JP2020009709A - Superconducting wire rod and insulated superconducting wire rod - Google Patents

Abstract

To provide a superconducting wire rod in which bubbles in the insulation covering when covering with insulation covering are hard to occur, and to provide an insulated superconducting wire rod in which the superconducting wire rod is covered with an insulation covering.SOLUTION: The superconducting wire rod 11 includes a channel 20 having a channel groove 21, and a superconducting core wire rod 35 housed in the channel groove 21 of the channel 20, and in which, characterized, the channel groove 21 and the superconducting core wire rod 35 are joined via a joining material layer 40 formed at the bottom of the channel groove 21, and when the channel groove 21 of the channel 20 is plane-viewed from the groove opening side, the joining material layer 40 is not seen in the inside of the channel groove 21.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a superconducting wire and an insulated superconducting wire.

  An insulated superconducting wire in which the surface of a superconducting wire is covered with an insulating film is known as one of the insulated conducting wires. This insulated superconducting wire is used, for example, in the fields of a magnetic resonance imaging (MRI) device, a nuclear magnetic resonance (NMR) device, a particle accelerator, a linear motor car, and a power storage device.

  As the superconducting wire, a superconducting multi-core wire (also referred to as a superconducting core material) composed of a metal base material and a plurality of superconducting filaments embedded in the metal base material is formed by a channel having a channel groove (a stabilizing material). ) (Wire-in-channel (WIC) structure) that is housed and fixed in a channel groove.

  When the superconducting state of the superconducting multi-core wire is partially broken and the state changes to the normal conducting state, the superconducting wire of the WIC structure can temporarily diverte the current flowing through the superconducting multi-core wire to the channel. In the meantime, the superconducting multi-core wire can be returned to the superconducting state. For this reason, in a superconducting wire having a WIC structure, it is necessary to cover the entire superconducting wire with an insulating film so that the current diverted to the channel does not leak outside.

  Patent Document 1 discloses a method of manufacturing an insulated superconducting wire having a WIC structure, in which a superconducting multi-core wire and a channel groove are joined by using solder to produce a superconducting wire, and then the surface of the superconducting wire is coated with an insulating resin. Thereafter, a method of heating at a temperature and for a time at which the insulating resin hardens and the solder does not melt is disclosed. In the insulated superconducting wire disclosed in Patent Document 1, solder is filled between the channel groove and the superconducting core wire, and the surface of the solder is covered with an insulating resin. Patent Document 1 discloses a method of coating the surface of a superconducting wire with an insulating resin, such as passing the superconducting wire through a tank of insulating paint or extruding the insulating resin.

European Patent No. 2118941

  By the way, when air bubbles are generated in the insulating film of the insulated superconducting wire, the portion where the air bubbles are generated is thin and the strength is reduced, so that the insulating film is likely to be broken, and the superconductivity of the insulated superconducting wire is extended for a long time. It can be difficult to maintain. Therefore, it is preferable that the insulating film has few bubbles. However, if the superconducting wire filled with solder between the channel groove and the superconducting core wire is coated with an insulating resin, the flux of the solder volatilizes, and air bubbles tend to be generated in the insulating film.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a superconducting wire in which bubbles are hardly generated in an insulating film when the insulating film is covered with the insulating film, and an insulating material in which the superconducting wire is coated with the insulating film. It is to provide a superconducting wire.

  In order to solve the above problems, a superconducting wire of the present invention includes a channel having a channel groove, and a superconducting core wire housed in the channel groove of the channel, wherein the channel groove and the superconducting core wire are provided. Are bonded via a bonding material layer formed at the bottom of the channel groove, and when the channel groove of the channel is viewed in plan from the groove opening side, the bonding material layer is inside the channel groove. It is characterized by not being seen.

  According to the superconducting wire of the present invention, the channel groove and the superconducting core wire are joined via the joining material layer formed at the bottom of the channel groove, and the insulating film is formed directly on the joining material. No need. Therefore, when the superconducting wire is covered with the insulating film, gas derived from the bonding material, such as solder flux, is less likely to enter the insulating film, and bubbles are less likely to be generated in the insulating film. In addition, since the channel groove and the superconducting core wire are joined via the joining material layer formed at the bottom of the channel groove, compared with the case where solder is filled between the channel groove and the superconducting core wire. As a result, the amount of the joining material used can be reduced. Therefore, when the superconducting wire is coated with the insulating film, the amount of gas generated due to the bonding material is reduced, and bubbles are less likely to be generated in the insulating film. Furthermore, when the channel groove of the channel is viewed in plan from the groove opening side, the bonding material layer is not seen inside the channel groove, and when the superconducting wire is covered with the insulating film, the bonding material layer Since the insulating resin does not come into contact, gas caused by the bonding material is less likely to enter the insulating film, and bubbles are less likely to be generated in the insulating film.

Here, in the superconducting wire of the present invention, it is preferable that the bonding material layer is a conductive bonding material layer.
In this case, since the bonding material layer is a conductive bonding material layer, and the conductivity between the superconducting core wire and the channel is improved, when the superconducting state of the superconducting core wire partially breaks and transitions to a normal conducting state. In addition, the current flowing through the superconducting core wire can be efficiently diverted to the channel.

In the superconducting wire of the present invention, it is preferable that the conductive bonding material layer is a cured body of a solder paste or a sintered body of a silver paste.
In this case, since the conductive bonding material layer is a cured body of the solder paste or a sintered body of the silver paste, and the conductivity between the superconducting core wire and the channel is reliably improved, the superconducting state of the superconducting core wire is partially changed. In the case where the superconducting wire breaks into the normal conducting state, the current flowing through the superconducting core wire can be efficiently and reliably diverted to the channel.

In the superconducting wire of the present invention, it is preferable that the superconducting core wire is a superconducting multicore wire composed of a metal base material and a plurality of superconducting filaments embedded in the metal base material.
In this case, since the superconducting core wire is a superconducting multicore wire and has high superconductivity, higher superconductivity can be maintained for a long period of time.

An insulated superconducting wire of the present invention includes the above-described superconducting wire and an insulating film covering at least a part of the superconducting wire.
According to the insulated superconducting wire of the present invention, since the insulating film is formed on the above-described superconducting wire, bubbles are hardly generated in the insulating film. For this reason, the insulated superconducting wire of the present invention can maintain high superconductivity for a long period of time.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide a superconducting wire rod in which bubbles are less likely to be generated in the insulating film when covered with the insulating coat layer, and an insulated superconducting wire rod in which the superconducting wire rod is covered with the insulating coat.

It is a cross section of a superconducting wire concerning a first embodiment of the present invention. It is a cross-sectional view showing an example of the manufacturing method of the superconducting wire concerning the first embodiment of the present invention. It is a cross section of an insulated superconducting wire concerning a second embodiment of the present invention.

  Hereinafter, a superconducting wire and an insulated superconducting wire according to an embodiment of the present invention will be described with reference to the attached drawings.

FIG. 1 is a cross-sectional view of the superconducting wire according to the first embodiment of the present invention.
As shown in FIG. 1, the superconducting wire 11 according to the first embodiment includes a channel 20 having a channel groove 21 and a superconducting core wire 35 housed and fixed in the channel groove 21. The channel groove 21 and the superconducting core wire 35 are joined via a joining material layer 40 formed at the bottom of the channel groove 21. The cross-sectional shape of the superconducting wire 11 is a substantially square shape having a curvature at a corner. The superconducting core wire 35 is a superconducting multicore wire 30 including a metal base material 31 and a plurality of superconducting filaments 32 embedded in the metal base material 31. The superconducting multifilamentary wire 30 has a circular cross section, and the bottom of the channel groove 21 has a curved shape along the superconducting multifilamentary wire 30. By making the bottom of the channel groove 21 curved along the superconducting multi-core wire 30, the thickness of the bonding material layer 40 can be reduced, and the amount of bonding material used can be reduced. The cross-sectional shape of the superconducting multi-core wire 30 is not particularly limited, and may be, for example, a rectangular shape having a curvature at a corner.

As a material of the channel 20, for example, copper, a copper alloy, aluminum, or an aluminum alloy can be used. As a material of the metal base material 31 of the superconducting multi-core wire 30, for example, copper, copper alloy, aluminum, and aluminum alloy can be used. As a material of the superconducting filament 32 of the superconducting multi-core wire 30, for example, an NbTi alloy or Nb ₃ Sn can be used.

  The bonding material layer 40 is formed on the bottom side (lower side in FIG. 1) of the channel groove 21 than the part where the inner wall surface of the channel groove 21 and the superconducting multi-core wire 30 are in direct contact. The bonding material layer 40 is not formed above a portion where the inner wall surface of the channel groove 21 and the superconducting multi-core wire 30 are in direct contact. Therefore, when the channel groove 21 of the channel 20 is viewed in a plan view from the groove opening side, the bonding material layer 40 is not seen inside the channel groove 21.

The bonding material layer 40 is preferably a conductive bonding material layer. The conductive bonding material layer is preferably a cured body of a solder paste or a sintered body of a silver paste.
The solder paste is a composition containing a solder powder and a flux. As the solder powder, Sn-based solder powder can be used. As the Sn-based solder powder, an alloy of Sn and one or more metals selected from the group consisting of Sb, Ag, and Cu can be used. The solder powder is preferably a Sn-Sb-based solder powder, a Sn-Ag-based solder powder, or a Sn-Ag-Cu-based solder powder. The type of the flux is not particularly limited, and various fluxes such as resin, organic, and inorganic can be used. The solder paste, for _example, a Sn 3.0 _{Ag 0.5} Cu powder 88.2 to 88.4 wt%, 2-4 wt% of diethylene glycol monohexyl ether, 2-ethyl-1,3-hexanediol A composition containing less than 1% by mass, 4 to 6% by mass of rosin, and other minor components can be used.

  The silver paste is a composition containing silver powder and a solvent. The silver powder is preferably a fine powder that can be sintered at a temperature of 150 ° C. or more and 300 ° C. or less. The silver powder preferably has a particle diameter in the range of 0.1 μm or more and 40 μm or less. The solvent preferably has a boiling point in the range of 150 ° C to 300 ° C. As the solvent, 2-methylpropanoate, α-terpineol, 2-ethylhexyl acetate, and 3-methylbutyl acetate can be used.

Next, a method for manufacturing a superconducting wire according to the first embodiment will be described.
FIG. 2 is a cross-sectional view illustrating an example of the method for manufacturing a superconducting wire according to the first embodiment. The superconducting wire 11 according to the first embodiment can be manufactured, for example, as follows.
As shown in FIG. 2, first, a bonding material paste is applied to the channel groove 21 of the channel 20 and dried to form a bonding material paste layer 41. Next, the superconducting multi-core wire 30 is accommodated in the channel groove 21. Next, the bonding material paste layer 41 is heated while the superconducting multi-core wire 30 is pressed against the channel groove 21, and then cooled, and the bonding material paste layer 41 is cured to form the bonding material layer 40. The width and the thickness of the bonding material layer 40 are adjusted so that the bonding material layer 40 cannot be seen inside the channel groove 21 when the channel groove 21 of the channel 20 is viewed in plan from the groove opening side. It is desirable to do.

  As the joining material paste, a solder paste and a silver paste can be used. In addition, a silver oxide paste containing silver oxide powder, a reducing agent, and a solvent can be used as the silver paste. This silver oxide paste forms a silver paste layer by the silver oxide powder being reduced by the reducing agent and changing into silver powder.

When a solder paste is used as the bonding material paste, the heating temperature of the bonding material paste layer 41 is preferably equal to or higher than the melting temperature of the solder powder and equal to or lower than the heat resistance temperature of the superconducting multi-core wire 30. When a silver paste is used as the bonding material paste, the temperature is preferably equal to or higher than the sintering temperature of silver powder and equal to or lower than the heat-resistant temperature of superconducting multi-core wire 30.
The heat resistant temperature of the superconducting multi-core wire 30 is a temperature at which the superconducting critical current value measured at a temperature of 4.2 K (Kelvin) is reduced by 5% from that before heating when the superconducting multi-core wire 30 is heated. is there.

Next, the insulated superconducting wire will be described.
FIG. 3 is a cross-sectional view of the insulated superconducting wire according to the second embodiment of the present invention.
The insulated superconducting wire 12 shown in FIG. 3 includes a superconducting wire 11 and an insulating film 50 that covers the superconducting wire 11. Since the superconducting wire 11 is the same as the superconducting wire 11 of the first embodiment described above, the same reference numerals are given and the detailed description is omitted.

The insulating film 50 preferably has a thickness in a range of 5 μm or more and 60 μm or less.
As a material of the insulating film 50, for example, it is generally used as a material of an insulating film of an insulating superconducting wire such as formalized polyvinyl alcohol resin, polyvinyl alcohol resin, polyamide imide resin, polyimide resin, polyester imide resin, polyester resin, and polyurethane resin. Can be used.

As a method of forming the insulating film 50 on the surface of the superconducting wire 11, for example, a coating method or an electrodeposition method can be used.
In the coating method, a varnish containing an insulating resin for forming an insulating film and a solvent is applied to the surface of the superconducting wire 11 to form a coating layer, and then the coating layer is heated to form the resulting insulating film on the superconducting wire 11. It is a method of baking. As a method of applying varnish to the surface of superconducting wire 11, a dipping method in which superconducting wire 11 is immersed in varnish can be used. The heating temperature at the time of heating the coating layer and baking the generated insulating film on the superconducting wire 11 is, for example, in the range of 200 ° C. or more and 450 ° C. or less, and the heating time is, for example, 0.5 minute or more and 20 minutes or more. Within the following range.

  In the electrodeposition method, the superconducting wire 11 and the electrode are immersed in an electrodeposition solution in which insulating resin particles having electric charge are dispersed, and a DC voltage is applied between the superconducting wire 11 and the electrode to form the superconducting wire 11. Is a method in which insulating resin particles are electrodeposited on the surface of the substrate to form an electrodeposited layer, and then the electrodeposited layer is heated to bake the resulting insulating film on the superconducting wire 11. The electrodeposition liquid can be prepared, for example, by adding a poor solvent or water for the insulating resin to a solution of the insulating resin. The heating temperature at the time of heating the electrodeposition layer and baking the generated insulating film on the superconducting wire 11 is the same as in the above-described coating method.

  According to the superconducting wire 11 of the first embodiment configured as described above, the channel groove 21 and the superconducting multi-core wire 30 are joined via the joining material layer 40 formed at the bottom of the channel groove 21. Therefore, the insulating film is not formed directly on the bonding material. Therefore, when the superconducting wire 11 is coated with the insulating film 50, a gas derived from the bonding material such as a flux of solder or a reducing agent of silver oxide hardly enters the insulating film 50, and bubbles are hardly generated in the insulating film 50. Become. Further, since the channel groove 21 and the superconducting multi-core wire 30 are joined via the joining material layer 40 formed at the bottom of the channel groove 21, the space between the channel groove and the superconducting core wire is filled with solder. The amount of the joining material used can be reduced as compared with the case of performing the bonding. Therefore, when the superconducting wire 11 is covered with the insulating film 50, the amount of gas generated due to the bonding material is reduced, and bubbles are less likely to be generated in the insulating film 50.

  In the superconducting wire 11 of the first embodiment, when the bonding material layer 40 is not seen inside the channel groove 21 when the channel groove 21 of the channel 20 is viewed in plan from the groove opening side, the superconducting wire 11 is insulated. Since the bonding material layer 40 and the insulating resin do not come into contact with each other when the coating is performed with the film 50, the gas due to the bonding material is less likely to enter the insulating film 50, and bubbles are less likely to be generated in the insulating film 50.

  In the superconducting wire 11 of the first embodiment, when the bonding material layer 40 is a conductive bonding material layer, the conductivity between the superconducting multi-core wire 30 and the channel 20 is improved. When the superconducting state is partially broken and transitions to the normal conducting state, the current flowing through the superconducting multi-core wire 30 can be efficiently diverted to the channel 20.

  In the superconducting wire 11 of the first embodiment, when the conductive bonding material layer is a cured body of a solder paste or a sintered body of a silver paste, the conductivity between the superconducting multi-core wire 30 and the channel is reliably improved. Therefore, when the superconducting state of the superconducting multi-core wire 30 partially breaks and the superconducting multi-core wire 30 transitions to the normal conducting state, the current flowing through the superconducting multi-core wire 30 can be efficiently and reliably diverted to the channel 20.

  Further, in the superconducting wire 11 of the first embodiment, when the superconducting core wire 35 is the superconducting multi-core wire 30, the superconducting wire has high superconductivity, so that higher superconductivity can be maintained for a long period of time.

  According to the insulated superconducting wire 12 of the second embodiment, since the insulating film 50 is formed on the above-described superconducting wire 11, bubbles are not easily generated in the insulating film 50. For this reason, the insulated superconducting wire 12 of the second embodiment can maintain high superconductivity for a long period of time.

As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the present invention.
For example, in the present embodiment, the superconducting multi-core wire 30 is used as the superconducting core wire 35, but the present invention is not limited to this case. For example, a single metal wire may be used as superconducting core wire 35.

  Next, the operation and effect of the present invention will be described with reference to examples.

[Example 1 of the present invention]
As the superconducting multi-core wire, a wire having a circular cross section (diameter: 0.66 mm, heat-resistant temperature: 300 ° C.) composed of a copper base material and an NbTi alloy filament embedded in the base material was prepared. In addition, a copper channel provided with a channel groove (groove width: 0.66 mm) whose bottom is curved along the shape of the superconducting multi-core wire was prepared as the channel.

A solder paste (solder powder: Sn ₉₅ Sb ₅ , melting point of solder powder: 238 ° C.) is applied to the bottom of the channel groove of the channel using a dispenser, and a solder paste layer having a width of 0.5 mm and a thickness of 0.03 mm is applied. Was formed. Next, the superconducting multi-core wire was accommodated in the channel groove. Next, while the superconducting multi-core wire was pressed against the channel groove, the solder paste layer was heated and melted at 260 ° C. for 3 minutes, then cooled, and the solder paste layer was cured to produce a superconducting wire. When the channel groove of the channel of the obtained superconducting wire was viewed in plan from the groove opening side, no cured body of the solder paste was found inside the channel groove.

  An insulating film was formed on the surface of the obtained superconducting wire by an electrodeposition method to produce an insulating superconducting wire. Specifically, an insulating film was formed as follows. First, a superconducting wire and an electrode were immersed in an electrodeposition solution containing polyamide-imide (PAI) particles having a negative charge and water. Then, a DC voltage is applied with the superconducting wire as a positive electrode and the electrode as a negative electrode, and PAI particles are electrodeposited on the surface of the superconducting wire so that the thickness of the film after drying becomes 40 μm, thereby forming an electrodeposition layer. did. The superconducting wire on which the electrodeposition layer was formed was dried and baked at a temperature of 280 ° C. for 4 minutes to produce an insulated superconducting wire.

  The entire surface of the insulating film of the obtained insulating superconducting wire was observed with a microscope, and the number of bubbles having a diameter of 100 μm or more was counted. As a result, the number of bubbles per meter of the insulated superconducting wire was less than 1 / m, and almost no bubbles were generated in the insulating film of the insulated superconducting wire.

[Example 2 of the present invention]
A superconducting wire was produced and obtained in the same manner as in Example 1 of the present invention, except that a silver paste (average particle diameter of silver powder: 10 μm, sintering temperature of silver powder: 250 ° C.) was used instead of the solder paste. An insulating film was formed on the surface of the superconducting wire by electrodeposition to produce an insulated superconducting wire. Then, the number of bubbles in the insulating film of the obtained insulating superconducting wire was counted in the same manner as in Inventive Example 1. As a result, the number of bubbles per meter of the insulated superconducting wire was less than 1 / m, and almost no bubbles were generated in the insulating film of the insulated superconducting wire.

[Comparative Example 1]
An insulated superconducting wire was manufactured in the same manner as in Inventive Example 1 except that the superconducting wire was prepared as follows.
The channel groove of the channel was filled with molten solder generated by heating Sn ₉₅ Sb ₅ solder to 260 ° C. Next, the superconducting multi-core wire was accommodated in the channel groove of the channel. Next, after removing the molten solder adhered to the channel surface, the molten solder was cooled and cured to produce an insulated superconducting wire. When the channel groove of the channel of the obtained superconducting wire was viewed in plan from the groove opening side, it was confirmed that the cured solder was exposed between the channel groove and the superconducting multi-core wire.

  The number of bubbles of the insulating film formed on the cured solder between the channel groove of the obtained insulated superconducting wire and the superconducting multi-core wire was counted in the same manner as in Inventive Example 1. As a result, the number of bubbles per meter of the insulated superconducting wire was 10 / m, and it was confirmed that many bubbles were generated in the insulating film on the cured solder of the insulated superconducting wire.

REFERENCE SIGNS LIST 11 superconducting wire 12 insulated superconducting wire 20 channel 21 channel groove 22 opening 30 superconducting multi-core wire 31 metal base material 32 superconducting filament 33 electric insulating layer 35 superconducting core wire 40 bonding material layer 41 bonding material paste layer 50 insulating film

Claims (5)

A channel having a channel groove, comprising a superconducting core wire housed in the channel groove of the channel,
The channel groove and the superconducting core wire are bonded via a bonding material layer formed at the bottom of the channel groove,
A superconducting wire, wherein the bonding material layer is not seen inside the channel groove when the channel groove of the channel is viewed in plan from the groove opening side.   The superconducting wire according to claim 1, wherein the bonding material layer is a conductive bonding material layer.   3. The superconducting wire according to claim 2, wherein the conductive bonding material layer is formed of a cured body of a solder paste or a sintered body of a silver paste. 4.   The said superconducting core wire is a superconducting multicore wire consisting of a metal base material and a plurality of superconducting filaments embedded in the metal base material, The superconducting core wire material according to any one of claims 1 to 3, wherein Superconducting wire.   An insulated superconducting wire, comprising: the superconducting wire according to any one of claims 1 to 4; and an insulating coating covering at least a part of the superconducting wire.

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