JP2010049919A - Bi2223 OXIDE SUPERCONDUCTIVE MULTICORE PRECURSOR WIRE MATERIAL, Bi2223 OXIDE SUPERCONDUCTIVE WIRE MATERIAL, AND MANUFACTURING METHOD OF Bi2223 OXIDE SUPERCONDUCTIVE WIRE MATERIAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multicore precursor wire material of an oxide superconductive wire material capable of improving superconductive characteristics. <P>SOLUTION: A Bi2223 oxide superconductive multicore precursor wire material is obtained by wire-drawing processing of a second metal tube after a plurality numbers of single core wires obtained by wire-drawing process are inserted into the second metal tube into which a first metal tube precursor powders of Bi2223 superconductive body are filled. The average value of Vickers hardness of the precursor powders after wire-drawing process measured by cross-sectional observation of the Bi2223 oxide superconductive multicore precursor wire material is 90 or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention is (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 ± δ} (δ is a number of about 0.1: The present invention relates to a method for producing an oxide superconducting wire containing a phase (hereinafter referred to as Bi2223), and more particularly to a method for producing an oxide superconducting wire for the purpose of improving the critical current value of the Bi2223 superconducting wire.

  In recent years, it has been reported that sintered oxides exhibit superconducting properties at a high critical temperature, and the practical application of superconducting technology has been promoted using this superconductor. The Bi2223 superconducting wire is a useful wire that exhibits a high critical current value even under cooling of liquid nitrogen or the like that can be obtained at a relatively low cost.

Such a manufacturing method of the Bi2223 superconducting wire is described in, for example, Japanese Patent Application Laid-Open No. 2007-26773 (Patent Document 1) and Japanese Patent Publication No. 11-506866 (Patent Document 2). Specifically, first, a metal tube is filled with a precursor powder mainly composed of a (BiPb) ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 ± δ} (δ is a number close to 0.1: hereinafter referred to as Bi2212) phase. After that, a single core material is formed by drawing. Thereafter, a plurality of single core materials are bundled and inserted into a metal tube, and drawn to form a multicore material having a multicore structure. The multi-core material is primarily rolled to form a tape-shaped wire. Subsequently, heat treatment is performed on the tape-shaped wire, and the Bi2212 phase is transformed into the Bi2223 phase to obtain a primary wire. Next, after the primary wire is secondarily rolled, a second heat treatment is performed to produce a Bi2223 superconducting wire.

JP 2007-26773 A Japanese National Patent Publication No. 11-506866

  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, the present invention provides a method for producing an oxide superconducting wire having a higher critical current value.

  Therefore, an object of the present invention is to provide a precursor wire for producing a Bi2223 oxide superconducting wire having a higher critical current value and a Bi2223 oxide superconducting wire having a high critical current value.

  In the present invention, after inserting a plurality of single core wires obtained by drawing a first metal tube filled with Bi2223 superconductor precursor powder into the second metal tube, the second metal tube Bi2223 oxide superconducting multi-core precursor wire obtained by drawing a wire, and the Vickers of the precursor powder after wire drawing measured by cross-sectional observation of the Bi2223 oxide superconducting multi-core precursor wire A Bi2223 oxide superconducting multi-core precursor wire characterized by having an average hardness value of 90 or more.

  In the present invention, the standard deviation of the Vickers hardness is preferably 20 or less.

  The manufacturing method of the oxide superconducting wire of the present invention includes a first heat treatment step for heat-treating the Bi2223 oxide superconducting multicore precursor wire, and rolling the heat-treated Bi2223 oxide superconducting multicore precursor wire. A rolling step and a second heat treatment step for heat-treating the rolled Bi2223 oxide superconducting multi-core precursor wire.

  The oxide superconducting wire of the present invention is a Bi2223 oxide superconducting wire manufactured by the above manufacturing method.

  According to the present invention, a Bi2223 oxide superconducting wire having a high critical current value can be obtained.

(Embodiment)
FIG. 1 is a partial cross-sectional perspective view schematically showing the structure of a Bi2223 oxide superconducting wire. 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 from a Bi2223 phase in which the atomic ratio of (Bi, Pb): Sr: Ca: Cu is approximated by a ratio of 2: 2: 2: 3. It has become. 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.

  Then, with reference to FIGS. 2-7, the manufacturing method of the Bi2223 superconducting wire in embodiment of this invention is demonstrated. In addition, FIG. 2 is a flowchart which shows the manufacturing method of Bi2223 superconducting wire in embodiment of this invention. FIG. 3 is a schematic perspective view showing a step (S1 step) of obtaining a single core bus in the embodiment of the present invention. FIG. 4 is a schematic perspective view showing a step (S2 step) of drawing a single core bus in the embodiment of the present invention. FIG. 5 is a schematic perspective view showing a multi-core fitting step (step S3) in the embodiment of the present invention. FIG. 6 is a schematic perspective view showing a step (step S4) of drawing the multicore bus in the embodiment of the present invention. FIG. 7 is a schematic perspective view showing a step (S6 step) of rolling the multi-core precursor wire in the embodiment of the present invention.

Referring to FIGS. 2 and 3, first, Bi2223 oxide superconductor precursor powder 31 is filled into metal tube 32 (step S1). The oxide superconductor precursor powder 31 has a Bi2212 phase as a main superconducting phase, a Bi2223 phase, an alkaline earth oxide (for example, (CaSr) CuO ₂ , (CaSr) ₂ CuO ₃ , (CaSr) ₁₄ Cu _24. O _{41 and the} like) and a Pb oxide (for example, Ca ₂ PbO ₄ , (BiPb) 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 31 due to the reaction between the precursor powder 31 and the metal tube 32 to form a compound.

  Next, as shown in FIGS. 2 and 4, the single core bus bar 41 filled with the precursor powder is drawn to a desired diameter, and the precursor powder 31 is coated with a metal such as silver as a core material. A single-core precursor wire 42 is prepared (step S2).

  Next, as shown in FIGS. 2 and 5, a large number of single-core precursor wires 42 are bundled and fitted into a metal tube 51 made of, for example, silver (multi-core fitting: step S3). Thereby, the multi-core bus 52 which has precursor powder as a core material is obtained.

  Next, as shown in FIGS. 2 and 6, the multicore bus 52 is drawn to a desired diameter, the precursor powder 31 is embedded in the metal sheath portion 61, and the cross-sectional shape is circular or polygonal. A core precursor wire 62 is produced (step S4). The present invention is characterized by this multi-core precursor wire. The characteristics of this multi-core precursor wire will be described in detail later.

  Next, as shown in FIG. 2, this multi-core precursor wire 71 is subjected to an intermediate heat treatment. (Step S5). The purpose of step S5 is to grow the Bi2212 crystal in the precursor powder 31 by heat treatment.

  Next, as shown in FIGS. 2 and 7, the multi-core precursor wire 62 after the intermediate heat treatment is rolled (primary rolling: step S6). Thereby, the tape-shaped precursor wire 71 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. By this heat treatment, the target Bi2223 phase is generated in the precursor powder.

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

  Subsequent to step S8, the wire is heat-treated at a temperature of, for example, about 830 ° C. under atmospheric pressure or a pressurized atmosphere (secondary heat treatment: step S9). The oxide superconducting wire shown in FIG. 1 is obtained by the above manufacturing process.

  In order to achieve a high critical current density in an oxide superconducting wire, high orientation of superconducting crystal grains is important. Eventually, the target Bi2223 phase may be oriented so that the ab plane direction of the Bi2223 phase is parallel to the tape surface.

  The orientation is mainly performed in the primary rolling process in step S6. Before the primary rolling, the precursor powder contains a Bi2212 phase as the main superconducting phase. This Bi2212 phase crystal is oriented by primary rolling. A Bi2223 phase structure that inherits the high orientation of the Bi2212 phase crystal is obtained by heat-treating the rolled wire rod in which the Bi2212 phase crystal is highly oriented to generate the Bi2223 phase.

  In order to achieve high orientation of the Bi2212 phase crystal, it is important to grow the Bi2212 phase crystal greatly before rolling. The reason is as follows.

  FIG. 8 shows a wire cross-sectional view schematically showing a change in crystal orientation inside the wire when the wire having a circular cross-sectional shape is rolled. In FIG. 8, the case of a single core wire is represented as a model. FIG. 8A shows the case where the Bi2212 phase crystal is large. In the precursor wire 81 having a circular cross section, a flat Bi2212 phase crystal 83 exists in the metal tube 82. In such a situation, if the Bi2212 phase crystal 83 has a sufficiently large size before rolling, the longitudinal direction (a-b plane direction) of each crystal is perpendicular to the direction of external force during rolling. It becomes the tape-like precursor wire rod 84 that is tilted so as to be aligned. On the other hand, as shown in FIG. 8B, when the Bi2212 phase crystal size 83 is small, the Bi2212 phase crystal 83 is not easily tilted and is not easily oriented, and the Bi2212 phase crystal 83 is not very oriented. Become. Therefore, increasing the size of the Bi2212 phase crystal 83 as much as possible before rolling is advantageous for orientation.

  In order to increase the size of the Bi2212 phase crystal before rolling, an intermediate heat treatment in step S5 is performed. The present invention is a multi-core precursor wire capable of growing a larger Bi2212 phase crystal by this intermediate heat treatment. .

  Details of the multi-core precursor wire produced in step S4, which is a feature of the present invention, will be described below. The multi-core precursor wire of the present invention has an average value of 90 or more Vickers hardness of the precursor powder measured by cross-sectional observation. High Vickers hardness means that it is hard because the precursor powder is densely packed. When the precursor powder is densely packed, there are many portions where the powders are in contact with each other, and reaction is likely to occur in the subsequent intermediate heat treatment. Therefore, the Bi2212 phase crystal grows greatly by the intermediate heat treatment. Thus, a harder, densely packed precursor powder state is preferred. The inventors have found that a high critical current value is easily obtained when the average value of the Vickers hardness is 90 or more.

  Vickers hardness is measured by a commonly used technique. The multi-core precursor wire after drawing has a diameter of about 2 mm. The multi-core precursor wire is cut at an arbitrary portion in a direction substantially perpendicular to the longitudinal direction of the wire. While observing the cross section with an optical microscope, the hardness of the portion where the precursor powder is present (filament portion) is measured at a plurality of points. The wire targeted in the present invention is a multi-core wire having 50 or more filaments. FIG. 9 is a cross-sectional view of a 61-core precursor wire. In the cross section shown in FIG. 9, assuming that the filaments 91 having substantially the same distance from the center are in the same layer (in the case of the filament 91, the third layer from the inside) Measure the filament hardness. A measurement point of about 20 to 50 is sufficient. The average Vickers hardness is calculated from the data. The standard deviation of Vickers hardness is also derived using the same data. Although the cross section of the multi-core precursor wire may not be as shown in FIG. 9, it is sufficient to select an equal number of measurement points from the inside, the outside, and an intermediate point thereof.

  A more preferable state in the present invention is that the hardness (density) of each filament is uniform. The optimum condition for the intermediate heat treatment correlates with the state of the filament part. For example, the optimum heat treatment condition differs between the portion where the Vickers hardness is 90 and the portion where 120 is Vickers hardness. When heat treatment is performed in accordance with the portion having a Vickers hardness of 90, the Bi2212 phase crystal of the portion having a Vickers hardness of 120 does not grow to the maximum. Therefore, in order to make the same heat treatment condition suitable for all filaments, it is preferable that the hardness (density) of each filament is uniform. The inventors have found that when the variation of the filament hardness is expressed by a standard deviation, a state where the standard deviation is 20 or less is more effective.

  By performing an intermediate heat treatment on the multi-core precursor wire as described above, and growing the Bi2212 phase crystal in the precursor powder greatly, a tape-like precursor wire having a highly oriented structure is obtained in the subsequent rolling process, As a result, a Bi2223 superconducting wire having a high critical current value can be produced.

  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 in a ratio of 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.

  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 61 wires and inserted into a silver pipe having an outer diameter of 25 mm and an inner diameter of 22 mm to form a multi-core bus bar. Prepare multiple multi-core busbars and stretch each to a diameter of 1.5 mm under different conditions (by changing the die angle used for wire drawing and the number of intermediate softening at 200 ° C for 1 hour in the middle of wire drawing). To line. Thus, the multi-core (61-core) precursor wires of Examples 1 to 4 and Comparative Examples 1 to 3 were obtained. Table 1 shows the drawing conditions of each multi-core precursor wire.

  The multicore precursor wire after drawing was cut at 1 m from the end, and the Vickers hardness of the filament part in the precursor wire was measured while observing the cross section with an optical microscope. The cross section was as shown in FIG. As described above, 5 filaments were extracted from each layer excluding the center as described above to obtain a total of 20 points. The measurement results (average values) are shown in Table 1.

This multi-core precursor wire is subjected to heat treatment (intermediate heat treatment) at 760 ° C. for 2 hours in the atmosphere. It cut | disconnected in the 1-m part from the end after heat processing, the cross section was observed with the scanning electron microscope (SEM), and the size of the Bi2212 phase crystal was measured. Select all 20 filaments, 5 filaments each from the inner layer to the outer layer, arbitrarily select 5 Bi2212 phase crystals contained in it (100 in total), count the size in the long direction as the crystal size, The average value was obtained. The results are shown in Table 1.
These multi-core precursor wires are rolled and processed into a tape-like wire having a thickness of 0.25 mm (primary rolling). The obtained tape-shaped wire is heat-treated at 830 ° C. for 50 hours and under an atmospheric pressure with an oxygen partial pressure of 8 kPa (primary heat treatment).

Next, the tape-shaped wire after the primary heat treatment is subjected to a rolling process again so as to have a thickness of 0.22 mm (secondary rolling). The tape-shaped wire rolled again is heat-treated at 830 ° C. for 50 hours, under an oxygen partial pressure of 8 kPa and a total pressure of 30 MPa to obtain a final superconducting wire (secondary heat treatment). The critical current value of the obtained superconducting wire was evaluated. The critical current value was measured in a self-magnetic field at a temperature of 77K. The critical current value was defined as a current value when an electric field of 10 ⁻⁶ V / cm was generated. The measurement results are shown in Table 1.

  As can be seen from Table 1, when the die angle during wire drawing and the number of intermediate softenings are changed, the filament hardness in the multicore precursor wire changes. By reducing the die angle from 11 ° to 9 °, the average Vickers hardness increases. Moreover, it tends to be harder as the number of intermediate softenings is smaller. Preferable is 3 times or less. This is because the work hardening of the sheath part (silver) affects the hardening of the filament part. During wire drawing, the silver hardens and breaks. Generally, in order to prevent this, a die with a large angle is used or intermediate softening is frequently performed. However, these operations are counterproductive in order to increase the hardness of the filament. In Examples 1 to 4 having an average Vickers hardness of 90 or more, the Bi2212 phase crystals are greatly grown to 2.5 μm or more after the intermediate heat treatment. As a result, a high critical current value of 170 A or more is obtained.

  Examples 5 to 7 were produced under the same conditions as in Example 2 except that only the temperature of intermediate softening was changed. Using them, superconducting wires were produced under the same conditions as in Example 2, and the average Vickers hardness, standard deviation of Vickers hardness, Bi2212 phase crystal, and critical current value were evaluated. The evaluation method is the same as in Example 2. The results are shown in Table 2.

  As can be seen from Table 2, the variation (standard deviation) in filament hardness in the multi-core precursor wire varies depending on the presence / absence of intermediate softening and its temperature. In Examples 1, 2, and 5 in which the variation (standard deviation) in the filament hardness is 20 or less, the Bi2212 phase crystal is greatly grown to 3.0 μm or more after the intermediate heat treatment. This is because the filament state in the multi-core precursor wire is uniform, and therefore the intermediate heat treatment conditions (760 ° C. in the atmosphere, 2 hours) applied for Bi2212 phase crystal growth are generally compatible. . As a result, a high critical current value of 180 A or more is obtained. From this result, it is preferable that the intermediate softening is not performed or is performed at a low temperature of 200 ° C. or lower.

  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. FIG. 3 is a wire cross-sectional view schematically showing a change in crystal orientation inside a wire when a wire having a circular cross-sectional shape is rolled. It is sectional drawing of a 61-core precursor wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Oxide superconducting wire 12 Oxide superconducting filament 13 Sheath part 31 Precursor powder 32 Metal tube 41 Single core bus 42 Single core precursor wire 51 Metal tube 52 Multicore bus 61 Metal sheath part 62 Multicore precursor wire 71 Tape shape Precursor wire 81 Precursor wire 82 having a circular cross section Metal tube 83 Bi2212 phase crystal 84 Tape-like precursor wire 91 Filaments having substantially the same distance from the center

Claims (4)

After inserting a plurality of single core wires obtained by drawing a first metal tube filled with Bi2223 superconductor precursor powder into the second metal tube, the second metal tube is drawn. Bi2223 oxide superconducting multi-core precursor wire obtained by
Bi2223 oxide superconducting multicore precursor, characterized in that an average value of Vickers hardness of the precursor powder after wire drawing is 90 or more, as measured by cross-sectional observation of the Bi2223 oxide superconducting multicore precursor wire. Body wire.   The Bi2223 oxide superconducting multi-core precursor wire according to claim 1, wherein the standard deviation of the Vickers hardness is 20 or less. A first heat treatment step of heat treating the Bi2223 oxide superconducting multi-core precursor wire according to claim 1 or 2;
A rolling step of rolling the heat treated Bi2223 oxide superconducting multi-core precursor wire;
And a second heat treatment step for heat-treating the rolled Bi2223 oxide superconducting multi-core precursor wire. A method for producing a Bi2223 oxide superconducting wire.   A Bi2223 oxide superconducting wire manufactured by the method for manufacturing a Bi2223 oxide superconducting wire according to claim 3.

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