JPH01105413A - Manufacture of oxide superconducting wire - Google Patents

Abstract

PURPOSE:To improve the superconductivity characteristic such as the critical current density by specifying the temperature increasing speed and the temperature decreasing speed at the time of applying heat treatment. CONSTITUTION:A superconducting element wire filled with an oxide superconductor or its precursor in a metal tube is applied with heat treatment so that it is heated to the preset baking temperature area at 200 deg.C/hr or below and baked at the preset baking temperature area then cooled to the room temperature at 50 deg.C/hr or below. The thermal stress to the superconductor due to the difference in the thermal expansion coefficient between the superconductor and the metal tube at the time of the heat treatment is thereby mitigated, cracks generated on the superconductor can be reduced, and a superconducting wire excellent in the superconductivity characteristic such as the critical current density is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application J] The present invention relates to superconducting wires used for superconducting magnet coils, power transport, etc., and relates to superconducting wires using oxide-based superconductors as superconductors.

"Prior Art" Recently, various oxide-based superconductors have been discovered whose critical temperature (T c ) for transitioning from a normal conductive state to a superconducting state exceeds the liquid nitrogen temperature. This type of oxide-based superconductor has the general formula A -B -Cu-0 (where A is a metal element in group a of the periodic table, such as Y, Sc, La, Yb, Er, Eu, Ho, Dy, etc.). Indicates one or more types, B is B e,
It is an oxide represented by one or more of Group Ila elements of the periodic table such as Mg, Ca, Sr, Ba, etc.), and is an oxide that is used for conventional alloy systems or intermetallic materials that require cooling with liquid helium. Since it can be used under much more advantageous cooling conditions than compound-based superconductors, it is being researched as an extremely promising superconducting material for practical use.

By the way, the following method is conventionally known as an example of a method for manufacturing a superconducting wire including such an oxide-based superconductor.

In order to manufacture oxide-based superconducting wire, A -B -Cu-
A mixed powder is created by mixing multiple raw material powders containing each element constituting the oxide superconductor represented by 0, and then this mixed powder is calcined to remove unnecessary components. The calcined powder was heat-treated to become superconducting powder, which was then filled into a metal tube, further reduced in diameter to obtain a wire with the desired diameter, and this wire was heat-treated to form a superconductor inside the metal tube. This is a method for manufacturing oxide-based superconducting wire.

[Problem to be solved by the invention] However, there is a difference in thermal expansion coefficient between the superconductor and the metal used for the metal tube, and in the conventional method described above, the metal tube is filled with powder to reduce its diameter. After processing, 80
0 to 1000 degrees Celsius (during heat treatment, the superconductor and metal tube undergo rapid temperature changes, force is applied to the superconductor, this stress causes cracks in the superconductor, and the superconductor There was a problem that the properties, especially the critical flow density, decreased.

The present invention has been made in view of the above problems, and aims to provide a method for manufacturing an oxide-based superconducting wire having excellent superconducting properties such as nasal current density.

"Means for Solving the Problems" The present invention provides a method for manufacturing an oxide superconducting wire comprising an oxide superconductor, as a means for solving the above problems. The superconducting strands are then filled with 1-lever and subjected to diameter reduction processing to obtain superconducting strands.Then, the superconducting strands of 1. Lever are heated to a predetermined firing temperature range, then fired at a predetermined calcination temperature range, and then heated to room temperature. When performing heat treatment to lower the temperature to
The temperature should be kept below 0°C/hour.

``Action J: A superconducting wire made of a metal tube filled with an oxide superconductor or its precursor is heated to 200°C to a specified firing temperature range.
/ hour or less, then fired at a predetermined firing temperature range,
Thereafter, by performing heat treatment to lower the temperature to room temperature at a rate of 50° C./hour or less, it is possible to alleviate the thermal response J to the superconductor that occurs due to the difference in coefficient of thermal expansion between the superconductor and the metal tube during heat treatment.

Hereinafter, the method for manufacturing an oxide-based superconducting wire of the present invention will be explained in more detail.

To manufacture an oxide superconducting wire by the method of the present invention, first, an oxide superconductor or its precursor is filled into a metal tube.

The oxide superconductor preferably used in the method of the present invention is A
-B -Cu-0 system (A is Y, Sc, La.

Ce, Pr, Nd, Pm, Eu, Gd, Tb, Sm, D
y, Ho, Er.

Indicates one or more elements of group ■a of the periodic table such as Tm, Yb, Lu, etc., and B is Ba, Sr, Mg, Ca, Ra
, Be, and other elements of group 11a of the periodic table).

Such an oxide superconductor is produced by uniformly mixing a compound powder of the above elements, a compound powder of element B, and a compound powder of Cu at a predetermined mixing ratio to create a mixed powder,
Next, this mixed powder is calcined to remove unnecessary components, and a superconducting powder obtained by heat-treating this calcined powder is preferably used.

Further, as the precursor of the oxide superconductor, the above-mentioned mixed powder and calcined powder are preferably used. In addition, as the compound of each of the above-mentioned elements, oxides, carbonates, fluorides, chlorides, bromides, oxalates, nitrates, etc. of each element can be used. For example, Y-B as an oxide superconductor
When using an a-Cu-0 based superconductor, particularly suitable raw material compounds include Y 203, BaO or Ba
These include CO3 and CuO.

In addition, the material of the metal tube is Ag, Cu, AuXP.
Single metals such as tXNi, Ti, Ta, Zr, Nb, silver alloys, Cu-Ni alloys, Cu-Al alloys, Ni
- Single metals or alloys having a melting point of 800° C. or higher, such as A i-based alloys, Ti-V-based alloys, monel metal, and stainless steel, are preferably used.

After filling the metal tube with the oxide superconductor or its precursor, the metal tube is reduced to a predetermined wire diameter to form a superconducting strand. This diameter reduction may be done by drawing or rolling, but it is also done by forging using a forging device such as a rotary swaging device and repeating forging multiple times as necessary until a predetermined wire diameter is achieved. This is particularly preferable because a high packing density can be obtained.

Next, this superconducting strand is heated at 100 per hour to a predetermined firing temperature range.
After raising the temperature to ~200°C, it is fired in a predetermined firing temperature range, and then a heat treatment is performed in which the temperature is lowered to room temperature at a rate of 20~100°C per hour. The firing temperature and heat treatment time are appropriately set depending on the type of oxide superconductor, but for example, Y-B
In the case of an a-Cu-0 based oxide superconductor, it is desirable to set the firing temperature to about 800 to 1000°C and maintain this temperature for 1 to several tens of hours. In this heat treatment, if the temperature is increased by more than 200℃/hour, the thermal stress applied to the superconductor will increase due to the difference in thermal expansion coefficient between the superconductor and the metal tube, and the crack prevention effect of the superconductor will not be sufficient. However, raising the temperature at a rate of 50° C./hour or less is not practical because it takes time to reach the predetermined firing temperature. In addition, if the temperature is lowered by more than 100°C/hour when the temperature is lowered, the thermal stress applied to the superconductor increases due to the difference in thermal expansion coefficient between the superconductor and the metal tube, similar to when the temperature is raised, and the effect of preventing cracks in the superconductor is increased. is not obtained sufficiently, and if the temperature is lowered within 50° C./hour, slow cooling to room temperature takes time and is not practical. In addition, the temperature rise and fall described above do not need to be raised or lowered continuously; instead, the temperature may be held constant for an arbitrary period of time during the temperature rise or fall, and then the temperature may be raised or lowered again. It's so good.

The atmosphere during this heat treatment may be a pure oxygen atmosphere, a mixed gas atmosphere of oxygen and an inert gas such as argon or nitrogen, or a mixed gas atmosphere of oxygen, an inert gas, and a halogen gas such as fluorine gas or chlorine gas. It is preferable to use an oxidizing atmosphere such as an atmosphere.

By performing such heat treatment, the powder in the metal tube is sintered to produce an oxide superconductor, and an oxide superconducting wire is obtained.

The method for producing an oxide superconducting wire according to the present invention involves heating a superconducting wire formed by filling a metal tube with an oxide superconductor or its precursor at a rate of 200°C/hour or less to a predetermined firing temperature range. After that, the superconductor is fired at a predetermined firing temperature range, and then subjected to a heat treatment in which the temperature is lowered to room temperature at a rate of 50°C/hour or less, thereby reducing thermal stress on the superconductor due to the difference in thermal expansion coefficient between the superconductor and the metal tube during heat treatment. This makes it possible to reduce cracks that occur in the superconductor, and to manufacture superconducting wires with excellent superconducting properties such as critical current density.

〔Example 〕

Based on the method of the present invention, an oxide superconducting wire comprising a Y-B a-Cu-0 superconductor was manufactured.

First, Y2O3, BaO, and CuO are Y:Ba:C
u= ]: Mixed uniformly at a ratio of 2:3 to obtain a mixed powder, this mixed powder was calcined in an oxygen atmosphere at 700°C for 24 hours to obtain a calcined powder, and this calcined powder was further calcined in an oxygen atmosphere, A superconducting powder was obtained by heat treatment at 900° C. for 24 hours. Next, this superconducting powder was filled into a silver tube with an outer diameter of 10 mm and an inner diameter of 7 mm, and further reduced by forging several times to an outer diameter of 1 mm using a rotary swaging device. And so.

Next, this superconducting wire was heated to 950°C for 2 hours in an oxygen atmosphere.
Continuously raise the temperature at 00℃/hour to 950℃ for 12
After holding for a period of time, heat treatment was performed to continuously lower the temperature to room temperature at a rate of 50° C./hour.

Through this heat treatment, Y is densely sintered inside the silver sheath.
An oxide superconducting wire in which a -Ba-Cu-0 based superconductor was formed was obtained. As a result of determining the critical temperature (Tc) and critical current density (Jc) of this superconducting wire, Tc=9]
It exhibited excellent superconducting properties with K,, Jc=10000 A/Cm' (at 77K).

"Effects of the Invention" - As explained above, the present invention provides a superconducting wire formed by filling a metal tube with an oxide superconductor or its precursor.
After increasing the temperature to a specified firing temperature range at a rate of 200°C/hour or less, the temperature is maintained within the specified firing temperature range, and then the room temperature is increased to 50°C/hour.
By performing heat treatment that lowers the temperature at a temperature below This has the effect of producing superconducting wires with excellent superconducting properties such as density.

Claims (1)

[Claims] A method for manufacturing an oxide superconducting wire comprising an oxide superconductor, comprising: filling a metal tube with the oxide superconductor or its precursor;
When the superconducting strand is further subjected to diameter reduction processing to become a superconducting strand, and then this superconducting strand is subjected to heat treatment in which the temperature is raised to a predetermined sintering temperature range, then held in the sintered temperature range, and then cooled to room temperature. A method for producing an oxide-based superconducting wire, characterized in that the temperature increase rate is 200°C/hour or less and the temperature fall rate is 50°C/hour or less.