JP2606393B2 - How to connect compound superconducting wires - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention can establish a stable superconducting connection in a compound-based superconducting wire, particularly an Nb ₃ Sn-based compound superconducting wire manufactured by a bronze method, and can mechanically connect the connecting portion. The present invention relates to an improved connection method capable of securing strength.

[Prior art] Various types of compound superconducting wires have been announced, but those that have been practically used are doped with Nb ₃ Sn or Ti to improve high magnetic field performance. Most of what we have planned is dominant.

If such a superconducting wire is based on an alloy, the exposed end of the superconducting wire need only be simply welded, and the connection is very easy.

However, when the connection target is a compound system, it is extremely troublesome. In other words, the superconducting portion of the compound-based superconducting wire is one in which a desired intermetallic compound is generated in the diffusion layer by contacting a metal element that generates the compound and performing diffusion heating, and the compound is also superconductive in the contact portion. Must be continuous with the line side. If the continuation is interrupted, the interrupted portion will no longer be a superconductor and will not be used as a superconducting wire.

There are various proposals for a method of manufacturing an Nb ₃ Sn-based superconducting wire, such as a surface diffusion method, a bronze method, an in-situ method, and a powder method.

However, it is currently the bronze method that has been applied to mass production on an industrial scale.

In this bronze method, as shown in FIG. 4, a large number of ultrafine Nb filaments 1 and 1 are embedded in a matrix of Cu-Sn bronze 2 and an Nb barrier 3 is provided on the outer periphery thereof. A plurality of sub-multi wires 4, 4 are embedded in a Cu stabilizing material 5 to obtain an Nb ₃ Sn-based superconducting wire 6.

Here, the Cu stabilizing material 5 serves as a stabilizing material as the character indicates, and the Nb barrier 3 is provided by an element diffused from the Cu-Sn bronze side. This is to prevent the diffusion to the stabilized Cu side by the Nb barrier 3 so that the conductivity does not decrease and the role as the stabilizing material does not become insufficient.

When this is heated to a temperature at which a predetermined Nb ₃ Sn compound is formed, the Nb filament 1 is formed as shown in FIG.
Diffusion occurs between Cu and Cu-Sn bronze to form an Nb ₃ Sn compound layer at the interface of the Nb filament, and this layer exhibits superconducting properties. The use of Cu-Sn bronze here is
It is also worth considering that Cu has the effect of promoting the reaction between Nb and Sn.

As a conventional example of such an Nb ₃ Sn superconducting wire connection method, there is a proposal as shown in FIG. In other words, the superconducting wires 6 and 6 'to be connected (although at this stage diffusion heating has not yet been performed and it is an intermediate product before the generation of the Nb ₃ Sn compound, The Cu-Sn stabilizing Cu5,5 'and Nb barriers 3,3' and the sub-multi wire Cu-Sn bronze matrix are dissolved with nitric acid etc.
Expose 1 and 1 ', 1'. The exposed Nb filaments 1, 1 and 1 ', 1' are joined in a twisted state as shown in the figure, and a bronze pipe 10 is further stuck from the tip of stabilized Cu5, 5 'to the twisted joint. After coating, the bronze pipe 10 and the twisted joint of the Nb filament were compressed together, and then the above-mentioned diffusion heating for producing Nb ₃ Sn was performed, and Nb was placed between the bronze pipe and the Nb filament.
_{3 This} is to generate a superconducting compound of the Sn layer.

Further, as another proposal example, after exposing Nb filaments in the same manner as described above, they are joined together,
b, After inserting into a Nb sleeve containing a mixture of Sn powder, compressively deforming and integrating, the joint is heated from the outside and heat treated, and Nb filament and Nb sleeve inside, Nb ₃ A method of forming a superconducting intermetallic compound of the Sn layer and connecting them has also been proposed.

[Problem to be Solved by the Invention] Of the two proposed examples described above, the outer case of the twisted Nb filaments 1 and 1 'and the bronze are obtained only by coating and compressing the bronze pipe 10 shown in FIG. Only the superconducting connection by the formation of Nb ₃ Sn is realized only at the contact portion of the pipe 10, and only an insufficient connection is obtained in terms of characteristics.

On the other hand, the latter, that is, the method of contacting Nb filaments in an Nb sleeve containing a mixture of Nb and Sn powder, compressing and deforming, and heating is performed by Nb filaments, Nb filament and the inside of the Nb sleeve, Nb ₃ in Nb powders. Although superconducting connection by Sn formation becomes possible, in actuality, when heating by heat treatment for Nb ₃ Sn generation, melting of Sn powder with a low melting point occurs first, and the gap for that in the Nb sleeve Can be. For this reason, the adhesion of Nb powder is reduced and Nb ₃ Sn
Are not formed, and a satisfactory superconducting connection is not always achieved. Moreover, depending on the method, it is not possible to employ 37 wt% Sn, which is the ratio of the stoichiometric values of Nb and Sn.

An object of the present invention is to solve the problems of the prior art as described above, on which can establish a stable superconducting connection in Nb ₃ Sn compound superconducting wire prepared by a compound superconducting wire in particular bronze process, the connection of the machine It is an object of the present invention to provide a novel method for connecting a compound superconducting wire which can secure a sufficient strength.

[Means for Solving the Problems] In the present invention, when connecting Nb ₃ Sn-based multifilament type superconducting wires to each other, first, the stabilized Cu, Nb barrier and Cu at the corresponding end of the superconducting wire to be connected are connected. -Sn bronze is dissolved and removed with an acid or the like to expose the Nb filaments for a predetermined length, then the exposed Nb filaments are twisted and joined to each other, and the twisted Nb filament is a mixture of powders of Nb, Sn, and Cu. And Nb around it
The sleeve is fitted and the connection thus formed is
Sn powder integrated compression from outside the connection portion in a state melted by heating to a temperature higher than the melting temperature of the Sn powder, the whole then connecting portion and the superconducting wire was heated at generation temperature of the Nb ₃ Sn, superconducting wire To generate a continuous compound of Nb ₃ Sn at the interface and connection of the Nb filament in the
Further, in the case of the above connection, the corresponding end of the superconducting wire to be connected is cut into an inclined surface so as to be slightly parallel,
The stabilized Cu, Nb barrier and Cu-Sn bronze are dissolved and removed with an acid or the like to expose and protrude the Nb filament to a length that does not protrude much more than the respective inclined surfaces,
A mixture of powders of Nb, Sn, and Cu is filled between the inclined surfaces from which the filaments protrude, and an Nb sleeve is attached to the outer periphery of the mixture, and the connection portion formed in this manner is lower than the melting temperature of the Sn powder. Heating to a high temperature, the connection portion is compression-integrated from the outside while the Sn powder is molten, and then the connection portion and the entire superconducting wire are heated at the Nb ₃ Sn generation temperature, and the interface of the Nb filament in the superconducting wire and At the connection
It produces a continuous compound of Nb ₃ Sn.

[Action] When exposing the Nb filament and compressing and integrating it with the mixed powder of Nb, Sn, and Cu, when the Sn that is in a molten state at a low temperature is heated to a state where it is first melted, and then compressed and integrated. In this case, if the Sn is in a molten state and the particles are compression-integrated, the molten Sn enters the gaps of the powders in the other fixed states uniformly, and there is no longer any gap after the compression and integration.
If ask performed diffusion generation of Nb ₃ Sn in this state, the entire connection unit Nb ₃ Sn is generated by the solid state, shrinkage i.e. voids caused by the melting of Sn as in the prior example do not occur, very stable Therefore, Nb ₃ Sn in a continuous state can be generated at the connection portion, and the characteristics as a superconducting connection can be remarkably improved.

[Example] Hereinafter, the present invention will be described with reference to examples.

FIG. 1 is an explanatory view showing a first embodiment according to the present invention, wherein the same reference numerals as those already described indicate substantially the same configuration.

The stabilized Cu5,5 'of the superconducting wires 6,6' to be connected is dissolved and removed by nitric acid. After that, the Nb barriers 3, 3 'appear, but they do not dissolve by nitric acid. Therefore, the Nb barriers 3, 3' are removed by performing transient dissolution with hydrofluoric acid mixed with an appropriate amount of hydrofluoric acid and nitric acid, When the Cu-Sn bronze matrix that appears thereafter is dissolved and removed again with nitric acid, only the Nb filaments 1,1 and 1 ', 1' remain thereafter.

The remaining Nb filaments 1, 1 and 1 ', 1' are appropriately twisted and joined, the outer periphery thereof is covered with an Nb sleeve, and the inside is filled with a mixed powder of Nb powder 7, Sn powder 8, and Cu powder 9. . The mixing ratio is Nb: Sn: Cu = 60: 37: 3 by weight, and the mixing ratio of Nb and Sn is the stoichiometric value of Nb ₃ Sn. 3 wt% of Cu is for promoting the reaction at the time of heat treatment for forming Nb ₃ Sn as described above.

In this state, it is heated above the melting temperature of Sn (232 ° C),
Nb sleeve with only the molten state and the others in the solid state
11 is compressed from the outside, and the whole connection is integrated.

In this way, the Sn that melts at a low temperature uniformly enters between other powders or Nb filaments or Nb sleeves, and voids are completely eliminated.

In this way, if it is compressed and integrated, then it is heated to the temperature at which Nb ₃ Sn is formed and maintained at that temperature for a required time,
A layer of Nb ₃ Sn is generated by diffusion near the interface between the Nb filaments of the superconducting wires 6, 6 ′ and near the interface where Nb and Sn are in contact with each other at the connection part. This Nb ₃ Sn layer is a superconducting wire 6,
A continuous layer is formed between 6 'and the connection, and the superconducting wires 6, 6' are superconductingly connected. In addition, no void is formed in the connecting portion as in the prior art, and an extremely stable superconducting connecting portion can be formed between the connected superconducting wires 6, 6 '.

FIG. 2 shows a second embodiment according to the present invention and is an explanatory view showing another connection method for connecting the superconducting wires 6, 6 'so that the connection strength can be sufficiently secured.

The present embodiment is characterized in that the ends of the superconducting wires 6, 6 'to be connected are formed on correspondingly parallel inclined surfaces as shown in the figure.

The step of exposing the Nb filament 1 (1 'is not shown in the figure) by etching the sub-multi line 4 (4' is not shown in the figure) is the same as the step described in FIG.

The difference in this embodiment is that the Nb filament
The protrusion length of the superconducting wires 1,1 is not made too large, and therefore, the interval between the inclined superconducting wires 6,6 'that are obliquely cut is not too large, and the Nb powder 7, Sn powder 8, Cu powder 9 The point is that the Nb sleeve 11 is bonded by filling the mixed powder of the above.

Below is the compression under heating above the melting point of Sn, and Nb ₃ S
In any case, such as the diffusion heat treatment for producing n, there is no difference from the case of FIG.

However, in the present embodiment, since the superconducting wires 6, 6 'are sufficiently close to each other and connected to the connecting portion via the inclined surface, the fusion of the mixed powder having weak mechanical properties in the longitudinal cross section is performed. The connection portion can be minimized, so-called a diffusion pressure contact state can be obtained, and the mechanical strength of the connection portion can be significantly improved. Moreover, there is no difference from the case of FIG. 1 in that the superconducting connection is achieved by the Nb ₃ Sn layer continuously produced by the mixed powder.

The specific numerical values in carrying out the present invention are as follows, and it was confirmed that the intended purpose of the present invention can be sufficiently exhibited.

The actual work in the molten state of Sn in FIG.
For 30 minutes, and the compression load was 45 kg / mm ² . Appropriate heating temperature is about 300 ℃ ~ 500 ℃.
If the temperature exceeds ℃, the superconducting properties deteriorate. The compression load is
Although no change in characteristics in 30~60kg / mm ² in the range of about, compressive load undesirably occur deformation exceeds 120 kg / mm ² wires.

After that, the whole connected superconducting wire was
Heated at a temperature of ℃ ~ 700 ℃ for about 100-200 hours, heat-treated, twisted Nb filament 1,1 ', Nb sleeve 11
It was also confirmed that an Nb ₃ Sn layer could be continuously formed inside and between the Nb _{7 and} Sn 8 powders, and that these and the Nb ₃ Sn of the superconducting wires 6, 6 ′ were in a continuous state.

In the example of FIG. 2 in which the end face to be connected is cut obliquely, it is appropriate to expose the Nb filament to a length of 2 to 10 mm. Thereafter, the heating temperature shown in the embodiment of FIG.
450 ° C. 30 minutes, by compression under conditions of compressive load 45kg / mm ^2, Cu-Sn bronze and Cu stabilizer is exposed to the slopes is in a connected state due to the diffusion pressure respectively, the mechanical strength is further improved .

Note that the use of the Nb sleeve for the connection portion causes the Cu stabilizing material at that portion to be missing, but this can be compensated for by further coating the Cu. Also, Nb
Nb, Sn, Cu powder put in the sleeve can be connected in a more uniform mixed state by using a so-called composite powder that coats copper around the Nb powder and further coats Sn around the Nb powder Becomes

[Effects of the Invention] As described above, according to the connection method according to the present invention, a stable superconducting connection can be established in the Nb ₃ Sn-based compound superconducting wire manufactured by the bronze method, and the mechanical strength of the connecting portion is also ensured. This is possible, and the industrial value of the present invention in the industry is extremely large.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state of implementing a method according to the present invention, FIG. 2 is an explanatory view showing another embodiment of the present invention,
FIG. 3 is an explanatory view of a conventional example, and FIG. 4 is an explanatory view showing a specific configuration of a superconducting wire by a bronze method. 1,1 ': Nb filament, 2,2': bronze, 3,3 ': Nb barrier, 4,4': submulti wire, 5,5 ': Cu stabilizer, 6,
6 ': superconducting wire, 7: Nb powder, 8: Sn powder, 9: Cu powder, 11: Nb
sleeve.

Claims (2)

(57) [Claims] 1. A method for connecting Nb ₃ Sn multifilament type superconducting wires to each other, comprising first stabilizing Cu, Nb barrier and Cu-Sn bronze at the corresponding end of the superconducting wire to be connected with an acid or the like. By dissolving and removing the Nb filament to expose a predetermined length of the remaining Nb filament, and then twisting and joining the exposed Nb filaments to each other.
n and Cu were inserted into the mixture of the respective powders, and an Nb sleeve was attached to the outer periphery thereof, and the connection thus formed was heated to a temperature higher than the melting temperature of the Sn powder to form the Sn.
In the state where the powder is melted, the connection part is compression-integrated from the outside, and then the connection part and the entire superconducting wire are heated at the Nb ₃ Sn generation temperature, and the Nb ₃ Sn A method for connecting a compound-based superconducting wire that generates a continuous compound. 2. A method for connecting Nb ₃ Sn-based multifilament type superconducting wires to each other, wherein the corresponding ends of the superconducting wires to be connected are cut into inclined planes so as to be in a slightly parallel state, and are stabilized. Cu, Nb barrier and Cu-Sn bronze are dissolved and removed with an acid or the like to expose and project the Nb filaments to a length that does not project much more than the respective inclined surfaces, and between the inclined surfaces from which the Nb filaments are projected. Nb, Sn,
Fill the mixture of each powder of Cu
The Nb sleeve is attached, and the connection thus formed is heated to a temperature higher than the melting temperature of the Sn powder, and the connection is compression-integrated from the outside under a state in which the Sn powder is melted, and then the connection and A method of connecting a compound superconducting wire in which the entire superconducting wire is heated at the Nb ₃ Sn generation temperature to form a continuous compound of Nb ₃ Sn at the interface and the connection portion of the Nb filament in the superconducting wire.