JP4375134B2 - Superconducting wire manufacturing method - Google Patents

Description

  The present invention relates to a method for producing an oxide superconducting wire, and more particularly to a method for producing a superconducting wire comprising a filament containing a Bi2223 phase and a sheath portion covering the filament.

  Conventionally, as a method of manufacturing an oxide superconducting wire, after filling a raw material powder of an oxide superconductor into a metal tube, by heat-treating the wire obtained by subjecting the metal tube to wire drawing or rolling, A method is known in which raw material powder of an oxide superconductor is sintered to obtain an oxide superconducting wire.

As a superconducting wire obtained by such a manufacturing method, for example, a superconducting wire using a Bi2223 phase which is a high-temperature superconducting wire is known (Non-Patent Document 1). In such a superconducting wire, voids may be formed between the oxide crystal phases by a heat treatment process for sintering at the time of production, and if such voids are formed, the superconducting properties are impaired. Therefore, the improvement was desired.
Naoki Arai, 6 others, “Development of high-temperature superconducting wire for silicon single crystal pulling furnace magnet”, SEI Technical Review, September 2001, No. 159, p. 123-128

  The present inventor conducted detailed research on the phenomenon of voids formed between oxide crystal phases in the above heat treatment step for sintering. As a result, the Bi2223 phase contained in the superconducting wire was made into a single phase. It has become clear that it is necessary to further promote and improve the orientation and further improve the bonding between crystals.

  However, there is no known study that examines in detail the relationship between the various conditions of the heat treatment step and the formation of voids, and there has been no particular study focusing on the oxygen atmosphere at the time of temperature increase or decrease.

  The present invention has been made in view of such a current situation. The object of the present invention is to further promote the formation of a single phase of the Bi2223 phase contained in the superconducting wire and to improve the orientation of the two crystals. It is another object of the present invention to provide a method for producing a superconducting wire that further improves the bondability of the wire and exhibits excellent superconducting properties.

  A method of manufacturing a superconducting wire according to the present invention is a method of manufacturing a superconducting wire having a filament containing a Bi2223 phase and a sheath portion covering the filament, and the oxygen content of the precursor of the superconducting wire up to the temperature at which heat treatment is performed. A temperature raising step for raising the temperature in a low oxygen atmosphere having a pressure of 0.07 to 0.09 atm, a heat treatment step for heat treating the precursor of the superconducting wire, and the precursor of the superconducting wire from the temperature at which the heat treatment is performed And a temperature lowering step of lowering the temperature in a high oxygen atmosphere having a pressure of 0.16 to 0.21 atm.

The Bi2223 phase in the present invention includes bismuth, lead, strontium, calcium, copper, and oxygen, and the atomic ratio (excluding oxygen) is (bismuth and lead): strontium: calcium: copper is 2: 2. It is a Bi—Sr—Ca—Cu—O-based 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 + Z} are included. In the formula, z represents the oxygen content, and it is known that the critical temperature (Tc) and the critical current (Ic) change as z changes.

  Here, the heat treatment step may include a heat treatment performed in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm, and a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm. It may also include a heat treatment performed in

  Further, the heat treatment step includes a heat treatment performed in a low oxygen atmosphere with an oxygen partial pressure of 0.07 to 0.09 atm and a high oxygen atmosphere of 0.16 to 0.21 atm. Heat treatment can also be performed in an oxygen atmosphere.

  The heat treatment step can be performed in a high oxygen atmosphere with an oxygen partial pressure of 0.16 to 0.21 atm for 50 hours to 100 hours, and the oxygen partial pressure is as low as 0.07 to 0.09 atm. It can also be performed in an oxygen atmosphere for 20 hours or more and 50 hours or less.

  Furthermore, the heat treatment step is performed in a low oxygen atmosphere with an oxygen partial pressure of 0.07 to 0.09 atm, and then performed in a high oxygen atmosphere with an oxygen partial pressure of 0.16 to 0.21 atm for 20 hours or more. It can also be performed for 100 hours or less.

  Further, the composition of the precursor of the filament before the heat treatment step can be such that the atomic ratio of Pb / (Bi + Pb) is 0.14 or more and 0.18 or less.

  In the present invention, by adopting the above-described configuration, the Bi2223 phase is decomposed into other components in the filament by performing the temperature raising step in a low oxygen atmosphere with an oxygen partial pressure of 0.07 to 0.09 atm. Without being generated, and this facilitates the single phase formation of the Bi2223 phase in the filament.

  In addition, by performing the temperature raising step in a low oxygen atmosphere in this way, the incorporation of Pb into the Bi2212 phase is promoted, and the production of the Bi2223 phase, which has better superconducting properties than the Bi2212 phase, is promoted. As a result, the Bi2223 phase is further promoted into a single phase. Details of the Bi2212 phase will be described later.

  Furthermore, Bi2223 phase nuclei generated in the filament in a low oxygen atmosphere can be slowly grown by being exposed to a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm. The thick and large crystals are densely formed along the surface of the wire with high orientation.

  Thus, the superconducting wire manufactured by the manufacturing method of the present invention exhibits extremely excellent superconducting characteristics due to the synergistic action of the above characteristics. Such excellent superconducting characteristics can be obtained by adjusting a factor that can be controlled very simply, that is, oxygen partial pressure, so that its industrial applicability is greatly improved.

  In addition, the superconducting wire manufactured by the manufacturing method of the present invention can be used for applications such as cables, magnets, transformers, current leads, and power storage devices.

  In the following description of the embodiments, description is made with reference to the drawings. In the drawings of the present application, the same reference numerals denote the same or corresponding parts.

<Superconducting wire>
The superconducting wire of the present invention has a structure having a filament containing a Bi2223 phase and a sheath portion covering the filament. FIG. 1 is a partial cross-sectional perspective view conceptually showing the structure. That is, the superconducting wire 1 of the present invention includes a filament 2 including a Bi2223 phase extending in the longitudinal direction and a sheath portion 3.

  Such a Bi2223 phase has the characteristic that the crystal growth is very fast in the a-axis and b-axis directions than the crystal axis c-axis, and thus has an oriented structure composed of thin plate crystals and aligned ab surfaces. It has the feature of being easy.

  Therefore, the superconducting current flowing through the superconducting wire of the present invention flows in and between the plate crystals having the ab planes (planes including the a-axis and b-axis) as described above, and thus Bi2223. The superconducting characteristics are improved by making the phase into a single phase, increasing the orientation of the plate-like crystal, and closely bonding the crystal grains.

  Here, increasing the orientation of the Bi2223 phase plate crystal means that a large number of Bi2223 phase crystals 4 are formed on the surface 5 of the superconducting wire 1 as shown in FIG. This refers to the state of being generated parallel to the longitudinal direction.

  On the other hand, as shown in FIG. 2B, when the orientation is inferior, a large number of voids 6 are generated, and as a result, the superconducting current becomes difficult to flow and the superconducting characteristics are inferior.

  In addition, as an index for judging the superiority or inferiority of the orientation of such a crystal, the misalignment (the angle between the ab surface of the Bi2223 phase crystal and the longitudinal direction of the superconducting wire, that is, θ in FIG. 2B) The angle shown). That is, the smaller the angle (deg) expressed as the misalignment, the higher the crystal orientation. Such misalignment can be statistically determined by measuring a rocking curve by X-ray diffraction.

  On the other hand, the sheath part is also called a sheath part, and has an action of protecting and supporting the filament. Such a sheath part is comprised with a metal, Preferably silver and a silver alloy can be used.

  FIG. 1 shows a multi-core wire structure in which a filament containing a plurality of Bi2223 phases is covered by a sheath portion, but the number of filaments is not particularly limited, and one filament In which a single core wire structure is covered with a sheath portion.

Moreover, although the said filament contains Bi2223 phase as a main component, the trace amount of other components may be contained. Examples of such other components include Bi2212 phase. The Bi2212 phase contains bismuth, lead, strontium, calcium, copper, and oxygen, and its atomic ratio (excluding oxygen) is (bismuth and lead): strontium: calcium: copper approximate to 2: 2: 1: 2. This is a Bi—Sr—Ca—Cu—O-based oxide superconducting phase. More specifically, those represented by the chemical formula (BiPb) ₂ Sr ₂ Ca ₁ Cu ₂ O _{8 + Z} are included. In the formula, z represents the oxygen content, and it is known that the critical temperature (Tc) and the critical current (Ic) change as z changes.

  In order to reduce the superconducting current flowing through the filament, the amount of such other components is preferably as small as possible, which is why the Bi2223 phase is desired to be single-phased.

  In addition, although the shape of the superconducting wire of the present invention is not particularly limited, a tape-like shape having a substantially rectangular cross-sectional shape can be mentioned as an example.

  More specifically, it has a width of 4.0 to 4.5 mm, a thickness of 0.2 to 0.25 mm, a short wire up to several meters in length, and the same width and thickness as this, and a length of 100 m to A long wire covering several kilometers can be mentioned.

<Manufacturing method of superconducting wire>
The method for producing a superconducting wire according to the present invention is a method for producing a superconducting wire having a filament containing a Bi2223 phase and a sheath portion covering the filament. The precursor of the superconducting wire is subjected to oxygen partial pressure up to a temperature at which heat treatment is performed. Is a temperature raising step for raising the temperature in a low oxygen atmosphere of 0.07 to 0.09 atm, a heat treatment step for heat treating the precursor of the superconducting wire, and the oxygen partial pressure from the temperature at which the precursor of the superconducting wire is heat treated. And a temperature lowering step for lowering the temperature in a high oxygen atmosphere of 0.16 to 0.21 atm.

  The superconducting wire manufacturing method of the present invention may include other steps as long as it includes at least the above three steps. For example, as shown in FIG. 3, the superconducting wire manufacturing method of the present invention can include a filling step, a wire drawing step, a rolling step and the like in addition to the above three steps.

  In addition, these steps can be performed twice or more independently including the above three steps. However, when the above three steps, that is, the temperature raising step, the heat treatment step, and the temperature lowering step are each performed twice or more, the above oxygen atmosphere is adopted when the first (first) is performed. In the subsequent steps, it is not always necessary to adopt the above oxygen atmosphere.

  Hereinafter, the manufacturing method of the superconducting wire of the present invention will be further described with reference to FIG. In addition, the manufacturing method of the superconducting wire of this invention can use the conventionally well-known apparatus known as an apparatus for manufacture of this kind of superconducting wire without a restriction | limiting in particular.

  First, the filling step (step S1) is a step of filling raw material powder (for example, oxide powder of each constituent metal) constituting the Bi2223 phase into a metal tube constituting the sheath portion. Depending on the filling method, a multi-core structure or a single-core structure can be used.

  Next, the wire drawing step (step S2) is a step of forming a wire precursor having a desired diameter and shape by drawing a metal tube filled with raw material powder. Thereby, the precursor of the wire which has the form which coat | covered raw material powder with the metal is obtained.

  The subsequent rolling step (step S3) is a step of rolling the wire rod precursor formed in the wire drawing step into a wire having a desired tape shape.

  Then, the superconducting wire of the present invention is manufactured by the temperature raising step (step S4), the heat treatment step (step S5), and the temperature lowering step (step S6) performed subsequently to the rolling step. The details of the temperature raising step (step S4), the heat treatment step (step S5), and the temperature lowering step (step S6) will be described later.

  Moreover, these rolling processes, temperature raising processes, heat treatment processes, and temperature lowering processes can be repeated twice (steps S7 to S10) or more as shown in FIG. By repeating these steps, the orientation of the Bi2223 phase can be further increased, and the bonds between the crystal grains of the Bi2223 phase can be made denser.

<Precursor>
The precursor of the superconducting wire in the present invention means an intermediate stage in the manufacturing process of the superconducting wire.

  For example, the superconducting wire precursor that is heated in the temperature raising step is a precursor of the superconducting wire formed through the filling step, the wire drawing step, and the rolling step, and is a precursor that is heat-treated in the heat treatment step. Is a precursor that has undergone the above-described temperature raising step, and a precursor that is cooled in the temperature-falling step is a precursor that has undergone the above-described heat treatment step.

  The precursor of the filament before the heat treatment step means a metal oxide before forming the Bi2223 phase, and the composition ratio of Bi and Pb in the precursor is Pb / (Bi + Pb) as an atomic ratio. It is preferably 0.14 or more and 0.18 or less. The reason is that in order to generate the Bi2223 phase (more precisely, (Bi, Pb) 2223 phase) in the heat treatment step, it is necessary to generate the (Bi, Pb) 2212 phase in which Pb enters the Bi2212 phase. This is because it is optimal that the atomic ratio is 0.14 or more and 0.18 or less in order to generate this. For this reason, when the atomic ratio is less than 0.14, since the amount of Pb is small, the (Bi, Pb) 2212 phase is difficult to be generated, and as a result, the (Bi, Pb) 2223 phase is difficult to be generated. If it exceeds 0.18, since there is a large amount of Pb (Bi, Pb), the 2223 phase is likely to be formed.

<Temperature raising process>
The temperature raising step in the present invention is a step of raising the temperature of the superconducting wire precursor in a low oxygen atmosphere having an oxygen (O ₂ ) partial pressure of 0.07 to 0.09 atm to a temperature at which heat treatment is performed. In this temperature raising step, the temperature is raised from the temperature at which the previous step is performed to the temperature at which the heat treatment is performed. However, since the previous step is a normal rolling step, the temperature is raised from room temperature. However, the temperature before the temperature rise is not particularly limited.

  In this way, by performing the temperature raising step in a low oxygen atmosphere with an oxygen partial pressure of 0.07 to 0.09 atm, the Bi2223 phase is efficiently generated in the filament without being decomposed into other components. The Bi2223 phase is promoted to be a single phase. Furthermore, the incorporation of Pb into the Bi2212 phase is promoted, the formation of the Bi2223 phase, which is superior in superconducting properties than the Bi2212 phase, is promoted, and combined with the above effects, the Bi2223 phase is further promoted to become a single phase. Become.

  A more preferable oxygen partial pressure in such a low oxygen atmosphere has a lower limit of 0.075 atm, and more preferably 0.08 atm. Moreover, the upper limit is 0.085 atm, More preferably, it is 0.08 atm.

  When the oxygen partial pressure is less than 0.07 atm, a large amount of Bi2223 phase is generated during the temperature raising step, and the Bi2223 phase may become thick and difficult to grow in the heat treatment step (sintering step). When the pressure exceeds 0.09 atm, the Bi2223 phase in the filament may be easily decomposed into other components.

  The other conditions are not particularly limited as long as the atmosphere is a predetermined low oxygen atmosphere. For example, the rate of temperature rise can be 1.0 to 5.0 ° C./min, more preferably 1.5 to 2.0 ° C./min.

  When the rate of temperature rise is less than 1.0 ° C./min, the Bi2223 phase may decompose into other components even in a low oxygen atmosphere, and when the rate of temperature rise exceeds 5.0 ° C./min, the temperature rises. There may be insufficient time for the (Bi, Pb) 2212 phase to be generated in the process, preventing the Bi2223 phase from becoming a single phase.

The gas component other than oxygen is not particularly limited as long as the oxygen partial pressure is in the above range, but an inert gas such as nitrogen (N ₂ ) gas or argon (Ar) is used. It is preferable.

<Heat treatment process>
The heat treatment step in the present invention is a step of heat-treating the superconducting wire precursor that has undergone the above temperature raising step. By this heat treatment, the precursor of the superconducting wire is sintered and Bi2223 phase crystals are grown.

  Such a heat treatment step is performed at a temperature of 835 to 850 ° C. When this temperature is less than 835 ° C., the Bi2223 phase may not be generated in a high oxygen atmosphere, and when the temperature exceeds 850 ° C., the filament itself and the sheath part may melt.

  Here, such a heat treatment step can be performed in a high oxygen atmosphere with an oxygen partial pressure of 0.16 to 0.21 atm, and is performed in a low oxygen atmosphere with an oxygen partial pressure of 0.07 to 0.09 atm. You can also. Thus, when the heat treatment step is performed in a low oxygen atmosphere, the oxygen partial pressure in the temperature raising step is kept as it is (of course, an arbitrary oxygen partial pressure is selected within the range of 0.07 to 0.09 atm). Is also possible).

  Further, such a heat treatment step can be performed in a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm and then in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm.

  In the case where the heat treatment process is performed in a high oxygen atmosphere as described above, the subsequent temperature drop process is the oxygen partial pressure as it is (of course, an arbitrary oxygen partial pressure is selected within the range of 0.16 to 0.21 atm). However, when this heat treatment step is performed in the above-mentioned low oxygen atmosphere, it is necessary to increase the oxygen partial pressure and then perform the next temperature lowering step. is there.

  Thus, in any case, by adopting the condition of processing in a low oxygen atmosphere and then in a high oxygen atmosphere, the Bi2223 phase nuclei generated in the filament under the low oxygen atmosphere are then subjected to oxygen partial pressure. Is exposed to a high oxygen atmosphere of 0.16 to 0.21 atm, it can grow slowly, and large and large crystals are produced with high orientation and denseness along the surface of the wire.

  The lower limit of the oxygen partial pressure of the high oxygen atmosphere in the above is preferably 0.165 atm, and more preferably 0.18 atm. Moreover, the upper limit is 0.205 atm, More preferably, it is 0.2 atm.

  When the oxygen partial pressure is less than 0.16 atm, the Bi2223 phase cannot grow slowly, and a thin crystal is likely to be formed. When the oxygen partial pressure exceeds 0.21 atm, the oxygen partial pressure is too high. In some cases, the (Bi, Pb) 2212 phase is difficult to generate and the Bi2223 phase is not generated.

  Moreover, the more preferable oxygen partial pressure of the low oxygen atmosphere in the above is 0.075 atm at the lower limit, and more preferably 0.08 atm. Moreover, the upper limit is 0.085 atm, More preferably, it is 0.08 atm.

  When the oxygen partial pressure is less than 0.07 atm, a large amount of Bi2223 phase may be generated and the crystal may not grow thick. When the oxygen partial pressure exceeds 0.09 atm, the phase in the filament is decomposed. As a result, nuclei of Bi2223 phase may be difficult to be generated.

The other conditions are not particularly limited as long as the atmosphere is an atmosphere having a predetermined oxygen partial pressure. For example, the gas component other than oxygen is not particularly limited as long as the oxygen partial pressure is in the above range, but an inert gas such as nitrogen (N ₂ ) gas or argon (Ar) is used. It is preferable.

  On the other hand, the treatment time can be 50 hours or more and 100 hours or less when the treatment is performed in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm. More preferably, the lower limit is 55 hours, more preferably 60 hours, and the upper limit is 90 hours, more preferably 80 hours. When the treatment time is less than 50 hours, the Bi2223 phase may not be converted into a single phase, and when it exceeds 100 hours, the Bi2223 phase may be decomposed into other components.

  Moreover, when performed in the low oxygen atmosphere whose oxygen partial pressure is 0.07-0.09 atm, it can be set to 20 hours or more and 50 hours or less. More preferably, the lower limit is 25 hours, more preferably 30 hours, and the upper limit is 45 hours, more preferably 40 hours. If the treatment time is less than 20 hours, the Bi2223 phase may not be converted to a single phase, and if it exceeds 50 hours, the Bi2223 phase may be decomposed into other components.

  Further, such a heat treatment step can be performed in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm after being performed in a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm. In such a case, the total processing time is preferably 20 hours or more and 100 hours or less. When the treatment time is less than 20 hours, the Bi2223 phase may not be converted to a single phase, and when it exceeds 100 hours, the Bi2223 phase may be decomposed into other components.

<Cooling process>
In the temperature lowering step in the present invention, the precursor of the superconducting wire that has undergone the heat treatment step is lowered in a high oxygen atmosphere having an oxygen (O ₂ ) partial pressure of 0.16 to 0.21 atm from the temperature at which the heat treatment is performed. It is a process. In this temperature lowering step, the temperature is lowered from the temperature at which the heat treatment is performed to the temperature at which the next step is performed, but usually the temperature is lowered to room temperature. However, the temperature after the temperature drop is not particularly limited.

  When the above heat treatment step is performed in a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm, the temperature lowering step is performed in such a high oxygen atmosphere, thereby reducing the low oxygen atmosphere in the filament. The nuclei of the Bi2223 phase produced below can grow slowly, and thick and large crystals are produced with high orientation and denseness along the surface of the wire.

  The more preferable oxygen partial pressure in such a high oxygen atmosphere has a lower limit of 0.165 atm, more preferably 0.18 atm. Moreover, the upper limit is 0.205 atm, More preferably, it is 0.2 atm.

  When the oxygen partial pressure is less than 0.16 atm, the inside of the filament may melt at the initial temperature drop (up to 830 ° C.) from the heat treatment temperature (835 to 850 ° C.), and the oxygen partial pressure becomes 0.21 atm. If exceeded, further crystal growth of the Bi2223 phase during temperature reduction may not be expected.

  The other conditions are not particularly limited as long as the atmosphere is a predetermined high oxygen atmosphere. For example, the temperature lowering rate can be 1.0 to 10 ° C./min, more preferably 1.5 to 3.0 ° C./min.

  When the temperature lowering rate is less than 1.0 ° C./min, the Bi2223 phase may be decomposed because it is an unstable phase, and when the temperature lowering rate exceeds 10 ° C./min, the highly oriented Bi2223 phase. May not be obtained, and cracks may occur in the filament due to the difference in thermal shrinkage between the sheath portion and the filament.

The gas component other than oxygen is not particularly limited as long as the oxygen partial pressure is in the above range, but an inert gas such as nitrogen (N ₂ ) gas or argon (Ar) is used. It is preferable.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1-4>
First, the raw material powder constituting the Bi2223 phase is filled into the silver tube constituting the sheath portion so that the silver ratio is 1.5 and the core portion includes 55 cores containing the Bi2223 phase. A filling step was performed.

  The silver ratio indicates the ratio of the total area of the sheath portion made of silver to the total area of the filament portion including the Bi2223 phase in the cross section of the precursor of the superconducting wire before the heat treatment step.

  Next, the superconducting wire precursor that has undergone such a filling step is subjected to a wire drawing step and a rolling step according to a conventional method so as to become a short wire having a length of 100 mm, a width of 4.2 mm, and a thickness of 0.23 mm. As a result, a superconducting wire precursor having a short shape with a silver ratio of 1.5, a length of 55 cores of 100 mm, a width of 4.2 mm, and a thickness of 0.23 mm was obtained.

  In this superconducting wire precursor, the Pb / Bi composition ratio of the filament precursor was 0.155 in the atomic ratio of Pb / (Bi + Pb).

  Subsequently, the superconducting wire precursor thus obtained was subjected to the heat treatment shown in Table 1 below in a low oxygen atmosphere where the oxygen partial pressure was 0.08 atm (gas components other than oxygen were nitrogen). A temperature raising step was performed in which the temperature was raised from room temperature at a rate of 1.6 ° C./min up to the temperature to be performed (heat treatment temperature).

  Thereafter, when the temperature for the heat treatment is reached, a high concentration of oxygen is introduced and a high oxygen atmosphere with a partial pressure of oxygen of 0.21 atm (the gas component other than oxygen is nitrogen) is used to increase the above temperature. A heat treatment step for performing heat treatment on the precursor of the superconducting wire after the temperature step was carried out for 50 hours.

  Thereafter, the present invention is carried out by carrying out a temperature lowering step in which the temperature of the precursor of the superconducting wire that has undergone the heat treatment step is lowered to room temperature at a rate of 1.6 ° C./min. A superconducting wire having a filament containing Bi2223 phase and a sheath portion covering the filament was obtained.

  With respect to the superconducting wire thus manufactured, the critical current (Ic) and the deviation of the Bi2223 phase orientation of the filament were measured. The results are shown in Table 1 below and FIGS. 4 and 5.

  The critical current (Ic) was measured by a four-terminal method in liquid nitrogen (77K), and the misalignment was obtained by X-ray diffraction rocking curve measurement.

  Further, as Comparative Example 1, the heat treatment step and the temperature lowering step are performed not in a high oxygen atmosphere but in a low oxygen atmosphere having an oxygen partial pressure of 0.08 atm (however, the temperature of the heat treatment step is 840 ° C. and the time is 30). Except for (time), everything else was obtained in the same manner to obtain a superconducting wire. For this superconducting wire, the critical current (Ic) and misalignment were measured in the same manner as described above, and the results are shown in Table 1 below.

  As is clear from Table 1, FIG. 4, and FIG. 5, the superconducting wires of Examples 1 to 4 all have improved critical current (Ic) as compared to the superconducting wire of Comparative Example 1 (Comparative Example 1 is 25A). In contrast, Examples 1-4 were 26-31 A).

  In addition, regarding the deviation in the orientation of the Bi2223 phase of the filament, the superconducting wires in Examples 1 to 4 all have less orientation deviation than the superconducting wire in Comparative Example 1 (Comparative Example 1 is 10.7 deg). On the other hand, Examples 1-4 were 8.6-10.0 deg).

  These results show that a superconducting wire excellent in superconducting properties can be obtained by performing the temperature raising step in a low oxygen atmosphere and then performing the heat treatment step and the temperature lowering step in a high oxygen atmosphere.

<Examples 5-7>
The same superconducting wire precursor as that of Examples 1 to 4 was obtained by carrying out the filling step, the wire drawing step, and the rolling step in the same manner as in Examples 1 to 4.

  Subsequently, the superconducting wire precursor thus obtained was subjected to the heat treatment shown in Table 2 below in a low oxygen atmosphere where the oxygen partial pressure was 0.08 atm (gas components other than oxygen were nitrogen). A temperature raising step was performed in which the temperature was raised from room temperature at a rate of 1.6 ° C./min up to the temperature to be performed (heat treatment temperature).

  Thereafter, when the temperature for the heat treatment is reached, the heat treatment step for 20 hours is performed on the precursor of the superconducting wire that has been subjected to the above temperature raising step while maintaining the low oxygen state with an oxygen partial pressure of 0.08 atm. did.

  Thereafter, a higher concentration of oxygen is introduced and a high oxygen atmosphere with an oxygen partial pressure of 0.21 atm (the gas component other than oxygen is nitrogen), whereby the precursor of the superconducting wire is subsequently heat treated. The heat treatment process of performing was performed for 30 hours.

  Thereafter, the present invention is carried out by carrying out a temperature lowering step in which the temperature of the precursor of the superconducting wire that has undergone the heat treatment step is lowered to room temperature at a rate of 1.6 ° C./min. A superconducting wire having a filament containing Bi2223 phase and a sheath portion covering the filament was obtained.

  With respect to the superconducting wire thus manufactured, the critical current (Ic) and the deviation of the Bi2223 phase orientation of the filament were measured. The results are shown in Table 2 below and FIGS. 6 and 7. The critical current (Ic) and the deviation in orientation were determined in the same manner as in Examples 1 to 4. For reference, the data of Comparative Example 1 are also listed.

  As is clear from Table 2 and FIGS. 6 and 7, the superconducting wires of Examples 5 to 7 all have improved critical current (Ic) as compared to the superconducting wire of Comparative Example 1 (Comparative Example 1 has 25A). On the other hand, Examples 5-7 were 31-34A).

  In addition, regarding the deviation of the orientation of the Bi2223 phase of the filament, the superconducting wires in Examples 5 to 7 all have less orientation deviation than the superconducting wire in Comparative Example 1 (Comparative Example 1 is 10.7 deg). On the other hand, Examples 5-7 were 8.1-9.2 deg).

  These results show that even if the temperature raising process is performed in a low oxygen atmosphere and then the heat treatment process is performed in the same low oxygen atmosphere, the heat conduction process and the temperature lowering process are further performed in a high oxygen atmosphere. It is shown that a superconducting wire excellent in the above can be obtained.

<Examples 8 to 10>
The same superconducting wire precursor as that of Examples 1 to 4 was obtained by carrying out the filling step, the wire drawing step, and the rolling step in the same manner as in Examples 1 to 4.

  Subsequently, the precursor of the superconducting wire obtained in this way was measured from room temperature up to 850 ° C. (heat treatment temperature) in a low oxygen atmosphere having an oxygen partial pressure of 0.08 atm (gas components other than oxygen were nitrogen). A temperature raising step for raising the temperature at a rate of 1.6 ° C./min was performed.

  Then, when it became 850 degreeC, the heat processing process for 20 hours was implemented with respect to the precursor of the superconducting wire which passed through the said temperature rising process in the low oxygen state whose oxygen partial pressure is 0.08 atm.

  Thereafter, high-concentration oxygen is further introduced at that temperature, and a high-oxygen atmosphere with an oxygen partial pressure of 0.21 atm (the gas component other than oxygen is nitrogen) is used as the precursor of the superconducting wire. On the other hand, the heat treatment step for performing the heat treatment was carried out for the time shown in Table 3 below (Note that in Example 8, the heat treatment step in the high oxygen atmosphere was not carried out, and the following temperature lowering step was carried out).

  Thereafter, the present invention is carried out by carrying out a temperature lowering step in which the temperature of the precursor of the superconducting wire that has undergone the heat treatment step is lowered to room temperature at a rate of 1.6 ° C./min. A superconducting wire having a filament containing Bi2223 phase and a sheath portion covering the filament was obtained.

  With respect to the superconducting wire thus manufactured, the critical current (Ic) and the deviation of the Bi2223 phase orientation of the filament were measured. The results are shown in Table 3 below and FIG. 8 and FIG. The critical current (Ic) and the deviation in orientation were determined in the same manner as in Examples 1 to 4. For reference, the data of Comparative Example 1 are also listed.

  As is clear from Table 3 and FIGS. 8 and 9, the superconducting wires of Examples 8 to 10 all have an improved critical current (Ic) as compared with the superconducting wire of Comparative Example 1 (Comparative Example 1 has 25 A). In contrast, Examples 8 to 10 were 26 to 34 A).

  In addition, regarding the deviation of the orientation of the Bi2223 phase of the filament, the superconducting wires of Examples 8 to 10 all have less orientation deviation than the superconducting wire of Comparative Example 1 (Comparative Example 1 is 10.7 deg). On the other hand, Examples 8 to 10 were 8.1 to 10.1 deg).

  These results show that even if the temperature raising process is performed in a low oxygen atmosphere and then the heat treatment process is performed in the same low oxygen atmosphere, the heat conduction process and the temperature lowering process are further performed in a high oxygen atmosphere. It is shown that a superconducting wire excellent in the above can be obtained.

<Examples 11 to 13>
In Examples 1-4, the filling step is the same as in Examples 1-4 except that the atomic ratio of Pb / (Bi + Pb) of the filament precursor before the heat treatment step is 0.143. The precursor of the superconducting wire similar to Examples 1-4 was obtained by implementing a wire drawing process and a rolling process.

  Subsequently, the precursor of the superconducting wire obtained in this way was measured from room temperature up to 842 ° C. (heat treatment temperature) in a low oxygen atmosphere with an oxygen partial pressure of 0.08 atm (gas components other than oxygen were nitrogen). A temperature raising step for raising the temperature at a rate of 1.6 ° C./min was performed.

  Thereafter, when the temperature reached 842 ° C., the heat treatment step in which heat treatment was continuously performed on the precursor of the superconducting wire in the low oxygen state where the oxygen partial pressure was 0.08 atm was described in Table 4 below. (For Example 11, this heat treatment step in a low oxygen atmosphere was not carried out, and the following heat treatment step in a high oxygen atmosphere was carried out).

  Thereafter, high-concentration oxygen is further introduced at that temperature, and a high-oxygen atmosphere with an oxygen partial pressure of 0.21 atm (the gas component other than oxygen is nitrogen) is used as the precursor of the superconducting wire. On the other hand, a heat treatment step for subsequent heat treatment was carried out for 50 hours.

  Thereafter, the present invention is carried out by carrying out a temperature lowering step in which the temperature of the precursor of the superconducting wire that has undergone the heat treatment step is lowered to room temperature at a rate of 1.6 ° C./min. A superconducting wire having a filament containing Bi2223 phase and a sheath portion covering the filament was obtained.

  With respect to the superconducting wire thus manufactured, the critical current (Ic) and the displacement of the Bi2223 phase of the filament were measured in the same manner as in Examples 1 to 4. The results are shown in Table 4 below.

  As Comparative Example 2, the heat treatment step and the temperature lowering step are performed not in a high oxygen atmosphere but in a low oxygen atmosphere with an oxygen partial pressure of 0.08 atm (however, the temperature of the heat treatment step is 840 ° C. and the time is 30 minutes). Except for (time), everything else was carried out similarly to Examples 11-13, and obtained the superconducting wire. With respect to this superconducting wire, critical current (Ic) and misalignment were measured in the same manner as described above, and the results are shown in Table 4 below.

  As is clear from Table 4, the superconducting wires of Examples 11 to 13 all have an improved critical current (Ic) as compared to the superconducting wire of Comparative Example 2 (comparative example 2 is 15A compared to Example 1). 11-13 was 19-25A).

  In addition, regarding the deviation of the orientation of the Bi2223 phase of the filament, the superconducting wires of Examples 11 to 13 are all less in alignment than the superconducting wire of Comparative Example 2 (Comparative Example 2 is 11.2 deg). In contrast, Examples 11 to 13 were 9.5 to 10.1 deg).

  These results show that even if the temperature raising process is performed in a low oxygen atmosphere and then the heat treatment process is performed in the same low oxygen atmosphere, the heat conduction process and the temperature lowering process are further performed in a high oxygen atmosphere. It is shown that a superconducting wire excellent in the above can be obtained.

<Examples 14 to 16>
In Examples 1-4, the filling step is the same as in Examples 1-4 except that the atomic ratio of Pb / (Bi + Pb) of the precursor of the filament before performing the heat treatment step is 0.177. The precursor of the superconducting wire similar to Examples 1-4 was obtained by implementing a wire drawing process and a rolling process.

  Subsequently, the precursor of the superconducting wire obtained in this way was measured from room temperature up to 838 ° C. (heat treatment temperature) in a low oxygen atmosphere with an oxygen partial pressure of 0.08 atm (gas components other than oxygen were nitrogen). A temperature raising step for raising the temperature at a rate of 1.6 ° C./min was performed.

  Thereafter, when the temperature reached 838 ° C., the heat treatment process for continuously heat-treating the above-mentioned superconducting wire precursor in a low oxygen state with an oxygen partial pressure of 0.08 atm is shown in Table 5 below. (For Example 14, this heat treatment step in a low oxygen atmosphere was not carried out, and the following heat treatment step in a high oxygen atmosphere was carried out).

  Thereafter, high-concentration oxygen is further introduced at that temperature, and a high-oxygen atmosphere with an oxygen partial pressure of 0.21 atm (the gas component other than oxygen is nitrogen) is used as the precursor of the superconducting wire. On the other hand, a heat treatment step for subsequent heat treatment was performed for 70 hours.

  Thereafter, the present invention is carried out by carrying out a temperature lowering step in which the temperature of the precursor of the superconducting wire that has undergone the heat treatment step is lowered to room temperature at a rate of 1.6 ° C./min. A superconducting wire having a filament containing Bi2223 phase and a sheath portion covering the filament was obtained.

  With respect to the superconducting wire thus manufactured, the critical current (Ic) and the displacement of the Bi2223 phase of the filament were measured in the same manner as in Examples 1 to 4. The results are shown in Table 5 below.

  As Comparative Example 3, the heat treatment step and the temperature lowering step are performed not in a high oxygen atmosphere but in a low oxygen atmosphere having an oxygen partial pressure of 0.08 atm (however, the temperature of the heat treatment step is 840 ° C. and the time is 30 minutes). Except for time, everything else was carried out similarly to Examples 14-16, and obtained the superconducting wire. Also for this superconducting wire, the critical current (Ic) and misalignment were measured in the same manner as described above, and the results are shown in Table 5 below.

  As is clear from Table 5, the superconducting wires of Examples 14 to 16 all have improved critical current (Ic) as compared to the superconducting wire of Comparative Example 3 (Comparative Example 3 is 15A compared to Example 1). 14 to 16 were 25 to 30 A).

  In addition, regarding the deviation of the orientation of the Bi2223 phase of the filaments, the superconducting wires of Examples 14 to 16 all have less orientation deviation than the superconducting wire of Comparative Example 3 (Comparative Example 3 is 10.9 deg). On the other hand, Examples 14-16 were 8.5-9.3 deg).

  These results show that even if the temperature raising process is performed in a low oxygen atmosphere and then the heat treatment process is performed in the same low oxygen atmosphere, the heat conduction process and the temperature lowering process are further performed in a high oxygen atmosphere. It is shown that a superconducting wire excellent in the above can be obtained.

  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 notional partial cross-sectional perspective view of a superconducting wire. (A) is a conceptual diagram showing a state in which a large number of Bi2223 phase crystals are generated in parallel to the longitudinal direction of the surface of the superconducting wire, and (b) is a diagram illustrating the Bi2223 phase crystals being the length of the surface of the superconducting wire. It is a conceptual diagram which shows the state which produced | generated many space | gap by producing | generating and producing | generating a shift | offset | difference in orientation with respect to a direction. It is process drawing which shows an example of the manufacturing method of a superconducting wire. It is the graph which showed the change of the critical current in the case where it does not implement the processing process of a high oxygen atmosphere in the manufacturing method of a superconducting wire. It is the graph which showed the change of the shift | offset | difference of orientation in the case where the process process of a high oxygen atmosphere is implemented in the manufacturing method of a superconducting wire. It is another graph which showed the change of the critical current in the case where the processing process of a high oxygen atmosphere is implemented in the manufacturing method of a superconducting wire. It is another graph which showed the change of the shift | offset | difference of orientation in the case where the process process of a high oxygen atmosphere is implemented in the manufacturing method of a superconducting wire. It is another graph which showed the change of the critical current in the case where the processing process of a high oxygen atmosphere is implemented in the manufacturing method of a superconducting wire. It is another graph which showed the change of the shift | offset | difference of orientation in the case where the process process of a high oxygen atmosphere is implemented in the manufacturing method of a superconducting wire.

Explanation of symbols

  1 Superconducting wire, 2 Filament containing Bi2223 phase, 3 sheath part, 4 Bi2223 phase crystal, 5 surface, 6 void.

Claims (8)

A method for producing a superconducting wire having a filament containing a Bi2223 phase and a sheath portion covering the filament,
Raising the temperature of the precursor of the superconducting wire to a temperature at which heat treatment is performed in a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm;
A heat treatment step of heat treating the precursor of the superconducting wire;
A temperature lowering step of lowering the precursor of the superconducting wire in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm from a temperature at which heat treatment is performed;
The manufacturing method of the superconducting wire characterized by including.   2. The method of manufacturing a superconducting wire according to claim 1, wherein the heat treatment step includes a heat treatment performed in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm.   The method of manufacturing a superconducting wire according to claim 1, wherein the heat treatment step includes a heat treatment performed in a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm.   The heat treatment step includes a heat treatment performed in a low oxygen atmosphere with an oxygen partial pressure of 0.07 to 0.09 atm and a high oxygen atmosphere of 0.16 to 0.21 atm. The method of manufacturing a superconducting wire according to claim 1, wherein the heat treatment is performed.   The method of manufacturing a superconducting wire according to claim 1 or 2, wherein the heat treatment step is performed in a high oxygen atmosphere having an oxygen partial pressure of 0.16 to 0.21 atm for 50 hours to 100 hours.   4. The method of manufacturing a superconducting wire according to claim 1, wherein the heat treatment step is performed in a low oxygen atmosphere having an oxygen partial pressure of 0.07 to 0.09 atm for 20 hours or more and 50 hours or less.   The method of manufacturing a superconducting wire according to claim 4, wherein the heat treatment step is performed for 20 hours or more and 100 hours or less.   The composition of the precursor of the filament before performing the heat treatment step is such that the atomic ratio of Pb / (Bi + Pb) is 0.14 or more and 0.18 or less. Manufacturing method of superconducting wire.

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