JPS597182B2 - Rotating anode for X-ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating anode for an X-ray tube, and more particularly to a rotating anode for an X-ray tube having a rhenium layer effective in preventing diffusion of carbon from a graphite substrate to a target plate.

Rotating anodes for X-ray tubes, which have a large heat capacity and provide a large X-ray output, are widely used in the medical field.

Conventionally, the rotating anode has been made of a metal such as tungsten or a tungsten alloy, which can withstand the thermal shock of the irradiated electron beam and has a high density, high melting point, and high atomic number, and is efficient in generating X-rays.

Alternatively, there is also a composite plate in which a relatively thick molybdenum plate is integrally bonded to the back surface of a tungsten plate as a heat absorber.

However, with the recent advances in X-ray technology, there is a strong demand for a rotating anode with a larger heat capacity that can withstand continuous load or instantaneous high load input.

Recently, in response to this demand, a rotating anode has been developed that has a structure in which a graphite material with low specific gravity and excellent heat radiation ability is used as a base material, and a tungsten plate or a composite plate of tungsten and molybdenum is integrally bonded to this base as a target plate. has been done.

However, in this rotating anode, the target plate is approximately 2
Heat is generated to 500 to 2,600°C, and therefore the joint between the target plate and the graphite base also becomes high temperature. When the temperature of the joint reaches 1,300°C or higher, carbon in the graphite base diffuses into the upper target plate. , a carbide layer, such as tungsten carbide, is formed at the junction.

The carbide layer is mechanically fragile and may be damaged by external forces such as vibrations during high speed rotation of the rotating anode.

As a result, inconvenient situations such as partial separation of the joint between the target plate and the graphite substrate, uneven heat conduction, and local abnormal heat generation are often caused.

For this reason, conventionally, between the graphite substrate and the target plate, a rhenium layer, which does not form carbide with carbon and prevents carbon from diffusing into the target plate, is used, for example, in a slurry consisting of rhenium metal powder and water or an organic binder. Rhenium is formed by coating the surface of a graphite substrate or by depositing rhenium on the surface of a graphite substrate by a CVD method.

Although the rhenium layer formed by the above method has certain effects, it does not have a dense structure, so it may not be able to sufficiently prevent the diffusion of carbon from the graphite substrate to the target plate.

The inventors of the present invention have conducted extensive research in order to resolve these difficulties, and have found that carbon diffusion is sufficient when using dense rhenium foil processed as a rhenium layer, especially rhenium foil with a processing rate of 85% or more. The present invention was completed based on the knowledge that this can be prevented.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved rotating anode for an X-ray tube that is less likely to form a carbide layer on a target plate.

That is, the rotating anode of the present invention is a rotating anode for an X-ray tube having an integral structure in which a rhenium layer is interposed between a graphite base and a target plate, and the rhenium layer is formed by processing a powder sintered body, especially one with a processing rate of 85% or more. It is characterized by being made of rhenium foil.

The rotating anode of the present invention uses a rhenium foil having a dense structure with a processing rate of 85 factors or higher.

The processing rate here means that when forming a rhenium metal foil by hot working (forging and rolling) a rhenium sintered body, which will be described later, the thickness of the sintered body is t1 and the thickness of the rhenium foil is t'. , t-t'/tX1 00.

This processing rate indicates the degree of flat structure of rhenium crystal grains and the degree of densification of the structure.

As the processing rate increases, the structure of the rhenium foil becomes denser, and the grain boundaries intertwine in a complicated manner, so it acts as a good barrier against the diffusion of carbon in the thickness direction, for example. It is thought that this will happen.

In the present invention, if the processing rate of the rhenium foil is less than 85 inches, it is difficult to sufficiently prevent carbon diffusion.

Further, although there is no particular upper limit to the processing rate, the thickness of rhenium foil that can actually be manufactured remains at about 5 μm.

Note that electrolytic polishing or the like can also be used to adjust the thickness of the rhenium foil.

Although it is not clear why the processing rate of the rhenium foil affects the state of carbide formation, it is thought that the density of the structure and the state of the crystal grains have an effect.

The thickness of the rhenium foil used may be selected in relation to the processing rate of the rhenium foil, but is preferably 5 to 400 μm.

Rhenium foils with a thickness of less than 5 μm are difficult to manufacture and are less effective in preventing the formation of a carbide layer;
If it exceeds 0 μm, rapid heat conduction from the target surface to the graphite substrate will be hindered.

Considering the effect of the presence of the rhenium layer and the relationship with ease of manufacture, it is more preferable that the thickness is 10 to 200 μm.

Such rhenium foil is produced, for example, as follows.

First, rhenium powder with a particle size of 1 to 3 μm is filled into a predetermined mold at room temperature. 5 tons/cwi
After compression preforming with
A molded body is formed by isostatic compression molding at i.

Then, this molded body is heated to, for example, 10-5 to 1o-6 Torr.
A sintered body is obtained by baking and solidifying in a vacuum furnace at a temperature of 2,300 to 2,400°C.

Furthermore, this sintered body is hot forged at a temperature of 1600 to 1800°C to form a rhenium foil.

Usually about 2 mm of rhenium foil is obtained at this stage.

Next, this rhenium foil is hot rolled at a temperature of 1,600 to 1,800° C. to a thickness of about 1 wn, and finally cold rolled to obtain a rhenium foil of the thickness used.

At this time, for rhenium foil with a processing rate of 85% or more,
A specific gravity of 20 or more can be obtained at the final stage.

In the rotating anode of the present invention, the target plate is either a tungsten plate or a composite plate formed by hot-pressing a molybdenum plate of a predetermined thickness on the back surface of a tungsten plate, but the carbide layer at the joint surface with the graphite substrate is A composite board with a molybdenum board, which is a heat absorber, is preferable in order to prevent the formation of.

The rotating anode of the present invention will be explained below based on examples.

Example 1) Preparation of Target Plate A tungsten plate with a diameter of 130 mm and a thickness of 2.5 mm and a molybdenum plate with a diameter of 130 mm and a thickness of 15 rrrm were prepared by a conventional method.

The tungsten plate was placed on the molybdenum plate and hot-pressed at 1600'C and 250@/crA in a hydrogen atmosphere.

After the tungsten plate and molybdenum plate are integrally joined,
A composite target plate was obtained by smoothing the lower surface of the molybdenum plate.

2) Preparation of rhenium foil Based on the above manufacturing method, length: 100 mm, width: 50 w, thickness: 2 m
Four sintered bodies of m were produced.

Each of these was hot forged at a temperature of 1700 to 1900°C, further hot rolled at 1700°C, and then cold rolled to obtain a working ratio of 75 (thickness 0.5 rrrm) and 80φ (
Thickness 0. 4 rran), 85% (thickness 0.3
trrm ), 90% (thickness 0.2 mm), 95
(thickness 0.1 rran) and 9 7. 5%
Six types of rhenium foils (thickness: 0.058 mm) were prepared.

3) Preparation of rotating anode The target plate obtained in 1) and 2) above and the rhenium foil were stacked together and heated to 250 kq in a hydrogen atmosphere at 1600°C.
A pressure of /crrf was applied and this state was maintained for about 1 hour.

Finally, the above-mentioned target plate/rhenium foil composite was layered on a graphite substrate with a diameter of 130rrrm and a thickness of 30rrrrrn, and the whole was heated at 1400°C under a nitrogen (inert) atmosphere with boron nitride powder as a compression medium. A pressure of about 200@/crA was applied from above and below, and this state was maintained for about 1 hour.

As a result, it was confirmed that the entire structure was integrally joined.

For comparison, particles with an average particle size of 1 to 3 μm were placed on a graphite substrate.
20L of m rhenium powder? (10ml) and 0.2S' organic binder to a thickness of approximately 500μm.
After applying the binder uniformly to the binder and removing it by heating, a rotating anode was fabricated by similarly bonding a composite target plate thereon.

Each rotating anode thus obtained was heated to 10" Torr.
The sample was left in a vacuum furnace at a temperature of about 1400° C. for 10 hours.

After cooling, the rotating anodes were taken out and each was cut vertically to expose the bonding surface.

The cut surface was observed under a microscope, and the thickness of the carbide layer formed on the molybdenum plate was measured.

The results are shown in Figure 1 as a relationship between processing rate and carbide layer thickness.

In addition, in the comparison target plate, the thickness of the carbide layer was formed unevenly and thickly.

Furthermore, we prepared rhenium foils with a constant thickness of 200 μm and different processing rates of 80%, 85%, 90%, and 95%, and used these to manufacture rotating anodes under the same conditions. After processing in the same manner as above, the thickness of the produced carbide layer was examined.

The results are shown in FIG. 2 as a relationship between the processing rate and the thickness of the formed carbide layer.

As is clear from FIG. 2, the formation of the carbide layer was found to be highly dependent on the processing rate of the rhenium foil.

[Brief explanation of drawings]

Figure 1 shows the relationship curve between the processing rate of rhenium foil and the thickness of the carbide layer formed on the target plate, and Figure 2 shows the relationship between the processing rate of rhenium foil with a thickness of 200 μm and the thickness of the carbide layer formed on the target plate. represents the relationship curve.

Claims (1)

[Claims] 1. A rotary anode for an X-ray tube having an integral structure in which a rhenium layer is interposed between a graphite base and a target plate, characterized in that the rhenium layer is made of rhenium foil obtained by do-ing the powder sintered body. A rotating anode for X-ray tubes. 2. The rotating anode for an X-ray tube according to claim 1, wherein the rhenium layer is a rhenium foil with a processing rate of 85 inches or more. 3. The rotating anode for an X-ray tube according to claim 1 or 2, wherein the rhenium foil has a thickness of 5 to 400 μm. 4. The rotating X-ray tube according to any one of claims 1 to 3, wherein the target plate is either a tungsten plate or a composite plate formed by integrally bonding a tungsten plate and a molybdenum plate. anode.