JPS603726B2 - Compound composite superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compound composite superconductor, particularly a compound composite superconductor in which an A3B type compound superconductor is formed in a matrix made of an alloy containing a compound-forming element B.

Compound superconductors have excellent properties such as high critical temperature, high critical magnetic field, and high critical current density, but they also have the fragility characteristic of intermetallic compounds.

In recent years, a core material made of a compound-forming element A or an alloy containing A and a matrix made of an alloy containing a compound-forming element B of these A3B type compounds, which become compound superconductors, have been processed into a composite material, which has been heat-treated. A so-called composite processing, selective diffusion method, has been developed in which an A3B type compound superconducting layer is formed at the interface between the two by selective diffusion. This method has made it possible to produce compound composite superconductors with good electromagnetic stability, but the problems caused by the round arms of intermetallic compounds remain unresolved. As the demand for superconductors becomes stronger, the stress applied to compound composite superconductors is becoming increasingly severe. These stresses include thermal stress during the cooling process from the compound formation temperature, tensile stress during the coil winding process, stress due to bending, and electromagnetic stress during the coil excitation process.These stresses cause strain in the compound superconducting layer. When the strain increases, the critical temperature, critical magnetic field, and critical current density of the compound composite superconductor are significantly reduced, making it difficult to generate a high magnetic field. In order to eliminate these drawbacks, a few compound composite superconductors with reinforcing materials have been proposed.

A compound composite superconductor having this type of reinforcing material and using niobium 3-tin as the compound is shown in FIGS. 1 and 2.

The compound composite superconductor shown in FIG. 1 consists of six bronze matrix niobium 3-tin composite superconductors 20 each having a circular cross section arranged around a reinforcing material 1 made of stainless steel wire, tungsten wire, etc. and having a circular cross section. is filled with a low melting point metal 3 such as indium to form an integrated structure. The compound composite superconductor shown in Figure 2 is a bronze matrix niobium 3-tin composite superconductor 20 with a rectangular cross section and a reinforcing material 1 made of stainless steel 11 coated with copper 12, which is bonded with a low melting point metal 3 such as solder. It has a similar structure. Compound composite superconductors with these reinforcing materials are reinforced with reinforcing materials that have high low-temperature strength, so the compound composite superconductors have high breaking strength and are resistant to external stress such as electromagnetic stress. , strain applied to the niobium 3-tin superconducting compound layer can be reduced.

However, the thermal stress generated during the cooling process from the formation temperature of the niobium-tritin-tin superconducting compound layer to the liquid helium temperature causes a strain of about 1% due to the difference in thermal shrinkage rate between the bronze and the niobium-tri-tin superconducting compound layer. This, combined with the strength of the intermetallic compound, lowers the critical temperature and critical magnetic field of the compound composite superconductor with such a cross-sectional structure, and as a result,
Particularly under high magnetic fields, there is a drawback that the critical current density decreases significantly.

The present invention aims to eliminate such drawbacks and provide a compound composite superconductor that has high performance and is capable of generating a high magnetic field. In a compound composite superconductor in which an A3B type compound superconducting layer is formed at the interface between a core material and a matrix made of an alloy containing a compound-forming element B by heat treatment on a composite material formed by processing, A3B Fine grains or pongee wires of a material (hereinafter simply referred to as low heat shrinkage material) whose heat shrinkage rate from the temperature that produces a type compound superconductor to the liquid helium temperature is smaller than the heat shrinkage rate of the alloy forming this matrix. It is characterized by being distributed.

That is, the present invention reduces the strain applied to the compound superconducting layer by reducing the difference in thermal shrinkage rate between the matrix and the compound superconducting layer by dispersing a low-shrinkable substance in the alloy forming the matrix. The objective is to achieve the objective by suppressing the actual deterioration in performance due to the strength of the intermetallic compound.

Examples will be described below. Figure 3 shows its structure, where 21 is a core made of an A3B-type compound-forming element A or an alloy containing A, 22 is a matrix made of an alloy containing an A3B-type compound-forming element B, and 23 is an A3B-type compound superconductor. Layer 24 is a granule or twill of low heat shrink material dispersed in matrix 22.

When manufacturing this A3B type compound composite superconductor by composite processing and selective diffusion method, a matrix 22 in which fine grains or pongee wires 24 of a low heat shrinkage material are uniformly dispersed in an alloy containing a compound-forming element B is used. Using this matrix 22, another compound-forming element A or an alloy containing A is composite-processed as the core wire 21, and the B element is diffused into the A element to form an A3B type compound superconducting layer 23. . In a compound composite superconductor with such a configuration, A
The thermal contraction rate of the matrix 22 surrounding the 3B type compound superconducting layer 23 can be brought close to the thermal contraction rate of the A3B type compound superconducting layer 23. It is possible to ensure that only compressive strain remains.

B-type composite superconductors can be produced by compound processing and selective diffusion methods using niobium-tritin, panadium-gallium, niobium-aluminum-tin, niobium-tin-gallium, etc., and compound-forming element B Examples of the matrix containing the alloy include a copper-tin alloy, a copper-gallium alloy, a copper-tin-aluminum alloy, a copper-tin-gallium alloy, and the like.

The low heat shrinkage material to be dispersed in such a matrix is 600-8, which produces a F type B compound superconductor.
At a temperature of
This includes substances such as hafnium, molybdenum, tantalum, titanium, tungsten, and zirconium, as well as shelving products, carbides, nitrides, oxides, etc. containing these substances. Next, the amount of low heat-shrinkable material to be dispersed in the matrix is such that the heat shrinkage rate of the alloy itself constituting the matrix is A.
Since the heat shrinkage rate is considerably higher than that of the 3B type compound superconducting layer, a small amount will have little effect.The amount of low heat shrink material varies depending on the composition of the alloy that makes up the matrix and the type of low heat shrink material. is 10 in volume percent
Percentages are necessary. On the other hand, by increasing the amount of the low heat shrinkage material, the heat shrinkage rate of the alloy constituting the matrix in which the low heat shrinkage material is dispersed can be brought close to that of the type B compound layer. It becomes difficult to process a matrix in which a substance is dispersed into a rod or tube shape, and the critical dispersion amount thereof is approximately 50% by volume. In addition, when a low heat shrinkage material is dispersed in a volume percentage of 40 to 50%, the A3B type compound superconducting layer will have a maximum of 0.5% due to the thermal stress generated during the cooling process from the B type compound formation temperature to the liquid helium temperature. Only about 5% compression strain remains,
It has also been revealed that strain below this level does not substantially reduce the critical temperature, critical magnetic field, and critical current density of the B-type compound superconducting layer. ``This compressive strain hardly changes even if the amount of the low heat shrink material dispersed is further increased. Therefore, the amount of the low heat shrink material dispersed in the matrix is 1
A volume percentage of 0 to 5M is desirable. Next, as a result of experiments by changing the dimensions and shape of the low heat shrinkable material to be dispersed, it was found that the heat shrinkage rate of the dispersed matrix was not significantly affected, but the aspect ratio of the pongee lines of the low heat shrinkable material ( It was found that the wires with a wire length/average diameter of 100 or more exhibited the smallest thermal shrinkage rate.

- The dimensions of the heat-shrinkable material are not particularly limited, but a diameter of microns or less is desirable from the viewpoint of subsequent workability.
Examples will be described below.

Example 1 Coin coins made of copper-tin alloy in which various low heat shrinkage substances were dispersed were prepared by high-pressure coagulation.

That is, in the melting scratches of copper and 10 weight percent tin, shelmets, graphite, hafnium, molybdenum, tantalum, titanium, tungsten, zirconium, titanium sideride, molybdenum carbide, zirconium nitride, and silicon oxide with an average diameter of several microns were found. The powders were forcibly blown into each powder to give a volume percentage of 20%, and then poured into a mold and solidified by applying a pressure of about several atmospheres. The coin has a diameter of 40 mm, a length of about 90 mm, and a weight of about 1 kilogram. This Zenitama has an outer diameter of 1
Hot extrusion processing was performed to obtain a tube with a diameter of 0 mm and an inner diameter of 8 mm. Next, a niobium wire with an outer diameter of 7 mm was inserted into the copper-tin alloy tube in which this low heat shrinkage material was dispersed, and wire drawing was performed to an outer diameter of 1 mm while adding intermediate sintering. Furthermore, 331 of these steel-tin alloy-coated niobium single-core composite wires were bundled, inserted into an oxygen-free steel tube with an outer diameter of 26 mm and an inner diameter of 22 mm, and processed to an outer diameter of 0.4 mm while applying intermediate sintering again. . As a result, in these samples, as shown in FIG.
One wire is pushed into the copper matrix 27.
This sample was heat treated in vacuum at 700 qo for 2 hours to form a niobium 3-tin superconducting compound layer 28 with a thickness of about 1 micron on the surface of each niobium filament 25. Table 1 shows the results of measuring the critical temperature of this sample using the four-terminal resistance method. The critical temperature in this table is defined as the temperature at which the resistance value of the sample becomes 1'2. For comparison, the results of measurements on a sample using a copper-1 weight percent tin tube in which no low heat shrinkage material is dispersed are also shown.・Note: Wso means weight, V means volume %.

This result shows that the critical temperature is 16.5 mm for the sample made of a matrix that does not contain a low heat shrinkage material. In contrast to blood, all samples using matrices containing low heat shrinkage materials showed a critical temperature of 17.1 K or higher, and among these, the sample in which silicon oxide (Si02) was dispersed had a critical temperature of 17.1 K or higher.
17. It showed an arc.

On the other hand, after performing these measurements, we removed the matrix with nitric acid and measured the critical temperature of the niobium filament containing the niobium-tritin superconducting compound layer alone.
7.8-18. It has been shown that the critical temperature of the dish can be demonstrated and that the thermal strain imposed on the niobium-tin superconducting compound layer can be reduced by dispersing a low heat shrinkage material in the matrix. Example 2 In the same manner as in Example 1,
Example 1 A tube in which copper-coated tungsten fibers having an outer diameter of 20 microns was dispersed at a volume percent of 2 in a copper-1 weight percent tin flaw was prepared by high-pressure coagulation, and the aspect ratio of the tungsten fiber was changed. A sample containing 331 niobium filaments similar to the case was prepared.

Then, heat treated in vacuum at 700 qo for two periods,
After forming a niobium 3-tin superconducting compound layer around the niobium filament, the critical temperature was measured. The results are shown in Table 2. Table 2 As is clear from the results, when the aspect ratio is 100 or more, the critical temperature of the sample becomes the highest.

Example 3 In the same manner as in Example 1, copper-plated tungsten powder with a diameter of several microns was dispersed in a molten tin with a weight percent of 1 to 1, and 331 niobium particles were dispersed in the same manner as in Example 1. A sample containing filament was prepared.

Then, heat treated in vacuum at 70,000 for 24 hours,
After forming a niobium tri-tin superconducting compound layer around the niobium filament, 4. The critical current of the sample was measured in chick liquid helium and an external magnetic field of 100 kOersted. The critical current was defined as the current value at which the voltage of the sample reached a value of 1 microvolt. Figure 5 shows the relationship between the amount of tungsten powder in the copper-tin matrix and the critical current density of the niobium-tritin superconducting compound layer.
For each, the amount of tungsten powder (volume percent), critical current density (A/) x 1, and the external magnetic field 1
The case of 00 kiloersted is shown. This result shows that when tungsten is used, the critical current density becomes almost constant at a volume percent of 3 or more, and adding more than this has little effect. In the above examples, the results were shown for the niobium tri-tin composite superconductor, but other A
Similar effects can be obtained with the 3B type compound composite superconductor.

Further, even if the cross-sectional shape and structure of the compound composite superconductor are different, the effect will not be reduced. In other words, in large-capacity A3B type compound composite superconductors, a diffusion barrier is provided to prevent element B from diffusing into the high-purity stabilizing material and increasing electrical resistance. The present invention can be applied even when a diffusion barrier is provided, and the effects of the present invention can be exhibited without any problems. In addition, when applying a compound composite superconductor with such a structure to a structure using a reinforcing material as shown in Fig. 1 or 2, stress applied from the outside such as electromagnetic stress and during the cooling process to the temperature of liquid helium must be applied. A compound composite superconductor having high stress resistance against any thermal stress that occurs can be obtained.

That is, by dispersing fine grains or pongee wires of a low heat shrinkage substance in a matrix made of an alloy containing compound-forming element B, thermal strain is added to the A3B type compound superconducting layer formed in contact with this matrix. This makes it possible to sufficiently exhibit the broken superconducting properties peculiar to the A3 matrix compound composite superconductor in a compound superconducting magnet.

Particularly, the effect is remarkable in high magnetic fields, and the critical current density at 100 kOersted or more can be significantly increased. This not only makes it easier to generate a high magnetic field, but also makes it possible to downsize the magnet.As a result, the amount of compound composite superconductor used and the amount of liquid helium used are reduced, which also provides economic advantages. big. As described above, the compound composite superconductor of the present invention makes it possible to provide a compound composite superconductor with high performance and capable of generating a high magnetic field.
It has great industrial effects.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of different conventional compound composite superconductors, FIG. 3 is a cross-sectional view of one embodiment of the compound composite superconductor of the present invention, and FIG. 4 is a cross-sectional diagram of another embodiment. FIG. 5 is a characteristic diagram showing the effects of one embodiment. 21... Cord wire, 22... Matrix, 23. ．． ...A3B type compound superconducting layer, 24...
...Pongee grains or pongee lines, which are low-mature contractile substances. Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. A core material made of a compound-forming element A or an alloy containing A of a type A_3B compound superconductor and a matrix made of an alloy containing a compound-forming element B are combined by processing, and then both are heat-treated. In a compound composite superconductor in which an A_3B type compound superconducting layer is formed on the interface of
Dispersed in the matrix are fine grains or fine wires of a substance whose thermal contraction coefficient from the temperature at which the A_3B type compound superconductor is produced to the temperature of liquid helium is smaller than the thermal contraction coefficient of the alloy forming the matrix. Characteristic compound composite superconductor. 2. The matrix is made of an alloy of copper and at least one element selected from the group consisting of tin, gallium, and aluminum, and the matrix has a thermal contraction rate from the temperature at which the A_3B type compound superconductor is produced to the temperature of liquid helium. Substances with a thermal shrinkage rate smaller than that of the alloy forming the are boron, graphite, hafnium, molybdenum, tantalum,
At least one selected from the group consisting of titanium, tungsten, and zirconium, or hafnium, molybdenum,
The compound composite superconductor according to claim 1, which is at least one substance selected from the group consisting of oxides, carbides, nitrides, and oxides of tantalum, titanium, tungsten, and zirconium. 3. The above-mentioned patent in which 10 to 50 volume percent of a substance whose thermal contraction rate from the temperature at which the A_3B type compound superconductor is produced to the temperature of liquid helium is smaller than the thermal contraction rate of the alloy forming the matrix is dispersed in the matrix. A compound composite superconductor according to claim 1 or 2. 4. The compound composite superconductor according to claim 1, wherein the thin wire has an aspect ratio (wire length/average diameter) of 100 or more.