JPH05282937A - Manufacture of bi oxide superconductive conductor - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing a Bi-based oxide superconductor having excellent superconducting properties. [Structure] A composite billet in which a raw material powder that can be a Bi-based oxide superconductor is filled in a metal tube is stretched to form a composite wire, and the composite wire is subjected to a predetermined final heat treatment. in the production method of the body, the intermediate with at least one, the Bi-based oxide superconductor or more temperature T _M of partial melting, the partial melting temperature T 10 ° C. higher temperature T _H following temperature ranges from _M to stretch during processing by heat treatment by reacting said raw material in the superconductor, the final heat treatment is less than the partial melting temperature T _M, than the partial melting temperature T _M
The temperature is 20 ° C. lower than the temperature T _L.

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 a Bi-based oxide superconductor having excellent superconducting properties, which is suitable as a conductor for magnets or cables, a conductor for current leads, or the like.

[0002]

2. Description of the Related Art In recent years, Y--Ba--Cu--O system, Bi--
(Pb) -Sr-Ca-Cu-O system, Tl-Ba-Ca
Oxide superconductors having a critical temperature (Tc) of -Cu-O system exceeding liquid nitrogen temperature have been found, and their application to cables, conductors for magnets, etc. is expected. Among them, Bi- (P
b) The -Sr-Ca-Cu-O-based oxide superconductor has a high critical temperature (Tc) of 110 K, which is a superconductor, and is rich in crystal orientation and has a high critical current density (Jc). Practical research is actively underway. By the way, since the above-mentioned oxide superconductor is brittle, a method in which it is processed in combination with a metal material having good workability is mainly used to form the oxide superconductor into a cable conductor or the like. This composite processing method is, for example, filling a metal tube with a raw material powder that can be an oxide superconductor to form a composite billet, and stretching this composite billet to form a composite wire rod having a desired shape. It is a manufacturing method in which the raw material powder is reacted with an oxide superconductor by performing a predetermined final heat treatment.

[0003]

However, when a Bi-based oxide superconductor is manufactured by the above-mentioned composite processing method, the raw material powder of the Bi-based oxide superconductor has a slow reaction rate to the oxide superconductor. Therefore, the heating temperature in the final heat treatment step is performed to a high temperature that is equal to or higher than the temperature T _{M at} which the Bi-based oxide superconductor partially melts. As a result, in the cooling process after the final heat treatment, the partially molten liquid phase is melted. However, there is a problem in that a non-superconducting phase precipitates at the crystal grain boundaries to reduce the bondability of the crystal grain boundaries, and the obtained oxide superconductor cannot have a high critical current density (Jc).

[0004]

In the present invention, as a result of earnest research in view of such a situation, when a Bi-based oxide superconducting body is manufactured by a composite processing method, Bi is produced during the stretching process.
When the intermediate heat treatment is performed at a temperature T _M or higher at which the oxide-based superconductor partially melts, strain is applied to the non-superconductor phase by the stretching process performed later, and the reaction of the raw material powder with the Bi-based oxide superconductor is promoted. In the final heat treatment step, if the heat treatment temperature is suppressed to a temperature lower than the partial melting temperature T _M of the Bi-based oxide superconductor, it is possible to prevent new non-superconductor phase from precipitating at the grain boundaries, and The inventors have found that the non-superconductor phase generated in the heat treatment step can be reacted with the superconductor phase, and thus found a method for efficiently producing a Bi-based oxide superconductor having excellent superconducting properties. That is, in the method of the present invention, a raw material powder that can be a Bi-based oxide superconductor is filled in a metal tube to form a composite billet, and the composite billet is stretched to form a composite wire rod having a desired shape. In the method for producing a Bi-based oxide superconductor for subjecting a composite wire to a predetermined final heat treatment, at least once during the stretching process, at a temperature T _M at which the Bi-based oxide superconductor partially melts or more, and the partial melting temperature T _M subjected to intermediate heat treatment at from 10 ° C. higher temperature T _H following temperature ranges, the final heat treatment is less than the partial melting temperature T _M, the partial melting temperature T _M
It is characterized in that it is applied in a temperature range not less than 20 ° C. lower than T _L.

[0005] In the present invention method, an intermediate heat treatment performed in the course stretching, in Bi-based oxide superconductor partial melt to a temperature T _M above, the partial melting temperature T _M than 10 ° C. higher temperature T _H following temperature range The reason for applying is in the partial melting temperature T
Is less than _M, and because the reaction rate of the superconductor becomes slow, and the precipitation amount of the non-superconducting phase and intermediate heat treatment temperature exceeds the partial melting temperature T _M than 10 ° C. higher temperature T _H is increased,
This is because it takes a long time to react the non-superconductor phase with the superconductor phase in the subsequent final heat treatment. Further, the final heat treatment is performed by the partial melting temperature T _{M of the} Bi-based oxide superconductor.
Less than in the partial melting temperature T _M of subjecting at from 20 ° C. lower temperature T _L above temperature range, the non-superconducting phase in the grain boundaries and the final heat treatment temperature is higher than the partial melting temperature T _M And the bondability of the grain boundaries is weakened, and if the temperature is lower than the partial melting temperature T _{M, which} is 20 ° C. lower than T _L , the non-superconductor phase precipitated in the intermediate heat treatment does not sufficiently react with the superconductor phase, This is because the superconducting property of the obtained Bi-based oxide superconducting body is deteriorated. Lower limit temperature T in the final heat treatment
_It is preferable that _L is about 10 ° C. lower than the partial melting temperature T _M, because a high Jc can be obtained without spending much time for the final heat treatment. Since the partial melting temperature T _M varies depending on the composition, it needs to be measured in advance for each Bi-based oxide superconductor to be used.

In the method of the present invention, the intermediate heat treatment may be performed any number of times during the stretching process, but at least once in the intermediate heat treatment, the temperature T _M at which the Bi-based oxide superconductor is partially melted is used. From the above, the partial melting temperature T _M
10 ° C. performed at a temperature T _H following temperature range. For the stretching process applied to the composite billet, usual stretching process methods such as extrusion, rolling, press compression, swaging, drawing, and wire drawing are applied. For the stretching process after the intermediate heat treatment, a process method in which compression such as press compression or rolling is applied is particularly preferable because it is easy to orient the crystal in the C axis where current easily flows and defects such as cracks can be adhered and eliminated. is there. In the method of the present invention,
The raw material powder that can be formed into a Bi-based oxide superconductor includes a Bi-based oxide superconductor, an intermediate that reacts with the Bi-based oxide superconductor by heat treatment in an oxygen-containing atmosphere,
For example, a mixture of constituent elements of a Bi-based oxide superconductor, a coprecipitated mixture, an oxide of constituent elements, an oxygen-deficient complex oxide, or the like is used. Any metal material may be used for the metal tube filled with the raw material powder.
The g alloy is preferable because it has excellent oxygen permeability and the characteristics of the obtained Bi-based oxide superconductor are improved.

[0007]

In the method of the present invention, the raw material powder that can be a Bi-based oxide superconductor is filled in a metal tube to form a composite billet, and the composite billet is stretched to form a composite wire rod having a desired shape. In the method for producing a Bi-based oxide superconducting body in which this composite wire is subjected to a predetermined final heat treatment, the partial melting is performed at least once during the stretching process at a temperature T _M at which the Bi-based oxide superconductor partially melts or higher. Temperature T
Since it subjected to intermediate heat treatment at 10 ° C. higher temperature T _H following temperature ranges than _M, the reaction of the Bi-based oxide superconductor material powder is made during the intermediate heat treatment, also part of the final heat treatment the Bi-based oxide superconductor below the melting temperature T _M, so applied in the partial melting temperature T 20 ° C. lower temperature T _L above temperature range than _M, without newly deposited non superconducting phase at the grain boundaries, produced during the intermediate heat treatment The non-superconductor phase described above can be promptly reacted with the superconductor phase. Further, the stretching process performed after the intermediate heat treatment adds strain to the non-superconductor phase, and promotes the reaction of the non-superconductor phase to the superconductor phase in the final heat treatment.

[0008]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 Bi: Pb: Sr: Ca: Cu was used as the starting material in an atomic ratio of 1.
A mixed powder was used in which an oxide containing the above element was mixed so as to be 95: 0.37: 2: 2.16: 3.21. The partial melting temperature T _M of this mixed powder is 835 to 838 ° C. under the atmospheric pressure of 1 atm.
Met. Next, mix this powder with an outer diameter of 20 mmφ and an inner diameter of 16 mmφ.
Was filled in an Ag pipe and the end was vacuum sealed by electron beam welding to form a composite billet. Next, this composite billet was swaged to form a wire rod having a diameter of 5 mm, and then this wire rod was rolled to finish a 0.2 mmt tape-shaped composite wire rod. Next, this tape-shaped composite wire was subjected to intermediate heat treatment at various temperatures above the partial melting temperature T _M of the oxide superconductor. Next, this intermediate heat-treated material was uniaxially pressed and then subjected to final heat treatment at various temperatures.
An 18 mm thick Bi-based oxide superconductor was manufactured. For each of the Bi-based oxide superconductors thus obtained, Jc was measured in liquid nitrogen temperature (77.3 K) under zero magnetic field. The results are shown in Table 1 together with the intermediate and final heat treatment conditions.

[0009]

[Table 1]

As is clear from Table 1, the method products of the present invention (Nos. 1 to 3) all had high Jc. When analyzed by X-ray diffractometry, some non-superconductor phase was detected after the intermediate heat treatment, but after the final heat treatment, the whole reacted with the superconductor phase. On the other hand, in No. 4 and No. 5 of the comparative example products, the final heat treatment temperature exceeded the partial melting temperature of the oxide superconductor, so that the non-superconductor phase was precipitated in the crystal grain boundaries and the bondability of the crystal grain boundaries was deteriorated. Further, in No. 6, the intermediate and final heat treatment temperatures were both lower than the partial melting temperature, so that the reaction to the superconductor phase was not sufficient, and all had low Jc values. Bi-Pb-Sr-Ca-Cu-O
The system superconductor has been described, but the method of the present invention is not limited to Bi-S.
The same effect can be obtained by applying it to other Bi-based oxide superconductors such as r-Ca-Cu-O.

[0011]

As described above, according to the method of the present invention, it is possible to efficiently produce a Bi-based oxide superconducting body having excellent superconducting properties, and to exert a remarkable industrial effect.

Claims (1)

[Claims] 1. A raw material powder capable of forming a Bi-based oxide superconductor is filled into a metal tube to form a composite billet, and the composite billet is stretched to form a composite wire rod having a desired shape, and then the composite wire rod. Bi that is subjected to the prescribed final heat treatment
In the method for producing a base oxide superconductor, at least once during the drawing process, at a temperature T _M or higher at which the Bi-based oxide superconductor partially melts, and 10 ° C. from the partial melting temperature T _M.
Subjected to intermediate heat treatment at a high temperature T _H following temperature ranges, the final heat treatment is less than the partial melting temperature T _M, characterized in that applied in the partial melting temperature T 20 ° C. lower temperature T _L above temperature range above _M A method for producing a Bi-based oxide superconductor.