JPS58198816A - Impregnation type negative electrode - Google Patents

Abstract

PURPOSE:To enable a negative electrode to operate in high current density with its longer duration of life by impregnating with an emitter the gap part in an overlapped part, formd by a mesh comprising a thin wire such as W, etc., and the winding of the mesh of a negative electrode substrate obtained by winding the mesh into a coil shape. CONSTITUTION:After W mesh with an arbitrary width is made a double shaped like vinegared rice rolled in layer, by rolling said mesh arbitrary times into an arbitrary diameter and the ends of the mesh 2 are fixed, it is fixed as required by means of laser welding, etc. Then, after dipping the mesh bundle in a methyl mechacrylate monomer, etc., and impregnating the holes of the mesh bundle with this monomer while subjecting the bundle to vacuum degassing, this monomer is polymerized and hardened. After heating said negative electrode substrate to thermally decompose and remove the impregnated methyl polymer, said substrate is heated under the atmosphere of hydrogen to obtain a clear negative electrode structure, and is made a negative electrode by impregnating said structure with an emitter under the atmosphere of hydrogen. Hereby, the negative electrode is enabled to operate with high current density with longer duration of life, along with the improvement of its reliability.

Description

[Detailed description of the invention] The present invention relates to the structure of an impregnated cathode.

Impregnated cathodes are characterized by long life, high current density, and operation, and are preferred for use in highly reliable, high-power electron tubes. FIG. 1 is a cross-sectional view schematically showing such an impregnated cathode structure, in which barium oxide (Bad), calcium oxide (Cab), and aluminum oxide (A#03) are contained in a cathode base 1 made of a sintered body of tungsten powder. ) A cathode substrate of an impregnated cathode formed by impregnating an electron-emitting metal oxide 2 (hereinafter referred to as ENTSTER) is brazed to a cathode support 3 made of a high-temperature metal such as molybdenum or tungsten. °
[The cathode substrate is heated to a predetermined temperature by the heater 4, and electrons are emitted from the surface of the cathode substrate.

Conventionally, such impregnated cathodes are made by press-forming tungsten powder and then sintering it at high temperatures in a hydrogen gas atmosphere to obtain the required density. For example, plasti impregnates the required cathode substrate.

After processing into a shape, the copper or plastic is extracted and removed by heating in vacuum or air to form a cathode substrate, and then an emitter is melted and impregnated in vacuum or in a hydrogen atmosphere. The porosity of the porous tungsten is a factor that greatly affects the characteristics of the impregnated cathode.If the porosity is large, it is advantageous for emitter impregnation work, but it may reduce the strength of the cathode structure or <Excessive evaporation of ivy causes deterioration of electron tube characteristics; conversely, if the porosity is small, it becomes difficult to impregnate the emitter, and the small amount of impregnation impedes the characteristic of high current density operation. be done. For this reason, in the conventional method, porous tungsten having the required porosity was obtained by finely adjusting each manufacturing condition from the grain size selection of the raw material tungsten powder to the sintering process.

Obtaining porous tungsten using conventional manufacturing methods has many problems with the raw materials and manufacturing methods, it is difficult to obtain the required porosity, and since it is a sintered body, it is difficult to obtain porous tungsten. There is no guarantee that the thickness and distribution of porosity can be made uniform; in fact, it is normal that the porosity is not uniform. This results in a lack of uniformity in emission, and furthermore, poor convergence of the electron beam, which can even result in a serious defect that impairs the function of the electron tube, for example.

On the other hand, the pores in porous tungsten must be open-bore, that is, the entire pore must communicate with the electron emitting surface, but in the powder sintering method, this depends on conditions such as press pressure and sintering temperature for 2 hours. Due to the occurrence of partial closed pores, the emitter is not impregnated, resulting in a cathode with non-uniform emission, and the effective volume of the cathode substrate is reduced, leading to the risk of losing its long life characteristic.

The present invention eliminates these problems and provides a highly reliable impregnated cathode that has a truly long life and is capable of high current density operation.

That is, a mesh made of fine heat-resistant metal wire such as tungsten is wound into a whole coil shape to form a seaweed-like Togane cathode substrate, and an emitter is impregnated into the gap between the mesh and the overlapped portion obtained by winding. It is characterized by

In the cathode according to the present invention, the number and size of the gaps, which correspond to the pores in the conventional method, can be freely changed by selecting the wire diameter and pitch of the tungsten mesh used as the raw material. It is possible to obtain a material with well-uniformed gap sizes, and the electrical conduction and thermal conduction of the cathode substrate itself are also uniform and adjusted to the designed values, which has a great advantage in terms of stability of isoelectronic emission.

Examples will be described below.

FIG. 2 is a diagram showing the main steps of the method for producing an impregnated cathode according to the present invention. In step A, the tungsten mesh of the intended width is wound to any desired diameter and any number of times to form a laver-wrapped sheet. In step B, the ends of the mesh are fixed by full resistance welding or metal wire, and then fixed by laser or electron beam welding if necessary. At this stage, heating the tungsten seaweed-shaped bundle (hereinafter referred to as mesh bundle) '1 in a hydrogen atmosphere to sinter the adjacent individual wires improves workability in the process. It was very effective. Next, in step C, the mesh bundle is immersed in methyl methacrylate monomer, degassed under reduced pressure, impregnated into the pores of the mesh bundle, and then the methyl methacrylate monomer is polymerized and hardened. In step E, the cathode substrate is cut into the desired cathode shape by a lathe.In step E, the cathode substrate is attached to a cathode support made of molybdenum.In step F, the cathode substrate is heated in air at 400°C for 1 hour. After removing the impregnated methyl methacrylate polymer by thermal decomposition, in step G, heat treatment was performed at 1000° C. for 10 minutes in a hydrogen atmosphere to obtain a clean cathode structure. In step H, the cathode substrate is impregnated with an emitter in a 5-hydrogen atmosphere to form a cathode. Unlike the so-called porous tungsten obtained by sintering, the cathode obtained in this way has homogeneous and regular pores, so impregnation of the emitter can be carried out smoothly and the amount of impregnated emitter can be reduced. The reliability of things also improves.

As explained above, according to the present invention, a mesh made of thin tungsten wires is wound a certain number of times in the shape of a whole seaweed roll to form a mesh bundle, and the emitter is placed in the gap between the overlapped portions obtained by winding the gaps between the thin tungsten wires. This eliminates the problem of non-uniform emission from the cathode surface, which was a major problem with conventional powder sintered cathodes, and makes it possible to obtain cathode gold for electron tubes with a stable and long life. It is.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an impregnated cathode, FIG. 2 is a main process diagram of an embodiment of the method for manufacturing an impregnated cathode of the present invention, and FIG. 3 is a schematic cross-sectional view of an impregnated cathode. FIG. 3 is a perspective view showing the state of winding. 1... Cathode base, 2... Emitter,
3... cathode support, 4... heater,
5...Tungsten mesh, 6...
The winding part. 7- Figure 3

Claims (1)

[Claims] An impregnated cathode characterized in that the cathode substrate is a mesh block made of a mesh made of fine tungsten wire wound into a coil shape, and an electron-emitting substance is impregnated into the gap portion of the overlap IIs created by the mesh and the winding. .