JPH1050151A - Compound superconductive wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily process a wire material and stably produce oxide superconductive wire material with stable properties by producing a superconductive wire material constituted of an oxide superconductor and a sheath material of silver or a silver alloy surrounding the superconductor. SOLUTION: As raw materials to constitute an oxide superconductor, materials to produce a lamella perovskite oxide superconductor, for example, La, Y, Sc, M, Cu single elements or oxides, are used and these elements or oxides are mixed in stoichiometric ratios to give raw materials 2. The raw materials are buried in the inside of a sheath member 3 made of silver or an alloy mainly containing silver and the diameter of the resultant member 3 is decreased by a method such as extrusion method to give a wire material with a desired diameter. Then, the wire material is heated and the raw materials 2 packed in the inside of the member 3 are converted into a continuous compound superconductor 1. Consequently, a compound type superconductor wire of a lamella perovskite type oxide superconductor with high critical temperature can be stably produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compound superconducting wire, and more particularly to a structure of a compound superconducting wire using an oxide superconductor.

[0002]

2. Description of the Related Art As a compound superconductor, a metallic A15 is used.
A type belonging to a crystal structure such as a type, a B1 type, a Chevrel type, a Laves type, or an oxide ceramic type perovskite type or a layered perovskite type is known. Among these, a layered perovskite-type oxide superconductor represented by La-Ba-Cu-O system has a critical temperature of 30K or more, and a perovskite such as Y-Ba-Cu-O system, layered perovskite, etc. An oxide superconductor composed of multiple phases is a very promising material because a material having a critical temperature exceeding 90 K can be obtained. However, these oxide superconductors have heretofore been produced only in the form of pellets obtained by sintering. In addition, when the application of a superconducting magnet or the like is considered, it is necessary to use a superconductor as a wire.

[0003] By the way, in order to make such an oxide superconductor into a wire, for example, copper or a copper alloy, which is usually used as a stabilizer for a conventional superconducting wire such as Nb ₃ Sn or NbTi, is used. It is conceivable that the oxide superconductor is formed in a copper sheath by using it as a sheath material.

However, according to various experiments conducted by the present inventors, when a copper sheath material is used, the oxide superconductor may not be at a predetermined level depending on the degree of preparation of the oxide superconductor raw material, heat treatment conditions, and the like. Due to the stoichiometric ratio required to exhibit the superconducting properties of oxygen, oxygen may be in a shortage form, and as a result, it is difficult to obtain an oxide superconducting wire having stable properties stably. There is a problem that there is.

[0005]

As described above, the oxide superconductor is a very promising material, but it is difficult to process it into a wire, and even if a copper sheath or the like is used, it has stable characteristics. However, it is difficult to stably obtain an oxide superconducting wire having the following problems, and it has been difficult to apply it to a superconducting magnet or the like.

Accordingly, an object of the present invention is to provide a compound superconducting wire which can be easily processed into a wire or the like and can stably obtain an oxide superconducting wire having stable characteristics.

[0007]

According to the present invention, there is provided a compound superconducting wire having an oxide superconductor and a sheath material made of silver or a silver alloy surrounding the oxide superconductor. Features.

The compound superconducting wire of the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view of a wire showing respective steps for illustrating an example of a manufacturing process of the compound superconducting wire of the present invention.

As raw materials for constituting the oxide superconductor of the present invention, for example, La-Sr-Cu-O, La-B
Layered perovskite type represented by a-Cu-O type (L
a _1-x M) ₂ CuO ₄ (M; Ba, Sr, Ca) as well as a continuous oxide superconductor such as Y—Ba—Cu—O or Sc—Ba—Cu—O Anything is fine. For example, La, Y, Sc, M, Cu alone or an oxide, or a carbonate, a nitrate, a hydroxide, or the like, which is converted into an oxide by heating, is used by mixing them in a stoichiometric ratio. It can be used as a raw material. A mixture obtained by calcining and pulverizing this mixture may be used as a raw material.

This raw material is embedded in a sheath material made of silver or an alloy mainly composed of silver (first step: first step).
Figure) (a)). Silver or silver alloy has low electric resistance,
It has excellent thermal conductivity, and this sheath material becomes a stabilizing material when a superconducting wire is formed. The form of the raw material to be embedded may be a powder or a linear form. For example, La, B
The respective metal lines of a and Cu can be buried at the same time.

Next is a second step. Here, the member obtained in the first step is subjected to surface reduction by a method such as extrusion, swaging, or drawing to obtain a wire having a desired wire diameter (FIG. 1 (b)). The form of the superconducting wire is not limited to a circular cross section, and various forms such as a ribbon shape can be considered.

Next is a third step. In this step, the second
The member subjected to the surface reduction processing to the desired wire diameter in the step is subjected to a heat treatment, and the raw material filled in the sheath material is made into a continuous compound superconductor (FIG. 1 (c)). This heat treatment temperature can be appropriately set so that an oxide superconductor can be formed, but the melting point of the sheath material becomes a substantial upper limit temperature. Although the lower limit is not particularly set, a temperature of 500 ° C. or higher is practically required to form an oxide superconductor.

The single core wire including one superconductor in the sheath material serving as the stabilizing material has been described above, but a plurality of holes may be provided in the sheath material to embed the raw materials in each. A multi-core wire may be configured by bundling a plurality of them and reassembling them into the stabilizing material.

In the present invention, Ag (silver) is used as the sheath material.
Alternatively, since an Ag (silver) alloy is used, Ag easily diffuses oxygen and Ag itself is not easily oxidized, so that sufficient oxygen can be supplied to the raw material from the outside during the heat treatment. Therefore, the following operation and effect can be obtained as compared with the case where copper or the like is used as the sheath material.

That is, when copper or the like is used as the sheath material, the stoichiometric ratio required for the oxide superconductor to exhibit the predetermined superconducting characteristics depends on the degree of preparation of the raw materials, the heat treatment conditions, and the like. In some cases, oxygen may be insufficient. However, when silver or a silver alloy is used, since silver easily diffuses oxygen and silver itself is hardly oxidized, sufficient oxygen can be supplied to the raw material from the outside during the heat treatment, and the above-described problem occurs. Absent.

Furthermore, in order to supply sufficient oxygen to the raw material, a part of the sheath material is deleted along the longitudinal direction of the wire so that the raw material can be brought into contact with an external oxidizing atmosphere during the heat treatment ( (Fig. 2).

When a sheath made of silver or a silver alloy is used as described above, the heat treatment is preferably performed at about 500 to 940 ° C. in an oxidizing atmosphere such as an oxygen atmosphere or the air. If the heat treatment temperature is too low, diffusion of oxygen is slow, and if the heat treatment is too high, the material is easily deformed.

[0018]

Embodiments of the present invention will be described below.

Embodiment 1 La, Sr, and Cu were added to an Ag sheath material (La _0.9 S
Raw materials mixed at a ratio so as to become a layered perovskite-type oxide superconductor represented by a composition formula of r _0.1 ) ₂ CuO ₄ were filled, and the end of the sheath material was closed. Then, after thinning by surface reduction processing, the resultant was subjected to an oxidizing heat treatment in the atmosphere at 700 ° C. for 7 days. As a result, a lamellar perovskite-type oxide superconductor represented by a composition formula of (La _0.9 Sr _0.1 ) ₂ CuO ₄ was obtained. A continuum was created inside the sheath material.

The critical temperature was 35 K, and the critical current was 10 A, showing good characteristics.

Embodiment 2 A superconducting wire was manufactured in the same manner as in Embodiment 1 except that Ba was used instead of Sr.

The critical temperature was 29 K and the critical current was 5 A, showing good characteristics.

Embodiment 3 A superconducting wire was manufactured in the same manner as in Embodiment 1 except that Ca was used instead of Sr.

The critical temperature was 29 K and the critical current was 5 A, showing good characteristics.

Embodiment 4 Instead of La, Sr, and Cu in Embodiment 1, Y, B
a and Cu were mixed at a ratio of (Y _0.4 Ba _0.6 ) CuO ₃ to produce a superconducting wire in the same manner.

The critical temperature was 96 K, and the critical current was 10 A, showing good characteristics.

Embodiment-5 Instead of La, Sr, and Cu in Embodiment 1, (Y _0.9
Ba _0.1) such that the ratio of CuO ₃ Y ₂ O _3, Ba
O and CuO were mixed and a superconducting wire was similarly manufactured.

The critical temperature was 80 K and the critical current was 12 A, showing good characteristics.

[0029]

As described above, according to the present invention, a compound superconducting wire using a layered perovskite type oxide superconductor having a high critical temperature can be stably obtained, and a superconducting magnet or the like can be obtained. It greatly contributes to the application of.

[Brief description of the drawings]

FIG. 1 is a sectional view of a superconducting wire of the present invention.

FIG. 2 is a cross-sectional view of the superconducting wire of the present invention.

[Explanation of symbols]

 1 ... superconductor 2 ... raw material 3 ... sheath material

Claims (5)

[Claims] 1. A compound superconducting wire comprising an oxide superconductor and a sheath made of silver or a silver alloy surrounding the oxide superconductor. 2. The oxide superconductor comprises La, Y and Sc.
The compound superconducting wire according to claim 1, wherein at least one of Ba, Sr, and Ca, and Cu and O are constituent elements. 3. The compound superconducting wire according to claim 1, wherein said oxide superconductor has a layered perovskite crystal structure. 4. The compound superconducting wire according to claim 1, wherein a part of the sheath material is deleted along a longitudinal direction of the wire material. 5. The compound superconducting wire according to claim 1, wherein said wire has a substantially circular or ribbon-shaped cross section.