JPH046764A - Connecting method for oxide superconductor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for joining oxide-based superconductors, and in particular,
The present invention relates to a bonding method that allows a simple bonding process and provides a superconducting bonded body with low connection resistance.

[Conventional technology]

Bonding of superconductors does not deteriorate superconducting properties, and
It is required to bond so that the resistance of the bonded portion is as low as possible. Bonding of oxide-based superconductors is extremely difficult because they are oxides and have poor metal wettability, and their superconducting properties are largely influenced by their composition.

One of the joining methods currently being discussed.

Applied Physics Letters 52 (21)
Pages 1819 to 1821 (1988) (App
l, Phys, Lett, 52 (21) p, 1
819-1921 (1981)), Ar
There is a method in which a precious metal is vapor-deposited after sputter etching using ions or the like, and a terminal is attached thereon by wire bonding. With this method, the connection resistance can be extremely small, on the order of 10-10 Ω. However, this connection resistance value is a value that can only be obtained under extremely limited conditions such as the size of the object to be joined and the method of connecting external terminals, and the applicable range is also limited. When considering bonding based on various future applications of oxide-based superconductors, it is essential to develop a bonding method that is not limited by the shape, size, material, etc. of the objects to be bonded.

On the other hand, as described in Japanese Patent Application Laid-Open No. 64-28284,
A method of heating and bonding using a brazing filler metal containing an active metal in a vacuum or an inert gas atmosphere is one of the bonding methods that is not limited by the shape, size, material, etc. of the objects to be bonded. However, heating in vacuum or in an inert gas atmosphere changes the composition of the superconductor and deteriorates its properties. To restore the properties, in an oxygen atmosphere or
Further heat treatment in the atmosphere is required, resulting in a multi-step process for bonding. In order to avoid deterioration of superconductor properties as much as possible and to simplify the process, it is desirable to develop other bonding methods.

[Problem to be solved by the invention]

Among the above conventional techniques, the bonding method using noble metal vapor deposition,
Although the connection resistance is low, there is a problem that the applicable range is limited and it is not suitable for joining various members for a variety of purposes. On the other hand, heating with active metal solder in vacuum or in an inert atmosphere has a wide range of applications, but may deteriorate the superconducting properties. At least a two-step process is required.

An object of the present invention is to provide a method for joining oxide-based superconductors that has a wide range of applications and a simpler joining process.

[Means to solve the problem]

In order to achieve the above object, by using an Ag-based or Ag-Cu alloy-based brazing filler metal, oxide-based superconductors or superconductors and other members can be directly bonded. . In addition, by using a brazing material and heating in an atmosphere with an oxygen concentration of 0.1% or more, it is possible to bond with only - times of heating steps.

That is, the present invention is a bonding of oxide-based superconductors, in which A,
This is a method for joining oxide-based superconductors, which is characterized by heating in an atmosphere with an oxygen concentration of 0.1% or more using a brazing filler metal based on a brazing material based on a brazing material based on a brazing material based on an oxide-based superconductor or an A g -Cu alloy. Note that the oxygen atmosphere may be applied only during cooling during the bonding process.

The present invention also relates to a joined body of oxide-based superconductors joined together by a joining method, or a joined body of the superconductor and another member.

Next, the present invention will be explained in detail.

As the brazing material that can be used in the present invention, in addition to silver or a silver-copper alloy, silver or a silver-copper alloy containing at least one element of group IIIb or group IVa of the periodic table can be suitably used. II
When containing Ib group and lVa group elements, it is desirable to use In among the IIIb group elements, and it is desirable to use Ti among the IVa group elements.

Further, the oxide-based superconductor of the present invention can be applied to all known oxide-based superconductors, including lanthanum-based, yttrium-based, bismuth-based, and thallium-based superconductors9 [Function] The present invention A is used as a brazing material for joining oxide superconductors.
G-based or Ag-Cu-based brazing filler metal is used. This allows direct bonding at temperatures below 1200 without impairing superconducting properties.

Precious metals such as silver and gold hardly react with oxide-based superconductors even at high temperatures, so they are very useful when connecting superconductors with low resistance. In particular, silver 5 itself has low electrical resistance and excellent oxygen permeability, so it is extremely advantageous for low-resistance bonding. However, in order to form an interface between these noble metals and superconductors, the wettability is extremely poor.

In addition, the bonding temperature must be lower than the melting point of the superconductor, which limits the method to vapor deposition.

As mentioned above, there are problems such as the need for additional bonding steps such as soldering after vapor deposition, which limits the range of applications.

Ag-based with a small amount of other elements added, or Ag
Cu-based brazing filler metals have improved wettability and a lower melting point, making direct bonding possible.

Furthermore, the present invention provides a method for joining oxide-based superconductors, including:
Heating is performed in an atmosphere with an oxygen concentration of 0.1% or more. As a result, bonding can be achieved with only -times of heating process.

It is known that in most oxide-based superconductors, the amount of oxygen in the composition largely controls the superconducting properties. If we take Y-based superconductors, which have a particularly high degree of absorption and release of oxygen elements among several superconductors, 673~
At 873, oxygen absorption and release become most active. Therefore, when bonding is performed using an Ag-based or Ag-Cu alloy-based brazing material, the brazing temperature is approximately 950 to 1200° C., so the characteristics change greatly depending on the amount of oxygen. By heating and bonding in an oxygen atmosphere, oxygen can be sufficiently absorbed into the superconductor, and bonding can be performed without losing superconducting properties. Furthermore, since oxygen absorption is dominant during the cooling process, a similar effect can be obtained by creating an oxygen atmosphere only during cooling. The oxygen concentration is 0.0 when using a brazing filler metal that does not contain group IIIb or rVa elements.
A wide oxygen concentration range of 1% or more can be applied. However, I
When using a brazing filler metal containing Group IIb or R/a group elements, an oxygen concentration of 0.5 to 2% is preferred.

Also, if only the cooling process is in an oxygen atmosphere.

The oxygen concentration preferably has a higher value of 10% or more.

Note that when the oxygen concentration is 0.1% or less, oxygen cannot be sufficiently incorporated into the superconductor only during the heating and cooling process during bonding, and the characteristics of the superconductor after bonding deteriorate.

〔Example〕

Examples of the present invention will be described below (Example 1) A strip-shaped YBazCuaO7-δ superconductor with a length of 12 m, a width of 4 mm, and a thickness of 1.511 I1 was coated with 72w%A g -28wt%Cu. A paste-like metal solder made by mixing Cu powder with an organic binder is printed and applied.

This was heated at 1123° C. for 5 minutes in included air and cooled in the oven. As a result, a bonded body of the oxide-based superconductor and metal was obtained. When the connection resistance of this junction was measured, it was 8.3
It was 10-7Ω·d. On the other hand, when similarly using an Ag-Cu alloy brazing material and heating it for 1123.5 minutes in an Ar atmosphere, it was found that the superconducting properties of the sample after bonding completely disappeared. However, as a result of heat treatment of this bonded body in an oxygen atmosphere at 773°C for a working time and then furnace cooling, the superconducting properties were restored, but the connection resistance was 2X10-5Ω・d, which was 5 atmospheres. A higher connection resistance was obtained than when heating inside.

As shown here, according to this example, a bonded body with low connection resistance at the superconductor bonded portion can be obtained by only - times of heating. The connection resistance was 10% or less compared to a two-step joining method in which heat brazing in an Ar atmosphere and then heat treatment in an oxygen atmosphere were performed.

<Example 2> 68wt%Ag-27wt%Cu-5wt%Ti on a YBazCuaO7-δ superconductor with a diameter of 1.5m and a length of 20m.
A paste-like metal solder having the composition was applied and heated at 1083 for 5 minutes in an atmosphere with an oxygen concentration of 2%, and then cooled in a furnace. When the connection resistance of this bonded body was measured, a small value on the order of 10-6 Ω·d was obtained.

<Example 3> A rectangular YB with a length of 10 cm, a width of 9 cm, and a thickness of 1.5 cm.
a 72wt%Ag on the 2Cu 307-δ superconductor
- Print and apply a paste-like metal solder made by mixing 28 wt% Cu alloy powder with an organic binder.

This was heated to 1123° C. for 5 minutes in an electric furnace through which Ar gas was flowed at a flow rate of 8 Ω/min, and then cooled in the furnace. During the cooling process, when the temperature inside the furnace decreased to 873 K, the flowing Ar gas was stopped, and instead, 02 gas was flowed at a flow rate of 200 mQ/win, and the furnace was cooled to room temperature in an O2 atmosphere. As a result, a bonded body of the oxide-based superconductor and metal was obtained. When the resistance of this joint was measured, it was 1×10″6Ω·d.

<Example 4> YBaz in the form of a strip of length 10 x 9 width 4 m and thickness 1.5 -
72wt%A g -2 on CuaO7-δ superconductor
A paste-like metal solder made by mixing 8wt% Cu-containing Cu powder with an organic binder is printed and applied.

This was heated at 1123 °C for 5 minutes in an atmosphere with an oxygen concentration of 0.5%, and then cooled in a furnace. The connection resistance of this bonded body is 1
The value was on the order of 0-7Ω·d, which was a very small value.

〔Effect of the invention〕

According to the present invention, oxide-based superconductors can be bonded to each other or to other members with extremely small connection resistance of several μΩ・d or less, and in addition, can be easily bonded using only a -stage heating process. Bonding becomes possible. There are no restrictions on the size or shape of the samples to be joined, and the range of applications is wider than that of conventional low resistance connection methods.

Claims (1)

[Claims] 1. In a method for joining oxide-based superconductors, an Ag-based or Ag-Cu alloy-based brazing material is used, and the oxygen concentration is 0.1%.
A method for bonding oxide-based superconductors, characterized by carrying out thermal bonding in the above atmosphere. 2. The method of joining oxide-based superconductors according to claim 1, wherein the metal solder contains at least one element selected from Group IIIb or Group IVa of the periodic table. 3. The oxide-based superconducting assembly according to claim 1, wherein the superconductors are joined to each other or to members such as metals and ceramics. 4. An oxide superconductor in which Ag or an alloy containing Ag and Cu as main components is in contact with the surface of the oxide superconductor. 5. The oxide superconducting wire according to claim 3, wherein the oxide superconductor is a superconducting wire, and the other member is a metal wire. 6. In claim 1, at least the cooling step 673-
A method for joining oxide-based superconductors that creates an atmosphere with an oxygen concentration of 0.1% or more only in a temperature range of 873K. 7. The method of joining oxide superconductors according to claim 1, wherein the brazing material is heated in a non-oxidizing atmosphere until the temperature reaches the melting point of the brazing material, and then the atmosphere is made to have an oxygen concentration of 0.1% or more.