JPS5933653B2 - Method for producing stabilized superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a stabilized superconductor that forms a superconducting compound or alloy by a diffusion reaction.

In the conventional method of producing a stabilized compound superconductor through a diffusion reaction process, a stabilizing metal was applied after the diffusion heat treatment process.

First, a superconducting compound is formed between two or more types of constituent elements including the constituent elements of the target superconductor by interdiffusion reaction. For example, Nb and Sn, ,A
l) Nb3Sn, , Nb3Al, , Nb by diffusion reaction from Al-Ge, , Ga) or alloys containing these, respectively.
3(Al-Ge), compound superconductors such as Nb3Ga,
Similarly, from V and Ga) Si, , Al, , Hf, , Zr or alloys containing these, V3Ga, , V3Sl, .
Compound superconductors such as V3Al, V2Hf, and VaZr are formed. Next, a stabilizing metal was attached to the surface of the composite containing the superconductor thus produced by the agate method or the soldering method. An example of this conventional method will be explained as follows.

After V and Cu-Ga alloy are crimped by rolling to form a composite strip, a diffusion reaction is caused by heating to form a V3Ga layer at the crimped interface, and a stabilizing metal layer is formed on the surface of this composite strip. It was provided by soldering or plating.

Figure 1 is a cross-sectional view of the stabilized compound superconductor tape made in this way, where 1 is the residual vanadium after the diffusion reaction, 2 is the V3Ga compound superconductor layer formed on the crimping surface, and 3 is the residual Cu after the diffusion reaction. -Ga alloy, 4 is a semiconductor layer, and 5 is a stabilizing metal copper layer. Stabilization of superconductors is a well-known process in which superconductivity itself is an unstable phenomenon, so by providing a stabilizing metal, electrical bypass,
The goal is to improve stability by adding effects such as magnetic damping and thermal diffusion. This stability is an essential element for practical superconductors. For this reason, the stabilizing metal must be a good electrical and thermal conductor, and must have good adhesion to the superconductor both electrically and thermally. Therefore, from the viewpoint of stabilizing the superconductor, the above-mentioned conventional method for producing a stabilized compound superconductor has various drawbacks.

In other words, in the method of bonding stabilizing metals using the soldering method, even if the performance of the stabilizing metal itself is good, there is a risk of damaging the brittle compound superconductor during bonding. After bonding with the superconductor, it is difficult to change its dimensions, and productivity is poor due to the process.

Furthermore, since solder is interposed between the superconductor and the superconductor, it inevitably has drawbacks such as high electrical and thermal resistance. Furthermore, even with the plating method, the stabilizing metal layer formed by plating has high electrical resistance and poor adhesion, resulting in poor performance, and therefore requires annealing. As a result, a diffusion reaction occurs between the constituent elements of the superconductor and the stabilizing metal, resulting in a decrease in the sluggishness of the stabilizing metal, resulting in a drawback that only poor electrical and thermal properties can be obtained. The following proposal has been made to improve this drawback.

As one example, in the case of a superconductor made of a compound or alloy containing niobium or vanadium, as shown in FIG. A composite layer of a core 8 of one of the constituent elements or an alloy containing the same and a matrix 9 of the other constituent element or an alloy containing the constituent element which diffuses and reacts with the superconducting element to form the target superconducting compound or alloy is provided. By creating a composite with a similar structure, it is possible to add a stabilizing metal even before the diffusion heat treatment.

By the diffusion heat treatment, a superconducting compound or alloy is formed at the interfaces where the metal tube 6 and the core 8 are in contact with the matrix 9, respectively. In addition, as shown in FIG. 3, for example, in the case of a Nb3Sn compound superconductor, a stabilizing material 7 is arranged inside the tantalum tube 10, and the target superconducting compound or Before diffusion heat treatment, by forming a composite with a composite layer of a core 8 of one of the constituent elements forming the alloy or an alloy containing the same and a matrix 9 of the other constituent element or the alloy containing the same. It provides stabilizing metals from.

By the diffusion heat treatment, a superconducting compound or alloy is formed at the interface where the core 8 and the matrix 9 are in contact, that is, around the core 8. In principle, these structures have good adhesion between the stabilizing metal and metals such as niobium, vanadium, and tantalum through mechanical processing before diffusion heat treatment, and also prevent a decrease in the purity of the stabilizing metal during diffusion heat treatment. .

However, when these composites are actually produced, there are the following problems. That is, if the metal tube used as the partition wall of niobium, vanadium, tantalum, etc. is thin, it will break during machining and the purity of the stabilizing metal will decrease during the diffusion process. 2
In order to improve the space factor of the superconductor in the conductor configuration, it is necessary to make the partition tube as thin as possible, but in such a case, the interdiffusion between the partition material and other elements cannot be ignored, and as a result, reduces the purity of the stabilizing metal.

5. A decrease in the purity of the stabilized metal during diffusion heat treatment will result in a decrease in the concentration of the original solute elements in the reaction system for producing the desired superconducting material, and it may take a long time to obtain the desired amount of superconductor. In some cases, it may even be impossible.

The present invention was obtained as a result of various studies to solve these problems, and it has a thin partition wall material, improved workability, prevents interaction with stabilizing metal, and achieves the desired superconducting material. This is a method for producing a stabilized superconductor that aids production reactions.

That is, as shown in FIG. 4a, the stabilizing material 7 is made of niobium,
Vanadium, tantalum, or metals based on these (
A core 8 made of one of the component elements or an alloy thereof constituting the target superconductor and a core 8 made of one of the component elements or an alloy thereof constituting the target superconductor are further surrounded by the diffusion reaction control material 11 on the outside thereof. Matrix 9 made of the alloy
and the composite thus obtained is subjected to diffusion heat treatment to form a superconductor around the core 8 or to make the entire core 8 a superconductor.

Here, the function of the partition material 10 made of niobium vanadium, tantalum, or an alloy thereof is to prevent mutual diffusion between the stabilizing metal 7 and at least two types of component elements or alloy components constituting the target superconductor. The partition material itself must not cause a diffusion reaction with any of these, or must react only to a very small extent. In addition, the form of the partition material may be one in which the stabilizing material 7 is simply surrounded as shown in FIG. A structure may be adopted in which the stabilizing material 7 is divided by providing a metal (partitioning material) 10, or a structure in which the stabilizing material surrounded by these partitioning materials is dispersed at several locations within the conductor may be used.

The reason for dividing the above-mentioned stabilizing material is to reduce AC loss related to the normal conducting portion of the conductor. Further, the reason why the stabilizing material is dispersed within the conductor is to improve heat transfer generated within the conductor. On the other hand, copper, silver, aluminum,
Diffusion reaction control material 11 made of gold, magnesium, lead, etc.
It has the following function. That is, 1. It prevents oxidation in the manufacturing process of metals such as niobium, vanadium, and tantalum surrounding the stabilizing metal. 2. It controls mutual diffusion by creating a solute element concentration gap outside the partition material. 3. Promote the desired superconductor production reaction occurring outside the partition walls and shorten the reaction time.

This substantially eliminates not only the diffusion of external solute elements into the stabilizing metal through the partition wall, but also the interdiffusion between the partition wall material and the stabilizing metal. 4 From a mechanical point of view, the stabilizing material is generally a pure metal and is extremely soft, and because there is a large difference in hardness and work hardening rate between the partition wall material and its outer metal layer and the stabilizing material, the partition wall material is hardened during processing. When buckling or pipe rupture occurs, the diffusion reaction control material also acts as a mechanical mitigation material to prevent such accidents.

Therefore, the present invention has the following effects.

Firstly, there is no decrease in the purity of the stabilizing metal, ensuring good electrical and thermal conductivity of the stabilizing metal itself, and, as mentioned above, perfect adhesion through mechanical processing makes the stabilizing metal and superconductor conductive. This makes it possible to easily produce a stabilized superconductor that has extremely low electrical and thermal resistance with the body. Furthermore, in the present invention, since the stabilizing metal is provided inside the superconductor, there are the following advantages.

That is, the practical thickness of one stabilizing metal layer is larger than that in the case where the stabilizing metal is provided on the outside, which is advantageous in terms of the size effect on electrical resistance and the magnetoresistance effect.

A two-stabilizing metal layer is provided on the inside of niobium, vanadium, tantalum, or a metal mainly composed of these, and a diffusion reaction control material is placed on the outside, which is necessary for producing the target superconducting compound or alloy. Only a diffusion reaction occurs.

Further, depending on the selection of the diffusion reaction system, the superconductor production reaction is promoted, so that a large amount of diffusion reaction layer can be formed in a correspondingly short time. 3. When forming superconductor layers having the same cross-sectional area, the effective thickness can be reduced for the same reason as 2 above.

Therefore, adiabatic stability
ity: The property of suppressing instability such as when the temperature of the superconductor rises due to heat generation in an adiabatic state when a flux jump occurs, and the magnetic flux penetrates further and repeats heat generation) and Dynamic stability: When heat is dissipated through a normal conductor, it is excellent in terms of both the above-mentioned adiabatic stability and the ability to suppress instability. 4. The stabilizing material is not exposed to the outside air, and contamination due to the atmosphere during diffusion heat treatment and the like can be prevented.

5. The stabilizing material is a pure metal and is softer than niobium, vanadium, or other constituent metals, so it can prevent sheath cracking or sheath breakage caused by machining.

In the present invention, compounds or alloys containing niobium or vanadium include, for example, Nb3SnlNb3AllNb3 (
M'e), Nb3 (g), V3Galv3si, V3A
Compounds such as llV2HfSV2Zl・, Ntil
These include, but are not limited to, alloys such as Nb-Zr.

Next, examples of the present invention will be shown.

Example 1 In order to obtain a composite as shown in FIG. 4a, first, a silver plate 7 was inserted into a vanadium (hereinafter referred to as V) pipe 10 covered with aluminum 11, and the outer diameter of the pipe was adjusted by draw bench processing. I made a 21m long silver composite rod with an outer diameter of 17mm.
Around this composite rod, 3mmφ niobium rods 8
30 trees are arranged in a forest at appropriate intervals, and Cu-
Cast a molten metal of 14 wt% Sn alloy 9 to a total diameter of 45 mm.
The outer diameter of

Next, this composite was extruded and processed by wire drawing to obtain a 0.12
After twisting 7 wires as m71Lφ, 650rC
The mixture was heated for 100 hours to form a Nb3Sn compound superconducting layer through a diffusion reaction.

Aluminum layer 11 was almost entirely diffused into the Cu-Sn alloy matrix as intended by the present invention.

On the other hand, the V tube 10 prevented contamination of Ag7. Next, the stranded wires were passed through molten indium to integrate them and then insulated with varnish. The critical current value of this stranded wire was measured and was found to be 70 A at 4.2 K and under a 70 kilogauss magnetic field. Using this twisted wire, the inner diameter is 30 mm,
A magnet with a coil having an outer diameter of 61 mu and a length of 72 mm was made. When a current of 68 A was applied at 4.2 K, a magnetic field of 72 kilogauss was generated. As a result, it was confirmed that the product was sufficiently durable for practical use. In addition, a wire made only of silver having the same shape as the silver core 7 of the stranded wire is heated at 650°C.
After heat treatment for 100 hours, the electrical resistance of 4.2 was measured at K, and there was no substantial difference between this value and the specific resistance of the silver core 7 of the superconducting wire of the above example. I couldn't help it.

Therefore, the silver core 7 contains Cu, . Sn. It was confirmed that V and M were not diffused. Example 2 As shown in FIG. 4b, seven copper rods 7 were inserted into the lotus root-shaped hole of a tantalum tube 10, and a silver tube 11 was coated on the outside.
Make a composite rod with an outer diameter of 21mm, and use this composite rod as the center and the area around it to be 3m77! 830 φ vanadium (hereinafter referred to as V) rods are arranged at appropriate intervals, and Cu is placed between them.
-18wt% Ga alloy 9 molten metal is cast and the whole is 457!
17! The outer diameter is Lφ.

Next, this composite is extruded and processed by wire drawing etc. so that each side has 6
m7! L hexagonal bar, outer diameter 45mmφ, inner diameter 39mm
C of φ: 61 pieces were combined into a 10wt% Ga alloy tube, the outer diameter was made to be 0.3mmφ by wire drawing, etc., and then 10mm.
A strand 12 was obtained by twisting the wire at the pitch. An air-core concentric stranded wire was made from 1215 of these strands with a pitch of 20m1L, and crushed with a Turk's head (two-way roll) to have a cross-sectional size of 0.25m7n x 4.1mm (see Figure 5 for simplicity). A molded stranded composite cable was obtained. The wire filling rate at this time was 95%. This cable is 1x10-JMoV! 625 in Hg vacuum furnace
C. for 50 hours to form a V3Ga compound superconductor at the interface between the vanadium rod and the copper-gallium alloy. When the cross section of the cable was examined with a microscope, the thickness of the tantalum partition inside the wire was more uniform than in Example 1, and no sheath cracks were observed. This is thought to be due to the reinforcement effect of the soft stabilizing material and the stress relaxation effect of the silver layer coated on the outside of the tantalum tube. Also, conventional V3
In the reaction system for forming a Ga compound superconductor in which silver was not involved, the reaction time was 75 hours, but in the reaction system in which silver was involved according to the present invention, the reaction was completed in 50 hours. This is considered to be because the diffusion reaction was promoted by the action of silver in the reaction system. Further, resistance measurements of the stabilized metal showed no substantial difference from the resistivity of copper before composite. Therefore, it was ensured that the tantalum walls, despite being approximately 1 micron thick, did not undergo interdiffusion to the extent that they contaminated the stabilizing material. As described above, as is clear from the examples, the present invention achieves complete adhesion between the stabilizing metal and the metal such as niobium, vanadium, or tantalum by machining or the like before diffusion heat treatment, and furthermore, during diffusion heat treatment, This prevents a decrease in the purity of the stabilizing metal.

Therefore, compared to the conventional method in which there was a great risk of deterioration of the purity of the stabilizing metal after the diffusion heat treatment step, the present invention guarantees good electrical and thermal conductivity of the stabilizing metal itself, and also has a mechanical property. Because of perfect adhesion through mechanical processing, it is possible to easily produce a stabilized superconductor in which the electrical and thermal resistance between the stabilized metal and the superconductor is extremely low. Furthermore, since the diffusion reaction control material is disposed around the outer periphery of the partition material, it is possible to effectively form a uniform superconductor, and the overall current density of the wire can be increased. The present invention is applicable not only to compound superconductors but also to obtaining alloy superconductors by diffusion heat treatment.

In particular, hollow superconducting wires and superconducting wires with complex shapes can be easily manufactured by processing the wire in the form of a composite with good workability and then performing post-diffusion heat treatment to transform it into the desired superconductor. Furthermore, the present invention is not limited to the method of producing a superconductor by processing a composite, but also includes a method of producing a superconductor by coating the surface of a stabilized metal with two or more constituent metal elements by plating vapor deposition or the like and performing diffusion heat treatment. Furthermore, whatever the shape of the stabilizer, niobium, vanadium or tantalum, or the external composite layer,
Included in the present invention. Easy drawing? Figures 1, 2, and 3 are cross-sectional views of a composite for producing a stabilized superconductor before a diffusion reaction according to the conventional method, and Figure 4 is a cross-sectional view of a composite for producing a stabilized superconductor before a diffusion reaction according to the present invention. FIG. 5 is a cross-sectional view of a manufacturing composite, and FIG. 5 is a cross-sectional view of a molded stranded compound superconducting wire obtained by the first method of the present invention.

7... Stabilizing material, 8... One of the component elements constituting the superconducting compound or alloy, or its alloy, 9
. . . The other component element constituting the superconducting compound or alloy or its alloy, 10 . . . Partition material, 11
... Diffusion reaction control material, 12 ... Element wire.

Claims (1)

[Claims] 1. In the production of a superconductor made of a compound or alloy containing niobium or vanadium, one or more of copper, silver, aluminum, and gold are substituted with niobium, vanadium, tantalum, or any of these as a stabilizing material. Surrounded by a partition material made of a main metal, and surrounded by one or more metals of copper, silver, aluminum, gold, magnesium, and lead as a diffusion reaction control material, and further outside. A method for producing a stabilized superconductor, which comprises placing at least two types of elements or alloys constituting the desired superconductor in contact with each other, and subjecting the thus obtained composite to a diffusion heat treatment. 2. The method for producing a stabilized superconductor according to claim 1, wherein a plurality of the stabilizing materials are embedded in a metal matrix of the partition wall material.