JPH11185847A - Bonding structure of oxidic superconductive wire and its connection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure superconductive connection at a connection part of an oxidic superconductive wire. SOLUTION: In an oxidic superconductive wire 1 formed by covering multiple superconductive cores 2 with a sheath 3 formed from Ag or the like, its connecting part 1A is so formed that each of its cut surfaces is formed by setting the cut angle so as to intersect with the axis of the oxidic superconductive wire at not more than 20 deg. and the cut surfaces are tightly fitted together in a condition in which the axes of the oxidic superconductive wires generally correspond with each other, a coating material 9 is placed around the connection part near the cut surfaces, and crystals of the superconductive cores 2 are formed in a state in which they have grown throughout the both sides of the cut surfaces by means of heat treatment or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining structure of an oxide superconducting wire and a method of connecting the same, and relates to a technique used for a superconducting cable, a magnet, a current lead wire and the like.

[0002]

2. Description of the Related Art Conventionally, an oxide superconducting wire 1 is formed by covering a plurality of superconducting cores 2 with a sheath 3 made of silver or the like as shown in FIG. By winding a plurality of layers around a former or the like, for example, a superconducting cable is formed. The oxide superconducting material used for the superconducting core 2 is Bi ₂ Sr ₂ Ca ₁
Cu ₂ O _x (Bi-based 2212 phase), Bi ₂ Sr ₂ Ca ₂ Cu ₃
O _y (Bi 2223 phase), Bi _1.6 Pb _0.4 Sr ₂ Ca ₂
Those having a composition such as Cu ₃ O _x , Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _y are used. Among them, Bi type, especially Bi
A system 2223 phase oxide superconducting material has been applied to the superconducting core 2.

On the other hand, as shown in FIG. 4 (a), one superconducting core 5 is used as an oxide superconducting wire (single core wire) 4.
The one covered by the sheath 6 is also used. Hereinafter, a connection method using such a single core wire 5 will be described with reference to FIGS. [Connection Surface Exposure: S1] At the connection end 4A, FIG.
As shown in (b), a part of the sheath 6 is peeled off by the connection length, and the connection surface 5B of the superconducting core 5 is exposed. [Connection Surface Contact: S2] As shown in FIG. 4C, the connection surfaces 5B of the superconducting core 5 are brought into contact with each other. [Pressing step: S3] Thereafter, pressure bonding is performed by a uniaxial press or the like, and as shown in FIG.
The connection between the members and the sheath 6 is made to form a connection portion 4B. [Heat treatment step: S4] 842 ° C.
The heat treatment is performed under processing conditions such as 150 hours and an oxygen partial pressure of 10%.

[0004]

However, when the oxide superconducting wire (multi-core wire) 1 as shown in FIG. 3 is used, the above-described method for connecting a single core wire cannot be applied, and a plurality of superconducting wires are not applicable. Since it is difficult to connect the cores to each other, there is a problem that the connection portion of the oxide superconducting wire may become a normal conducting connection.

The present invention has been made in view of the above circumstances, and aims to achieve the following objects. Superconducting connection must be ensured at the connecting portion of the oxide superconducting wire. To increase the connection area in the superconducting core. Bonding in a state where crystals of the oxide superconducting material have grown over both sides of the connection surface.

[0006]

A plurality of superconducting cores are made of Ag.
In the oxide superconducting wire formed by being covered with a sheath made of the above, a cut surface is formed such that a connection portion thereof intersects with the axis of the oxide superconducting wire at a cutting angle of 20 degrees or less, and the cut surface is formed. The surfaces are brought into close contact with each other so as to substantially overlap the axis of the oxide superconducting wire, and a coating material is disposed around the connection portion near the cut surface, and the crystal of the superconducting core is spread on both sides of the cut surface by heat treatment or the like. It is formed as a grown state. The covering material is made of the same material as the sheath, and the covering material and the sheath are integrated. Each of the cut surfaces is smoothly formed as a mirror-like smooth surface. In a method for connecting an oxide superconducting wire formed by covering a plurality of superconducting cores with a sheath made of Ag or the like, the surface of the connecting end of the oxide superconducting wire is separated from the surface of the connection end by a release material or the like. A pretreatment step of performing the treatment, a sealing step of sealing the superconducting core on the end face of the oxide superconducting wire with a sealing material such as solder, and the outside of the sealing material,
In order to reinforce the connection end, a connection end reinforcement step of integrally covering up to the surface of the sheath so as to include a cut surface position to be described later with a reinforcing material made of an epoxy resin or the like; A cutting step of cutting at a cutting plane defined by a cutting plane position intersecting with a cutting angle set with respect to an axis of the wire, removing a reinforcing agent, and bringing the cut planes into contact with each other to form two oxide superconducting wires; A connecting surface contacting step in which the axes are positioned so as to substantially overlap with each other, and a connecting portion formed of the same material as the sheath and located on the surface of the connecting portion in the longitudinal direction of the oxide superconducting wire including the cut surface position A coating process for covering the surface of the substrate, a pressurizing process for applying a pressure treatment to the connection portion, and a heat treatment step for performing a heat treatment on the connection portion under a temperature condition set to a temperature at which the oxide superconducting material can be partially melted. With the door. In the cutting step, it is preferable that the cutting angle between the axis of the oxide superconducting wire and the cut surface is in a range of 20 degrees or less, and the load condition at the time of cutting is 5 g or less. The heat treatment step includes a high-temperature heat treatment performed in a range of 850 ° C. to 875 ° C. for about 0.5 hours to 1 hour, and a low-temperature heat treatment performed in a range of 820 ° C. to 840 ° C. for about 20 hours to 100 hours. Is preferably a heat treatment atmosphere in the range of 7% to 20%. The thickness of the coating material is preferably set to 0.2 mm or less, more preferably 0.1 mm or less.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a joining structure of an oxide superconducting wire and a method of connecting the same according to the present invention. In FIG. 1, reference numeral 1 denotes an oxide superconducting wire, 2 denotes a superconducting core, 3 denotes a sheath, 7 denotes a sealing material, 8 denotes a reinforcing material, and 9 denotes a covering material.

An oxide superconducting wire 1 is formed by covering a plurality of superconducting cores 2 with a sheath 3 made of a sheath material such as Ag, as shown in FIG.
As shown in the figure, the connecting portion 1A is made of an oxide superconducting wire 1
(Connection end) 1B. The oxide superconducting conductor 1 has, for example, a width of about 0.5 mm to 5 mm and a thickness of about 0.5 mm.
It is in the form of a tape in the range of about 05 mm to 0.7 mm, for example, 4.0 mm in width and 0.20 mm in thickness. The superconducting core 2 is made of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x (Bi ₂
212 phase), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y (Bi 2223
Phase), Bi _1.6 Pb _0.4 Sr ₂ Ca ₂ Cu ₃ O _x , Tl ₂ Ba ₂
It has a composition represented by Ca ₂ Cu ₃ O _y , etc., and for example, a Bi-based 2223 phase Bi-based oxide superconducting material is selected. The sheath 3 is made of a noble metal such as Ag, Pt, or Au or an alloy thereof, and is made of, for example, Ag. As shown in FIG. 1D, a cut surface S is formed at the connecting portion 1A so as to intersect with the axis L of the oxide superconducting wire 1 at a cutting angle θ of 20 degrees or less. The cut surfaces S of the oxide superconducting wire 1 are brought into close contact with each other so as to substantially overlap the axis L of the oxide superconducting wire 1, and a coating material 9 is disposed around the connection portion 1A near the cut surface S, and heat treatment is performed. Thereby, the crystal of superconducting core 2 is formed in a state of growing over both sides of cut surface S. The covering material 9 is made of the same material as the sheath 3, and the covering material 9 and the sheath 3 are integrated.

Hereinafter, a connection method for such an oxide superconducting wire will be described with reference to FIG.

[Pretreatment step: S10] At the connection end 1B of the oxide superconducting wire 1, as shown in FIG.
The surface of the connection end 1B is subjected to surface cleaning with diluted nitric acid or the like, and surface treatment with a release material such as silicon grease, and surface treatment with a release material. [Sealing Step: S11] At the end face 1C of the oxide superconducting wire 1, as shown in FIG. 1 (b), the superconducting core 2 is sealed with a sealing material 7 such as solder. [Connection End Reinforcing Step: S12] In order to reinforce the connection end 1B, the outside of the sealing material 7 is reinforced with a reinforcing material 8 made of an epoxy resin or the like so as to include a cut surface position C described later. Cover as far as the surface. [Connection surface contact step: S13] Connect the connection end 1B to FIG.
As shown in (b), the oxide superconducting wire 1 is cut at a cutting plane position C defined by a cutting plane S that intersects with an axis L of the oxide superconducting wire 1 at a cutting angle θ. Here, the cutting angle θ between the axis of the oxide superconducting wire 1 and the cut surface S is set to a range of 20 degrees or less, and the load condition at the time of cutting is set to 5 g or less. The cut surface S is cut by, for example, a diamond cutter so that each of the cut surfaces S is smoothly formed into a mirror surface. [Connection surface contact step: S14] Reinforcing agent 8 from connection end 1B
Is removed, and the cut surfaces S of the two oxide superconducting wires 1 are brought into contact with each other, and the two oxide superconducting wires 1 are positioned so that the axes L thereof substantially overlap with each other. [Covering Step: S15] As shown in FIG. 1C, for example, the same material as that of the sheath 3 is located on the surface of the connecting portion 1A in the longitudinal direction of the oxide superconducting wire 1 including the cut surface position C. The surface of the connection portion 1A is covered with the covering material 9 made of Ag.
The thickness of the coating material 9 is set to 0.1 mm or less. [Pressing process: S16] The connecting portion 1A covered with the covering material is subjected to a pressing process by a uniaxial press or the like. [Heat Treatment Step: S17] Heat treatment is performed on the connection portion 1A under a temperature condition set in a range of 825 ° C. to 855 ° C. at which the oxide superconducting material can be partially melted. On this occasion,
It has a high-temperature heat treatment performed in the range of 850 ° C. to 875 ° C. for about 0.5 hours to 1 hour, and a low-temperature heat treatment performed in the range of 820 ° C. to 840 ° C. for about 20 hours to 100 hours. Also, the heat treatment atmosphere is set so that the oxygen concentration condition is in the range of 7% to 20%. Here, if heat treatment is performed for a long time at a temperature higher than 850 ° C., the Bi2223 phase is decomposed, and at about 820 ° C., the reaction speed of the bonding portion is low, and good connection cannot be obtained. Therefore, the range of the temperature condition is set as described above,
After the joining portions are connected by a melt by a high-temperature heat treatment for a short time, a low-temperature heat treatment that encourages crystal growth is given. [Post-processing: S18] Post-processing such as surface treatment for smoothing the coating material 9 and the sheath 2 at the connection portion 1A is performed.

In the connection method as described above, the cut end 1B is reinforced by the reinforcing member 8 and the load at the time of cutting is reduced by 5%.
g or less, it is possible to suppress the influence on the internal structure of the connection end 1B at the time of cutting. Since the cutting angle θ is set to 20 degrees or less, the area of the cut surface S can be increased, and as a result, the superconducting cores 2 of the oxide superconducting wires 1 to be connected can be connected almost in a contact state. Become. In the heat treatment step S17, by setting the processing temperature to a temperature at which the Bi-based 2223 phase oxide superconducting material can be partially melted, crystals can be grown on both sides of the cut surface S, and the oxide other than the connection portion 1A can be grown. A critical current value substantially equal to that of superconducting wire 1 can be obtained.

[0012]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples.

(Example) Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y (B
i2223 phase) In a superconducting wire having a width of 4.0 mm and a thickness of 0.2 mm in which a plurality of superconducting cores having a composition represented by the formula After performing surface treatment with a release material such as silicon grease, the connection end was sealed with solder, and the connection end was reinforced with a reinforcing material such as an epoxy resin. The connection end was cut by a diamond cutter at a cutting plane position set at a cutting angle θ = 20 ° set with respect to the axis L of the oxide superconducting wire 1 to form a cut plane. The reinforcing agent is removed from the connection end, the cut surfaces of the two oxide superconducting wires are brought into contact with each other, and the two oxide superconducting wires are positioned so that their axes are substantially overlapped with each other and have a thickness of 0.1 mm. And covering the surface of the connection portion at the surface of the connection portion in the longitudinal direction of the oxide superconducting wire including the cut surface by the coating material comprising CIP.
Pressurization is performed by (cold isostatic press). Then
High-temperature heat treatment performed at a temperature condition of 850 ° C. as a time condition of 0.5 hour, and low-temperature heat treatment performed at a temperature condition of 825 ° C. as a time condition of 100 hours, and in both the high-temperature heat treatment and the low-temperature heat treatment, Heat treatment was performed in an oxygen concentration atmosphere with an oxygen concentration of 8% to obtain an oxide superconducting wire.

(Comparative Example 1) In the above embodiment, the cutting angle θ was set to 30 °, and the connecting portions were connected in the same manner to obtain an oxide superconducting wire. (Comparative Example 2) An oxide superconducting wire having no connection portion in the above example was produced.

Measurement experiments were performed on the oxide superconducting wire obtained in the above example and the oxide superconducting wires obtained in Comparative Examples 1 and 2 under the following conditions. External magnetic field: 0T Temperature: 77K Critical current value of the oxide superconducting wire in the example: 9.8
A. Critical current value of oxide superconducting wire in Comparative Example 1:
5A Critical current value of oxide superconducting wire in Comparative Example 2: 10
A As a result, in the oxide superconducting wire having the connection portion, when the cutting angle θ is 20 degrees or less, the critical current value is substantially equal to 95% as compared with the oxide superconducting wire having no connection portion. Taking a value was measured.

[0016]

According to the joining structure of the oxide superconducting wire and the method of connecting the same according to the present invention, the following effects can be obtained. (1) Since the cutting angle θ is set to 20 degrees or less, the area of the cut surface can be increased, and as a result, the superconducting cores of the oxide superconducting wires to be connected can be connected almost in a contact state. Therefore, the connection area of the superconducting core can be increased. (2) In the heat treatment step, by setting the processing temperature to a temperature at which the oxide superconducting material can be partially melted, it is possible to make a crystal of the oxide superconducting material grow on both sides of the connection surface. (3) Since the above and the cut end reinforcing material are reinforced and the load at the time of cutting is suppressed to 5 g or less, the influence on the internal structure of the connection end at the time of cutting is suppressed. Since the crystal is grown on both sides of the cut surface, the connection of the superconducting core can be secured at the connection portion of the oxide superconducting wire, and as a result, the critical current is substantially equal to that of the oxide superconducting wire other than the connection portion. Value can be obtained.

[Brief description of the drawings]

FIG. 1 is a side cross-sectional view showing a working procedure in an embodiment of a bonding structure of an oxide superconducting wire and a connection method thereof according to the present invention.

FIG. 2 is a flowchart showing an operation procedure in an embodiment of a joining structure of an oxide superconducting wire and a connecting method thereof according to the present invention.

FIG. 3 is a perspective view showing a conventional oxide superconducting wire (multi-core wire).

FIG. 4 is a side sectional view showing an operation procedure in a conventional method for connecting an oxide superconducting wire (single body wire).

FIG. 5 is a flowchart showing an operation procedure in a conventional method of connecting an oxide superconducting wire (single body wire).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting wire, 1A ... Connection part, 1B ... Connection end, 1C ... End face, 2 ... Superconducting core, 3 ... Sheath, 7 ... Sealing material, 8 ... Reinforcement material, 9 ... Coating material, C ... Cut surface Position, S ...
Cutting surface, θ ... cutting angle

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Saito 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Co., Ltd.

Claims (4)

[Claims] In a bonding structure of an oxide superconducting wire formed by covering a plurality of superconducting cores with a sheath, a position where a connecting portion intersects an axis of the oxide superconducting wire at a cutting angle of 20 degrees or less. A cut surface is formed, and the cut surfaces are brought into close contact with each other so that the axes of both oxide superconducting wires are substantially overlapped with each other. A coating material is disposed around a connection portion near the cut surface, and heat treatment is performed. And a bonding structure of the oxide superconducting wire, wherein the crystal of the superconducting core is bonded so as to grow on both sides of the cut surface. 2. The joint structure for an oxide superconducting wire according to claim 1, wherein the cut surface is a mirror-like smooth surface. 3. A method for connecting an oxide superconducting wire formed by covering a plurality of superconducting cores with a sheath, wherein the connecting end of the oxide superconducting wire is separated from the surface of the connecting end by a release material or the like. A pretreatment step of performing a surface treatment;
A sealing step of sealing the superconducting core at the end face of the oxide superconducting wire with a sealing material, and a sheath for reinforcing the outside of the sealing material with a reinforcing material to include a cut surface position to be described later with a reinforcing material. The connection end portion is reinforced by a step of reinforcing the connection end portion, which covers the entire surface of the oxide superconducting wire, and the cut end surface is oxidized by a cut surface defined by a cut surface position intersecting with the axis of the oxide superconducting wire at a cutting angle set. A cutting step in which the cutting angle between the object superconducting wire and the axis line is 20 degrees or less, and removing the reinforcing agent, leaving the cut surface in a contact state, 2
A connecting surface contacting step in which the axes of the oxide superconducting wire of the present invention are positioned so as to substantially overlap with each other, and the same material as the sheath which is located on the surface of the connecting portion in the longitudinal direction of the oxide superconducting wire including the cut surface position A coating step of covering the surface of the connection part with a coating material comprising: and a heat treatment step of performing a heat treatment on the connection part under a temperature condition set to a temperature at which partial melting of the oxide superconducting substance is possible. Method of connecting oxide superconducting wires. 4. The method according to claim 1, wherein in the heat treatment step, 850 ° C. to 87 ° C.
It has a high-temperature heat treatment performed in the range of 5 ° C. for about 0.5 hours to 1 hour and a low-temperature heat treatment performed in the range of 820 ° C. to 840 ° C. for about 20 hours to 100 hours, and has an oxygen concentration of 7% to 20%. The method for connecting an oxide superconducting wire according to claim 3, wherein the heat treatment is performed in an atmosphere.