JPH10149729A - Oxide superconductive wire rod and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the critical current density of the whole of a wire material by forming a cross sectional area of a core of an oxide superconductive wire arranged at a center or an inner peripheral side larger than that of a core of an oxide superconductive wire arranged outside. SOLUTION: Periphery of a core 1, which is formed of an oxide superconductor, is coated with the metal sheath material 2 so as to form an oxide superconductive wire 23 having a hexagonal or circular cross section. At the same time, several kinds of oxide superconductive wires 3b, 3c having a different core ratio from each other are manufactured. At this stage, core ratio is set small in order of wires 3a, 3b, 3c so that the wire 3a has the maximum core ratio. To the case where cross sectional area of the core 1 of the wire 3a is set at 100, cross sectional area of the core 1 of the wire 3c is set at 50-85. An oxide superconductive wire bundle is inserted into a metal sheath material 4 so as to manufacture a multi-core billet 5, and diameter thereof is reduced so as to manufacture an oxide superconductive multi-core material 7. With this structure compressive stress is evenly applied to the whole of the oxide superconductive wire rod, and the oxide superconductors having the even shape are distributed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxide superconducting wire, and more particularly to an oxide superconducting wire used for a coil, a power supply conductor, and a power transmission conductor.

[0002]

2. Description of the Related Art As a typical method for producing an oxide superconducting wire (for example, an oxide superconducting element wire or an oxide superconducting multifilamentary wire), there is a metal-coating method (powder-in-tube method).

In the metal coating method, first, an oxide superconducting powder prepared in advance (including a powder which becomes an oxide superconductor by performing an appropriate heat treatment) is coated with a metal sheath material (Ag sheath) of an appropriate size. (Often used) to form a billet having a core inside.

[0004] The billet is subjected to mechanical processing such as extrusion, drawing, and rolling to form a predetermined wire shape. Thereafter, the wire is subjected to a heat treatment to produce an oxide superconducting wire. At this time, if necessary, mechanical processing and heat treatment may be repeatedly performed after the heat treatment.

In the case of a multifilamentary wire, a multifilamentary billet is formed by inserting a large number of wires obtained by performing the above-mentioned mechanical processing into a pipe-shaped metal sheath material to form a multifilament billet.
After mechanical processing is again performed to obtain a predetermined wire shape, heat treatment is performed to produce an oxide superconducting multi-core wire.

FIG. 2 is a cross-sectional view of a conventional oxide superconducting wire.
Shown in FIG. 2A shows an example of a cross-sectional view of a multifilament billet for forming an oxide superconducting wire, and FIG.
FIG. 2C shows another example of a cross-sectional view of a multifilament billet for forming an oxide superconducting wire, FIG. 2C shows a cross-sectional view of an oxide superconducting multicore wire, and FIG. Shows a cross-sectional view of a rectangular oxide superconducting multi-core wire, and FIG. 2 (e) shows a cross-sectional view of a tape-shaped oxide superconducting multi-core wire.

As shown in FIG. 2 (a), the oxide superconducting multifilamentary wire has a core 21 covered with a metal sheath material 22 and has a regular hexagonal cross section. 23 are bundled (usually often arranged so as to form a hexagon) and then inserted into a metal sheath material (often using an Ag sheath) 24 having a predetermined inner diameter. The core billet 25 is manufactured, and mechanical processing such as wire drawing and / or rolling is performed on the multi-core billet 25 to obtain a predetermined wire rod as shown in FIGS. 2 (c), (d) and (e). It is formed into a shape, and finally, the multifilamentary wire is subjected to a heat treatment to be manufactured.

As shown in FIG. 2B, a large number of oxide superconducting wires 33 having a round cross section are bundled concentrically and then inserted into a metal sheath material 34 having a predetermined inner diameter. An oxide superconducting multi-core wire may be manufactured using the multi-core billet 35 manufactured as described above.

As shown in FIGS. 2 (c), (d) and (e), the oxide superconducting multifilamentary wire is formed by mechanical processing into a round oxide superconducting multifilamentary wire 27, a rectangular oxide superconducting multifilamentary wire. The core wire 28, the tape-shaped oxide superconducting multi-core wire 29 and the like are formed.

Oxide superconducting multi-core wires 27, 28, 29
Has a structure in which the oxide superconductors 21c, 21d, 21e are dispersed in the metal matrices 26c, 26d, 26e.

The heat treatment of the oxide superconducting wire is performed by Nb ₃ Sn
In many cases, the heating is performed at a higher temperature (800 to 900 ° C.) and in an oxygen atmosphere than a wire using a metal-based compound superconducting wire. For this reason, considering the reactivity with the oxide superconductor as the metal base material to be composited with the oxide superconductor, A
g or Ag alloy, Au or Au alloy, or the like is often used.

Here, the oxide superconducting wire is a brittle material as apparent from the fact that the oxide superconductor is a kind of ceramic. For this reason, there is a problem that the oxide superconducting wire or the conductor is brittle against mechanical strain such as bending or tension applied to the conductor. Therefore, in recent years, in consideration of characteristics against mechanical strain, a metal sheath material that is composited with an oxide superconductor such as an Ag sheath is alloyed and strengthened, or a multi-core structure is becoming mainstream.

Further, products using an oxide superconducting wire (for example, a coil or the like) are often manufactured by a method of winding a wire and then performing a heat treatment (so-called wind & react method). In this case, since the heat treatment conditions are severe, ordinary organic insulating materials cannot be used,
A heat-resistant insulating material such as a ceramic paper (for example, alumina paper) or a ceramic fiber (for example, alumina fiber or glass fiber) braid is used.

Here, in the heat treatment of long wires by the wind & react method, if the wires are in contact with each other, the wires will fuse together during the heat treatment. Countermeasures are taken such as winding or winding an insulating material such as ceramic paper or ceramic fiber braid between wires as a spacer.

The oxide superconductor has a crystal plane through which current can easily flow and a crystal axis direction through which current does not easily flow, and has a very strong two-dimensional property from the electrical characteristics and crystal structure. When an oxide superconductor is used as a wire, it is often used as a polycrystalline body. Therefore, the bonding property between crystal planes through which a current easily flows (hereinafter referred to as the bonding property between crystals) determines superconducting characteristics. It is an important factor.

Here, in order to improve the bondability between crystals, it is a necessary condition that a plate-like crystal having a strong two-dimensional property is oriented, and the bondability of the crystal and the crystal orientation are synonymously expressed. Often. It has been found that there is a correlation between the crystal orientation and the critical current density Jc.

An oxide superconducting wire produced by a metal coating method typified by an Ag sheath method is generally formed into a tape by performing a drawing process followed by a rolling process. The reason for forming into a tape shape is to improve the crystal orientation in consideration of the characteristics of the oxide superconductor as described above. Also, it has been found that there is a correlation that if the thickness of the core made of the oxide superconductor in the oxide superconducting wire is large, the crystals are unlikely to be oriented.

As a method for producing a multifilament billet for forming a multifilamentary oxide superconducting wire, as shown in FIG. 2A, a number of hexagonal oxide superconducting wires 2 having a hexagonal cross section are used.
In general, a multifilament billet 25 is manufactured by bundling 3 in a hexagonal shape (honeycomb shape) and inserting the hexagonal oxide superconducting element bundle into a metal sheath material 24.

[0019]

However, since this hexagonal oxide superconducting wire bundle is inserted into the metal sheath material 24, it is inevitable between the outermost periphery of the oxide superconducting wire bundle and the metal sheath material 24. Large gaps occur in this is,
The same applies to a multifilament billet 35 produced by bundling oxide superconducting element wires 33 having a round cross section concentrically and inserting the concentric oxide superconducting element bundle into a metal sheath material 34.

A multi-core billet 25 having a round cross section formed by subjecting a multi-core billet 25 having a gap between the outermost periphery of the oxide superconducting element bundle and the metal sheath material 24 to a diameter reduction process. In this case, since the amount of deformation of the oxide superconducting element wire 23 is larger at the outer peripheral part than at the central part of the oxide superconducting element bundle, as shown in FIG. The shape of the oxide superconductor 21c in the portion is easily disturbed.

Since the disorder of the shape of the oxide superconductor 21c in the outer peripheral portion of the oxide superconducting multi-core wire 27 leads to a decrease in crystal orientation, the oxide superconducting multi-core wire 27 having a round cross section has the following characteristics. There has been a problem that the critical current density Jc at the outer peripheral portion is low and the critical current density Jc at the central portion is high, causing variations.

In the case of rectangular or tape-shaped oxide superconducting multi-core wires 28 and 29 formed by subjecting a multi-core billet to a diameter reduction process and a rolling process, a portion in contact with a rolling roll (not shown) Is subjected to compressive stress, and the thickness of the oxide superconductors 21d and 21e in that portion is reduced. However, since a flow that is not compressive stress but tends to spread in a direction perpendicular to the compression direction occurs in a portion that is not in contact with the rolling roll, as shown in FIGS. The thickness of the superconductors 21d and 21e remains large.

In the case of such a rectangular or tape-shaped oxide superconducting multifilamentary wire 28 or 29, the critical current density Jc is high in the thin portion of the oxide superconductor at the center of the wire,
Since the critical current density Jc is low in the portion where the thickness of the oxide superconductor is large at both ends in the width direction of the wire (the left and right ends in the figure), there is a problem that a uniform current does not flow through the entire wire.

That is, the critical current density Jc of the entire wire does not increase, and a magnetic field (magnetic field strength and homogeneity) as designed does not occur in an oxide superconducting conductor such as a coil manufactured using these oxide superconducting wires. There was such a problem.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an oxide superconducting wire in which a uniform current flows through the entire wire and the critical current density of the entire wire is high.

[0026]

In order to solve the above-mentioned problems, an invention according to claim 1 is an oxide comprising a plurality of cores made of an oxide superconductor arranged in a metal matrix in a hexagonal or concentric shape. In the superconducting wire, the cross-sectional area of the core of the oxide superconducting wire on the center or inner peripheral side is larger than the cross-sectional area of the core of the oxide superconducting wire on the outer side.

According to a second aspect of the present invention, when the sectional area of the core of the oxide superconducting element wire at the center or the innermost periphery is 100,
The cross-sectional area of the outermost core of the oxide superconducting element wire is 50 to
2. The oxide superconducting wire according to claim 1, wherein a difference is provided in the radial direction so as to be 85.

According to a third aspect of the present invention, there is provided the oxide superconducting wire according to any one of the first and second aspects, wherein the cross-sectional shape of the oxide superconducting wire is round.

According to a fourth aspect of the present invention, there is provided the oxide superconducting wire according to the third aspect, wherein the oxide superconducting wire is subjected to a rolling process so that a cross-sectional shape thereof is tape-shaped or rectangular.

According to a fifth aspect of the present invention, a multifilament billet is formed by inserting a large number of oxide superconducting wires whose cores are made of an oxide superconductor and hexagonally or concentrically inserted into a pipe-shaped metal sheath material. In a method for producing an oxide superconducting wire, in which a multifilament billet is subjected to mechanical working to form a predetermined wire shape and then subjected to a heat treatment, the cutting of the core of the oxide superconducting wire at the center or inner peripheral side is performed. A multi-core billet is formed by arranging a number of the above-mentioned oxide superconducting wires so that the area thereof is larger than the cross-sectional area of the above-mentioned core of the above-mentioned oxide superconducting wires.

The reason for limiting the above numerical range will be described below.

When the cross-sectional area of the core of the central or innermost oxide superconducting element wire is 100, the difference in the radial direction is such that the cross-sectional area of the core of the outermost oxide superconducting element wire is 50 to 85. The reason is that when the cross-sectional area of the core of the outermost oxide superconducting element wire is larger than 85, the stabilizing material coated around the core during diameter reduction or rolling with large deformation This is because the metal matrix cannot absorb all the deformation, and the shape of the core is disturbed. Further, when the cross-sectional area of the core of the outermost oxide superconducting element wire is smaller than 50, the core ratio (oxide superconductor ratio) of the entire oxide superconducting wire is excessively reduced, and the critical current density Jc of the entire wire is reduced. This is because it becomes smaller.

According to the above configuration, since the cross-sectional areas of the respective cores have a difference in the radial direction, the respective cores have a substantially uniform shape.
An oxide superconducting wire can be obtained in which a uniform current flows through the entire wire and the critical current density of the entire wire is high.

[0034]

Embodiments of the present invention will be described below.

As described above, a large gap is formed between the hexagonal or concentrically arranged oxide superconducting element bundle and the metal sheath material. Alternatively, when rolling was performed, the amount of deformation (compressive stress) was greater in the oxide superconducting element wire at the outer peripheral portion in the oxide superconducting element bundle.

The present inventors have paid attention to the difference in fluidity with respect to hardness and deformation between the stabilizer (metal matrix) coated around the core of the oxide superconducting element wire and the oxide superconductor as the core. .

Since the stabilizing material is a metal, it is soft (Vickers hardness: about 90) and easily deformed by an external force. However, since the oxide superconductor is a ceramic, it is hard (Vickers hardness: about 120) and is hardly deformed by an external force. If it is forcibly deformed, the shape of the core is easily disturbed.

Therefore, by increasing the ratio of the stabilizing material (the core ratio in the oxide superconducting element wire) to the outer peripheral portion of the oxide superconducting element bundle in the oxide superconducting element bundle,
It has been found that a large amount of deformation can be absorbed by the stabilizing material and the shape of the core can be stabilized.

The oxide superconducting wire of the present invention is obtained by disposing a metal matrix (for example, Ag) around each oxide superconductor having a substantially uniform shape.

The oxide superconductor is not particularly limited, and examples thereof include Y-Ba-Cu-O-based, La-B
a-Cu-O system (La is a lanthanum series element), Bi-
(Pb) -Sr-Ca-Cu-O, Tl- (Pb)-
Ba-Sr-Ca-Cu-O system, Hg-Ba-Sr-C
a-Cu-O type and the like.

Examples of the metal matrix include Ag and Ag alloys, Ag and Ag alloys coated with Ag alloys having different compositions, other metals, oxides, or composites of metals and oxides. Ag alloys, other metals, oxides, or composites of metals and oxides with different compositions are arranged inside the Ag alloy and Ag alloys. Ag alloys, other metals with different compositions inside Ag and Ag alloys , An oxide, or a composite of a metal and an oxide. Needless to say, Au may be used instead of Ag as appropriate.

The shape of the oxide superconducting wire is round,
Examples include a rectangular shape, a tape shape, and a pipe shape.

As the type of the oxide superconducting wire, an oxide superconducting multi-core wire, various oxide superconducting multi-core wires are assembled,
Laminated or composite ones, and those obtained by further multiplying each oxide superconducting multi-core wire rod and the like are included.

FIG. 1 shows a cross-sectional view of the oxide superconducting wire of the present invention. FIG. 1A shows an example of a cross-sectional view of a multifilament billet for forming an oxide superconducting wire.
FIG. 1B shows another example of a cross-sectional view of a multifilament billet for forming an oxide superconducting wire, and FIG. 1C shows a cross-sectional view of the oxide superconducting multifilament wire. (D) shows a cross-sectional view of the rectangular oxide superconducting multi-core wire, and FIG.
Shows a cross-sectional view of a tape-shaped oxide superconducting multi-core wire.

As shown in FIGS. 1A and 1B, the outer periphery of a core 1 (11) made of an oxide superconductor is covered with a metal sheath material (metal matrix) 2 (12) to form a hexagonal cross section. A shape or round oxide superconducting element wire 3a (13a) is produced. At the same time, several kinds (two kinds in the figure) of oxide superconducting wires 3b, 3c... (13b, 13c...) Having different core ratios (core sectional area / oxide superconducting wire sectional area) are also produced. At this time, the oxide superconducting wires 3a (13a) are maximized so that the core ratio of the oxide superconducting wires 3a (13a) is maximized.
a), the oxide superconducting element wire 3b (13b), the oxide superconducting element wire 3c (13c),...

Thereafter, the oxide superconducting element wire 3a (13a)
And six oxide superconducting wires 3b (13b) around the oxide superconducting wires 3a (13a), and a large number of oxide superconducting wires 3c (13c) Book) to be arranged in a hexagonal or concentric shape. At this time, the cross-sectional area of the core 1 of the central or innermost oxide superconducting element wire (the oxide superconducting element wire 3a (13a) in the figure) is set to 1
00, the cross-sectional area of the core 1 of the outermost oxide superconducting element wire (the oxide superconducting element wire 3c (13c) in the figure) is 5
0 to 85.

The hexagonal or concentric oxide superconducting element bundle is inserted into the metal sheath material 4 (14) to produce a multi-core billet 5 (15).

The multi-core billet 5 is subjected to a diameter reducing process,
As shown in FIG. 1C, the round oxide superconducting multi-core wire 7
Is prepared.

Further, the rectangular oxide superconducting multifilamentary wire 8 or the tape-shaped oxide superconducting multifilamentary wire 9 shown in FIGS. 1D and 1E is the round oxide superconducting wire shown in FIG. 1C. A wire having a form such as the multifilament wire 7 is formed by drawing or rolling a rectangular die.

Also in the method for manufacturing an oxide superconducting wire of the present invention, a large compressive stress is applied to the outer peripheral portion or both ends in the width direction of the oxide superconducting wire, and a small compressive stress is applied to the central portion of the oxide superconducting wire. .

However, the core ratio of the oxide superconducting wire at the outer peripheral portion or both ends in the width direction of the oxide superconducting wire is
The core ratio of the oxide superconducting wire at the center of the oxide superconducting wire is smaller than that of the oxide superconducting wire, so that the amount of deformation absorption at the outer peripheral portion or both ends in the width direction of the oxide superconducting wire is increased.

As a result, a uniform compressive stress is applied to the entire oxide superconducting wire, resulting in a structure in which the oxide superconductor having a substantially uniform shape is dispersed in the oxide superconducting wire.

That is, according to the method for producing an oxide superconducting wire of the present invention, the criticality is determined at the outer peripheral portion of the round oxide superconducting multifilamentary wire, and at both ends in the width direction of the rectangular / tape-shaped oxide superconducting multifilamentary wire. A uniform current flows through the entire wire without lowering the current density Jc, and the critical current density Jc (Overall Jc) of the entire wire is greatly improved.

[0054]

【Example】

(Example 1) Bi ₂ Sr ₂ Ca ₁ Cu ₂ O prepared in advance
_X oxide superconducting powder was mixed with three kinds of Ag pipes (pipe A: outer diameter 15 mm, inner diameter 13 mm, pipe B: outer diameter 15
mm, inner diameter 12.5 mm, pipe C: outer diameter 15 mm, inner diameter 12 mm) at a packing density of 1.65 g / cm ³ . Thereafter, each Ag pipe is subjected to cold drawing to form an outer diameter of 2.57 mm, and three types of wires having different oxide superconducting core ratios (wire A: core ratio 0.5, wire B: core ratio 0. 45, wire C: core ratio 0.4) is prepared. Table 1 shows the specifications of each wire (wire A, wire B, wire C).

[0055]

[Table 1]

Next, with one wire A as a center, six wires B are arranged around the wire A, and twelve wires C are arranged around a bundle of the wires A and B. A wire bundle consisting of 19 cores is manufactured.

An outer diameter of 15 mm and an inner diameter of 13 mm
Ag alloy (Ag-0.015wt% Mg-0.015wt% Ni)
Insert into a pipe to make a multi-core billet. This multifilament billet is subjected to wire drawing to form a multifilament wire having an outer diameter of 1.00 mm.

Bi ₂ Sr ₂ Ca ₁ Cu was added to this multifilamentary wire.
₂ O _X system characteristic partial melting superconducting wire - Xu cooling heat treatment (heating at a rate of 300 ° C. / hr from room temperature to 884 ° C. →
The oxide superconducting wire (wire D) is prepared by holding at 884 ° C for 10 minutes → gradually cooling from 884 ° C to 834 ° C at a rate of 5 ° C / hr → holding at 834 ° C for 1 hour → furnace cooling) in an oxygen stream. .

At the same time, a wire bundle consisting of wire A having all 19 cores is prepared, and the same process as wire D is performed to prepare an oxide superconducting wire (wire E).

The superconducting properties of the wire D and the wire E were evaluated. Table 2 shows the evaluation results. As an evaluation,
Critical current value Ic at liquid helium temperature (4.2K)
(A), Jc of the whole oxide superconducting wire (hereinafter referred to as Over)
(A / cm ² )), core ratio, average critical current density of the core (hereinafter, average core Jc; (A
/ Cm ² )) and core shape.

The measurement of the critical current value Ic was performed by the usual four-terminal method, and the threshold value of the critical current value Ic was 1 μV / cm. The core ratio was measured by observing the cross section. The core shape is
A core having a good shape was regarded as good, and a core having a poor shape was regarded as bad.

[0062]

[Table 2]

As shown in Table 2, the core ratio of the wire D manufactured by the method of manufacturing an oxide superconducting wire of the present invention is smaller than that of the wire E manufactured by the method of manufacturing a conventional oxide superconducting wire. ing. However, while the core shape of the wire E does not maintain the state at the time of the multifilament billet at all,
The core shape of the wire D substantially maintained the state at the time of the multifilament billet, and was good. Further, the critical current value Ic, the OverallJc, and the average core Jc of the wire D were about twice as large as those of the wire E.

Example 2 (Bi, Pb) prepared in advance
₂ Sr ₂ Ca ₂ Cu ₃ O _X oxide superconducting powder was mixed with three kinds of Ag pipes (pipe F: outer diameter 15 mm, inner diameter 13 m
m, pipe G: outer diameter 15 mm, inner diameter 12.5 mm, pipe H: outer diameter 15 mm, inner diameter 12 mm).
Each is filled with 65 g / cm ³ . Thereafter, each Ag pipe is subjected to cold drawing to form an outer diameter of 2.57 mm, and three types of wires having different oxide superconducting core ratios (wire F: core ratio 0.5, wire G: core ratio 0. 45, wire H;
A core ratio of 0.4) is prepared. Each wire (wire F, wire G,
Table 3 shows the specifications of the wire rod H).

[0065]

[Table 3]

Next, with one wire F as the center, six wires G are arranged around the wire F, and twelve wires H are arranged around the bundle of the wires F and G. A wire bundle consisting of 19 cores is manufactured.

The bundle of wires is made to have an outer diameter of 15 mm and an inner diameter of 13 mm
Ag alloy (Ag-0.015wt% Mg-0.015wt% Ni)
Insert into a pipe to make a multi-core billet. The multifilament billet is subjected to wire drawing to form a multifilament wire having an outer diameter of 1.50 mm.

This multifilamentary wire is cold-rolled to the first stage to form a tape-like multifilamentary wire having a thickness of 0.5 mm and a width of 3 mm. Thereafter, the tape-shaped multifilamentary wire is subjected to a first-stage heat treatment at 840 ° C. for 50 hours in the air using an electric furnace to produce a first oxide superconducting intermediate wire.

After that, the second oxide superconducting intermediate wire is
Step rolling, thickness 0.25mm, width 4.5mm
Then, using an electric furnace, in the air, 840 ℃, 50
A second heat treatment of hr is performed to produce a second oxide superconducting intermediate wire.

Then, the second oxide superconducting intermediate wire is further subjected to third-stage rolling to form a thickness of 0.15 mm and a width of 5.1 mm.
A third-stage heat treatment at 0 ° C. for 50 hours is performed to produce an oxide superconducting wire (wire I).

At the same time, a wire bundle consisting of wire F, all of which have 19 cores, is manufactured, and the same process as wire I is performed to manufacture an oxide superconducting wire (wire J).

The superconducting properties of the wire I and the wire J were evaluated. Table 4 shows the evaluation results. As an evaluation,
Critical current value Ic at liquid nitrogen temperature (77K)
(A), Overall Jc (A / cm ² ), core ratio, average core Jc (A / cm ² ), and core thickness.

The measurement of the critical current value Ic was performed by the usual four-terminal method, and the threshold value of the critical current value Ic was 1 μV / cm. The core ratio and core thickness were measured by observing the cross section.

[0074]

[Table 4]

As shown in Table 4, the wire I produced by the method for producing an oxide superconducting wire of the present invention has a smaller core ratio than the wire J produced by the conventional method for producing an oxide superconducting wire. ing. However, the core thickness of the wire J is 10
While there was a variation of 50 μm, the core thickness of the wire I was 10-20 μm on average. In addition, the critical current value Ic, the Overall Jc, and the average core Jc of the wire I were about three to four times the value of the wire J.

(Example 3) Bi ₂ Sr ₂ C prepared in advance
a ₁ Cu ₂ O _X oxide superconducting powder was mixed with three types of Ag alloy (Ag-10 at% Au) pipe (pipe K: outer diameter 15).
mm, inner diameter 13mm, pipe L: outer diameter 15mm, inner diameter 1
2.5mm, pipe M: outer diameter 15mm, inner diameter 12mm)
Each is filled with a packing density of 1.65 g / cm ³ .
Thereafter, each of the Ag pipes is subjected to cold drawing to form an outer diameter of 2.57 mm.
A type of wire (wire K: core ratio 0.5, wire L: core ratio 0.45, wire M: core ratio 0.4) is prepared. Table 5 shows the specifications of each wire (wire K, wire L, wire M).

[0077]

[Table 5]

Next, with one wire K as the center, six wires L are arranged around the wire K, and 12 wires M are arranged around the bundle of the wire K and the wire L. A wire bundle consisting of 19 cores is manufactured.

This wire rod bundle is formed with an outer diameter of 15 mm and an inner diameter of 13 mm
Into an Ag alloy (Ag-10 at% Au) pipe to produce a multifilament billet. The multifilament billet is subjected to wire drawing to form a multifilament wire having an outer diameter of 1.50 mm.

Next, the multifilamentary wire is subjected to cold rolling to produce a tape-like multifilamentary wire having a thickness of 1 mm and a width of 1.7 mm. Thereafter, the tape-shaped multi-core wire is subjected to a rectangular die drawing process to produce a flat multi-core wire having a thickness of 0.9 mm and a width of 1.6 mm.

Thereafter, Bi ₂ S was added to this rectangular multifilamentary wire.
Partial melting-slow cooling heat treatment characteristic of r ₂ Ca ₁ Cu ₂ O _X -based superconducting wire (heating from room temperature to 884 ° C. at a rate of 300 ° C./hr→holding at 884 ° C. for 10 minutes → 5 from 884 ° C. to 834 ° C.) Slow cooling at a rate of ° C / hr → 834 ° C for 1 hour
(retention → furnace cooling) in an oxygen stream to produce an oxide superconducting wire (wire N).

At the same time, a wire bundle consisting of the wire K with all 19 cores is prepared, and the same process as for the wire N is performed to prepare an oxide superconducting wire (wire O).

The superconducting properties of the wire N and the wire O were evaluated. Table 6 shows the evaluation results. As an evaluation,
Critical current value Ic at liquid helium temperature (4.2K)
(A), Overall Jc (A / cm ² ), core ratio, average core Jc (A / cm ² ), and core shape.

The measurement of the critical current value Ic was performed by the usual four-terminal method, and the threshold value of the critical current value Ic was 1 μV / cm. The core ratio was measured by observing the cross section. The core shape is
A core having a good shape was regarded as good, and a core having a poor shape was regarded as bad.

[0085]

[Table 6]

As shown in Table 6, the core ratio of the wire N manufactured by the method of manufacturing an oxide superconducting wire of the present invention is smaller than that of the wire O manufactured by the method of manufacturing a conventional oxide superconducting wire. ing. However, while the core shape of the wire O does not maintain the state at the time of the multifilament billet at all,
The core shape of the wire rod N almost maintained the state at the time of the multifilament billet, and was good. Also, the critical current value Ic, OverallJc, and average core Jc of the wire N were about twice as large as those of the wire O.

That is, the critical current density Jc in the core of the wire is obtained by the method for manufacturing an oxide superconducting wire according to the present invention.
And an oxide superconducting wire having excellent superconducting properties such as high critical current value Ic of the entire wire and high critical current density Jc of the entire wire.

The oxide superconducting wire obtained by the present invention can be used for a coil, a power supply conductor, a power transmission conductor, and the like. In particular, a coil produced by using the oxide superconducting wire of the present invention generates a magnetic field (magnetic field strength and homogeneity) as designed, so that a NMR (nuclear magnetic resonance) or MRI
This is very useful for magnets requiring high homogeneity, such as (magnetic resonance tomography examination devices).

[0089]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) An oxide superconducting wire in which a uniform current flows through the entire wire and the critical current density of the entire wire is high can be obtained.

(2) Since the core ratio of the oxide superconducting wires forming the oxide superconducting wire is slightly lower than in the conventional case, the workability of various processes is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an oxide superconducting wire of the present invention.

FIG. 2 is a cross-sectional view of a conventional oxide superconducting wire.

[Explanation of symbols]

 1,11 core 2,12 metal sheath material (metal matrix) 3,13 oxide superconducting element wire 4,14 metal sheath material (metal matrix) 6 metal matrix

Claims (5)

[Claims] 1. An oxide superconducting wire in which a number of cores made of an oxide superconductor are arranged in a metal matrix in a hexagonal or concentric manner, wherein said oxide superconducting element wire on the center or inner peripheral side is provided. An oxide superconducting wire, wherein a cross-sectional area of a core is larger than a cross-sectional area of the core of the oxide superconducting element wire in an outer portion. 2. When the sectional area of the core of the oxide superconducting element wire at the center or the innermost periphery is set to 100, the sectional area of the core of the oxide superconducting element wire at the outermost periphery is 50 to 85. 2. The oxide superconducting wire according to claim 1, wherein a difference is provided in a radial direction. 3. The cross-sectional shape of the oxide superconducting wire is:
3. The oxide superconducting wire according to claim 1, which has a round shape. 4. The oxide superconducting wire according to claim 3, wherein the oxide superconducting wire is subjected to a rolling process to have a tape-like or rectangular shape in cross section. 5. A multi-core billet formed by inserting a large number of oxide superconducting wires whose cores are made of an oxide superconductor into a pipe-shaped metal sheath material in a hexagonal or concentric manner. In the method for producing an oxide superconducting wire after subjecting the wire to a predetermined wire shape and subjecting the wire to heat treatment, the cross-sectional area of the core of the oxide superconducting element wire at the center or the inner peripheral side is the outer peripheral portion. A method for producing an oxide superconducting wire, comprising arranging a large number of the oxide superconducting wires so as to be larger than the cross-sectional area of the core of the oxide superconducting wires to form a multifilament billet.