JP4569053B2 - Superconducting wire manufacturing method and superconducting wire - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a superconducting wire, and to a superconducting wire, in particular, a method of manufacturing a MgB ₂ superconducting wire having a high critical current density characteristic relates MgB ₂ superconducting wire obtained from this.
[0002]
[Prior art]
MgB ₂ is attracting attention as a superconductor having a high critical temperature and capable of being processed into a wire. As a standard manufacturing method for obtaining a wire using MgB ₂ as a superconducting component, a metal pipe filled with a superconducting powder composed of reacted MgB ₂ is drawn into a hexagonal cross section, Further, a plurality of these are incorporated into a metal pipe to form a multi-core structure, followed by wire drawing to a predetermined size, and finally heat treatment at about 600 to 800 ° C. to fix the MgB ₂ powders together. A method of bonding by a phase reaction is common.
[0003]
As another standard manufacturing method, Mg and B (boron) powder, which is a raw material for MgB ₂ , is filled in a metal pipe and drawn into a hexagonal cross section. A method of forming MgB ₂ by performing a drawing process to a predetermined size after being assembled to form a multi-core structure, and performing a heat treatment at the above temperature is considered.
[0004]
[Problems to be solved by the invention]
However, according to the manufacturing method described above, in the case of the former method, if an oxide film is present on the surface of the MgB ₂ powder, a different phase precipitates at the boundary of the powder particles during the final heat treatment. Even if superconductivity is shown, the current flow is hindered at the boundary between the particles, and the improvement of the overall critical current density characteristic cannot be obtained.
[0005]
For this reason, although there are many reports on bulk bodies of MgB ₂ superconductors, the critical current density characteristics comparable to the Nb-Ti superconducting wires or Nb3Sn superconducting wires that have already been put into practical use are available for the superconductors with wire configuration. The facts that are shown have not yet been reported.
[0006]
On the other hand, in the case of the latter method, the Mg powder has the property of easily generating an oxide film on the surface, and thus has the same problem as the former. The production of Mg powder as a raw material is difficult because the particle size is on the order of μm, and there is a high risk of causing a dust explosion in the Mg powder, which is not a preferable method from the viewpoint of safety.
[0007]
Accordingly, an object of the present invention, with a high critical current density characteristics can be obtained to provide a method of manufacturing a MgB ₂ superconducting wire which does not require powder of Mg, a MgB ₂ superconducting wire obtained from this is there.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for producing a superconducting wire having MgB ₂ as a constituent member exhibiting superconductivity.
Composing a composite sheet material combining a Mg sheet and a powdery B layer,
Forming a composite bar by winding the composite sheet material on a metal core,
An object of the present invention is to provide a method for producing a superconducting wire, characterized in that MgB ₂ is produced by subjecting a linear body obtained by subjecting the composite rod-like body to a predetermined processing such as wire drawing, as a heat treatment.
[0009]
In order to achieve the above object, the present invention provides a superconducting wire having MgB ₂ as a constituent member exhibiting superconductivity.
By subjecting a composite rod-shaped body obtained by combining a composite sheet material combining a Mg sheet and a powdered B layer on a metal core to a predetermined shape such as wire drawing to heat treatment to a linear body The present invention provides a superconducting wire characterized by being produced MgB ₂ .
[0010]
In many cases, the above-mentioned striate body is configured on the basis of an assembly of the above-described composite rod-shaped bodies. Specifically, after extruding a composite rod-like body and gathering together a plurality of processed bodies processed by surface-reducing means such as swaging and wire drawing, a surface of a predetermined size is obtained by subjecting it to surface-reducing processing. Copper pipes are used for the assembly of the surface-reduced body of the composite rod-shaped body, and extrusion is performed with a plurality of surface-reduced bodies inserted in this. After that, by performing a surface-reducing process, a filament having a predetermined size is obtained.
[0011]
As the composite sheet material of Mg sheet and powdery B layer in the above production method, for example, a layer of B formed on Mg sheet by coating or spreading, or both sides of B layer are Mg There are conceivable forms sandwiched between sheets, among which the latter form prevents the detachment of B powder during processing and produces an effect of stably holding the B layer. I can say that.
[0012]
The ratio of Mg and B is preferably such that the latter is 2 ± 0.2 mol with respect to the former 1. From the stoichiometric ratio of MgB ₂ , the molar ratio of both should be Mg: B = 1: 2, but the melting point of Mg is as low as 650 ° C. It is as high as 2300 ° C. Therefore, at the final heat treatment temperature of 600 to 800 ° C., B component that does not react with Mg may remain in the wire, so this is prevented and the space factor of MgB ₂ is increased. In order to increase the ratio, a ratio of B by a maximum of 0.2 mol is recommended as a preferable form.
[0013]
On the other hand, the setting of the molar ratio in which B is 0.2 mol opposite to this is larger in the surface area of the powdery B than the sheet-like Mg, and accordingly, when the thickness of the composite sheet material of Mg and B is large, Alternatively, if the thickness of the Mg layer and B layer when processed into the final wire before heat treatment is on the order of several tens of μm, there is a possibility that unreacted Mg may remain. The ratio is set to a maximum of 0.2 mol.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a superconducting wire manufacturing method according to the present invention and a superconducting wire obtained therefrom will be described.
FIG. 1 shows a production procedure. First, in the step (1) of (a), a powdery B having an average particle diameter of 0.9 μm and a purity of 99.9% is prepared. Slurry 1 is prepared by mixing with glycerin as a binder.
[0015]
Next, the slurry 1 was applied by screen printing on the 0.2 mm thick Mg sheet 2a as shown in (2) and then dried in an Ar gas atmosphere at 200 ° C., as shown in (3). The glycerin is evaporated to form a powdery B layer 3.
[0016]
Next, after confirming that the molar ratio of Mg and B in the obtained composite is Mg: B = 1: 1.1, in the step (b), the same Mg sheet 2b as the sheet 2a is formed. The composite sheet material 4 having a predetermined structure in a sandwich shape with a molar ratio of Mg: B = 1: 2.2 is manufactured by laminating on the layer 3.
[0017]
(C) shows a step of manufacturing a composite rod-like body by winding the composite sheet material 4 on an Nb core material 5 having a diameter of 8 mm so as to form 10 layers, and (d) shows a single billet performed thereafter. The assembly processing process is shown.
[0018]
In the step (d), first, the composite rod-like body 6 obtained in the step (c) is inserted into a copper pipe 7 having an inner diameter of 25 mm × an outer diameter of 27 mm, and this is inserted into an inner diameter of 27.1 mm × an outer diameter of 29 mm. A single billet is constructed by inserting a copper plug and an iron plug into the front and rear ends of the pipe 8.
[0019]
(E) shows the extrusion process by a hydrostatic extruder, and extrudes the single billet obtained in the process (d) so that the outer diameter becomes 12 mm. Next, the extruded billet is drawn into a hexagonal wire 9 having a hexagonal cross section with an opposite side dimension of 1.4 mm in the step (f), and these are assembled into a multi billet in the step (g).
[0020]
In the multi billet formation, the hexagonal wire 9 is cut into a length of 150 mm, and 349 pieces of the hexagonal wire 9 are in close contact with each other in a copper pipe 10 having an inner diameter of 29 mm × an outer diameter of 32 mm × a length of 150 mm. Insertion is performed by attaching a copper plug and an iron plug to the front end and the rear end of the pipe 10, respectively.
[0021]
Next, the multi billet 11 is extruded to a predetermined diameter by a hydrostatic extruder in the step (h), and then subjected to wire drawing until it becomes a linear body having an outer diameter of 0.8 mm in the step (i). After that, in step (j), heat treatment is performed in an Ar atmosphere at 700 ° C. × 5 hours, whereby MgB ₂ is generated.
[0022]
FIG. 2 shows the correlation between the magnetic field and critical current density of the MgB ₂ -based superconducting wire obtained as described above. According to the figure, the MgB ₂ -based superconducting wire manufactured according to the present embodiment can obtain a critical current density characteristic similar to Nb—Ti at a temperature of 10K, and it is 7 to 7 by a 10K class conduction cooling method. This shows that it is possible to produce a magnet that generates a magnetic field of 8T.
[0023]
In order to reduce the load on the refrigerator based on the inherently high critical temperature of the MgB ₂ -based superconductor and to provide a superconducting magnet without quenching based on an ultrafine multi-core configuration, the superconductivity obtained from the embodiment of FIG. It can be said that the usefulness of the wire is great.
[0024]
【The invention's effect】
As described above, according to the method of manufacturing a superconducting wire according to the present invention, a composite sheet material in which an Mg sheet and a powdered B are combined is formed by applying powdered B on the Mg sheet. In addition, the composite rod-shaped body wound on a metal core is subjected to predetermined processing such as wire drawing, and heat treatment is performed on the obtained striated body to produce MgB ₂ , which requires Mg powdering. A practical manufacturing method can be provided. And, thereby resulting MgB ₂ superconducting wire has a high critical current density characteristic, it is possible to constitute a superconducting magnet or the like rich in practicability.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of a method of manufacturing a superconducting wire according to the present invention, and (a) to (j) show the procedure.
FIG. 2 is an explanatory diagram showing the correlation between the magnetic field and critical current density of the MgB ₂ -based superconducting wire obtained from the embodiment of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Slurry 2a, 2b Mg sheet 3 Powdery B layer 4 Composite sheet material 5 Nb core material 6 Composite rod-like body 7, 8, 10 Copper pipe 9 Hexagonal wire 11 Multi billet

Claims (5)

In the method of manufacturing a superconducting wire having MgB ₂ as a constituent member exhibiting superconductivity,
Composing a composite sheet material that combines the layer of Mg and powder B formed in a sheet,
Forming a composite bar by winding the composite sheet material on a metal core,
Wherein the composite rod-like body inserted into the pipe made of copper, and further, superconducting wire, characterized in that to produce the MgB ₂ by heat treatment in the striatum obtained by performing a predetermined reduction process of wire drawing Manufacturing method.   2. The method of manufacturing a superconducting wire according to claim 1, wherein the heat treatment step is performed on an object obtained by gathering a plurality of surface-reduced bodies of the composite rod-shaped body and processing the same into the linear body. .   2. The step of configuring the composite sheet material is performed such that the composite sheet material has a configuration in which the powdery B layer is sandwiched from both sides by the Mg sheet. Manufacturing method of superconducting wire.   2. The superconducting wire according to claim 1, wherein the step of forming the composite rod-shaped body is performed such that a molar ratio of Mg to B is Mg: B = 1: 2 ± 0.2. Production method. In a superconducting wire having MgB ₂ as a constituent member showing superconductivity,
The MgB ₂ is a composite rod-like body in which a composite sheet material obtained by combining the Mg sheet and the powdery B layer is wound around a metal core by applying powdered B on an Mg sheet. was inserted into the pipe made of copper, the superconducting wire, characterized by performing predetermined processing of the wire drawing is a MgB _2, which is to produce by applying a heat treatment to those with striatum.

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