JP3836299B2 - Connecting method of oxide superconductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for connecting an oxide superconducting conductor used in the fields of superconducting power cables, superconducting magnets, superconducting energy storage devices, superconducting power generation devices, medical MRI devices, superconducting current leads, and the like.
[0002]
[Prior art]
Oxide superconducting conductors include YBCO, etc. by chemical vapor deposition (CVD) etc. on a tape-like substrate made of various metal materials such as silver, platinum, stainless steel, copper, nickel alloy such as Hastelloy. A thin film of an oxide superconducting conductor is known.
In such a tape-shaped oxide superconducting conductor, research and development have been advanced to obtain an oxide superconducting layer having excellent crystal orientation and to obtain an oxide superconducting conductor having a high critical current density. As such an oxide superconducting conductor, an intermediate layer made of yttrium-stabilized zirconia (YSZ) or the like having an excellent crystal orientation is formed on a base material, and an oxide superconducting conductor is formed thereon. It has been.
[0003]
By the way, in order to apply such a tape-shaped oxide superconducting conductor to practical equipment, it is indispensable to establish a technology for connecting the oxide superconducting conductor, and the development thereof is desired.
As a method for connecting an oxide superconducting conductor obtained by depositing an oxide superconducting layer on such a tape-like substrate, a method for connecting an oxide superconducting conductor disclosed in Japanese Patent No. 2688923 is known. In this method of connecting oxide superconductors, a plurality of oxide superconductors are placed in contact with each other in a vacuum vessel, the oxide superconductors are heated, and the above-mentioned contact is made from the nozzle toward the contact portion. Superfine powder of the same material as that of the oxide superconducting conductor is ejected and deposited at the contact portion, and is sintered to join these oxide superconducting conductors.
[0004]
[Problems to be solved by the invention]
However, in such an oxide superconductor connection method, since the oxide superconductor thin film is only formed on the contact portion of the oxide superconductor, its stability for use in various applications is obtained. Was insufficient, and there was a problem in the strength of the joint. There is also a problem that the critical current density in the oxide superconductor after connection is lowered.
[0005]
In order to solve the problems such as the strength of the connection part and the decrease in the critical current density, the present inventors previously described in Japanese Patent Application No. 10-310264 the following oxide superconductors: The connection structure and connection method are proposed.
First, a first connection structure and a connection method as shown in FIG. 11 have been proposed. In this example, an intermediate layer 2 is formed on a tape-like substrate 1, an oxide superconducting layer 3 is formed on the intermediate layer 2, and a stabilized silver layer 4 is further formed on the oxide superconducting layer 3. The stabilized silver layer 4 is formed on the tape-shaped oxide superconductor 5, and a part of the stabilized silver layer 4 is joined via the solder 6. In this method, two oxide superconducting conductors 5 and 5 are connected.
In this method, the oxide superconducting layer 3 is used to reduce the resistance in metal layers such as the solder 6 and the stabilized silver layer 4 and the contact resistance generated between the stabilized silver layer 4 and the oxide superconducting layer 3. Is added to reduce the conductor wrap area W (contact surface).
[0006]
Further, a second connection structure and a connection method as shown in FIG. 12 have been proposed. In this example, an intermediate layer 12 is formed on a tape-like substrate 11, an oxide superconducting layer 13 is formed on the intermediate layer 12, and a stabilized silver layer 14 is further formed on the oxide superconducting layer 13. This is a method for connecting the oxide superconductors 15 and 15 to each other using the short superconducting tape 18 as a molten binder. Specifically, the end portions of the oxide superconducting conductors 15 and 15 are butted together, and a superconducting tape 18 in which the oxide superconducting layer 17 is formed on the silver base material 16 is melt-bonded on the connecting portion, and stable on these. The silver halide layer 14 is formed. In this method, in order to ensure the strength of the joint portion, the superconducting tape 18 is used and the surface of the connection portion is covered with the stabilized silver layer 14. If it does in this way, the base material 11 and the intermediate | middle layer 12 are high intensity | strength and a high melting-point material, the connection of the base materials 11 and 11 is difficult, and the base materials 11 and 11 are still faced | matched Even in such a case, the strength of the connecting portion can be ensured.
[0007]
The present invention has the same problems as those of the preceding inventions, and further advances these inventions. The connection work of the oxide superconductor is easier, the strength of the connection is high, and the oxide superconductor It is an object of the present invention to obtain a method for connecting an oxide superconducting conductor that is improved in stability and has little reduction in critical current density even after connection.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the first invention, a method for connecting oxide superconducting conductors in which an oxide superconducting layer is formed on a tape-like base material, the ends of each oxide superconducting conductor Then, the oxide superconducting layer at the end portion is removed to expose a part of the base material, and then the exposed base materials of each oxide superconducting conductor are butted together and then joined. A connecting oxide superconducting layer for connecting each oxide superconducting layer is formed on the part, the exposed part, and each oxide superconducting layer so as to straddle them, and then connected to the oxide superconducting layer. Provided is a method for connecting an oxide superconducting conductor , in which a surface protective layer is formed on the oxide superconducting layer so as to straddle them.
In this connection method, it is preferable that the length in the joining direction of the contact portion between one oxide superconductor and the other oxide superconductor of the connecting oxide superconductor layer is 10 to 30 mm.
[0009]
The second invention is a method for connecting oxide superconducting conductors in which an oxide superconducting layer is formed on a tape-shaped base material, at the end of each oxide superconducting conductor, The oxide superconducting layer is removed to expose a part of the base material, and then the exposed base materials of each oxide superconducting conductor are butt-joined to each other. Then, a noble metal layer for connection is formed, and then an oxide superconductor layer for connection for connecting the oxide superconductor layer of each oxide superconductor is formed on the noble metal layer for connection and the oxide superconductor layer. Provided is a method for connecting an oxide superconducting conductor which is formed so as to straddle and then forms a surface protective layer on the oxide superconducting layer and the connecting oxide superconducting layer so as to straddle them.
In this connection method, it is preferable that the length of the contact portion between one oxide superconductor and the other oxide superconductor in the connection oxide superconductor layer is 10 to 30 mm.
Further, these connection methods can be effectively used for an oxide superconducting conductor using silver as a base material.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As an oxide superconducting conductor to which the method for connecting oxide superconducting conductors of the present invention is applied, for example, a structure as shown in FIG. 1 is suitable.
The oxide superconducting conductor 25 is obtained by forming an oxide superconducting layer 23 on a tape-like base material 21.
As the base material 21 of the oxide superconducting conductor 25 having such a structure, various metal materials such as silver, platinum, stainless steel, copper, nickel alloy such as Hastelloy are used. Among them, silver (hereinafter, Ag and Are preferably used.
[0011]
The oxide superconductor constituting the oxide superconducting layer 23 is represented by a composition of Y ₁ Ba ₂ Cu ₃ O _7-x , Y ₂ Ba ₄ Cu ₈ O _y , and Y ₃ Ba ₃ Cu ₆ O _y. YBCO type, or (Bi, Pb) ₂ Ca ₂ Sr ₂ Cu ₃ O _y , (Bi, Pb) ₂ Ca ₂ Sr ₃ Cu ₄ O _y , or Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _An oxide superconductor with a high critical temperature typified by a composition such as _y , Tl ₁ Ba ₂ Ca ₂ Cu ₃ O _y , Tl ₁ Ba ₂ Ca ₃ Cu ₄ O _y, etc. is used. In such a case, a YBCO-based oxide superconducting conductor is preferably used.
[0012]
The oxide superconducting conductor 25 having such a structure has the following characteristics. Ag is a nonmagnetic, low-resistance metal material and has a role of stabilizing the oxide superconductor. Therefore, in the oxide superconducting conductor 25 using Ag as the base material 21, since the base material 21 plays a role as a stabilizing material, a stabilizing layer such as a stabilizing silver layer or the like is not provided on the surface. Also good.
Ag has a lattice constant close to that of an oxide superconductor, particularly a YBCO crystal, and has a low reactivity with YBCO. Therefore, if Ag is used for the base material 21, the oxide superconducting layer 23 (in particular, the YBCO layer) having in-plane orientation can be formed without forming an intermediate layer thereon.
In such an oxide superconducting conductor 25, compared to an oxide superconducting conductor in which an intermediate layer is formed on another metal substrate, the connection of the substrate 21 portion is relatively easy, and at the same time, the substrate 21 itself is Since it serves as a stabilizer, it is not necessary to form a stabilized silver layer.
[0013]
As a method for connecting such oxide superconducting conductors 25, first, as shown in FIG. 2, a part of the oxide superconducting layers 23, 23 at the connecting end portions of the plurality of oxide superconducting conductors 25, 25 to be connected is formed. The substrate 21 is exposed by removing.
As a method for removing the oxide superconducting layer 23, phosphoric acid etching, laser etching, or the like is used.
The connection portion etched in this way is about 1 to 10 mm.
[0014]
Next, as shown in FIG. 3, the exposed end portions of the base materials 21 and 21 of the oxide superconducting conductors 25 and 25 are brought into contact with each other, and are heated and pressed to join the base materials 21 and 21 together. To do. The heating temperature at this time is preferably a temperature near the melting point at which the base material 21 is in a semi-molten state. For example, when silver is used for the base material 21, the heating temperature is 961 to 963 ° C. In this case, if the temperature is less than 961 ° C., the base material 21 is not sufficiently bonded, and if it exceeds 963 ° C., the base material 21 portion becomes completely liquid and becomes inconvenient.
Next, the surface of the bonded portion is polished and flattened.
[0015]
Next, as shown in FIG. 4, a connecting oxide superconducting layer 26 made of an oxide superconductor made of the same material as that of the oxide superconducting layer 23 is formed at this junction.
As a method for forming the connecting oxide superconducting layer 26 at this time, an RF sputtering method or a CVD method is used.
In the CVD method at this time, the oxygen partial pressure condition is set to be slightly higher than usual so that the already formed oxide superconducting layer 23 is not damaged, that is, is not melted.
At this time, the thickness of the connecting oxide superconducting layer 26 is preferably up to about twice the thickness of the oxide superconducting layer 23.
[0016]
In addition, the length A of the contact portion between one oxide superconducting conductor 25 and the other oxide superconducting conductor 25 in the connecting oxide superconducting layer 26 varies depending on the strength of the intended connecting portion. A range of ˜30 mm is preferred. If the wrap length is less than 10 mm, the connection between the oxide superconducting conductors 25 becomes insufficient, and if it exceeds 30 mm, it is uneconomical because it requires formation costs and labor.
[0017]
Next, as shown in FIG. 5, a surface protective layer 24 is formed on the connecting oxide superconducting layer 26 and the oxide superconducting layer 23.
The surface protective layer 24 is made of a noble metal, and examples of the noble metal include gold, platinum, and silver. Among these, silver is highly effective as a stabilizing material and is preferably used.
According to such a connection method of the oxide superconducting conductor 25, the oxide superconducting conductor can be easily connected and the strength of the connecting portion is high because the base materials 21 are joined to each other.
[0018]
Next, a second embodiment of the method for connecting oxide superconducting conductors of the present invention will be described. An oxide superconducting conductor suitable for carrying out this connection method includes the structure shown in FIG. Hereinafter, this connection method will be described with reference to FIGS.
First, as shown in FIG. 6, in the same manner as in the first embodiment, a part of the oxide superconducting layers 23, 23 at the connection end of the oxide superconducting conductor 25 is removed to expose the base materials 21, 21. Let
Next, as shown in FIG. 7, in the same manner as in the first embodiment, these oxide superconducting conductors 25 and 25 are brought into contact with each other with the ends where the base materials 21 and 21 are exposed, and these are heated. The base materials 21 and 21 are joined by pressure welding.
Next, the surface of the bonded portion is polished and flattened.
[0019]
Next, as shown in FIG. 8, a connection layer 31 made of a noble metal is formed at this joined portion. The connection layer 31 is provided to fill a step between the base material 21 and the oxide superconducting layer 23. By providing this connection layer 31, the stability at the connection portion is further improved, and the discontinuity at the step can be eliminated.
The thickness of the connection layer 31 is set to 1 × 10 ⁻⁶ to 2 × 10 ⁻⁶ m, and any thickness that can eliminate the step is used.
The connection layer 31 can be formed by a film forming method such as an RF sputtering method or a CVD method, and is made of an oxide superconductor made of the same material as the oxide superconducting layer 23. As conditions for sputtering at this time, for example, RF power 300 W, pressure 6.5 × 10 ⁻¹ Pa, and room temperature can be used.
Examples of the noble metal include gold, platinum, silver, and the like. Among them, silver is highly effective as a stabilizer and is preferably used.
[0020]
Next, in order to connect the oxide superconducting layer 23, a connecting oxide superconducting layer 32 made of an oxide superconductor made of the same material as the oxide superconducting layer 23 is formed.
As a method for forming the connecting oxide superconducting layer 32, a film forming method such as a CVD method is used.
[0021]
Further, the length B of the contact portion of the connecting oxide superconducting layer 32 between the one oxide superconducting conductor 25 and the other oxide superconducting conductor 25 differs depending on the strength of the intended connecting portion. A range of ˜30 mm is preferable, and if the length of the wrap length is less than 10 mm, the connection between the oxide superconducting conductors 25 becomes insufficient.
[0022]
Next, a surface protective layer 34 is formed on the connecting oxide superconducting layer 32 and the oxide superconducting layer 23. The thickness of the surface protective layer 34 is preferably 1 × 10 ^{−6 to} 3 × 10 ⁻⁶ m.
The surface protective layer 34 is made of a noble metal, and examples of the noble metal include gold, platinum, silver, etc. Among them, silver is highly effective as a stabilizer and is preferably used.
[0023]
According to such a connection method, the oxide superconducting conductors 25 can be easily connected to each other, the base material 21 is joined, and the connection layer 31 and the connecting oxide superconducting layer 32 are formed. The strength of the part is also high.
According to such a connection method, since the connection layer 31 is provided, the connection portions of the oxide superconducting conductors 25 and 25 have high stability and high strength. In addition, the decrease in critical current density can be minimized, and the oxide superconducting conductor 25 is useful as a connection method.
[0024]
【Example】
(1) Production of oxide superconducting conductor A composition of YBa ₂ Cu ₃ O _{7-x is formed} by CVD on a tape-like substrate 21 made of Ag and having a width of 10 mm, a length of 100 mm, and a thickness of 0.2 mm. The oxide superconducting layer 23 was formed with a thickness of 0.5 μm to obtain an oxide superconducting conductor.
[0025]
(2) Connection (Example 1)
Two oxide superconducting conductors 25 were used, and the oxide superconducting conductors were connected by the connection method shown in FIGS.
First, the oxide superconducting layer at one end of each oxide superconducting conductor was removed by phosphoric acid etching over a length of 5 mm from the end to expose the base material.
Next, the end portions where the base materials were exposed were butted against each other, and were pressed against each other while being heated to 962 ° C.
Next, the surface of the joint portion was polished and flattened.
Subsequently, a YBa ₂ Cu ₃ O _7-x connecting oxide superconducting layer having the same composition as that of the oxide superconducting layer was formed at a thickness of 0.5 × 10 ⁻⁶ m on this connecting portion by CVD. The wrap length A at this time was 20 mm.
Next, a surface protective layer was formed on the oxide superconducting layer and the connecting oxide superconducting layer in each oxide superconducting conductor.
[0026]
(Example 2)
Two oxide superconducting conductors 25 were used, and the oxide superconducting conductors were connected by the connection method shown in FIGS.
First, the oxide superconducting layer at one end of each oxide superconducting conductor was removed by phosphoric acid etching over a length of 5 mm from the end to expose the base material.
Next, the end portions where the base materials were exposed were butted against each other, and were pressed against each other while being heated to 962 ° C.
Next, the surface of the joint portion was polished and flattened.
Subsequently, a connection layer made of Ag was formed on the bonding portion and the exposed portion of the base material by RF sputtering.
Subsequently, a YBa ₂ Cu ₃ O _7-x connecting oxide superconducting layer having the same composition as that of the oxide superconducting layer was formed at a thickness of 0.5 × 10 ⁻⁶ m on this connecting portion by CVD.
The wrap length at this time was 20 mm.
[0027]
(Comparative Example 1)
The oxide superconducting conductor 25 was connected in the same manner as in Example 1 except that the length of the wrap length A was 5 mm.
[0028]
In Examples 1 and 2 and Comparative Example 1, the connection ratio was determined. For the connection ratio, the critical current density (Jc1) of the oxide superconductor 25 before connection is measured by the four-terminal method (terminals are indicated by dotted lines in FIG. 1), and the critical current density (Jc2) in the oxide superconductor after connection is measured. ) Is measured by a four-terminal method (terminals are indicated by dotted lines in FIG. 10), and these ratios Jc2 / Jc1 × 100 (%) are shown. If this value is low, it indicates that the critical current density (Jc) of the oxide superconductor after connection has decreased.
Example 1 82%
Example 2 100%
Comparative Example 1 32%
[0029]
From this result, it can be seen that a good critical current density is maintained even after connection in the example.
[0030]
【The invention's effect】
As described above, the connection method of the first oxide superconducting conductor of the present invention can easily connect the oxide superconducting conductor as described above. Moreover, since the base materials are joined together and the oxide superconducting layer is connected by the connecting oxide superconducting conductor, the strength of the connecting portion is high and the stability of the connecting portion is high. In addition, there is little decrease in critical current density in the oxide superconductor after connection.
[0031]
Further, in the second connection method of the present invention, the oxide superconducting conductor can be easily connected as in the first connection method. In addition, since the base materials are joined and a connection layer made of stabilized silver is provided, and a connection oxide superconducting layer is formed thereon, the oxide superconducting layers are connected to each other. The stability at the part is higher, and the strength of the connecting part is higher. Further, the decrease in critical current density in the oxide superconductor after connection is reduced.
[0032]
Furthermore, if the above connection method is applied to an oxide superconducting conductor whose base material is silver, the structure is simple, so that the connection can be easily made. Little decrease in current density.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an oxide superconducting conductor suitable for implementing the method for connecting oxide superconducting conductors of the present invention.
FIG. 2 is a cross-sectional view for explaining one step of an example of a method of connecting oxide superconducting conductors of the present invention.
FIG. 3 is a cross-sectional view for explaining one step of an example of a method of connecting oxide superconducting conductors of the present invention.
FIG. 4 is a cross-sectional view for explaining one process of an example of a method for connecting oxide superconducting conductors of the present invention.
FIG. 5 is a cross-sectional view for explaining one process of an example of a method for connecting oxide superconducting conductors of the present invention.
FIG. 6 is a cross-sectional view for explaining one step of an example of the method for connecting oxide superconducting conductors of the present invention.
FIG. 7 is a cross-sectional view for explaining one step of an example of a method of connecting oxide superconducting conductors according to the present invention.
FIG. 8 is a cross-sectional view for explaining one step of an example of a method for connecting oxide superconducting conductors of the present invention.
FIG. 9 is a cross-sectional view for explaining one step of an example of the method for connecting oxide superconducting conductors of the present invention.
FIG. 10 is a cross-sectional view for explaining one step of an example of the method for connecting oxide superconducting conductors of the present invention.
FIG. 11 is a cross-sectional view showing an example of a connection structure of a conventional oxide superconducting conductor.
FIG. 12 is a cross-sectional view showing an example of a connection structure of a conventional oxide superconducting conductor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 21 ... Base material 23 ... Oxide superconducting layer 25 ... Oxide superconducting conductors 24, 34 ... Surface protection layer 26 ... Connecting oxide superconducting layer 32 ... Connecting oxide superconducting Layer 31 ... Connection layer

Claims (5)

A method for connecting oxide superconducting conductors in which an oxide superconducting layer is formed on a tape-shaped substrate,
At the end of each oxide superconducting conductor, the oxide superconducting layer at that end is removed to expose a portion of the substrate, and then the exposed substrates of each oxide superconducting conductor are butted together and joined. Then, a connecting oxide superconducting layer for connecting each oxide superconducting layer is formed on the joining portion and the exposed portion of the base material and on each oxide superconducting layer so as to straddle them. A method for connecting an oxide superconducting conductor, comprising forming a surface protective layer on the oxide superconducting layer and the connecting oxide superconducting layer so as to straddle them . The length in the joining direction of the contact portion between one oxide superconducting conductor and the other oxide superconducting conductor of the connecting oxide superconducting layer is 10 to 30 mm. Connection method of oxide superconducting conductors. A method for connecting oxide superconducting conductors in which an oxide superconducting layer is formed on a tape-shaped substrate,
  At the end of each oxide superconductor, the oxide superconducting layer at that end is removed to expose a portion of the substrate, and then the exposed substrates of each oxide superconductor are butted together and joined. Then, a noble metal layer for connection is formed on the joint portion and the exposed portion of the base material, and then the oxide superconductor layer of each oxide superconductor conductor is formed on the noble metal layer for connection and the oxide superconductor layer. Forming a connecting oxide superconducting layer for connecting them, and then forming a surface protective layer on the oxide superconducting layer and the connecting oxide superconducting layer. A method for connecting an oxide superconducting conductor. 4. The oxide superconductivity according to claim 3, wherein a length of a contact portion between one oxide superconductor and the other oxide superconductor of the connecting oxide superconductor layer is 10 to 30 mm. 5. Conductor connection method. The method for connecting oxide superconducting conductors according to any one of claims 1 to 4, wherein silver is used as the base material.

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