JP2004304163A - Oxide superconducting current lead, its manufacturing method, and superconducting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide superconducting current lead through which a current of ≥1,000 A can be made to flow even under an external magnetic field of 0.5 T when the lead is cooled with liquid nitrogen and has a contact resistance value of ≤0.5 μΩ when the current is made to flow through the lead, and to provide a method of manufacturing the lead. <P>SOLUTION: After a metallic electrode 10 having an installing groove 31 for installing an oxide superconductor 60 and a drift suppressing member 50 having a size matching the installing groove 31 are manufactured and a molten junction metal is applied to the electrode 10 and the member 50; the end of the oxide superconductor 60 coated with silver and the molten junction metal is installed to the installing groove 31, and the flowing out of the molten junction metal is prevented. Then the current lead 1 is manufactured by joining the metallic electrode 10, oxide superconductor 60, and drift suppressing member 50 to each other with a pore-free junction metal by melting the junction metal by heating the metal, foaming the metal by deaerating the metal in a vacuum, and then, bursting the formed bubbles by giving mechanical shocks to the bubbles through the drift suppressing member 50, and, in addition, coating the oxide superconductor 60 with a coating member 70. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an oxide superconducting current lead used for supplying a current to a superconducting system such as a superconducting magnet used for MRI, linear, SMES, and the like, a manufacturing method thereof, and a superconducting system.

  A current lead used to supply a large current to a superconducting magnet or the like supplies a current of several hundred to several thousand amps from a power supply at room temperature to a superconducting system such as a cryogenic superconducting magnet. Conventionally, a copper wire having a low electric resistance has been used as the current lead. However, when the copper wire is used as a current lead and the wire diameter of the copper wire is increased in order to reduce the Joule heat generated when a predetermined large current is applied to the current lead, the copper wire has this large wire diameter. Heat infiltration by heat conduction into the superconducting system side via the copper wire occurred, and power loss of the refrigerator and loss of He gas of the refrigerant due to the heat invasion were large. To solve this problem, Patent Document 1 proposes that an oxide superconductor having a lower thermal conductivity than copper and generating no Joule heat even when a large current flows is interposed in the middle of the current lead.

JP-A-63-200307

In recent years, the development of superconducting applied equipment has progressed, and the required level of performance for oxide superconducting current leads has also become higher.In addition to being able to flow larger current, less heat generated by Joule, heat intrusion from the outside world There has been a demand for less.
Incidentally, in the SMES for power storage, which is a main use of the oxide superconducting current lead, one example of the required level of the oxide superconducting current lead of 1MJ class SMES is a high temperature side temperature of 77K, a low temperature side temperature of 4.2K, and an external magnetic field of 0K. Under 1.5T, a current of 1000 A or more can be passed as a predetermined current, and the heat penetration from the high temperature side to the low temperature side is 0.5 W or less. If the characteristics of the oxide superconducting current lead can satisfy this level, a relatively low-cost and compact refrigerator can be used for cooling the SMES for power storage.

  However, since the oxide superconductor used for the oxide superconducting current lead is a ceramic, it has poor bondability with a metal, and has a poor bonding property with a metal electrode (generally, a copper electrode is used). Electrical resistance that cannot be ignored (hereinafter referred to as contact resistance) is generated. For this reason, when a predetermined current is applied to the oxide superconducting current lead, a problem of heat generation due to Joule heat has occurred.

  Therefore, in order to reduce the above-described contact resistance, first, an attempt was made to interpose silver in the form of silver coat between the oxide superconductor and the copper electrode. In other words, paying attention to the fact that the contact resistance value between silver and the oxide superconductor is lower than the contact resistance value between copper and the oxide superconductor, crimping a silver foil onto the oxide superconductor, applying a silver paste material, or After silver is sprayed and adhered, it is baked to form a silver coat, and the oxide superconductor with the silver coat and the copper electrode are joined using a joining metal such as solder, for example, to form an oxide. It was a superconducting current lead.

However, as a result of an increase in the current flowing through the current lead, in the current lead using the above-described oxide superconductor with a silver coat, the generated Joule heat cannot be overlooked. Therefore, in order to suppress the generation of Joule heat while passing a predetermined current through the current lead, the oxide superconductor was increased in size and the contact area with the copper electrode was increased.
As a result, although the generation of Joule heat could be suppressed, it was necessary to increase the size of the oxide superconductor in order to increase the contact area between the oxide superconductor and the copper electrode. Heat penetration from the high temperature side to the low temperature side via the oxide superconductor increased.

Thus, for example, an oxide superconducting current lead as shown in FIG. 6 has been considered.
An oxide superconducting current lead 100 shown in FIG. 6 has a copper electrode as a metal electrode on both sides of a rare-earth-based oxide superconductor 110 manufactured by a melting method, which allows a large current to flow even with a small cross-sectional area. 120 are connected. The two end portions 112 of the rare-earth oxide superconductor 110 have a large cross-sectional area, but the central portion 111 has a small cross-sectional area. On the other hand, also in the copper electrode 120, the contact portion 121 in contact with the both end portions 112 of the oxide superconductor is gouged so as to surround the both end portions 112, so that both can secure a wide contact area.
The oxide superconducting current lead 100 was able to suppress both generation of Joule heat and heat intrusion from the high-temperature side to the low-temperature side even when a predetermined current is passed.

  However, among the oxide superconductors, a rare-earth oxide superconductor manufactured by a melting method, which is suitable for a current lead, has a molded body in which only a central portion is narrow and narrow as shown in FIG. Is difficult to do. For this reason, in order to manufacture an oxide superconductor having such a shape, first, a rectangular parallelepiped rare earth-based oxide superconductor having a size capable of securing a sufficient contact area with a metal electrode is manufactured. In order to reduce heat penetration through the rare-earth oxide superconductor, it was necessary to take a step of cutting the central portion to reduce the cross-sectional area. However, in this case, when the predetermined current value flowing to the oxide superconducting current lead is large, a large-sized rare-earth oxide superconductor must be manufactured, and the rare-earth oxide superconductor must be largely cut. However, the yield of the rare earth oxide superconductor is very low, and it takes a lot of man-hours. Further, since the size of the metal electrode is increased, it is difficult to reduce the size of the oxide superconducting current lead as a whole.

  The present invention has been made to solve the above problems, and has the following configuration.

That is, in a first configuration for solving the above-described problem, a metal electrode is provided on both sides of an oxide superconductor, and a bonding metal is formed at a bonding portion formed by the oxide superconductor and the metal electrode. An oxide superconducting current lead in which the oxide superconductor and the metal electrode are joined by the joining metal provided,
An oxide superconducting current lead, wherein the volume of holes in the joining metal provided at the joining portion is 5% or less of the volume of the joining portion.

A second configuration is the oxide superconducting current lead according to the first configuration,
An oxide superconducting current lead, wherein a silver coat is provided on a surface of the oxide superconductor joined by the joining metal.

A third configuration is the oxide superconducting current lead according to the first or second configuration,
The joining metal is a solder containing at least one of Cd, Zn, and Sb and at least one of Pb, Sn, and In, and is an oxide superconducting current lead.

In a fourth configuration, a metal electrode is provided on both sides of the oxide superconductor, and a bonding metal is provided at a bonding portion formed by the oxide superconductor and the metal electrode. A method for producing an oxide superconducting current lead in which an oxide superconductor and the metal electrode are joined,
When joining the oxide superconductor and the metal electrode with the joining metal, the joining portion is heated to a temperature equal to or higher than the melting point of the joining metal, and then the pressure is reduced to degas the joining metal. A method for manufacturing an oxide superconducting current lead, comprising the steps of:

A fifth configuration is a method for manufacturing an oxide superconducting current lead according to the fourth configuration,
A method for manufacturing an oxide superconducting current lead, comprising providing a sealing member that suppresses the joining metal from flowing out of the joining portion when the joining metal is heated and degassed.

  A sixth configuration is a superconducting system using the oxide superconducting current lead according to any one of the first to third configurations.

The present inventors prepared a sample of an oxide superconducting current lead, measured the value of the contact resistance at the joint surface between the oxide superconductor and the metal electrode in detail, and determined the sample for each sample of the oxide superconducting current lead. And found that the value of the contact resistance was not constant. Therefore, in order to investigate the cause of the variation in the contact resistance value, the joint surface between the oxide superconductor and the metal electrode was disassembled in detail over the entire surface and examined.
As a result, it was found that the bonding metal on the bonding surface between the oxide superconductor and the metal electrode had pores. When the volume of the holes in the joining metal was integrated, it was found that the volume was approximately 30% or more of the volume of the joining portion. Therefore, as described in the first configuration, when the volume of the holes in the bonding metal is set to 5% or less of the volume of the bonding portion, the contact resistance value between the oxide superconductor and the metal electrode is reduced, At the contact portion between the oxide superconductor and the metal electrode, it is possible to join the metal electrode without expanding the cross-sectional area of the oxide superconductor and suppress the Joule heat generated even when a predetermined current flows. Was.

  As described in the second configuration, by interposing a silver coat between the bonding metal and the oxide superconductor, the contact resistance between the oxide superconductor and the metal electrode can be further reduced. As a result, a predetermined current was able to flow stably.

  As described in the third configuration, when a solder containing at least one of Cd, Zn, and Sb as a bonding metal and containing at least one of Pb, Sn, and In is used, a metal electrode and an oxide can be formed. Since the peeling between the superconductors and the cracks in the oxide superconductor can be suppressed, the oxide superconducting current lead using the above-described solder as the joining metal was able to stably flow a predetermined current. .

  As described in the fourth configuration, after the bonding metal used for the oxide superconducting current lead is heated to a temperature equal to or higher than the melting point, the pressure is reduced and degassed, so that the bonding metal provided in the bonding portion is removed. Was able to reduce the volume of pores.

  As described in the fifth configuration, at the time of degassing the joining metal, a sealing member that suppresses the outflow of the joining metal to a portion where the joining metal joint comes into contact with the outside is provided, and the joining metal is provided. By suppressing the outflow from the joining portion, it is possible to avoid the occurrence of vacancies due to an insufficient amount of the joining metal in the joining portion, and the joining metal is diffused to portions other than the joining portion, and It was also possible to avoid an increase in contact resistance.

  As described in the sixth configuration, the superconducting system using the oxide superconducting current lead according to any one of the first to third configurations is capable of moving from a high temperature side to a low temperature side even when a predetermined current is applied. Since the heat intrusion into the refrigerator is small, the load on the refrigerator can be reduced, and a superconducting system with low production cost and running cost can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing an example of installing an oxide superconductor on a metal electrode in the oxide superconducting current lead according to the present invention, and FIG. 2 is a metal electrode on which the oxide superconductor shown in FIG. 1 is installed. FIG. 3 is a perspective view in the case where a sealing member is provided, FIG. 3 is a conceptual diagram of characteristic measurement of the oxide superconducting current lead according to the present invention, and FIG. FIG. 5 is a perspective view when the joined body is placed in a mold in order to cover the body with a covering member. FIG. 5 is an oxide superconductor and a metal in an oxide superconducting current lead manufactured by a conventional technique. It is a schematic cross section of the joint part with an electrode.

  In FIG. 1, an oxide superconducting current lead (hereinafter, referred to as a current lead) 1 according to the present invention includes a metal electrode 10, a drift suppression member 50, an oxide superconductor 60, and a covering member 70. . Although not shown, a metal electrode similar to the metal electrode 10 is provided at the other end of the oxide superconductor 60 so as to face the same.

  First, the metal electrode 10 has a plate-shaped lead wire joining portion 20 and a rectangular parallelepiped oxide superconductor mounting portion (hereinafter, referred to as a mounting portion) 30. A desired number of lead wire installation holes 21 for installing lead wires, bus bars, and the like are provided in the lead wire joint portion 20. On the other hand, an oxide superconductor installation groove (hereinafter, referred to as an installation groove) 31 is provided on the upper surface 34 and the opposed surface 33 of the installation portion 30, and the oxide superconductor transfer portion is provided on the opposed surface 33. (Hereinafter referred to as a succession part.) 32 is provided in a U-shape with an open upper part so as to surround the installation groove 31. Further, the inner wall of the installation groove 31 improves the adhesion to the metal for bonding described later, and the lead wire bonding portion 20 is made of tin, tin, or the like in advance in order to reduce the contact resistance with the lead wire or bus bar bonded thereto. It is preferable to provide plating mainly containing a simple substance or an alloy of silver, gold, nickel, zinc, and palladium, or a laminate of the plating.

  Next, the drift suppression member 50 has a drift suppression member main body 51 and a drift suppression member protrusion (hereinafter, referred to as a protrusion) 52, and has a shape that can be fitted into the installation groove 31 described above. After being set in the installation groove 31, the metal electrode 10 is integrated. The drift suppressing member 50 and the installation groove 31 are also preliminarily plated with tin, silver, gold, nickel, zinc, palladium as a main component or an alloy in order to improve the adhesion with a bonding metal described later, or It is preferable to provide a plating laminate.

  Next, the oxide superconductor 60 has a prismatic shape, and silver coats 61 are provided on both ends of the prism. In the present embodiment, the silver coating for measurement 62 is provided at an appropriate position from the end of the prism for evaluating the electrical characteristics of the current lead described later.

  Further, a covering member 70 for covering the oxide superconductor 60 is provided between the facing surfaces 33 of the metal electrodes 10 facing each other with the prism-shaped oxide superconductor 60 interposed therebetween. The covering member 70 is supported by the transfer portion 32 provided on the facing surface 33 and is fixed to the metal electrode 10.

Here, as the oxide superconductor 60, it is preferable to use a rare-earth-based oxide superconductor manufactured by a melting method, which allows a large current to flow even with a small cross-sectional area. This is because heat intrusion into the cryogenic superconducting magnet can be further reduced by reducing the cross-sectional area of the oxide superconductor 60 necessary for flowing a predetermined current.
In addition, since the oxide superconductor 60 has substantially the same cross-sectional area throughout, it can be manufactured by cutting from the oxide superconductor serving as the base material. No processing is required.

  Next, the installation of the oxide superconductor 60 and the drift suppression member 50 on the metal electrode 10 will be described. The installation groove 31 provided in the metal electrode 10 has a shape in which the end of the oxide superconductor 60 is fitted. -It is preferable that the height and depth are 3 x 3 x 10 mm or more.

  The end of the oxide superconductor 60 is installed in the installation groove 31, and the drift suppression member 50 is further installed thereon. The gap between the drift suppressing member 50 and the installation groove 31 is preferably about 0.05 to 0.5 mm on one side. The gap between the drift suppressing member 50 and the installation groove 31 serves as a deaerator 42 described with reference to FIG. At this time, if the gap is 0.05 mm or more, deaeration of the joining metal proceeds sufficiently, and if the gap is 0.5 mm or less, unnecessary increase in contact resistance due to an increase in the volume of the joining metal can be avoided, which is preferable. .

  Returning to FIG. 2 again, when the drift preventing member 50 is installed in the installation groove 31, the drift preventing member main body 51 is substantially flush with the upper surface 34 and the facing surface 33 of the metal electrode, and the protrusion 52 is Preferably, the size is such that it is integrated with. When the end of the oxide superconductor 60 is installed in the installation groove 31 and the drift suppression member 50 is further installed thereon, the metal electrode 10 including the installation groove 31 and the drift suppression member 50 is The portion surrounded by the end of the superconductor 60 constitutes a joining portion.

  It is preferable that the five surfaces of the oxide superconductor 60 constituting the joint portion facing the installation groove 31 and the drift suppression member 50 be previously silver-coated 61 from the viewpoint of reducing the contact resistance at this portion. As the silver coating method, a coating and baking method of a silver paste material, a plating method, a vapor deposition method, a sputtering method, a thermal spraying method, and the like can be applied, and thus may be appropriately selected from the viewpoint of productivity and mass productivity. Then, it is preferable that a joining metal for joining the oxide superconductor 60 to the installation groove 31 be melt-coated on the silver coat 61. As the joining metal, various solders having a melting point of 300 ° C. or less are preferably used in order to prevent the oxide superconductor from being heated and oxygen being released therefrom. Among them, from the viewpoint of increasing the adhesiveness of the joining portion and lowering the contact resistance, for example, Pb-Sn-based or In-based, to which Cd, Zn, Sb, etc. are added so as to increase the adhesiveness with ceramic and the wettability. It is desirable to use the solder material of the above.

  That is, a solder containing any one or more of Cd, Zn, and Sb and containing one or more of Pb, Sn, and In has a high adhesive strength to both the metal electrode and the oxide superconductor. Therefore, due to the difference in linear expansion between the metal electrode and the oxide superconductor, stress is generated between the metal electrode and the oxide superconductor due to the thermal history up to the temperature of liquid nitrogen or lower and room temperature. However, this stress can be prevented from being concentrated locally. As a result, peeling between the metal electrode and the oxide superconductor and generation of cracks in the oxide superconductor can be suppressed. It is considered that it was possible to flow stably.

Here, Cerasolzer (registered trademark) will be described as a preferable example of the ceramic solder material.
Cerasolza 143 Asahi Glass Co., Ltd. Ingredients: Sn: 45-51 (Wt%), Pb: 26-32, Cd: 16-22, Zn: 2-4, Sb: 1-3
Melting point: 143 ° C
Cerasolza 123, manufactured by Asahi Glass Co., Ltd. Ingredients: In: 44 to 50 (Wt%), Cd: 45 to 50, Zn: 1 to 3, Sb: less than 1 Melting point: 123 ° C.

  The end portion of the oxide superconductor 60 is inserted into the installation groove 31 provided in the metal electrode 10, and the drift suppression member 50 is installed thereon to form a joining portion, and a joining metal is provided there to provide a joining metal. By adopting a configuration in which the electrode 10 and the oxide superconductor 60 are joined, the metal electrode 10 and the oxide superconductor 60 are all electrically joined in a state of surface contact. Can be reduced. Of course, as another embodiment, a metal electrode is formed in a cap shape and an oxide superconductor is filled therein, or a metal electrode is formed in a structure capable of dividing the metal electrode and sandwiching the oxide superconductor. It is also possible to adopt an assembled form, and the structure of the oxide superconductor may be cylindrical or cylindrical.

  The joining metal is also melt-coated in the installation groove 31, and the oxide superconductor 60 in which the joining metal is melt-coated on the silver coat is installed, and the oxide superconductor 60 and the installation groove 31 are formed. A molten joining metal is placed on the joining portion to be formed, and this is solidified to join the two.

  In the joining using the joining metal, gaseous components such as air are involved when applying or pouring the molten joining metal on the oxide superconductor 60 or on the wall of the installation groove 31 in order to install the melted joining metal. . The gaseous components entrained in the molten joining metal form voids inside when the joining metal is solidified. When the holes are formed in the joining metal, the flow path of the current flowing between the metal electrode and the oxide superconductor through the joining metal is narrowed, and when a predetermined current, for example, 1000 A is applied, It is considered that the portion caused the increase in the contact resistance value.

Here, the relationship between the contact resistance value between the metal electrode and the oxide superconductor and the bonding metal in which holes are formed will be described with reference to FIG.
In FIG. 5, a portion of the oxide superconductor 60 on which the silver coating 61 is provided is installed in the installation groove 31 provided in the metal electrode 10, and the junction formed by the metal electrode 10 and the oxide superconductor 60 is formed. The joining metal 90 is provided in the portion. When the metal electrode 10 and the oxide superconductor 60 were joined by using the joining metal 90 according to the conventional technique, the holes 91 were present in the joining metal 90. The ratio of the volume of the holes 91 to the volume of the joint portion can be measured, for example, by the following method. That is, the joint portion may be sequentially cut, the ratio of the cross-sectional area of the joint portion and the cross-sectional area of the holes 91 appearing on the cut surface may be measured, and the values may be sequentially integrated.

  When the metal electrode 10 and the oxide superconductor 60 are joined using the joining metal 90 by a conventional method, the ratio of the volume of the holes 91 to the volume of the joining portion occupies about 50%. There was found. The existence of the holes 91 in the joining metal 90 was considered to be a factor of the contact resistance value between the metal electrode and the oxide superconductor.

  Therefore, as a method of suppressing and avoiding the generation of holes in the joining metal, it has been considered that the above-described application of the joining metal is performed in a vacuum. However, from the viewpoint of workability and productivity, the application of the joining metal is performed in the air, and the oxide superconductor 60 is installed in the installation groove 31 and heated to melt the joining metal. In addition, the present inventor has found that it is preferable to expose the part in a vacuum and remove gaseous components in the joining metal by a vacuum degassing method. As the conditions for the vacuum degassing, the heating temperature of the joining metal may be set to a temperature equal to or higher than the melting point. From the viewpoint of deaeration proceeding in a short time and suppressing oxidation of the joining metal, a melting point of about +15 to 100 ° C. It is desirable that The effect can be obtained if the surrounding vacuum degree is 0.01 MPa or less, but it is more preferable if the surrounding vacuum degree is 10 Pa or less since deaeration is completed in 4 to 5 seconds. If the temperature and the time are at these levels, it is not necessary to consider that oxygen escapes from the oxide superconductor 60.

  Further, at the time of this vacuum degassing, when the molten joining metal flows out of the installation groove 31 and diffuses into other portions of the metal electrode 10, the inside of the installation groove 31 is diffused while the amount of the bonding metal is insufficient. In a part, it causes the contact resistance value of the part to increase, which is not preferable. Therefore, it is preferable to adopt a configuration for suppressing this.

A specific configuration example for suppressing the loss of the joining metal will be described with reference to FIG.
In FIG. 2, the end of oxide superconductor 60 is installed in installation groove 31 provided in metal electrode 10. And the sealing member 41 is installed along the outer peripheral edge of the installation groove 31 and the oxide superconductor. When the sealing member 41 is installed along the outer peripheral edge of the installation groove 31, the sealing member 41 may be installed so as not to block the deaeration section 42 formed by inserting the drift preventing member 50 into the installation groove 31. preferable. The sealing member 41 is made of silicon rubber or the like which does not deteriorate even at a temperature equal to or higher than the melting point of the joining metal, has appropriate adhesive strength to the metal electrode 10 and the oxide superconductor 60, and is easy to install. It can be used favorably.

  When the installation of the sealing member 41 on the metal electrode 10 is completed, the metal electrode 10 and the oxide superconductor 60 are heated to a temperature 15 to 100 ° C. higher than the melting point of the bonding metal, and the bonding metal is heated under the above conditions. When vacuum degassing is performed, the generated gas component is discharged from the degassing section 42. At this time, if the generated holes are difficult to burst due to the high viscosity of the molten joining metal, the holes generated by applying a mechanical shock using, for example, an ultrasonic vibrator with an ultrasonic soldering hand are ruptured. It is preferable to perform vacuum degassing. In the present embodiment, first, after the gas component is vacuum-degassed from the molten joining metal, the drift suppression member 50 is inserted into the installation groove 31, and the vacuum degassing is performed again. At this time, by applying a mechanical impact via the drift suppression member 50, the rupture of the holes in the molten joining metal can be easily realized. As a result, the volume of vacancies in the joining metal provided at the joint formed by the installation groove 31 of the metal electrode 10, the drift suppressing member 50, and the oxide superconductor 60 is reduced to 5% or less of the volume of the joint. It became possible to suppress.

  Here, the degassing conditions in the joining metal were changed, and a plurality of current lead samples were prepared in which the ratio of the volume of the joining portion to the porosity in the joining metal had various values. Then, the contact resistance value of the joint portion of the prepared current lead sample was measured using a contact resistance value measuring method described later, and the ratio of the volume of the joint portion and the voids in the joining metal, and the contact resistance value, Sought a relationship.

Here, as an example of the oxide superconductor 60, a Gd-based oxide superconductor having a rectangular parallelepiped shape having a length of 3 mm, a width of 5 mm, and a length of 90 mm was used. The size of the Gd-based oxide superconductor is set to this value in order to reduce heat penetration through the oxide superconductor to 0.3 W or less. Of course, the cross-sectional shape may be square or circular. 10 mm at both ends of the Gd-based oxide superconductor was joined to a metal electrode (at this time, the joining area between the oxide superconductor and the metal electrode was 175 mm ² ), and the joining metal with respect to the volume of the joining portion. The contact resistance value was measured by changing the ratio of pores in the inside.

  Then, when the degassing operation in the joining metal is not performed, as described above, the ratio of the vacancies in the joining metal is about 30 to 50% of the volume of the joining portion, and a predetermined current is applied. In this case, the magnitude of the contact resistance was about 0.8 to 1.2 μΩ, and the variation in the contact resistance depending on the sample was large. However, when the ratio of vacancies in the joining metal is 5% or less of the volume of the joining portion, the magnitude of the contact resistance when a predetermined current is applied falls below 0.5 μΩ, and at the same time, the contact resistance Variation has also been reduced.

Here, as described above, since the amount of heat penetration through the Gd-based oxide superconductor is 0.3 W or less, the heat penetration due to this heat transfer and the 1000A when the low temperature side is cooled to 4.2K. It has been found that the amount of heat entering the low-temperature side, which is obtained by adding the Joule heat generated by the contact resistance at the time of energization, is sufficiently lower than 0.5 W.
Therefore, it has been found that the oxide superconductor has a shape as it is cut from the base material and can be used as an oxide superconducting current lead without performing a large cutting process. As a result, compared to the oxide superconducting current lead that requires cutting work on the oxide superconductor, it is possible to greatly reduce the amount of the oxide superconductor used, and at the same time, to reduce the entire oxide superconducting current lead. Miniaturization is also possible.

  Here, returning to FIG. 1, when joining of the metal electrode 10 and the oxide superconductor 60 is completed, the sealing member is removed, and the metal electrode 10 provided opposite to both ends of the columnar oxide superconductor 60 is removed. It is preferable to provide the covering member 70 in a form that covers the oxide superconductor 60 therebetween. Since the covering member 70 protects the oxide superconductor 60 mechanically and environmentally, GFRP or the like, which is a resin material containing glass fiber, is preferably used.

The step of providing the covering member on the oxide superconductor will be described with reference to FIG.
FIG. 4 is a perspective view showing a state in which an oxide superconductor having metal electrodes bonded to both ends is installed in a mold for coating a coating member.
In FIG. 4, an oxide superconductor 60 having the above-described metal electrodes 10 bonded to both ends is provided in a mold 80. The installation portion 30 of the metal electrode 10 and the mold 80 having a U-shaped cross section form a mold space 81. Further, the oxide superconductor transfer portion 32 and the drift suppression member protrusion 52 project from the metal electrodes 10 on both sides toward the mold space 81.
On the other hand, a glass fiber is impregnated with a thermosetting resin to prepare a prepreg of GFRP. Then, the prepared prepreg of GFRP was filled in a mold space 81, and was heated and cured to obtain a coating member of the oxide superconductor 60. As a result, the covering member is fitted with the drift suppressing member protrusion 52 protruding from the metal electrode 10 and the oxide superconductor transfer portion 32 and exhibits mechanical strength, so that the covering member is excellent in electrical characteristics, mechanical and environmentally friendly. A robust current lead could be manufactured.

  By using the current leads described above in a superconducting system, the cooling efficiency of the superconducting system is significantly improved, so that the production cost can be reduced by reducing the capacity of the refrigerator and the running cost of the system can be reduced. became.

The characteristic evaluation of the manufactured current lead will be described with reference to FIG.
In FIG. 3, the oxide superconductor 60 has a width of 5 mm and a thickness of 3 mm, and an Ag paste is baked at positions of 10 mm in width at both ends and positions of 15 to 17 mm from both ends. The metal wires 10 are joined to the metal electrode 10 as silver coats 61 up to the positions with a width of 10 mm at both ends, and lead wires are connected as the measurement silver coats 62 at positions from 15 to 17 mm from both ends. A bus bar is connected to the lead wire joints 20 of the two metal electrodes 10 provided on the current lead 1, and each bus bar is connected to a power supply (not shown). As the power supply, a power supply that supplies, for example, a current of 1060 A as a predetermined current was used. The current passes through the installation portion 30 from the lead wire joint portion 20, flows through the oxide superconductor covered by the covering member 70, and reaches the installation portion 30 of the corresponding metal electrode 10.

  When the current lead 1 was cooled to 77 K and a current of 1060 A was passed between the two bus bars, the potential difference between the installation portion 30 and 15 mm from the end of the oxide superconductor 60 was measured. The contact resistance value R was calculated.

Hereinafter, embodiments of the present invention will be described in more detail based on examples.
(Example 1)
1) Manufacture of columnar oxide superconductor Each raw material powder of Sm ₂ O ₃ , BaCO ₃ , and CuO is weighed so that the molar ratio is Sm: Ba: Cu = 1.6: 2.3: 3.3. After that, only BaCO ₃ and CuO were fired at 880 ° C. for 30 hours to obtain a calcined powder of BaCuO ₂ and CuO (BaCuO ₂ : CuO = 2.3: 1.0 in molar ratio). Next, the previously weighed Sm ₂ O ₃ was added to the calcined powder, and further, a Pt powder (average particle size: 0.01 μm) and an Ag ₂ O powder (average particle size: 13.8 μm) were added and mixed. Then, it was calcined at 900 ° C. in the air for 10 hours to obtain a calcined powder containing Ag. However, the Pt content was 0.42 wt%, and the Ag content was 15 wt%. This Ag-containing calcined powder was pulverized with a pot mill to obtain a synthetic powder having an average particle size of about 2 μm.

When the obtained synthetic powder was analyzed by powder X-ray diffraction, Sm _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O _7-x phase and Sm _{2 + r} Ba _{1 + s} (Cu _{1- d} Ag _d ) O _5-r phase was observed.

This synthetic powder was press-molded into a plate having a length of 77 mm, a width of 106 mm and a thickness of 26 mm to prepare a precursor. Then, the precursor was set in the furnace, and the following steps were performed.
First, the temperature is raised from room temperature to 1100 ° C. in 70 hours, and the temperature is maintained at this temperature for 20 minutes to bring the precursor into a semi-molten state, and then 5 ° C. above and below the precursor so that the upper part of the precursor is on the low temperature side. / Cm, and the temperature was lowered at 0.4 ° C / min until the upper temperature reached 1025 ° C.

Contact Here, had been prepared in advance by melting method, the crystal of Nd _1.8 Ba _2.4 Cu _3.4 O _x composition containing 0.5 wt% of Pt not contain Ag, vertical and horizontal 2 mm, manufactured by cutting the thickness of 1mm The seed crystal is brought into contact with the upper center of the precursor so that the growth direction is parallel to the c-axis. Then, the upper temperature was lowered from 1025 ° C. to 1015 ° C. at a rate of 1 ° C./hr. After maintaining at this temperature for 100 hours, the temperature is gradually cooled to 945 ° C. over 70 hours, and then the lower part of the precursor is cooled to 945 ° C. in 20 hours so that the upper and lower temperature gradients become 0 ° C./cm. Thereafter, the mixture was gradually cooled to room temperature over 100 hours to crystallize the precursor, thereby obtaining a crystal sample of the oxide superconductor.

When a crystal sample of this oxide superconductor was cut near the center in the vertical direction and the cross section was observed by EPMA, it was confirmed that the crystal sample was in the Sm _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O _7-x phase. The Sm _{2 + r} Ba _{1 + s} (Cu _1-d Ag _d ) O _5-y phase of about 0.1 to 30 μm was finely dispersed.
Here, p, q, r, s, and y were values of -0.2 to 0.2, respectively, and x was a value of -0.2 to 0.6. Also, b and d were values of 0.0 to 0.05, and were about 0.008 on average. Further, Ag of about 0.1 to 100 μm was finely dispersed throughout the crystal sample. In addition, pores having a particle size of about 5 to 200 μm were dispersed in a portion deeper than 1 mm from the surface. In addition, the entire crystal sample is uniformly oriented so that the thickness direction of the disk-shaped material reflects the seed crystal so that the thickness direction is parallel to the c-axis, and the misorientation of the orientation between adjacent crystals is 3 ° or less. A single crystal sample was obtained. When a portion deeper than 1 mm was cut out from the surface of the crystal sample and the density was measured, it was 6.87 g / cm ³ (91.2% of the theoretical density 7.53 g / cm ³ ).

  After removing a 1 mm portion from the surface of the obtained crystal sample, a columnar oxide superconductor having a width of 5 mm, a thickness of 3 mm, and a length of 90 mm was cut out so that the length direction became parallel to the ab plane of the crystal. Further, a columnar sample of 3 mm × 3 mm × 20 mm (one of the 3 mm directions is the c-axis direction of the crystal) was cut out from the sample, and the temperature dependence of the thermal conductivity after the annealing was measured. The average value was about 113 mW / cmK, which was low even though silver contained 15 wt%.

2) Installation of silver coat on columnar oxide superconductor First, an organic vehicle prepared by mixing 10 wt% of ethylcellulose, 30 wt% of terpineol, 50 wt% of dibutyl phthalate, and 10 wt% of butyl carbitol acetate, and Ag having an average particle size of 3 μm. The powder and the powder were mixed at a weight ratio of 3: 7, and 2% of a phosphoric acid ester was added to prepare an Ag paste.

  The prepared Ag paste was applied to a thickness of 50 μm with a width of 2 mm at a position of 10 mm at both ends of the columnar oxide superconductor prepared at 1) and at a position of 15 mm from the left and right ends, and subjected to vacuum impregnation. After that, it was dried in an oven at 80 ° C. in the atmosphere. Next, the columnar oxide superconductor to which the Ag paste was applied was again baked at 920 ° C. for 10 hours in a furnace to bake Ag to form a silver coat, thereby producing a silver-coated oxide superconductor. The film thickness of Ag after baking was about 30 μm.

3) Annealing treatment of the silver-coated oxide superconductor The silver-coated oxide superconductor is placed in another gas-replaceable furnace, and the furnace is first evacuated to 0.1 Torr by a rotary pump and then into the furnace. Oxygen gas was poured into the atmosphere at an atmospheric pressure in which the oxygen partial pressure was 99% or more. Thereafter, while flowing oxygen gas at a flow rate of 0.5 L / min into the furnace, the temperature was raised from room temperature to 450 ° C. for 10 hours, and then gradually cooled from 450 ° C. to 250 ° C. over 400 hours. The temperature was lowered from 10 ° C. to room temperature in 10 hours, and the silver-coated oxide superconductor was annealed.

4) Preparation of metal electrode and drift suppression member A metal electrode and a drift suppression member were fabricated by processing oxygen-free copper having a purity of 4N, and each surface was plated with Sn. This metal electrode has a lead wire joint portion and an installation portion (oxide superconductor installation portion), the lead wire joint portion has two bolt holes, and the joint surface of the installation member has a joint strength on the opposite surface. There is a succession section to increase the Note that the drift suppression member is cut by 3.5 mm in the height direction and 0.5 mm in the width direction from the size of the installation groove provided in the metal electrode in view of the installation of the oxide superconductor and the filling of the joining metal. It was a processed shape.

5) Installation of Oxide Superconductor on Metal Electrode A PbSn-based solder Cerasolzer 143 (hereinafter referred to as Cerasolzer) is melt-coated as a bonding metal in the installation groove of the metal electrode, and Ag is added thereto. An oxide superconductor obtained by melt-coating Cerasolzer to the baked end 10 mm is set, heated and temporarily fixed. After the completion of the temporary fixing, heat-resistant silicone rubber is provided as a sealing member from the outer periphery of the oxide superconductor to the outer edge of the installation groove to perform a process for preventing the outflow of the Cerasolzer.

6) Deaeration treatment of joining metal After the outflow prevention treatment is completed, the metal electrode is heated at 180 ° C, which is higher than the melting point of the Cerasolzer (143 ° C), to sufficiently melt the Cerasolzer, and quickly placed in a vacuum vessel. Degas at 100 Pa for 2 minutes. Next, the metal electrode is heated again to 180 ° C., and a drift preventing member coated with Cerasolzer in advance is applied thereto, and is again placed in a vacuum vessel and degassed at about 100 Pa for 2 minutes. Then, a mechanical shock is applied to the holes of the existing Cerasolzer by using an ultrasonic soldering hand through the drift suppression member to burst the holes.

As a result, the metal electrode, the oxide superconductor, and the drift suppression member are joined by a joining metal that does not include holes in a state that is favorable both electrically and mechanically. After joining is completed, the sealing member is removed.
In this example, in order to measure the characteristics of the prepared current lead, a portion having a diameter of 0.1 mm for characteristic measurement was applied to a portion where Ag was baked provided at a position of 15 to 17 mm from the end of the oxide superconductor. Were connected using a Cerasolzer.

7) Installation of Coating Member An adhesive of a thermosetting epoxy resin composed of a bisphenol A type epoxy resin and an aromatic amine was prepared, and vacuum impregnated into glass cloth fibers and chopped glass fibers to obtain a GFRP prepreg.
Next, both ends were placed in a mold so that only the oxide superconductor portion of the oxide superconductor to which the copper electrode was joined was covered with GFRP. First, a glass cloth fiber prepreg is placed along the inner wall of the mold, and then the chopped glass fiber prepreg is filled into the mold space around the oxide superconductor and covered with the glass cloth fiber prepreg. Then, it was thermally cured at 120 ° C. to produce a glass fiber-coated oxide superconductor current lead sample.

8) Characteristic evaluation of current lead In the manufactured current lead sample, a bus bar is connected to the metal electrode lead wire joint, the metal electrode and the oxide superconductor are cooled down to 77 K, and 1060 A is supplied between both metal electrodes. did. Then, while energizing, the voltage between the metal electrode and the stainless steel wire for property measurement connected to a position 15 to 17 mm from the end of the oxide superconductor was measured, and the voltage between the metal electrode and the oxide superconductor was measured. Was calculated, it was found that the contact resistance value on both sides of the current lead sample was a very low value of 0.19 μΩ.

Further, the current lead sample was cooled to 4.2K, and the contact resistance between the metal electrode and the oxide superconductor was calculated in the same manner. As a result, the contact resistance on both sides was a very low value of 0.03 μΩ. It turned out to be.
When the current lead sample was cooled to 4.2 K on the low temperature side and 77 K on the high temperature side, the amount of heat infiltrated by heat transfer to the low temperature side was 0.28 W.
On the other hand, when the critical current value of the current lead sample in a 77 K, 0.5 T magnetic field was measured by applying a current to 2000 A, it was found that no resistance was generated and the current was 2000 A or more. Therefore, when the cross section of the superconductor sample was ground from 3 mm × 5 mm to φ1.9 mm to a width of about 0.7 mm, and the effective cross-sectional area was reduced and the energization test was performed again, the critical current value was 670 A. If this result is converted back to 3 mm × 5 mm in the current lead sample, it is a value equivalent to about 3500 A in a magnetic field of 0.5 T.

From the above, in the current lead sample, when one of the metal electrodes was set to the high temperature side (77K) and the other was set to the low temperature side (4.2K) and a current of 1000A was applied in a 0.5T magnetic field, the heat on the low temperature side was changed. The amount of generation was found to be a very low value of 0.31 W in total.
Lastly, the joints on both sides of the current lead sample were cut, and the percentage of the volume of the holes in the joining metal provided at the joints was measured. As a result, it was found that one occupied 0.07% of the volume of the joined portion and the other occupied 0.08%.

(Example 2)
1) Manufacture of columnar oxide superconductor Gd ₂ O ₃ , BaCO ₃ , and CuO raw material powders are weighed and mixed in a molar ratio of Gd: Ba: Cu = 1: 2: 3, and mixed. Baked at 30 ° C. for 30 hours, pulverized to an average particle size of 3 μm using a pot mill, baked again at 930 ° C. for 30 hours, crushed to a mean particle size of 10 μm with a raikai machine and a pot mill, A powder of Gd ₁ Ba ₂ Cu ₃ O _{7-x as} a powder was prepared.
Next, the respective raw material powders are weighed and mixed so that Gd: Ba: Cu = 2: 1: 1, fired at 890 ° C. for 20 hours, and then pulverized to an average particle diameter of 0.7 μm using a pot mill. Then, a powder of Gd ₂ BaCuO _{5 as} the _second calcined powder was produced.

The first and second calcined powders were weighed so that Gd ₁ Ba ₂ Cu ₃ O _7-x : Gd ₂ BaCuO ₅ = 1: 0.4, and further Pt powder (average particle size 0.01 μm) and Ag ₂ O powder (average particle size: 13.8 μm) was added and mixed to obtain a synthetic powder. However, the Pt content was 0.42 wt%, and the Ag content was 15 wt%.

This synthetic powder was press-molded into a plate shape having a length of 22 mm, a width of 120 mm and a thickness of 26 mm using a mold to prepare a precursor. Then, the precursor was set in the furnace, and the following steps were performed.
First, the temperature was raised from room temperature to 1100 ° C. in 70 hours, and the temperature was maintained at this temperature for 20 minutes to bring the precursor into a semi-molten state, and then 5 ° C. above and below the precursor so that the upper part of the precursor was on the low temperature side. / Cm, and the temperature was lowered at 0.4 ° C / min until the upper temperature reached 995 ° C.

Here, had been prepared in advance by fusion method, a seed crystal of Nd _1.8 Ba _2.4 Cu _3.4 O _x composition containing 0.5 wt% of Pt not contain Ag, vertical and horizontal 2 mm, manufactured by cutting the thickness of 1mm The seed crystal placed is brought into contact with the upper center of the precursor so that the growth direction is parallel to the c-axis. Then, the temperature of the upper part was decreased from 995 ° C. to 985 ° C. at a rate of 1 ° C./hr. After maintaining at this temperature for 100 hours, the temperature is gradually cooled to 915 ° C. over 70 hours, and then the lower part of the precursor is cooled to 915 ° C. in 20 hours so that the upper and lower temperature gradients become 0 ° C./cm. After that, crystallization was performed by gradually cooling to room temperature over 100 hours to obtain a crystal sample of the oxide superconductor.

The crystal sample of this oxide superconductor was cut near the center in the vertical direction, and the cross section was observed by EPMA. As a result, it was found that the Gd _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O _7-x phase The Gd _{2 + r} Ba _{1 + s} (Cu _1-d Ag _d ) O _5-y phase of about 0.1 to 30 μm was finely dispersed.
Here, p, q, r, s, and y were values of -0.2 to 0.2, respectively, and x was a value of -0.2 to 0.6. Also, b and d were values of 0.0 to 0.05, and were about 0.008 on average. Further, Ag of about 0.1 to 100 μm was finely dispersed throughout the crystal sample. In addition, pores having a particle size of about 5 to 200 μm were dispersed in a portion deeper than 1 mm from the surface. In addition, the entire crystal sample is uniformly oriented so that the thickness direction of the disk-shaped material reflects the seed crystal so that the thickness direction is parallel to the c-axis, and the misorientation of the orientation between adjacent crystals is 3 ° or less. A single crystal sample was obtained. When a portion deeper than 1 mm was cut out from the surface of the crystal sample and the density was measured, it was 7.0 g / cm ³ (91.1% of the theoretical density of 7.68 g / cm ³ ).

  After removing a 1 mm portion from the surface of the obtained crystal sample, a columnar oxide superconductor having a width of 5 mm, a thickness of 3 mm and a length of 105 mm was cut out so that the length direction was parallel to the ab plane of the crystal. In addition, a columnar sample of 3 mm × 3 mm × 20 mm (either the 3 mm direction is the c-axis direction of the crystal) was cut out from this sample, and the temperature dependence of the thermal conductivity after annealing was measured. Despite containing 15 wt%, the integrated average value from a temperature of 77K to 10K was a low value of about 141 mW / cmK.

Or later,
2) Installation of silver coating on columnar oxide superconductor 3) Annealing treatment of silver-coated oxide superconductor 4) Preparation of metal electrode and drift suppression member 5) Installation of oxide superconductor on metal electrode 6) Bonding Metal degassing 7) Installation of covering member 8) Characteristic evaluation of current lead was performed in the same manner as in Example 1, and the following results were obtained.
First, when the contact resistance of the joint between the metal electrode and the oxide superconductor at both ends of the current lead sample was calculated, one was 0.2 μΩ and the other was very low, 0.21 μΩ. There was found.

Further, the current lead sample was cooled to 4.2K, and the contact resistance between the metal electrode and the oxide superconductor was calculated in the same manner. As a result, the contact resistance on both sides was a very low value of 0.03 μΩ. It turned out to be.
When the current lead sample was cooled to 4.2 K on the low-temperature side and 77 K on the high-temperature side, the amount of heat infiltrated by heat transfer to the low-temperature side was 0.33 W.
On the other hand, when the critical current value of the current lead sample in a 77 K, 0.5 T magnetic field was measured by applying a current to 2000 A, it was found that no resistance was generated and the current was 2000 A or more. Then, when the cross section of the superconductor sample was ground from 3 mm × 5 mm to φ1.9 mm to a width of about 0.7 mm, the effective cross-sectional area was reduced, and the energization test was performed again, the critical current value was 530 A. When this result is converted back to 3 mm × 5 mm in the current lead sample, it is a value corresponding to about 2800 A in a magnetic field of 0.5 T.

From the above, in the current lead sample, when one of the metal electrodes was set to the high temperature side (77K) and the other was set to the low temperature side (4.2K) and a current of 1000A was applied in a 0.5T magnetic field, the heat on the low temperature side was changed. The amount of generation was found to be a very low value of 0.36 W in total.
Lastly, the joints on both sides of the current lead sample were cut, and the percentage of the volume of the holes in the joining metal provided at the joints was measured. As a result, it was found that both occupy about 0.1% of the volume of the joint.

(Example 3)
1) Manufacture of columnar oxide superconductor Raw material powders of Sm ₂ O ₃ , BaCO ₃ , and CuO were weighed and mixed so that the molar ratio Sm: Ba: Cu = 1: 2: 3, and mixed. Baked at 30 ° C. for 30 hours, pulverized to an average particle size of 3 μm using a pot mill, baked again at 930 ° C. for 30 hours, crushed to a mean particle size of 10 μm with a raikai machine and a pot mill, A powder of Sm ₁ Ba ₂ Cu ₃ O _7-x was prepared.
Next, the respective raw material powders are weighed and mixed so that Sm: Ba: Cu = 2: 1: 1, fired at 890 ° C. for 20 hours, and then pulverized to an average particle diameter of 0.7 μm using a pot mill. Then, a powder of Sm ₂ BaCuO _{5 as} the _second calcined powder was produced.

The first and second calcined powders were weighed so that Sm ₁ Ba ₂ Cu ₃ O _7-x : Sm ₂ BaCuO ₅ = 1: 0.4, and further Pt powder (average particle size 0.01 μm) and Ag ₂ O powder (average particle size: 13.8 μm) was added and mixed to obtain synthetic powder A. Then, similarly, the first and second calcined powders were weighed so as to be 1: 0.3, and Pt powder and Ag ₂ O powder were added and mixed to obtain synthetic powder B. However, in both of the synthetic powders A and B, the Pt content was 0.42 wt% and the Ag content was 10 wt%.

These two types of synthetic powders A and B are press-formed using a mold into a plate having a length of 22 mm, a width of 120 mm, and a thickness of 26 mm, respectively, and a precursor A using the synthetic powder A and a synthetic powder B are used. Precursor B was prepared. Then, the precursors A and B were set in the furnace, and the following steps were performed.
First, the temperature was raised from room temperature to 1100 ° C. in 70 hours, and the temperature was maintained at this temperature for 20 minutes to bring the precursor into a semi-molten state, and then 5 ° C. above and below the precursor so that the upper part of the precursor was on the low temperature side. / Cm, and the temperature was lowered at 0.4 ° C / min until the upper temperature reached 995 ° C.

Here, had been prepared in advance by fusion method, a seed crystal of Nd _1.8 Ba _2.4 Cu _3.4 O _x composition containing 0.5 wt% of Pt not contain Ag, vertical and horizontal 2 mm, manufactured by cutting the thickness of 1mm The seed crystal placed is brought into contact with the upper center of the precursor so that the growth direction is parallel to the c-axis. Then, the temperature of the upper part was decreased from 995 ° C. to 985 ° C. at a rate of 1 ° C./hr. After maintaining at this temperature for 100 hours, the temperature is gradually cooled to 915 ° C. over 70 hours, and then the lower part of the precursor is cooled to 915 ° C. in 20 hours so that the upper and lower temperature gradients become 0 ° C./cm. Thereafter, crystallization was performed by gradually cooling to room temperature over 100 hours to obtain a crystal sample A of the oxide superconductor from the precursor A and a crystal sample B of the oxide superconductor from the precursor B.

When the crystal samples A and B of the oxide superconductor were cut in the vicinity of the center in the vertical direction and their cross sections were observed by EPMA, both of them were Sm _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O The Sm _{2 + r} Ba _{1 + s} (Cu _1-d Ag _d ) O _5-y phase of about 0.1 to 30 μm was finely dispersed in the _7-x phase. Here, p, q, r, s, and y were values of -0.2 to 0.2, respectively, and x was a value of -0.2 to 0.6. Also, b and d were values of 0.0 to 0.05, and were about 0.008 on average. Further, Ag of about 0.1 to 100 μm was finely dispersed throughout the crystal sample. In addition, pores having a particle size of about 5 to 200 μm were dispersed in a portion deeper than 1 mm from the surface. In addition, the entire crystal sample is uniformly oriented so that the thickness direction of the disk-shaped material reflects the seed crystal so that the thickness direction is parallel to the c-axis, and the misorientation of the orientation between adjacent crystals is 3 ° or less. As a result, crystal samples A and B in the form of single crystals were obtained. A portion deeper than 1 mm was cut out from the surface of each of the crystal samples A and B, and the density was measured. As a result, 6.7 g / cm ³ (theoretical density of 7.38 g / cm ³⁾ was obtained for the crystal A having a composition of 1: 0.4. Of Crystal B produced with a composition of 1: 0.3 was 6.7 g / cm ³ (91.2% of the theoretical density of 7.35 g / cm ³ ).

After removing a 1 mm portion from the surface of the obtained crystal samples A and B, a columnar oxide superconductor A having a width of 3 mm, a thickness of 3 mm, and a length of 90 mm was set so that the length direction became parallel to the ab plane of the crystal. B was cut out.
Further, a columnar sample of 3 mm × 3 mm × 20 mm (one of the 3 mm directions is the c-axis direction of the crystal) was cut out from the sample, and the temperature dependence of the thermal conductivity after the annealing was measured. A was about 62.1 mW / cmK and B was about 62.9 mW / cmK in the integrated average value from 1 to 10 K, which were low values despite the fact that silver contained 10 wt%.

Or later,
2) Installation of silver coat on columnar oxide superconductors A and B 3) Annealing treatment of silver coat oxide superconductors A and B 4) Preparation of metal electrode and drift suppression member 5) Preparation of oxide superconductors A and B Installation on metal electrode 6) Deaeration treatment of joining metal 7) Installation of covering member was performed in the same manner as in Example 1, and current lead A using oxide superconductor A and current using oxide superconductor B Lead B was obtained.
8) Evaluation of Characteristics of Current Leads A and B The electrical characteristics of the obtained current leads A and B were measured in the same manner as in Example 1, and the following results were obtained.
First, when the contact resistance value at the junction between the metal electrode and the oxide superconductor at both ends of the current lead A was calculated, one was 0.28 μΩ and the other was a very low value of 0.29 μΩ. Similarly, at the junction of the current lead B, one was found to be 0.30 μΩ and the other was at a very low value of 0.29 μΩ.

Further, when the current leads A and B were cooled down to 4.2K and the contact resistance between the metal electrode and the oxide superconductor was calculated in the same manner, the contact resistance on both sides of both A and B was 0.1. It turned out to be a very low value of 05 μΩ.
Further, when the low temperature side of the current lead sample was cooled to 4.2K and the high temperature side was cooled to 77K, the heat intrusion into the low temperature side due to heat transfer was about 0.15 W for both A and B.
On the other hand, the critical current value at 77 K of the current lead sample was 1300 A for A and 1500 A for B in a magnetic field of 0.5 T.
From the above, in the current lead sample, when one of the metal electrodes was set to the high temperature side (77K) and the other was set to the low temperature side (4.2K) and a current of 1000A was applied in a 0.5T magnetic field, the heat on the low temperature side was changed. The amount of generation was found to be a very low value of 0.2 W in total.
Lastly, the joints on both sides of the current leads A and B were cut, and the percentage of the volume of the holes in the joining metal provided at the joints was measured. . As a result, it was found that one of the current leads A occupies 0.06%, the other occupies 0.07%, the one of the current leads B occupies 0.07%, and the other occupies 0.08%.

(Example 4)
In Example 1, an oxide superconductor current lead sample was manufactured in the same manner as in Example 1, except that the temperature of 6) the deaeration treatment of the joining metal was changed to 160 ° C.
Similar to Example 1, when the contact resistance value of the joint between the metal electrode and the oxide superconductor on both sides of the current lead sample was calculated, one was 0.3 μΩ, and the other was 0.27 μΩ. It turned out to be a low value.
Further, the current lead sample was cooled to 4.2K, and the contact resistance between the metal electrode and the oxide superconductor was calculated in the same manner. As a result, it was found that both sides had a very low value of 0.05 μΩ. did.
On the other hand, the critical current value and heat of penetration of the current lead sample in a 77 K, 0.5 T magnetic field were almost the same as those in Example 1.

From the above, in the current lead sample, when one of the metal electrodes was set to the high temperature side (77K) and the other was set to the low temperature side (4.2K) and a current of 1000A was applied in a 0.5T magnetic field, the heat on the low temperature side was changed. The amount of generation was found to be a very low value of about 0.38 W in total.
Lastly, the joints on both sides of the current lead sample were cut, and the percentage of the volume of the holes in the joining metal provided at the joints was measured. As a result, it was found that one occupies 5% of the volume of the joined portion, and the other occupies 4%.

(Comparative Example 1)
Same as Example 2 except that the set temperature of the ultrasonic solder gloves was set to 160 ° C. and 180 ° C. without performing the step of “6) Deaeration treatment of bonding metal”, and current leads were manufactured respectively. And "8) Evaluation of characteristics of current lead".
First, for the sample joined at 160 ° C., the contact resistance of the joint between the metal electrode and the oxide superconductor on both sides of the current lead sample was calculated in the same manner as in Example 1. It was found that the absolute value was large at 0.8 μΩ and the other value was 0.9 μΩ, and the variation in the contact resistance value was also large.
In the sample joined at the setting of 180 ° C., the flowing out of the joining metal was large. However, when the contact resistance was calculated, one was 1.2 μΩ and the other was 1.1 μΩ. Also turned out to be great.

  Lastly, the joints on both sides of the current lead sample were cut, and the percentage of the volume of the holes in the joining metal provided at the joints was measured. As a result, it was found that one of the samples joined at the setting of 160 ° C. occupied 30% of the volume of the joined portion, and the other occupied 35% of the volume of the joined portion. It was found that the joint occupied 50% of the volume and the other 45%.

As described above, metal electrodes are provided on both sides of the oxide superconductor, and a bonding metal is provided at a bonding portion formed by the oxide superconductor and the metal electrode, and by the bonding metal, An oxide superconducting current lead in which the oxide superconductor and the metal electrode are joined,
The volume of holes in the bonding metal provided in the bonding portion is an oxide superconducting current lead having a volume of 5% or less of the volume of the bonding portion, and the oxide superconducting current lead is an oxide superconductor. As a result, a sufficient current flow path is secured between the oxide superconductor and the metal electrode. The resistance value and low heat penetration to the low temperature side are realized.

  FIG. 7 shows a list of processing conditions and evaluation results of Examples 1 to 4 and Comparative Example 1 described above. In FIG. 7, one of the joining portions between the metal electrode and the oxide superconductor on both sides of the current lead sample is conveniently described as “right” and the other as “left”.

It is a perspective view which shows the example of installation of the superconductor to the metal electrode of the current lead which concerns on this invention. FIG. 2 is a perspective view when a sealing member is provided on the metal electrode shown in FIG. 1. It is a conceptual diagram of the characteristic measurement of the oxide superconducting current lead which concerns on this invention. It is a perspective view when the joined body of an oxide superconductor and a metal electrode is put in a metal mold. FIG. 4 is a cross-sectional view of a joining portion between an oxide superconductor and a metal electrode according to a conventional technique. 1 is a perspective view of an oxide superconducting current lead according to a precursor invention. 5 is a list of processing conditions and evaluation results of Examples 1 to 4 and Comparative Example.

Explanation of reference numerals

1. (Oxide superconductor) Current lead 10. Metal electrode 31. (Oxide superconductor) Installation groove 41. (Outer edge of oxide superconductor installation groove) Sealing member 42. Deaeration unit 50. Drift preventing member 60. Oxide superconductor 61. Silver coat 70. Covering member

Claims (6)

A metal electrode is provided on both sides of the oxide superconductor, and a bonding metal is provided at a bonding portion formed by the oxide superconductor and the metal electrode. An oxide superconducting current lead joined to a metal electrode,
An oxide superconducting current lead, wherein the volume of holes in the joining metal provided at the joining portion is 5% or less of the volume of the joining portion. An oxide superconducting current lead according to claim 1,
An oxide superconducting current lead, wherein a silver coat is provided on a surface of the oxide superconductor joined by the joining metal. The oxide superconducting current lead according to claim 1 or 2,
An oxide superconducting current lead characterized in that the bonding metal is a solder containing at least one of Cd, Zn, and Sb and at least one of Pb, Sn, and In. A metal electrode is provided on both sides of the oxide superconductor, and a bonding metal is provided at a bonding portion formed by the oxide superconductor and the metal electrode. A method for manufacturing an oxide superconducting current lead in which a metal electrode is joined,
When joining the oxide superconductor and the metal electrode with the joining metal, the joining portion is heated to a temperature equal to or higher than the melting point of the joining metal, and then the pressure is reduced to degas the joining metal. A method for manufacturing an oxide superconducting current lead, comprising the steps of: It is a manufacturing method of the oxide superconducting current lead of Claim 4, Comprising:
A method for manufacturing an oxide superconducting current lead, comprising: providing a sealing member that suppresses the joining metal from flowing out of the joining portion when the joining metal is heated and degassed.   A superconducting system using the oxide superconducting current lead according to any one of claims 1 to 3.

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