JP2550188B2 - Oxide-based high temperature superconductor, joining method and brazing material - Google Patents

Description

The present invention relates to a method for joining oxide-based high-temperature superconductors, a brazing filler metal for joining, and the above-mentioned superconductor joined body joined by the brazing filler metal. The present invention relates to the joining of oxide-based high temperature superconductors, which is very simple and can obtain a joined body having a low resistance at the connecting portion.

[Conventional technology]

The superconducting joint is a functional joint which requires that the joint lose its superconducting properties and that the resistance of the joint at liquid nitrogen temperature is as close to zero as possible.

At present, the main purpose of joining oxide-based high-temperature superconductors is to connect terminals when evaluating superconducting characteristics.

Conventionally, as the joining method, a method of soldering In while applying ultrasonic waves is known as a generally used method, but there is a problem in practical use due to a large connection resistance. It is necessary to reduce the connection resistance at least until the amount of heat generated by the connection resistance becomes smaller than the amount of heat radiation. On the other hand, Abride Physic Letters 52 (21) pp. 1819-
1821 (1988) (Appl.Phys.Lett.52 (21) PP1819-1
821 (1988)), a method of depositing a noble metal after sputter etching with Ar ions, etc., and then attaching a terminal by wire bonding on it has a connection resistance of 10 ^-10 Ω.
・ There is an effect that it can be made extremely small as cm ² . However, this joining method has limitations on the size of the article to be joined, the connection of the lead wires, and the like, and thus limits the range of applications. In the future, when considering joining based on various applications of oxide-based high-temperature superconductors, it is desired to develop a connection method that is not limited by the shape, size, material, etc. of the objects to be joined. Especially when considering the application to superconducting magnets, the connection should be made in order to eliminate quenching due to heat generation due to resistance and to improve stability, and to minimize current attenuation when used in the persistent current mode. It is essential to reduce the resistance as much as possible.

[Problems to be Solved by the Invention]

In the above-mentioned conventional technology, the connection resistance is large in indium soldering with a simple method and the connection method by vapor deposition on one side has a small connection resistance, but the materials that can be bonded to the oxide-based high temperature superconductor are limited. However, there is a problem that it is not suitable for joining with various members for various purposes.

An object of the present invention is to solve the above-mentioned problems of the prior art,
(EN) An oxide high-temperature superconductor, a method for joining the same, and a brazing material, which have low connection resistance and a wide range of applications, and which can be easily joined by a joining process.

[Means for solving the problem]

The present invention, on the surface of the oxide-based high temperature superconductor, by weight,
1 to 7% of Be, Mg, Ca, Sr, Ba and Ra, or 2 to 10% in total of 2 to 10%, or Zn1 to 40%, or Cd5 to 75%, or Mn, Fe, Co , Ni, Cr, Cu and Pd, one of 0.5 to 5%, or two or more of them in a total amount of 1 to 7.5%, and the balance is I
A high-temperature oxide-based superconductor is characterized in that a brazing material made of an alloy of n is joined, and the electrical resistivity of the joint decreases with a decrease in temperature.

The oxide-based high temperature superconductor is a wire rod, and the wire rods or the wire rod and the metal wire are joined by the brazing material.

The present invention relates to a method for joining oxide-based high-temperature superconductors, wherein the superconductors are the same or the superconductor and a metal are 1 to 7% by weight of one of Be, Mg, Ca, Sr, Ba and Ra. Or 2 to 10% in total of 2 to 10%, or Zn1 to 40%, or Cd5 to 75
%, Or one of Mn, Fe, Co, Ni, Cr, Cu and Pd, 0.5 to 5%, or two or more of the total amount of 1 to 7.5%,
A brazing material made of an alloy with the balance being In is joined by being heated and melted at a temperature of 150 to 350 ° C., and the electrical resistivity of the joined portion is decreased with a decrease in temperature. The heating and melting are preferably performed by bringing an ultrasonic iron heated to a predetermined temperature into contact with the brazing material, and the ultrasonic frequency is preferably 10 to 100 KHz. Also as an output
10 to 1000 W is preferable. By applying ultrasonic vibration to the brazing material, a high bonding strength of the brazing material to the oxide can be obtained. The melting point of the brazing material is preferably 100 to 300 ° C.

According to the present invention, by weight, one of Be, Mg, Ca, Sr, Ba and Ra is
~ 7% or 2 to 10% in total, containing 2 to 10% in total, the balance being made of In alloy, Zn 1 to 40 wt% and the balance being made of In alloy, Cd 5 to 75 wt% And the balance is In alloy, by weight, Mn, Fe, Co, Ni, C
For oxide-based high temperature superconductor bonding, characterized by comprising an alloy containing 0.5 to 5% of one of r, Cu and Pd, or 1 to 7.5% of two or more in total, with the balance being In. It is in brazing material.

The present invention is applicable to rotor and stator coils of rotating machines, energy storage coils, plasma container coils of the fusion device, power transmission and distribution cables, transformer coils, particle accelerator coils, MRI magnet coils, and NMR magnets. Coil, electron microscope coil, atomic absorption spectrometer magnet coil, linear motor car magnet coil, transportation motor rotor and stator coil wire, which is made of an oxide-based high-temperature superconductor. An apparatus using an oxide-based high-temperature superconducting wire, characterized in that the electric conductors or the superconductor and the metal are joined by the brazing material.

As the oxide-based high temperature superconductor of the present invention, all known oxide-based superconductors can be applied, and examples thereof include lanthanum-based, yttrium-based, thallium-based and bismuth-based.

Specific compounds include the following perovskite type oxides.

ABO ₃ ; A is Ba, Pb, La, Pr or Nd, B is Cu, Mg, Mn, Fe, Co, or Ni, A _1-x A ′ _x BO ₃ ; A and B are the same as above, A ′ is Ca, Ba, Sr or
PdO such as BaPb _1-x Bi _x O ₃ , BaPbO ₃ , LaCuO ₃ ,
LaCoO ₃ ,, (La _1-x Sr _x ) CoO ₃ , (La _1-x Sr _x ) CrO ₃ , (La _1-x Sr
_x ) CrO ₃ −δ or SrFeO ₃ .

A ₂ BO ₄ ; A is rare earth metal, B is transition metal. Examples of such materials include La ₂ CuO ₄ and La ₂ NiO ₄ .

A ₂ ( _1-x ) ′ _2x BO ₄ ; A and A ′ are Group III B and Group II
It is an element of A. Periodic Table, respectively, and B are transition metals. Such as (La _1-x Sr _x ) ₂ C
uO ₄ , (La _1-x Ba _xx ) ₂ CuO ₄ , (Y _1-x Ba _x ) ₂ CuO ₄ , (Y _1-x S
r _x ) ₂ CuO ₄ or (Sc _1-x Sr _x ) ₂ CuO ₄ .

AB ₂ C ₃ O _7-x ; A is Y, La, Nd, Dy, Sm, Eu, Gd, Ho, Er, Tm or Yb,
B is Ba, Sr, Ca or Sc, C is mainly Cu, such as YBa ₂ Cu ₃ O _7-x , LnBa ₂ Cu ₃ O _7-x , Ln is a lanthanoid, YSr ₂ Cu ₃ O _7-x , YBa ₂ Cu _3-x Ni
_x O _7-y , YBa ₂ Cu _3-x Ag _x O _7-y , YBaCaCu ₃ O _7-x , Y _0.75 Sc _0.25 Ba ₂
There is Cu ₃ O _7-x or YBa ₂ Cu ₃ F ₂ O _y .

A ₂ (B, C) ₃ D _{2 + x} O ₈ ; A is Bi or Tl, B is Ba or Sr, C is Ca, D
Is Cu, such as Bi ₄ Sr ₃ Ca ₃ Cu _{4 + x} O ₁₆ or Tl ₄ Ba ₂ Ca ₂ Cu _{4 + x} O ₁₆ .

AB ₂ O ₄ as spinel oxide, A is Li, B is Ti, L
There is iTi ₂ O ₄ .

INDUSTRIAL APPLICABILITY The present invention can be applied to the joining of superconductors of any shape, but has so far been most used as a superconductor material. In addition, in its use, the terminal is joined to the superconductor, the characteristics of the superconductor are measured, and the method is used as a method for evaluating the characteristics of the superconductor.

The preferred composition of the brazing material according to the present invention is as follows. In particular, Mn, Fe, Co, Ni, Cr, Pd other than Cu alone are 0.5 to 2
%, And 1 to 3% by weight for composites is preferable. Especially Zn is 2
〜 20%, Mn, Fe, Ni, Co are 0.5 to 1.5 for one or more of them.
%, Ca, Mg and Sr are preferably 1 to 5%.

As a coating material for the superconducting wire, a material that does not react with an oxide is used, and Au, Ag, Cu or an alloy thereof is used.

[Action]

The present invention uses, as a brazing material for joining an oxide-based high temperature superconductor, an alloy containing the stable metal element in the +2 valent state and the balance being In. As a result, it becomes possible to obtain a joined body having a small connection resistance between the superconductor and the brazing material.

When the In unit is used as a brazing filler metal for joining a superconductor as in the conventional case, the softness, adhesion, workability, etc. of In are advantageous for wetting, but there is a drawback that the connection process is large. It is presumed that this is because indium oxide was generated at the bonding interface with the superconductor, and the reaction product formed a high resistance layer. Therefore, if the above-mentioned metals are added to In, a crystal structure in which some of the indium is replaced with these added metals is obtained at the time when indium oxide is generated at the interface. It is considered that indium oxide, which is a semiconductor close to the body, becomes more conductive. Since indium is in the +3 valence state,
A +2 valent metal is convenient for forming an impurity level. A similar effect is expected when a +4 valent metal is added,
No reduction in connection resistance was observed when an In alloy containing Sn, Pb, etc. was used. In oxide-based high temperature superconductors such as YBa ₂ Cu ₃ O _7- δ, it should be noted that the constituent elements other than oxygen are in the +2 valence and +3 valence states. It is also considered to be advantageous in having an effect.

The In alloy used here can have a melting point of 300 ° C. or lower by appropriately selecting the ratio of the additional element,
Since the joining can be performed at a relatively low temperature, the heating of the joining does not impair the characteristics of the superconductor. Further, for the above reason, not only the joining process becomes very simple, but also the shape and size of the article to be joined are almost completely unrestricted.

Join at a lower temperature (the brazing temperature is about 50% higher than the melting point)
The melting point of the alloy used is 100 ° C to 3 ° C, considering that the temperature is higher by 100 ° C and that a bondability problem occurs below 100 ° C.
Example: Example 1 An example of the present invention will be described in comparison with a conventional example.

As shown in FIG. 1, 75 wt% In-25 wt% C was deposited on a rectangular YBa ₂ Cu ₃ O ₇ −δ superconductor 1 having a length of 15 mm, a width of 4 mm, and a thickness of 1 mm.
Place the d alloy 2 and use the iron 3 that vibrates ultrasonically. While applying ultrasonic waves to the solder, bring the iron 3 that is heated to 180 ° C into contact with the brazing material, heat and melt it, and braze it with the copper wire 4. I went. The brazing thickness was about 1 mm. By this, YBa ₂ C
A joined body of u ₃ O ₇ −δ superconductor and metal was obtained. Bonding with a clean metal surface was provided by applying ultrasonic waves with an ultrasonic soldering iron. The oscillation frequency was 60 KHz and the oscillation output was 15 W.

When the connection resistance of this joint portion was measured, a temperature-resistivity curve as shown in FIG. 2 was obtained. FIG. 3 shows the results of measuring the connection resistance by bonding with In, which has been generally used in the past, by the same method. Comparing these results, FIG. 3 shows a semiconductor-like behavior in which the connection resistance increases as the temperature decreases, and the resistivity was 77,400 μΩ · cm ² at 77K. On the other hand, the curve of FIG. 2 of the present invention shows almost the same behavior as the resistance curve of superconductivity in which the resistivity decreases with decreasing temperature, and in particular, the resistivity rapidly decreases at 77K.
The resistivity at 77K was 37.5 μΩ · cm ² .

As shown here, according to the present embodiment, it is possible to obtain a joined body in which the connection resistance of the superconductor joined portion is small in a very simple process. Connection resistance is approx.
It was reduced to 1/200.

Example 2 A 98 wt% In-2 wt% Zn alloy was placed on a YBa ₂ Cu ₃ O ₇ −δ superconductor having a length of 15 mm, a width of 4 mm, and a thickness of 1 mm, and heated to 200 ° C. while applying ultrasonic waves. , Brazed with copper wire. When the connection resistance of the obtained joined body was measured, the temperature-resistivity curve exhibited the same behavior as the temperature-resistance curve of superconductivity, and the connection resistance at 77K was 80.2 μΩ · cm, as in Example 1. ²
It was.

Example 3 YBa having a length of 100 mm, a width of 7 mm and a thickness of 0.1 mm as shown in FIG.
₂ Cu ₃ O ₇ -δ _Two ribbon-shaped wire rods 1 (Ag sheath) are butted against each other at their inclined cross-sections, and 75 wt% In-25 wt% Cd alloy foil 2 is put between both wire rods. Further, the above-mentioned In alloy 6 or In6 was arranged so as to be sandwiched from both sides at the connection portion, and these were simultaneously heat-bonded to 180 ° C. in the same manner as in Example 1. The soldering iron was brought into contact with the solder 6 and heated. When the brazing material melted, a slight pressure was applied to improve the adhesion. As a result, a joined body of the superconducting wires was obtained. When the critical current density of this junction line was measured,
It was Jc = 740 A / cm ² . It was found that the critical current density of this ribbon-shaped wire before joining was Jc = 800 A / cm ² , and the decrease in Jc due to joining was slight.

This was applied to a superconducting coil, and a coil was produced from the wire material joined by this joining method. Furthermore, the coil was used to form a superconducting magnet. Here, as compared with the case where the coil is formed without a joint, the characteristics are almost unchanged and a stable magnet is obtained. This superconducting magnet can also be applied to magnetic levitation trains, accelerators, power storage, etc.

The oxide superconducting wire joined by the brazing material of the present invention is used for rotor and stator coils of rotating machines, energy storage coils, fusion device magnet coils, power transmission and distribution cables, transformer coils, particle accelerators. Coil, MRI and NMR
Can be used as a coil for a magnet, a coil for an electron microscope, a coil for an atomic absorption spectrometer, a rotor for a motor of a train, an automobile, an elevator, and an escalator, a coil for a stator, and a coil for a linear motor car.

Example 4 FIG. 5 shows that, in contrast to the joining by the end face of Example 3, one end of both sheaths was removed and exposed at the end, and joining was performed in a plane, and the joining was performed in the same manner as in Example 3. This method has a merit that the joint surface can be enlarged. The joining method is the same as in the third embodiment.

Example 5 As in Example 4, the end of the superconducting wire was exposed from the sheath, and the exposed part was joined with a copper wire.

99 wt% In-1 wt% N at the tip cross section of YBa ₂ Cu ₃ O ₇ -δ ribbon wire 1 (Ag sheath) with 100 mm length, 7 mm width and 0.1 mm thickness
Place the i alloy and heat it to 180 ° C while applying ultrasonic waves,
I brazed with a copper wire. As a result, YBa ₂ Cu ₃ O ₇
A bonded body of the -δ superconducting wire and the metal wire was obtained. When the critical current density of this joined body was measured, the value of Jc was almost the same as the value obtained with the superconducting wire before joining, as in Example 3, and there is a possibility that the superconductivity may break due to the resistance of the connecting portion. I knew it wasn't.

Example 6 A 75 wt% In-25 wt% Cd alloy was placed on a rectangular Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x superconductor having a length of 15 mm, a width of 4 mm and a thickness of 1 mm, and the same procedure as in Example 1 was performed. While applying ultrasonic waves, it was heated to 180 ° C. and brazed with a copper wire. The connection area was 4 mm ² , and the brazing thickness was about 1 mm. As a result, a joined body of Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x superconductor and metal was obtained. When the current-voltage characteristics (hereinafter referred to as VI characteristics) and connection resistance at 77 K ° of this junction were measured, a current-voltage curve as shown in FIG. 6 was obtained. For comparison, FIG. 7 shows the results of measuring the VI characteristics by performing the same joining with In. In Fig. 7, a convex curve is shown, showing a semiconductor-like behavior that deviates from Ohm's law in which current and voltage are proportional, and the resistivity at 77K ° is 3
It was 2100 μΩ · cm ² . On the other hand, when the method of the present invention is used, as can be seen from FIG. 6, there is a downwardly-convex superconducting curve, and the resistivity at 77 K ° is 300 μΩ · cm ^2, which is about 1 in the case of In. It was possible to reduce to / 100.

Example 7 A 75 wt% In-25 wt% Cd alloy was used as a brazing material on a strip-shaped YBa ₂ Cu ₃ O ₇ -δ superconductor having a length of 15 mm, a width of 4 mm, and a thickness of 1 mm, and ultrasonic waves were applied in the same manner as described above. While applying, it was heated to 180 ° C. to obtain four copper wire terminals as shown in a perspective view in FIG. Of the four terminals, both ends were used as current terminals and the inner two were used as voltage terminals. The critical current density Jc was measured using an apparatus as shown in FIG. Current terminal 7
Is connected to the positive side of the direct current and terminal 10 is directly connected to the negative side through a shunt resistor (or standard resistor).
The voltage terminals 8 and 9 were connected to the plus and minus terminals of the digital multimeter, respectively. An XY recorder was used to display the measurement results. The X-side terminal of the XY recorder was connected in parallel with the shunt resistor, and the Y-side terminal was connected in parallel with the digital multimeter. With liquid nitrogen (77 K °) and a magnetic field of 0, the Jc of this sample was 1250 A / cm ² . For comparison, measurement was also performed on the same sample in which terminals were formed using In as a brazing material. The connection area is almost the same. In this case, Jc = 160 A / cm ^2, which was a value of about 1/8. This is because the connection resistance between SC and In is large, and the breakage of the superconducting state due to heat generation may occur even at a lower current. Therefore, there is a problem in measuring the true Jc value. By performing superconducting property evaluation using the joining method and brazing material of the present invention, it becomes possible to obtain highly reliable measured values. In addition, the ease of forming terminals is very important in the evaluation of superconducting characteristics, which is performed at any time during the superconducting development process.

Example 8 A brazing material of 75 wt% Cd-25 wt% In alloy was used on the same superconductor as in Example 7, and the brazing material was heated and melted while applying ultrasonic waves as in the previous example, and a copper wire was similarly bonded. As a result of measuring the current density of this joined body, the value was the same as that in the above-mentioned example.

〔The invention's effect〕

According to the present invention, when the oxide-based high-temperature superconductor is joined to another member, it has a connection portion having a connection resistivity as small as several tens of μΩ · cm ² , and the process is very simple. Becomes There is no limitation on the size and shape of the sample to be joined, and since it can be done at low temperature, its application range is conventional low resistance connection such as oxide high temperature superconductors and joining of the superconductor with metal or other ceramics. Wider than the method.

Further, according to the present invention, since the heat generated by the connection resistance can be suppressed further, the current value that can be conducted is increased and the stability is improved in the high magnetic field magnet, the superconducting magnet used in MRI and the like. Also, in the characteristic evaluation of the Jc value and the like of the superconductor, it becomes possible to obtain a measured value closer to the true value.

[Brief description of drawings]

FIG. 1 is a perspective view showing a joining method according to an embodiment of the present invention,
FIG. 2 is a graph showing the relationship between the temperature and the resistivity of the connection portion of one embodiment of the present invention, and FIG. 3 is a graph showing the relationship between the temperature and the resistivity of the connection portion when joined using In. 4 and 5 are vertical cross-sectional views of the joint portion according to one embodiment of the present invention, FIG. 6 is a graph showing the current-voltage relationship of the connection portion according to one embodiment of the present invention, and FIG. FIG. 8 is a graph showing the relationship between the current and voltage of the connection portion when they are joined together, FIG. 8 is a Jc measuring device configuration diagram of an oxide high temperature superconductor according to an embodiment of the present invention, and FIG. 9 is a copper wire. It is a perspective view of the connected sample. 1 …… YBa ₂ Cu ₃ O ₇ −δ Superconductor 2 …… 75wt% In-25wt
% Cd alloy, 3 ... Super wave soldering iron, 4 ... Copper wire, 5 ...
… Ag sheath, 6 …… In alloy or In, 7,10 …… Current terminal, 8,9 …… Voltage terminal.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H01B 13/00 565 H01B 13/00 565D H01R 43/00 ZAA H01R 43/00 ZAAZ (72) Inventor Takao Funamoto 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Masahiro Ogihara 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (56) References JP 63- 284767 (JP, A) JP 60-255947 (JP, A) JP 50-133792 (JP, A) JP 61-165293 (JP, A) JP 3-150273 (JP, A)

Claims (8)

(57) [Claims] 1. A surface of an oxide-based high-temperature superconductor, by weight,
1 to 7% of Be, Mg, Ca, Sr, Ba and Ra, or 2 to 10% in total of 2 to 10%, or Zn1 to 40%, or Cd5 to 75%, or Mn, Fe, Co , Ni, Cr, Cu and Pd, one of 0.5 to 5%, or two or more of them in a total amount of 1 to 7.5%, and the balance is I
An oxide-based high-temperature superconductor characterized in that a brazing material made of an alloy of n is joined, and the electrical resistivity of the joint decreases with a decrease in temperature. 2. The oxide high-temperature superconductor according to claim 1, wherein the oxide-based high-temperature superconductor is a wire rod, and the wire rods or the wire rods and metal wires are joined by the brazing filler metal. Oxide-based high temperature superconducting material. 3. A method for joining oxide-based high-temperature superconductors, wherein the superconductors are the same or the superconductors and a metal are, by weight, one of Be, Mg, Ca, Sr, Ba and Ra. % Or 2 or more kinds in total amount of 2 to 10%, or Zn1 to 40%, or Cd5 to 75
%, Or one of Mn, Fe, Co, Ni, Cr, Cu and Pd, 0.5 to 5%, or two or more of the total amount of 1 to 7.5%,
Oxide-based high-temperature superconductivity characterized in that the brazing filler metal made of an alloy with the balance being In is joined by heating and melting at a temperature of 150 to 350 ° C, and the electrical resistivity of the joint decreases as the temperature decreases. How to join the body. 4. By weight, one of Be, Mg, Ca, Sr, Ba and Ra is 1
An oxide-based brazing filler material for high-temperature superconductor joining, comprising 7% or 2 to 10% in total of 2 to 10% and the balance being In. 5. An oxide-based brazing filler material for joining a high-temperature superconductor, comprising an alloy containing 1 to 40% by weight of Zn and the balance being In. 6. An oxide-based high-temperature superconductor joining brazing material comprising an alloy containing Cd of 5 to 75% by weight and the balance of In. 7. By weight, one of Mn, Fe, Co, Ni, Cr, Cu and Pd is contained in an amount of 0.5 to 5%, or 2 or more are contained in a total amount of 1 to 7.5%, and the balance is In. A brazing filler material for joining an oxide-based high-temperature superconductor characterized by comprising an alloy. 8. A rotor / stator coil for a rotating machine, an energy storage coil, a plasma container coil for a fusion device, a power transmission / distribution cable, a transformer coil, a particle accelerator coil, an MRI magnet coil, and an NMR coil. A coil for a magnet, a coil for an electron microscope, a coil for an atomic absorption spectroscope, a coil for a linear motor car, a coil wire for a rotor or a stator of a motor for a transportation system is made of an oxide-based high-temperature superconductor. An oxide high temperature superconducting wire is used which is characterized in that superconductors or the superconductor and metal are joined by a brazing material according to any one of claims 4 to 7. apparatus.