JPH04328215A - Manufacture of bi-series oxide type superconductive wire - Google Patents

Abstract

PURPOSE:To manufacture an oxide superconductive wire with a high critical current density. CONSTITUTION:Fabrication is made once for a flake-form superconductive body 10 with excellent crystal orientation obtained by the band melting method or a directional melted solidified substance using a seed material. The resultant is again crushed, put fully in a metal sheath 11, compacted with pressure, and subjected to a heat treatment. According to this procedure, wherein intermediate product once oriented in the flake form is again crushed, is compacted with pressure, and undergoes heat treatment, an oxide type superconductive wire can be accomplished which includes oxide superconductor having a high critical current density, ensuring that the superconductor producing rate is high and impurities are less included.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Bi-based oxide superconducting wire with excellent crystal orientation and high critical current density.

0002

[Prior Art] Conventionally, a sheath material made of silver contained Bi.
Oxide superconducting wires comprising oxide superconductors of this type are known. In this type of superconducting wire, (BiPb)2Sr2Ca2Cu3Ox known as 2223 phase
As an example of a method for manufacturing an oxide superconductor having the following composition, the method described below with reference to FIGS. 3 to 7 is known.

[0003] In this manufacturing method, first, Bi2O3, P
Each powder of bO, SrCO3, CaCO3, and CuO was
:Pb:Sr:Ca:Cu=1.6:0.4:2:2:
3 to create the mixed powder 1 shown in FIG.
A sintered body is obtained by calcining for about 200 hours. Next, the crushed product 4 obtained by crushing this sintered body is filled into a silver pipe 3 as shown in FIG. 4, and then the diameter is reduced by swaging wire drawing as shown in FIG. As shown in FIG. 7, the 2223-phase oxide superconductor is formed inside the silver sheath by compacting it using a rolling and pressing machine 5, and then heat-treating it in a heating furnace 6 as shown in FIG.
I am getting .

[0004] The superconducting wire 7 obtained in this way has a magnetic field of 104 A/cm2 (external magnetic field 0 T) at liquid nitrogen temperature.
It exhibits a high critical current density.

[0005]

However, the superconducting wire 7 obtained by the above manufacturing method has a problem in that the critical current density varies in the longitudinal direction of the wire. That is, when we measured the critical current density at various positions in the longitudinal direction of the obtained superconducting wire, we found that there were some parts where the critical current density decreased significantly, as shown in Figure 8. It turned out that there was some variation.

[0006] There are various possible causes of this problem, one of which is the low rate of superconducting phase formation. That is, heat treatment reduces the conductor's cross-sectional area by 10
There is no problem if 0% is converted into a superconducting phase, but it is known that in reality, various proportions of non-superconducting phases, impurity elements, and unreacted phases are included. Therefore, it is considered that one effective method for obtaining a superconducting wire with a high critical current density is to ensure a reaction of the superconducting phase as uniform as possible and close to 100%.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the invention according to claim 1 provides a method for producing a Bi-based oxide superconductor by subjecting a mixed raw material containing elements constituting a Bi-based oxide superconductor to consolidation treatment and heat treatment. This oxide superconductor is melted, a seed material is brought into contact with this melt, and a pulling treatment is performed to adhere and generate a directional melted solidified material on the seed material. Crushing the directional melt solidified body,
Swaging process after filling inside the metal sheath,
Consolidate by wire drawing, rolling or press processing,
Thereafter, heat treatment is performed to generate a Bi-based oxide superconductor inside the metal sheath.

[0008] In order to solve the above-mentioned problem, the invention according to claim 2 subjects a mixed raw material containing elements constituting the Bi-based oxide superconductor to consolidation treatment and heat treatment to produce a Bi-based oxide superconductor. forming the oxide superconductor, partially melting the oxide superconductor, and moving the partially melted zone to partially melt the entire oxide superconductor one or more times to turn the oxide superconductor into a melted band material, and then This molten material is crushed and filled inside the metal sheath, and then consolidated by swaging, wire drawing, rolling, or pressing, and then heat-treated to form a Bi-based oxide superconductor inside the metal sheath. It is something that generates.

[Function] Directional solidification using seed material crystals or band melting material that has been partially melted by band melting is a crystalline body with a certain degree of crystal orientation and particularly high c-axis orientation. Even when it is a pulverized product, it is a pulverized product that maintains the flaky crystal shape characteristic of Bi-based superconductors. Therefore, if this pulverized material is filled into a metal sheath, consolidated by swaging, wire drawing, rolling or pressing, and then heat treated, the flaky crystals arranged in the longitudinal direction of the wire can be further heat treated. The degree of orientation is increased in the longitudinal direction. Therefore, from this wire, an oxide superconductor with a small amount of unreacted portions, a small amount of impurities, and a good crystal orientation can be obtained. In addition, since the crystals of the Bi-based flaky superconductor are oriented again, the grain boundaries of the oxide superconductor crystals may become pinning centers for magnetic flux, contributing to the improvement of the magnetic field characteristics of critical current density. .

The present invention will be explained in more detail below. To carry out the method of the present invention, first, a starting material for a Bi-based oxide superconductor is prepared. As a starting material, a Bi compound, a Pb compound, a Sr compound, a Ca compound, a Cu compound, or a composite oxide thereof is used. The compound may be any of oxides, sulfides, carbonates, fluorides, etc. of each element. Specifically used in this example is BiCO
3, Bi2O3, SrCO3, CaCO3, PbO, C
It is powder or granules such as uO.

[0010] Once each of the above powders has been prepared, Bi:S
r:Ca:Cu:O=2:2:2:3, 2:2:3:4
Alternatively, a mixed raw material is obtained by mixing in a ratio such as 2:2:1:2 or a composition such as (BiPb)2Sr2Ca2Cu3Ox. Next, the mixed raw materials were placed in the atmosphere at 780 to 850°C for several hours to 100°C.
Calcination is performed by heating for about an hour to remove unnecessary components. Next, this calcined product is pressed to form a green compact. Next, either a directional solidification process using a seed material or a band melting process using a heater is performed.

[0011] In the directional solidification process, a seed material is immersed in a molten body obtained by melting the green compact, and the directional molten solidified body is attached to the seed material by pulling up the seed material at a constant speed. . The seed material used here is a metal material (for example, Pt) whose melting point is higher than the melt temperature, or a small piece-shaped crystal such as MgO or SrTiO3, which has a crystal structure similar to that of an oxide superconductor. Also good. Band melting treatment is a process in which a heat-treated powder compact is melted in a band shape using a heating device, and the melted band portion is moved to the end of the compact to melt the entire compact once or multiple times. .

Next, the solidified body or band melted body subjected to the directional solidification treatment or band melting treatment is subjected to heat treatment. This heat treatment is a treatment of heating at 820 to 840° C. for several hours to about 100 hours. Through this treatment, the solidified body or the molten band becomes a Bi-based oxide superconductor. This oxide superconductor produces a flaky crystal structure unique to Bi-based oxide superconductors and exhibits superconductivity, but is still lacking in terms of critical current density.

Next, the superconductor is pulverized and compacted into a rod-like shape, and then this molded body is inserted into a metal pipe made of silver or the like, and subjected to wire drawing, rolling, pressing, etc. The oxide superconductor is formed inside the metal sheath by appropriately reducing the diameter to obtain a tape-shaped or circular cross-sectional wire, and then heat-treating this at 820-840°C for several hours to 100 hours. A tape-shaped or linear superconducting wire can be obtained.

FIG. 1 shows an example of the structure of a tape-shaped Bi-based oxide superconducting wire produced by the process described above. In this superconducting wire 10, a band-shaped conductor portion 12 made of an oxide superconductor is formed inside a hollow tape-shaped sheath material 11 made of silver.

In this superconducting wire 10, the crushed flake-like structure of the superconductor produced in an intermediate step is further filled into a metal pipe, consolidated by processing, and then further heat-treated to form a superconductor. Therefore, it is possible to obtain a conductor section 12 that includes an oxide superconductor having a uniform composition with a high superconductor production rate and a small amount of unreacted portions. Also,
The pulverized material is consolidated and heat-treated once the crystal orientation has been adjusted by the directional solidification method or zone melting method, so it is compared to oxide superconducting wire obtained by simply filling a metal pipe with the starting material and then heat-treating it. Then, the conductor portion 12 of the oxide superconductor with finer crystals and better orientation can be obtained. Furthermore, since the flaky crystals are arranged in the longitudinal direction of the wire, the crystal grain boundaries of the superconductor act as pinning centers for magnetic flux, and the magnetic field characteristics of the critical current density are slightly improved.

[0016]

[Example] (Example 1) BiCO3, SrCO3 and Ca
Each powder of CO3 and CuO is converted into Bi2Sr2Ca2Cu3O.
The mixture was mixed to have the composition x, calcined at 780°C for 5 hours, and pulverized. The crushed material was crushed into diameter 1.5 with a rubber press.
It was compacted into a mm rod shape. This rod-shaped body is heated to 930°C to partially melt it, and a seed material is immersed in this melted body and pulled up at a constant speed to form a fiber-like material with a diameter of 0.3 mm that is attached to the seed crystal and solidified. A Bi-based superconducting wire was obtained. This superconducting strand was heat-treated at 780° C. for 100 hours to produce a superconductor having a critical temperature of 83 K and a critical current density of 4000 A/cm 2 . Thereafter, this superconductor was ground into thin flakes using a ball mill or mortar.

Next, this pulverized product was compression-molded into a rod-shaped body with a diameter of 3 mm, and then inserted into a silver pipe with an outer diameter of 6 mm and an inner diameter of 4 mm, and swaging and wire drawing were repeatedly performed to obtain a wire rod with a diameter of 2 mm. Ta. After that, this wire rod was subjected to rolling and pressing, and then heated to 840℃ in the atmosphere.
Heat treated for 00 hours, thickness 0.2mm, width 2
．． A tape-shaped Bi-based superconducting wire with a 5 mm silver sheath was obtained. The critical temperature of this superconducting wire was improved to 83K and the critical current density to 8000A/cm2 (77K, magnetic field 0T).

FIG. 2 shows the relationship between the critical current density of the superconducting wire and the magnetic field. In Figure 2, as a comparative example,
BiCO3, SrCO3, CaCO3, and CuO powders were mixed to have a composition of Bi2Sr2Ca2Cu3Ox, calcined at 780°C for 5 hours, and the pulverized product was filled into a silver pipe of the same size as above, and the same as above. The critical current density of the Bi-based superconducting wire obtained by consolidation is also shown.

From FIG. 2, it has been found that the Bi-based oxide superconducting wire produced by the method of the present invention exhibits a smaller rate of decrease in critical current density in a high magnetic field than the superconducting wire of the comparative example. In addition, the Bi-based superconducting wire of the comparative example decreases to about 1/10 in a 0.1 T magnetic field, and decreases to 1/100 or less in a 1 T magnetic field, but the superconducting wire of the present invention example At 0.1T it becomes 1/3, and at 1T it becomes 1/3.
We were able to suppress the decrease to about 10%. When the obtained superconducting wire was observed using a scanning electron microscope (SME), the Bi-based superconductor portion inside the superconducting wire of the comparative example was as follows.
It was shaped like a stack of large flake-like crystals,
The one of the present invention had a shape in which smaller flake-like crystals were more densely stacked.

(Example 2) Bi2O3, SrCO3 and C
aCO3, CuO, and PbO powders in Bi2Bi1.9
A mixed raw material was obtained by mixing to have a composition of Ca2.2Cu4Pb0.5Ox, which was calcined at 780° C. for 10 hours and pulverized. The crushed material is pressed into a diameter of approximately 3m using a rubber press.
Consolidate into a cylindrical shape of m and heat at 840-870℃ for 10-100℃.
Heat treated in air for hours. The compacted body was partially melted by applying a CO2 laser beam to the solidified body, and a directional solidified body was created while moving the laser beam. The obtained Bi-based superconductor exhibited a critical temperature of 84K and a critical current density of 5000A/cm2 (77K, 0T).

[0021] Thereafter, this superconductor was pulverized using a ball mill or mortar, and a green compact having a diameter of 3 mm was obtained using a rubber press. Next, this compact was inserted into a silver pipe with an outer diameter of 8 mm and an inner diameter of 4 mm, and was repeatedly subjected to swaging, wire drawing, rolling, and pressing, and was appropriately subjected to intermediate heat treatment (810°C, 5 hours). Finished, thickness 0.15mm
A silver tape wire with a width of 4 mm was obtained. Thereafter, this tape wire was heated to 820 to 840°C for 10 to 10 minutes in the atmosphere.
A Bi-based tape-shaped superconducting wire with a silver sheath was obtained by heat treatment of heating for 0 hours. The critical temperature of this superconducting wire is 8
3.5K, critical current density is 7500A/cm2 (77K
, magnetic field 0T). Also, the 0.5T (
The critical current density at 77K) was 500A/cm2, an improvement of 1.5 times.

(Example 3) After calcining the powder mixture raw material blended for the Bi-based 2212 phase and pulverizing it into a powder of about 1 μm, silver powder with a particle size of about 1 to 2 μm was added in a weight ratio of 5 to 2 μm. 10
% mixed. This mixed powder was repeatedly press-molded, pulverized, and heat treated (840-860°C, 1-100 hours) to obtain a rod-shaped sample with a diameter of about 5 mm. This rod-shaped sample is partially melted by the zone melting method, and while the melted zone is moved, the diameter of approximately 3
A solidified rod of mm was obtained. The critical temperature of the solidified rod after heat treatment is 90K, and the critical current density is 3500A/cm2 (
77K, 0T).

[0023] After finely pulverizing this solidified rod and compacting it into a bar shape, it is inserted into a silver pipe with an outer diameter of 10 mm and an inner diameter of 5 mm, and is subjected to swaging, wire drawing, rolling, and pressing to form the final product. A silver tape wire with a thickness of 0.2 mm and a width of 5 mm was obtained. This wire was heated to 820 to 840℃ for 50
When heat treated for a period of time, a Bi-based superconducting wire with improved critical temperature of 90 K and critical current density of 5600 A/cm2 was obtained.

[Effects of the Invention] As explained above, according to the present invention, a directional solidified body using a seed material or a band melted body partially melted by band melting is used, and a crystal body whose crystal orientation is uniform to some extent is used. Therefore, the pulverized product of this crystal remains a pulverized product while maintaining the flaky crystal shape characteristic of Bi-based superconductors. Therefore, if this pulverized material is filled into a metal sheath, compacted, and heat treated, the flaky crystals will be easily oriented in the longitudinal direction of the wire even after the compaction heat treatment. Therefore, if this wire is heat-treated, an oxide superconducting wire with less unreacted portions, less impurities, and good crystal orientation can be obtained. In addition, since the crystals of the Bi-based flake-like superconductor are oriented, the grain boundaries of the oxide superconductor crystals are considered to serve as pinning centers for magnetic flux, contributing to the improvement of the magnetic field characteristics of the critical current density. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an oxide superconducting wire according to an embodiment of the present invention.

FIG. 2 is a graph showing the results of measuring the relationship between the magnetic field and critical current density of the oxide superconducting wire obtained in the example.

FIG. 3 is an explanatory diagram showing a state in which mixed powder is calcined in a conventional method.

FIG. 4 is an explanatory diagram showing a state in which a metal pipe is filled with calcined powder in a conventional method.

FIG. 5 is an explanatory diagram showing a state in which wire is drawn in a conventional method.

FIG. 6 is an explanatory diagram showing a state of rolling with rolls in a conventional method.

FIG. 7 is an explanatory diagram showing a final heat treatment state in a conventional method.

FIG. 8 is a graph showing measurement results of critical current density for each distance of a conventional oxide superconducting wire.

[Explanation of symbols]

10...Superconducting wire, 11...Sheath material, 12...
・Superconducting part

Claims (2)

[Claims] Claim 1: Forming a Bi-based oxide superconductor by subjecting a mixed raw material containing elements constituting the Bi-based oxide superconductor to consolidation treatment and heat treatment, and melting the oxide superconductor; After bringing the seed material into contact with this molten material, a pulling process is performed to form a directional molten solidified material that adheres to the seed material, and then this directional molten solidified material is crushed and filled into the inside of a metal sheath, after which it is processed. A method for manufacturing a Bi-based oxide superconducting wire, which comprises compacting and then heat-treating to produce a Bi-based oxide superconductor inside a metal sheath. 2. Forming a Bi-based oxide superconductor by subjecting a raw material mixture containing elements constituting the Bi-based oxide superconductor to consolidation treatment and heat treatment, and partially melting the oxide superconductor. , move this partially melted band body to melt the entire oxide superconductor one or more times to form a band melted material, which is then crushed, filled inside a metal sheath, and then consolidated by processing, B, characterized in that a Bi-based oxide superconductor is generated inside the metal sheath by subsequent heat treatment.
A method for producing an i-based oxide superconducting wire.