JP4893117B2 - Oxide superconducting wire manufacturing method and superconducting equipment - Google Patents

Description

The present invention is used for superconducting application equipment such as superconducting cables, superconducting coils, superconducting transformers, superconducting power storage devices, etc. (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 ± δ} (δ is about 0.1) Number: Hereinafter, it relates to a method of manufacturing an oxide superconducting wire including a phase (hereinafter referred to as (Bi, Pb) 2223), and more specifically, a method of manufacturing an oxide superconducting wire for the purpose of improving the critical current value of (Bi, Pb) 2223 About.

  An oxide superconducting wire mainly composed of (Bi, Pb) 2223 phase produced by a metal sheath method has a high critical temperature and a useful value showing a high critical current value even under relatively simple cooling such as liquid nitrogen temperature. (For example, refer nonpatent literature 1). Therefore, if further improvement in performance (critical current value) is realized, the range of practical use is expanded.

  In addition, it is considered that by using the (Bi, Pb) 2223 superconducting wire, it is possible to reduce energy loss far more than when using a conventional normal conductor. Therefore, development of superconducting application equipment such as a superconducting cable, a superconducting coil, a superconducting transformer, and a superconducting power storage device using a (Bi, Pb) 2223 superconducting wire as a conductor is being promoted simultaneously.

  As a method for increasing the critical current value of a superconducting wire, a method of sintering a (Bi, Pb) 2223 series superconducting wire in a pressurized atmosphere is employed (see Patent Document 1 and Non-Patent Document 1). . As a result, the critical current value at the liquid nitrogen temperature is improved from about 100 A to 120 A class.

JP 2002-093252 A SEI Technical Review, March 2004, No. 164, p36-42

  The effect of improving the critical current value is also recognized by the above technique. However, considering the needs from the future market, further increase of the critical current value is desired. Therefore, an object of the present invention is to provide a method for producing an oxide superconducting wire having a higher critical current value.

  The present inventors investigated the relationship between rolling processing during the manufacturing process of (Bi, Pb) 2223 wire and the packing powder before and after that, and improved the critical current value by giving the packing powder characteristics before the rolling process. I found out.

  The present invention includes a wire drawing step of drawing a wire in a form in which a precursor powder of (Bi, Pb) 2223 superconductivity is coated with a metal, a rolling step of rolling the wire after the wire drawing step, and after the rolling step A heat treatment step of heat-treating the wire, and adding an intermediate heat treatment between the wire drawing step and the rolling step to make the crystal grain size of the precursor powder in the wire larger than the crystal grain size after wire drawing This is a method for producing an oxide superconducting wire.

  In the present invention, it is preferable that the average size in the direction perpendicular to the c-axis of the crystal grains of the precursor powder is 2 μm or more by the intermediate heat treatment.

  In the present invention, the intermediate heat treatment is preferably performed under conditions of 1 hour to 5 hours in an oxygen-containing atmosphere at a temperature of 700 ° C. or higher and 800 ° C. or lower.

  In the present invention, the (Bi, Pb) 2223 superconducting precursor powder preferably has a tetragonal Bi2212 phase as a main phase.

  Moreover, this invention is a superconducting apparatus which contains the oxide superconducting wire manufactured by the manufacturing method in any one of said as a conductor.

  According to the production method of the present invention, a (Bi, Pb) 2223 oxide superconducting wire having a high critical current value can be obtained. Moreover, by using the oxide superconducting wire of the present invention as a conductor, it is possible to realize superconducting equipment such as a high-performance superconducting cable, a superconducting coil, a superconducting transformer, and a superconducting power storage device.

(Embodiment)
FIG. 1 is a partial cross-sectional perspective view schematically showing the configuration of an oxide superconducting wire. For example, a multi-core oxide superconducting wire will be described with reference to FIG. The oxide superconducting wire 11 has a plurality of oxide superconductor filaments 12 extending in the longitudinal direction and a sheath portion 13 covering them. The material of each of the plurality of oxide superconductor filaments 12 is preferably a Bi—Pb—Sr—Ca—Cu—O based composition, and the atomic ratio of (Bi, Pb): Sr: Ca: Cu is particularly about 2. The material including the (Bi, Pb) 2223 phase expressed by the ratio of 2: 2: 3 is optimal. The material of the sheath part 13 is comprised from metals, such as silver and a silver alloy, for example.

  Next, the manufacturing method of said oxide superconducting wire is demonstrated.

  FIG. 2 is a flowchart showing a manufacturing process of the oxide superconducting wire in the embodiment of the present invention. 3 to 7 are diagrams showing each step of FIG.

Referring to FIGS. 2 and 3, first, oxide superconductor precursor powder 31 is filled into metal tube 32 (step S1). This oxide superconductor precursor powder 31 has, for example, a (Bi, Pb) ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 ± δ} (δ is a number close to 0.1: hereinafter referred to as (Bi, Pb) 2212) phase. (Bi, Pb) 2223 phase, alkaline earth oxides (for example, (Ca, Sr) CuO ₂ , (Ca, Sr) ₂ CuO ₃ , (Ca, Sr) ₁₄ Cu ₂₄ O ₄₁ etc.) , And a Pb oxide (for example, Ca ₂ PbO ₄ , (Bi, Pb) ₃ Sr ₂ Ca ₂ Cu ₁ O _z ). The metal tube 32 is preferably made of silver or a silver alloy. This is to prevent compositional deviation of the precursor powder due to the reaction between the precursor powder and the metal tube to form a compound.

  Next, as shown in FIG. 2 and FIG. 4, the metal tube 41 filled with the precursor powder is drawn to a desired diameter, and the precursor 42 is used as a core material and coated with a metal such as silver. The core wire 43 is produced (step S2).

  Next, as shown in FIGS. 2 and 5, a large number of single core wires 51 are bundled and fitted into a metal tube 52 made of, for example, silver (multi-core fitting: step S3). Thereby, the multi-core structure material which has many precursor powders as a core material is obtained.

  Next, as shown in FIGS. 2 and 6, the multi-core structural member 61 is drawn to a desired diameter, the precursor powder 62 is embedded in the metal sheath portion 63, and the cross-sectional shape is circular or polygonal. An isotropic multi-core bus 64 is produced (step S4). Thereby, an isotropic multi-core bus 64 having a form in which the precursor powder 62 of the oxide superconducting wire is covered with a metal is obtained.

  Next, as shown in FIG. 2, the isotropic multi-core bus 71 is subjected to an intermediate heat treatment. (Step S5). This step is a feature of the present invention. Details of this step will be described later.

  Next, as shown in FIGS. 2 and 7, the isotropic multi-core bus bar 71 is rolled (primary rolling: step S6). Thereby, the tape-shaped precursor wire 72 is obtained.

  Next, the tape-shaped precursor wire is heat-treated (primary heat treatment: step S7). This heat treatment is performed at a temperature of about 830 ° C., for example, under atmospheric pressure or in a pressurized atmosphere of 1 MPa to 50 MPa. The target (Bi, Pb) 2223 superconducting phase is generated from the precursor powder by heat treatment.

  Thereafter, the wire is rolled again (secondary rolling: step S8). In this way, voids generated by the primary heat treatment are removed by performing the secondary rolling.

  Subsequently, the wire is heat-treated at a temperature of, for example, 830 ° C. (secondary heat treatment: step S9). Also at this time, heat treatment is performed under atmospheric pressure or in a pressurized atmosphere. The oxide superconducting wire shown in FIG. 1 is obtained by the above manufacturing process. The oxide superconducting wire is obtained by the above manufacturing process.

  Details of the intermediate heat treatment in step S5, which is a feature of the present invention, will be described below. In order to achieve a high critical current density in an oxide superconducting wire, high orientation of superconducting crystal grains is important. For this purpose, rolling in step S6 is performed. In this method, the wire is deformed in a uniaxial direction into a tape shape, and the ab plane direction of the (Bi, Pb) 2223 superconducting crystal is oriented so as to be parallel to the tape surface.

  FIG. 8A shows a cross-sectional view of a wire rod, in which an isotropic multi-core bus bar having a circular cross-sectional shape is rolled and a change in the internal crystal is schematically represented. In FIG. 8, the case of a single core wire is represented as a model. In the isotropic bus 81 having a circular cross section, various crystals 83 including a flat superconducting phase are present in the metal tube 82. In such a situation, if the superconducting crystal has a sufficiently large size before rolling, each crystal has a longitudinal direction (a-b plane direction) at the time of rolling when it becomes the tape material 84 by the rolling operation. It falls down so that it is perpendicular to the direction of external force, and the direction is aligned. On the other hand, as shown in FIG. 8B, when the crystal size is small, the crystal 83 is not easily tilted and is not easily oriented. Therefore, it is advantageous for orientation that the size of the crystal 83 is as large as possible before rolling.

  By the way, the wire rod is subjected to wire drawing in steps S2 and S4 before rolling. This wire drawing process is a diameter reduction process, and each metal tube undergoes a reduction deformation of about 1/10 to 1/100 in the diameter from the state filled in step S1.

  In this deformation, the filled precursor powder also receives an external force and is crushed to reduce the crystal size. Even if a rolling operation is performed in such a situation, orientation is unlikely to occur. Therefore, in the present invention, an intermediate heat treatment is performed before rolling in order to enlarge the crystal grains that are crushed and reduced in the wire drawing step.

  A wire cross-sectional view schematically showing the effect of the present invention is shown in FIG. The crystal grains of the precursor powder are broken by the wire drawing process. Heat treatment is performed on the crystal grains that have become smaller to increase the crystal grain size. A highly oriented structure can be obtained by rolling the enlarged crystal grains.

  As a measure of the intermediate heat treatment condition, it is easy to optimize the heat treatment condition if it is determined based on the size of the crystal grain in the direction perpendicular to the c-axis (the width of the plate crystal). The inventors have experimentally found that the effect is large when the average size of the crystal grains in the direction perpendicular to the c-axis is 2 μm or more.

  The “average size in the direction perpendicular to the c-axis” will be described. In the isotropic bus bar after drawing or after intermediate heat treatment, each crystal grain exists so that the ab plane direction and the bus bar longitudinal direction are substantially parallel. When a cross section perpendicular to the longitudinal direction is observed in such a bus, the side surfaces (ac surface, bc surface, or ab-c surface) of each crystal can be seen. Measure the longer side on this side. In some cases, the actual crystal has a direction size perpendicular to the c-axis that is longer than the visible side surface, but at least the size of the portion appearing in the cross section. Therefore, this observed length is defined as “size of each crystal”. The crystal size is measured for crystals of about several tens to one hundred, and the average value is calculated. The value is defined as “average size”.

  It has also been found that the specific intermediate heat treatment condition as described above is 1 hour to 5 hours at a temperature of 700 ° C. to 800 ° C. in an oxygen-containing atmosphere.

On the other hand, the degree of crystal grain growth in this intermediate heat treatment is affected by the components constituting the precursor powder. In the precursor powder to be filled, (Bi, Pb) 2212 phase that is orthorhombic and Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 ± δ that} is tetragonal (δ is a number close to 0.1: Two 2212 phases (referred to as Bi2212) are mixed. These ratios can be adjusted at the stage of preparing the precursor powder. The Bi 2212 phase absorbs Pb from the surrounding Pb compound and can replace the (Bi, Pb) 2212 phase. When this reaction occurs, a very large (Bi, Pb) 2212 phase is easily generated from the Bi 2212 phase. Therefore, it is preferable that the precursor powder as the main phase is a tetragonal Bi2212 phase, which is more effective when subjected to an intermediate heat treatment.

  As described above, a highly oriented structure can be obtained by rolling a wire containing large superconducting crystal grains. When the processing after step S6 is performed on the basis of this highly oriented wire, a superconducting wire having a high critical current value can be manufactured.

  Moreover, since the superconducting device according to the present invention is composed of the superconducting wire having a high critical current value as described above, it has excellent superconducting characteristics. Here, the superconducting device is not particularly limited as long as it includes the superconducting wire, and examples thereof include a superconducting cable, a superconducting coil, a superconducting transformer, and a superconducting power storage device. For example, in superconducting cables and superconducting transformers used in AC applications, the loss in operating current value decreases due to the improvement of the critical current value. On the other hand, the maximum generated magnetic field and the maximum stored energy are greatly increased in devices mainly using DC, such as a superconducting coil and a superconducting power storage device.

(Example)
Hereinafter, based on an Example, this invention is demonstrated further more concretely.

Raw material powder (Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , CuO) is Bi: Pb: Sr: Ca: Cu = 1.8: 0.3: 1.9: 2.0: 3.0 The mixture is subjected to heat treatment at 700 ° C. for 8 hours, pulverization, heat treatment at 800 ° C. for 10 hours, pulverization, heat treatment at 820 ° C. for 4 hours, and pulverization in the air to obtain a precursor powder. In addition, by injecting a nitric acid aqueous solution in which five types of raw material powders are dissolved into a heated furnace, the water content of the metal nitrate aqueous solution particles evaporates, the thermal decomposition of the nitrate, and the reaction and synthesis of metal oxides. Precursor powder can also be produced by a spray pyrolysis method that instantly raises. The precursor powder thus produced is a powder mainly composed of the Bi2212 phase. In addition, a part of the heat treatment conditions is changed to obtain a precursor powder in which the (Bi, Pb) 2212 phase is the main phase.

  The precursor powder produced as described above is filled in a silver pipe having an outer diameter of 25 mm and an inner diameter of 22 mm, and drawn to a diameter of 2.4 mm to produce a single core wire. The single core wires are bundled into 55, inserted into a silver pipe having an outer diameter of 25 mm and an inner diameter of 22 mm, and drawn to a diameter of 1.5 mm to obtain a multi-core (55 core) wire.

  This multi-core wire is heat treated. The heat treatment atmosphere was set at a total pressure of 1 atm (0.1 MPa) and an oxygen partial pressure of 0.0001 MPa, and the heat treatment was performed at various temperatures with the time fixed at 2 hours. Table 1 shows the temperature conditions and sample numbers. Then, the edge part was cut out and the crystal grain size (crystal size before rolling) was measured by observing a cross section perpendicular | vertical to a longitudinal direction with an electron microscope. As for the average grain size, the side size of the longer one of the crystal side surfaces shown in the cross section as described above is measured for 100 crystals selected arbitrarily. And the average value is calculated. The results are shown in Table 1.

  After the heat treatment, the multi-core wire is rolled and processed into a tape-like wire having a thickness of 0.25 mm. The obtained tape-shaped wire is subjected to primary heat treatment at 830 ° C. for 30 to 50 hours in an atmosphere having a total pressure of 1 atm (0.1 MPa) and an oxygen partial pressure of 8 kPa.

  The tape-shaped wire after the primary heat treatment is re-rolled to a thickness of 0.23 mm. The tape-shaped wire after re-rolling is subjected to a secondary heat treatment at 830 ° C. for 50 to 100 hours in a pressurized atmosphere containing an oxygen partial pressure of 8 kPa and a total pressure of 30 MPa. The critical current value (Ic) of the produced wire was measured.

For the critical current value, a current-voltage curve was measured by a four-terminal method at a temperature of 77 K and in a zero magnetic field, and a current that generates a voltage of 1 × 10 ⁻⁶ V per 1 cm of wire was defined as the critical current value.

  Further, as an evaluation of the orientation of the (Bi, Pb) 2223 crystal, the following average misalignment angle α is measured. The average misalignment angle α is the average angle formed between the surface formed by the a-axis and the b-axis of each (Bi, Pb) 2223 crystal and the tape surface (width × length surface) of the wire. Say. The smaller the average misorientation angle α of (Bi, Pb) 2223 crystal, the higher the orientation of (Bi, Pb) 2223 crystal. The average misorientation angle α of the (Bi, Pb) 2223 crystal is calculated as ½ of the half width of the diffraction peak derived from the (0,0,24) plane of the (Bi, Pb) 2223 phase. Ic and α are shown in Table 1.

  Sample 1 (comparative example) is not subjected to intermediate heat treatment. Sample 2 (Example) and thereafter are subjected to intermediate heat treatment. Sample 1 not subjected to intermediate heat treatment has an average crystal size before rolling of 0.5 μm. Further, the critical current value after the completion of all the steps is 120A, and the deviation angle α is 11 °. In samples 2 to 10 subjected to the intermediate heat treatment according to the present invention, the average crystal size before rolling is larger than that of sample 1. Further, both the critical current value and the deviation angle α are improved as compared with the sample 1.

  When samples 2 to 10 are compared, high critical current values of 160 A or more are obtained in samples 4 to 9 in which the intermediate heat treatment temperature is in the range of 700 ° C. or higher and 800 ° C. or lower. Further, when the main phase of the precursor powder is changed (comparison between samples 6 and 7), it can be seen that the effect is greater when the Bi2212 phase is the main phase.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. 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 a partial section perspective view showing typically the composition of an oxide superconducting wire. It is a flowchart which shows the manufacturing process of the oxide superconducting wire in embodiment of this invention. It is a figure which shows S1 step in FIG. It is a figure which shows S2 step in FIG. It is a figure which shows S3 step in FIG. It is a figure which shows S4 step in FIG. It is a figure which shows S5 step in FIG. It is wire rod sectional drawing showing typically the change of the crystal inside a metal pipe at the time of rolling. It is wire rod sectional drawing which expressed the effect of the present invention typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Oxide superconducting wire, 12 Oxide superconducting filament, 13 Sheath part, 31 Precursor powder, 32 Metal tube 41 Metal tube filled with precursor powder, 42 Precursor, 43 Single core wire, 51 Single core wire, 52 Metal tube 61 multi-core structural material, 62 precursor raw material powder, 63 metal sheath part, 64 isotropic multi-core bus bar, 71 isotropic multi-core bus bar, 72 tape-like precursor wire 81 isotropic bus bar, 82 metal tube, 83 crystal, 84 tape material.

Claims (4)

(Bi, Pb) a wire drawing step of drawing a wire in a form in which a precursor powder of 2223 superconductor is coated with silver or a silver alloy ;
A rolling step of rolling the wire after the wire drawing step;
A heat treatment step of heat-treating the wire after the rolling step,
The (Bi, Pb) 2223 superconducting precursor powder includes a tetragonal Bi2212 phase as a main phase,
Furthermore, it is made of a material containing at least one of orthorhombic (Bi, Pb) 2212 phase, (Bi, Pb) 2223 phase, alkaline earth oxide, Pb oxide,
Production of an oxide superconducting wire characterized in that an intermediate heat treatment is applied between the wire drawing step and the rolling step so that the crystal grain size of the precursor powder in the wire is larger than the crystal grain size after the wire drawing. Method.   2. The method for producing an oxide superconducting wire according to claim 1, wherein an average size in a direction perpendicular to the c-axis of the crystal grains of the precursor powder is set to 2 μm or more by the intermediate heat treatment.   3. The oxide superconductivity according to claim 1, wherein the intermediate heat treatment is performed at a temperature of 700 ° C. or more and 800 ° C. or less in an oxygen-containing atmosphere for 1 to 5 hours. A manufacturing method of a wire. The superconducting apparatus which contains the oxide superconducting wire manufactured by the manufacturing method in any one of Claim 1 to 3 as a conductor.

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