JP3590567B2 - Manufacturing method of oxide superconducting wire and oxide superconducting wire - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wire having a high critical current density using a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor and a method for producing the same.
[0002]
[Prior art]
When a wire is manufactured using an oxide superconductor, the main manufacturing methods include 1) PIT (Powder in Tube) method 2) Coating method 3) Thin film method.
[0003]
In the PIT method of 1), the superconducting powder is filled into a metal tube made of Ag or the like which does not react with the superconductor even when heated together with the oxide superconductor, and wire drawing, rolling and heat treatment are repeated. It is a method of processing into. This method is used when producing a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconducting wire. The Bi-based oxide superconductor has a property that the crystal grows in a plate shape, and the plate-shaped crystal is easily oriented in the longitudinal direction in the step of extending the superconductor in the PIT method. Here, since the superconducting current has the property of easily flowing in the longitudinal direction of the plate-like crystal, a wire having relatively good characteristics can be manufactured.
[0004]
The coating method 2) is a method in which an organic binder is added to the oxide superconducting powder to form a paste, which is coated on the surface of a silver tape and heat-treated to obtain a wire. This method is mainly used when creating a _{Bi 2 Sr 2 Ca 1 Cu 2} O x based oxide superconducting wire.
[0005]
The thin film method 3) is a method in which an intermediate layer having a lattice constant close to or less reactive with the oxide superconductor is formed on the surface of the metal tape, and a superconducting thin film is laminated thereon to form a wire.
This method is mainly used when preparing a Y ₁ Ba ₂ Cu ₃ O _x -based oxide superconducting wire.
[0006]
[Problems to be solved by the invention]
As described above, the three typical methods of manufacturing a wire have been described. However, the PIT method 1) is considered to be closest to the practical level in consideration of the manufacturing process, cost, superconductivity, and the like. However, although the critical current density remains at 20,000 to 25,000 A / cm ² even in the wire obtained by this method, characteristics of 50,000 A / cm ² or more are desired for practical use. I have.
An object of the present invention is to improve the superconducting properties of a wire obtained by the above-mentioned PIT method and to reach a practical level.
[0007]
[Means for Solving the Problems]
A first invention is a method for producing an oxide superconducting wire having a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor as a main component, wherein BiO _1.5 , PbO, SrCO having a predetermined composition ratio is used. ₃ , CaCO ₃ and CuO are mixed, calcined under predetermined conditions, then pressed under predetermined conditions to obtain a molded body, inserted into a metal pipe, drawn under predetermined conditions, Rolled into a wire rod, the wire rod is fired at 840 to 845 ° C. in the air for 50 to 200 hours, and after the firing step is completed, or at a temperature of 805 to 825 ° C. when the temperature of the firing step is lowered, the wire is heated to 4 to 845 ° C. A method for manufacturing an oxide superconducting wire, comprising performing a wire annealing treatment for 30 hours.
[0008]
A second invention is a wire having a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor manufactured by the manufacturing method according to the first invention in a metal sheath material, Between the grain boundaries of the oxide superconductor crystal particles in the oxide superconductor, CuO particles having a particle size of 1 μm or less, Cu ₂ O particles, and at least one of Ca ₂ PbO ₄ particles is contained. Oxide superconducting wire.
[0009]
Embodiment
FIG. 1 is a schematic TEM photograph of a cross section of an oxide superconductor in a metal sheath oxide superconducting wire according to an embodiment of the present invention. In FIG. 1, the superconducting crystal 11 has a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor as a main component and is oriented in the longitudinal direction of the wire. The contact between the superconducting crystals at the crystal grain boundaries is well maintained. On the other hand, at least one precipitate 12 of CuO, Cu ₂ O and Ca ₂ PbO ₄ having a particle size of 0.1 to 1 μm is found at the crystal grain boundary.
[0010]
FIG. 2 is a schematic TEM photograph of a cross section of an oxide superconductor contained in a metal sheath oxide superconducting wire manufactured in the same manner as the present invention except that the wire annealing treatment is not performed. In FIG. 2, the superconducting crystal 21 has a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor as a main component and is oriented in the longitudinal direction of the wire. A non-superconducting phase 22 of a film-like and amorphous body mainly containing Bi, Pb, Sr, Ca, Cu, and O as main components is formed at a crystal grain boundary, and a contact area between superconducting crystals is limited. I have. On the other hand, at least one precipitate of CuO, Cu ₂ O and Ca ₂ PbO ₄ having a particle size of 0.1 to 1 μm was not found at the crystal grain boundary.
[0011]
FIG. 3 is an external view and a cross section of a metal sheath oxide superconducting wire produced by the PIT method. Ag, Au, and Pt are preferable for the metal sheath material 31 from the viewpoint of thermal stability to the oxide superconductor 32. The oxide superconductor 32 is based on (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x .
[0012]
Hereinafter, embodiments of the present invention will be described with reference to these drawings.
The oxide superconductor 32 in the (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based metal sheath oxide superconducting wire of FIG. 3 manufactured by the conventional PIT method is observed with a TEM (transmission electron microscope). As shown in FIG. 2, a non-superconducting phase 22 in the form of a film mainly composed of Bi, Pb, Sr, Ca, Cu, and O is formed at the grain boundaries of the superconducting crystal 21. It is considered that the presence of the non-superconducting phase 22 reduces the substantial area through which the current can flow between the superconducting crystals 21 and limits the critical current value and the critical current density. Therefore, in order to increase the critical current value and the critical current density in the (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconducting wire, it is necessary to improve the electrical coupling state between the oxide superconducting crystals 21. Considered important.
[0013]
Therefore, the process of forming the non-superconducting phase 22 of the film-like amorphous body is clarified, and if the non-superconducting phase can be eliminated or its generation can be prevented, an oxide having a critical current value and a critical current density at a practical level can be obtained. We have realized that a superconducting wire can be manufactured.
[0014]
The process of forming the non-superconducting phase 22 of the film-like amorphous body is considered as follows.
When the metal sheath wire filled with the oxide superconducting synthetic powder, which is the raw material of the oxide superconductor 32, is fired in the air at 840 to 845 ° C for 50 to 150 hours, a high Tc is obtained in the metal sheath. The (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x crystal of the superconducting phase shown grows at the fastest rate, and the metal-sheath oxide superconducting wire shown in FIG. 3 is obtained. However, since this crystal growth is accompanied by a liquid phase, a liquid phase always intervenes between growing crystal grain boundaries. As the crystal growth progresses, the amount of liquid phase at the crystal grain boundaries also decreases, but it is thought that the liquid phase in the thermal equilibrium state finally remains and the non-superconducting phase 22 of the film-like amorphous body is formed in the cooling step after firing. Can be
[0015]
The present inventor completely terminates the firing or applies heat of an appropriate temperature to a metal sheath wire at an appropriate time when the temperature of the sintering process is lowered (hereinafter, referred to as wire annealing process), thereby forming the metal sheath wire in the firing process. The non-superconducting phase of the formed film-like amorphous body is changed into an oxide superconducting phase and at least one precipitate of CuO, Cu ₂ O and Ca ₂ PbO ₄ at a slow reaction rate, so that the film-like amorphous body 22 disappears or disappears. The inventors of the present invention have conceived that the generation can be prevented and completed the present invention.
[0016]
That is, as a result of this reaction, the non-superconducting phase 22 of the film-like amorphous body, which has become an obstacle to the transport current, has at least one of superconducting crystal 11 having a high Tc and CuO, Cu ₂ O and Ca ₂ PbO ₄ having a particle size of 1 μm or less. That is, it has changed into two precipitates 12.
Although the precipitate 12 is a non-superconducting phase but has a small particle size, even if it exists in the grain boundary, it does not not only hinder the transport current but also the presence of the precipitate It can be used as an index of change to body crystal 11.
[0017]
Embodiment 1
Each raw material powder of BiO _1.5 , PbO, SrCO ₃ , CaCO ₃ and CuO having a particle size of 0.1 to 10 μm and a purity of 3 to 4 N is mixed to obtain BiO _1.5 : PbO: SrCO ₃ : CaCO ₃ : CuO = After preparing a mixed powder sample having a composition ratio of 1.85: 0.35: 1.90: 2.05: 3.05, it was calcined in the air at a temperature of 740 to 820 ° C. for 10 to 100 hours. Obtain superconducting synthetic powder. Next, 1.2 g of this superconducting synthetic powder was filled in a cylindrical rubber mold having a hollow portion of 3.8 mmφ × 95 mmL and a wall thickness of 10 mm, the openings at both ends were sealed with rubber stoppers, and a cold isostatic press was used. Pressure molding is performed at a maximum pressure of 1.5 t / cm ² to obtain a molded body of about 1.95 mmφ × 90 mmL. The molded body was inserted into an Ag pipe having an inner diameter of 2.0 mmφ and an outer diameter of 3.0 mmφ × 100 mmL.
[0018]
The Ag pipe is drawn and rolled to form a wire. This wire was placed in an electric furnace and fired in an air atmosphere. Heat to 840 ° C. at a rate of temperature increase of 2 ° C./min and hold for 150 hours, then return to room temperature at a rate of 3 ° C./min, tape-shaped Ag sheath oxide about 5.0 mm wide and about 0.2 mm thick A superconducting wire was obtained. The region of the superconducting portion in the wire had a width of about 4 mm and a thickness of about 0.07 mm.
When the critical current value and the critical current density at this point were measured, the critical current value was 29.4 A at a temperature of 77 K and a self-magnetic field, and was about 10,500 A / cm ² at the critical current density.
The critical current value and the critical current density were measured using a four-terminal method. The current value when 1 μV / cm was generated between the voltage terminals under a self-magnetic field at 77 K was defined as the critical current value, and the cross-sectional area was 1 cm. ^The current value converted into ² was defined as the critical current density.
[0019]
Next, FIG. 4 shows a critical current value as a result of treating the Ag sheath oxide superconducting wire after completion of sintering at the wire annealing temperature and annealing time shown in FIGS. It is shown in FIG. However, the rate of temperature rise during annealing was 2.67 ° C./min, and the rate of temperature fall was 1.33 ° C./min.
From this, it was found that a wire having a high critical current value (Ic) and a high critical current density (Jc) can be obtained in the range of the annealing temperature of 805 to 820 ° C. and the processing time of 4 to 30 hours.
Further, it has been found that the critical current density (Jc) exceeds 44,000 A / cm ² in the range of the annealing temperature of 810 to 815 ° C. and the processing time of 12 to 16 hours.
[0020]
Embodiment 2
Each raw material powder of BiO _1.5 , PbO, SrCO ₃ , CaCO ₃ and CuO having a particle size of 0.1 to 10 μm and a purity of 3 to 4 N is mixed to obtain BiO _1.5 : PbO: SrCO ₃ : CaCO ₃ : CuO = a: After preparing a mixed powder sample having a composition ratio of 0.35: 1.90: 2.05: 3.05, it was calcined in the air at a temperature of 740 to 820 ° C. for 10 to 100 hours and superconducting synthesis. Get the powder. However, a is varied between 1 ≦ a ≦ 3 to prepare a plurality of mixed powder samples, and then calcined in air at a temperature of 740 to 820 ° C. for 10 to 100 hours to obtain a plurality of superconducting synthetic powders. Next, 1.2 g of each of the superconducting synthetic powders was filled into a cylindrical rubber mold having a hollow part of 3.8 mmφ × 95 mmL and a wall thickness of 10 mm, and the openings at both ends were sealed with rubber stoppers, and cold isostatic pressure was applied. Pressure molding is performed with a press at a maximum pressure of 1.5 t / cm ² to obtain a molded body of about 1.95 mmφ × 90 mmL. The molded body was inserted into an Ag pipe having an inner diameter of 2.0 mmφ and an outer diameter of 3.0 mmφ × 100 mmL.
[0021]
These Ag pipes are drawn and rolled to form wires. These wires were placed in an electric furnace and fired in an air atmosphere. Heat to 840 ° C. at a rate of temperature increase of 2 ° C./min and hold for 150 hours, then return to room temperature at a rate of 3 ° C./min, tape-shaped Ag sheath oxide about 5.0 mm wide and about 0.2 mm thick A superconducting wire was obtained. The region of the superconducting portion in the wire had a width of about 4 mm and a thickness of about 0.07 mm.
At this point, the critical current value and critical current density of these wires were measured.
The critical current value was measured using a four-terminal method. The current value when a voltage of 1 μV / cm was generated between the voltage terminals under a self-magnetic field at 77 K was defined as the critical current value, and the cross-sectional area was converted to 1 cm ² . The current value was defined as the critical current density.
[0022]
Next, each Ag sheath oxide superconducting wire after sintering was annealed at 815 ° C. for 12 hours. However, the rate of temperature rise during annealing was 2.67 ° C./min, and the rate of temperature fall was 1.33 ° C./min. After the annealing treatment, the critical current value and the critical current density of these wires were measured again.
The results are shown in FIG. From this, it was found that the critical current value and the critical current density of the Ag sheath oxide superconducting wire increased by the wire annealing treatment when 1.5 ≦ a ≦ 2.1.
[0023]
The same test as above was performed on b this time.
However, the composition ratio of the mixed powder sample is BiO _1.5 : PbO: SrCO ₃ : CaCO ₃ : CuO = 1.85: b: 1.90: 2.05: 3.05 and 0 ≦ b ≦ 0.6 Changed b.
As a result, when 0.14 ≦ b ≦ 0.45, it was found that the critical current value and the critical current density of the Ag sheath oxide superconducting wire increased by the wire annealing treatment.
[0024]
The same test as above was performed for c this time.
However, the composition ratio of the mixed powder sample is BiO _1.5 : PbO: SrCO ₃ : CaCO ₃ : CuO = 1.85: 0.35: c: 2.05: 3.05 and b is between 1 ≦ c ≦ 3. Was changed.
As a result, it was found that the critical current value and the critical current density of the Ag sheath oxide superconducting wire increased by the wire annealing treatment when 1.6 ≦ c ≦ 2.2.
[0025]
The same test as above was performed on d this time.
However, the composition ratio of the mixed powder sample is BiO _1.5 : PbO: SrCO ₃ : CaCO ₃ : CuO = 1.85: 0.35: 1.90: d: 3.05 and d is between 1 ≦ d ≦ 3. Was changed.
As a result, it was found that when 1.7 ≦ d ≦ 2.3, the critical current value and the critical current density of the Ag sheath oxide superconducting wire increased by the wire annealing treatment.
[0026]
【The invention's effect】
According to the present invention, the critical current density of the oxide superconducting wire manufactured by the PIT method can be increased to a practical level of 50,000 A / cm ² or more. If this wire and the wire making method are applied to, for example, a power transmission cable, a cable without power transmission loss greatly contributes to efficient use of power and cost reduction.
[0027]
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a cross-sectional TEM photograph of an oxide superconductor in a wire after a wire annealing treatment according to the present invention.
FIG. 2 is a schematic TEM photograph of a cross-section of an oxide superconductor in a wire manufactured in the same manner as in the present invention except that an annealing process is not performed.
FIG. 3 is an external view and a cross section of a metal sheath oxide superconducting wire.
FIG. 4 is a table showing the relationship between wire annealing conditions (temperature / time) and the critical current value (Ic) of the wire in the present invention.
FIG. 5 is a table showing the relationship between wire annealing conditions (temperature / time) and the critical current density (Jc) of the wire in the present invention.
FIG. 6 shows a critical current value (Ic) and a critical current density (Jc) before and after wire annealing (815 ° C., 12 hours) of an oxide superconducting wire prepared by changing the composition ratio of BiO _{1.5 in} the present invention. FIG. 3 is a table showing the values of.

Claims (2)

A method for producing an oxide superconducting wire mainly comprising (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor,
After mixing BiO _1.5 , PbO, SrCO ₃ , CaCO ₃ and CuO having a predetermined composition ratio, calcining them under predetermined conditions, and then press-molding them under predetermined conditions to obtain a compact, a metal pipe is formed. And wire drawn and rolled under predetermined conditions to obtain a wire, and the wire is fired at 840 to 845 ° C. in the air for 50 to 200 hours. After the firing process is completed, or the temperature of the firing process is lowered. A wire annealing treatment at a temperature of 805 to 820 [deg.] C. for 4 to 30 hours. A wire having a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor manufactured by the manufacturing method according to claim 1 in a metal sheath material,
Between the grain boundaries of the oxide superconductor crystal particles in the oxide superconductor, CuO particles having a particle size of 1 μm or less, Cu ₂ O particles, and at least one of Ca ₂ PbO ₄ particles is contained. Oxide superconducting wire.

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