JP4857435B2 - Oxide superconducting current lead, manufacturing method thereof, and superconducting system - Google Patents

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 in MRI, linear, SMES, etc., a manufacturing method thereof, and a superconducting system.

  A current lead used when supplying a large current to a superconducting magnet or the like is for supplying a current of several hundred to several thousand amperes 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 value has been used as the current lead. However, if a 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 passed through the copper wire, then this wire diameter is increased. Heat penetration due to heat conduction occurred to the superconducting system via the copper wire, and the power loss of the refrigerator and the loss of He gas of the refrigerant due to this heat penetration were large. Therefore, Patent Document 1 proposes to interpose an oxide superconductor, which has a thermal conductivity smaller than copper and does not generate Joule heat even when a large current flows, in the middle of the current lead.

Japanese Utility Model Publication No. 63-230307

In recent years, the development of superconducting application equipment has progressed, and the level of required performance for oxide superconducting current leads has become high, allowing more current to flow, less Joule heat generation, and heat penetration from the outside world. Less has been required.
Incidentally, in the SMES for power storage, which is the main application of the oxide superconducting current lead, examples of the required level for the oxide superconducting current lead of 1MJ class SMES are the high temperature side temperature 77K, the low temperature side temperature 4.2K, the external magnetic field 0 Under 5T, a predetermined current of 1000 A or more can be passed, and the heat penetration from the high temperature side to the low temperature side is 0.5 W or less. This is because 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 power storage SMES.

  However, the oxide superconductor used in the oxide superconducting current lead is a ceramic and has poor bondability with a metal, and at the joint surface with a metal electrode (generally, a copper electrode is used) Electric resistance that cannot be ignored (hereinafter referred to as contact resistance) occurs. 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 value of the contact resistance described above, it was first attempted to interpose silver in the form of a silver coat between the oxide superconductor and the copper electrode. That is, it is noted that the contact resistance value between silver and the oxide superconductor is lower than the contact resistance value between copper and the oxide superconductor, and a silver foil is pressure-bonded to the oxide superconductor, a silver paste material is applied, or After thermally spraying and adhering silver, this is baked into a silver coat, and the oxide superconductor with the silver coat and the copper electrode are joined using a joining metal such as solder, and the 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 allowing a predetermined current to flow through the current lead, the oxide superconductor has been increased in size to increase the contact area with the copper electrode.
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 increased through the oxide superconductor.

Thus, for example, an oxide superconducting current lead as shown in FIG. 6 has been considered.
The oxide superconducting current lead 100 shown in FIG. 6 has a copper electrode as a metal electrode on both sides of a rare earth oxide superconductor 110 manufactured by a melting method capable of flowing a large current even with a small cross-sectional area. 120 is connected. The both end portions 112 of the rare earth oxide superconductor 110 have a large cross-sectional area, while the central portion 111 has a small cross-sectional area. On the other hand, also in the copper electrode 120, the contact part 121 which contact | connects the both ends 112 of an oxide superconductor is wrapped so that both ends 112 may be wrapped, and both can ensure a wide contact area.
The oxide superconducting current lead 100 was able to suppress both generation of Joule heat and heat penetration from the high temperature side to the low temperature side even when a predetermined current was passed.

  However, among oxide superconductors, suitable for current leads, rare-earth oxide superconductors manufactured by the melting method are manufactured in a shape in which only the central portion is narrowed as shown in FIG. Difficult to do. Therefore, in order to produce 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 produced, and then In order to reduce the heat intrusion through the rare earth oxide superconductor, it is necessary to take a step of cutting the central portion to reduce the cross-sectional area. However, in this case, when a predetermined current value flowing to the oxide superconducting current lead is large, a large-scale rare earth oxide superconductor must be manufactured and the rare earth oxide superconductor must be largely cut. The yield of the rare earth-based oxide superconductor is very poor and requires a lot of man-hours. Further, since the metal electrode portion is enlarged, 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, the first configuration for solving the above-described problem is that a metal electrode is provided on both sides of the oxide superconductor, and a bonding metal is present at a joint portion formed by the oxide superconductor and the metal electrode. An oxide superconducting current lead provided, wherein the oxide superconductor and the metal electrode are joined by the joining metal;
The oxide superconducting current lead is characterized in that the volume of pores in the bonding metal provided in the bonding portion is 5% or less of the volume of the bonding portion.

The second configuration is the oxide superconducting current lead according to the first configuration,
The oxide superconducting current lead is characterized in that a silver coat is provided on the 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 bonding metal is an oxide superconducting current lead characterized in that it is solder containing at least one of Cd, Zn, and Sb and at least one of Pb, Sn, and In.

In the fourth configuration, 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. A method of manufacturing 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 depressurized to deaerate the joining metal. It is a manufacturing method of an oxide superconducting current lead characterized by having a process.

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

  The 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 the oxide superconducting current lead, measured the value of the contact resistance at the interface between the oxide superconductor and the metal electrode in detail, and for each sample of the oxide superconducting current lead And found that the value of contact resistance is 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 examined in detail over the entire surface.
As a result, it has been found that there is a void in the bonding metal on the bonding surface between the oxide superconductor and the metal electrode. And when the volume of the void | hole in this metal for joining was integrated | accumulated, it turned out that it is about 30% or more of the volume of a junction part. Therefore, as described in the first configuration, when the volume of the voids in the bonding metal is 5% or less of the volume of the bonded portion, the contact resistance value between the oxide superconductor and the metal electrode is reduced, It is possible to suppress the Joule heat generated even when a predetermined current is passed by joining the metal electrode without enlarging the cross-sectional area of the oxide superconductor at the contact portion between the oxide superconductor and the metal electrode. It was.

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

  As described in the third configuration, when a solder containing one or more of Cd, Zn, and Sb and one or more of Pb, Sn, and In is used as a bonding metal, a metal electrode and an oxide are used. Since it is possible to suppress peeling between superconductors and cracks in the oxide superconductor, the oxide superconducting current lead using the above-described solder as a bonding metal can 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 the melting point or higher, the pressure is reduced and degassed, whereby the bonding metal provided in the bonding portion It was possible to reduce the volume of pores.

  As described in the fifth configuration, when the joining metal is degassed, a sealing member that suppresses the joining metal from flowing out to a portion where the joining metal joint comes into contact with the outside world is provided. By suppressing the outflow from the joining portion, the occurrence of voids due to insufficient amount of joining metal in the joining portion is avoided, and the joining metal diffuses to portions other than the joining portion. It was also possible to avoid an increase in the contact resistance value.

  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 has a high current side to a low temperature side even when a predetermined current flows. Since there is little heat penetration, the burden on the refrigerator can be reduced, resulting in a superconducting system with low production and running costs.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing an installation example of an oxide superconductor on a metal electrode in an 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 conceptual diagram of characteristic measurement of an oxide superconducting current lead according to the present invention, and FIG. 4 is a diagram of bonding of an oxide superconductor and a metal electrode. FIG. 5 is a perspective view when the joined body is placed in a mold in order to coat a covering member on the body, and FIG. 5 is a diagram of an oxide superconductor and a metal in an oxide superconducting current lead manufactured by a conventional technique. It is a typical cross-sectional view of a junction 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 has a metal electrode 10, a drift suppressing 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 opposite to the other end of the oxide superconductor 60.

  First, the metal electrode 10 includes a flat lead wire joint portion 20 and a rectangular parallelepiped oxide superconductor installation portion (hereinafter referred to as an installation portion) 30. The lead wire joint portion 20 is provided with a desired number of lead wire installation holes 21 for installing lead wires, bus bars and the like. 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 opposing surface 33 of the installation part 30, and the oxide superconductor inheriting part is provided on the opposing surface 33. (Hereinafter, referred to as a “passing part”) 32 is provided in a U-shape with the upper part opened so as to surround the installation groove 31. Further, the inner wall of the installation groove 31 improves the adhesion with a bonding metal, which will be described later, and the lead wire bonding portion 20 is preliminarily made of tin, in order to reduce the contact resistance with the lead wire or bus bar to be bonded thereto. It is preferable to provide a plating containing silver, gold, nickel, zinc, palladium alone or an alloy as a main component, or a laminate of the plating.

  Next, the drift suppression member 50 includes 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 the installation groove 31 is inserted, it is integrated with the metal electrode 10. The drift suppressing member 50 and the installation groove 31 are also plated with tin, silver, gold, nickel, zinc, palladium as a main component or an alloy as a main component in advance in order to improve adhesion with a bonding metal described later. It is preferable to provide a laminate of plating.

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

  Furthermore, a covering member 70 that covers the oxide superconductor 60 is provided between the opposing surfaces 33 of the metal electrodes 10 that face each other with the prismatic oxide superconductor 60 interposed therebetween. The covering member 70 is supported by the inheriting 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 capable of flowing a large current even with a small cross-sectional area. This is because heat penetration 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, the oxide superconductor 60 can be manufactured by cutting out from the oxide superconductor as a base material, and after this cutting, a larger cutting There is no need to process.

  Next, installation of the oxide superconductor 60 and the drift suppressing 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 portion of the oxide superconductor 60 is filled, but considering that a large current of 1000 A or more flows through the portion, its width -The height and depth are preferably 3 x 3 x 10 mm or more.

  In the installation groove 31, the end of the oxide superconductor 60 is installed, and the drift suppressing 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. And the clearance gap between this drift suppression member 50 and the installation groove | channel 31 becomes the deaeration part 42 demonstrated in FIG. At this time, if the gap is 0.05 mm or more, deaeration of the bonding metal proceeds sufficiently, and if it is 0.5 mm or less, an unnecessary increase in contact resistance due to an increase in the volume of the bonding metal can be avoided. .

  Returning again to FIG. 2, when the drift suppression member 50 is installed in the installation groove 31, the drift suppression member main body 51 is substantially flush with the upper surface 34 and the opposing surface 33 of the metal electrode, and the protrusion 52 is the inheriting portion 32. It is preferable that the size be integrated with the above. And when the edge part of the oxide superconductor 60 is installed in the installation groove | channel 31, and also when the drift suppression member 50 is installed on it, the metal electrode 10 containing this installation groove | channel 31 and the drift suppression member 50, and an oxide A portion surrounded by the end portion of the superconductor 60 constitutes a joint 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 suppressing member 50 are previously coated with silver 61 from the viewpoint of reducing the contact resistance of this portion. As a silver coating method, a silver paste material coating and baking method, a plating method, a vapor deposition method, a sputtering method, a thermal spraying method, and the like can be applied. Therefore, the method may be appropriately selected from the viewpoints of productivity and mass productivity. And it is preferable to melt-apply the joining metal for joining the oxide superconductor 60 to the installation groove 31 on the silver coat 61. As this bonding metal, various solders having a melting point of 300 ° C. or lower are preferably used in order to avoid that the oxide superconductor is heated and oxygen is released therefrom. Above all, from the viewpoint of increasing the adhesion of the joint portion and lowering the contact resistance, for example, Pb-Sn system and In system to which Cd, Zn, Sb, etc. are added so as to increase adhesion and paintability with ceramics. It is desirable to use this solder material.

  That is, the solder containing one or more of Cd, Zn, and Sb and containing one or more of Pb, Sn, and In has high adhesion strength with both the metal electrode and the oxide superconductor. For this reason, due to the difference in linear expansion between the metal electrode and the oxide superconductor, a stress is generated between the metal electrode and the oxide superconductor due to the temperature of liquid nitrogen or lower and the thermal history up to 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 the occurrence of cracks in the oxide superconductor can be suppressed, and the resistance does not increase even when the thermal history is repeated. It is thought that it was able to flow stably.

Here, Cerasolzer (registered trademark) is described as a preferred example of the solder material for ceramic.
Cerasolza 143 manufactured by 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: 44-50 (Wt%), Cd: 45-50, Zn: 1-3, less than Sb: 1 Melting point: 123 ° C

  An end portion of the oxide superconductor 60 is inserted into the installation groove 31 provided in the metal electrode 10, and a drift suppressing member 50 is installed thereon to form a joint portion. 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 surface contact state. Is preferable. Of course, as another embodiment, the metal electrode is formed in a cap shape and the oxide superconductor is filled therein, or the metal electrode can be divided, and the metal electrode is sandwiched between the oxide superconductors. It is also possible to take a form of assembling, and the structure of the oxide superconductor may be cylindrical or cylindrical.

  In the installation groove 31, the bonding metal is melt-coated, and the oxide superconductor 60 in which the bonding metal is melt-coated is installed on the silver coat. The oxide superconductor 60 and the installation groove 31 are connected to each other. A molten bonding metal is placed at the bonding portion to be formed, and this is solidified and bonded together.

  In the joining using this joining metal, in order to install the melted joining metal on the oxide superconductor 60 or on the wall of the installation groove 31, a gaseous component such as the atmosphere is involved when performing coating or injection. . The gaseous component entrained in the molten bonding metal forms voids inside when the bonding metal solidifies. When a hole is formed in the bonding metal, the flow path of the current flowing between the metal electrode and the oxide superconductor through the bonding metal is narrowed. It is thought that the part was the cause of 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 the holes are formed will be described with reference to FIG.
In FIG. 5, in the installation groove 31 provided in the metal electrode 10, a portion coated with the silver coat 61 of the oxide superconductor 60 is installed, and a junction constituted by the metal electrode 10 and the oxide superconductor 60. The metal 90 for joining is provided in the part. Then, when the metal electrode 10 and the oxide superconductor 60 are bonded using the bonding metal 90 according to the conventional technique, the holes 91 exist in the bonding metal 90. The ratio of the volume of the air holes 91 to the volume of the joint portion can be measured by the following method, for example. That is, the joint portion is sequentially cut, the ratio of the cross-sectional area of the joint portion and the cross-sectional area of the hole 91 appearing on the cut surface is measured, and the values are sequentially integrated.

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

  Therefore, as a method for suppressing or avoiding the generation of voids in the bonding metal, it has been considered to apply the bonding metal described above in a vacuum. However, from the viewpoint of workability and productivity, when the joining metal is applied in the atmosphere, the oxide superconductor 60 is placed in the installation groove 31 and heated to melt the joining metal and join them. Furthermore, it has been conceived that it is preferable to expose the part in a vacuum and remove the gaseous component in the bonding metal by vacuum degassing. As a condition for this vacuum deaeration, the heating temperature of the bonding metal may be higher than the melting point, but from the viewpoint of allowing the deaeration to proceed in a short time and suppressing the oxidation of the bonding metal, the melting point is about +15 to 100 ° C. Is desirable. The effect can be obtained if the ambient vacuum is 0.01 MPa or less, but if it is 10 Pa or less, degassing is completed in 4 to 5 seconds, which is more desirable. At this level of temperature and time, it is not necessary to consider that oxygen escapes from the oxide superconductor 60.

  Further, when the melted bonding metal flows out of the installation groove 31 and diffuses to other portions of the metal electrode 10 during the vacuum degassing, the amount of the bonding metal is insufficient in the installation groove 31 but diffused. In a portion, it causes an increase in the contact resistance value of that portion, which is not preferable, so it is preferable to adopt a configuration that suppresses this.

A specific configuration example for suppressing the loss of the bonding metal will be described with reference to FIG.
In FIG. 2, the end portion of the oxide superconductor 60 is installed in the installation groove 31 provided in the metal electrode 10. A sealing member 41 is installed along the outer peripheral edge of the installation groove 31 and the oxide superconductor. In addition, when installing the sealing member 41 along the outer peripheral edge of the installation groove 31, it is possible to install the deaeration part 42 formed by inserting the drift suppressing member 50 into the installation groove 31 so as not to be blocked. preferable. As the sealing member 41, silicon rubber or the like that does not change even at a temperature equal to or higher than the melting point of the bonding metal, has an appropriate adhesive force to the metal electrode 10 or the oxide superconductor 60, and is easy to install. Can be used for personal use.

  When the installation of the sealing member 41 to 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 removed according to the above conditions. When the vacuum deaeration is performed, the generated gas component is discharged from the deaeration unit 42. At this time, if the generated void is difficult to burst due to the high viscosity of the molten bonding metal, for example, using an ultrasonic vibrator of an ultrasonic soldering hand, the void generated by mechanical impact is ruptured. And vacuum degassing is preferably performed. In the present embodiment, first, after the gas component is vacuum degassed from the molten bonding metal, the drift suppressing member 50 is fitted into the installation groove 31 and vacuum deaeration is performed again. At this time, by applying a mechanical impact through the drift suppressing member 50, it is possible to easily realize the rupture of the voids in the molten bonding metal. As a result, the volume of the voids in the bonding metal installed in the joint portion formed by the installation groove 31 of the metal electrode 10, the drift suppressing member 50, and the oxide superconductor 60 is 5% or less of the volume of the joint portion. It became possible to suppress it.

  Here, the deaeration conditions in the bonding metal were changed, and a plurality of current lead samples having various values of the ratio of the volume of the bonding portion to the holes in the bonding metal were prepared. Then, the contact resistance value of the joined portion of the produced current lead sample was measured using a contact resistance value measuring method described later, the ratio between the volume of the joined portion and the voids in the joining metal, the contact resistance value, Sought the relationship.

Here, as an example of the oxide superconductor 60, a Gd-based oxide superconductor manufactured by a melting method 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 reason why the size of the Gd-based oxide superconductor is set is that the heat penetration through the oxide superconductor is 0.3 W or less. Of course, the cross-sectional shape may be square or circular. Both end portions 10 mm of the Gd-based oxide superconductor are joined to the metal electrodes (at this time, the joining area of the oxide superconductor and the metal electrode is 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 the pores inside.

  Then, when the deaeration operation in the joining metal is not performed, as described above, the ratio of the holes in the joining metal is about 30 to 50% of the volume of the joining portion, and a predetermined current is passed. The magnitude of the contact resistance value at that time was about 0.8 to 1.2 μΩ, and the variation in the contact resistance value depending on the sample was also large. However, when the ratio of the voids in the bonding metal is 5% or less of the volume of the bonded portion, the contact resistance value when a predetermined current flows is less than 0.5 μΩ, and at the same time, the contact resistance value There was less variation.

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 1000 A 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 added to the Joule heat generated by the contact resistance during energization, is well below 0.5 W.
Therefore, it has been found that the oxide superconductor has a shape as 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 an oxide superconducting current lead that requires cutting in the oxide superconductor, the amount of oxide superconducting current can be greatly reduced, and at the same time, the entire oxide superconducting current lead can be reduced. Miniaturization is also possible.

  Returning to FIG. 1, when the 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 so as to cover the oxide superconductor 60 therebetween. Since the covering member 70 protects the oxide superconductor 60 mechanically and environmentally, GFRP which is a resin material containing glass fibers is preferably used.

The process 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 at both ends is installed in a mold for coating a covering member.
In FIG. 4, an oxide superconductor 60 in which the above-described metal electrode 10 is bonded to both ends is installed 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 inheriting portion 32 and the drift suppressing member protruding portion 52 protrude from the metal electrodes 10 on both sides toward the mold space 81.
Meanwhile, a glass fiber is impregnated with a thermosetting resin to prepare a GFRP prepreg. The prepared GFRP prepreg was filled into the mold space 81 and heated and cured to obtain a covering member for the oxide superconductor 60. As a result, the covering member fits with the drift suppressing member protrusion 52 and the oxide superconductor inheriting portion 32 protruding from the metal electrode 10 and exhibits mechanical strength. Therefore, the covering member is excellent in electrical characteristics, mechanical and environmental. 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 remarkably 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 a position of 10 mm width at both ends and a position from 15 to 17 mm from both ends. And, up to the position of the width of 10 mm at both ends, it is joined to the metal electrode 10 as the silver coat 61, and the lead wire is connected as the measurement silver coat 62 at the position from 15 to 17 mm from both ends. Bus bars are 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 source (not shown). As the power source, a power source that supplies a current of 1060 A, for example, 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 this current lead 1 was cooled to 77K and a current of 1060 A was passed between both 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, based on an Example, embodiment of this invention is described in detail.
Example 1
1) Manufacture of columnar oxide superconductor Weigh each raw material powder of Sm ₂ O ₃ , BaCO ₃ and CuO 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 BaCuO ₂ and CuO calcined powder (in terms of molar ratio BaCuO ₂ : CuO = 2.3: 1.0). Next, the previously weighed Sm ₂ O ₃ is added to the calcined powder, and Pt powder (average particle size 0.01 μm) and Ag ₂ O powder (average particle size 13.8 μm) are added and mixed. And it baked at 900 degreeC in air | atmosphere for 10 hours, and was set as the calcining powder containing Ag. However, the Pt content was 0.42 wt% and the Ag content was 15 wt%. The Ag-containing calcined powder was pulverized with a pot mill to obtain a synthetic powder having an average particle size of about 2 μm.

The obtained synthetic powder was analyzed by powder X-ray diffraction. As a result, 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 confirmed.

This synthetic powder was press-molded into a plate shape having a length of 77 mm, a width of 106 mm, and a thickness of 26 mm to prepare a precursor. And this precursor was installed in the furnace and the following processes were performed.
First, the temperature is raised from room temperature to 1100 ° C. in 70 hours, and kept 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 portion of the precursor is on the low temperature side. A temperature gradient of / cm was applied, and the temperature was lowered at 0.4 ° C./min until the upper temperature reached 1025 ° C.

Here, an Nd _1.8 Ba _2.4 Cu _3.4 O _x composition crystal containing 0.5 wt% of Pt and not including Ag, which was previously prepared by a melting method, was cut into 2 mm length and 1 mm thickness and manufactured. The seed crystal was brought into contact with the upper center of the precursor so that the growth direction was parallel to the c-axis. The temperature of the upper part was lowered from 1025 ° C. to 1015 ° C. at a rate of 1 ° C./hr. After maintaining at this temperature for 100 hours, it 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 temperature gradient is 0 ° C./cm. Then, it was gradually cooled to room temperature over 100 hours to crystallize the precursor, and a crystal sample of an oxide superconductor was obtained.

When a crystal sample of this oxide superconductor was cut near the center in the vertical direction and the cross section was observed with EPMA, it was found in the Sm _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O _7-x phase. In addition, about 0.1 to 30 μm of Sm _{2 + r} Ba _{1 + s} (Cu _1-d Ag _d ) O _5-y phase 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. Moreover, b and d were values of 0.0 to 0.05, and were about 0.008 on average. Furthermore, about 0.1 to 100 μm of Ag was finely dispersed throughout the entire 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 reflects the seed crystal and is uniformly oriented so that the thickness direction of the disk-shaped material is parallel to the c-axis, and the deviation 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 this 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 was parallel to the ab plane of the crystal. Further, a columnar sample of 3 mm × 3 mm × 20 mm (where 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 the annealing treatment was measured. The integrated average value from 10 to 10K was about 113 mW / cmK, which was a low value despite the inclusion of 15 wt% silver.

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

  The prepared Ag paste was applied to both ends 10 mm of the column-shaped oxide superconductor prepared in 1), and 15 mm from the left and right ends with a width of 2 mm, a thickness of 50 μm, and vacuum impregnation treatment was performed. And then dried in an oven at 80 ° C. in the atmosphere. Next, the columnar oxide superconductor coated with this Ag paste was fired again at 920 ° C. for 10 hours in the furnace body, and Ag was baked 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 was placed in another furnace capable of gas replacement. First, the furnace was evacuated to 0.1 Torr with a rotary pump, and then into the furnace. Oxygen gas was flowed into the atmosphere of atmospheric pressure with an oxygen partial pressure of 99% or more. Thereafter, while oxygen gas is flowed into the furnace at a flow rate of 0.5 L / min, the temperature is raised from room temperature to 450 ° C. over 10 hours, and then gradually cooled from 450 ° C. to 250 ° C. over 400 hours. The temperature was lowered from 0 ° C. to room temperature in 10 hours, and the silver-coated oxide superconductor was annealed.

4) Production of metal electrode and drift suppressing member A metal electrode and a drift suppressing member were fabricated by processing oxygen-free copper having a purity of 4N, and Sn plating was applied to each surface. This metal electrode has a lead wire joint portion and an installation portion (oxide superconductor placement portion), the lead wire joint portion has two bolt holes, and the bonding strength of the covering member on the opposite surface of the installation portion There is provided a succession part to increase The drift suppression member is expected to be installed in the height direction by 3.5 mm and in the width direction by 0.5 mm from the size of the installation groove provided in the metal electrode, considering the installation of the oxide superconductor and the filling of the bonding metal. It was set as the processed shape.

5) Installation of oxide superconductor on metal electrode Cerasolzer 143 (hereinafter referred to as Cerasolzer), which is a PbSn solder, is melt-coated as a bonding metal in the metal electrode installation groove, and Ag is added thereto. An oxide superconductor in which Cerasolzer is melt-coated is placed on the baked end 10 mm, and is temporarily fixed by heating. When the temporary fixing is completed, heat-resistant silicon rubber is provided as a sealing member from the outer periphery of the oxide superconductor to the outer edge of the installation groove, and processing for preventing the cerasolzer from flowing out is performed.

6) Joining metal deaeration treatment When the outflow prevention treatment is completed, the metal electrode is heated at 180 ° C., which is higher than the melting point (143 ° C.) of the Cerasolzer, and the Cerasolzer is sufficiently melted. Deaerate at 100 Pa for 2 minutes. Next, the metal electrode is heated again to 180 ° C., and a member for suppressing drift, to which Cerasolzer has been melt-coated in advance, is applied, and again placed in a vacuum vessel and deaerated at about 100 Pa for 2 minutes. Then, a mechanical shock is applied by the ultrasonic soldering hand through the drift suppressing member, and the holes of the existing Cerasolzer are ruptured.

As a result, the metal electrode, the oxide superconductor, and the drift suppressing member are bonded in a preferable state both electrically and mechanically by the bonding metal that does not include the voids. When the joining is completed, the sealing member is removed.
In this example, in order to measure the characteristics of the manufactured current lead, the diameter of 0.1 mm for characteristic measurement was applied to the portion baked with Ag provided at a position of 15 to 17 mm from the end of the oxide superconductor. These stainless steel lead wires were connected using Cerasolzer.

7) Installation of covering member A thermosetting epoxy resin adhesive 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 of the oxide superconductor with the copper electrode bonded thereto were placed in the mold so that only the oxide superconductor portion 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 an oxide superconductor current lead sample coated with glass fiber.

8) Characteristic evaluation of current lead In the manufactured current lead sample, a bus bar is connected to the lead wire joint of the metal electrode, the metal electrode and the oxide superconductor are cooled to 77K, and 1060A is energized between the two metal electrodes. did. Then, while energizing, the voltage between the metal electrode and the oxide superconductor was measured between the metal electrode and the oxide superconductor by measuring the voltage between the stainless steel wire for characteristic measurement connected at a position of 15 to 17 mm from the end of the oxide superconductor. As a result, the contact resistance values on both sides of the current lead sample were found to be very low, 0.19 μΩ.

Further, when the current lead sample was cooled to 4.2 K and the contact resistance value between the metal electrode and the oxide superconductor was calculated in the same manner, the contact resistance value on both sides was as very low as 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 heat penetration amount due to heat transfer to the low temperature side was 0.28 W.
On the other hand, when the critical current value in the 77K, 0.5T magnetic field of the current lead sample was measured by applying current up to 2000A, it was found that there was no generation of resistance and it was 2000A or more. Then, when the cross section of the superconductor sample was ground from 3 mm × 5 mm to φ1.9 mm and the width was about 0.7 mm, the effective cross-sectional area was reduced and the current test was performed again. As a result, the critical current value was 670A. When this result is converted back to 3 mm × 5 mm in the current lead sample, it is a value corresponding 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 is on the high temperature side (77K) and the other is the low temperature side (4.2K) and 1000 A is energized in a magnetic field of 0.5 T, the heat on the low temperature side The amount of generation was found to be a very low value of 0.31 W in total.
Finally, the joint portions on both sides of the current lead sample were cut, and the percentage of the volume of the joints in the bonding metal placed in the joint portion was measured. As a result, it was found that one occupies 0.07% of the volume of the joint portion and the other occupies 0.08%.

(Example 2)
1) Production of columnar oxide superconductor Gd ₂ O ₃ , BaCO ₃ , and CuO raw material powders are weighed and mixed so that the molar ratio is Gd: Ba: Cu = 1: 2: 3. After firing at 30 ° C. for 30 hours, the powder is pulverized to an average particle size of 3 μm using a pot mill, again baked at 930 ° C. for 30 hours, and then pulverized to an average particle size of 10 μm using a lykai machine and pot mill. A powder of Gd ₁ Ba ₂ Cu ₃ O _{7-x that is} a powder was produced.
Next, each raw material powder is 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 size of 0.7 μm using a pot mill. and, to prepare a powder of Gd ₂ BaCuO ₅ is a second calcined powder.

The first and second calcined powders are 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. And this precursor was installed in the furnace and the following processes were performed.
First, the temperature is raised from room temperature to 1100 ° C. in 70 hours, and kept 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. A temperature gradient of / cm was applied, and the temperature was lowered at 0.4 ° C./min until the upper temperature reached 995 ° C.

Here, a seed crystal of Nd _1.8 Ba _2.4 Cu _3.4 O _x composition containing 0.5 wt% of Pt not containing Ag, which was prepared in advance by a melting method, was cut into 2 mm length and 1 mm thickness and manufactured. The deposited seed crystal is brought into contact with the upper center of the precursor so that the growth direction is parallel to the c-axis. The temperature of the upper part was lowered from 995 ° C. to 985 ° C. at a rate of 1 ° C./hr. After maintaining at this temperature for 100 hours, it 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 temperature gradient is 0 ° C./cm. Then, crystallization was performed by gradually cooling to room temperature over 100 hours to obtain a crystal sample of an oxide superconductor.

A crystal sample of this oxide superconductor was cut near the center in the vertical direction and the cross section was observed with EPMA. As a result, it was found in the Gd _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O _7-x phase. Further, a 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. Moreover, b and d were values of 0.0 to 0.05, and were about 0.008 on average. Furthermore, about 0.1 to 100 μm of Ag was finely dispersed throughout the entire 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 reflects the seed crystal and is uniformly oriented so that the thickness direction of the disk-shaped material is parallel to the c-axis, and the deviation 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 this crystal sample and the density was measured, it was 7.0 g / cm ³ (91.1% of the theoretical density 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, when a columnar sample of 3 mm × 3 mm × 20 mm (where 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 suppressing member 5) Installation of oxide superconductor on metal electrode 6) For bonding Metal deaeration treatment 7) Installation of covering member 8) The current lead characteristics were evaluated in the same manner as in Example 1, and the following results were obtained.
First, when the contact resistance value of the joint part 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 as 0.21 μΩ. There was found.

Further, when the current lead sample was cooled to 4.2 K and the contact resistance value between the metal electrode and the oxide superconductor was calculated in the same manner, the contact resistance value on both sides was as very low as 0.03 μΩ. It turned out to be.
Further, 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 heat penetration amount due to heat transfer to the low temperature side was 0.33 W.
On the other hand, when the critical current value in the 77K, 0.5T magnetic field of the current lead sample was measured by applying current up to 2000A, it was found that there was no generation of resistance and it was 2000A or more. Therefore, when the cross section of the superconductor sample was ground from about 3 mm × 5 mm to φ1.9 mm and the width was about 0.7 mm, the effective cross-sectional area was reduced and the current test was performed again. The critical current value was 530A. 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 is on the high temperature side (77K) and the other is the low temperature side (4.2K) and 1000 A is energized in a magnetic field of 0.5 T, the heat on the low temperature side The generated amount was found to be a very low value of 0.36 W in total.
Finally, the joint portions on both sides of the current lead sample were cut, and the percentage of the volume of the joints in the bonding metal placed in the joint portion was measured. As a result, it was found that both occupied about 0.1% of the volume of the joint portion.

(Example 3)
1) Production of columnar oxide superconductor Sm ₂ O ₃ , BaCO ₃ , and CuO raw material powders are weighed and mixed so that the molar ratio is Sm: Ba: Cu = 1: 2: 3, and 920 After firing at 30 ° C. for 30 hours, the powder is pulverized to an average particle size of 3 μm using a pot mill, again baked at 930 ° C. for 30 hours, and then pulverized to an average particle size of 10 μm using a lykai machine and pot mill. A powder of Sm ₁ Ba ₂ Cu ₃ O _{7-x which is} a powder was produced.
Next, the 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 size of 0.7 μm using a pot mill. and, to prepare a powder of Sm ₂ BaCuO ₅ is a second calcined powder.

The first and second calcined powders are 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 diameter 0.01 μm) and Ag ₂ O powder (average particle size 13.8 μm) was added and mixed to obtain a synthetic powder A. 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 a synthetic powder B. However, in both 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-molded into a plate shape having a length of 22 mm, a width of 120 mm and a thickness of 26 mm, respectively, using a mold, and a precursor A and a synthetic powder B using the synthetic powder A are used. Precursor B was prepared. And this precursor A and B was installed in the furnace body, and the following processes were performed.
First, the temperature is raised from room temperature to 1100 ° C. in 70 hours, and kept 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. A temperature gradient of / cm was applied, and the temperature was lowered at 0.4 ° C./min until the upper temperature reached 995 ° C.

Here, a seed crystal of Nd _1.8 Ba _2.4 Cu _3.4 O _x composition containing 0.5 wt% of Pt not containing Ag, which was prepared in advance by a melting method, was cut into 2 mm length and 1 mm thickness and manufactured. The deposited seed crystal is brought into contact with the upper center of the precursor so that the growth direction is parallel to the c-axis. The temperature of the upper part was lowered from 995 ° C. to 985 ° C. at a rate of 1 ° C./hr. After maintaining at this temperature for 100 hours, it 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 temperature gradient is 0 ° C./cm. Then, it was gradually cooled to room temperature over 100 hours for crystallization 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 near the center in the vertical direction and the cross section was observed with EPMA, both were Sm _{1 + p} Ba _{2 + q} (Cu _1-b Ag _b ) ₃ O. 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. Moreover, b and d were values of 0.0 to 0.05, and were about 0.008 on average. Furthermore, about 0.1 to 100 μm of Ag was finely dispersed throughout the entire 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 reflects the seed crystal and is uniformly oriented so that the thickness direction of the disk-shaped material is parallel to the c-axis, and the deviation of the orientation between adjacent crystals is 3 ° or less. Single crystalline crystal samples A and B were obtained. When a portion deeper than 1 mm was cut out from the surfaces of the crystal samples A and B and the density was measured, the crystal A produced with a composition of 1: 0.4 was 6.7 g / cm ³ (theoretical density 7.38 g / cm ^3). In the crystal B produced with a composition of 1: 0.3, it 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 so that the length direction is parallel to the ab plane of the crystal, B was cut out.
Further, a columnar sample of 3 mm × 3 mm × 20 mm (where 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 the annealing treatment was measured. A was about 62.1 mW / cmK, B was about 62.9 mW / cmK, and the values were low despite containing 10 wt% of silver.

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 electrodes and drift suppressing members 5) Preparation of oxide superconductors A and B Installation on metal electrode 6) Deaeration treatment of joining metal 7) Installation of covering member is performed in the same manner as in Example 1, and current lead A using oxide superconductor A, 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 values of the junctions between the metal electrode and the oxide superconductor at both ends of the current lead A were calculated, one was 0.28 μΩ and the other was very low, 0.29 μΩ. Similarly, at the junction portion of the current lead B, it was found that one is 0.30 μΩ and the other is very low, 0.29 μΩ.

Further, the current leads A and B were cooled to 4.2 K, and the contact resistance value between the metal electrode and the oxide superconductor was calculated in the same manner. It was found to be a very low value of 05 μΩ.
Further, 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 heat penetration amount due to heat transfer to the low temperature side 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 is on the high temperature side (77K) and the other is the low temperature side (4.2K) and 1000 A is energized in a magnetic field of 0.5 T, the heat on the low temperature side The amount of generation was found to be a very low value of 0.2 W in total.
Finally, the joint portions on both sides of the current leads A and B were cut, and each percentage of the volume of the joint portion measured by the volume of the holes in the joining metal installed in the joint portions was measured. . As a result, it was found that one of the current leads A occupies 0.06%, the other 0.07%, one of the current leads B 0.07%, and the other 0.08%.

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

From the above, in the current lead sample, when one of the metal electrodes is on the high temperature side (77K) and the other is the low temperature side (4.2K) and 1000 A is energized in a magnetic field of 0.5 T, the heat on the low temperature side The generated amount was found to be a very low value of about 0.38 W in total.
Finally, the joint portions on both sides of the current lead sample were cut, and the percentage of the volume of the joints in the bonding metal placed in the joint portion was measured. As a result, it was found that one accounted for 5% of the volume of the joint and the other accounted for 4%.

(Comparative Example 1)
As in Example 2, but without performing the step of “6) Deaeration treatment of metal for joining”, the set temperatures of ultrasonic soldering hands are set to 160 ° C. and 180 ° C., and current leads are manufactured respectively. And “8) Characteristic evaluation of current leads”.
First, with respect to a sample joined at a setting of 160 ° C., the contact resistance value of the joined portion 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, 0.8 μΩ, and the other 0.9 μΩ, and the variation in contact resistance value was large.
In the sample joined at 180 ° C., the joining metal flowed out greatly, but when the contact resistance value was calculated, one was 1.2 μΩ, the other was 1.1 μΩ, the absolute value was large, and the contact resistance value varied. Was also found to be large.

  Finally, the joint portions on both sides of the current lead sample were cut, and the percentage of the volume of the joints in the bonding metal placed in the joint portion was measured. As a result, it was found that one of the samples bonded at 160 ° C. accounted for 30% of the volume of the bonded portion, and the other accounted for 35%. It was found that 50% of the volume of the joint portion and the other accounted for 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. An oxide superconducting current lead in which the oxide superconductor and the metal electrode are joined,
The oxide superconducting current lead has a volume of pores in the joining metal provided in the joining portion of 5% or less of the volume of the joining portion. The oxide superconducting current lead is an oxide superconductor. As a result of ensuring a sufficient current flow path between the metal electrode and the metal electrode, even if the oxide superconductor used has substantially the same cross-sectional area throughout, low contact under certain conditions Achieved resistance and low heat penetration to the low temperature side.

  A list of processing conditions and evaluation results of Examples 1 to 4 and Comparative Example 1 described above is shown in FIG. In FIG. 7, for convenience, one of the joining portions of the metal electrode and the oxide superconductor on both sides of the current lead sample is 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. It is a perspective view at the time of providing a sealing member in the metal electrode shown in FIG. It is a conceptual diagram of the characteristic measurement of the oxide superconducting current lead according to the present invention. It is a perspective view at the time of putting the conjugate | zygote of an oxide superconductor and a metal electrode in a metal mold | die. It is a cross-sectional view of the junction part of an oxide superconductor and a metal electrode based on a prior art. 1 is a perspective view of an oxide superconducting current lead according to a precursor invention. FIG. It is a table | surface of the processing conditions and evaluation result of Examples 1-4 and a comparative example.

Explanation of symbols

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. Diffusion suppression member 60. Oxide superconductor 61. Silver coat 70. Covering member

Claims (6)

Metal electrodes are provided on both sides of the oxide superconductor, and a joining metal is provided at a joint portion formed by the oxide superconductor and the metal electrode. The joining metal forms the oxide superconductor and the oxide superconductor. An oxide superconducting current lead joined to a metal electrode,
The oxide superconducting current lead, wherein a volume of pores in the bonding metal provided in the bonding portion is 5% or less of a volume of the bonding portion. The oxide superconducting current lead of 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,
The oxide superconducting current lead is characterized in that the bonding metal is solder containing at least one of Cd, Zn, and Sb and at least one of Pb, Sn, and In. Metal electrodes are provided on both sides of the oxide superconductor, and a joining metal is provided at a joint portion formed by the oxide superconductor and the metal electrode. The joining metal forms the oxide superconductor and the oxide superconductor. A method of 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 depressurized to deaerate the joining metal. A method for producing an oxide superconducting current lead, comprising a step. A method of manufacturing an oxide superconducting current lead according to claim 4,
A method of manufacturing an oxide superconducting current lead, comprising: a sealing member that suppresses the joining metal from flowing out of the joining portion during heating and degassing of the joining metal.   A superconducting system using the oxide superconducting current lead according to any one of claims 1 to 3.

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