JP2004335116A - Process for manufacturing bismuth 2212 superconductive compound multicore wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a bismuth 2212 superconductive compound multi-core wire in which supercurrent stably flows and is improved in critical current density characteristic. <P>SOLUTION: When the bismuth 2212 oxide is annealed after partial melting to be made a superconductor, highest attained temperature in partial melting is made to a temperature of ≥0.6°C and ≤2°C with respect to the melting point of the bismuth 2212 oxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The invention of this application relates to a method for producing a bismuth 2212 superconducting composite multifilamentary wire. More specifically, the invention of this application relates to a bismuth 2212 superconducting composite multifilamentary wire capable of producing a bismuth 2212 superconducting composite multifilamentary wire having a stable supercurrent flow and an improved critical current density characteristic. It relates to a manufacturing method.
[0002]
[Prior art and its problems]
An oxide superconducting composite multifilamentary wire in which a number of oxide superconductors are embedded in a silver or silver alloy sheath can achieve relatively high critical current density characteristics (for example, Patent Document 1). reference).
[0003]
However, its critical current density characteristics are not high enough to be practical. This is because the oxide superconductors are bonded together in the silver or silver alloy sheath and the crystal becomes coarse. As described above, for the oxide superconducting composite multifilamentary wire, although the multifilamentary structure that is effective for stably flowing the superconducting current is possible, the effect brought by the multifilamentation is sufficiently obtained. The fact is that it has not been done.
[0004]
The invention of this application has been made in view of such circumstances, and it is possible to manufacture a bismuth 2212 superconducting composite multifilamentary wire in which a superconducting current flows stably and the critical current density characteristics are improved. An object of the present invention is to provide a method for manufacturing a bismuth 2212 superconducting composite multifilamentary wire.
[0005]
[Patent Document 1]
JP-A-11-329112
[Means for Solving the Problems]
The invention of this application solves the above problem by embedding a plurality of bismuth 2212 oxide single-core wires coated with silver or a silver alloy in a silver or silver alloy sheath, and then applying the bismuth 2212 oxide. Is a method for producing a bismuth 2212 superconducting composite multifilamentary wire using a superconductor as a superconductor. A method for producing a bismuth 2212 superconducting composite multifilamentary wire, wherein the melting point of the bismuth 2212 oxide is 0.6 ° C. or more and 2 ° C. or less, is provided.
[0007]
Hereinafter, examples will be shown, and the method for producing the bismuth 2212 superconducting composite multifilamentary wire of the present invention will be described in more detail.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, the bismuth 2212 superconducting composite multifilamentary wire manufacturing method of the invention of this application embeds a plurality of bismuth 2212 oxide single core wires coated with silver or a silver alloy in a silver or silver alloy sheath. After that, the manufacturing method uses bismuth 2212 oxide as a superconductor. Here, the bismuth 2212 oxide is, as generally known, a compound oxide represented by a composition formula Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x which becomes a superconductor having a critical temperature of about 90 K by appropriate heat treatment. Things.
[0009]
In the method for producing a bismuth 2212 superconducting composite multifilamentary wire according to the invention of the present application, when the bismuth 2212 oxide is partially melted and then gradually cooled to obtain a superconductor, the highest ultimate temperature at the time of partial melting is reduced. The melting point of bismuth 2212 oxide is set to 0.6 ° C. or more and 2 ° C. or less. As described above, by performing a precise heat treatment to set the maximum temperature at which the bismuth 2212 oxide is partially melted to a temperature of 0.6 ° C. or more and 2 ° C. or less from the melting point of the bismuth 2212 oxide, the bismuth 2212 superconductor is obtained. Is suppressed, and the bonding of the multi-core bismuth 2212 superconductors to each other is suppressed. The manufactured bismuth 2212 superconducting composite multifilamentary wire can stably flow a supercurrent, and has sufficiently high critical current density characteristics, which is preferable for practical use.
[0010]
Note that the melting point of the bismuth 2212 oxide can be measured using a differential thermal analyzer. When the bismuth 2212 oxide moves from the solid phase to the liquid phase, an endothermic peak is observed in the differential thermal analyzer, and the starting position of the endothermic peak can be used as the melting point. The melting point of bismuth 2212 oxide tends to depend on the oxygen partial pressure. When the oxygen partial pressure is 1 atm, 0.2 atm, and 0.05 atm, the melting points are 881 ° C, 871 ° C, and 861 ° C, respectively. Measured.
[0011]
In the method of manufacturing the bismuth 2212 superconducting composite multifilamentary wire of the invention of the present application, the type of silver alloy is not particularly limited, and examples thereof include an Ag-Mg alloy. The ratio of Mg in the Ag-Mg alloy is, for example, 0.02 to 0.5 wt%.
[0012]
【Example】
Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO powders are blended so that Bi: Sr: Ca: Cu = 2: 2: 1: 2, and this powder is subjected to a heat treatment at 850 ° C. for 12 hours. went. The bismuth 2212 powder calcined in this manner was packed in a silver or silver alloy sheath and rolled to produce a single core wire. A large number of the single-core wires were bundled, packed in a silver alloy sheath, and then rolled. The above steps were repeated to prepare a multifilamentary wire having a wire diameter of 1.0 mmφ and a multifilamentary number of 127 × 7. The produced multifilamentary wire was cut into about 3 to 4 cm, and placed in a tubular electric furnace in which oxygen at 1 atm was constantly flowing. This tubular electric furnace enables temperature control of ± 1 ° C. Partial melting-annealing heat treatment was performed in such a tubular electric furnace. The temperature pattern of the partial melting-annealing heat treatment is as follows: after leaving at 600 ° C. for 5 hours, the temperature is raised to the maximum attained temperature (T _max ) in 2 hours, and then T _max −60 at a cooling temperature of 2 ° C./hour. After gradually cooling to a temperature and then decreasing the temperature to about 200 ° C. at 50 ° C./hour, the furnace was cooled. And _Tmax was changed by about 1 degreeC from 880.5 degreeC to 886.4 degreeC by 1 degree, and the wire was produced. A current was passed through each of the produced wires in a magnetic field of 4.2 K and 10 T, and the critical current density was measured. The critical current was determined as a voltage of 1 μV / cm as a criterion.
[0013]
FIG. 1 is a diagram showing the heat treatment temperature dependence of the critical current value of each multifilamentary wire.
[0014]
No current flows at all up to 881 ° C., but it was confirmed that the _maximum current of 425 A suddenly flowed at 882.5 ° C., and when T _max exceeded 882.5 ° C., the critical current value was reduced to about half. .
[0015]
In order to investigate the cause, cross sections in the longitudinal direction of the multifilamentary wire manufactured at each temperature were observed. The result is the photograph of FIG. The dark area in the photograph is the bismuth 2212 oxide superconductor, and the bright area is the silver or silver alloy sheath. The bismuth 2212 superconductor was not melted by the heat treatment at 881.5 ° C. Therefore, it is considered that the coupling between the crystal grains necessary for the current to flow is insufficient, and the current did not flow. It is understood that the heat treatment at 882.3 ° C. has little coupling between adjacent bismuth 2212 superconductors, and a critical current can be stably passed. In the heat treatment at 886.4 ° C., it is confirmed that the adjacent bismuth 2212 superconductors are bonded and the crystal grains are coarsened. When the crystal grains are coarsened in this way, the flow of the superconducting current becomes non-uniform, a stable current cannot be passed, and impurities and the like are generated, which causes a decrease in the critical current density.
[0016]
From the above, in the partial melting and slow cooling treatment when bismuth 2212 oxide is used as a superconductor, the highest temperature at the time of partial melting is set to be 0.6 ° C. or more and 2 ° C. or less from the melting point of bismuth 2212 oxide. It has been proved that the critical current flows stably and is effective for improving the critical current density characteristics.
[0017]
Of course, the invention of this application is not limited by the above embodiments and examples. It goes without saying that various aspects are possible for details such as the structure of the multifilamentary wire and the type of silver alloy for the sheath.
[0018]
【The invention's effect】
As described in detail above, the invention of this application provides a bismuth 2212 superconducting composite multifilamentary wire in which the superconducting current flows stably and the critical current density characteristics are improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a maximum temperature reached during partial melting and a critical current.
FIG. 2 is a photograph showing a cross-sectional structure in the longitudinal direction of a multifilamentary wire obtained at a maximum ultimate temperature of 881.5 ° C., 882.3 ° C., and 886.4 ° C. upon partial melting.

Claims (1)

After a plurality of single-core wires of bismuth 2212 oxide coated with silver or a silver alloy are embedded in a sheath of silver or silver alloy, a bismuth 2212 superconducting composite multi-core wire having bismuth 2212 oxide as a superconductor is used. When the bismuth 2212 oxide is partially melted and then gradually cooled to obtain a superconductor, the highest temperature at the time of partial melting is 0.6 ° C. or more and 2 ° C. or less from the melting point of bismuth 2212 oxide. A method for producing a bismuth 2212 superconducting composite multifilamentary wire, characterized in that:

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