JP3397038B2 - Superconducting connection method and superconducting connection structure for superconducting wires - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of superconducting an oxide-based superconducting wire and a metal-based superconducting wire, or oxide-based superconducting wires to each other, and a structure in which they are superconductingly connected. High resolution NM
The present invention relates to a superconducting connection method and a superconducting connection structure useful when applying an oxide-based superconducting wire as a material of a superconducting magnet used in an R analyzer.

[0002]

2. Description of the Related Art The superconducting phenomenon is being widely used in various fields such as high-current power transmission and strong magnetic field generation equipment by taking advantage of the characteristic that a large current can flow with zero resistance. In particular, a superconducting magnet used in a high-resolution NMR analyzer performs a strong magnetic field by transmitting a large current and performs a permanent current operation using zero resistance, and is a typical application that can be realized only by using the superconducting phenomenon. is there.

Conventionally, as a superconducting wire used as a material for a superconducting magnet, metal-based superconducting wires such as NbTi, Nb ₃ Sn, Nb ₃ Al have been known. These metal-based superconducting wires are used for MRI medical diagnostic equipment, It has been applied to various devices such as a high resolution NMR device that requires a highly accurate and stable magnetic field. In these cases, in order to effectively utilize the above-mentioned characteristics, the superconducting wires used in the device are connected to each other while maintaining the superconducting state, so that the permanent current flows in a loop shape.

In recent years, an oxide-based superconductor having a critical temperature exceeding liquid nitrogen temperature has been discovered, and it is expected that the application technology of superconductivity will be further expanded by utilizing this oxide-based superconductor. For these reasons, a technique of forming a superconducting magnet with an oxide-based superconducting wire has been attempted. In order to operate these superconducting magnets in the persistent current mode, it is necessary to connect the oxide superconducting wires to each other or to connect the oxide superconducting wires to the metal superconducting wires in a superconducting state. Also, a permanent current switch that temporarily turns ON / OFF the superconducting state by heat or magnetic field is indispensable.

With respect to metal-based superconducting wires, both the superconducting connection method and the application to a persistent current switch have been technically established and have already been put to practical use. For example, Nb
For Ti multifilamentary wire rods, a method is known in which the ends of the wire rods are immersed in an acid, the stabilized copper constituting the wire rods is etched away, the NbTi filaments are exposed, and then the filaments are superconductingly connected ( For example, JP-A-63-62
110, JP-A-62-272502, etc.).

However, this method cannot be applied to oxide superconducting wires. That is, silver or a silver alloy as a stabilizing material (hereinafter sometimes represented by "silver")
When the sheath material part made of is etched with an acid, the oxide superconductor itself, which is a filament, is also dissolved by the acid. For this reason, there is still no known example of operating a superconducting magnet composed of an oxide superconducting wire in a permanent current mode.

Several methods have been already known for connecting oxide superconducting wires without etching them (for example, Japanese Patent Laid-Open No. 4-363883). However, in all of these techniques, when heat-treating the superconducting wire or the main body of the superconducting magnet, the heat treatment of the connecting portion is simultaneously performed to realize the superconducting connection.
This results in heat treatment of the permanent current switch at the same time as the main body magnet, which is not suitable for the actual manufacturing process.

Further, the technique proposed so far is to cut off the silver sheath of the oxide superconducting wire with a cutter or the like to mechanically separate the silver sheath material, so that this technique is a single core tape-shaped wire. Other than that is difficult to apply. Moreover, from the viewpoint of increasing the critical current density, the actual oxide superconducting magnet is generally composed of a wire material containing a large number of filament groups inside. In order to make it, it is absolutely necessary to enable the superconducting connection of the oxide superconducting multicore wire and the application of the wire to the persistent current switch.

[0009]

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and an object thereof is to realize a good superconducting connection of an oxide superconducting multifilamentary wire and to make the oxide superconducting multifilamentary wire permanent. Enables application to current switches,
It is intended to enable the operation of the oxide superconducting magnet in the permanent current mode.

[0010]

Means for Solving the Problems The present invention capable of achieving the above-mentioned object means that in superconducting connection between an oxide-based superconducting wire and a metal-based superconducting wire, or oxide-based superconducting wires, Melting point of alloy with silver is 500 ℃
The following metal or alloy is heated to form a melt, and the end portion of the wire to be connected is immersed in the melt to melt the sheath material made of silver or silver alloy at the end and separated from the superconducting filament group. A superconducting connection method for a superconducting wire, which is characterized in that the wire to be connected is then superconductingly connected by solidifying and solidifying the melt.

In the above superconducting connection method, it is preferable that the dipping step is performed twice or more. As the metal or alloy for melting the sheath material made of silver or a silver alloy, a metal or alloy containing one or more elements selected from the group consisting of Bi, Ga, Hg, In, Pb and Sn, or Alloys may be mentioned. By the above method, a superconducting connection structure that maintains a good superconducting state can be realized.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The operation of the present invention will be described while explaining the background of the completion of the present invention. We have
An experiment was conducted to clarify the defects in the conventional superconducting connection. First of all, a solenoid is wound with a silver sheath oxide superconducting multi-core wire, and a solenoid coil as shown in Fig. 1 is prepared.
Heat treatment was performed according to the sort pattern shown in FIG. In the heat pattern shown in FIG. 2, an oxide superconductor (Bi: Sr: Ca: Cu ratio of approximately 2: 2: 1: 2) called Bi-2212 is produced from the raw material powder to realize high orientation. Is a partially melted slow cooling process that is commonly employed to do so (eg, Cryogenics 35 (1995) 127-133).

When the generated magnetic field was measured by energizing the above coil, it was 1.8 T (Tesla) with no external magnetic field of 4.2K.
Could be generated. After confirming this, a superconducting connection with a persistent current switch was tried. The permanent current switch portion used at this time is normally used in metal magnets and is composed of NbTi multi-core wire (FIG. 3). This NbTi multifilamentary wire can be easily formed by etching stabilized copper with nitric acid.
The filament could be exposed. Also NbTi
In order to connect the filament to the oxide superconducting filament, it is necessary to expose the oxide filament as well.

When an attempt was made to etch the silver sheath material with nitric acid in order to separate the silver sheath material portion of the oxide superconducting wire, the oxide superconducting filament was also dissolved by the acid at the same time as the silver sheath material portion. The filament portion could not be exposed by etching. After all, it was difficult to realize a superconducting connection by the acid etching method.

Based on the above-mentioned progress, the present inventors have worked on the development of a method of melting only the silver sheath without melting the oxide filament. And various literature on chemical etching of silver (eg Metallographic Etching e
d. Giinter Petzow Published from American Society
for metals.) and attempted superconducting connection of oxide superconducting wire. As a result, it was found that when a mixed solution of (hydrogen peroxide water + ammonia water) was used, only the silver could be peeled off and the oxide filament could be exposed without dissolving the oxide superconductor filament.

Next, the superconducting connection between the oxide filament and the NbTi filament was tried. First, the oxide filament and the NbTi filament were brought close to each other and pressure-bonded. However, according to this method, the oxide filament was instantly crushed into brittleness, and it was difficult to perform pressure bonding. Next, an attempt was made to bring the oxide filament and the NbTi filament as close to each other as possible and to pour solder between them. The outline of this method is schematically shown in FIG. By this method, the connection parts were once connected.

In order to confirm whether or not this connection portion is actually a superconducting connection, the current-voltage characteristic of the connection portion was examined at 4.2K. The result is shown in FIG.
It was found that the current-voltage characteristic has a slight slope from zero current, and a complete zero resistance has not been realized. I made several samples and made similar attempts,
The situation was exactly the same.

In order to elucidate the cause of this, a chemical / physical analysis was carried out. As a result, when silver was separated by a mixed solution of hydrogen peroxide water and ammonia water, the appearance of the oxide superconducting filament was found to change. However, it was revealed that the oxide surface was altered by the influence of the mixed solution, although it was not possible. And since this surface alteration layer does not become a superconducting layer,
The connection is the same as when the normal conducting resistance is inserted in series.
It was thought that it would have the inclination as seen in.

Based on the above findings, the present inventors have further studied a method for exfoliating silver without damaging the oxide filament. And in the process of this examination, the following was clarified. That is, The melting point of silver is about 920 ° C. at atmospheric pressure, but almost all the silver is solid-dissolved in lead, and the higher the proportion of lead, the lower the melting point. The present invention effectively utilizes such a phenomenon.

For example, when silver is put into lead which is heated to about 350 ° C. and melted, the silver at the interface quickly solid-dissolves in lead, and the melting point lowers to start melting.
By utilizing this, it became possible to remove the silver coating without damaging the oxide superconducting filament.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and it is a technique of the present invention to change the design in view of the above-mentioned and the following points. It is included in the target range.

[0022]

EXAMPLE FIG. 6 is an explanatory view showing the procedure for carrying out the method of the present invention. First, as shown in FIGS. 6 (a) and 6 (b), it is necessary to immerse the silver sheath of the oxide wire into a lead-based solder (melt) which is heated to about 350 ° C. and melted.
Repeat (or more) times. At this time
The reason why only the step (a) is performed (that is, the dipping step is performed only once) is as follows. That is, the dipping / melting process is 1
This is because if the number of turns is increased, the concentration of silver in the alloy around the filament becomes high and it becomes difficult to form a superconductor layer. By adding the step of FIG. 6 (b), the content of silver in the lead alloy adjacent to the filament is reduced, and good superconducting characteristics are exhibited.

Next, in FIG. 6 (c), NbTi is finally obtained by solidifying and solidifying the molten lead-based solder.
The filament and the oxide superconducting filament are connected. Then, a superconducting current flow path of NbTi filament-lead alloy-oxide filament is formed. FIG. 7 shows the measurement result of the current-voltage characteristic at 4.2K in the superconducting connection structure created by this procedure.

As is apparent from FIG. 7, Ic (critical current)
It can be seen that a superconducting connection of = 115 A has been achieved. To demonstrate that a perfect superconducting connection has been achieved by the present invention, a permanent current switch constructed with NbTi wire was used to make the coil set shown in FIG. And the NbTi wire of the permanent current switch,
The method of the present invention was applied to the connection with the oxide coil. Central magnetic field strength (B) after shifting to permanent current operation
9 shows the change with time. As is clear from FIG. 9, although the initial damping is a little large, the permanent current operation of B = 0.84T is realized.

In the above embodiments, the case where lead is used as the metal for melting the silver sheath has been described, but the above metal used in the present invention is not limited to lead, but the metal or alloy itself to be melted exhibits superconducting characteristics, and Any material can be used as long as it can melt the silver sheath at 500 ° C. or lower without impairing the crystallinity of the oxide superconducting filament. As such a metal, Bi, Ga, Hg, In, Sn or the like can be used, although the performance of the superconducting connection portion is good or bad. That is, Bi, Ga, Hg, In,
One or two selected from the group consisting of Pb and Sn
More than one metal or alloy can be used.

As described above, the present invention is based on Bi, Ga,
It is possible to effectively utilize that the alloy of silver or a metal or alloy containing at least one kind of Hg, In, Pb, Sn and the like has a low melting point, without damaging the oxide superconducting filament, and without causing a silver sheath. The material could be separated.

The reason why the silver sheath material could be effectively separated by using the above metal or alloy could be considered as follows. That is, when the silver sheath material is immersed in a bath obtained by heating and melting the above metal or alloy, the melting point of silver alone is about 900 ° C., whereas an alloy is formed at the interface between the silver sheath material and the melt. Since the melting point of the silver alloy is 500 ° C. or lower, it is considered that silver is melted and diffused in the melt.

As described above, the (alloying → melting reaction) at the interface is repeated, and the silver sheath material can be separated at a temperature of 500 ° C. or lower which does not damage the oxide superconducting filament. Incidentally, when the wire rod is taken out from the melt, the molten alloy adheres to the filament, but the concentration of silver in the melt is reduced during the final separation treatment so that the alloy composition exhibits good superconducting properties, Finally, a good superconducting connection can be formed.

[0029]

The present invention is configured as described above, and does not damage the oxide superconducting filament,
Good superconducting connection was realized.

[Brief description of drawings]

FIG. 1 is a schematic view showing a solenoid coil made of a silver sheath oxide multifilamentary wire.

FIG. 2 is a diagram showing an example of a final heat treatment pattern when producing an oxide superconducting wire solenoid coil.

FIG. 3 is a schematic diagram showing a persistent current switch made of NbTi multi-core wire.

FIG. 4 is a diagram schematically showing how superconducting connection is made by a conventional method.

FIG. 5 is a diagram showing current-voltage characteristics of a wire rod that is superconductingly connected by a conventional method.

FIG. 6 is an explanatory view showing a procedure for carrying out the method of the present invention.

FIG. 7 is a diagram showing current-voltage characteristics of a superconducting connection produced by the method of the present invention.

FIG. 8 is a diagram showing a coil set for demonstrating that superconducting connection has been achieved.

FIG. 9 is a diagram showing a time change of a magnetic field when a coil set produced by the method of the present invention is operated in a persistent current mode.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-1-183083 (JP, A) JP-A-7-192837 (JP, A) JP-A-7-254473 (JP, A) JP-A-4- 363883 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01R 43/00 H01R 4/68

Claims (4)

(57) [Claims] 1. When superconducting an oxide-based superconducting wire and a metal-based superconducting wire, or oxide-based superconducting wires to each other in a superconducting manner, they exhibit superconducting properties and a melting point of an alloy with silver of 50.
A metal or alloy having a temperature of 0 ° C. or lower is heated to form a melt, and the end portion of the wire to be connected is immersed in the melt to melt the sheath material made of silver or a silver alloy at the end portion to obtain a superconducting filament group. A superconducting connection method for a superconducting wire, characterized in that the wire to be connected is superconductingly connected by separating and then solidifying and solidifying the melt. 2. The superconducting connection method according to claim 1, wherein the immersion step according to claim 1 is performed twice or more. 3. A metal or alloy for melting a sheath material made of silver or a silver alloy is Bi, Ga, Hg, I.
A metal or alloy containing one or more elements selected from the group consisting of n, Pb and Sn.
Alternatively, the superconducting connection method described in 2. 4. A superconducting connection structure, which is superconductingly connected by the method according to any one of claims 1 to 3.