JPS6337929B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron tube cathode formed from thoriated tungsten wire.

Generally, the cathode of an electron tube such as a magnetron is
A thorium tungsten wire formed in a spiral shape is used, and the surface of this thorium tungsten wire is coated with, for example, Japanese Patent Publication No. 52-1983 in order to stabilize the so-called emission and increase the lifespan.
As described in Japanese Patent No. 44196, a carbonized layer is formed.

This carbonized layer is formed, for example, by forming a thorium tungsten wire into a spiral shape and then heat-treating the wire in a hydrocarbon atmosphere. Conventionally, before performing such a carbonization treatment, in order to remove the residual strain generated inside the tungsten wire during the forming of the tungsten wire,
For example, tungsten wires are heat treated in a non-oxidizing atmosphere consisting of hydrogen gas.
That is, this heat treatment is performed, for example, by heating the thorium tungsten wire to 2000° C. to 2200° C. and holding it for about 20 seconds, thereby secondary crystallizing the thorium tungsten.

In this way, after forming the above-mentioned carbide layer along the outer circumference of the thorium tungsten wire, the carbide layer will not fall off even if heat cycles or vibrations are applied to the thorium tungsten wire, thereby increasing the durability of the thorium tungsten wire. can improve sexual performance.

However, even in the electron tube cathode manufactured in this manner, its durability is not fully satisfactory. Therefore, the inventors of the present invention have conducted extensive research to improve the durability of such electron tube cathodes, and have discovered the following.

That is, the number of crystals in the cross section of the tungsten wire forming the electron tube cathode manufactured as described above is usually 700 or more per square millimeter, but this number is reduced to 500 per square millimeter. It has been found that when the number of particles is less than 1, the durability is greatly improved.

The figure shows the improvement in durability time when the durability time of the conventional product is set to 1. The range of arrows in the figure shows the variation in durability time depending on the number of crystals, and the curve shows each variation. It is the average of . As is clear from this figure, the number of crystals per square millimeter is
When the number of crystals is 500 or less, the variation in durability time becomes smaller and the durability time clearly begins to increase.When the number of crystals is 200, the durability time is almost double compared to the conventional one, even when looking at the range of variation. .

The present invention has been made based on this knowledge, and consists of a thorium tungsten wire with a carbide layer formed on the outer periphery, and the number of crystals in the cross section of the thorium tungsten wire is 500 or less per square millimeter. The present invention aims to provide an electron tube cathode characterized by the following.

The details of the present invention will be explained below.

The electron tube cathode of the present invention is made of a thorium tungsten wire with a carbonized layer formed along its outer periphery.
The number of crystals in the cross section is 500 or less per square millimeter.

Such an electron tube cathode of the present invention is manufactured, for example, as follows.

That is, first, a thorium tungsten wire is wound into a coil at a predetermined pitch. Then, a current is applied to the thorium tungsten wire, and the thorium tungsten wire is heated to, for example, 2000° C. to 2200° C. in a hydrogen atmosphere and held for about 20 seconds, causing secondary recrystallization in the thorium tungsten wire. At this time, if the heating rate and cooling rate are slowed down, the number of crystals during recrystallization increases accordingly. Therefore, conditions such that the number of crystals is 500 or less per square millimeter in the cross section of the thorium tungsten wire can be appropriately set depending on the shape of the thorium tungsten wire.

For example, in the case of a cathode with a wire diameter of 0.6 mm and a coil diameter of 6 mm, after performing the above heat treatment, it is held at a high temperature of 2000°C for 20 seconds in a hydrocarbon atmosphere to form a carbonized layer, and then this is further heated in a hydrogen gas atmosphere, for example. A preferable product can be obtained by heat-treating the tungsten wire at a high temperature of 2000°C for 20 seconds in a non-oxidizing atmosphere such as .

In an electron tube cathode manufactured under such heat treatment conditions, the number of crystals in the cross section of the thorium tungsten wire is approximately 250 per square millimeter, and its durability is longer than that of a conventional electron tube cathode, as shown in the figure. This has improved significantly.

As described above, according to the electron tube cathode of the present invention, the durability time can be greatly improved compared to the conventional electron tube cathode.

[Brief explanation of the drawing]

The drawing is a graph showing the relationship between the number of crystals in the cross section of a thorium tungsten wire and its durability time.

Claims (1)

[Claims] 1. An electron tube cathode comprising a thorium tungsten wire with a carbonized layer formed on the outer periphery, and characterized in that the number of crystals in a cross section of the thorium tungsten wire is 500 or less per square millimeter.