JP3233308B2 - Rotating anode for X-ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant structural material used at a high temperature exceeding 900 DEG C., and more particularly to a rotary anode for an X-ray tube required to generate high-power X-rays.

[0002]

2. Description of the Related Art In recent years, in the field of medical diagnostic imaging, there has been a demand for higher definition of images and shorter inspection time.
Higher output X-ray generation is required in the line CT and the like. For this reason, a conventional fixed anode X-ray tube cannot be used, and a rotating anode X-ray tube has been widely used. In such a high-output rotating anode for X-ray tubes,
There has been proposed a structure in which tungsten or a tungsten-rhenium alloy serving as an X-ray generation layer is coated on a lightweight graphite substrate having a large heat capacity.

In addition, a large amount of heat generated simultaneously with the generation of X-rays causes a carbide generation reaction between the graphite substrate and the X-ray generation layer, and the formation of brittle tungsten carbide. At the same time, it has been proposed that rhenium, which is a high melting point metal, is used as a carbon diffusion barrier (intermediate layer) (Japanese Patent Publication No. 47-8263). However, rhenium is not only expensive, but also has a problem that its properties as a carbon diffusion barrier are insufficient.

[0004] For this reason, as disclosed in JP-A-53-144289, it has been proposed to use osmium, rhodium, lutemium, platinum, palladium, and platinum-chromium alloy as an intermediate layer instead of rhenium.

However, these metals cannot be said to be inexpensive as compared with rhenium, and more inexpensive materials have been proposed. One is Hei 4-1 540 33 JP technology, 2 of TiN / SiC, in place of the intermediate layer of rhenium
We propose a structure in which different types of ceramic films are stacked.
However, Si-based ceramics easily form silicide with other metal elements, which may cause a decrease in adhesion strength.
There was a problem that C decomposed into metal Si and carbon, and the X-ray generation layer peeled off.

[0006]

As described above, when a large amount of high-output X-rays are generated, not only the conventionally used materials cannot suppress the diffusion of carbon, but also
Heat-resistant structural materials such as a rotating anode for an X-ray tube have problems such as being thermally unstable.

[0007]

SUMMARY OF THE INVENTION The present invention provides a heat-resistant structural material which solves the above-mentioned problems, particularly a structural material suitable for a rotating anode for an X-ray tube. in the structure having an X-ray generating layer Te, the intermediate layer is aluminum nitride, the boron titanium, of zirconium boride 1
It is characterized by being either a single-layer structure composed of different types or a laminated structure composed of two or more of rhenium, aluminum nitride, titanium nitride, titanium boride, and zirconium boride.

The present inventors have found that aluminum nitride, titanium nitride, titanium boride, and zirconium boride are preferred as carbon diffusion barriers in the rotating anode for X-ray tubes. The four types of ceramics listed here may be used alone or two or more types may be laminated.
Alternatively, even in combination with conventionally used rhenium, an excellent carbon diffusion preventing effect and an effect of maintaining the interface strength for a long period of time can be exhibited.

In the rotating anode for an X-ray tube, of the irradiation energy of the supplied electron beam, energy consumed for generating X-rays is 1% or less, and most of the energy is converted into heat. As a result, the temperature of the anode may be 2500 to 3000 ° C. on the outermost surface to be irradiated with the electron beam, and may be about 1000 ° C. for the entire anode.

In this regard, all four materials (aluminum nitride, titanium nitride, titanium boride, and zirconium boride) have melting points well over 2000 ° C. as shown in Table 1, and decompose until reaching the melting point. It is a stable material without any problems.

[0011]

[Table 1]

Further, these four types of materials not only hardly cause a carbide generation reaction but also hardly generate a reaction with tungsten or a tungsten-rhenium alloy which is an X-ray generation layer. The rotation speed of the rotating anode for the X-ray tube is 3000 to 100
Since the rotation speed is as high as 00 revolutions / minute, an extremely large peeling force is applied. For this reason, it is a fatal defect that brittle tungsten carbide is easily generated between the substrate and the graphite, and an intermetallic compound is easily generated between the substrate and the X-ray generation layer. The four types of ceramic materials found as a result of intensive studies by the present inventors have been stable alongside rhenium, which is a conventional material, and this was supported by the calculation of free energy for carbide formation.

Further, as shown in Table 2, these four types of materials are characterized in that they have a thermal expansion coefficient close to that of graphite as a base material or tungsten or a tungsten-rhenium alloy as an X-ray generation layer.

[0014]

[Table 2]

In a rotating anode for an X-ray tube, when it is used, it is repeatedly heated and cooled from room temperature to a high temperature exceeding 1000 ° C., so that graphite as a base material having a coefficient of thermal expansion or an X-ray generation layer is used. Must be close to that of tungsten or a tungsten-rhenium alloy. It is most preferable to have the same coefficient of thermal expansion, but if there is a slight difference, it is possible to reduce the thermal stress acting on the interface between the respective materials by lamination with metal rhenium.

As described above, in a rotating anode structure for an X-ray tube that generates X-rays on a graphite substrate via an intermediate layer,
A single-layer structure in which the intermediate layer is made of one of aluminum nitride, titanium nitride, titanium boride, and zirconium boride;
Alternatively, by using any one of a laminated structure including two or more of rhenium, aluminum nitride, titanium nitride, titanium boride, and zirconium boride, a long life without peeling even when high-power X-rays are generated Can be obtained inexpensively.

The laminated structure of these four types of ceramics or rhenium is formed by a vapor phase synthesis method such as a CVD method such as a thermal CVD method or a plasma CVD method, or a PVD method such as an ion plating method .

Hereinafter, a method of forming these four ceramic materials, rhenium, tungsten and a tungsten-rhenium alloy will be described by taking a CVD method as an example.

The following reaction can be used as a method for forming aluminum nitride. AlCl ₃ + NH ₃ → AlN + 3HCl It is preferable to use H ₂ in addition to AlCl ₃ and NH ₃ as a source gas. H ₂ acts not only as a carrier gas but also as a chloride reducing agent. In order to carry out the reaction efficiently, the molar ratio of the source gas is NH ₃ / AlCl ₃ =
1 to 5, H ₂ / AlCl ₃ = 2 to 10 are preferred.
The reaction temperature is preferably from 1000 to 1300 ° C.

The following reaction can be used as a method for forming titanium nitride. _{TiCl 4 + N 2/2 +} 2H 2 → TiN +
_{4HCl TiCl 4 + NH 3 + H} 2/2 → TiN +
4HCl In order to carry out the reaction efficiently, the molar ratio of the source gas is N ₂ /
TiCl ₄ = 0.5 to 5, NH ₃ / TiCl ₄ = 1 to 1
5, H ₂ / TiCl ₄ = 2 to 8 is preferred. The reaction temperature is preferably from 650 to 1700 ° C.,
00 ° C is more preferred.

The following reaction can be used as a method for forming titanium boride. TiCl ₄ + 2BCl ₃ + 5H ₂ → TiB ₂
+ 10 HCl In order to carry out the reaction efficiently, the molar ratio of the source gas is BCl
_{3 / TiCl 4 = 2~8, H} 2 / TiCl 4 = 5~10
Is preferred. Further, the reaction temperature is preferably from 1000 to 1200 ° C.

As a method for forming zirconium boride, the following reaction can be used. ZrCl ₄ + 2BCl ₃ + 5H ₂ → ZrB ₂
+ 10 HCl In order to carry out the reaction efficiently, the molar ratio of the source gas is BCl
₃ / ZrCl ₄ = 2-8, H ₂ / ZrCl ₄ = 5-10
Is preferred. Further, the reaction temperature is preferably from 1000 to 1200 ° C.

The following reaction can be used for forming the rhenium film. ReF ₆ + 3H ₂ → Re + 6HF In order to efficiently form rhenium, the molar ratio of the source gas is preferably H ₂ / ReF ₆ = 4 to 10. The reaction temperature is preferably from 400 to 1000C. Further, as a method for forming rhenium, a hydrogen reduction method or a thermal decomposition method of rhenium chloride can be used.

The following reaction can be used to form tungsten and a tungsten-rhenium alloy which are the outermost surface of the rotating anode for an X-ray tube. WF ₆ + 3H ₂ → W + 6HF ReF ₆ + 3H ₂ → Re + 6HF In order to efficiently form tungsten, the molar ratio of the source gas is preferably H ₂ / WF ₆ = 4 to 10. The reaction temperature is preferably from 400 to 1000C. When forming a tungsten-rhenium alloy, the WF ₆ / ReF ₆ molar ratio is adjusted so as to obtain a desired alloy composition ratio, and the ReF ₆
The gas flow ratio may be determined. As a method for forming tungsten and a tungsten-rhenium alloy, a hydrogen reduction method or a thermal decomposition method of tungsten and rhenium chlorides can also be used.

The content of rhenium in the tungsten-rhenium alloy is preferably in the range of 1 to 10 atomic%. This is because if less than 1%, the effect of adding rhenium to suppress ductility reduction and the effect of increasing the recrystallization temperature cannot be obtained, and if more than 10% of rhenium has no further effect on the above purpose, This is because it becomes an obstacle to heat conduction.

[0026]

【Example】

(Example 1) The thermal expansion coefficient was 5.5 × 1 by using the CVD method.
0 ^-6 (1 / K) on the graphite substrate to form an aluminum nitride and tungsten -3% rhenium alloy, tungsten -3% rhenium alloy is structure according to the present invention (500 microns
m) / aluminum nitride (25 μm) / graphite.

This sample was heat-treated at 2200 ° C. in a vacuum atmosphere for 0.5 hours or 2 hours, and the diffusion behavior of carbon was investigated. The carbon diffusion distance into the tungsten-3% rhenium alloy was investigated by polishing the cross section of the sample after the heat treatment and measuring the hardness distribution in the depth direction of the sample using a micro Vickers hardness meter. The measurement conditions of the micro Vickers hardness were a load of 50 g and a load time of 10 seconds.

FIG. 1 shows the results of an examination of the cross-sectional hardness distribution after the heat treatment. The hardness of the sample subjected to the heat treatment for 2 hours changed greatly. The micro-Vickers hardness of metal tungsten and tungsten-3% rhenium alloy in which carbon is not diffused is 400 to 500, and the hardness of tungsten carbide is 1000 or more, so that carbon diffuses to a position where the hardness is greatly reduced. Can be determined to be From this result, no diffusion of carbon was observed in the sample heat-treated for 0.5 hour, and carbon diffused to a position of 120 μm in the sample heat-treated for 2 hours.

Reference Example 2 The thermal expansion coefficient was 6.5 × 10 ⁻⁶ (1 /
The titanium nitride and tungsten is formed on a graphite substrate K), data tungsten (500 [mu] m) / titanium nitride (25.mu.
m) / A sample made of graphite was prepared. This sample was heat-treated in the same manner as in Example 1, and the diffusion behavior of carbon was investigated.
As a result, carbon was 150 μm in the sample heat-treated for 0.5 hour, and 32 μm in the sample heat-treated for 2 hours.
It was diffused to a distance of 0 μm.

Reference Example 3 A coefficient of thermal expansion of 6.5 × 1 was obtained by using an ion plating method.
0 ^-6 titanium nitride is formed on a graphite substrate (1 / K),
Furthermore tungsten -7% rhenium alloy formed by a thermal CVD method, data tungsten -7% rhenium alloy (50
0 μm) / titanium nitride (21 μm) / graphite. This sample was heat-treated in the same manner as in Example 1, and the carbon diffusion behavior was investigated. The result is 0.5 carbon
The sample heat-treated for 140 hours spread to a distance of 310 μm in the sample heat-treated for 2 hours.

(Example 4) Titanium boride and a tungsten-5% rhenium alloy were formed on a graphite substrate having a coefficient of thermal expansion of 5.5 × 10 ^-6 (1 / K) by the CVD method. Tungsten-5% rhenium alloy (50
0 μm) / titanium boride (23 μm) / graphite. This sample was heat-treated in the same manner as in Example 1, and the diffusion behavior of carbon was investigated. The result is carbon
The sample heat-treated for 0.5 hours diffused to a distance of 60 μm, and the sample heat-treated for 2 hours diffused to a distance of 180 μm.

Example 5 Zirconium boride and tungsten are formed on a graphite substrate having a coefficient of thermal expansion of 5.5 × 10 ⁻⁶ (1 / K) by using a CVD method. (500 μm) / zirconium boride (2
1 μm) / a sample made of graphite was prepared. This sample was heat-treated in the same manner as in Example 1, and the diffusion behavior of carbon was investigated. As a result, carbon was 50 μm in the sample heat-treated for 0.5 hour, and 1 μm in the sample heat-treated for 2 hours.
It diffused to a distance of 70 μm.

(Example 6) Titanium nitride was deposited on a graphite substrate having a coefficient of thermal expansion of 6.5 × 10 ^-6 (1 / K) by CVD.
Rhenium and tungsten-3% rhenium alloy were formed, and a sample composed of tungsten-3% rhenium alloy (500 μm) / rhenium (22 μm) / titanium nitride (19 μm) / graphite having a structure according to the present invention was prepared. This sample was heat-treated in the same manner as in Example 1, and the diffusion behavior of carbon was investigated. As a result, carbon was diffused to a distance of 70 μm in the sample heat-treated for 0.5 hours and to 200 μm in the sample heat-treated for 2 hours.

(Comparative Example 1) Rhenium and tungsten are formed on a graphite base material having a thermal expansion coefficient of 5.5 × 10 ⁻⁶ (1 / K) by CVD, and tungsten (500 μm) having a conventional structure is formed. / Rhenium (25 μm) / graphite. This sample was heat-treated in the same manner as in Example 1, and the diffusion behavior of carbon was investigated. As a result, the carbon was 330 μm in the sample heat-treated for 0.5 hour,
The sample heat-treated for 2 hours diffused to a distance of 450 μm.

(Comparative Example 2) Silicon carbide and a tungsten-6% rhenium alloy were formed on a graphite substrate having a coefficient of thermal expansion of 5.5 × 10 ⁻⁶ (1 / K) by using a CVD method, and a conventional structure was used. Tungsten-6% rhenium alloy (500 μm)
/ Silicon carbide (21 μm) / graphite. This sample was heat-treated in the same manner as in Example 1, and the diffusion behavior of carbon was investigated. As a result, carbon was peeled off at the silicon carbide portion as the intermediate layer in both the samples heat-treated for 0.5 hours and 2 hours, and the diffusion distance of carbon could not be measured.

FIG. 2 shows the results of carbon diffusion by heat treatment of the sample on which the ceramic and rhenium intermediate layers were formed.
Shown in It can be seen from each of the samples that the carbon diffused deeper with the elapse of the heat treatment time. However, it was confirmed that the carbon diffusion distance was shorter in each example than in Comparative Example 1. Also, it was confirmed that the silicon carbide intermediate layer shown in Comparative Example 2 had a problem of being thermally unstable.

The heat treatment performed in the above embodiment was performed at 2200 ° C., which is far higher than the actual use temperature. However, this test is not only an accelerated test, but is performed at a temperature exceeding 2000 ° C. in actual use. It also has the meaning of evaluating the stability of the material when it is performed. In this sense, since the product of the present invention is thermally stable and has a large carbon diffusion suppressing effect, it has been confirmed that the product is excellent as a rotating anode for a high-output X-ray tube.

In each of the above examples, the thickness of the intermediate layer and the X-ray generation layer and the coefficient of thermal expansion of the graphite substrate were made as uniform as possible in order to suppress variations in the experimental data. Therefore, when the structure according to the present invention is applied to an actual rotating anode for an X-ray tube, taking into consideration the highest ultimate temperature during use, the intermediate layer is not limited to the film thickness and the coefficient of thermal expansion described in the above embodiment. Needless to say, the thickness of the X-ray generation layer and the coefficient of thermal expansion of the substrate can be appropriately selected.

[0039]

As described above. The rotating anode for an X-ray tube according to the present invention can suppress the carbide formation reaction between tungsten and graphite, and can generate high-output X-rays for a long period of time. Therefore, a high-output X-ray source can be manufactured, which is extremely useful not only for medical use but also for improving the analysis accuracy of industrial X-ray analyzers and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of measuring the cross-sectional hardness distribution of a structural sample of the present invention having a structure of tungsten-3% rhenium alloy / aluminum nitride intermediate layer / graphite substrate after heat treatment at 2200 ° C.

FIG. 2 is a graph showing a carbon diffusion preventing effect of a sample having various intermediate layers.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-154403 (JP, A) JP-A-2-186543 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 35/10

Claims (7)

(57) [Claims] 1. A laminated structure of the carbon-based material and a metal or ceramic, an intermediate layer for preventing diffusion of carbon from the carbon-based material to a metal or ceramic, aluminum nitride (AlN), boric titanium (TiB ₂ ) A heat-resistant structural material having a single-layer structure of one of zirconium boride (ZrB ₂ ) and formed by a vapor phase synthesis method. 2. A laminated structure of a carbon-based material and a metal or a ceramic, wherein the intermediate layer for preventing diffusion of carbon from the carbon-based material to the metal or the ceramic comprises rhenium (Re), aluminum nitride (AlN), A laminated structure composed of two or more kinds of titanium nitride (TiN), titanium boride (TiB ₂ ), and zirconium boride (ZrB ₂ )
And a heat-resistant structural material formed by a gas phase synthesis method. 3. A X-ray tube rotary anode having an X-ray generating layer via an intermediate layer on the graphite substrate, the intermediate layer is aluminum nitride (AlN), boric titanium (TiB _2), zirconium boride ( A rotating anode for an X-ray tube, characterized by having a single layer structure of one of ZrB ₂ ) and being formed by a vapor phase synthesis method. 4. An X-ray tube rotary anode having an X-ray generating layer on a graphite substrate with an intermediate layer interposed therebetween, wherein the intermediate layer is composed of rhenium (Re), aluminum nitride (AlN), titanium nitride (TiN), boron nitride. A laminated structure comprising two or more of titanium boride (TiB ₂ ) and zirconium boride (ZrB ₂ ),
A rotating anode for an X-ray tube, which is formed by a gas phase synthesis method. 5. The rotating anode for an X-ray tube according to claim 3, wherein the X-ray generating layer is made of tungsten. 6. The rotating anode for an X-ray tube according to claim 3, wherein the X-ray generating layer is made of a tungsten-rhenium alloy. 7. The rotary anode for an X-ray tube according to claim 6, wherein the content of rhenium in the tungsten-rhenium alloy is 1 to 10 atomic%.