JP2014130730A - Connection structure and connection method of oxide superconductive wire material, and oxide superconductive wire material using the connection structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection structure and connection method of an oxide superconductive wire material.SOLUTION: There is provided a connection structure of first and second oxide superconductive wire materials which an intermediate layer, an oxide superconductive layer and a protective layer containing Ag or Ag alloy are laminated on a tape-like base material and the protective layers near each end of the first and second oxide superconductive wire materials are arranged opposite with each other, a part of the protective layer arranged oppositely is joined by a silver joint layer and a part of the protective layer arranged oppositely is jointed by a solder joint layer.

Description

  The present invention relates to an oxide superconducting wire connecting structure, a connecting method, and an oxide superconducting wire using the connecting structure.

One of the electrical devices that can solve energy problems in recent years is a superconducting device such as a cable, a coil, a motor, and a magnet using an oxide superconductor as a low-loss conductive material. As superconductors used in these superconducting devices, for example, oxide superconductors such as RE-123 series (REBa ₂ Cu ₃ O _7-x : RE is a rare earth element including Y and Gd) are known. This oxide superconductor exhibits superconducting properties near the temperature of liquid nitrogen and can maintain a relatively high critical current density even in a strong magnetic field, and thus is expected as a practically promising conductive material.

  In order to use the above-described oxide superconductor in an electric device, it is common to process the oxide superconductor into a wire and use it as a power supply conductor or coil. Specifically, an oxide superconducting layer is formed on a tape-shaped metal substrate via an intermediate layer having a good crystal orientation, and a protective layer made of Ag or an Ag alloy is formed so as to cover the oxide superconducting layer. An oxide superconducting wire can be obtained by forming a stabilization layer.

  In order to apply the RE-123 series oxide superconducting wire to a practical device, a technique for connecting the oxide superconducting wire is desired. For example, a technique for connecting a protective layer or a stabilization layer of a pair of oxide superconducting wires with solder is known. However, this connection method has a problem that the connection resistance is high because it depends on the electrical resistivity specific to the solder. Therefore, in Patent Document 1, after applying a silver paste to the surface of the protective layer near the end of the oxide superconducting wire to be connected, the conductive metal layers are pressure-bonded in a stage exhibiting fluidity, and dried as they are. A method of integrating by a solid phase reaction in which a silver paste layer is interposed between contact surfaces is disclosed.

Japanese Patent Laid-Open No. 7-192837

  However, in the technique described in Patent Document 1, the connection between the oxide superconducting wires is made by a solid phase reaction of Ag, so that the mechanical strength is weak. There was a risk of the connection being lost. In addition, the resistance value of the connection portion may be increased depending on the components contained in the silver paste used for bonding.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an oxide superconducting wire connection structure and a connection method having high mechanical strength and low connection resistance.

In order to solve the above problems, the oxide superconducting wire connecting structure according to the present invention is a pair of oxides in which an intermediate layer, an oxide superconducting layer, and a protective layer made of Ag or an Ag alloy are laminated on a tape-like substrate. A superconducting wire connecting structure, wherein the protective layers in the vicinity of the end portions of the pair of oxide superconducting wires are opposed to each other, and at least a part of the opposingly arranged protective layers Are bonded by a silver bonding layer, and at least a part of the facing protective layers are bonded by a solder bonding layer.
According to the present invention, the connection resistance of the connection structure can be reduced by having the silver bonding layer at the connection portion between the protective layers of the oxide superconducting wire. Moreover, by having a solder joint layer in a connection part, the silver joint layer with low mechanical strength can be reinforced and the mechanical strength of a connection structure can be improved. In addition, since the solder bonding layer is also conductive, an unexpected excessive load is applied to the connection structure, the silver bonding layer is damaged, and the electrical connection through the silver bonding layer is broken. However, the solder joint layer serves as a bypass, and electrical connection of the connection structure can be prevented from being disconnected.

Further, the oxide superconducting wire connecting structure according to the present invention is characterized in that the silver bonding layer is sandwiched between solder bonding layers in the longitudinal direction of the pair of oxide superconducting wires.
According to the present invention, in the longitudinal direction of the pair of oxide superconducting wires, the protective layers on both sides of the silver bonding layer are bonded to each other by the solder bonding layer, thereby increasing the mechanical strength more effectively. it can.

The oxide superconducting wire connecting structure of the present invention comprises first, second, and third oxide superconducting wires, and the first oxide superconducting wire and the second oxide superconducting wire are The first oxide superconducting wire and the first oxide superconducting wire are arranged so that the ends to be connected are adjacent to each other, and the side on which the oxide superconducting layer is formed is aligned with respect to the base material, and straddles the adjacent ends. The protective layer of the third oxide superconducting wire is bridged to the protective layer of the second oxide superconducting wire, the protective layers of the first and third oxide superconducting wires, and the second and third At least a part of the protective layers of the oxide superconducting wire is joined by a silver bonding layer, and the protective layers of the first and third oxide superconducting wires and the protection of the second and third oxide superconducting wires are protected. At least part of the layers are joined by the solder joint layer It is characterized in that is.
According to the present invention, since the connection resistance is low, the mechanical strength is high, and the pair of oxide superconducting wires to be connected are arranged with the lamination direction aligned, the inversion of the oxide superconducting wire at the connection portion is reversed. It is possible to provide a connection structure without the above.

The oxide superconducting wire of the present invention is an oxide superconducting wire connected by the connection structure, and the outer periphery of the oxide superconducting wire including the connection structure is hermetically sealed from the outside by a plating coating layer or a metal tape. It is covered with.
According to the present invention, the oxide superconducting wire including the connection structure is completely sealed from the outside, and deterioration of the oxide superconducting layer due to moisture can be prevented.

The method for connecting oxide superconducting wires of the present invention uses a pair of oxide superconducting wires having an intermediate layer, an oxide superconducting layer, and a protective layer made of Ag or an Ag alloy on a tape-shaped substrate, and A step of facing the protective layers in the vicinity of each end of the oxide superconducting wire, and sandwiching the foil made of Ag or an Ag alloy between the protective layers; and the foil via the pair of oxide superconducting wires Heating while pressing from the thickness direction, bonding the protective layer and the foil by diffusion bonding to form a silver bonding layer, and a portion where the protective layers are overlaid, the silver bonding layer formed And a step of joining the protective layers in the unfinished region with solder.
ADVANTAGE OF THE INVENTION According to this invention, a connection structure with small connection resistance can be supplied by forming a silver joining layer in the connection part of the protective layers of an oxide superconducting wire. Further, by forming a solder bonding layer at the connection portion, it is possible to reinforce the silver bonding layer having a low mechanical strength and increase the mechanical strength. In addition, since the solder bonding layer is also conductive, an unexpected excessive load is applied to the connection structure, the silver bonding layer is damaged, and the electrical connection through the silver bonding layer is broken. However, the solder joint layer serves as a bypass, and electrical connection of the connection structure can be prevented from being disconnected.

Also, the method for connecting the oxide superconducting wire of the present invention is characterized in that oxygen is supplied to the oxide superconducting layer at the same time by performing the step of bonding by diffusion bonding and forming a silver bonding layer in an oxygen atmosphere. It is characterized by performing an oxygen annealing process for adjusting the structure.
According to the present invention, the heat treatment process for diffusion bonding can be performed simultaneously with the oxygen annealing process for supplying oxygen to the oxide superconducting layer and adjusting its crystal structure, thereby adding new production equipment and manufacturing processes. This is not necessary and can be performed at low cost.

  According to the present invention, the connection resistance of the connection structure can be reduced by having the silver bonding layer at the connection portion between the protective layers of the oxide superconducting wire. Moreover, by having a solder joint layer in a connection part, the silver joint layer with low mechanical strength can be reinforced and the mechanical strength of a connection structure can be improved. In addition, since the solder bonding layer is also conductive, an unexpected excessive load is applied to the connection structure, the silver bonding layer is damaged, and the electrical connection through the silver bonding layer is broken. However, the solder joint layer serves as a bypass, and electrical connection of the connection structure can be prevented from being disconnected.

FIG. 1 is a schematic diagram showing an oxide superconducting wire according to the present invention and its end. It is a cross-sectional schematic diagram which shows 1st Embodiment of the connection structure which concerns on this invention. FIG. 3A is a schematic diagram showing a connection method according to the present invention, FIG. 3A shows a state in which a foil is sandwiched between a pair of oxide superconducting wires, and FIG. 3B shows diffusion bonding and diffusion. FIG. 3C shows a state in which a joined structure is formed, and FIG. 3C shows a state in which a connection structure is formed by performing solder joining. It is a cross-sectional schematic diagram which shows 2nd Embodiment of the connection structure which concerns on this invention. FIG. 5A is a schematic cross-sectional view showing an example in which the connection structure shown in FIG. 4 is airtight with the outside. FIG. 5A shows an example covered with a plating coating layer, and FIG. A covered example is shown.

  Hereinafter, embodiments of an oxide superconducting wire according to the present invention will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

(Oxide superconducting wire)
FIG. 1 is a cross-sectional view of an oxide superconducting wire 1 according to the present invention. The oxide superconducting wire 1 has a structure in which an intermediate layer 11, an oxide superconducting layer 12, and a protective layer 13 are laminated in this order on a tape-like base material 10. Based on FIG. 1, each component of the oxide superconducting wire 1 will be described in detail. However, the present invention is not limited to the following embodiments.

  The base material 10 may be any material that can be used as a base material for a normal oxide superconducting wire, and is preferably a long tape having flexibility. In addition, the material used for the base material 10 preferably has a metal having high mechanical strength, heat resistance, and easy to be processed into a wire, for example, a nickel alloy such as stainless steel or hastelloy. And various heat-resistant metal materials, or materials in which ceramics are arranged on these metal materials. Among them, Hastelloy (trade name, manufactured by Haynes, USA) is preferable as a commercial product. This kind of Hastelloy includes Hastelloy B, C, G, N, W, etc., which have different amounts of components such as molybdenum, chromium, iron, cobalt, etc., and any kind can be used here. Further, as the base material 10, an oriented Ni—W alloy tape base material in which a texture is introduced into a nickel alloy can be used. What is necessary is just to adjust the thickness of the base material 10 suitably according to the objective, Usually, 10-500 micrometers, Preferably it is 20-200 micrometers.

As the intermediate layer 11, for example, a structure in which a diffusion prevention layer, a bed layer, an alignment layer, and a cap layer are stacked in this order can be applied.
As a result of heat treatment when forming another layer on the upper surface of this layer, the diffusion preventing layer diffuses part of the constituent elements of the base material 10 when the base material 10 or other layers receive a thermal history. And it has a function which suppresses mixing into the oxide superconducting layer 12 side as an impurity. The specific structure of the diffusion preventing layer is not particularly limited as long as it can exhibit the above-described function, but Al ₂ O ₃ , Si ₃ N ₄ , or GZO (which has a relatively high effect of preventing contamination of impurities) A single layer structure or a multilayer structure composed of Gd ₂ Zr ₂ O ₇ ) or the like is desirable.

The bed layer is used to suppress the reaction of the constituent elements at the interface between the base material 10 and the oxide superconducting layer 12 and to improve the orientation of the layer provided on the upper surface than this layer. The specific structure of the bed layer is not particularly limited as long as it can exhibit the above functions, but Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , Dy ₂ O ₃ , Er ₂ O, which have high heat resistance. ₃ , a single layer structure or a multilayer structure composed of rare earth oxides such as Eu ₂ O ₃ and Ho ₂ O ₃ is desirable.

The alignment layer controls the crystal orientation of the cap layer and the oxide superconducting layer 12 formed thereon, suppresses the constituent elements of the substrate 10 from diffusing into the oxide superconducting layer 12, 10 and the oxide superconducting layer 12 have a function of reducing a difference in physical characteristics such as a coefficient of thermal expansion and a lattice constant. The material of the alignment layer is not particularly limited as long as it can express the above function, but when a metal oxide such as Gd ₂ Zr ₂ O ₇ , MgO, ZrO ₂ —Y ₂ O ₃ (YSZ) is used, In an ion beam assisted vapor deposition method (hereinafter also referred to as IBAD method) described later, a layer having high crystal orientation is obtained, and the crystal orientation of the cap layer and the oxide superconducting layer 12 can be improved. Particularly preferred.

The cap layer strongly controls the crystal orientation of the oxide superconducting layer 12 to be equal to or higher than that of the oriented layer, diffuses the elements constituting the oxide superconducting layer 12 into the intermediate layer 11, and the oxide superconducting layer 12. It has a function of suppressing the reaction between the gas used when laminating and the intermediate layer 11. The material of the cap layer is not particularly limited as long as it can exhibit the above functions, but is CeO ₂ , LaMnO ₃ , Y ₂ O ₃ , Al ₂ O ₃ , Gd ₂ O ₃ , ZrO ₂ , Ho ₂ O _3. From the viewpoint of lattice matching with the oxide superconducting layer 12, metal oxides such as Nd ₂ O ₃ and Zr ₂ O ₃ are preferable. Among these, CeO ₂ and LaMnO ₃ are particularly suitable from the viewpoint of matching with the oxide superconducting layer 12.
Here, when CeO ₂ is used for the cap layer, the cap layer may include a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.

The oxide superconducting layer 12 has a function of flowing current when in the superconducting state. As the material used for the oxide superconducting layer 12, a material composed of an oxide superconductor having a generally known composition can be widely applied. For example, copper such as RE-123 series superconductor, Bi series superconductor, etc. Examples include oxide superconductors. The composition of the RE-123 series superconductor is, for example, REBa ₂ Cu ₃ O _(7-x) (RE represents a rare earth element such as Y, La, Nd, Sm, Er, Gd, and x represents oxygen deficiency). mentioned, _{specifically, Y123 (YBa 2 Cu 3 O} (7-x)), Gd123 (GdBa 2 Cu 3 O (7-x)) and the like. The composition of the Bi-based superconductor, for _{example, Bi 2 Sr 2 Ca n-} 1 Cu n O 4 + 2n + δ (n is the number of layers of CuO _2, [delta] represents an excess oxygen.) Include. In this copper oxide superconductor, the base material is an insulator, but it becomes an oxide superconductor with a well-crystallized structure by incorporating oxygen by the oxygen annealing treatment described in the connection method described later, and has the property of exhibiting superconducting properties. have.
Moreover, the material of the oxide superconductor layer 12 used in this embodiment is a copper oxide superconductor. Hereinafter, unless otherwise specified, the material used for the oxide superconductor layer 12 is a copper oxide superconductor. .

  The protective layer 13 bypasses an overcurrent generated at the time of an accident, or suppresses a chemical reaction that occurs between the oxide superconducting layer 12 and a layer provided on the upper surface of this layer. It has a function of preventing deterioration of superconducting characteristics caused by entering the other layer and breaking the composition. Moreover, in order to make it easy to take in oxygen to the oxide superconducting layer 12, it has the function to make oxygen permeate | transmit easily at the time of a heating. For this reason, it is preferable that the protective layer 13 is formed from Ag or a material containing at least Ag. The material for forming the protective layer 13 may be a mixture or alloy containing noble metals such as Au and Pt, or an alloy containing In and Pd. A plurality of these may be used.

  1 is provided only on the upper surface of the oxide superconducting layer 12. However, when the protective layer 13 is formed by a film formation method such as sputtering, the base material 10, the intermediate layer 11, the oxidation layer 13 are formed. Ag particles wrap around the side surface of the superconductor layer 12 to form a thin Ag layer, and a thin Ag layer is also formed on the back side of the substrate 10. However, since what is important in the present invention is the portion of the protective layer 13 that covers the upper surface of the oxide superconducting layer 12, the Ag layer formed on the side and back sides of the oxide superconducting wire 1 is particularly problematic. The illustration is omitted.

(First embodiment)
Next, it has a structure equivalent to the oxide superconducting wire 1 described above, but two oxide superconducting wires before the oxygen annealing treatment are prepared, one of which is the first oxide superconducting wire 2, and the other As a second oxide superconducting wire 3, a connection structure 30 of the first embodiment in which these are connected will be described with reference to FIG.

  As shown in FIG. 2, the connection structure 30 of the first embodiment is a structure that connects the first oxide superconducting wire 2 and the second oxide superconducting wire 3. The first and second oxide superconducting wires 2 and 3 are arranged such that the protective layers 13 in the vicinity of the end portions 2a and 3a face each other and are overlapped with each other. Are joined by a silver bonding layer 14. Further, in the longitudinal direction of the first and second oxide superconducting wires 2 and 3, the protective layers 13 on both sides of the silver bonding layer 14 are bonded to each other by the solder bonding layer 22 to constitute the connection structure 30. .

The silver bonding layer 14 is made of Ag or an Ag alloy bonded to the protective layer 13 by diffusion bonding. As the Ag alloy, for example, an Ag—In alloy or an Ag—Pd alloy can be used. The diffusion bonding is a bonding method in which Ag is solid-phase diffused by applying pressure to the bonding surfaces and performing heat treatment at 300 to 600 ° C.
Conventionally known solder can be used for the solder bonding layer 22, for example, In solder containing In as a main component, Sn, Sn—Ag alloy, Sn—Bi alloy, Sn—Cu alloy, Sn—Zn. Sn solder made of an alloy containing Sn as a main component, such as a Pb-based alloy, Pb—Sn-based alloy solder, eutectic solder, low-temperature solder, and the like can be used. These solders can be used alone or in combination of two or more. . Among these, it is preferable to use solder having a melting point of 300 ° C. or less.

Since Ag or Ag alloy has a low volume resistivity, the connection resistance of the connection structure 30 can be reduced by providing the silver bonding layer 14 at the connection portion. However, since the silver bonding layer 14 is bonded to the protective layers 13 and 13 of the first and second oxide superconducting wires 2 and 3 by diffusion bonding, the mechanical strength is low.
In the present embodiment, the protective layers 13 on both sides of the silver bonding layer 14 are bonded to each other by the solder bonding layer 22 in the longitudinal direction of the first and second oxide superconducting wires 2 and 3. Since the solder bonding layer 22 has high mechanical strength and the solder bonding layer 22 reinforces both sides of the silver bonding layer 14, the mechanical strength of the connection structure 30 can be increased.

Further, since the solder bonding layer 22 has high conductivity, an unexpected excessive external force or the like is applied to the connection structure 30, so that the bonding portion between the silver bonding layer 14 and the protective layers 13 and 13 is damaged, and the silver bonding Even when the electrical connection through the layer 14 is disconnected, the solder bonding layer 22 serves as a bypass, and the electrical connection of the connection structure 30 can be prevented from being disconnected.
In this embodiment, the solder bonding layer 22 is formed on both sides of the silver bonding layer 14 in the longitudinal direction, but the solder bonding layer 22 may be formed only on one side of the silver bonding layer 14.

(Connection method for oxide superconducting wire)
Next, a connection method in which the first and second oxide superconducting wires 2 and 3 are connected to form the connection structure 30 will be described with reference to FIGS. 3 (a), 3 (b), and 3 (c).
First, as shown in FIG. 3A, the vicinity of the end portions 2a and 3a of the first oxide superconducting wire 2 and the second oxide superconducting wire 3 are overlapped. When superposing, a foil 14A made of Ag or an Ag alloy is sandwiched between the protective layer 13 of the first oxide superconducting wire 2 and the protective layer 13 of the second oxide superconducting wire 3.
The foil 14A is preferably made of the same type of metal as the protective layer 13. For example, when the protective layer 13 is made of Ag, an Ag—In alloy, or an Ag—Pd alloy, Ag, an Ag—In alloy, an Ag—Pd alloy, or the like can be used as the foil 14A. Among these, it is most preferable that both the protective layer 13 and the foil 14A are Ag.

  When both the protective layer 13 and the foil 14A are made of Ag, the thickness of the foil 14A is preferably 0.1 μm or more and 50 μm or less. When the thickness is less than 0.1 μm, diffusion bonding between the protective layer 13 and the foil 14A is difficult to occur. In addition, since the height of the gap 16 is narrow, it is difficult to fill the gap 16 with solder when forming the solder bonding layer 22 in a later process. On the other hand, if the thickness is larger than 50 μm, a step formed between the first oxide superconducting wire 2 and the second oxide superconducting wire 3 in the connection structure 30 becomes large, and the connection structure 30 is wound in a coil shape. When it is turned, the winding becomes uneven due to the step. As a result, the magnetic field generated when current is passed through the wound oxide superconducting wires 2 and 3 may be non-uniform. Further, if the winding is not uniform, the unwinding speed is not constant when the coil wound in the manufacturing process is unwound, which may cause a problem.

The foil 14 </ b> A is disposed over the entire width of the overlapping portion using an object having substantially the same width as that of the first and second oxide superconducting wires 2 and 3. Further, the foil 14A is the center of the overlapping portion of the first and second oxide superconducting wire 2, the length is disposed over the H _14, from both sides of the foil 14A at the overlapping portions of the first and second end 2a of the oxide superconducting wire 2, the 3a, each gap 16 of length _{H 16, H 16} are provided.

  Next, by sandwiching an overlapping portion of the first and second oxide superconducting wires 2 and 3 from the thickness direction with a vise (vise) or the like, the first and second oxide superconducting wires 2 and 3 are interposed. Then, pressure is applied to the foil 14A. The pressure is preferably 1 to 30 MPa. When the pressure is less than 1 MPa, diffusion bonding between the protective layer 13 and the foil 14A does not occur. Further, when the pressure is increased at a pressure exceeding 30 MPa, the oxide superconducting layer 12 may be cracked in the crystal structure to deteriorate the superconducting characteristics.

In a state where the overlapping portion of the first and second oxide superconducting wires 2 and 3 is pressurized by a vice, the heat treatment is performed by storing in a heating furnace having an oxygen atmosphere. The heat treatment time is 10 to 25 hours when the temperature of the heating furnace is 300 to 500 ° C., and 1 to 25 hours when the temperature of the heating furnace is 500 to 600 ° C. By performing such heat treatment, the foil 14A and the protective layers 13 and 13 of the first and second oxide superconducting wires 2 and 3 are diffusion-bonded to form a silver bonding layer 14, and FIG. The diffusion bonded body 31 shown in FIG.
Further, oxygen annealing is simultaneously performed by heating in an oxygen atmosphere. That is, by supplying oxygen to the oxide superconducting layers 12 of the first and second oxide superconducting wires 2 and 3 via the protective layer 13 and adjusting the crystal structure thereof, the oxide superconductor having good superconducting characteristics. The oxide superconducting layer 12 is made of the above crystal.

  The heat treatment step in which the foil 14A and the protective layers 13 and 13 of the first and second oxide superconducting wires 2 and 3 are diffusion bonded and the silver bonding layer 14 is formed can be performed simultaneously with the oxygen annealing step. There is no need to add new production equipment and manufacturing processes, and it can be performed at low cost.

Next, after removing from the heating furnace and sufficiently cooling the gap 16 of the diffusion bonded body 31, a solder foil of approximately the same thickness as the gap 16 or slightly thinner is inserted and the diffusion bonded body 31 is heated to melt the solder. Then, the solder is solidified by cooling, and a solder bonding layer 22 is formed as shown in FIG. The heating means is not particularly limited, but can be heated by, for example, a soldering iron.
The temperature at the time of heating the solder is preferably 300 ° C. or less. Thereby, it can suppress that the characteristic of the oxide superconducting layer 12 which performed the oxygen annealing process with the heat of soldering deteriorates.
Through the above steps, the connection structure 30 can be formed.

(Second Embodiment)
Next, it has the same structure as the oxide superconducting wire 1 described with reference to FIG. 1, but three oxide superconducting wires before the oxygen annealing treatment are prepared, and these are the first oxide superconducting wires. 4, the connection structure 32 of 2nd Embodiment connected as the 2nd oxide superconducting wire 5 and the 3rd oxide superconducting wire 6 is demonstrated based on FIG. In addition, about the component same as the above-mentioned 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

As shown in FIG. 4, the connection structure 32 has a configuration in which the first oxide superconducting wire 4 and the second oxide superconducting wire 5 are connected via the third oxide superconducting wire 6.
That is, in the connection structure 32, the first oxide superconducting wire 4 and the second oxide superconducting wire 5 are adjacent to each other with the end portions 4 a and 5 a provided with a predetermined gap 7. In addition, the lamination direction of the 1st and 2nd oxide superconducting wire 4 and 5 corresponds. Further, the protective layer 13 of the third oxide superconducting wire 6 is bridged to the protective layer 13 of the first and second oxide superconducting wires 4 and 5 so as to straddle the end portions 4a and 5a. And the protective layers 13 and 13 of the third oxide superconducting wires 4 and 6, and at least a part of the protective layers 13 and 13 of the second and third oxide superconducting wires 5 and 6 are silver bonding layers 14. And at least a part of the protective layers 13 and 13 of the first and third oxide superconducting wires 4 and 6 and the protective layers 13 and 13 of the second and third oxide superconducting wires 5 and 6. Are bonded by the solder bonding layer 22.

The connection structure 32 of the second embodiment is different from the connection structure 30 of the first embodiment described above in one end of the first oxide superconducting wire 4 (in the vicinity of the end 4a) and one end of the third oxide superconducting wire 6. (Applied to and near the first end portion 6a), and connected to the other end of the third oxide superconducting wire 6 (near the second end portion 6b) and one end (end portion) of the second oxide superconducting wire 5. It can be explained that the connection is applied to the vicinity of 5a.
With such a structure, it is possible to provide a connection structure that not only exhibits the various effects of the first embodiment but also does not cause the reverse of the oxide superconducting wire at the connection portion.

(Coated connection structure)
FIG. 5A shows an example in which the oxide superconducting wires 4, 5, and 6 connected by the connection structure 32 of the second embodiment are covered with the plating coating layer 20 in an airtight manner.
A protective layer 13 is provided on the oxide superconducting layer 12 of the oxide superconducting wires 4, 5, and 6 to prevent the oxide superconducting layer 12 from being deteriorated by moisture. However, the protective layer 13 is likely to generate pinholes and cannot reliably prevent the ingress of moisture, and may react with moisture contained in the air or the like to deteriorate the superconducting characteristics. Further, in the connection structure 32 shown in FIG. 4, the end portions 4a, 5a, 6a, and 6b of the first, second, and third oxide superconducting wires 4, 5, and 6 are exposed. In the portions 4a, 5a, 6a, and 6b, the oxide superconducting layer 12 may react with moisture to deteriorate the superconducting characteristics.
Thus, the oxide superconducting wire 33 including the connection structure 32 can be covered with the plating coating layer 20 to form the oxide superconducting wire 33 having a structure that prevents moisture from entering.

  The thickness of the plating coating layer 20 is desirably 10 μm or more and 100 μm or less. When the thickness of the plating coating layer 20 is smaller than 10 μm, a pinhole may occur in the plating coating layer 20, and there is a possibility that moisture may enter from the pinhole. Moreover, when the thickness of the plating coating layer 20 exceeds 100 μm, the thickness of the oxide superconducting wire 33 becomes too thick, which may cause inconvenience in use, and also increases the plating cost. Therefore, the thickness of the plating coating layer 20 is desirably 10 μm or more and 100 μm or less.

Since the base material 10 and the oxide superconducting layer 12 have a higher electrical resistance than the protective layer 13 at room temperature, it is difficult to form the plating coating layer 20 only by a normal electrolytic plating method. Therefore, the plating coating layer 20 having a thickness of 10 μm or more can be formed only by electroless plating, or after the metal coating is covered with a metal by the electroless plating method, the metal layer can be further thickened by the electrolytic plating method. it can.
Examples of the metal used for the plating coating layer 20 include copper, nickel, gold, silver, chromium, tin, and the like, and one or a combination of two or more of these metals can be used.
Further, when a metal having good conductivity is used as the metal used for the plating coating layer 20, the plating coating layer 20 functions as a stabilization layer that plays a role of bypassing overcurrent generated at the time of an accident together with the protective layer 13. To do.

FIG. 5B shows an example in which the oxide superconducting wires 4, 5, and 6 connected by the connection structure 32 of the second embodiment are covered with the metal tape 21 in an airtight manner.
The metal tape 21 is formed through the solder layer 23 so as to airtightly cover the periphery of the oxide superconducting wires 4, 5, 6 including the connection structure 32, and has a structure that prevents moisture from entering. 34 is configured.

  The oxide superconducting wire 34 having a structure covered with the metal tape 21 is formed on the surface of the metal tape 21 provided with the solder layer 23 on one side or both sides, and the oxide superconducting wires 4, 5, 6 including the connection structure 32. Is formed by wrapping and bending the peripheral surfaces of the oxide superconducting wires 4, 5, and 6 so as to form a substantially C-shaped cross section, and heating and melting the solder layer 23 and pressurizing it with a roll. Can do. Alternatively, the oxide superconducting wires 4, 5, 6 may be formed so as to be hermetically covered by spirally winding a metal tape 21 provided with a solder layer 23 on the outer periphery.

The metal tape 21 and the connection structure 32 are joined via the solder layer 23. The connection structure 32 has a step near the ends 6a and 6b of the third oxide superconducting wire 6 because the third oxide superconducting wire 6 is bridged. It is desirable to be filled with 23a. Further, it is desirable that the gap 7 formed between the end portions 4a and 5a of the first and second oxide superconducting wires 4 and 5 is also filled with the solder filling portion 23b.
Note that FIG. 5B is a schematic cross-sectional view showing the steps formed in the connection structure 32 in an emphasized manner, but actually the length in the longitudinal direction of the connection structure 32 is shown. The step is sufficiently small and can be easily filled with solder.

  Although it does not specifically limit as a metal material which comprises the metal tape 21, It is preferable to use what consists of comparatively cheap materials, such as copper, brass (Cu-Zn alloy), copper alloys, such as Cu-Ni alloy, and stainless steel. Of these, copper is preferable because it has high conductivity and is inexpensive. When the oxide superconducting wire 34 is used for a superconducting fault current limiter, the material used for the metal tape 21 is preferably a high resistance metal such as a Ni-based alloy such as Ni—Cr.

  Even when the oxide superconducting wires 4, 5, 6 including the connection structure 32 are covered with the metal tape 21, the same effect as that obtained when the plating coating layer 20 is used can be obtained.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to these Examples.
(Sample preparation)
An Al ₂ O ₃ (diffusion prevention layer; film thickness 150 nm) film was formed by sputtering on a tape-shaped Hastelloy (trade name, manufactured by Haynes, USA) having a width of 10 mm and a thickness of 0.1 mm. On top, Y ₂ O ₃ (bed layer; film thickness 20 nm) was formed by ion beam sputtering. Next, MgO (metal oxide layer; film thickness: 10 nm) is formed on the bed layer by ion beam assisted vapor deposition (IBAD method), and 0.5 μm thick is formed thereon by pulse laser vapor deposition (PLD method). CeO ₂ (cap layer) was formed. Next, a 2.0 μm-thick GdBa ₂ Cu ₃ O _7-δ (oxide superconducting layer) is formed on the CeO ₂ layer by a PLD method, and a 10 μm-thick Ag layer (protective layer) is formed on the oxide superconducting layer by a sputtering method. ) Was formed. Thereby, a plurality of oxide superconducting laminates shown in FIG. 1 were produced. This oxide superconducting wire is commonly used in the following examples and comparative examples.

A pair of the oxide superconducting wires described above is prepared, these protective layers are faced to each other, and the vicinity of the end portion is overlapped by 80 mm, the width is 10 mm, the length is 40 mm (that is, H ₁₄ = 40 mm in FIG. 3A), and the thickness is 25 μm. The foils made of Ag were stacked on top of each other. The distance from each end of the pair of oxide superconducting wires to the foil was 20 mm (that is, H ₁₆ = 20 mm in FIG. 3A).

Next, the portion sandwiching the foil is sandwiched between stainless steel vice, a pressure of 10 MPa is applied to the foil, the state is stored in a heating furnace in an oxygen atmosphere, and heat treatment is performed at 500 ° C. for 5 hours. And a protective layer of a pair of oxide superconducting wires were diffusion bonded, and at the same time, an oxygen annealing treatment was performed to form a diffusion bonded body (see FIG. 3B).
Further, after the diffusion bonded body is taken out from the heating furnace and sufficiently cooled, a 20 μm In solder foil is inserted, and the In solder is melted by a soldering iron heated to 250 ° C. and then solidified to form a solder bonding layer. Then, a connection structure was formed (see FIG. 3C), and the sample of Example 1 was manufactured.

In the preparation procedure of Example 1 described above, a pair of oxide superconducting wires were subjected to oxygen annealing treatment, and then overlapped by 80 mm, and the entire overlapped region was joined by In solder to produce a connection structure of Comparative Example 1.
Further, in the manufacturing procedure of Example 1 described above, a pair of oxide superconducting wires are overlapped by 80 mm, an Ag foil having the same shape as the overlapped region is sandwiched by a vice, and a pressure of 10 MPa is applied to the foil. The connection structure of Comparative Example 2 was fabricated by heat treatment (same conditions as in Example 1) in which it was stored in a heating furnace in an oxygen atmosphere as it was and oxygen annealing treatment was performed simultaneously with diffusion bonding.

(Evaluation method and results)
The connection structures of the samples of Example 1 and Comparative Examples 1 and 2 were subjected to connection resistance measurement and bending test. The connection resistance was measured by passing an electric current through each connection sample in liquid nitrogen. Also, in the bending test, the connection structure of each sample was bent at a bending radius of 200 mm, 100 mm, and 50 mm along the stacking direction, and then it was visually determined whether or not the diffusion bonding portion and the solder bonding portion were damaged. .
Table 1 shows the measurement results of the connection resistance together with the area of the joint.
Table 2 shows the results of the bending test as ◯ when no damage was observed by visual inspection, and x when damage was observed.
When referring to Table 1, pay attention to the difference in digits (difference in index of 10) in connection resistance values.

(Comparison of Examples and Comparative Examples)
When Example 1 and Comparative Examples 1 and 2 are compared with reference to the values of connection resistance values in Table 1, the connection resistance of Comparative Example 2 (connection only by diffusion bonding) is the lowest, and then Example 1 (diffusion bonding and The connection resistance of the connection by solder bonding) is low, and the connection resistance of Comparative Example 1 (connection by only solder bonding) is the highest.
On the other hand, referring to the results of the bending test in Table 2, in Comparative Example 2, damage at the joint was observed at bending radii of 100 mm and 50 mm. In contrast, no damage was observed in Example 1 and Comparative Example 1.
From these results, it was found that the connection resistance can be lowered by connection only by diffusion bonding (Comparative Example 2), but the mechanical strength against bending is weak, and the joint portion is damaged by bending of 100 mm or less. In addition, it was confirmed that in the connection only by solder bonding (Comparative Example 1), the bending resistance of 50 mm or more is not damaged and has high mechanical strength but relatively high connection resistance.
The connection by diffusion bonding and solder bonding (Example 1) is a connection structure in which mechanical strength is ensured and connection resistance is low, and the mechanical strength and connection resistance are balanced. It can be said.
From these, the superiority of the present connection structure and connection method according to the present invention was confirmed.

DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting wire, 2, 4 ... 1st oxide superconducting wire, 2a, 3a, 4a, 5a, 6a, 6b ... End part, 3, 5 ... 2nd oxide superconducting wire, 6 ... 3rd Oxide superconducting wire, 7 ... gap, 10 ... substrate, 11 ... intermediate layer, 12 ... oxide superconducting layer, 13 ... protective layer, 14 ... silver bonding layer, 14A ... foil, 16 ... gap, 22 ... solder bonding Layer, 30 ... Connection structure, 31 ... Diffusion bonded body, H ₁₄ , H ₁₆ ... Length

Claims (6)

A connection structure of a pair of oxide superconducting wires in which an intermediate layer, an oxide superconducting layer, and a protective layer made of Ag or an Ag alloy are laminated on a tape-shaped substrate,
The protective layers in the vicinity of each other end of the pair of oxide superconducting wires are arranged to face each other,
At least a part of the opposing protective layers is bonded by a silver bonding layer,
A connecting structure for an oxide superconducting wire, wherein at least a part of the opposing protective layers are bonded by a solder bonding layer.   2. The oxide superconducting wire connecting structure according to claim 1, wherein the silver bonding layer is sandwiched between solder bonding layers in a longitudinal direction of the pair of oxide superconducting wires. Comprising first, second and third oxide superconducting wires;
The first oxide superconducting wire and the second oxide superconducting wire are arranged such that the ends to be connected are adjacent to each other, and the side on which the oxide superconducting layer is formed is aligned with the base material,
The protective layer of the third oxide superconducting wire is bridged to the protective layer of the first oxide superconducting wire and the second oxide superconducting wire so as to straddle the adjacent ends.
At least a part of the protective layers of the first and third oxide superconducting wires and the protective layers of the second and third oxide superconducting wires are bonded by a silver bonding layer,
The protective layers of the first and third oxide superconducting wires and at least a part of the protective layers of the second and third oxide superconducting wires are joined by a solder joint layer. The connection structure of the oxide superconducting wire according to claim 1 or 2. An oxide superconducting wire connected by the connection structure according to any one of claims 1 to 3,
An oxide superconducting wire, wherein an outer periphery of the oxide superconducting wire including the connection structure is airtightly covered with a plating coating layer or a metal tape. Using a pair of oxide superconducting wires having a protective layer made of an intermediate layer, an oxide superconducting layer, and Ag or an Ag alloy on a tape-shaped substrate,
A step of facing the protective layers in the vicinity of each other end of the pair of oxide superconducting wires, and overlapping with a foil made of Ag or an Ag alloy interposed therebetween;
Heating while pressing the foil from the thickness direction through the pair of oxide superconducting wires, bonding the protective layer and the foil by diffusion bonding to form a silver bonding layer;
Connecting the oxide superconducting wire, wherein the protective layer is a portion where the protective layers are overlapped with each other, and the protective layer in a region where the silver bonding layer is not formed is bonded with solder. Method.   The oxygen annealing process is performed, in which the step of forming a silver bonding layer by bonding by diffusion bonding is performed in an oxygen atmosphere, and oxygen annealing is simultaneously performed to supply oxygen to the oxide superconducting layer to adjust its crystal structure. Item 6. A method for connecting an oxide superconducting wire according to Item 5.

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