WO2021107248A1

WO2021107248A1 - Method for manufacturing high-temperature superconductive coil by using diffusion bonding and high-temperature superconductive coil manufactured thereby

Info

Publication number: WO2021107248A1
Application number: PCT/KR2019/017404
Authority: WO
Inventors: 하홍수; 김성규; 조전욱
Original assignee: 한국전기연구원
Priority date: 2019-11-28
Filing date: 2019-12-10
Publication date: 2021-06-03
Also published as: KR20210066542A

Abstract

The present invention relates to a method for manufacturing a high-temperature superconductive coil by using diffusion bonding and a high-temperature superconductive coil manufactured thereby and, more specifically, to a high-temperature superconductive coil capable of fixing the winding state of a high-temperature superconductive wire material through diffusion bonding of silver (Ag) and to a manufacturing method therefor. The technical subject of the present invention is directed to: a method for manufacturing a high-temperature superconductive coil by using diffusion bonding; and a high-temperature superconductive coil manufactured thereby, wherein the method comprises: a first step of forming a high-temperature superconductive wire material containing a metal substrate and a superconductive layer; a second step of forming silver (Ag) coating films on the top and bottom surfaces of the high-temperature superconductive wire material; a third step of winding the high-temperature superconductive wire material with the silver coating films; and a fourth step of subjecting the wound high-temperature superconductive wire material to heat treatment to allow the silver coating films, which are formed on and thus bonded to the top and bottom surfaces of the high-temperature superconductive wire material, to be formed into diffusion bonding layers with no interfaces through diffusion bonding of silver (Ag).

Description

Method for manufacturing high-temperature superconducting coil using diffusion bonding and high-temperature superconducting coil manufactured thereby

The present invention relates to a method of manufacturing a high-temperature superconducting coil using diffusion bonding and a high-temperature superconducting coil manufactured by the method, and more particularly, to a high-temperature superconducting coil capable of fixing the winding state of a high-temperature superconducting wire through diffusion bonding of silver (Ag). It relates to a high-temperature superconducting coil and a method for manufacturing the same.

In general, a superconducting wire refers to a material with an electrical resistance of 0, and a material with a current resistance close to 0 near the liquid helium temperature of 4K is called a low temperature superconductor (LTS). A material that exhibits superconductivity near 90K that can be used in high-temperature liquid nitrogen is called a high-temperature superconductor (HTS).

Among them, high temperature superconducting wire shows high critical temperature, critical current density and critical magnetic field, so it can be applied to power equipment such as superconducting magnets, superconducting cables, superconducting motors and superconducting generators. It is expected that it will be possible to construct more economical high-temperature superconducting wire as it has a greater cost reduction than that of generation wire.

In particular, since the high-temperature superconducting wire has a plate-like structure, the strength in the thickness direction is 1/10 or less compared to the strength in the longitudinal direction. Due to this plate-like structure, coils are mainly manufactured by the pancake winding method.

In order to fix the high-temperature superconducting wire after winding the coil, hard impregnation using epoxy, impregnation using Teflon, silicon, paraffin, etc., and soft impregnation in which only one side is impregnated with epoxy are used.

For example, in the 'second-generation high-temperature superconducting coil manufacturing method (registration number: 10-1531001)', a non-adhesive insulating film is placed inside each bobbin wing and the superconducting wire is wound so that the superconducting wire does not come into contact with the bobbin wing, For superconducting wire, the contents of winding by laminating an impregnated material such as epoxy on the upper or lower surface have been suggested.

However, in the case of impregnation using epoxy, due to the low thickness direction strength of the high-temperature superconducting wire, the high-temperature superconducting wire is damaged due to the difference in the amount of heat shrinkage between the high-temperature superconducting wire and the epoxy when cooling to a cryogenic temperature, resulting in deterioration of the coil performance.

In addition, in the case of impregnation using Teflon, silicon, or paraffin, there is a problem in that it is difficult to properly fix the high-temperature superconducting wire in the coil due to the low adhesion and strength of the material used for impregnation.

Therefore, it is an urgent need for research on new technology to prevent damage to high-temperature superconducting wires that may occur due to thermal stress due to differences in the amount of thermal contraction between materials at cryogenic temperatures and to maintain the coil in an intact state.

The present invention was invented to solve the above problems, and by fixing the winding state of the high-temperature superconducting wire through diffusion bonding of silver (Ag), high-temperature superconducting wire that can be generated by thermal stress due to the difference in heat shrinkage between materials at cryogenic temperatures. It is a technical solution to provide a method for manufacturing a high-temperature superconducting coil using diffusion bonding and a high-temperature superconducting coil manufactured by the method so as to prevent breakage of the high-temperature superconducting coil.

In order to solve the above problems, the present invention provides a first step of forming a high-temperature superconducting wire including a metal substrate and a superconducting layer; a second step of forming a silver (Ag) coating film on the upper and lower portions of the high-temperature superconducting wire; a third step of winding the high-temperature superconducting wire on which the silver coating film is formed; and the silver coating film formed on the upper and lower portions of the high-temperature superconducting wire by heat treatment of the wound high-temperature superconducting wire and bonded to each other is formed as a diffusion bonding layer without an interface through diffusion bonding of silver (Ag). It provides a method of manufacturing a high-temperature superconducting coil using diffusion bonding, comprising the steps of:

In the present invention, in the fourth step, it is characterized in that the heat treatment for 2 to 24 hours at 300 ~ 500 ℃ under an oxygen atmosphere.

In the present invention, in the fourth step, the high temperature superconducting wire material and the diffusion bonding layer are repeatedly formed in sequence, and the high temperature superconducting wire material adjacent to each other up and down is fixed in a wound state through the diffusion bonding layer. characterized.

In order to solve the above other problems, the present invention provides a high-temperature superconducting coil using diffusion junction, characterized in that it is formed by the above method.

The method for manufacturing a high-temperature superconducting coil using diffusion bonding of the present invention according to the means for solving the above problems and the high-temperature superconducting coil manufactured by the method have the following effects.

First, by forming a silver coating film on the upper and lower parts of the high-temperature superconducting wire, winding it, and forming a diffusion bonding layer while the silver (Ag) of the silver coating film is diffusion bonded through heat treatment, the high-temperature superconducting wire is wound through this diffusion bonding layer It has the effect of obtaining a high-temperature superconducting coil in which the

Second, unlike the method of impregnating using existing polymer materials, by using diffusion bonding of silver (Ag) to achieve the impregnation of the coil by junction between turns and turns of high-temperature superconducting wire, the operation of the coil There is an effect of preventing damage to the high-temperature superconducting wire due to thermal stress applied in the thickness direction of the high-temperature superconducting wire while cooling to the cryogenic region.

Third, because the entire coil has high specific heat and thermal conductivity because it is impregnated through silver (Ag) instead of impregnated through a polymer material with low thermal conductivity, it is possible to maintain the coil in an intact state by preventing a local temperature rise. there is an effect

Fourth, heat conduction can be made quickly between turns and turns of high-temperature superconducting wire wound through a diffusion bonding layer made of silver (Ag), so it is operated at very low temperatures, and even if heat is partially generated, heat Since it is quickly discharged and can be cooled easily, it has a high cooling lasting effect.

1 is a cross-sectional view of a high-temperature superconducting coil before heat treatment according to the present invention.

2 is a cross-sectional view of a high-temperature superconducting coil after heat treatment according to the present invention.

3 is a flowchart according to the present invention;

4 is an exemplary diagram of a process according to the present invention;

5 is a side view of a high-temperature superconducting wire according to the present invention.

6 is a SEM photograph of a silver (Ag) diffusion junction.

7 is a ×200 enlarged photograph of FIG. 6 .

8 is a ×1,000 enlarged photograph of FIG. 6

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First of all, since the high-temperature superconducting wire has a plate-like structure, the strength in the thickness direction is very weak at 1/10 or less than the strength in the longitudinal direction. Due to the plate-like structure of such a high-temperature superconducting wire, a layer winding method is sometimes used when manufacturing a coil, but it is mainly manufactured by a pancake winding method.

Usually, the high-temperature superconducting wire is usually impregnated with epoxy for fixing after winding. In the case of high-temperature superconducting wire, due to its low strength in the thickness direction, it is damaged when cooled to cryogenic temperatures, and thus the performance of the coil is deteriorated. Recently, research on coils through the NI (no-insulation) or MI (metal-insulation) method without impregnation has been attempted, but this also has a disadvantage in that coil performance is deteriorated due to deformation of high-temperature superconducting wire under high magnetic field. .

Therefore, in the present invention, it is an object of the present invention to provide a coil in which deformation does not occur through diffusion bonding of silver (Ag), a metal between high-temperature pyroelectric wires, so that there is no change in resistance between turns during coil fabrication.

1 is a cross-sectional view of a high temperature superconducting coil (C) before heat treatment according to the present invention. Referring to FIG. 1 , silver (Ag) is coated on both sides of a high temperature superconducting wire 100 to form a silver coating film 200 . It can be seen that the silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100 exists in a state separated from each other by the interface I.

2 is a cross-sectional view of a high-temperature superconducting coil (C) after heat treatment according to the present invention. Referring to FIG. 2 , a silver coating film 200 formed on the upper and lower portions of the high temperature superconducting wire 100 through heat treatment on the high temperature superconducting wire 100 that is formed and wound and bonded to each other is silver (Ag). By creating a diffusion bonding layer 210 without an interface (I) through diffusion bonding, the high-temperature superconducting wire 100 is fixed in a winding state through this diffusion bonding layer 210 as an example It can be seen that it is indicated by

That is, the high-temperature superconducting coil (C) is formed by winding the high-temperature superconducting wire 100 and the silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100, and is formed in the upper and lower portions of the high-temperature superconducting wire 100. The silver coating film 200 bonded to each other is formed as a diffusion bonding layer 210 without an interface through diffusion bonding of silver (Ag), and the high-temperature superconducting wire 100 through the diffusion bonding layer 210. is fixed in a wound state.

The high-temperature superconducting coil (C) integrated by maintaining the winding state of the high-temperature superconducting wire 100 through such diffusion bonding of silver (Ag) is, as shown in FIG. 3 showing a flowchart according to the present invention, in the first step (S10). ), the second step (S20), the third step (S30) and the fourth step (S40) can be manufactured through.

4 is an exemplary view of a process according to the present invention, in the first step (S10), the second step (S20), the third step (S30) and the fourth step (S40) with reference to FIG. 4 together with FIG. The content will be described in more detail below.

First, the first step is a step of forming the high-temperature superconducting wire 100 including the metal substrate 110 and the superconducting layer 130 (S10).

5 is a side view of the high-temperature superconducting wire 100 according to the present invention. Referring to FIG. 5 , the high-temperature superconducting wire 100 may be formed by sequentially stacking a metal substrate 110 , a buffer layer 120 , a superconducting layer 130 , a protective layer 140 , and a stabilization layer 150 . Able to know. This high-temperature superconducting wire 100 is prepared in a state wound on the first reel (R1).

The metal substrate 110 is intended to impart flexibility and strength to the high-temperature superconducting wire, and is made of nickel (Ni) alloy hastelloy or stainless steel because it should not be oxidized by high temperature during subsequent heat treatment. can A general metal such as iron (Fe) is not preferable for application of the metal substrate 110 because oxidation occurs.

The buffer layer 120 _{may be formed as a single layer or a plurality of layers of a material such as Al 2} O ₃ , Y ₂ O ₃ , MgO and LMO on the upper surface of the metal substrate 110 within a predetermined thickness range. The buffer layer 120 prevents contamination of the superconducting layer 130 by preventing a metal material such as an impurity element of the metal substrate 110 from diffusing into the superconducting layer 130 .

The superconducting layer 130 is formed on the upper surface of the buffer layer 120 by a physical or chemical method, and may be made of a rare earth element having high temperature superconducting properties, and the rare earth element is yttrium (Y) and a lanthanide element or a combination thereof. can be made in combination. Preferably, a rare earth element-barium-copper-oxygen (RE-Ba-Cu-O) system may be used, and examples of the RE-Ba-Cu-O system include samarium-barium-copper-oxygen (SmBCO), gadolinium- Barium-Copper-Oxygen (GdBCO), Holmium-Barium-Copper-Oxygen (HoBCO), Europium-Barium-Copper-Oxygen (EuBCO), Diprosium-Barium-Copper-Oxygen (DyBCO) and Yttrium-Barium-Copper -Oxygen (YBCO) may be any one or more, but any one applicable to the superconducting layer 130 other than the above-described type may be used.

The protective layer 140 is thinly coated on the superconducting layer 130 to increase the bonding strength of the stabilizing layer 150 , and is laminated on the silver protective layer 141 and the silver protective layer 141 made of silver (Ag). The copper protective layer 142 may be formed.

The stabilization layer 150 is generally applicable to the high-temperature superconducting wire 100, and may be SUS, Cu, or a Cu alloy, which is obvious to those skilled in the art, so a description thereof will be omitted.

However, although the metal substrate 110, the buffer layer 120, the superconducting layer 130, the protective layer 140 and the stabilization layer 150 are illustrated as the high-temperature superconducting wire 100 in FIG. 5, it is limited to this structure. It is not only possible to use various types of high-temperature superconducting wires.

Next, the second step is a step of forming the silver coating film 200 on the upper and lower portions of the high-temperature superconducting wire 100 (S20).

The present invention is not for bonding a pair of high-temperature superconducting wires in a state in which they are arranged to face each other, but for winding and fixing a single high-temperature superconducting wire 100, so that in the second step, it is wound on the first reel R1. In the process of rewinding the existing high-temperature superconducting wire 100 to the second reel R2, the upper and lower portions of the high-temperature superconducting wire 100, that is, the surface of the metal substrate 110 and the surface of the stabilization layer 150, silver (Ag) It consists of a process of forming the silver coating film 200 made of.

In particular, silver (Ag), which is a metal with the lowest electrical resistance among metals, is used because diffusion bonding is not formed due to oxidation reaction in ordinary metals.

Such silver (Ag) is a physical vapor deposition (PVD) method such as thermal evaporation, e-beam evaporation, sputtering, chemical vapor deposition using heat or plasma It can be formed on the upper and lower parts of the high-temperature superconducting wire 100 through various methods such as (chemical vapor deposition, CVD), atomic layer deposition (ALD), plating, etc. In addition to the above-described method, silver (Ag) can be coated. If possible, various methods can be applied.

Next, the third step is a step of winding the high-temperature superconducting wire 100 on which the silver coating film 200 is formed (S30).

That is, in the third step, the high-temperature superconducting wire 100 having the silver coating film 200 formed thereon is wound on the second reel R2. At this time, when the high-temperature superconducting wire 100 having a silver coating film 200 formed on the upper and lower surfaces is wound on the second reel R2 while applying tension, the upper and lower parts of the high-temperature superconducting wire 100 are in close contact with each other by pressure, and the winding is wound. is done

Finally, in the fourth step, the silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100 by heat treatment of the wound high-temperature superconducting wire 100 is bonded to each other by diffusion bonding of silver (Ag). It is a step in which the diffusion bonding layer 210 without an interface is formed (S40).

That is, the interface (I) of the two layers of the silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100 adjacent to each other up and down in the state of applying heat under a certain condition in an oxygen atmosphere is lost and the interface (I) of the two layers disappears, so that the bond is formed and mutual bonding A single diffusion bonding layer 210 is formed.

As the diffusion bonding layer 210 is repeatedly formed on the upper and lower portions of the high-temperature superconducting wire 100 wound in this way, silver (Ag) of the diffusion bonding layer 210 formed on the upper and lower portions of the high-temperature superconducting wire 100 adjacent to each other up and down. Since the atoms are not separated in a state in which they are bonded to each other, the winding state of the high-temperature superconducting wire 100 can be maintained in a fixed state.

In other words, the fourth step is a step characteristic of the present invention, and the silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100 wound through heat treatment is bonded to each other at the interface (I) or the bonding surface. As diffusion of (Ag) atoms occurs, the silver coating film 200 bonded to each other is bonded to each other in a solid phase to create a diffusion bonding layer 210 without an interface (I), thereby winding by the diffusion bonding layer 210 . In this state, it can be said that the winding state of the high-temperature superconducting wire 100 adjacent to each other can be fixed.

The heat treatment in the fourth step may be performed at 300 to 500° C. for 2 to 24 hours under an _{oxygen (O 2 ) atmosphere, and the critical conditions will be described as follows.}

First of all, since superconducting properties easily lose and receive oxygen, oxygen must be in an oxygen atmosphere, and oxygen is sufficiently oxidized to have superconducting properties, so heat treatment must be performed under an oxygen partial pressure of 1 atm.

With respect to the temperature condition, when the temperature is less than 300° C., the diffusion bonding reaction of silver (Ag) forming the silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100 and bonded to each other does not completely occur. Since the interface I between the silver coating films 200 formed on the upper and lower surfaces of the wire 100 still exists, it is difficult to maintain the winding state of the high-temperature superconducting wire 100 . On the other hand, if the heat treatment is performed in excess of 500° C., there is a concern that the superconducting properties of the superconducting layer 130 are adversely affected.

Regarding the time condition, diffusion bonding should occur while atoms of silver (Ag) constituting the silver coating film 200 diffuse and move to the silver coating film 200 adjacent to each other. In the case of heat treatment in less than 2 hours, silver (Ag) ) is insufficient time for the diffusion movement of atoms to occur completely. On the other hand, when it exceeds 24 hours, a more excellent effect does not appear in diffusion bonding compared to the case of heat treatment for less than 24 hours. Therefore, when heat treatment is performed for more than 24 hours, it only takes a lot of time, so there is an advantage in the process. none.

The silver coating film 200 formed on the upper and lower portions of the high-temperature superconducting wire 100 through heat treatment on the high-temperature superconducting wire 100 wound in this fourth step and bonded to each other is silver (Ag) through diffusion bonding. It is created as a diffusion bonding layer 210 without an interface (I), and the high-temperature superconducting wire 100 may be fixed in a wound state through the diffusion bonding layer 210 .

Hereinafter, an embodiment of the present invention will be described in more detail as follows. However, the following examples are merely illustrative to aid the understanding of the present invention, and the scope of the present invention is not limited thereby.

Prepare a high-temperature superconducting wire that is pancake wound on a circular reel, which is a bobbin for winding, including a metal substrate and a superconducting layer, and deposit silver (Ag) on the upper and lower parts while unwinding the wound high-temperature superconducting wire to form a silver coating film, 10 turns pancake wound at 3kgf on a new reel The high-temperature superconducting wire wound in this way _{was heat-treated under O 2 at} 500° C. for 5 hours to form a single diffusion bonding layer in which the silver coating film does not have an interface. Since the diffusion bonding layer is bonded as a single layer, separation of the wound high-temperature superconducting wire constituting the high-temperature superconducting coil did not occur by physical force.

6 is an SEM photograph of a silver (Ag) diffusion junction. Referring to FIG. 6 , after a silver coating film is formed on the upper and lower parts of the high temperature superconducting wire, the silver coating film is formed on the upper and lower parts of the high temperature superconducting wire at positions adjacent to each other through heat treatment and is in contact with each other by diffusion bonding of silver (Ag). It can be seen that the state of the diffusion bonding layer 210 having no interface due to this occurrence is shown in the SEM photograph.

FIG. 7 is a ×200 enlarged photograph of FIG. 6 . Referring to FIG. 7 , a 200-fold magnification of the silver coating film formed on the upper and lower portions of the high-temperature superconducting wire at positions adjacent to each other through diffusion bonding of silver (Ag) through the heat treatment to form the diffusion bonding layer 210, magnified 200 times. It can be seen that there is no interface in the diffusion bonding layer 210 .

FIG. 8 is a ×1,000 enlarged photograph of FIG. 6 . Referring to FIG. 8, a 1,000-fold magnification of a silver coating film formed on the upper and lower portions of the high-temperature superconducting wire at positions adjacent to each other through diffusion bonding of silver (Ag) through the heat treatment to form the diffusion bonding layer 210, magnified by 1,000 times. It can be seen that there is no interface in the diffusion bonding layer 210 in FIG. 8 as well.

From the above, in the present invention, in a state in which a silver coating film 200 is formed on the upper and lower portions of the high temperature superconducting wire 100, after winding, the silver coating film 200 is bonded to the upper and lower portions of the high temperature superconducting wire 100 adjacent to each other vertically through heat treatment. A high-temperature superconducting wire wound through the diffusion bonding layer 210 by diffusion-moving silver (Ag) atoms from the surface toward the corresponding silver coating film 200 to form a diffusion bonding layer 210 without an interface (I). It can be seen that the shape of (100) can be maintained and fixed.

In particular, as the silver (Ag) atoms of the silver coating film 200 are actively diffused with each other, fixing and integrating the wound high-temperature superconducting wire 100 is ensured, thereby preventing cracking due to the difference in the coefficient of thermal expansion.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains.

Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to illustrate, and the scope of the technical spirit of the present invention is not limited by these embodiments.

The protection scope of the present invention should be construed by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims

A first step of forming a high-temperature superconducting wire including a metal substrate and a superconducting layer;

a second step of forming a silver (Ag) coating film on the upper and lower portions of the high-temperature superconducting wire;

a third step of winding the high-temperature superconducting wire on which the silver coating film is formed; and

A fourth step in which the wound high-temperature superconducting wire is heat-treated to form an interface-free diffusion bonding layer through diffusion bonding of silver (Ag) in the silver coating film formed on the upper and lower portions of the high-temperature superconducting wire and bonded to each other A method of manufacturing a high-temperature superconducting coil using diffusion bonding, comprising:
According to claim 1,

In the fourth step,

A method of manufacturing a high-temperature superconducting coil using diffusion bonding, characterized in that heat treatment is performed at 300-500° C. for 2 to 24 hours in an oxygen atmosphere.
According to claim 1,

In the fourth step,

The high-temperature superconducting wire and the diffusion bonding layer are repeatedly formed in sequence,

The method of manufacturing a high-temperature superconducting coil using diffusion bonding, characterized in that the high-temperature superconducting wires adjacent to each other vertically are fixed in a wound state through the diffusion bonding layer.
A high-temperature superconducting coil using diffusion junction, characterized in that it is formed by any one of claims 1 to 3.