JP2854596B2 - Compound superconducting conductor and method for producing the same - Google Patents

Description

The present invention relates to a compound superconductor and a method for producing the same, and more particularly to an electric resistance of a stabilizing material by diffusion of constituent elements of the compound superconductor. The present invention relates to a compound superconductor in which the critical current density of the entire superconductor is prevented and a method of manufacturing the same.

(Prior art) Nb ₃ Sn is currently used as a superconducting conductor.
And those using compound superconductors such as Nb ₃ Al, Nb-Ti
The use of alloy superconductors such as Nb-Zr is known, and their use in applications such as power transmission cables and superconducting coils capable of forming strong magnetic fields with little power consumption is being studied in various places. . For example, a superconductor using the above compound superconductor has been conventionally manufactured by the following method.

That is, taking the Nb ₃ Sn multi-superconducting wire as an example of the superconducting conductor, first fill the Nb tube with a Cu-Sn alloy, coat the outer periphery of the Nb tube with Cu, and integrate it with a swaging machine. The rod is formed into a regular hexagonal rod while reducing the surface to a predetermined outer diameter. Next, many of these hexagonal rods
After being inserted into a stabilizing material consisting of a Cu tube and integrated with a swaging machine, the surface is reduced to a predetermined outer diameter. After that, by performing a heat treatment at the generation temperature of Nb ₃ Sn, Sn in the Nb tube is diffused and reacted with Nb,
An Nb ₃ Sn superconductor layer is formed on the surface of the Nb tube.

FIG. 3 shows a multi-superconducting wire manufactured in this manner, in which an Nb ₃ Sn superconductor layer 2 is disposed on a Cu-Sn core 1 and diffusion of residual components of an Nb tube is placed thereon. The prevention layer 3 and the stabilizing material 4 made of Cu are sequentially formed. Note that the stabilizing material 4 serves as a current path at the time of normal conduction transition of the Nb ₃ Sn superconductor layer 2 to prevent burnout and the like.

(Problems to be Solved by the Invention) By the way, Cu which becomes such a superconducting wire stabilizing material 4
Usually has a residual resistance ratio (hereinafter referred to as RRR) of 200 to 30.
At 0, the specific resistance ρ at 20 [K] is １1 × 10 ⁻⁸ [Ω · c
m] and a very low purity. However, when Sn in the Cu—Sn core 1 diffuses into the stabilizer 4 during the heat treatment, the stabilizer 4 is contaminated with Sn.

The diffusion preventing layer 3 has a function of preventing the diffusion of Sn into the stabilizing material 4, but the effect of preventing the diffusion of Sn into the stabilizing material 4 during the heat treatment is not always sufficient. Moreover, it is inevitable that Nb or the like, which is a material of the diffusion preventing layer 3, diffuses into the stabilizing material 4.

As described above, when Nb, Sn, etc. diffuse into the stabilizing material 4,
RRR of stabilizer 4 is 1 to 10, ρ at 20 [K] is 1 × 1
0 ^-7 to 1 × 10 ^-6 [Ωcm], which is 1 compared to pure Cu.
There has been a problem that the electrical resistance increases by as much as two orders of magnitude, thereby impairing the stability of the superconducting wire.

Further, in order to suppress the diffusion of the impurity element into the stabilizing material 4, the heat treatment temperature is reduced and the heat treatment time is shortened. In this case, however, the formation of the Nb ₃ Sn layer is suppressed. However, there is a disadvantage that only those having low superconductivity such as critical current density can be obtained.

On the other hand, in the conventional multi-superconducting wire using the compound superconductor as described above, the superconducting characteristics such as the critical current density are almost determined by the number of core wires having the Nb ₃ Sn superconductor layer 2. Therefore, in order to increase the critical current density, the number of core wires must be increased, but with the current technology, there is a limit to increasing the number of cores, and furthermore, a superconducting wire with improved superconducting properties such as critical current density Is desired.

The present invention has been made to address such problems of the prior art, and while keeping the electric resistance of the stabilizer low, the compound superconducting conductor further improved in superconducting properties such as critical current density and the like. It is intended to provide a manufacturing method.

[Constitution of the Invention] (Means for Solving the Problems) That is, a compound superconducting conductor of the present invention is a compound superconducting conductor in which a stabilizing material is provided on the outer peripheral side of a Cu-based matrix in which a large number of core wires including the compound superconductor are embedded. In the conductor,
The same type of fibrous compound superconductor as the compound superconductor of the core wire is distributed in the Cu-based matrix,
A diffusion preventing layer made of a metal oxide containing an oxide of a constituent element of the compound superconductor is provided between the Cu-based matrix and the stabilizing material.

Further, the method for producing a compound superconductor of the present invention includes the step of reacting by heat treatment to form a compound superconductor, wherein one of the elements constituting the compound superconductor in which a large number of wires including the compound superconductor material are embedded is embedded. Step of integrating the stabilizing material on the outer peripheral side of the containing Cu-based matrix, and in this integrated structure, in a vacuum or in a non-oxidizing atmosphere after forming an oxide layer on the surface of the stabilizing material Alternatively, under a partial pressure of oxygen lower than the atmospheric oxygen partial pressure and an oxygen partial pressure capable of forming an oxide layer on the surface of the stabilizing material, a heat treatment is performed in a generation temperature range of the compound superconductor to stabilize the Cu-based matrix. Forming a diffusion prevention layer made of a metal oxide containing an oxide of a constituent element of the compound superconductor between the materials.

The compound superconductor material which reacts by the heat treatment used in the present invention to form a compound superconductor includes Nb and Sn which are Nb ₃ Sn forming materials and Nb and Al which are Nb ₃ Al forming materials.
For example, a superconducting wire is formed by filling a material containing Sn or Al into an Nb tube.

The wires of these superconducting wires are embedded in a Cu-based matrix containing one of the elements constituting the compound superconductor, for example, Nb, and a stabilizing material made of Cu is integrally formed on the outer peripheral side of the Cu-based matrix. Thus, a structure serving as a prototype of the compound superconductor of the present invention is formed. The structure according to the present invention may have any shape as long as the surface of the stabilizing material is in contact with oxygen gas. ,
Various structures such as a tape material in which a Cu matrix and a stabilizing layer are laminated can be used.

The alloy constituting the above-mentioned Cu-based matrix is a Cu-based alloy used for a so-called in-situ method, for example,
Nb is distributed in a fibrous form by subjecting a Cu-Nb alloy to strong working. Cu, which is a stabilizing material, is basically made of pure copper containing only unavoidable impurities having excellent conductivity.For example, a solid solution strengthened copper alloy such as Cr, Zr, Ti, Zn, etc. It is also possible to use a laminate with a particle dispersion strengthened copper alloy or the like.

The heat treatment in the method for producing a compound superconducting conductor of the present invention includes the step of reacting the compound superconducting material to form a compound superconductor, and the oxidation formed on the surface of Cu of the stabilizing material between the stabilizing material and the Cu matrix. This is for forming a strong diffusion prevention layer made of an oxide of a constituent element of the compound superconductor or an oxide of an additional element with oxygen diffused from the material layer. Further, impurities that are dissolved in a trace amount in the stabilizer are precipitated as oxides by this heat treatment, and the conductivity of the stabilizer is further improved.

The following two types of compound superconductors are formed by the heat treatment.

For example, due to the reaction of these compound superconductor materials in a strand filled with a material containing Sn in an Nb tube.

Reaction between the constituent element of one compound superconductor, such as Sn, which has diffused the compound superconductor layer formed in the strand by the heat treatment, and the other fibrous constituent element, such as Nb, previously dispersed in a Cu matrix By.

The above compound superconductor is based on the so-called Nb tube method, and the above compound superconductor actively promotes the constituent elements of the compound superconductor that inevitably diffuse during heat treatment for compound superconductor generation by the Nb tube method. It is a compound superconductor obtained by a so-called in-situ method.

And, in the present invention, if the above-mentioned in situ method is simply used in combination with the Nb tube method, the stabilizer is contaminated by the constituent elements of the compound superconductor in which the stabilizer is diffused,
By forming a diffusion preventing layer made of a metal oxide of these diffusion elements between the stabilizer and the Cu matrix, the purity of Cu as the stabilizer is maintained.

This diffusion prevention layer is subjected to the above heat treatment after (A) forming a Cu oxide layer on the surface of the stabilizing material.

(B) The above heat treatment is performed under an oxygen partial pressure lower than the atmospheric oxygen partial pressure and capable of forming a Cu oxide layer on the surface of the stabilizer.

For example, it is formed by reacting oxygen diffused from an oxide layer formed on the surface of Cu of the stabilizing material with a constituent element or an additive element of the compound superconductor.

Note that the Cu oxide layer may be made of CuO, Cu ₂ O alone or CuO.
And a mixture of Cu ₂ O and the like.

The Cu oxide layer on the surface of the stabilizing material according to the above (A) is formed, for example, in a normal pressure treatment atmosphere having an oxygen concentration of 10% or more.
It can be formed by performing a heat treatment at a temperature of 100 ° C. to 400 ° C. for about 1 to 120 hours. The Cu oxide layer can also be formed by forming a Cu oxide layer by CVD, chemically oxidizing using a blackening agent, or applying a paste-like paint containing Cu oxide. can do.

Then, the heat treatment is performed on the structure in which the Cu oxide is formed on the outer periphery of the stabilizing material in this manner. The conditions of this heat treatment are as follows: under atmospheric pressure, under high vacuum (1 × 10 ⁻⁴ Torr or less),
Under an inert gas atmosphere, for example, Nb ₃ Sn
10 to 400 hours at 50 ° C to 770 ° C, 750 ° C to 95 for Nb ₃ Al
It is about 1 to 100 hours at 0 ° C.

If the Cu oxide layer formed on the surface of the stabilizing material is too thin, for example, less than 0.1 μm, the amount of oxygen in the oxide layer is reduced, and the formation of the diffusion prevention layer is insufficient, and is low.
On the contrary, if the thickness of the Cu oxide layer exceeds 10 μm with respect to the wire diameter (outer diameter) of 1 mm, the amount of oxygen entering the stabilizing material becomes too large. If the thickness becomes too large, the thickness of the diffusion prevention layer is increased, and the volume of the stabilizer is reduced due to oxidation, and the strength, RRR, and critical current density may be reduced. Therefore, it is desirable to set the thickness of the Cu oxide layer in consideration of these balances.

In the case where heat treatment is performed while forming a Cu oxide layer on the surface of the stabilizing material according to the above (B), for example, 1 × 10 ⁻³ Torr to 1 × under an oxygen partial pressure lower than the atmospheric oxygen partial pressure. Ten
By performing heat treatment in a low vacuum of about ^-1 Torr for 3 to 100 hours, a compound superconductor is formed while forming a diffusion preventing layer.

By using high-purity Cu containing about 0.3 wt% of oxygen as a stabilizer, it is possible to omit the formation of an oxide layer and directly perform heat treatment at the compound superconductor generation temperature.

The diffusion prevention layer composed of the metal oxide layer formed by these heat treatments does not necessarily have to be formed continuously, but may be formed discontinuously. By thus forming the metal oxide layer discontinuously,
Good heat conduction between the compound superconductor and the stabilizing material can be maintained.

When the compound superconducting conductor obtained by the present invention is applied to a product that can be subjected to heat treatment, the heat treatment of the present invention may be performed in the process of assembling the product. For example,
In the case where a superconducting coil is formed using the superconducting wire manufactured according to the present invention, a coil before heat treatment is wound around a coil bobbin, and in this state, a compound superconductor and a diffusion prevention layer are formed. May be performed.

(Function) In the present invention, the heat treatment at the compound superconductor formation temperature causes the constituent elements of the compound superconductor to inevitably diffuse into the Cu matrix in which the core wires of these compound superconductors are embedded, Reacts with the constituent elements of the other compound superconductor dispersed in
The same thing as the compound superconductor by the in-situ method is formed in the Cu-based matrix. Thereby, the superconductivity such as the critical current density of the entire compound superconductor is improved by the amount of the compound superconductor distributed in the Cu-based matrix. Further, since the Cu-based matrix in which the fibrous compound superconductor is distributed by the in-situ method has higher mechanical strength than pure copper, the strength of the entire compound superconductor can be improved.

Further, simply using the in-situ method alone may lead to contamination of the stabilizer by the diffusion element and decrease the conductivity of the stabilizer, but in the present invention, Cu formed on the surface of the stabilizer is used. Oxygen in the oxide diffuses into the stabilizing material during heat treatment, oxidizes and precipitates impurities diffused from the superconductor constituent material, and consists of a strong metal oxide between the stabilizing material and the Cu-based matrix An anti-diffusion layer is formed, whereby an increase in the electrical resistance of the stabilizer can be suppressed, and the stability of the compound superconducting conductor is improved. In addition, impurities contained in the stabilizer are also precipitated as oxides, and the conductivity is further improved.

(Example) Next, an example of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 2 is a sectional view showing a schematic structure of an Nb ₃ Sn multi-superconducting wire according to one embodiment of the present invention.

In this multi-superconducting wire, a Nb ₃ Sn core wire 12 formed by a Nb tube method, that is, a Cu-Sn layer 14 disposed inside an Nb tube 13 is provided in a matrix 11 of a Cu alloy formed by a 20 wt% Nb-Cu alloy. A plurality of Nb ₃ Sn core wires 12 having an Nb ₃ Sn layer 15 formed therebetween are distributed and embedded. In addition, in the Cu alloy matrix 11, a fibrous
Nb ₃ Sn16 is distributed. And Cu alloy matrix 1
A diffusion prevention layer 1 made of an oxide such as Nb or Sn
A multi-superconducting wire is formed by forming a stabilizing material 18 made of high-purity Cu via 7.

That is, unlike the conventional superconducting wire using the Nb tube method, the Cu alloy matrix 11 and the stabilizing material 18
Between the Cu as the, Nb oxide, Sn oxide, a diffusion prevention layer 17 made of an oxide of a constituent element or an additive element of a compound superconductor such as an oxide of Ti is provided,
In the Cu alloy matrix 11, fibrous Nb ₃ Sn 16 is distributed by an in-situ method.

Next, a method for manufacturing the multi-superconducting wire having the above structure will be described.

Nb with 1% by weight of Ti added inside a cylindrical matrix 11 made of a 20wt% Nb-Cu alloy with an outer diameter of 50mm and an inner diameter of 40mm
A tube 13 is inserted, and a composite wire 14 having an outer diameter of 20 mm coated with a Cu coating on the Sn wire so that the Sn concentration is 70% is inserted therein. Make body wires.

Next, a number of these wires are bundled, and the outer diameter of the stabilizing material 18 is obtained.
It is inserted along the axial direction into an oxygen-free high-purity Cu tube with a diameter of 24.7 mm and an inner diameter of 20.8 mm, and is further integrated and surface-reduced to an outer diameter of 1 mm.

In addition, the Cu alloy matrix
The Nb crystallized in the 20 wt% Nb-Cu alloy of No. 11 is distributed by being stretched into an extremely thin fibrous shape in the axial direction.

Next, the integrated structure was placed in an atmosphere in which an argon gas containing 20% oxygen was flowed at a rate of 0.2 l / min.
Heat treatment is performed under the condition of 00 ± 10 ° C. × 48 hours to form a Cu oxide layer on the surface of the stabilizer 18 made of oxygen-free high-purity Cu.

Thereafter, the structure is subjected to a heat treatment at 700 ° C. for 30 hours in an atmosphere in which an argon gas is flown at 0.2 l / min. This heat treatment, along with Nb ₃ SN15 is formed by reaction between Sn that has diffused Nb tube 13 and the interior of the Cu coating, distribution to the Nb ₃ Sn layer 15 Sn and Cu alloy matrix 11 that has diffused The fibrous Nb reacts to form fibrous Nb ₃ Sn16 by an in-situ method. Also,
Simultaneously with the formation of these Nb ₃ Sn 15 and 16, Nb and Ti on the surface of the Nb tube 13 and Sn and the like diffused in the Nb ₃ Sn layer 15 react with oxygen diffused in the stabilizing material 18 to produce Cu A diffusion preventing layer 17 made of an oxide such as Nb, Sn, or Ti is formed on the interface between the marix 11 and the stabilizing material 18. The formation of the diffusion preventing layer 17 allows the stabilizing material 18 to be formed.
Contamination with Sn or Nb is prevented.

Incidentally, in order to compare ρ at 20 [K] with RRR, which is a standard for stability, the above-mentioned conventional compound superconducting wire (the wire diameter and the number of core wires are the same as in Example 1 above).
When the above characteristics of the compound superconducting wire having the structure of this embodiment shown in FIG. 2 were measured, the RRR of the conventional structure was 3.3 and ρ was 6.3 × 10 ^-7 [Ωcm]. On the other hand, in the structure of this embodiment, RRR is 233 and ρ is 1.1
× 10 ⁻⁸ [Ω · cm], which indicates that the compound superconducting wire according to this example prevents the stabilizing material from being contaminated by the presence of the diffusion preventing layer 17 and clearly suppresses the increase in electric resistance. did.

The measured these critical current density, whereas the ones of the conventional structure was 450A / mm ² at 15 Tesla,
In the structure of this example, it was found that the superconductivity was clearly improved by 600 A / mm ² at 15 Tesla and the presence of Nb ₃ Sn 16 by the in-situ method.

Further, when these tensile strengths were measured, the conventional structure had a strength of 13 kg / mm ² and 0.4% proof stress, whereas the structure of this example had a tensile strength of 20 kg / mm ² and 0.4% proof strength. . This is because Nb ₃ Sn16
This is considered to be because the mechanical strength of the Cu alloy matrix 11 in which was precipitated was improved.

Example 2 The structure before forming a Cu oxide layer on the surface of the stabilizing material 18 in Example 1 was evacuated to low vacuum (1 × 10 ⁻³ To
rr to about ¹ × 10 ^-1 Torr)
Heat treatment at 0 ° C. for 30 hours to form Nb ₃ Sn 15 and 16, and to form an oxide layer continuously on the surface of the stabilizer with oxygen remaining in the furnace. Oxygen was reacted with Sn or the like diffused in the Nb or Nb ₃ Sn layer to form a diffusion prevention layer 17 of these oxides.

When the RRR, the electric resistance, and the critical current density of the multi-superconducting wire obtained in this example were measured, the same results as in Example 1 were obtained.

Example 3 When arranging a large number of strands in Example 1 in a stabilizer composed of oxygen-free high-purity Cu pipe as a stabilizer, a strand positioned in advance in the outermost layer was used as a stabilizer. Nb ₃ Sn was processed under the same conditions as in Example 1 except that the contacting side was processed so as to have a shape having a concave portion, and the surface was reduced so that the distance from the stabilizing material surface caused a difference of about 25 to 30 μm after the surface reduction processing. A multi-superconducting wire was manufactured.

The cross section of the superconducting wire thus obtained was observed with a microscope. The observation results are schematically shown in FIG.

As is clear from the figure, the Nb ₃ Sn layer 1 of the outermost core
5 A metal oxide layer made of a discontinuous Nb, Ti, Sn oxide, 17 were found.

Further, the RRR of this superconducting wire is 230, which is comparable to that of the superconducting wire produced in Example 1, and the stabilizing material 18 is contaminated by making the diffusion preventing layer 17 made of a metal oxide layer discontinuous. Confirmed that there is no.

Thus, by forming the diffusion prevention layer 17 made of a metal oxide layer discontinuously, heat transfer to the Nb ₃ Sn layer 15 stabilizer 18 from Cu alloy matrix 11 which is embedded it becomes extremely good Thus, the stability of the superconducting wire can be secured.

Example 4 A structure serving as a prototype of a multi-superconducting wire before surface oxidation treatment in Example 1 was wound around a stainless steel winding over 18 layers, and then a Cu oxide layer was formed under the same conditions as in Example 1. Formation and heat treatment at the formation temperature of the compound superconductor were performed to produce a superconducting coil.

When the RRR of each layer of the superconducting coil was measured, the average was 200 and almost no difference was observed between the layers.

[Effects of the Invention] As described above, according to the present invention, a compound superconductor formed by an in-situ method is formed together with a compound superconductor formed by a normal tube method, so that superconducting properties such as critical current density and tensile strength are reduced. With improved and stabilizing material
Since a strong diffusion prevention layer composed of an oxide such as a superconductor constituent element is formed between the Cu-based matrices, the conductivity of the stabilizing material is maintained, and the stability is improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a cross section of a superconducting wire manufactured according to one embodiment of the present invention, and FIG. 2 is a diagram showing a partially enlarged cross-sectional state of a superconducting wire manufactured according to another embodiment of the present invention. ,
FIG. 3 is a cross-sectional view of a compound superconducting wire manufactured by a conventional method. 11 ... Cu alloy matrix, 12 ... Nb ₃ Sn core wire, 13 ... N
b tube, 14… Cu-Sn alloy, 15… Nb ₃ Sn layer, 16…
Fibrous Nb ₃ Sn, 17: diffusion preventing layer, 18: stabilizing material.

Claims (2)

(57) [Claims] 1. A compound superconductor having a stabilizing material provided on an outer peripheral side of a Cu-based matrix in which a large number of core wires including a compound superconductor are embedded, wherein the same type of compound superconductor as the core wire is provided in the Cu-based matrix. While the fibrous compound superconductor is distributed,
A compound superconducting conductor, wherein a diffusion preventing layer made of a metal oxide containing an oxide of a constituent element of the compound superconductor is provided between the Cu-based matrix and the stabilizing material. 2. An outer periphery of a Cu-based matrix in which a large number of strands containing a compound superconductor material which reacts by heat treatment to form a compound superconductor are embedded and contain one of the elements constituting the compound superconductor. Integrating a stabilizing material on the side, and forming an oxide layer on the surface of the stabilizing material on the integrated structure, in a vacuum or in a non-oxidizing atmosphere, or in the atmosphere. Under a partial pressure of oxygen lower than the pressure and capable of forming an oxide layer on the surface of the stabilizing material, a heat treatment is performed in a generation region of the compound superconductor to form the compound superconductor between the Cu-based matrix and the stabilizing material. Forming a diffusion prevention layer composed of a metal oxide containing an oxide of a constituent element.