JP2001332146A - Oxide superconducting wire rod and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a superconducting characteristics of a metal sheathe Bi-based oxide superconducting wire rod fabricated by PIT method to reach a practical level. SOLUTION: By performing a heat treatment (wire rod annealing) on a wire rod under a given condition after a burning process, a non-superconducting phase of a film amorphous body formed in the burning process is changed into a superconducting crystal having a high Tc and the precipitates of CuO, Cu2O, and Ca2PbO4 whose particle sizes are 1 μm or less, so that the electrical coupling conditions between grain boundaries are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to (BiPb) ₂ S
The present invention relates to a wire having a high critical current density using an r ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor and a method for producing the same.

[0002]

2. Description of the Related Art When a wire is manufactured using an oxide superconductor, 1) PIT (Powder)
In Tube) method 2) Coating method 3) Thin film method.

In the PIT method of 1), the superconducting powder is filled in a metal tube made of Ag or the like which does not react with the superconductor even when it is heated together with the oxide superconductor. This is a method of repeatedly processing into a wire. 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 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 an 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 of 3) is a method in which an intermediate layer having a lattice constant close to that of an oxide superconductor or having low reactivity is formed on the surface of a metal tape, and a superconducting thin film is laminated thereon to form a wire. It is. This method is mainly used when preparing a Y ₁ Ba ₂ Cu ₃ O _x -based oxide superconducting wire.

[0006]

The method of manufacturing three typical wires has been described above. However, considering the manufacturing process, cost, superconducting characteristics, and the like, the most practical level is considered to be 1). PIT method. However, even with the wire obtained by this method, the critical current density is from 20,000 to
Remains to 25,000A / cm ^2, but for practical use has been desired 50,000A / cm ² or more properties. 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]

According to a first aspect of the present invention, BiO _1.5 , PbO, SrCO ₃ , CaCO ₃ and CuO having a predetermined composition ratio are mixed, calcined under predetermined conditions, and then calcined under predetermined conditions. After obtaining a molded body by pressure molding, it is inserted into a metal pipe, 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. A method of manufacturing an oxide superconducting wire, comprising performing a wire annealing treatment at a temperature of 805 to 825 [deg.] C. for 4 to 30 hours after completion of the firing step or at the time of lowering the temperature of the firing step.

[0008] In the second invention, (Bi)
A wire having a _{Pb) 2 Sr 2 Ca 2 Cu} 3 O x based oxide superconductor, between the grain boundaries of the oxide superconductor crystal grains in the oxide superconductor in a particle size 1μm or less of Cu
An oxide superconducting wire comprising at least one of O particles, Cu ₂ O particles, and Ca ₂ PbO ₄ particles.

[0009]

FIG. 1 shows a metal according to an embodiment of the present invention.
Cross section of oxide superconductor in sheath oxide superconducting wire
It is a schematic diagram of a TEM photograph. In FIG. 1, superconducting crystal 1
1 is (BiPb)_TwoSr_TwoCa_TwoCu_ThreeO_xOxide superconductivity
The body is the main component and is oriented in the longitudinal direction of the wire. crystal
Good contact between superconducting crystals at grain boundaries is maintained.
You. On the other hand, CuO having a particle size of 0.1 to 1 μm
Cu_TwoO and Ca_TwoPbO _FourAt least one precipitate 1 of
2 can be seen.

FIG. 2 is a schematic TEM photograph of a cross section of an oxide superconductor 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 is (BiPb) ₂ S
The main component is an r ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor, which is oriented in the longitudinal direction of the wire. Bi, P mainly at the grain boundaries
An amorphous non-superconducting phase 22 is formed in the form of a film containing b, Sr, Ca, Cu, and O as main components, and the contact area between superconducting crystals is limited. On the other hand, CuO, Cu ₂ O and Ca ₂ P having a particle size of 0.1 to 1 μm
At least one precipitate of bO ₄ was not found.

FIG. 3 shows a metal sheet produced by the PIT method.
1 is an external view and a cross section of an oxide superconducting wire. Metal sheath material
31 is A from the viewpoint of thermal stability to the oxide superconductor 32.
g, Au and Pt are preferred. The oxide superconductor 32 is (B
iPb)_TwoSr_TwoCa_TwoCu_ThreeO _xSystem.

An embodiment of the present invention will be described below with reference to these drawings.
The state will be described. FIG. 3 manufactured by the conventional PIT method
(BiPb)_TwoSr_TwoCa_TwoCu_ThreeO_xMetal sheath oxidation
The oxide superconductor 32 in the material superconducting wire is TEM (transmission type).
When observed with an electron microscope), as shown in FIG.
Bi, Pb, Sr, Ca, C mainly at the grain boundaries of the conducting crystal 21
non-super amorphous and non-superficial film composed mainly of u and O
A conductive phase 22 is formed. This non-superconducting phase 22 exists.
, The current can substantially flow between the superconducting crystals 21.
Critical area and critical current value and critical current density are limited
It is thought that it is done. Therefore, (Bi
Pb)_TwoSr_TwoCa_TwoCu_ThreeO _xOxide superconducting wire
To increase the critical current value and critical current density by
To improve the electrical coupling between the superconducting crystals 21
Is considered important.

Therefore, the process of forming the non-superconducting phase 22 of this film-like amorphous body is clarified, and if the non-superconducting phase can be eliminated or its generation can be prevented, the critical current value and critical current density at practical levels can be reduced. It has been conceived that an oxide superconducting wire having the same can be produced.

The process of forming the non-superconducting phase 22 of a film-like amorphous body is considered as follows. A metal sheath wire filled with an oxide superconducting synthetic powder, which is a raw material of the oxide superconductor 32, is heated at 840 to 845 ° C.
When sintering is performed for 0 to 150 hours, a superconducting phase (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ showing a high Tc is formed in the metal sheath.
The _Ox crystal 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 the crystal grain boundaries that grow. As the crystal growth progresses, the amount of the liquid phase at the crystal grain boundaries also decreases, but the liquid phase in the thermal equilibrium state finally remains and the non-superconducting phase 22
Is considered to be formed.

The inventor of the present invention completes the sintering process or applies heat at an appropriate temperature to a metal sheath wire for an appropriate time during the sintering process when the temperature is lowered (hereinafter referred to as wire annealing process). The non-superconducting phase of the film-like amorphous body formed in the step (a) is slowly reacted with the oxide superconducting phase and at least one of CuO, Cu ₂ O and Ca ₂ PbO ₄ .
The present invention has been completed by assuming that it is possible to prevent the disappearance or generation of the film-like amorphous body 22 by changing it into two precipitates.

That is, as a result of this reaction, the non-superconducting phase 22 of the film-like amorphous body, which has been an obstacle to the transport current, has a superconducting crystal 11 having a high Tc and a Cu
This turned into at least one precipitate 12 of O, Cu ₂ O and Ca ₂ PbO ₄ . Although the precipitate 12 is a non-superconducting phase but has a small particle size, its presence in the grain boundary does not not only hinder the transport current but also the presence of the precipitate Body crystal 1
It can be used as an index of the change to 1.

[0017]

Example 1 B having a particle size of 0.1 to 10 μm and a purity of 3 to 4 N
The raw material powders of iO _1.5 , PbO, SrCO ₃ , CaCO ₃ and CuO are mixed to form BiO _1.5 : PbO: SrCO ₃ :
CaCO ₃ : CuO = 1.85: 0.35: 1.90:
After preparing a mixed powder sample having a composition ratio of 2.05: 3.05, a temperature of 740 to 820 ° C., 10 to 100 hours,
It is calcined in the air to obtain superconducting synthetic powder. Next, 1.2 g of this superconducting synthetic powder was filled with a hollow portion of 3.8 mmφ × 95 mm.
L, filling a cylindrical rubber mold having a thickness of 10 mm, sealing the openings at both ends with rubber stoppers, press-molding with a cold isostatic press at a maximum pressure of 1.5 t / cm ² , about 1.95 mmφ × 9
Obtain a 0 mmL molded body. This molded body is 2.0 mm in inner diameter
φ, an outer diameter of 3.0 mmφ × 100 mmL was inserted into an Ag pipe.

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 rise 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 with width of about 5.0mm and thickness of about 0.2mm A superconducting wire was obtained. The region of the superconducting portion in the wire has 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 time were measured, the critical current value was 29.4 A at a temperature of 77 K and under a self-magnetic field, and was approximately 10,5 at a critical current density.
It was 00 A / cm ² . The critical current value and the critical current density were 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 1 cm. ^The current value converted into ² was defined as the critical current density.

Next, the critical current value obtained by treating the Ag-sheathed oxide superconducting wire after the completion of sintering at the wire annealing temperature and annealing time shown in FIGS. 4 and 5 is shown in FIG. The values are shown in FIG. However, the rate of temperature rise during annealing was 2.67 ° C./min, and the rate of temperature decrease was 1.33 ° C./min.
min. Thus, the annealing temperatures 805-8
It has been 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 20 ° C. and the treatment time of 4 to 30 hours. Further, the annealing temperature 81
It was also found that the critical current density (Jc) exceeded 44,000 A / cm ² in the range of 0 to 815 ° C. and the treatment time of 12 to 16 hours, and almost reached a practical level.

[0020]

Example 2 B having a particle size of 0.1 to 10 μm and a purity of 3 to 4 N
The raw material powders of iO _1.5 , PbO, SrCO ₃ , CaCO ₃ and CuO are mixed to form BiO _1.5 : PbO: SrCO ₃ :
CaCO ₃ : CuO = a: 0.35: 1.90: 2.0
After preparing a mixed powder sample having a composition ratio of 5: 3.05, it is calcined in the air at a temperature of 740 to 820 ° C for 10 to 100 hours to obtain a superconducting synthetic powder. Where a is 1 ≦ a ≦ 3
And preparing a plurality of mixed powder samples, and then calcining 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 with a hollow portion of 3.8 mmφ × 95 mm.
L, filling a cylindrical rubber mold having a thickness of 10 mm, sealing the openings at both ends with rubber stoppers, press-molding with a cold isostatic press at a maximum pressure of 1.5 t / cm ² , about 1.95 mmφ × 9
Obtain a 0 mmL molded body. This molded body is 2.0 mm in inner diameter
φ, an outer diameter of 3.0 mmφ × 100 mmL was inserted into an Ag pipe.

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 rise 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 with width of about 5.0mm and thickness of about 0.2mm 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 time, 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.

Next, each of the Ag sheath oxide superconducting wires after sintering was annealed at 815 ° C. for 12 hours. However, the rate of temperature rise during annealing is 2.67.
° C / min, and the temperature decreasing rate 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 were increased by the wire annealing treatment when 1.5 ≦ a ≦ 2.1.

The same test as described above was performed for b. However, the composition ratio of the mixed powder sample was BiO _1.5 : Pb
O: SrCO ₃ : CaCO ₃ : CuO = 1.85: b:
1.90: 2.05: 3.05, and b was changed between 0 ≦ b ≦ 0.6. As a result, 0.14 ≦ b ≦ 0.45
At this time, it was found that the critical current value and the critical current density of the Ag sheath oxide superconducting wire were increased by the wire annealing treatment.

The same test as described above was performed for c. However, the composition ratio of the mixed powder sample was BiO _1.5 : Pb
O: SrCO ₃ : CaCO ₃ : CuO = 1.85: 0.3
5: c: 2.05: 3.05 and b was changed between 1 ≦ c ≦ 3. As a result, it was found that the critical current value and the critical current density of the Ag sheath oxide superconducting wire were increased by the wire annealing treatment when 1.6 ≦ c ≦ 2.2.

A test similar to the above was performed on d this time. However, the composition ratio of the mixed powder sample was BiO _1.5 : Pb
O: SrCO ₃ : CaCO ₃ : CuO = 1.85: 0.3
5: 1.90: d: 3.05, and d was changed between 1 ≦ d ≦ 3. 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]

According to the present invention, the critical current density of the oxide superconducting wire manufactured by the PIT method is set to a practical level of 5%.
It became possible to raise it to 000 A / cm ² or more. If this wire and the wire making method are applied to, for example, a power transmission cable, the cable will have no power transmission loss, and will greatly contribute 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 and time) and the critical current value (Ic) of the wire in the present invention.

FIG. 5 is a table showing a relationship between wire annealing conditions (temperature / time) and critical current density (Jc) of the wire in the present invention.

FIG. 6 shows a wire annealing treatment (8) 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 critical current values (Ic) and critical current densities (Jc) around (15 ° C., 12 hours).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Hofumi Murakami 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Kazuya Yamaguchi 1-2-2, Marunouchi, Chiyoda-ku, Tokyo No. F-term in Dowa Mining Co., Ltd. (Reference) 4G047 JA05 JC10 KA18 KB04 LA02 LB01 4G048 AA05 AB05 AC04 AD04 AE05 5G321 AA06 CA07 CA30 DB18 DB47 DB54

Claims (2)

[Claims] 1. BiO _1.5 , PbO, Sr having a predetermined composition ratio
CO 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, and drawn under predetermined conditions. After rolling, the wire is fired at 840 to 845 ° C. in the air for 50 to 200 hours, and after the firing process is completed,
Alternatively, a method for producing an oxide superconducting wire, comprising performing a wire annealing treatment at a temperature of 805 to 820 ° C. for 4 to 30 hours when the temperature is lowered in the firing step. 2. A metal sheath material comprising (BiPb) ₂ Sr ₂ C
a wire having an a ₂ Cu ₃ O _x -based oxide superconductor,
CuO particles having a particle diameter of 1 μm or less, Cu ₂ O, between grain boundaries of oxide superconductor crystal particles in the oxide superconductor.
An oxide superconducting wire comprising at least one of particles and Ca ₂ PbO ₄ particles.