JPH11111081A - Oxide superconducting wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high (n) value, high critical current density and high mechanical strength by surrounding a conductor around which an Ag sheath is arranged, further by a shock absorbing metallic sheath which has high specific resistance and is harder than the Ag sheath and softer than an Ag alloy sheath of an electric wire envelope. SOLUTION: An oxide core 10 is surounded by an Ag sheath 11 and a shock absorbing metallic sheath 12 of Ag-0.1 wt.% Ni, and this is collected by 19 pieces, and a periphery is covered with an Ag alloy sheath 13 of Ag-0.3 wt.% Mg-0.3 wt.% Ni. In the shock absorbing metallic sheath 12, high specific resistance is set to 1-×10<9> Ωm, and hardness is set to 65 Hv, and hardness of the Ag sheath 11 is set to 38 Hv, and hardness of the Ag alloy sheath 13 is set to 95 Hv. The shock absorbing metallic sheath 12 is arranged, and the hardness is reduced inward from the Ag alloy sheath 13, and wire drawing work is facilitated, and a high (n) value is obtained. Separation between the oxide cores is restrained by the shock absorbing metallic sheath 12 having high specific resistance, and a Jc overall is improved, and the Ag shaeth 11 is also arranged, and diffusion of a shock absorbing metallic sheath 12 component to the oxide cores is restrained in heat treatment, and critical current density is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting wire having a cross-sectional structure in which a core wire of an oxide superconductor is surrounded by a coating layer.

[0002]

2. Description of the Related Art Metal-based materials have been known as superconducting materials. Recently, however, oxidation has a higher superconducting transition temperature and a higher upper critical magnetic field (the highest magnetic field capable of maintaining superconductivity) than this metal-based superconducting material. Superconductors have been found. Among the oxide superconductors, for example, Bi-based oxide is 1
It is expected to have an upper critical magnetic field of 00 T or more, and even in a high magnetic field of 21 T or more, 10 ⁵ A /
It is reported that a high current density of cm ² can be obtained. Incidentally, the Nb ₃ Sn wire of the metallic superconducting wire is known as a typical one for a high magnetic field, but even the Nb ₃ Sn wire can be used at a practical level (10 ⁴ A / cm ² ).

[0003] Various applications are expected to take advantage of such features of the oxide superconductor. For example, it has been considered that the oxide superconductor is used as a wire and used as a coil of a strong magnetic field magnet. The obtained oxide superconducting magnet generates a higher magnetic field than a metal-based superconducting magnet using a metal-based superconducting material as a coil.

There is a nuclear magnetic resonance (NMR) analyzer as an analyzer utilizing a high magnetic field. The NMR analyzer is an apparatus capable of determining even the molecular structure of a complicated polymer protein. The higher the value, the greater the amount of information increases, allowing more detailed determination of the molecular structure, and the time required for measurement is reduced.

[0005] As described above, the oxide superconducting wire has a high critical current density (Jc), so that a large current can flow and a strong magnetic field can be generated. Therefore, such an oxide superconducting wire is used. Thus, the production of a superconducting magnet for NMR with higher performance is expected.

However, when a large current is applied under a strong magnetic field, a strong electromagnetic force acts. At this time, the tensile stress acting on the wire is large, for example, several hundred MPa, so that the oxide superconductor itself is easily deformed. This deformation sharply lowers the critical current density.

Therefore, an oxide superconducting wire having sufficient mechanical strength and not being deformed by overcoming the above-mentioned stress has been disclosed in Japanese Patent Application Laid-Open No. Hei 8-
No. 241635 (conventional example). This conventional oxide superconducting wire has an Ag superconductor around a core wire (hereinafter, sometimes referred to as an oxide core).
(Generally pure silver) A double-sheath structure wire in which a sheath is arranged to form a core-sheath structure, and an Ag alloy sheath is further arranged around a bundle of a plurality of unit core wires of the core-sheath structure. The oxide superconducting wire has a high strength by the Ag alloy sheath while preventing the additive element in the Ag alloy sheath from reacting with the oxide superconducting material and causing deterioration of the characteristics by the Ag sheath. This structure achieves high mechanical strength and high critical current density.

A conventional method for manufacturing an oxide superconducting wire is as follows.
Further, the composite is wrapped with an Ag alloy to form a composite, and after the composite is drawn, heat treatment is performed. The heat treatment sinters the raw material powder to form an oxide superconductor.

The superconducting magnet for NMR is required to have high magnetic field stability in addition to the high generated magnetic field as described above. Therefore, a commercially available metal-based superconducting magnet for NMR is operated in a permanent current mode in order to maintain the magnetic field stability for a long time. In this permanent current mode, current is supplied from an external power supply up to a predetermined current,
In this mode, the current continues to flow through the superconducting coil with the power supply removed.

[0010]

In an NMR superconducting magnet using an oxide superconducting wire, the oxide superconducting wire has a high critical current density (Jc), as described above.
In addition to the property of exhibiting high mechanical strength, a property of exhibiting a high n value as described below is required.

The n value is a value corresponding to a slope when the current density and the generated electric field are logarithmically plotted, and is an amount reflecting the longitudinal uniformity of the current distribution in the wire. In other words, the more the cross-sectional structure of the wire, particularly the shape of the oxide core (oxide superconducting material), is uniform in the longitudinal direction, the higher the n value becomes, which is advantageous for the operation in the permanent current mode.

For example, in an oxide superconducting wire (conventional example) in which a plurality of oxide cores are wrapped with an Ag sheath and further wrapped with an Ag alloy sheath, the cross-sectional shape and cross-sectional area of the oxide core are not uniform in the longitudinal direction. Sometimes, even if the critical current of an oxide core in one cross section is higher than the current flowing through the oxide core, if the critical current in another cross section is lower than the conduction current, the oxide core changes to a critical current. A diversion will occur in another oxide core that has room. At that time, a current flows through the normal conducting portion (Ag sheath portion) to generate resistance, and the current flowing through the coil as a whole is attenuated. As a result, it is difficult to operate in the permanent current mode. Therefore, it is considered that the shape of the oxide core should be uniform in the longitudinal direction in order to prevent such branching.

By the way, in the above-mentioned conventional example, the hardness of the material constituting the wire differs greatly. For example, when the processed wire is represented by Vickers hardness, oxide core: 28
Hv, Ag sheath: 38Hv, Ag alloy sheath (Ag-
0.3 wt% Mg-0.3 wt% Ni): 95 Hv. As described above, when the hardness difference between the low hardness portion of the oxide core or Ag and the high hardness portion of the Ag alloy covering the oxide core or Ag is large, the balance of the stress applied during wire drawing is slightly disturbed, and A large disturbance occurs in the shape of the core. As a result, there is a problem that the above-mentioned n value becomes low.

In general, when processing a material having a hardness distribution inside, a structure in which the hardness of the outermost periphery of the processed material is high and the hardness gradually decreases from the outermost periphery toward a portion having the lowest hardness. With such a structure, the stress at the time of processing is uniformly transmitted to the wire, and a relatively uniform processed product can be obtained.

However, in the conventional example described above, the hardness step is large as described above, and in addition, a plurality of unit core wires in which an oxide core is wrapped in an Ag sheath are bundled.
Since the distance to the surrounding Ag alloy sheath (high hardness) is long especially at the central portion (low hardness), it is difficult for the stress at the time of processing to be transmitted uniformly to the central portion. It tends to be uniform.

On the other hand, an oxide superconducting wire in which the above-mentioned branching is prevented has been proposed in Japanese Patent Application Laid-Open No. Hei 7-169342 (conventional example). The oxide superconducting wire has a plurality of oxide cores arranged in a stabilizing material layer (Ag or the like), and has a high specific resistance Ag-Al between the oxide core and the stabilizing material layer. An alloy or an Ag-Mg alloy layer is provided. In this conventional example, the Ag-Al alloy (or Ag-Mg alloy) layer increases the cross resistance between the oxide cores and reduces the shunt.

However, in the conventional example, an oxide core and Ag
Since the alloy is in contact, the additional element in the Ag alloy diffuses into the oxide core during the heat treatment during processing as described above, and hinders good crystallization of the oxide superconducting material.
There is a problem that the critical current density is reduced.

In addition, the conventional example does not have a structure in which the hardness gradually decreases toward the oxide core, but has a low hardness A
g (stabilizing material layer) exists on the outermost periphery and has a structure in which a hard Ag alloy covers a low-grade oxide core. Is processed preferentially, and there is also a problem that the Ag alloy is left without being processed.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an oxide superconducting wire which satisfies all the characteristics of a high n value, a high critical current density, and a high mechanical strength. Aim.

[0020]

An oxide superconducting wire according to the present invention has a cross section in which a unit core wire in which an Ag sheath is arranged around a core wire (oxide core) of an oxide superconductor is further surrounded by an Ag alloy sheath. In an oxide superconducting wire having a structure,
The gist is that the unit core wire is surrounded by a buffer metal sheath, and the buffer metal sheath has a high specific resistance and is harder than the Ag sheath and softer than the Ag alloy sheath (first invention).

By interposing the buffer metal sheath in this way, the structure is such that the hardness gradually decreases from the outermost Ag alloy sheath of the wire toward the oxide core, so that the stress at the time of wire drawing is reduced by the oxide core. Until it reaches evenly,
Uniform processing can be easily performed. As a result, the n value is improved.

Further, since the buffer metal sheath of high specific resistance surrounds the periphery of the unit core wire, the electric resistance between the oxide cores becomes large, and the shunt can be suppressed. Therefore, Jc overall is improved. Note that Jc overall is obtained by dividing the critical current by the total cross-sectional area of the wire.

On the other hand, since the Ag sheath layer covers the periphery of the oxide core, the components of the buffer metal sheath do not diffuse into the oxide core during the heat treatment, so that the critical current density does not decrease.

If a part of the thickness of the conventional Ag sheath is made of the above-mentioned buffer metal sheath, the cross-sectional area ratio of the Ag alloy sheath is not reduced as compared with the conventional example, so that not only the mechanical strength does not decrease, but also Since the buffer metal sheath has higher strength than the Ag sheath, the mechanical strength is rather improved.

Further, in the present invention, it is preferable that a plurality of the unit core wires surrounded by the buffer metal sheath be bundled and disposed in the Ag alloy sheath.

When unit core wires (oxide core and Ag sheath) of low hardness are bundled as in the conventional example, the distance to the center becomes long in the whole bundle (low hardness portion), and as described above, Is difficult to transmit to the center. However, in the present invention, since the individual unit cores (the oxide core and the Ag sheath) are covered with the buffer metal sheath having an intermediate hardness as described above, the low-hardness portion becomes thin and the low-hardness portion (the unit core) The distance to the center is short. That is, although the buffer metal sheath has an intermediate hardness, the stress during wire drawing is transmitted uniformly to the center of the oxide core by interposing the intermediate hardness portion between the low hardness unit core wires. Therefore, uniform processing is performed, and the n value is improved.

[0027] The oxide superconducting wire according to the present invention is the oxide superconducting wire having a sectional structure in which a unit core having an Ag sheath disposed around a core of the oxide superconductor and further surrounded by an Ag alloy sheath. Around a plurality of unit core wires bundled, has a cross-sectional structure in which a buffer metal matrix is arranged, the buffer metal matrix has a high specific resistance,
The gist of the invention is that it is harder than the Ag sheath and softer than the Ag alloy sheath (second invention).

Since the buffer metal matrix is disposed around the unit core wire, the structure is such that the hardness gradually decreases from the Ag alloy sheath to the oxide core as described above, and uniform processing can be performed, and the n value is improved. I do.

Further, it is preferable that a plurality of unit core wires each having a buffer metal matrix arranged around the bundle are bundled, and have a cross-sectional structure surrounded by the Ag alloy sheath.

Alternatively, the oxide superconducting wire according to the present invention comprises:
A plurality of unit core wires in which an Ag sheath is disposed around the core wire of the oxide superconductor, and a plurality of buffer metal wires having a high specific resistance and being harder than the Ag sheath and softer than the Ag alloy sheath, The gist is that the plurality of unit core wires and the plurality of buffer metal wires have a cross-sectional structure bundled in a dispersed state and surrounded by an Ag alloy sheath (third invention).

As described above, since the plurality of buffer metal wires are dispersed and bundled in the plurality of unit core wires, the buffer metal wires simulately surround the unit core wire. The stress is transmitted uniformly to the oxide core, and uniform processing can be performed. As a result, the n value is improved. In addition, due to the presence of the buffer metal wire, similarly to the above, it is possible to increase the electric resistance when a current crosses from one oxide core to another oxide core, and it is possible to suppress the shunt.

Further, in the present invention, each of the unit core wires is surrounded by a buffer metal sheath, and the buffer metal sheath has a high specific resistance, is harder than the Ag sheath, and is softer than the Ag alloy sheath. preferable.

By using the above-mentioned buffer metal wire having a high specific resistance and the above-mentioned buffer metal sheath having a high specific resistance together,
n value can be further improved, and Jc overall
Also, the mechanical strength can be higher.

[0034] In the present invention, the distance between the oxide superconductor core wires closest to each other across the buffer metal matrix or the buffer metal wire is D, and the maximum cross-sectional diameter of the oxide superconductor core wire is d. When 1.3 <D / d
It is preferred that ≦ 5.0. More preferably D / d
Is 1.5 or more, and D / d is 2.5 or less.

If the value of D / d is too low, Jc overall improves, but the n value decreases. Conversely, if the value of D / d is too high, the n value will increase, but the Jc overall will decrease. Therefore, the above range was set. Further, in the present invention, a plurality of the oxide superconducting wires may be bundled and further surrounded by an Ag alloy sheath.

The phrase "the buffer metal sheath, the buffer metal matrix, or the buffer metal wire has a high specific resistance" means that the specific resistance is higher than that of Ag, for example, 5.0 × 10 at 4.2K. It is desirable to have a specific resistance of ^-10 Ωm or more.

The buffer metal sheath and the buffer metal matrix include an Ag—Ni alloy, an Ag—Mg—Ni alloy,
Pt, Pd and the like are suitable. Table 1 below shows the Vickers hardness and specific resistance of these and Ag.

[0038]

[Table 1]

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the oxide superconducting wire according to the present invention will be described in more detail with reference to examples, but the following examples do not limit the present invention.
The present invention can be implemented with appropriate modifications without departing from the gist of the following description, and they are all included in the technical scope of the present invention.

<Embodiment 1 (First Invention)> FIG.
1 is a schematic sectional view showing an oxide superconducting wire according to Example 1 of the present invention. As shown in FIG. 1, the oxide superconducting wire of Example 1 has an oxide core 10 surrounded by an Ag sheath 11 and further surrounded by a buffer metal sheath 12 (Ag-0.1 wt% Ni). Are collected, and a triple sheath structure in which an Ag alloy sheath (Ag-0.3wt% Mg-0.3wt% Ni) 13 covers the periphery thereof is provided.

Ag-0.1 w of the buffer metal sheath 12
t% Ni has a specific resistance of 1.0 × 10 ^-9Ωm and high
The hardness at room temperature is 65 Hv, and the Ag sheath 11
Hardness 38Hv (room temperature) and Ag alloy sheath (Ag-0.3wt% Mg
(−0.3 wt% Ni) 13 with a hardness of 95 Hv (room temperature).

Next, a method of manufacturing the oxide superconducting wire of Example 1 will be described. Bi as oxide superconducting material
_{Using 2} Sr ₂ CaCu ₂ O _x , a calcined powder of this oxide superconducting material is filled in an Ag pipe, and this is further mixed with an Ag alloy (Ag-0.1 wt%) for the buffer metal sheath.
Ni) with a pipe made of the oxide superconducting powder.
The heavy pipe was wire-drawn while having a hexagonal cross section.

After the wire drawing, it was cut and bundled into 19 pieces, and this was made into a cylindrical Ag-0.3 wt% Mg-0.3 wt% Ni (Ag
(For alloy sheath) to assemble a billet.
The billet is subjected to hydrostatic extrusion to perform integration and surface reduction, and further, wire-drawing to a predetermined size, and an outer diameter of 1.3.
mm 19-core round wire was obtained.

<Embodiment 2 (first invention)> In Embodiment 2, Ag-0.1 wt% N for the buffer metal sheath of Embodiment 1 is used.
In place of i, Pt is used, and the oxide superconducting wire according to the second embodiment also has a cross-sectional structure similar to that of FIG. That is, the oxide core 10 is covered twice with an Ag sheath 11 and a buffer metal sheath 12 (Pt), and further, an Ag alloy sheath 13
It has a cross-sectional structure of a triple sheath surrounded by.

The Pt of the buffer metal sheath 12 has a high specific resistance of 5.5 × 10 ⁻¹⁰ Ωm and a hardness of 63 Hv.
(Room temperature), the Ag sheath 11 and the Ag alloy sheath (A
g-0.3wt% Mg-0.3wt% Ni).

Next, the manufacturing method of the second embodiment will be described. Oxide superconducting material (Bi ₂ Sr ₂ CaCu ₂ O _x )
Was calcined in an Ag pipe, Pt plating was applied thereto, and wire drawing was performed so that the cross section became hexagonal. In this case, the total thickness of the Ag sheath 11 and the buffer metal sheath 12 (Pt) in the second embodiment is equal to the Ag sheath 11 and the buffer metal sheath 12 (Ag-0.1w) in the first embodiment.
t% Ni). Further, a 19-core round wire was obtained in the same manner as above.

Third Embodiment (Third Invention) FIG. 2 is a schematic sectional view showing an oxide superconducting wire according to a third embodiment. As shown in FIG. 2, the wire according to the third embodiment includes a unit core wire 15 having an Ag sheath 11 disposed around an oxide core 10 and a plurality of buffer metal wires (Ag-0.3 wt% Ni) 14. It is bundled in a dispersed state, and this is further Ag alloy sheath (Ag-0.3wt% Mg-0.3% Ni)
13.

The specific resistance of the buffer metal wire 14 is 1.5 × 10
^-9 Ωm, hardness is 78 Hv (room temperature), and Ag
Hardness 38Hv (room temperature) of sheath 11 and Ag alloy sheath 1
And a hardness of 95 Hv (room temperature). The distance between the adjacent oxide cores 10 across the buffer metal wire 14 is D,
Assuming that the sectional diameter of the oxide core 10 is d, D / d in Example 3 was 1.2.

Next, a method of manufacturing the oxide superconducting wire of Example 3 will be described. Bi ₂ Sr as oxide superconducting material
_Using 2CaCu ₂ O _x , the calcined powder of this oxide superconducting material was filled in an Ag pipe, drawn into a hexagonal cross section, and cut into 42 pieces (unit core wire 1).
5). Further, an Ag alloy (Ag-0.
(3 wt% Ni) rod was drawn while similarly forming a hexagonal cross section, and then cut into 13 pieces (buffer metal wire 1).
4). 13 buffer metal wires 14 and 42 unit core wires 1
5 in a dispersed state and bundled, cylindrical Ag-0.3 wt% M
It was set in g-0.3 wt% Ni (for Ag alloy sheath) to produce a billet. The billet was subjected to hydrostatic extrusion to perform integration and surface reduction, followed by wire drawing to a predetermined size to obtain a 42-core round wire having an outer diameter of 1.3 mm.

Example 4 (Third Invention) Oxide Core 10
Is smaller than that of the third embodiment, and D / d = 2.5. Other than the above, the outer diameter is 1.
A 3 mm 42-core round wire was produced.

Embodiment 5 (Second Invention) FIG. 3 is a schematic sectional view showing an oxide superconducting wire according to Embodiment 5. The wire of Example 5 has an Ag sheath 11 around the oxide core 10.
Are bundled and covered with a buffer metal matrix (Ag-0.3wt% Ni) 16, and seventeen of these 19-core wires are bundled to form an Ag alloy sheath (Ag-0.3wt% Mg). -
It has a cross-sectional structure surrounded by 0.3 wt% Ni) 13.

In the wire of the fifth embodiment, the distance between the adjacent oxide cores 10 across the buffer metal matrix 16 is D,
When the sectional diameter of the oxide core 10 is d, D / d is 4.
It was 0.

Next, a method for manufacturing the oxide superconducting wire of Example 5 will be described. Bi ₂ Sr as oxide superconducting material
_{Using 2} CaCu ₂ O _x , the calcined powder of this oxide superconducting material was filled in an Ag pipe, drawn into a hexagonal cross section, and cut into 19 pieces (unit core wire 1).
5). Ag alloy for buffer metal matrix (Ag-0.
Nineteen of the above hexagonally drawn wires were bundled and inserted into the inside of a 3 wt% Ni) tube to produce a billet (19 core wires).
After the billet was subjected to hydrostatic extrusion, it was divided into seven parts, which were then divided into seven holes by an Ag alloy (Ag-0.3 wt% Mg-
Each was set in 0.3 wt% Ni) to assemble a billet. Thereafter, further isostatic extrusion was performed and wire drawing was performed to obtain a 19 × 7 core round wire having an outer diameter of 1.3 mm.

<Embodiment 6 (second invention)> The thickness of the unit core wire 15 is reduced so that D / d = 5.1. A superconducting wire was manufactured.

Embodiment 7 FIG. 4 is a schematic sectional view showing an oxide superconducting wire according to Embodiment 7 of the present invention. As shown in FIG. 4, in the wire rod of the seventh embodiment, the oxide core 10 is double-covered by the Ag sheath 11 and the buffer metal sheath (Ag-0.1 wt% Ni) 12, and the double unit core wire 25 is further provided. And a plurality of buffer metal wires (Ag-0.3wt% Ni) 14 are bundled in a dispersed state and further surrounded by an Ag alloy sheath (Ag-0.3wt% Mg-0.3wt% Ni) 13. is there. The D / d of the seventh embodiment was 1.2, which is the same as that of the third embodiment.

Next, a method for manufacturing the oxide superconducting wire of Example 7 will be described. Bi ₂ Sr as oxide superconducting material
_{Using 2} CaCu ₂ O _x , the calcined powder of this oxide superconducting material is filled into an Ag pipe, and this is further mixed with an Ag alloy (Ag-0.1 wt% Ni) for the buffer metal sheath
And then wire-drawing the double pipe containing the oxide superconducting powder so as to have a hexagonal cross section.
It was cut into books (double unit core wire 25). In this case, the Ag
The total thickness of the pipe and the Ag alloy (Ag-0.1 wt% Ni) pipe was made equal to the thickness of the Ag pipe of Example 4 above.

For a buffer metal wire rod, an Ag alloy (Ag alloy) is used.
A rod of (−0.3 wt% Ni) was drawn while similarly forming a hexagonal cross section, and then cut into seven pieces (buffer metal wire 14).

The seven buffer metal wires 14 and the 48 double unit core wires 25 are bundled in a dispersed state, and these are bundled into a cylindrical A.
It was set in g-0.3 wt% Mg-0.3 wt% Ni (for Ag alloy sheath) to produce a billet. The billet was subjected to hydrostatic extrusion and further subjected to wire drawing to obtain a 48-core round wire having an outer diameter of 1.3 mm.

<Comparative Example (corresponding to Conventional Example)> FIG. 5 is a schematic sectional view showing an oxide superconducting wire of a comparative example. The wire of this comparative example has an oxide core 10 covered with an Ag sheath 11,
Further, it has a double sheath cross-sectional structure wrapped with an Ag alloy sheath 13.

Next, a method of manufacturing the oxide superconducting wire of the comparative example
Is described. Oxide supercharged in the same manner as in Examples 1 to 7 above.
Bi as conductive material_Two Sr_Two CaCu_Two O _x Using this
Fill the calcined powder into an Ag pipe so that the cross section becomes hexagonal
And wire drawing was performed. The thickness of the above Ag pipe
And the Ag pipe and the Ag alloy pipe in the first embodiment.
Was equal to the total thickness. Then cut and bundle 19
Cylindrical Ag alloy (Ag-0.3wt% Mg-0.3wt
% Ni) to assemble a billet. That
Thereafter, an isostatic extrusion is performed, and a wire drawing process is performed.
A 3 mm 19-core round wire was obtained.

[Test] From the oxide superconducting wires of Examples 1 to 7 and Comparative Example, two samples each having a length of 1000 mm were prepared.
After cutting out one piece and winding it on a test coil having a diameter of 30 mm and performing partial melting at a temperature of 860 ° C. to 910 ° C.,
Bi-2212 was crystallized while cooling at a rate of 1-5 ° C / h.

With respect to this oxide superconducting wire, 4.2
The critical current at K, 0T is divided by the cross-sectional area of the wire, and J
asked for rall. Further, the n value when an electric field reference of 0.1 to 1 μV / cm was used was determined.

The other one of the cut pieces was heat-treated under the same conditions, and a tensile test was performed at room temperature using this wire. Since the amount of deformation that the oxide superconductor can withstand is about 0.2%, in this tensile test, the stress (0.2% proof stress) until 0.2% deformation was obtained. The results are shown in Table 2 below.

[0064]

[Table 2]

As can be seen from Table 2 above, in Examples 1 and 2, the n value was greatly improved and the 0.2% proof stress was also improved as compared with the comparative example.

In Example 3, the n value and the 0.2% proof stress were equal to those of the comparative example, but the Jc overall was improved. On the other hand, Example 4 was the same as Comparative Example in terms of 0.2% proof stress, but the n value was greatly improved, and Jc overall was also slightly improved. From this result, when the value of D / d is low, the n value does not improve much,
When Jc overall is high, while D / d is high, Jc o
It can be seen that the improvement in verall is small, but the n value tends to increase. In Example 5, all the values were improved as compared with the comparative example. In Example 6, Jc overall was lower than that of Comparative Example, but n value and 0.2% proof stress were improved. From these results, it is understood that those having a value of D / d of 1.3 to 5.0 are more preferable.

In Example 7, all the values are greatly improved as compared with the comparative example, and it is understood that the combination of the buffer metal sheath and the buffer metal wire is more preferable.

As described above, Examples 1 to 7 all have a high n value,
It exhibited the properties of high critical current density and high mechanical strength.

In Examples 1 to 7, the Ag alloy sheath 13 was made of Ag-0.3 wt% Mg-0.3 wt
% Ni was used, but is not limited thereto.
i, Mn, Zr, etc. in a small amount,
Any alloy may be used as long as it does not generate an intermetallic compound and forms a solid solution.

As an oxide superconductor, Bi ₂ Sr ₂ C
Although aCu ₂ O _x (Bi-2212) was used, the invention is not limited to this. For example, (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _y
Of course, other oxide superconductors such as (Bi-2223) may be used.

Further, the present invention is not limited to the cross-sectional structure shown in FIGS. 1 to 4. For example, as shown in a schematic cross-sectional view of FIG. 6, a unit core wire 15 in which an Ag sheath 11 is arranged around an oxide core 10 is used.
May be bundled, covered with a buffer metal matrix 16, and further surrounded by an Ag alloy sheath 13 (second invention).

Further, for example, a plurality of the oxide superconducting wires shown in FIG. 1 may be bundled and further covered with an Ag alloy sheath.

[0073]

According to the oxide superconducting wire of the present invention, since the oxide core can be processed uniformly, the shunt between the oxide cores can be suppressed, and a high n value can be realized. in addition,
The mechanical strength represented by 0.2% proof stress and Jc overall can also be kept higher than conventional products. Therefore, if the oxide superconducting wire according to the present invention is used, the production of an oxide superconducting magnet having higher performance than that of a conventional metal-based superconducting magnet can be expected, and a high-performance NMR analyzer can be manufactured. It is extremely advantageous for other superconducting applications.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an oxide superconducting wire according to Examples 1 and 2 of the present invention.

FIG. 2 is a schematic sectional view showing an oxide superconducting wire according to Examples 3 and 4 of the present invention.

FIG. 3 is a schematic sectional view showing an oxide superconducting wire according to Examples 5 and 6 of the present invention.

FIG. 4 is a schematic sectional view showing an oxide superconducting wire according to a seventh embodiment of the present invention.

FIG. 5 is a schematic sectional view showing an oxide superconducting wire of a comparative example (conventional example).

FIG. 6 is a schematic sectional view showing another embodiment of the oxide superconducting wire according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Oxide core 11 Ag sheath 12 Buffer metal sheath 13 Ag alloy sheath 14 Buffer metal wire 15 Unit core wire 16 Buffer metal matrix 25 Double unit core wire

Claims (9)

[Claims] 1. An oxide superconducting wire having a cross-sectional structure in which a unit core in which an Ag sheath is disposed around a core of an oxide superconductor and further surrounded by an Ag alloy sheath, wherein the unit core is surrounded by a buffer metal sheath. An oxide superconducting wire, wherein the buffer metal sheath has a high specific resistance and is harder than the Ag sheath and softer than the Ag alloy sheath. 2. The oxide superconducting wire according to claim 1, wherein each of the plurality of unit core wires surrounded by the buffer metal sheath is bundled and disposed in the Ag alloy sheath. 3. An oxide superconducting wire having a cross-sectional structure in which a unit core in which an Ag sheath is disposed around a core of an oxide superconductor and further surrounded by an Ag alloy sheath, wherein a plurality of unit cores are bundled. A buffer metal matrix, the buffer metal matrix has a high specific resistance, and the A
An oxide superconducting wire, characterized in that it is harder than g sheath and softer than the Ag alloy sheath. 4. The oxide superconducting material according to claim 3, wherein a plurality of unit core wires each having a buffer metal matrix arranged around them are bundled and have a cross-sectional structure surrounded by the Ag alloy sheath. wire. 5. A plurality of unit core wires each having an Ag sheath arranged around a core wire of an oxide superconductor, and a buffer metal wire having a high specific resistance and being harder than the Ag sheath and softer than the Ag alloy sheath. Having a plurality, the plurality of unit core wires and the plurality of buffer metal wires,
An oxide superconducting wire having a cross-sectional structure which is bundled in a dispersed state and surrounded by an Ag alloy sheath. 6. The buffer metal sheath according to claim 5, wherein each of the unit core wires is surrounded by a buffer metal sheath, and the buffer metal sheath has a high specific resistance and is harder than the Ag sheath and softer than the Ag alloy sheath. Oxide superconducting wire. 7. When the distance between the oxide superconductor core wires that are closest to each other across the buffer metal matrix or the buffer metal wire is D, and the maximum cross-sectional diameter of the oxide superconductor core wire is d, The oxide superconducting wire according to any one of claims 4 to 6, wherein 3 <D / d ≤ 5.0. 8. An oxide superconducting wire in which a plurality of the oxide superconducting wires according to claim 1, 2, 5 to 7 are bundled and further surrounded by an Ag alloy sheath. 9. The buffer metal sheath, the buffer metal matrix, or the buffer metal wire has a specific resistance of 5.0 × 10 ⁻¹⁰ Ωm or more at 4.2K.
The oxide superconducting wire according to any one of the above.