JPH06203670A - Manufacture of bi oxide superconducting wire - Google Patents

Abstract

PURPOSE:To manufacture a long superconducting wire excellent in superconductive characteristic by winding a composite sheet consisting of an Bi oxide superconductor and silver on a silver core material after being subjected to a specified heat treatment, and inserting it into a silver billet to perform diameter contracting work and heat treatment. CONSTITUTION:A composite sheet consisting of a Bi oxide superconductor and silver is wound on a silver sore material, inserted into a silver billet, and then subjected to diameter contracting work. The resulting composite multilayer wire is heat-treated to provide an Bi oxide superconducting wire. Prior to the heat treatment of the composite multilayer wire, the composite sheet is heat- treated at 650-800 deg.C at least once. This heat treatment of the composite sheet is preferably conducted in the atmosphere of oxygen, nitrogen or combination thereof, and also preferably conducted prior to the winding of the composite sheet on the silver core material. Thus, the oil and moisture adhered during the working are surely removed, work hardening of silver is eliminated, and a long material or coil excellent in superconducting characteristic can be easily provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Bi-based oxide superconductor applicable to magnets, coils, power application conductors and the like.

[0002]

2. Description of the Related Art A so-called oxide high-temperature superconductor whose critical temperature exceeds liquid nitrogen temperature, represented by Y-type, Bi-type, and Tl-type, is made into a wire material and is made into a conductor to be a power application conductor such as a magnet, a coil, or a current lead. Attempts have been made to use it as.

The most common of these attempts is the so-called powder-in-tube method in which the powder of these oxide superconductors is filled in a metal sheath material such as silver and the diameter is reduced. There is a wire rod manufacturing technology. This method has great advantages over other methods in terms of workability in forming a wire and electromagnetic stability of the wire.

However, with the single-core tape wire obtained by the powder-in-tube method, a high Jc value can be obtained but only a low Ic value can be obtained, and the Jc value varies greatly depending on the direction of the applied magnetic field. There was also a problem of orientation. In order to solve these problems, the following jelly roll type multi-layer wire is manufactured.

That is, a silver box-shaped buret is filled with pre-baked powder to form a composite material, which is rolled to a predetermined thickness to produce a composite sheet, and then the composite sheet is applied to a silver core material to a predetermined thickness. After wrapping only one layer, insert into a silver pipe.
After that, both ends of this silver pipe are sealed with silver lids to form a composite buret, and this composite buret is drawn into a composite multilayer wire rod by drawing such as swaging and drawing, and heat-treated to obtain a superconducting wire rod.

[0006]

However, in the above-mentioned method for producing a composite multi-layer wire, the superconducting property of the wire after heat treatment may be deteriorated due to the oil and water attached during processing. This tendency is particularly remarkable in the production of long wires. Further, since the composite sheet is obtained by rolling the composite material, work hardening occurs and it is difficult to wind the composite core material.

The present invention has been made as a result of extensive studies in view of the above problems of the prior art.
It is an object of the present invention to provide a method for producing a Bi-based oxide superconductor which is capable of producing a long wire or coil having excellent superconducting properties and is excellent in workability.

[0008]

According to the present invention, a composite sheet of an oxide superconductor and silver is wrapped around a silver core material, inserted into a silver buret, and then subjected to diameter reduction processing to form a composite multilayer wire material. In the method for manufacturing a composite multilayer wire rod, the composite sheet is heat-treated at least once at 650 ° C. to 800 ° C. before the heat treatment of the composite multilayer wire rod.
The heat treatment of this composite sheet is preferably performed in an oxygen atmosphere, a nitrogen atmosphere, or a mixed atmosphere thereof.

The reason for setting the lower limit of the heat treatment temperature to 650 ° C. in the present invention is to take work hardening of silver. That is,
To obtain work hardening of silver, the melting point of silver is 960 ° C (1233
K) or less and about ⅔ of its melting point, 549 ° C. (822
This is because a temperature of K) or higher is desirable. The reason why the upper limit of the heat treatment temperature is set to 800 ° C. is that the final heat treatment temperature of the Bi (2223) -based superconductor is 840 ° C. to 860 ° C.
The final heat treatment temperature of the i (2212) series superconductor is 880.
Since it is ℃ -910 ℃, 800 ℃ during buret making
This is because heat treatment at a higher temperature is not desirable.

Further, in the present invention, the atmosphere during the heat treatment is
The reason why a nitrogen atmosphere, an oxygen atmosphere, or a mixed atmosphere thereof is desirable is to avoid water and carbon in the air.

[0011]

In the method for producing a Bi-based oxide superconductor according to the present invention, the composite sheet of oxide superconductor and silver is heat-treated at least once at 650 ° C. to 800 ° C. before the final heat treatment of the composite multilayer wire. It is possible to remove oil and water that are attached during processing. Further, if the heat treatment of the composite sheet is performed in an oxygen atmosphere, a nitrogen atmosphere, or a mixed atmosphere thereof, it is possible to avoid moisture and carbon in the air, and it becomes easier to remove oil and moisture. Further, if heat treatment is performed before winding the composite sheet around the silver core material, the heat treatment eliminates the work hardening of silver and facilitates the spiral winding of the composite sheet around the silver core material.

[0012]

EXAMPLES The present invention will be specifically described below based on examples.

(Example 1) Bi ₂ O ₃ , SrCO ₃ , C
Raw material powders of aCO ₃ and CuO are Bi: Sr: Ca:
Cu was mixed and mixed so that the atomic ratio was 2: 2: 1: 2, and then the mixed powder was calcined in the air at 800 ° C. for 50 hours, and then the pulverized calcined powder was again heated at 800 ° C., 50 It was calcined for a period of time and then used as a calcined powder having an average particle size of 5 μm. This calcinated powder has an external shape of width 30 mm and length 100 m.
m, depth 10 mm, and thickness 5 mm were filled in a silver box-shaped buret to obtain a composite material. Then roll this composite,
A composite sheet having a thickness of 0.35 mm and a width of 40 mm was prepared. This composite sheet is placed in an atmosphere of 25% oxygen and 75% nitrogen for 7 days.
It heat-processed at 50 degreeC for 5 hours. This heat-treated composite sheet was wrapped around a silver core material having an outer diameter of 12 mm for 11 layers, and then inserted into a silver pipe having an outer diameter of 25 mm and an inner diameter of 20 mm, and again in an atmosphere of 25% oxygen and 75% nitrogen at 750 ° C. for 5 hours. Heat treated. Next, after sealing both ends of the silver pipe with silver lids, an outer diameter of 3
mm composite multilayer wire.

Next, the following heat treatment was performed on the composite multilayer wire having a length of 1 m. That is, after the melting temperature of the Bi-based superconductor was held at 885 ° C. for 10 minutes, 0.3
It was cooled to 850 ° C. at a rate of ° C./h and kept at this temperature for 50 hours.

The Jc value of the composite multilayer wire obtained by the above heat treatment was measured. As a result, 77K,
Jc = 1.5 × 10 ⁴ A / cm ² , 77K, 0.
At 1T, a high Jc value of Jc = 1.1 × 10 ⁴ A / cm ² was exhibited. In addition, the cross-sectional shape of the composite multi-layer wire material well retained the multi-layer spiral structure.

Comparative Example 1 The same composite sheet as in Example 1 was wound around the silver core material as it was without heat treatment and inserted into a silver pipe. At this time, since the composite sheet is not heat-treated, the silver sheet portion forming the composite sheet remains work-hardened. Therefore, it is difficult to wind the composite sheet in a tightly contacted state, and the wound composite sheet has a gap and the shape is greatly distorted. Therefore, in order to insert into the same silver pipe as in Example 1,
It was necessary to wind the composite sheet around the silver core material in nine layers, which is less than in the case of Example 1.
Then, the silver pipe having the composite sheet inserted therein was subjected to wire drawing in the same manner as in Example 1 without heat treatment. At this time, wire breakage occurred frequently, but the wire was drawn to an outer diameter of 3 mm to obtain a composite multilayer wire material. The composite multilayer wire having a length of 1 m was subjected to the same heat treatment as in Example 1, and Jc similar to that in Example 1 was performed.
Values were measured.

The Jc value of the composite multilayer wire of this comparative example is Jc = 0.5 × 10 ⁴ A / cm ² , 7 at 77K and 0T.
At 7K and 0.1T, Jc = 0.1 × 10 ⁴ A / cm ² , showing a low Jc value. Further, the cross-sectional shape of the composite multi-layer wire material was greatly distorted.

[0018]

As described above, according to the method for producing a Bi-based oxide superconductor of the present invention, the composite multilayer wire is 650 ° C. to 800 ° C. at least once before the final heat treatment.
Since the composite sheet of the oxide superconductor and silver is heat-treated, the oil and water attached to the composite sheet during processing can be removed. Further, if the heat treatment is performed in an oxygen atmosphere, a nitrogen atmosphere, or a mixed atmosphere thereof, it is possible to avoid moisture and carbon in the air, so that it is easier to remove oil and moisture adhered during processing. . Further, if heat treatment is performed before winding the composite sheet around the silver core material, the work hardening of silver is eliminated, so that the composite sheet can be easily spirally wound around the silver core material. Therefore, according to the method for producing a Bi-based oxide superconducting wire of the present invention, it is possible to easily produce a Bi-based oxide superconducting wire having a high Jc value.

Claims (3)

[Claims] 1. A Bi-based oxidation in which a composite sheet of a Bi-based oxide superconductor and silver is wrapped around a silver core material, inserted into a silver buret, and then subjected to diameter reduction processing to form a composite multilayer wire material, and the composite multilayer wire material is heat-treated. In the method for producing a superconducting wire, the composite multi-layer wire is heated at least once before heat treatment.
A method for producing a Bi-based oxide superconducting wire, comprising heat-treating the composite sheet at 0 ° C to 800 ° C. 2. The method for producing a Bi-based oxide superconducting wire according to claim 1, wherein the heat treatment of the composite sheet is performed in an oxygen atmosphere, a nitrogen atmosphere, or a mixed atmosphere thereof. 3. The method for producing a Bi-based oxide superconducting wire according to claim 1 or 2, wherein the heat treatment of the composite sheet is performed before winding around the silver core material.