JPS5834539A - Impregnation-type cathode - Google Patents

Abstract

PURPOSE:To obtain a long life impregnated-type cathode secular-change of whose electron emission characteristic is small, by a using a tungsten layer of large porosity rate as the lower layer and by using tungsten layer of small porosity rate as the surface layer of the captioned cathode. CONSTITUTION:The figure shows as impregnated-type cathode 10 designed by the present invention, a holding cylinder 3 made of molybdenum, and a cathode structure 11 of a heater 4 buried in sintered alumina 5. The captioned cathode 10 is a laminated structure consisting of two layers, that is, the surface layer 1 with the porosity rate of 20% and the lower layer 2 with the porosity rate of 40%. In the captioned cathode 10, the evaporation amount of Ba can be suppressed and the necessary amount of Ba can be supplied by reducing the porosity rate of the surface layer 1, so that the consumption-time of Ba can be prolonged. On the other hand, by enlarging the porosity rate of the lower layer 2, the supply amount of Ba from the inside of the vacant-hole to the surface layer can be increased, the depreciation of Ba-covering degree necessary for electron emission can be suppressed, and the secular-change of current can be minimized.

Description

[Detailed description of the invention] This invention relates to the construction of long-life impregnated ffi@poles.

A general impregnated cathode is made of a porous tungsten pellet having a porosity of 15 to 45 cm and an electron emitting material such as 5B&0 2A40.・Produced by melting and impregnating 3CaO.

This cathode is activated by heating at 1200° C. for several hours in a vacuum. At this time, free B1 is generated by the following reaction.

SB ao ・2A40s ・3CaO+3/4W=
3/4Ca*BaWO5+3/4CatBaA40s+
5/48 mA404 +9/4 B *This free B
a passes through the pores of porous tungsten and adsorbs to the tungsten surface, forming a monoatomic layer, resulting in a decrease in work function.1 The speed of Ba reaching the surface is related to the effective radius and length of the pores. do.

On the other hand, adsorption B a (Ba + B10
) evaporates depending on the cathode temperature, but Ba is always supplied from inside the tungsten. However, the impregnating material (Ba compound) is consumed with the operating time, and it takes time for the tungsten to diffuse 8m from the inside of the hole to the surface, resulting in B
1 Adsorption If (also referred to as coverage) decreases and the work function increases. Therefore, the life of this cathode is determined by the balance between the 8 m supply from the inside of the hole and the evaporation from the surface.

Figure 1 shows the electron emission characteristics when the porosity of tungsten can be varied from 14.7% to 29%. Although the initial data shows that the larger porosity - bX changes over time, this is because, as mentioned above, a sufficient amount of Ba is supplied from inside the pores to maintain the surface coverage necessary for electron emission. It is. If the porosity is small, Ba is procured on the surface.
Due to the small amount of surface 1[1[[, the current decreases rapidly.

On the other hand, if we consider long-term operation, that is, the lifespan of the electron tube, the opposite result may be obtained.

If the porosity is urgent, the amount of Ba (Ba+Ba0) diffused to the surface is large and the impregnation material 1 inside the porous tungsten is used.
*The time to remove %A is faster. FIG. 2 shows the influence of porosity in the case of long-term operation. Here, M indicates the characteristics of a cathode with a porosity of 20%, and B indicates the characteristics of a cathode with a porosity of 40. Assuming that the time when the current value drops to 50% of the initial value is 46, it can be said that the cathode man has a lifespan several times longer than the cathode B. On the other hand, the lifespan is set to the initial value of 9.
5- and the results are completely opposite; the Cm cathode has a longer life.

As mentioned above, the porosity of porous tungsten has a very large effect on the electron emission characteristics, especially the aging characteristics.

A conventional impregnated cathode uses a tungsten pellet having a certain porosity in accordance with the required characteristics of the electron tube used.

Therefore, from the initial stage, the change in current over time is small (11tI cathode BK@sho) and has a long life (said cathode BK), and Ba is quickly supplied from the cathode, that is, from inside the pores.

At the same time, obtaining a cathode with a low amount of OBm evaporation from the surface is essential compared to a conventional cathode made from a fixed porosity. It was 51 difficulties.

It is an object of the present invention to provide a long-life impregnated cathode.

The present invention is characterized in that the cathode is formed by stacking at least two or more tungsten pellets having different porosity.

An example of the impregnated cathode according to OR#4 is characterized in that it is used in the lower layer of the tungsten layer tube with a high porosity and in the surface layer of the tungsten layer tube with a small porosity.

According to this invention, in order to speed up the supply of B& from the inside of the pores to the surface, a tungsten layer with a high porosity is used as the lower layer, and in order to suppress the amount of Ba evaporating excessively from the surface, the porosity is reduced. By using a small tungsten layer as the t-m electrode surface layer, an impregnated cathode with a long life and little change in electron emission characteristics over time can be obtained.

An embodiment of the present invention will be described below with reference to the drawings. 11
3WJ shows the cathode structure 11 of the impregnated cathode IO according to the present invention, the support cylinder 3 made of molybdenum, and the HE I4 embedded in the Alina sintered body 5. Impregnated yin @lO
It has a structure in which two layers are laminated: a surface layer 1 having a porosity of 20 cm and a lower layer 2 having a porosity of 40 cm, and is produced by the following process.

First, tungsten powder having a particle size of about 4 square meters is pressed and sintered at 2200°C to produce a porous tungsten ingot with a porosity of 20ts. Then, it is impregnated with, for example, oxygen-free copper to improve machinability and processed into predetermined dimensions.

Steel is completely removed by vacuum treatment at 1800°C. This creates the surface layer l. Porosity 4011
The lower layer 24 is formed in the same manner as the surface layer l.

In this case, it is preferable that the first surface layer 1 be equal to or thinner than the lower layer 2.

Next, the lower layer 2 and the surface layer 1 are placed in a stacked manner in a molybdenum cylinder 3, and the side surfaces are joined by brazing or welding. After that, a heater 4 made by pre-winding a thin Mengesten wire into a coil shape was installed in a molybdenum cylinder 3 together with a mixture of aluona powder and an organic binder, and the mixture was heated to about -1700°C. Sinter things. Next, an impregnating machine containing barium oxide, calcium oxide, and aluminum oxide in a molar ratio of 5:3:20 was used to coat the surface layer.

Place it on top and melt and impregnate it at about 1600°C.

In this manner, the cathode assembly 11 is completed.

In this manufacturing process, the impregnated cathode 1o is formed from two layers, a surface layer 1 and a lower layer 2.

There is no difference from the conventional manufacturing method.

In the impregnated m cathode 1° of the present invention made in this way, I
By reducing the porosity of II plane layer 1, BiJi
Since only the required amount of B& can be supplied while keeping the liJit low, the total consumption time of Ba can be lengthened. -From inside the pores by increasing the porosity of the inferior layer 2! !
Increase the amount of B&supply on both sides.

It has the great advantage of suppressing the downcomer tube required for electron emission and reducing the change in current over time.

Electron emission 4 when there is an impregnated cathode with all phases according to the Yaki example
It is shown as cathode C in the 11th tjK2 diagram. Compared to a cathode with constant porosity, its aging characteristics are smaller.

In the #M example, the case of two layers was explained, but the cathode may be composed of three or more layers having different porosity, and various choices can be made depending on the characteristics of the electron tube. Further, contrary to the previous embodiment, a layer with large pores is provided on the electron emitting surface in order to improve the electron emission characteristics.

A layer with a low porosity may be used as the base layer, and it is possible to combine 8i.

[Brief explanation of the drawing]

Figure 1 shows the initial electron emission characteristics of impregnated m cathodes fabricated with different porosity, l! Figure 2 shows the life characteristics of a cathode with a porosity of 201 g and 40 -, and Figure 3 is a sectional view of an impregnated m cathode in an embodiment of the present invention. 1...Surface layer (electron emitting surface) %2...Lower layer (significant voids), 3...Molybdenum support cylinder, 4...Heater, 5...Arunna sintered body%10...・Impregnated cathode%
11... Cathode structure. Musi first U300 /1l

Claims (1)

[Claims] (1)? ! Porous tungsten with different porosity - constituted by laminating at least two or more layers and used as an electron emission source
Features an impregnated cathode. 141. The impregnated cathode according to claim 0, wherein the laminated structure is such that the layer with larger pores is formed as a lower layer and the layer with smaller porosity is formed as an electron emitting surface. -) The impregnated cathode according to claim α), characterized in that, in the laminated structure, the layer with smaller porosity is formed as a lower layer, and the layer with larger porosity is formed as an electron emitting surface.