JP2006216243A - Oxide superconducting wire and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide superconducting wire with a circular or rectangular cross section which has an engineering critical current density equivalent to that of a tape-shaped bismuth-based oxide superconducting wire and is easily used as cable conductors and magnet windings, and to provide an oxide superconducting wire which achieves a lower silver ratio at low cost by suppressing the amount of silver or silver alloy used as stabilizers. <P>SOLUTION: The oxide superconducting wire comprises a core material 16 made of metal, a matrix 22 made of the stabilizer that is arranged outside the core material, and a filament 21 made of a plurality of oxide superconductors buried in the matrix. The filament is formed so as to be flat-shaped and distributed around the core material in a layered form in the cross section of the wire and to be spirally drawn in the longitudinal direction of the wire, and the engineering critical current density of 15,000 A/cm<SP>2</SP>or higher is obtained at temperatures of liquid nitrogen in a self magnetic field. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oxide superconducting wire having a high engineering critical current density characteristic Je and having a circular or rectangular cross-sectional shape, in particular, a bismuth-based oxide superconducting wire and a method for producing the same.

Conventionally, bismuth-based oxide superconducting wires are manufactured using a so-called powder-in-tube method. The powder-in-tube method is a method of obtaining a wire by filling a powder of a raw material capable of forming an oxide superconductor into a tube of a stabilizing material and subjecting it to plastic processing and heat treatment. In the preparation of the raw material powder, the oxide or carbonate powder of the element constituting the superconductor is blended at a predetermined blending ratio and sintered, and then the sintered product is pulverized.
The stabilizer tube filled with the raw material powder is made of, for example, silver or a silver alloy. For the plastic working, wire drawing, rolling, press working or the like is used.

There are two types of silver sheath wire using silver or a silver alloy for the stabilizing material tube, a tape-shaped wire having a flat cross section and a round wire having a circular cross section. In the case of a round wire, it is created by repeating drawing and heat treatment without rolling, but in the case of a tape-like wire, it is created by rolling and heat treatment.

However, in the conventional oxide superconducting wire, the tape-shaped wire is rolled, so that a rolling facility is required and the manufacturing cost is high, and in terms of application, when the wire is used as a superconductor in a cable or a magnet, Since the cross section is tape-shaped, conventional cable technology and magnet winding technology are not applied. Furthermore, the use of a large amount of silver, which is an expensive sheath material, has various problems such as high raw material costs.
On the other hand, in contrast to the tape-shaped wire, one round wire has a convenient and economical aspect that the conventional technology can be applied without problems both in production and in later application of cables and magnets. However, since the engineering critical current density (hereinafter referred to as Je) is remarkably small as compared with a tape-shaped wire obtained by rolling, practicality was lacking.

  The reason why high Je characteristics can be obtained with a tape-shaped bismuth-based superconducting wire is that the compressive force in the rolling process increases the density of the powder that is the raw material for oxide superconductivity, and a bismuth crystal structure with good orientation is realized in the subsequent heat treatment process. Due to being. On the other hand, in the case of a round wire rod, the rolling process is not performed, and in the wire drawing process, the powder is simply elongated in the longitudinal direction, and the powder density cannot be improved. This mechanism is experimentally confirmed by the fact that the silver ratio (volume of silver in the wire / volume of superconductor) increases after rolling and heat treatment.

Further, in the case of a round wire having a multi-core structure, conventionally, as shown in FIG. 7, a plurality of superconducting wires 11 obtained by filling a raw material powder of an oxide superconductor into a silver tube and drawing it are made of silver. After fitting into the tube 18, the composite billet 24 is created by attaching the lids 14 and 15 made of silver to both ends of the tube 18. Further, the composite billet 24 is repeatedly subjected to wire drawing and heat treatment a predetermined number of times, thereby producing a multi-core oxide superconducting round wire 25. As shown in FIG. 8, the oxide superconducting round wire 25 prepared in this way has a large number of filaments 21 made of an oxide superconductor embedded in a matrix 22 made of a silver stabilizer in the cross section of the wire. The filament 21 is stretched in one direction in the longitudinal direction of the wire. Accordingly, as in the case of the single-core round superconducting wire, a conventional multi-core oxide superconducting round wire has not been able to obtain high Je characteristics only by drawing unless it is rolled.

Patent Documents 1 and 2 listed below are examples of attempts to improve Je of a bismuth-based oxide superconducting round wire. The oxide superconducting round wire disclosed in Patent Document 1 has a substantially concentric multiple ring structure in which metal, silver or a silver alloy and an oxide superconductor are alternately laminated, and the oxide in the wire It is said that c-axis orientation can be achieved by reducing the interface distance between superconductivity and metal. However, the critical current density (hereinafter referred to as Jc) value of this wire is an order of magnitude higher than that of other conventional round wires, but is an order of magnitude smaller than that of a tape-shaped wire. It was not reached.

Further, in Patent Document 2, five layers of fitting wires obtained by filling an oxide superconductor into a silver pipe are arranged along each side surface around a silver core rod, and fitted into the silver pipe. An oxide superconducting wire obtained by performing heat treatment a plurality of times has been disclosed. However, the fitting line is a tape-like line that has been substantially rolled, and the Jc of the wire having an approximate circular cross-section formed using this is more than the Jc disclosed in the Patent Document 1. Although it was high, it did not reach the Jc level of the tape-shaped wire.
Since Jc described in Patent Documents 1 and 2 was evaluated using a superconducting wire in the specification, strictly in Jc (= Ic / cross-sectional area of superconductor, Ic is a critical current) And Je (= Ic / cross-sectional area of superconducting wire).

JP-A-4-262308 JP-A-9-259660

  An object of the present invention is to provide an oxide superconducting wire having a Je characteristic equivalent to that of a bismuth-based oxide superconducting tape-like wire and having a circular or rectangular cross section that is easy to use as a cable conductor or a winding for a magnet. It is to provide a stranded wire using a wire, a cable, a magnet, and the like.

  It is a further object of the present invention to provide an oxide superconducting wire that reduces the amount of silver or silver alloy used in the stabilizing material and realizes a low silver ratio at a low cost.

The authors are able to leave compressive residual stress in the periphery of the wire cross-section even during wire drawing, and the powder that is the raw material of the oxide superconductor is flattened not only in the filament axis direction but also in the lateral direction. As a result, it was found that even in the wire drawing process, the raw material powder was subjected to a compressive force equivalent to that of rolling and high density could be realized.

That is, in the present invention, in an oxide superconducting wire comprising a core material, a matrix made of a stabilizing material disposed outside the core material, and a filament made of an oxide superconductor embedded in the matrix in a large number, The filament is flat in the cross section of the wire and is distributed in layers around the core material, and is formed by extending in a spiral shape in the longitudinal direction of the wire, and is 15000 A / cm ² in a self-magnetic field in liquid nitrogen. Provided is an oxide superconducting wire characterized by exhibiting the above critical current density, particularly a bismuth-based oxide superconducting wire having a circular or rectangular cross-sectional shape.

In the oxide superconducting wire of the present invention, since the compression effect cannot be obtained by wire drawing at the center of the cross section, the critical current (hereinafter referred to as Ic) is extremely high even if the oxide superconductor is disposed in this portion. Only slightly increased. For this reason, the oxide superconductor is disposed only in the periphery of the cross section, and oxygen permeability is not required at the center of the cross section.

Thereby, in this invention, the said core material consists of copper or a copper alloy, and the coating layer which consists of a barrier material which prevents the spreading | diffusion of the copper of the said core material and the said stabilization material is formed in the outer periphery of the said core material The oxide superconducting wire described above is provided.

  In addition, the present invention provides a superconducting stranded wire formed by twisting a plurality of the oxide superconducting wires, and a superconducting cable and a magnet using the oxide superconducting wire.

The oxide superconducting wire according to the present invention has made it possible to produce a round wire having Je characteristics equivalent to that of a conventional tape wire without using the rolling process that has been unavoidable until now. The authors named this wire an oxide superconducting wire having a TRIC type structure.

In this TRIC type wire, the central portion of the cross section of the wire does not need oxygen permeability, so there is no need to dispose expensive silver. By placing copper in this portion and covering with a barrier material such as Nb or Ta that prevents diffusion with surrounding silver, a low-cost oxide superconducting wire with a reduced amount of silver used can be obtained.

Further, if a TRIC type oxide superconducting wire, which is a round wire, is used as a strand, the cable conductor required for the superconducting power cable can be easily configured using a conventional cable forming technique. Magnetization can also be easily realized by conventional winding technology.

Furthermore, in the method for manufacturing an oxide superconducting wire according to the present invention, continuous superconducting strands may be wound in multiple layers on a core material, so that superconducting strands need not be straightened, cut, deburred, etc. Making composite billets is easy.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 to 5 show an embodiment of the present invention.
Each of the superconducting wires 11 shown in FIGS. 1- (A) to (D) is formed of an oxide superconductor 12 and a matrix 13 made of a stabilizing material. In the present embodiment, the single-core superconducting round strand 11 shown in FIG. 1- (A) is used, but the present invention is not limited to this, and a rectangular strand (FIG. 1- (B)) or a multi-core A superconducting element wire (FIG. 1- (C), (D)) or the like can also be used.

For the superconducting wire 11, an oxide superconductor, preferably a bismuth-based oxide superconductor is used. For example, a bismuth-based oxide superconductor mainly composed of a bismuth-based 2223 phase, a 2212-phase, or the like, or a powder serving as a raw material thereof is filled in a tube made of a stabilizing material, and a wire is produced by a powder-in-tube method. .
The superconducting wire 11 of the present embodiment is a round wire, and its dimensions are, for example, an outer diameter of 2 mmφ and a silver ratio of 1.5.

In the present invention, the stabilizing material forming the matrix includes silver or a silver alloy, such as a silver (Ag) -gold (Au) alloy, a silver (Ag) -manganese (Mn) alloy, silver (Ag) -titanium (Ti ) Alloy, silver (Ag) -antimony (Sb) alloy is used, preferably an Ag-Mg alloy.

On the other hand, a mandrel composed of the rod-shaped core 16 shown in FIG. 2 and the lids 14 and 15 made of silver or a silver alloy on both ends thereof is manufactured. The core material 16 is made of copper or a copper alloy, but in order to prevent diffusion of copper and a silver stabilizing material, a niobium (Nb) or niobium (Nb) -copper (Cu) alloy coating layer is formed on the outside. Used. Since the core material 16 made of copper or copper alloy is used without using the silver core material, the silver ratio of the manufactured oxide superconducting round wire 20 can be reduced.
As for the dimensions of the mandrel, for example, the outer diameter of the core 16 is 10 mm, the outer diameters of the lids 14 and 15 are 25 mm, and the total length is 750 mm.

  Next, as shown in FIG. 3, the superconducting element wire 11 is wound around the outer periphery of the core member 16, the adjacent turns are brought into close contact with each other, and spirally wound in three layers to form a superconducting element wire wound body 17. Then, a tube 18 having an outer diameter of 25 mmφ and an inner diameter of 21 mmφ made of a stabilizing material such as silver or a silver alloy is placed on the outer periphery, and the tube 18 made of silver and the silver lids 14 and 15 are electron beam welded in a vacuum. Thereafter, the composite billet 19 is produced by performing HIP processing and cutting off. This is drawn, and heat treatment at 830 ° C. for 72 hours is repeated three times to obtain an oxide superconducting round wire 20 having a wire diameter of 1.0 mmφ shown in FIG.

  In the cross section of the obtained round wire 20, as shown in FIG. 4, flat filaments 21 embedded in a silver or silver alloy matrix 22 are distributed in layers around the core material, Further, in the longitudinal direction, as shown by dotted lines in FIG. 5, each filament 21 stretched in a ribbon shape is spiral. Accordingly, the filament 21 is stretched not only in one direction in the longitudinal direction but also in a direction perpendicular to the longitudinal direction. This causes a compressive stress to exist around the filament 21 and adds an effect similar to rolling to the oxide superconductor. As a result, superconducting properties can be obtained at the liquid nitrogen temperature in the oxide superconducting wire of the present invention, and the Je properties can be improved.

When Ic of the obtained round wire 20 was measured only in a self-magnetic field in liquid nitrogen, 120 A (Je = 15279 A / cm ² ) was obtained. This is the same Ic characteristic as a tape-like bismuth wire having the same cross-sectional area.

As another embodiment related to the present invention, the oxide superconducting wire obtained in the above embodiment can be processed into a cross-sectional shape shown in FIG. 1 and used as a strand. In this case, the filament of the strand is previously formed in a spiral shape in the longitudinal direction. This is spirally wound on a mandrel as shown in FIG. 2 to obtain a superconducting winding body. Further, after a composite billet as shown in FIG. 3 is formed, it is extruded, drawn and heat-treated in the same manner as described above. As shown, an oxide superconducting wire having a filament 23 that spirally extends in the longitudinal direction while twisting is obtained.

Sectional view of a superconducting wire used in an embodiment of the present invention Sectional drawing of a mandrel with a lid used in an embodiment of the present invention Sectional view of a composite billet made in an embodiment of the present invention Sectional drawing of the superconducting wire created in the embodiment of the present invention Explanatory drawing which shows the presence state of the filament in the superconducting wire created by embodiment of this invention Explanatory drawing which shows the presence state of the filament in the superconducting wire created by other embodiment of this invention Cross section of composite billet by conventional manufacturing method Cross section of superconducting wire by conventional manufacturing method

Explanation of symbols

11: Superconducting wire 12: Oxide superconductor 13, 22, 27: Stabilizer matrix 14, 15: Lid 16: Core material 17: Superconducting wire wound body 18: Tube 19, 24: Composite billet 20, 25 : Round wire 21, 23: Filament

Claims (7)

An oxide superconducting wire comprising: a core material made of metal; a matrix made of a stabilizing material disposed outside the core material; and a filament made of an oxide superconductor embedded in the matrix. However, it is flat in the cross section of the wire and distributed in a layered manner around the core material, and is formed to extend in a spiral shape in the longitudinal direction of the wire, and is 15000 A / cm ² or more in a self-magnetic field at a liquid nitrogen temperature. An oxide superconducting wire characterized by exhibiting an engineering critical current density of The core material is made of copper or a copper alloy, and a coating layer made of a barrier material for preventing diffusion of copper of the core material and the stabilizing material is formed on the outer periphery of the core material. The oxide superconducting wire according to claim 1. The oxide superconducting wire according to claim 1 or 2, wherein a cross-sectional shape of the oxide superconducting wire is circular or rectangular. 4. The oxide superconducting wire according to claim 1, wherein the oxide superconductor is made of a bismuth-based oxide. A superconducting stranded wire formed by twisting a plurality of the oxide superconducting wires according to claim 1. A superconducting cable using the oxide superconducting wire according to claim 1. A magnet using the oxide superconducting wire according to claim 1.

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