JPH06223649A - Manufacture of bi oxide superconducting wire - Google Patents

Abstract

PURPOSE:To manufacture a superconducting wire which does not exhibit electrical anisotropy in a magnetic field, without requiring rolling process. CONSTITUTION:Calcined powders of Bi, Pb, Sr, Ca and Cu blended together in a predetermined mole ratio are subjected to CIP process and then subjected to heat treatments to achieve growth of a superconducting phase by 60% or higher. The critical current density (Jc) of a superconducting wire, manufactured by inserting the molding of the powders into an Ag rod, disposing an Ag pipe outside it and drawing the molding into a round wire which is then heat treated, has a value of 15000A/cm<2> at 77.3K and at 0T and does not show dependency on electrical anisotropy in a magnetic field, i.e., the direction H of the magnetic field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a superconducting wire, and more particularly to improvement of a method of manufacturing a Bi-based oxide superconducting wire by a metal sheath method.

[0002]

2. Description of the Related Art Bi-based oxide superconductors are 80 to 11
Since it has a critical temperature (Tc) of 0K and Tc exceeds the liquid nitrogen temperature (77K), it is expected to be put to practical use in fields such as electronics, power transportation, and strong magnetic field generation. The density (Jc) is reaching the practical level.

In order to put oxide superconductors into full-scale practical use, it is indispensable to establish a wire rod forming technology, and a metal sheath is one of the promising methods for producing long wire rods having a high Jc. The method (Ag sheath method) is known.

According to this method, a silver pipe is filled with a mixed powder or a calcined powder in which the constituent elements of the oxide superconductor are mixed in a predetermined molar ratio, and this is processed into a linear shape by wire drawing or rolling. After that, heat treatment is performed, and the reason why Ag is used is that it has excellent workability, does not react with the internal oxide during heat treatment, and that Ag has a substantially oxygen-permeable function.

This Ag sheath method utilizes the fact that each crystal grain has a plate-like structure, particularly in the case of a Bi-based oxide superconductor, by applying a compressive force by rolling after drawing. During the heat treatment, the c-axis of the crystal is oriented perpendicular to the plate surface, so that the crystal orientation can be enhanced, resulting in Jc
There is an advantage that can be improved.

[0006]

However, in the above Ag sheath method, the final shape is a tape shape in order to obtain a dense and highly oriented crystal structure, which causes the following problems. That is, when forming a coil,
Since the wire has a tape shape, it can be wound only in a pancake shape, and since the wire having such a shape has electrical anisotropy in a magnetic field, when the magnetic field is applied parallel to the c-axis of the crystal, There is a drawback that the Jc and the like are significantly reduced. Therefore, the coil shapes that can be manufactured are limited.

The present invention has been made to solve the above-mentioned problems, and it is a Bi-based oxide superconducting material having a high Jc after wire drawing without requiring the application of compressive force by rolling. It is an object to provide a method of manufacturing a wire.

[0008]

In order to achieve the above object, the method for producing a Bi-based oxide superconducting wire of the present invention comprises:
(A) a step of molding a raw material powder containing elements constituting a Bi-based oxide superconductor in a predetermined ratio to produce a cylindrical molded body, and (b) a heat treatment of the cylindrical molded body. The step of growing the superconducting phase by 60% or more, and (c) inserting a metal rod into the molded body after this heat treatment, and arranging a metal tube made of the same material as this metal rod on the outside thereof to form a composite. The step of forming a body and the step (d) of subjecting the composite to wire drawing and then heat treatment are sequentially performed.

The raw material powder in the above invention contains the elements constituting the oxide superconductor in a predetermined ratio.
As the raw material powder, a mixed powder in which powders of oxides, carbonates, nitrates and the like containing these elements are mixed at a predetermined molar ratio, and a calcined powder obtained by calcination and grinding of the mixed powder are used. .

As a method of molding the raw material powder, it is preferable to obtain a molded body having a uniform density.
In addition to IP (cold static pressure press) and HIP (hot static pressure press), cold press and the like are used.

Further, heat treatment is performed to grow the superconducting phase of the molded cylindrical body, and this temperature range is 840.
It is preferably 870 ° C. Outside this temperature range, the amount of impurity phase produced increases. By this heat treatment, the superconducting phase is grown to a ratio of 60% or more in order to make the subsequent rolling process unnecessary, and more preferably in the range of 70 to 80%, the bulk density is 3.0 g / cm ³ or more. To do. The reason for this is that if the growth rate of the superconducting phase is less than 60%, a large number of voids are formed inside due to the generation of the superconducting phase which is an expansion reaction during the heat treatment after the wire drawing, and the Jc is lowered. When the ratio exceeds 80%, the crystal destroyed by the wire drawing process cannot be recovered by the subsequent heat treatment, and the Jc similarly decreases. On the other hand, if the bulk density is less than 3.0 g / cm ³ , the disturbance of the interface between the sheath and the core becomes large during processing, and the characteristics deteriorate.

The metal rod inserted into the molded body after the heat treatment and the metal tube arranged on the outside have excellent malleability, do not react with the superconductor in the heat treatment temperature range, and are non-oxidizing and non-magnetic. Materials are used. For example, Ag, A
u, Pt or alloys thereof are adopted.

The area reduction rate of wire drawing applied to the composite is 80.
% Or more is preferable. If the area reduction rate is less than this, a sufficiently dense structure cannot be obtained.

[0014]

In the above-mentioned invention, the cylindrical compact formed by molding the raw material powder is heat-treated to grow the superconducting phase to 60% or more, and then the metallic material is placed inside and outside the compact. By performing the wire drawing work, the crystal destroyed by the wire drawing work is recovered by the subsequent heat treatment and the production fraction of the superconducting phase is improved. As a result, the crystal orientation is improved and a high Jc superconducting wire can be obtained. That is, there is no need for a process of orienting the c-axis of the superconducting phase which becomes the nucleus in the raw material powder by rolling and growing it by heat treatment.

[0015]

EXAMPLES An example of the present invention will be described below.

Example Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ , CuO
Powder of Bi: Pb: Sr: Ca: Cu = 1.80:
After being mixed in a molar ratio of 0.40: 2.00: 2.00: 3.00 and mixed by a wet mixing method, in the air, at 840 ° C.
Heat treatment was performed at the temperature of, and this was crushed to produce a calcined powder.

The calcined powder is subjected to CIP processing to obtain an outer diameter φ.
After forming a cylindrical molded body having a diameter of 4.5 mm and an inner diameter of 2.5 mm, heat treatment was performed in the atmosphere at 850 ° C. for 100 hours to grow a superconducting phase. The ratio of the superconducting phase at this time is XRD
(X-ray diffraction) Results obtained from peak intensity on chart 7
It was 5%.

Then, the outer diameter φ
Insert a 2.0 mm Ag rod, and then add an outer diameter of φ7.
After being housed in an Ag pipe having a diameter of 0 mm and an inner diameter of 5.0 mm, wire drawing was performed to form an outer diameter of 1.04 mm. The area reduction rate of this wire drawing was 98%.

The superconducting wire produced by subjecting this wire to a heat treatment at 840 ° C. for 50 hours in the air has a Jc of 77.3 K,
It was 15000 A / cm ² at 0T.

Regarding the superconducting wire manufactured according to the above-mentioned embodiment, electric anisotropy in a magnetic field, ie, Jc, in a cross section perpendicular to the axial direction x of the superconducting wire 1 shown in FIG. 2 (a). Of magnetic field direction H of 77.3K, magnetic field strength of 800
The results measured under Gaussian conditions are shown in FIG. The measurement results are shown as normalized values of Jc (θ) / Jc (θ = 0).
Comparative Example A calcined powder prepared in the same manner as in the above example had an outer diameter φ
After being housed in an Ag pipe having a diameter of 7.0 mm and an inner diameter of 5.0 mm, wire drawing was performed to form an outer diameter of 1.04 mm.

This wire is rolled to a thickness of 0.17
After being formed into a tape having a size of mm, it was heat-treated at 840 ° C. for 100 hours in the air. The ratio of the superconducting phase at this time is XR
The result was 70% as determined from the peak intensity on the D (X-ray diffraction) chart.

Next, the above tape was further subjected to intermediate rolling to form a thickness of 0.15 mm, and then 84 in air.
Jc of superconducting wire manufactured by heat treatment at 0 ℃ x 50 hours
Was 77.3K and 10000A / cm ² at 0T.

For the superconducting tape 2 produced by the above comparative example, the dependence of Jc on the magnetic field direction H was measured in the cross section perpendicular to the axial direction x of the tape shown in FIG. The results obtained are also shown in FIG.

[0024]

As described above, according to the method for producing a Bi-based oxide superconducting wire of the present invention, the following advantages can be obtained.

(A) By arranging the metal rod at the center, uniform pressure can be applied to the molded body, so that the crystal orientation and densification are improved.

(B) The rolling process can be omitted and the process is simplified.

(C) Since it does not exhibit electrical anisotropy in a magnetic field, the shape of the coil that can be manufactured is not limited.

[Brief description of drawings]

FIG. 1 shows the dependence of Jc on a magnetic field direction H in a cross section perpendicular to an axial direction x of a superconducting wire manufactured by a method of an example of the present invention and a superconducting tape manufactured by a method of a comparative example. Graph.

2A is a diagram showing the positional relationship between the axial direction x and the magnetic field direction H of the superconducting wire shown in FIG. 1, and FIG. 2B is a diagram showing the axial direction x and the magnetic field direction H of the superconducting tape shown in FIG. The figure which shows a positional relationship.

[Explanation of symbols]

 1 ... Superconducting wire 2 ... Superconducting tape H ... Magnetic field direction

Claims (2)

[Claims] 1. A step of: (a) molding a raw material powder containing elements constituting a Bi-based oxide superconductor in a predetermined ratio to produce a cylindrical molded body; and (b) the cylindrical molding. A step of subjecting the body to heat treatment to grow a superconducting phase by 60% or more, and (c) a metal rod made of the same material as the metal rod outside the metal rod while inserting the metal rod into the molded body after the heat treatment. Arranging to form a complex,
(D) A method for producing a Bi-based oxide superconducting wire, which comprises a step of subjecting the composite to a wire drawing process and then a heat treatment. 2. The method for producing a Bi-based oxide superconducting wire according to claim 1, wherein the wire drawing is performed with a surface reduction rate of 80% or more.