurality, the porous tungsten substrate has a network crack at intervals of several times to several tens of times the average particle diameter of the tungsten powder. Shaped cathode. 2. The impregnated cathode according to claim 1, wherein the particle size of the tungsten powder is 1 μm or more and 10 μm or less. 3. An electron tube using the impregnated cathode according to claim 1.