JP2009170276A - Manufacturing method of bi2223 superconducting wire rod, and bi2223 superconducting wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconducting wire rod manufacturing method and a superconducting wire rod increasing the degree of orientation of a superconducting phase crystal to increase the critical current density in a manufacturing method of a Bi2223 superconducting wire rod. <P>SOLUTION: The method includes a filling step of filling a metallic tube with powder of a precursor containing a Bi2201 phase as a main superconducting phase, a drawing step of drawing the metallic tube filled with the precursor powder, a rolling step of rolling the wire rod obtained after the drawing step, and a heat-treating step of heat-treating the wire rod obtained after the rolling step. Intermediate heat treatment is added between the drawing step and rolling step such that the Bi2201 phase in the precursor power reacts with a Bi2212 phase to turn the main superconducting phase to the Bi2212 phase. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a manufacturing method of a Bi2223 superconducting wire and a Bi2223 superconducting wire, for example, a manufacturing method of a Bi2223 superconducting wire and a Bi2223 superconducting wire that can improve superconducting characteristics.

  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 precursor powder mainly composed of a Bi2212 phase is filled in a metal tube, and then a single core material is formed by wire 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

  However, in the manufacturing method of the Bi2223 superconducting wire described in Patent Documents 1 and 2, the orientation of the Bi2223 phase crystal may be insufficient after the second heat treatment, and there is room for improvement in superconducting characteristics.

  Accordingly, an object of the present invention is to provide a method for producing a Bi2223 superconducting wire capable of improving superconducting characteristics.

  Specifically, in order to improve the superconducting characteristics, that is, the critical current density, a manufacturing method is provided in which a crystal composed of a superconducting phase is more highly oriented.

  The manufacturing method of the Bi2223 superconducting wire of the present invention performs the following steps.

  A filling step of filling a metal tube with a precursor powder containing a Bi2201 phase as a main superconducting phase; a wire drawing step of drawing a metal tube filled with the precursor powder to obtain a wire; and a wire after the wire drawing step A Bi2201 phase in the precursor powder by adding an intermediate heat treatment between the wire drawing step and the rolling step, and a heat treatment step of heat-treating the wire after the rolling step. The main superconducting phase is changed to the Bi2212 phase by reacting with the Bi2212 phase.

  According to the present invention, the drawn wire containing the precursor powder whose main superconducting phase is the Bi2201 phase is heat-treated, so that the precursor powder whose Bi2212 phase is the main superconducting phase is used as the filling powder. A Bi2212 phase having a large particle size can be generated in the wire after the wire. This is because the Bi2201 phase reacts with the surrounding non-superconducting phase and easily grows into a large Bi2212 phase crystal.

  When a wire containing such a large Bi2212 phase crystal is rolled, the Bi2212 phase crystal is easily tilted in the ab plane (CuO crystal plane) direction. Therefore, the wire rod after rolling has a high orientation of the Bi2212 phase crystal. When heat-treating the rolled wire rod containing the highly oriented Bi2212 phase, the Bi2212 phase is maintained and transformed into the Bi2223 phase, so that the final Bi2223 phase also has a high orientation and a high critical current density. realizable.

The “Bi2201 phase” includes bismuth, strontium, copper and oxygen, and bismuth (Bi): strontium (Sr): copper (Cu) is 2: 2: 1 as the atomic ratio (excluding oxygen). And an oxide superconducting phase approximately expressed as follows, and bismuth and lead (Bi + Pb): strontium (Sr): copper, including bismuth, lead, strontium, calcium, copper, and oxygen. It is an oxide superconducting phase in which (Cu) is approximated to 2: 2: 1. More specifically, those represented by chemical formulas of Bi ₂ Sr ₂ Cu ₁ O _{6 + δ} and (BiPb) ₂ Sr ₂ Cu ₁ O _{6 + δ} (δ is a number close to 0.1) are included.

The “Bi2212 phase” includes bismuth, strontium, calcium, copper and oxygen, and the atomic ratio (excluding oxygen) is bismuth (Bi): strontium (Sr): calcium (Ca): copper (Cu). ) Is expressed as an approximation of 2: 2: 1: 2, and bismuth, lead, strontium, calcium, copper, and oxygen, and its atomic ratio (excluding oxygen) is bismuth and lead (excluding oxygen). Bi + Pb): an oxide superconducting phase in which strontium (Sr): calcium (Ca): copper (Cu) is approximated as 2: 2: 1: 2. More specifically, Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 + δ} and (BiPb) ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 + δ} (δ is a number close to 0.1) are included.

The “Bi2223 phase” includes bismuth, lead, strontium, calcium, copper, and oxygen, and the atomic ratio (excluding oxygen) is (bismuth + lead): strontium: calcium: copper 2: 2. It is an oxide superconducting phase expressed by approximating 2: 3. More specifically, those represented by the chemical formula (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} (δ is a number close to 0.1) are included.

The main superconducting phase in the precursor powder and after the heat treatment is determined as follows. Bi2201 (1.1.5) peak intensity I2201, Bi2212 (1.1.5) peak intensity I2212 and Bi2223 (1.1.9) peak intensity I2223 identified by the X-ray diffraction θ / 2θ scan method. Judgment is made according to (Equation 1). For example, when focusing on the Bi2201 phase,
Volume fraction of Bi2201 = I2201 / (I2201 + I2212 + I2223) × 100 (Equation 1)
The value of (Expression 1) is defined as the volume fraction, and if this value is 60 (unit:%) or more, the Bi2201 phase is said to be the main superconducting phase.

  In the manufacturing method of the Bi2223 superconducting wire, the volume fraction as the main superconducting phase of the Bi2201 phase in the precursor powder is preferably 80% or more.

  Thereby, since the crystal can be more oriented in the rolling process, the superconducting characteristics can be further improved.

  In the method for manufacturing the Bi2223 superconducting wire, the intermediate heat treatment is preferably performed in a temperature range of 700 ° C. or higher and 800 ° C. or lower.

  This is because when the heat treatment temperature is less than 700 ° C., there is little transformation from the Bi2201 phase to the Bi2212 phase, and when it exceeds 800 ° C., a Bi2223 phase that is not desired to be generated in the intermediate heat treatment stage is generated.

  In the manufacturing method of the Bi2223 superconducting wire, the intermediate heat treatment is preferably performed for 30 minutes or more.

  When the heat treatment time is less than 30 minutes, the transformation from the Bi2201 phase to the Bi2212 phase does not occur sufficiently. When heat treatment is carried out for 30 minutes or more, it transforms to almost 100% Bi2212 phase. Thereafter, even if the heat treatment is continued under the same conditions, the ratio of the superconducting phase does not change.

  In the Bi2223 superconducting wire manufacturing method, the intermediate heat treatment is preferably performed in an atmosphere having an oxygen concentration of 6% or more and 10% or less.

  When the oxygen concentration during the heat treatment is less than 6% or more than 10%, the non-superconducting phase tends to grow larger than the transformation to the Bi2212 phase, which is not preferable.

  The Bi2223 superconducting wire of the present invention is manufactured by the method for manufacturing the Bi2223 superconducting wire. As a result, a Bi2223 superconducting wire with improved superconducting properties can be obtained.

  According to the manufacturing method of the Bi2223 superconducting wire and the Bi2223 superconducting wire of the present invention, the superconducting characteristics, so-called critical current density, can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view showing a Bi2223 superconducting wire manufactured by a method of manufacturing a Bi2223 superconducting wire in an embodiment of the present invention. A Bi2223 superconducting wire in the present embodiment will be described with reference to FIG. As shown in FIG. 1, the Bi2223 superconducting wire 11 in the present embodiment includes a plurality of filaments 12 that are a plurality of superconductors extending in the longitudinal direction, and a sheath portion 3 that covers them. Each material of the plurality of filaments 12 is formed of a Bi2223 phase in which the atomic ratio of (bismuth and lead): strontium: calcium: copper is approximated by a ratio of 2: 2: 2: 3, May contain some Bi2212 phase and inevitable impurities. The material of the sheath portion 13 is made of a metal such as silver or a silver alloy. The filament 12 is not particularly limited to a plurality, and may have a single core structure.

  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 process of obtaining a single core bus in the embodiment of the present invention. FIG. 4 is a schematic perspective view showing a process 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 process in the embodiment of the present invention. FIG. 6 is a schematic perspective view showing a process of drawing a multicore bus in the embodiment of the present invention. FIG. 7 is a schematic perspective view showing a process of rolling the heat-treated multifilamentary wire in the embodiment of the present invention.

First, as shown in FIGS. 2 and 3, the Bi2201 phase ((BiPb) ₂ Sr ₂ Cu ₁ O _{6 + δ} or Bi ₂ Sr ₂ Cu ₁ O _{6 + δ} ) is the main superconducting phase, and the balance is the Bi2212 phase ((BiPb) ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 + δ} or Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 + δ} ) and a precursor powder 31 that is a non-superconducting phase are filled in a metal tube 32 to obtain a single-core bus bar 33 (step S1). . The non-superconducting phase is, for example, an alkaline earth oxide such as (Ca, Sr) CuO ₂ , (Ca, Sr) ₂ CuO ₃ and (Ca, Sr) ₁₄ Cu ₂₄ O ₄₁ , Ca ₂ PbO ₄ and Pb oxides such as (Bi, Pb) ₃ Sr ₂ Ca ₂ Cu ₁ O _z are exemplified.

  Specifically, Bi, Pb, Sr, Ca and Cu are used as the raw material powder. For example, Bi: Pb: Sr: Ca: Cu = 1.7: 0.4: 1.9: 2.0: 3.0 The raw material powder is mixed so that the composition ratio is as follows. This is subjected to heat treatment at about 700 ° C. to 860 ° C. a plurality of times to prepare a precursor powder 31 containing a Bi2201 phase as a main superconducting phase and a small amount of Bi2212 phase and a non-superconducting phase. The precursor powder is produced, for example, by a spray pyrolysis method in which the moisture of the particles of the metal nitrate aqueous solution is evaporated to cause thermal decomposition of nitrate, reaction between metal oxides, and synthesis instantaneously. Then, a metal tube 32 made of silver or the like is prepared. Thereafter, for example, using the supply member 34 and utilizing the weight of the precursor powder 31, the precursor powder 31 is filled in the metal tube 32 to form a single core bus 33. Moreover, after filling the precursor powder 31 into the metal tube 32, heating and pressurization may be performed.

  The metal tube 32 is preferably made of silver or a silver alloy. Thereby, the precursor powder 31 and the metal tube 32 react to form a compound, thereby preventing compositional deviation of the precursor powder 31.

  Next, as shown in FIGS. 2 and 4, the single core bus 33 is drawn (step S2). Specifically, the wire drawing machine 41 is used to reduce the diameter of the single core bus 33 and to extend the length. In this wire drawing process, the diameter of the metal tube filled with the precursor powder 31 in step S1 undergoes a diameter reduction deformation of about 1/10 to 1/100, for example. As a result, a single core wire 42 having a circular or polygonal cross section, which is covered with the metal tube 12 using the precursor powder 31 as a core material, is produced.

  Next, as shown in FIGS. 2 and 5, a number of the single core wires 42 are bundled and fitted into a metal tube 51 made of a metal such as silver (multi-core fitting: step S3). As a result, a multi-core bus bar 52 having a large number of precursor powders 31 as a core material is obtained.

  Next, as shown in FIGS. 2 and 6, the multicore bus 52 is drawn (drawing of the multicore bus: step S4). Specifically, using a wire drawing machine 61, a multi-core wire 62 drawn from the multi-core bus 52 is processed.

  Next, as shown in FIG. 2, the multi-core wire 62 after the multi-core bus wire drawing step (step S4) is heat-treated (intermediate heat treatment: step S5). In step S5, the Bi2201 phase in the precursor powder 31 is transformed into a Bi2212 phase by heat-treating the precursor powder 31. Thereby, in the precursor powder 31, the Bi2212 phase in which crystals grow greatly becomes the main superconducting phase.

  Specifically, in step S5, it is preferable to heat-treat the multifilamentary wire 62 in an atmosphere having an oxygen concentration of 6% or more and 10% or less under the conditions of a temperature of 700 ° C. to 800 ° C. and a time of 30 minutes or more. As a result, the Bi2201 phase crystals in the precursor powder 31 are transformed into Bi2212 phase crystals having a large particle size.

  Next, as shown in FIG. 2 and FIG. 7, the tape material 72 is obtained by rolling the multifilamentary wire 62 after the intermediate heat treatment step (step S5) (primary rolling: step S6). Specifically, as shown in FIG. 7, a tape material 72 is formed by applying pressure to the multicore wire 62 so as to be sandwiched between two rolling members 71 from a direction perpendicular to the longitudinal direction of the multicore wire 62. .

Next, the tape shape 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). 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 Bi2223 superconducting wire 11 shown in FIG. 1 is obtained by the above manufacturing process.

  In the Bi2223 superconducting wire 11 obtained in the present embodiment, the FWHM (Full Width at Half Maximum) of the (0.0.24) peak measured by the XRD rocking curve of the superconducting crystal composed of the Bi2223 phase is: The orientation is improved by 10 ° or less. In addition, FWHM means the half value width of the (0.0.24) peak measured with the XRD rocking curve, and is an index indicating in-plane orientation. FWHM is an inclination angle of the direction in which the superconducting crystal composed of the Bi2223 phase extends with respect to the direction in which the superconducting wire 11 extends (the direction in which current flows in the superconducting wire 11). The smaller the FWHM value, the better the in-plane orientation.

  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. 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. In the primary rolling, the Bi2212 phase crystal is oriented. 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 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, each crystal has a longitudinal direction (a-b plane direction) perpendicular to an external force direction during rolling. As a result, the tape material 84 is aligned in the same direction. 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. Therefore, increasing the size of the Bi2212 phase crystal 83 as much as possible before rolling is advantageous for orientation.

  It is an object of the present invention to increase the Bi2212 phase crystal size before rolling. There is also a method of increasing the crystal size of the Bi2212 phase by using a precursor powder containing the Bi2212 phase as the main superconducting phase and applying heat treatment thereto. However, in this method, the Bi2212 phase crystal size is at most about 3 μm in the longitudinal direction (a-b plane direction). On the other hand, in the method of transforming from the Bi2201 phase to the Bi2212 phase as in the present invention, the Bi2212 phase crystal size is 5 μm or more. This is because the Bi2201 phase takes in the surrounding non-superconducting phase and grows into the Bi2212 phase.

  When the orientation of the wire produced by the method of the present invention is evaluated by the Bi2212 phase rocking curve of the tape material after rolling, the Bi2212 phase (0.0.12) peak FWHM falls from 17 ° to 15 ° or less of the conventional production method. Improved. The rocking curve of the final Bi2223 phase is also improved from about 12 ° to 10 ° or less.

  Furthermore, in order to increase the Bi2212 phase crystal size, it is preferable that the particle size of the non-superconducting phase contained in the precursor powder is small. When the particle size of the non-superconducting phase is large, the reaction from the Bi2201 phase to the Bi2212 phase does not occur smoothly, and the Bi2212 phase crystal is large and difficult to grow. As the particle size of the non-superconducting phase, it is preferable that the average value of the maximum major axis of secondary particles formed only by the non-superconducting phase is 1 μm or less.

  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.

[Example]
Hereinafter, based on an Example, this invention is demonstrated further more concretely.

(Effect of main superconducting phase ratio: Examples 1 to 5, Comparative Examples 1 to 3)
Raw material in which Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO are mixed as raw materials so as to have a ratio of Bi: Pb: Sr: Ca: Cu = 1.8: 0.3: 2: 2: 3 The powder was subjected to heat treatment in air at 700 ° C. for 8 hours, pulverization, heat treatment at 800 ° C. for 10 hours, pulverization, and various heat treatments at 750 ° C. to 820 ° C. for 1 to 5 hours, and the main superconducting phase was Bi2201 phase or Bi2212 Eight kinds of precursor powders to be phases were prepared. At this stage, the Bi2223 phase does not occur. The ratio of Bi2201 phase to Bi2212 phase (Bi2201 phase: Bi2212 phase) contained in the eight precursor powders is as follows. Comparative Example 1 (0:10, Bi2201 phase volume fraction 0%), Comparative Example 2 (2: 8, Bi2201 phase volume fraction 20%), Comparative Example 3 (5: 5, Bi2201 phase volume fraction) 50%), Example 1 (6: 4, volume fraction of Bi2201 phase 60%), Example 2 (7: 3, volume fraction of Bi2201 phase 70%), Example 3 (8: 2, Bi2201 phase) Volume fraction of 80%), Example 4 (9: 1, volume fraction of Bi2201 phase 90%), Example 5 (10: 0, volume fraction of Bi2201 phase 100%). These powders were pulverized to obtain a precursor powder for filling. Eight kinds of precursor powders for filling were filled in metal tubes made of silver each having an outer diameter of 25 mm and an inner diameter of 22 mm.

  Next, the metal tube filled with the precursor powder was drawn to produce a single core wire having a diameter of 2.4 mm. Next, 55 single-core wires were bundled and fitted into a metal tube made of silver having an outer diameter of 25 mm and an inner diameter of 22 mm to obtain a multi-core bus bar. Furthermore, the multifilament bus was drawn to obtain a multifilamentary wire having a diameter of 1.1 mm.

  In order to transform the Bi2201 phase into the Bi2212 phase, the remaining 8% of the multifilamentary wires produced above were heat-treated at 750 ° C. for 1 hour in an atmosphere of nitrogen. The multifilamentary wire after the heat treatment was cut, the cross section was observed with a scanning electron microscope (SEM), and the size of the Bi2212 phase crystal was measured. As a measuring method, 100 Bi2212 phase crystals appearing in the cross section were arbitrarily selected, the size in the long direction was counted as the crystal size, and the average value thereof was obtained. The results are shown in Table 1.

  Next, each multifilamentary wire was rolled into a tape material having a thickness of 0.23 mm. The rocking curve FWHM of these tape materials was measured. The rocking curve FWHM was determined from the XRD measurement of the precursor powder after removing the silver coating of the tape material. The XRD peak used is the (0.0.12) peak of the Bi2212 phase. The results are shown in Table 1.

  As can be seen from Table 1, the example in which the main superconducting phase (existing at a ratio of 60% or more) in the precursor powder is the Bi2201 phase has a large Bi2212 phase crystal size after the multi-core wire heat treatment. Therefore, the FWHM of the Bi2212 phase (0.0.12) peak, which is an index of crystal orientation, is also small. That is, the orientation of the Bi2212 phase is good.

(Effect of intermediate heat treatment temperature: Examples 3, 6 to 9)
For the multifilamentary wire used in Example 3, the heat treatment temperatures were 650 ° C. (Example 6), 700 ° C. (Example 7), 750 ° C. (Example 3), 800 ° C. (Example 8), and 850 ° C. Intermediate heat treatment was performed as (Example 9). The heat treatment time is 1 hour. The precursor powder after the heat treatment was evaluated by an X-ray diffraction θ / 2θ scan method, and the superconducting phase ratio was calculated using (Equation 1). The results are shown in Table 2.

  As can be seen from Table 2, when the heat treatment temperature is lower than 700 ° C., the Bi2201 phase is not completely transformed into the Bi2212 phase. When the temperature exceeds 800 ° C., Bi2223 phase that is not desired to be generated is generated at this stage. Therefore, it can be said that the intermediate heat treatment temperature is preferably 700 ° C. or higher and 800 ° C. or lower.

(Effect of intermediate heat treatment time: Examples 3, 10 to 13)
With respect to the multifilamentary wire used in Example 3, the heat treatment temperature was set to 750 ° C., and the time was 10 minutes (Example 10), 20 minutes (Example 11), 30 minutes (Example 12), 60 minutes ( Example 3), intermediate heat treatment was performed for 90 minutes (Example 13). The ratio of the superconducting phase in the precursor powder after the heat treatment was evaluated in the same manner as described above. The results are shown in Table 3.

  As can be seen from Table 3, when the heat treatment time is less than 30 minutes, the Bi2201 phase is not completely transformed into the Bi2212 phase. On the other hand, in 30 minutes or more, the Bi2212 phase becomes 100%, and the Bi2223 phase does not appear and there is no change. Therefore, a heat treatment time of 30 minutes or more is sufficient.

(Effect of intermediate heat treatment atmosphere: Examples 3, 10 to 13)
For the multifilamentary wire used in Example 3 above, the oxygen concentration during heat treatment was 2% (Example 14), 4% (Example 15), and 6% (Example) under the conditions of a heat treatment temperature of 750 ° C. for 1 hour. 16), 8% (Example 17), 10% (Example 3), 12% (Example 18), and 14% (Example 19) were subjected to intermediate heat treatment. The size of the non-superconducting phase crystal in the precursor powder after the heat treatment was evaluated by SEM observation of the cross section of the multicore wire. For the evaluation, any 10 non-superconducting crystals were selected, the major axis was counted as the size, and the average value was calculated. The results are shown in Table 4.

  As can be seen from Table 4, when the oxygen concentration in the heat treatment atmosphere is less than 6%, the size of the non-superconducting phase crystal is 3 μm or more. This non-superconducting phase is mainly a Ca—Cu—O-based compound. Even when the oxygen concentration exceeds 10%, the non-superconducting phase crystal size is large. In this case, Ca—Pb—O-based compounds were mainly precipitated in the non-superconducting phase. From these results, it can be seen that the transformation from the Bi2201 phase to the Bi2212 phase proceeds satisfactorily when the oxygen concentration in the heat treatment atmosphere is 6% or more and 10% or less.

(Superconducting wire: Comparative Example 4, Example 20)
The tape material rolled in Comparative Example 1 and Example 3 was heat-treated at 830 ° C. for 50 hours, under an oxygen partial pressure of 8 kPa and under atmospheric pressure. The rolling process was performed again so that the thickness was 0.22 mm. The re-rolled tape material was 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. The superconducting wire using Comparative Example 1 is referred to as Comparative Example 4, and the superconducting wire using Example 3 is referred to as Example 20.

The FWHM and critical current value Ic of the rocking curve were measured for the superconducting wires of Example 20 and Comparative Example 4. The FWHM of the rocking curve was obtained by measuring the (0.0.24) peak of the Bi2223 phase. The critical current value was measured at a temperature of 77 K in a self magnetic field. The critical current value was defined as a current value when an electric field of 10 ⁻⁶ V / cm was generated.

  The critical current value of Example 20 was 250 A and FWHM was 9 °, and the critical current value of Comparative Example 4 was 210 A and FWHM was 12 °. From these results, it can be seen that the superconducting wire manufactured according to the present invention has higher superconducting characteristics than the wire manufactured by the prior art.

  As described above, by using the precursor powder containing the Bi2201 phase as the main superconducting phase and heat-treating the wire containing the precursor powder, the Bi2201 phase in the precursor powder is transformed into the Bi2212 phase. It was confirmed that the superconducting characteristics can be improved.

  The Bi2223 superconducting wire manufactured by the Bi2223 superconducting wire manufacturing method of the present invention can improve the superconducting characteristics. Therefore, the Bi2223 superconducting wire manufactured by the method for manufacturing the Bi2223 superconducting wire of the present invention can be suitably used for superconducting equipment such as a superconducting cable, a superconducting transformer, a superconducting current limiter, and a power storage device.

It is a schematic perspective view which shows the Bi2223 superconducting wire manufactured with the manufacturing method of the Bi2223 superconducting wire in embodiment of this invention. It is a flowchart which shows the manufacturing method of Bi2223 superconducting wire in embodiment of this invention. It is a schematic perspective view which shows the process of obtaining the single core bus-line in embodiment of this invention. It is a schematic perspective view which shows the process of drawing the single core bus-line in embodiment of this invention. It is a schematic perspective view which shows the process of multi-core fitting in embodiment of this invention. It is a schematic perspective view which shows the process of drawing the multi-core bus-line in embodiment of this invention. It is a schematic perspective view which shows the process of rolling the heat-treated multifilamentary wire in embodiment of this invention. It is wire rod sectional drawing showing typically the change of the crystal orientation inside a metal pipe at the time of rolling.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Superconducting wire 12 Filament 13 Sheath part 31 Precursor powder 32 Metal tube 33 Single core bus 34 Supply member 41 Wire drawing machine 42 Single core wire 51 Metal tube 52 Multi-core bus wire 61 Wire drawing machine 62 Multi-core wire 71 Rolling member 72 Tape material 81 Circular wire 82 Metal tube 83 Crystal 84 Tape material

Claims (6)

A filling step of filling a metal tube with a precursor powder containing a Bi2201 phase as a main superconducting phase;
A wire drawing step of drawing a metal tube filled with the precursor powder to obtain a wire;
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,
Between the wire drawing step and the rolling step, an intermediate heat treatment is applied to cause the Bi2201 phase in the precursor powder to react with the Bi2212 phase so that the main superconducting phase becomes the Bi2212 phase. The manufacturing method of Bi2223 superconducting wire.   The method for producing a Bi2223 superconducting wire according to claim 1, wherein the volume fraction of the Bi2201 phase in the precursor powder as a main superconducting phase is 80% or more.   The method for producing a Bi2223 superconducting wire according to claim 1 or 2, wherein the intermediate heat treatment is performed in a temperature range of 700 ° C or higher and 800 ° C or lower.   The method of manufacturing a Bi2223 superconducting wire according to any one of claims 1 to 3, wherein the intermediate heat treatment is performed for 30 minutes or more.   The method of manufacturing a Bi2223 superconducting wire according to any one of claims 1 to 4, wherein the intermediate heat treatment is performed in an atmosphere having an oxygen concentration of 6% or more and 10% or less.   The Bi2223 superconducting wire manufactured by the manufacturing method of the Bi2223 superconducting wire according to any one of claims 1 to 5.

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