JPS6188420A - Osmium coated impregnated 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] [Field of Application of the Invention] The present invention is directed to the use of tungsten (W), molybdenum (Mo)-
Tantalum (Ta), rhenium (Re), iridium (
This relates to an oxidation-resistant osmium (Os) coating provided on a substrate made of a heat-resistant metal such as Ir), nickel (Ni), or an alloy of these metals. The present invention relates to an oxidation-resistant osmium coating coated on the electron emitting surface of an impregnated cathode impregnated with a radioactive substance in order to improve the electron emission efficiency of the impregnated cathode.

[Background of the invention]

An impregnated cathode is one in which the pores of a porous metal substrate are impregnated with an electron-emitting substance made of an alkaline earth metal. Current density cathode.

Porous metal substrates include W, Mo, Ta, Re, I
Heat-resistant metals such as r, Ni, and alloys of these metals are used. In general, as a porous metal base,
Tungsten, which has a high melting point, low vapor pressure, and high ion bombardment resistance, is used, and Bad and C are used as electron emitting materials.
ab, AQ20. The following compounds are used. In the operating state of this impregnated cathode, the electron-emitting material impregnated into the porous tungsten reacts with the tungsten to generate free barium, which passes through the pores in the substrate to the cathode substrate surface, that is, the electron-emitting surface. The barium reaches the surface and further diffuses to the surface to form a barium monatomic adsorption layer on the electron emitting surface. As a result, the work function of the impregnated cathode is the same as that of the tungsten substrate (4.5 eV
) and barium (2,3 eV), which has a work function of 1.9 to 2. It is as low as OeV.

The thermionic emission current density J of metal is expressed by the Richardson-Dushman equation (J = AT2exp (-eφ/kT)),
(Here, A is the thermionic constant and T is the absolute temperature of the cathode.

e is the electron charge, φ is the work function, and k is Boltzmann's constant). That is, the thermionic emission current density,
(2) is the maximum saturation current density that can be obtained from a substance at a certain temperature; the higher the temperature and the smaller the work function, the higher the thermionic emission current density J. The impregnated cathode is a cathode that forms a barium monatomic adsorption layer on the surface of a tungsten substrate to reduce the work function and improve the thermionic emission current density at low temperatures.

In an impregnated cathode, electron emission characteristics can be improved depending on the type of cathode substrate. For example, there is an osmium-coated impregnated cathode proposed by Philips (Japanese Patent Publication No. 47-21343).
. This cathode is an impregnated type cathode in which a porous tungsten base is impregnated with an electron emitting material, and an osmium coating layer is provided on the electron emitting surface of the cathode. In this operating state of the cathode, a barium monatomic adsorption layer is formed on the osmium surface, and the work function is further reduced compared to the case of a tungsten substrate, 1.7~
1.8 eV), and the thermionic emission current density is further improved.

- As an example, when comparing the saturation current density at 1000°C of an impregnated cathode based on W and an osmium-coated impregnated cathode in which an osmium coating layer with a thickness of 0.5 mm is provided on the electron emitting surface of the cathode, Compared to the former, the latter osmium-coated impregnated cathode provides a saturation current density approximately three times higher.

On the other hand, this osmium-coated impregnated cathode has the disadvantage that thermionic emission characteristics deteriorate due to oxidation of the coating layer to the level of an impregnated cathode that is not coated with osmium. In other words, osmium is extremely easily oxidized at low temperatures, and osmium oxide (Os') has a high vapor pressure (1
, 78×10'Pa at 500° C.), it evaporates and disappears from the cathode during the manufacturing process of the electron tube, resulting in deterioration of thermionic emission characteristics. Furthermore, osmium oxide (osO4) vapor is harmful to the human body.

As mentioned above, the osmium-coated impregnated cathode has the advantage of excellent thermionic emission characteristics as long as the osmium coating layer is maintained, but this osmium coating layer oxidizes during the manufacturing process of the electron tube. The fatal drawback of osmium oxide, which easily evaporates and disappears, has hindered its practical application.

Now, in the currently common method of manufacturing an electron tube, the electron tube is manufactured through a sealing process shown with reference to FIG. 1, and the cathode is mainly oxidized during this sealing process.

A general sealing process in an electron tube manufacturing method will be explained with reference to FIG. The cathode 1 is fixed to an electrode group 2 for electron beam focusing so as to maintain geometric dimensions, and the electrode group 2 is further fixed to an evacuation pipe 4 via a support fitting 3. In the sealing process, the vacuum exhaust pipe 4 is attached to the holder 5,
It is inserted along the inner hole of the neck part 7 provided in the electron tube 6.

Next, the area around the connecting portion 8 is heated with a gas burner 9 or the like, and the vacuum exhaust pipe 4 is connected to the neck portion 7 at the connecting portion 8. This process is called the sealing process in electron tube manufacturing. The sealing process is generally performed in the atmosphere, and the temperature around the cathode 1 is raised to about 400° C. by the heat of the gas burner 9, so that the cathode 1 is oxidized. In particular, in the case of an osmium-coated impregnated cathode, there is a problem that osmium is oxidized and vaporized during the sealing process and disappears from the cathode surface, degrading thermionic emission characteristics.

On the other hand, for the purpose of preventing oxidation of the cathode 1 in the above-mentioned sealing process, a method has been proposed in which the surroundings of the cathode 1 are replaced with a non-oxidizing gas atmosphere such as nitrogen gas or argon gas for sealing. Although this method is effective in terms of preventing oxidation of the cathode, it requires replacing the atmosphere with a non-oxidizing atmosphere during the sealing process, making it more labor-intensive to manufacture electron tubes than the conventional sealing process. This method has disadvantages in that it takes a long time, requires complicated manufacturing equipment, and is expensive.

[Purpose of the invention]

An object of the present invention is to provide an oxidation-resistant osmium coating that can prevent oxidation and evaporation of osmium even when an osmium-coated substrate or an osmium-coated impregnated cathode is placed in oxidizing conditions, which eliminates the drawbacks of the prior art as described above. The purpose is to

[Summary of the invention]

The oxidation-resistant osmium coating of the present invention is characterized by being formed on a substrate made of heat-resistant metals such as tungsten, molybdenum, tantalum, rhenium, iridium, and nickel, or alloys of these metals, or on substrates made of these metals and alloys as main components. In an osmium coating coated on the electron emitting surface of an impregnated cathode, which is a porous substrate impregnated with an electron emitting substance made of a barium compound or the like, the osmium coating coats the substrate or the electron emitting surface with a non-oxidizing property. A part of the base metal is impregnated into the osmium film by heat treatment to impart oxidation resistance in an atmosphere, and the surface of the osmium film is covered with a layer of the base metal. . The osmium coated with the oxidation-resistant osmium film of the present invention will not oxidize and evaporate even if placed under atmospheric oxidation conditions, so when used in an osmium-coated impregnated cathode, it will not evaporate during the sealing process. It is possible to prevent the disappearance of osmium in the process, and it is possible to eliminate the drawbacks of the above-mentioned conventional techniques.

In addition, when performing the heat treatment for imparting oxidation resistance in the above-mentioned non-oxidizing atmosphere, the preferable temperature for the type of base metal is as follows.

W: 1000-1500℃.

Mo: 900-1400°C.

Ta: 900-1500°C.

Re: 1000-1500℃.

Ir: 900-1400°C.

-Ni: 600-1100°C.

[Embodiments of the invention]

The present invention will be explained in more detail below with reference to Examples.

[Example 1] A coating of osmium (O8) was applied to a tungsten (W) plate.
．． A sample coated with a thickness of 5 mm (hereinafter abbreviated as ○s/W sample) was used. O5 is a high melting point metal and was coated by electron beam evaporation.

A normal Os/W sample without any treatment is
When subjected to atmospheric oxidation treatment at 200° C. or higher, Os was oxidized and evaporated and disappeared from the W substrate. This state is shown by the broken line (,) in FIG.

On the other hand, in the Os/W samples mentioned above, those that were heat-treated at 1100°C for 2 hours in a non-oxidizing atmosphere, such as vacuum, were oxidized in the air, as shown by the solid line (b) in Figure 2. The osmium did not oxidize or evaporate even when exposed to water.

Os when the Os/W sample is treated in a non-oxidizing atmosphere
The graph in FIG. 3 shows the change in concentration of and W. The vertical axis is the concentration ratio (relative value) from the analysis results by IMA (mass spectrometer), and the horizontal axis is the depth from the surface of the Os coating.
It is. Therefore, 0.511In on the horizontal axis is O5
This is the position of the surface of the W plate before being coated with the film.

In Figure 3, curve (c) shows the change in Os concentration, curve (d) shows the case where W has penetrated to the surface of the O8 film, and curve (e) shows the case where W has penetrated to the surface of the O8 film. This figure shows the case where the infiltration reaches the middle of the O8 coating.

As is clear from the graph in Figure 3, when the Os/W sample is heat-treated in a non-oxidizing atmosphere, W from the substrate penetrates into the Os film and eventually covers the surface of the Os film, causing the Os
This forms a protective layer of W against oxidation. That is, by heat-treating the Os/W sample in a non-oxidizing atmosphere, W on the substrate penetrates into the O5 film and the surface of the O8 film is covered with a protective layer of W.

Referring to FIG. 3, in the state shown by curve (d) in which W of the substrate penetrates to the surface of the Os film, the O5 film becomes oxidation resistant. On the other hand, in the state of curve (e), the O5 film on the portion of the substrate into which W has not penetrated disappears due to oxidation. In addition, in this heat treatment, W on the substrate penetrates into the O5 film, but no alloy or compound of W and Os is formed.1 In this way, the heat treatment for imparting oxidation resistance according to the present invention When the treated O5 film is exposed to atmospheric oxidation, W becomes an oxide film and covers the surface of the O5 film, thereby preventing oxidation of Os. This W oxide film can be easily removed by reheating in vacuum.
A clean O3 film is obtained again.

The heat treatment conditions for imparting oxidation resistance to the OS film are preferably such that the partial pressure of an oxidizing gas such as H2O, CO2, etc. is I x 10-' Torr or less in vacuum in the case of vacuum heat treatment. This is caused by oxidizing gas in the atmosphere during heat treatment.
This is to prevent s from being consumed by oxidation and evaporation. Further, the heat treatment may be performed in a non-oxidizing gas, for example, hydrogen, argon, or nitrogen gas having a dew point of -50° C. or lower.

Note that in the above embodiment, W is used for the substrate.

The thickness of the O5 film was 0.577In, but the heat treatment was
The purpose is to partially infiltrate the substrate into the No. 5 coating, and the temperature and time of the heat treatment vary depending on the thickness of the Os coating and the type of substrate. Generally, the thicker the Os coating and the higher the melting point of the substrate metal, the higher the R treatment temperature and the longer the time. For example, for a 0.511 thick Os film, 1100°C for 1 hour on a W substrate; t
ooo°C, 1 hour; For a Ni substrate, heat treatment for imparting oxidation resistance to the Os film is possible by heat treatment at 600°C for 11 hours.

[Example 2] BaO1Cab was added to the pores of a porous W substrate with a porosity of 26%.
, A1120. An impregnated cathode was prepared by impregnating it with an electron-emitting material consisting of the following materials and polishing the surface to form a smooth electron-emitting surface. O is deposited on the electron emitting surface of this cathode by electron beam evaporation.
s to 0.5. The osmium film was deposited to a thickness of cm to produce an osmium-coated impregnated cathode.

Next, in a vacuum of IX 1O-5 Torr or less,
A heat treatment for imparting oxidation resistance is carried out at °C for 12 hours. 1. W on the substrate is infiltrated and diffused into the Os coating to cover the surface of the Os coating with a part of the W on the substrate. This is an embodiment of the present invention. The sample was an impregnated cathode coated with an oxidation-resistant osmium film.

The results of testing the oxidation resistance of the thermionic emission characteristics of the oxidation-resistant osmium-coated impregnated cathode according to the present invention described above are as follows. A comparison is shown in the graph of FIG.

The comparative sample, which is a conventional osmium-coated impregnated cathode not according to the present invention, was not subjected to the heat treatment for imparting oxidation resistance in vacuum in the above-mentioned example. For comparison samples,
The thermionic emission characteristics of the sample itself, which was not subjected to heat treatment in the atmosphere, were as shown by the group of white dots 21 in FIG. This comparison sample was subjected to oxidation treatment at 450°C for 10 minutes in the air, and its thermionic emission characteristics were as shown by the group of black square points 22 in Figure 4, compared to those not subjected to oxidation treatment. The value deteriorated to about 1/3 or less. On the other hand 1
The osmium-coated impregnated cathode of the sample according to the present invention was subjected to a heat treatment for imparting oxidation resistance at 1100° C. for 2 hours in a vacuum according to the present invention.

The thermionic emission characteristics of the cathode subjected to oxidation treatment at 500°C for 10 minutes in the atmosphere were good, maintaining the original characteristics of the osmium-coated impregnated cathode, as shown by the group of black dots 23 in Figure 4. Ta.

As is clear from this example, the device according to the present invention can sufficiently withstand heat treatment in the atmosphere, and has excellent performance without any deterioration in the sealing process of ordinary electron tube manufacturing.

〔Effect of the invention〕

As mentioned above, osmium coatings coated on substrates made of heat-resistant metals such as tungsten, molybdenum, tantalum, rhenium, iridium, nickel, etc. or alloys of these metals, or In an osmium coating coated on the electron emitting surface of an impregnated cathode in which a porous substrate made of a heat-resistant metal or an alloy of these metals is impregnated with an electron emitting substance, the osmium coating covers the electron emitting surface of the substrate or the impregnated cathode. After that, heat treatment is performed to impart oxidation resistance in a non-oxidizing atmosphere at a temperature at which osmium does not form an alloy or compound with these heat-resistant metals or their alloys, and a part of the base metal is infiltrated into the osmium coating. The oxidation-resistant osmium coating of the present invention, which is formed by diffusion to form a protective layer of the base metal on the surface of the osmium coating, exhibits extremely beneficial effects.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining the sealing process in the manufacture of a conventional electron tube. Figure 2 is a graph showing the amount of osmium lost by atmospheric oxidation treatment for samples in which a tungsten plate is coated with an osmium film, with and without heat treatment to impart oxidation resistance according to the present invention. be. Third
The figure shows IMA that tungsten from the substrate has penetrated into the osmium coating when a sample in which a tungsten plate is coated with an osmium coating is heat-treated in a non-oxidizing atmosphere.
It is a graph of 1 degree change. FIG. 4 is a graph showing the heat resistance of the thermionic emission characteristics of the impregnated cathode coated with the osmium film according to the example of the present invention, together with that of a comparative sample. 1... Cathode 2... Electrode group 3... Support fitting 4... Vacuum exhaust pipe 5... Holder
6...Electron tube 7...Neck part 8...
・Connection part 9...Gas burner

Claims (2)

[Claims] (1) In an osmium coating coated on a substrate made of a heat-resistant metal such as tungsten, molybdenum, tantalum, rhenium, iridium, or nickel or an alloy of these metals, the osmium coating is applied to the substrate in a non-oxidizing atmosphere. The base metal is heat-treated to impart oxidation resistance, a part of the base metal is impregnated into the osmium film, and the surface of the osmium film is covered with a layer of the base metal. Oxidation-resistant osmium coating. (2) In the oxidation-resistant osmium coating according to claim 1, the osmium coating coated on the substrate includes tungsten, molybdenum, tantalum, rhenium,
An osmium film coated on the electron emitting surface of an impregnated cathode, which is a porous substrate mainly made of heat-resistant metals such as iridium and nickel, or alloys of these metals, and impregnated with an electron emitting substance.