JPH04292812A - Manufacture of bismuth-based oxide superconductive wire - Google Patents

Abstract

PURPOSE:To manufacture a bismuth-based oxide superconductive wire having high critical current density and critical current while lessening the production of non-superconductive phase. CONSTITUTION:A superconductive wire manufacturing method involves the steps of filling a metal sheath with bismuth-based oxide superconductor or its raw material powder, plastic-processing the metal sheath filled with the powder to make it a wire, carrying out primary heating the resulting wire, carrying out plastic process or pressing process of the wire after the heating process, carrying out secondary heating the processed wire, and powder having composition ratio of (Bi+Pb):Sr:Ca:Cu:2.2:2:2:3 with + or -5% allowances respectively and 0.3<=Pb<=0.4 is used as the powder with which the sheath is filled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing bismuth-based oxide superconducting wire.

0002

[Prior Art] Bismuth-based oxide superconducting materials are 110
It is known to have a high critical temperature of about K. By coating such bismuth-based oxide superconducting material with metal,
It is known that a wire rod having a high critical current density can be obtained by plastic working it into a tape shape and then heat treating it.

In particular, it is known that the critical current density can be further increased by repeating plastic working and heat treatment multiple times.

[0004] In addition, some bismuth-based oxide superconductors have a critical temperature of 110K, and others have critical temperatures of 80K and 1
It is known that there are 0K ones. Furthermore, 11
It is also known that when attempting to manufacture a 0K phase superconductor, a non-superconducting phase appears in some parts.

In the bismuth-based oxide superconductor, the above-mentioned 110K phase is Bi or (Bi, Pb):Sr:
The composition ratio of Ca:Cu is said to be 2:2:2:32
It is known that the 80K phase has a 2212 phase with a composition ratio of approximately 2:2:1:2.

[0006]

[Problems to be Solved by the Invention] In order to stably use bismuth-based oxide superconductors using inexpensive liquid nitrogen (77.3K) as a cooling medium, it is necessary to
It is desirable to generate as much 2223 phase as K phase as possible.

Furthermore, when a superconductor is used as a wire, it is necessary to obtain not only a high critical current density but also a high critical current.

[0008] The object of the present invention is to
To provide a method for producing a bismuth-based oxide superconducting wire, which uses a composition as close as possible to the 23 phase, reduces the number of non-superconducting phases produced when obtaining the 110K phase, and can obtain high critical current density and critical current. be.

[0009]

[Means for Solving the Problems] The manufacturing method of the present invention includes:
A step of filling a metal sheath with powder of a bismuth-based oxide superconductor or its raw material, a step of plastic working the metal sheath filled with the powder to form a wire rod, and a step of converting this wire rod into a wire rod.
The process includes a step of performing a secondary heat treatment, a step of plastic working or pressing the wire rod after the heat treatment, and a step of performing a secondary heat treatment of the wire rod after the work. :Ca:Cu=
It is characterized by using powder with a composition centered around 2.2:2:2:3, each within a range of ±5%, and 0.3≦Pb≦0.4.

[0010] In this invention, the time of the primary heat treatment is
It is preferable that it is 100-250 hours. Further, it is preferable that the powder filled in the metal sheath has a maximum particle size of 2.0 μm or less and an average particle size of 1.0 μm or less.

Furthermore, in the present invention, the bismuth-based superconductor as a powder filled into the metal sheath or its raw material generally consists of a polycrystal or an aggregate of a superconducting phase and a non-superconducting phase.

[0012] The material of the metal sheath used in this invention is a material that does not react with the bismuth-based oxide superconductor;
It is also preferable to use a metal or alloy with low resistance. Examples of such materials include silver or silver alloys.

[0013]

Effects of the Invention: By using powder having the above composition ratio, the present inventors have succeeded in reducing the formation of non-superconducting phases, mainly Ca-Cu-O, after heat treatment to generate 110K phase. I discovered what I can do. This invention is
It is based on this fact.

[0014] In order to obtain a high critical current density, it is necessary to cause grain growth of the high temperature phase, and the metal sheath is filled with an aggregate of mainly Bi-based low temperature phases and non-superconducting phases. By using such an aggregate, a high temperature phase can be generated after heat treatment.

[0015] Generally, it is known that a Bi-based high-temperature phase is easily formed when a large amount of Ca or Cu is blended. Therefore, in the past, a slightly larger amount of Ca was added to generate a high-temperature phase. However, as a result of analysis of the component ratio of the high temperature phase, Bi+Pb:Sr:Ca:Cu=2.18
:1.97:1.95:3:3.00, which is the composition ratio of this invention, Bi+Pb:Sr:Ca
:Cu=2.2:2:2:3 was found to be appropriate for the generation of high temperature phase.

It has been found that the powder to be filled into the metal sheath is preferably a fine powder having a maximum particle size of 2.0 μm or less and an average particle size of 1.0 μm or less. It is thought that by using such a fine powder, the reaction can be greatly activated, making it easier to generate a high-temperature phase.

According to the present invention, after the heat treatment for producing the 110K phase, the production of the non-superconducting phase is reduced to 1 in volume ratio.
0% or less, and the thickness (in the a-b plane direction of the matrix) can be made to be 2 μm or less in size. As a result, the proportion of the superconducting phase increases, the generation of defects due to processing during heat treatment can be prevented, and crystal growth can be promoted. Therefore, according to the present invention, a superconducting wire having high critical current density and critical current can be manufactured.

[0018] In this invention, the time of the primary heat treatment is as follows:
100 hours or more is preferable. This means that the heat treatment time is 1
This is because if the heating time is less than 0.00 hours, the formation of the high-temperature phase or its grain growth will be incomplete. Also, the heat treatment time is 2
Preferably it is 50 hours or less. This is because when the time exceeds 250 hours, the agglomeration of different phases begins to affect the characteristics, which conversely causes a decrease in the critical current density.

[0019]

[Example] Bi2 O3, PbO, SrCO3, C
aCO3 and CuO powder, Bi:Pb:S
r:Ca:Cu=1.8:0.4:2.0:X:3.0
(X = 1.8, 2.0, or 2.2), with three types of composition ratios, and Bi:Pb:Sr:Ca:Cu.
=1.6:0.4:2.0:2.0:3.0 were weighed and mixed. These samples in order
～■. Next, the mixture was heat-treated at 800°C for 20 hours, crushed, and then heat-treated at 860°C for 2 hours to obtain a powder for filling.

[0020] Each of the obtained powders was pulverized to a maximum particle size of 2.0 μm and an average particle size of 1.0 μm.

Thereafter, each of the obtained powders was filled into a silver pipe having an outer diameter of 6.0 mm and an inner diameter of 4.0 mm, and then wire-drawn to a diameter of 1.0 mm. Next, this wire rod was rolled to a thickness of 0.17 mm and pressed.

[0022] Thereafter, as a primary heat treatment, 84
Heat treatment was performed at 5°C for 50 hours, 100 hours, 150 hours, 200 hours, 250 hours, and 300 hours, and then pressing was performed again and a secondary heat treatment was performed at 840°C.
, heat treatment was performed for 50 hours.

Regarding each wire rod obtained in this way,
The critical current in each case was measured at a temperature of 77.3 K and in a zero magnetic field. Table 1 shows the obtained Jc and I
Indicates the value of c. In Table 1, the values in the upper row indicate Jc,
Its unit is 104 A/cm3, the lower row shows Ic, and its unit is A.

[0024]

[Table 1]

As is clear from the results in Table 1, the oxide superconducting wire according to the present invention is excellent in Jc and Ic.

Claims (1)

[Claims] [Claim 1] Composition ratio is Bi+Pb:Sr:Ca:C
filling a metal sheath with powder having a composition centered around u=2.2:2:2:3, each within a range of ±5%, and satisfying 0.3≦Pb≦0.4, and the powder A step of plastic working the metal sheath filled with the metal to form a wire rod, a step of primary heat treatment of this wire rod, a step of plastic working or pressing of the wire rod after heat treatment, and a step of secondary heat treatment of the wire rod after processing. A method for manufacturing a bismuth-based oxide superconducting wire, comprising steps.