JP4770747B2 - Oxide superconducting wire and method for producing the same - Google Patents

Description

  The present invention relates to an oxide superconducting wire and a method for manufacturing the same, and more particularly to an oxide superconducting wire used in the fields of electric power, transportation, high energy, medicine, and the like, and a method for manufacturing an oxide superconducting wire.

  Practical application of superconducting technology using oxide superconductors with high critical temperatures is being promoted. Yttrium-based oxides exhibit a superconducting phenomenon at a temperature of 90K and bismuth-based oxides at a temperature of 110K. These oxide superconductors are expected to be put to practical use because they exhibit superconducting properties in liquid nitrogen that is available at a relatively low cost.

  In order to pass, for example, an alternating current for power supply to such a superconductor, the superconductor is covered with a silver sheath, the silver sheath is covered with a high resistance body, and the high resistance body is further covered with a metal. Such a superconducting wire is used (for example, see Patent Document 1).

In Patent Document 1, an oxide superconducting wire is formed by forming a ceramic body as a high-resistance body interposed between a plurality of oxide superconductors by subjecting a binder and ceramic powder to extrusion and then thermally decomposing the binder. The manufacturing method of this is proposed.
JP 2002-75080 A

  In the method for manufacturing an oxide superconducting wire proposed in Patent Document 1, when the binder is thermally decomposed, the binder may not be completely thermally decomposed and a part of the binder component may remain. When a part of the binder component remains, there is a problem that the residual component of the binder is vaporized when heat treatment for generating or sintering the superconductor is performed, and voids are generated inside the wire.

  Further, when the binder is pyrolyzed, the density of the ceramic body is lowered and becomes non-uniform. Subsequent processing may cause the ceramic body to be broken and reduce the AC loss reduction effect. In addition, if the superconductor is affected during processing due to a decrease in the density of the ceramic body, the performance of the superconductor such as critical current deteriorates.

  Furthermore, when thermally decomposing the binder, there has been a problem of releasing decomposition gases such as carbon dioxide and hydrocarbon gas, which are environmental loads.

  Therefore, a main object of the present invention is to provide an oxide superconducting wire that can solve the problems caused by the thermal decomposition of the binder as described above, and can reduce AC loss, and a method for manufacturing the same.

The method for manufacturing an oxide superconducting wire according to the present invention includes a step of filling a raw material for an oxide superconductor into a small-diameter first metal tube made of silver or a silver alloy. In addition, the method includes a step of forming a single core wire by plastic working the first metal tube. Moreover, the process of producing an AgCl insulating film by the anodic oxidation on the surface of a single core wire, and forming a covering rod is provided. In addition, the method includes a step of forming a multi-core billet by inserting a plurality of covering rods into a second metal tube having a large diameter made of silver or a silver alloy. Moreover, the multi-core billet is plastically processed to form a multi-core wire. In addition, the method includes a step of heat-treating the multi-core wire to generate an oxide superconductor from the raw material while maintaining a uniform structure of the insulating film without generating voids inside the oxide superconducting wire.

  In this case, since a silver compound that can be formed without using a binder is used as the insulating film, when the heat treatment for generating or sintering the oxide superconductor is performed, the residual components of the binder are vaporized and the inside of the oxide superconducting wire No voids are formed in Moreover, since the binder is not used, the density of the insulating film does not decrease and becomes non-uniform, and the uniform structure of the insulating film is maintained even in subsequent processing, and the AC loss is reduced. Since there is no decrease in the density of the insulating film, the oxide superconductor is also processed uniformly, so that the critical current does not decrease. In addition, since no binder is used, cracked gases such as carbon dioxide and hydrocarbon gas, which are environmental loads, are not released.

  In addition, a single-core wire insulating film serving as a high resistance barrier for reducing AC loss is anodized on a first metal tube made of, for example, silver or a silver alloy (for example, the first metal tube in an aqueous NaCl solution). Can be produced by anodizing. Anodization provides a uniform insulating film in a short time, so it is safe and productive, and the load on the surrounding environment is small. Further, the insulating film may be formed by processing or chemically changing the material of the first metal tube surface by a method other than anodic oxidation.

Preferably, the method further includes a step of forming an AgCl insulating film on the surface of the multi-core wire by anodic oxidation after the step of generating the oxide superconductor. In this case, since an insulating film is formed on the surface of the oxide superconducting wire and wire insulation is performed, current transfer occurring between the superconducting wires is suppressed, and AC loss can be reduced. The insulating film that becomes the wire insulation of the oxide superconducting wire can be produced by anodic oxidation (for example, anodic oxidation in a NaCl aqueous solution) of a second metal tube made of, for example, silver or a silver alloy. Anodization provides a uniform insulating film in a short time, so it is safe and productive, and the load on the surrounding environment is small. Further, the insulating film may be formed by processing or chemically changing the material of the second metal tube surface by a method other than anodic oxidation.

The oxide superconducting wire according to the present invention includes a plurality of oxide superconductors. Moreover, the 1st coating layer which consists of silver or a silver alloy which coat | covers each outer periphery of a some oxide superconductor is provided. In addition, a plurality of oxide superconductors are embedded, covering the outer periphery of the first covering layer, and having an insulating layer made of AgCl made by anodic oxidation , in which no voids are formed and the structure is uniformly maintained . Moreover, the 2nd coating layer which consists of silver or a silver alloy which coat | covers the outer periphery of an insulating layer is provided.

  In this case, since the outer periphery of the first covering layer is covered with an insulating layer (for example, an insulating film made of a silver compound produced by anodizing the first covering layer made of silver or a silver alloy). In addition, each of the plurality of oxide superconductors can be reliably electrically separated, and AC loss can be reduced. Since the insulating layer contains a silver compound and does not use a binder, there are no voids inside the oxide superconducting wire, and the structure of the insulating film is kept uniform, so AC loss is reduced. ing. Since there is no decrease in the density of the insulating film, the oxide superconductor is also processed uniformly, so that the critical current does not decrease.

  According to the oxide superconducting wire and the manufacturing method thereof of the present invention, problems due to the thermal decomposition of the binder can be solved, and further, the AC loss of the oxide superconducting wire can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a cross-sectional view of an oxide superconducting wire according to Embodiment 1 of the present invention. As shown in FIG. 1, the oxide superconducting wire 120 includes a plurality of filaments 117 as a plurality of oxide superconductors. In addition, a sheath body 110 made of silver is provided as a first coating layer that covers the outer periphery of each of the plurality of filaments 117. A plurality of filaments 117 are embedded, and an AgCl insulating film 112 as an insulating layer covering the outer periphery of the sheath body 110 is provided. In addition, a sheath body 114 made of silver is provided as a second coating layer covering the outer periphery of the AgCl insulating film 112. The oxide superconducting wire 120 is in the form of a tape and extends from the near side to the far side of the page.

The filament 117, the sheath body 110, the AgCl insulating film 112, and the sheath body 114 are formed in a flat shape so as to extend in the lateral direction. The filament 117 is made of, for example, (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _X. A plurality of filaments 117 are arranged in the oxide superconducting wire 120, and a sheath body 110 and an AgCl insulating film 112 are formed so as to be interposed between the plurality of filaments 117. The oxide superconducting wire 120 may be twisted before being formed into a flat shape, and in that case, a plurality of filaments 117 are formed so as to extend spirally with respect to the central axis of the oxide superconducting wire 120. Has been.

Next, a method for manufacturing the oxide superconducting wire shown in FIG. 1 will be described. 2-6 is a figure for demonstrating the manufacturing method of the oxide superconducting wire shown in FIG. First, as shown in FIG. 2, a raw material powder 100 of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{X used as} a raw material of an oxide superconducting filament is formed on a sheath body 110 made of silver as a first metal tube having a small diameter. Fill. This is drawn (plastic processing) to obtain a silver-coated rod 101 as a single core wire. The raw material powder of the oxide superconducting filament may be formed to form a rod, the rod may be inserted into the sheath body 110, and this may be drawn to form the silver-coated rod 101. The shape of the silver-coated rod 101 may be a hexagonal shape, for example. For the sheath body 110, for example, a silver alloy pipe such as an Ag—Mg alloy, an Ag—Mn alloy, or an Ag—Cu alloy pipe may be used. The silver alloy is an alloy composed of silver and main alloy components such as Mg, Mn, and Cu. However, the silver alloy may contain inevitable impurities.

  As shown in FIG. 3, an insulating film is formed on the surface of the silver-coated rod 101 using an AgCl film forming apparatus 300. The AgCl film forming apparatus 300 includes a supply device 302, a winding device 303, a cleaning device 304, a film forming tank 305, a dryer 306, and a power source 308 inside a dark box 301 for preventing photodecomposition of AgCl. With. The silver-coated rod 101 is supplied from the supply device 302, passes through the cleaning device 304, the film formation tank 305, and the drying device 306, and then wound up by the winding device 303.

  The surface of the sheath body 110 (see FIG. 2) as a surface on which the film is formed is purified by the cleaning device 304 in the silver-coated rod 101 supplied from the supply device 302. As the cleaning device 304, for example, a cleaning tank or an ultrasonic cleaning device can be used. The silver-coated rod 101 whose surface has been purified is electrically connected to the positive side of the power supply 308 at a connector 309. As the connector 309, for example, a roller or a brush can be used.

  In the film forming tank 305, an AgCl insulating film 112 is formed on the surface of the silver-coated rod 101 (see FIG. 4). That is, the inside of the film forming tank 305 is filled with the electrolytic solution 307. In the electrolytic solution 307, a cathode 310 such as a copper plate, which is electrically connected to the negative side of the power source 308, is provided. When the power source 308 is driven, electrons move from the power source 308 to the cathode 310, the electrolytic solution 307, the silver-coated rod 101, and the connector 309 in this order, and return to the power source 308 again. That is, a current flows through the connector 309, the silver-coated rod 101, the electrolytic solution 307, and the cathode 310 by the power source 308. Since the silver-coated rod 101 functions as an anode in the electrolytic solution 307, when a direct current is passed, anodization occurs in which the surface of the metal (that is, silver) serving as an electrode is oxidized by electrolysis. As shown in FIG. 4, an AgCl insulating film 112 is formed on the surface of the sheath body 110 of the silver-coated rod 101 by anodic oxidation, and an AgCl insulating film-coated rod 113 is formed.

  For example, when a 10% NaCl aqueous solution is used as the electrolytic solution 307 and a current of about 30 mA is passed for several minutes by driving the power supply 308, an AgCl insulating film 112 having a thickness of 10 μm is formed on the surface of the silver-coated rod 101. be able to.

  Returning to FIG. 3, in the dryer 306, the electrolytic solution 307 remaining on the surface of the AgCl insulating coating rod 110 is removed by drying. Then, the AgCl insulating coating rod 113 is wound up by the winding device 303.

  Next, as shown in FIG. 5, a plurality of AgCl insulating film-coated rods 113 are bundled and inserted into a sheath body 114 made of silver as a large-diameter second metal tube, and fitted into a multi-core. Billet 115 is formed. The multi-core billet 115 is heated to 200 ° C. in a vacuum to remove moisture inside and seal the terminal under the vacuum.

Next, as shown in FIG. 6, the multicore billet 115 is drawn by plastic working to form a multicore round wire 116 as a multicore wire. The multi-core round wire 116 is rolled to form a rectangular cross section into a tape shape. In addition, heat treatment is performed to generate an oxide superconductor (that is, (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _X ) in the filament 117. Further, secondary rolling is performed, and heat treatment is performed in a high-pressure atmosphere to perform final sintering. AgCl contained in the AgCl insulating film 112 is also melted during the heat treatment. At this time, the AgCl insulating film covering rod 113 is bundled and surrounded by the sheath body 114, so that the shape of the AgCl insulating film 112 is maintained after the heat treatment. .

  In this way, as shown in FIG. 1, it is possible to obtain an oxide superconducting wire 120 in which a plurality of oxide superconductor filaments 117 are embedded in an AgCl insulating film 112 and a sheath body 114 is disposed outside thereof. . For the sheath body 114, for example, a metal tube made of a silver alloy such as an Ag—Mg alloy, an Ag—Mn alloy, or an Ag—Cu alloy pipe having a round cross section with an outer diameter of φ26 mm and an inner diameter of φ22 mm can be used. is there.

  In the oxide superconducting wire according to the first embodiment described above, since no binder is used at the time of manufacturing, when the heat treatment for generating or sintering the oxide superconductor is performed, the residual component of the binder is vaporized and the oxide superconductivity. No voids are generated inside the wire 120. Moreover, since the binder is not used, the density of the insulating film does not decrease and becomes non-uniform, and the uniform structure of the insulating film is maintained even in subsequent processing, and the AC loss is reduced. Since there is no decrease in the density of the insulating film, the oxide superconductor is also processed uniformly, so that the critical current does not decrease. In addition, since no binder is used, cracked gases such as carbon dioxide and hydrocarbon gas, which are environmental loads, are not released.

  Further, the AgCl insulating film 112 serving as a high resistance barrier for reducing AC loss can be produced by anodic oxidation in a NaCl aqueous solution of the sheath body 110 made of, for example, silver or a silver alloy. By anodizing, a homogeneous AgCl insulating film 112 can be obtained in a short time, so it is safe and excellent in productivity, and the load on the surrounding environment is small. Note that the material of the insulating film is not limited to AgCl, and it is preferable that the insulating film is formed of a silver compound such as silver sulfide, silver bromide, and silver iodide.

(Embodiment 2)
FIG. 7 is a cross-sectional view of the oxide superconducting wire according to the second embodiment. The manufacturing method of the oxide superconducting wire according to Embodiment 2 includes basically the same steps as the manufacturing method of the oxide superconducting wire according to Embodiment 1 described above. However, in the second embodiment, after the final sintering for generating the oxide superconductor, for example, the AgCl film forming apparatus 300 shown in FIG. 3 is used on the surface of the sheath body 114 (that is, the surface of the multifilamentary wire). The method further includes the step of producing an insulating film. As a result, an AgCl insulating film 118 is formed on the surface of the oxide superconducting wire 120 as shown in FIG.

  In the oxide superconducting wire 120 according to the second embodiment, the AgCl insulating film 118 is formed on the surface, and since the wire insulation is performed, the AC loss can be reduced. The AgCl insulating film 118 serving as the element insulation of the oxide superconducting wire 120 can be produced by anodic oxidation in the NaCl aqueous solution of the sheath body 114 that is the second metal tube made of silver or a silver alloy. Anodization provides a uniform insulating film in a short time, so it is safe and productive, and the load on the surrounding environment is small. As in the first embodiment, the material of the insulating film is not limited to AgCl, and it is preferable that the insulating film is formed of a silver compound such as silver sulfide, silver bromide, and silver iodide.

  Examples of the present invention will be described below. Samples were prepared by the method for manufacturing an oxide superconducting wire according to the present invention, and experiments were conducted to clarify the superconducting characteristics of each sample.

Sample A was an oxide superconducting wire using a conventional organic binder as a comparative example. First, a raw material powder of a filament of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _X was filled in a silver pipe. A silver pipe was drawn to produce a single core wire. Next, a cellulosic organic binder was added to the SrCO ₃ powder pulverized to an average particle size of about 1 μm, mixed well, mixed with water, kneaded, and the clay was coated around the single core wire by extrusion. The coated ceramic coating (SrCO ₃ powder + cellulose organic binder) was sufficiently dried and then bundled and inserted into an Ag—Mg alloy pipe and fitted.

The fitting pipe was heated to 600 ° C. in the atmosphere to pyrolyze the binder, and the fitting pipe was heated to 200 ° C. in vacuum to further remove moisture inside, and the terminal was sealed under vacuum. Next, the fitting pipe was drawn and rolled into a tape. Then, heat treatment was applied to the fitting pipe to generate (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _X in the filament. Further, secondary rolling was performed, and heat treatment was performed in a high-pressure atmosphere to perform final sintering. Sample A was prepared by the above manufacturing method.

  Sample B was manufactured according to the manufacturing method shown in Embodiment Mode 1. An Ag-Mg alloy pipe was used for the sheath body 114. Sample C was manufactured according to the manufacturing method shown in Embodiment Mode 2. The dimensions of the samples A to C were 2.6 mm in width and 0.18 mm in thickness. Samples A to C were prepared so that the oxide superconducting wire includes 37 filaments.

  For samples A to C, the critical current value Ic was measured in liquid nitrogen at a temperature of 77 K under a self-magnetic field. For samples A to C, an AC magnetic loss was measured by a magnetization method by applying an external magnetic field (magnetic field: 0.1 T, frequency: 50 Hz) in a direction perpendicular to the length direction of the wire and parallel to the tape surface. Further, for samples A to C, the defects generated in the samples were investigated, and the number of defects generated per 1 km was determined.

AC loss W _i for each sample from the length and critical current value of the measured samples were calculated according to the following equation.

W _i = (AC loss of sample i) / {(critical current value of sample i) · (length of sample i)}
The unit of _{W i} is a W / A · m.

  A value obtained by dividing the AC loss value by the AC loss value of Sample A was defined as an AC loss normalized according to the following equation.

Standardized AC loss <W _i > = W _i / W _A
Table 1 shows the critical current value, the number of defects generated, and the normalized AC loss for samples A to C.

  From Table 1, the critical current value is increased, the number of defects generated is decreased, and the AC loss is reduced in Sample B and Sample C, which are the products of the present invention, compared to Sample A which is a comparative example. I understand that. Therefore, it has been shown that an oxide superconducting wire having superior superconducting characteristics and less occurrence of defects can be obtained by the present invention.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is sectional drawing of the oxide superconducting wire according to Embodiment 1 of this invention. It is a perspective view which shows the 1st process of the manufacturing method of the oxide superconducting wire shown in FIG. It is a schematic diagram of an AgCl insulating film forming apparatus. It is a perspective view which shows the 2nd process of the manufacturing method of the oxide superconducting wire shown in FIG. It is a perspective view which shows the 3rd process of the manufacturing method of the oxide superconducting wire shown in FIG. It is a perspective view which shows the 4th process of the manufacturing method of the oxide superconducting wire shown in FIG. 6 is a cross-sectional view of an oxide superconducting wire according to Embodiment 2. FIG.

Explanation of symbols

  100 oxide superconductor raw material powder, 101 silver coated rod, 110 sheath body, 112 AgCl insulating film, 113 AgCl insulating film coated rod, 114 sheath body, 115 multi-core billet, 116 multi-core round wire, 117 filament, 118 AgCl insulation Film, 120 oxide superconducting wire, 300 AgCl film forming device, 301 dark box, 302 supply device, 303 winding device, 304 cleaning device, 305 film forming tank, 306 dryer, 307 electrolyte, 308 power supply, 309 connector, 310 Cathode.

Claims (3)

Filling a metal tube made of silver or a silver alloy with a raw material of an oxide superconductor;
Forming the single core wire by plastic working the metal tube;
Producing an AgCl insulating film by anodic oxidation on the surface of the single core wire to form a coated rod;
Inserting a plurality of the covering rods into a metal tube made of silver or a silver alloy to form a multi-core billet;
Plastically processing the multicore billet to form a multicore wire;
Heat-treating the multifilamentary wire, and maintaining the uniform structure of the insulating film without generating voids inside the oxide superconducting wire, and generating the oxide superconductor from the raw material. A manufacturing method of a wire. The method for producing an oxide superconducting wire according to claim 1, further comprising a step of producing an AgCl insulating film on the surface of the multi-core wire by anodic oxidation after the step of producing the oxide superconductor. A plurality of oxide superconductors;
A first coating layer made of silver or a silver alloy covering the outer periphery of each of the plurality of oxide superconductors;
An insulating layer made of AgCl made by anodic oxidation , in which a plurality of the oxide superconductors are embedded, covering the outer periphery of the first coating layer, and voids are not formed inside, and the structure is uniformly maintained;
An oxide superconducting wire comprising: a second coating layer made of silver or a silver alloy that covers the outer periphery of the insulating layer.

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