JP3050573B2 - Manufacturing method of oxide superconducting conductor - Google Patents

Description

The present invention relates to a method for manufacturing an oxide superconducting conductor used for a magnet wire, a power cable, a power storage link, a magnetic shield, a Meissner effect application device, and the like.

[Conventional technology and its problems]

As is well known recently, Y-Ba-Cu-O system, Bi-Sr-Ca-Cu
Oxide superconductors such as -O-based and Tl-Ba-Ca-Cu-O-based were found. Since this oxide superconductor is a substance having a high critical temperature (Tc) which becomes superconducting with an inexpensive cooling medium such as liquid nitrogen, research into practical use in various fields is underway.

The oxide superconductor has a layered perovskite type crystal structure and therefore has a strong crystal anisotropy, and the current easily flows to the ab plane containing Cu-O atoms. This is a necessary condition for obtaining a high critical current density (Jc), and since the crystal grain boundary becomes an obstacle to energization, it is important to reduce the crystal grain interface in the energization direction.

By the way, these oxide superconductors cannot be processed like a metal because they are brittle.To make them into oxide oxide superconductors of a predetermined shape, for example, a raw material that can be made oxide superconductor is Ag. A method has been applied in which the material is filled into a pipe made of steel or the like, and is elongated into a predetermined shape, and then subjected to a predetermined heat treatment to cause a solid-phase reaction with the oxide superconductor.

However, the oxide superconductor obtained in this way has a polycrystalline structure with a random crystal orientation and has a large current-carrying resistance at the crystal grain boundaries due to the weak coupling state of the crystal grain boundaries, and therefore has a high Jc value. There was a problem that can not be obtained.

Also, a method of forming a highly oriented oxide superconductor on a substrate by a vapor phase growth method such as a PVD method or a CVD method has been proposed.
It is necessary to strictly control the conditions for producing a substrate by using a single crystal having a crystal structure similar to that of an oxide superconductor and epitaxially growing it on the substrate, and requiring a long heat treatment after film formation. The productivity was poor.

[Means and Actions for Solving the Problems]

The present invention has been made as a result of intensive studies in view of such a situation, and an object of the present invention is to provide a method for efficiently manufacturing an oxide superconducting conductor having excellent superconducting characteristics.

That is, the present invention relates to a method in which the raw material powder of an oxide superconductor is subjected to an oxygen partial pressure.
After calcining in an atmosphere of 10 ^{-5 to} 200 Torr, the calcined powder obtained by pulverizing and classifying the calcined powder is filled into a metal tube having a core material arranged at a predetermined position, and then this is elongated to form a metal. The thickness of the calcined powder layer between the inner surface of the tube and the core material or between the core materials is set to 0.001 to 1.0 mm. Thereafter, the calcined powder layer is partially applied to the dissected material in an oxygen-containing atmosphere. After heating at a temperature T1 higher than the temperature at which
a first heat treatment step of cooling at a rate of min, and a step of heating the oxide superconductor layer crystallized through the first heat treatment step at a temperature T2 lower than the temperature T1 by 20 to 150 ° C. in an oxygen-containing atmosphere. Two heat treatment steps are sequentially performed.

The calcined powder used in the method of the present invention includes, for example, alkaline earth metals, rare earth elements and copper oxides, carbonates, sulfates, nitrates, sulfides, halides, alkoxides or elemental or alloys of each element. A material obtained by mixing a predetermined amount of the raw material powder of the oxide superconductor of No. 1 and heating to 500 to 1000 ° C. in an atmosphere having an oxygen partial pressure of 10 ^{−5 to} 200 Torr is crushed and classified. It reacts with the oxide superconductor by heat treatment in the containing atmosphere.

In the method of the present invention, the metal tube filled with the calcined powder and the core material arranged in the metal tube are made of a metal that is non-reactive with the oxide superconductor and has excellent electrical conductivity and thermal conductivity. Is used, for example, Ag, Ag-Pd, Ag-Au,
Ag-Cu, Ag-Mg, Ag-Pt, Ag-Ir, Au, Au-Ni, Au-C
u, Au-Ag-Cu, Au-Pd-Ag, Au-Ir, Pt-Ir, Pt-I
r, Pt-Pd, Pd, Pd-Ni, Pd-Co, Ni-Cr, Ni-Cr-C
Those made of materials such as o, Ni-Fe, Ni-Fe-Co, Fe-Cr, and Fe-Ni-Cr (SUS) are preferable.

In the above description, the materials of the metal tube and the core material may be different, but the same material is preferable because it is easily processed.

In the method of the present invention, the shape and configuration of the metal tube and the core material are such that the thickness of each part of the calcined powder layer after the elongation is 0.001.
The shape is not particularly limited as long as it is within the range of 1.0 mm, and any shape such as a round shape, an elliptical shape, and a square shape can be used.

Hereinafter, the configuration of the oxide superconductor manufactured by the method of the present invention will be described with reference to the cross-sectional views shown in FIGS.

That is, the oxide superconducting conductor of the present invention shown in FIG. 1 has a cylindrical core 2 disposed at the center in a metal tube 1 having a circular cross section, and the conductor shown in FIG. A cylindrical core material 3 and a cylindrical core material 2 having different diameters are arranged concentrically in a metal tube 1 to form a multi-core structure. The conductor shown in FIG. One rectangular tube-shaped core material 5 and one rectangular prism-shaped core material 6 are concentrically arranged in a metal tube 4 of a mold and multi-core, and the conductor shown in FIG. In order to obtain an Ic value, a plurality of columnar cores 2 are arranged at predetermined intervals in a metal tube 1 having a circular cross section, and the calcined powder 7 is filled in the gap between each metal tube and the core material. It is a conductor.

As a method for elongating the metal tube filled with the calcined powder, any elongation method such as rolling, extrusion, pressing, groove roll rolling, swaging, drawing or the like is applied.

In the method of the present invention, the calcined powder layer as the inner layer of the above-mentioned stretch-processed material is to be crystallized by C-axis orientation in the first heat treatment step, and the heating temperature T ₁ is, for example, Bi. In the case of a system oxide superconductor, it is a temperature at which at least a part of the calcined powder layer is melted at a temperature of about 880 to 920 ° C. or higher.

Thus to heat temperatures T ₁ is desirably determined by measuring the melting temperature by performing the thermal analysis for each condition such as composition.

In the method of the present invention, the cooling rate from the temperature T ₁ of the 100 ° C. /
If it exceeds min, crystallization is impaired, and at a low speed of less than 0.01 ° C / min, phase separation and coarsening of crystal grains occur, so
It is necessary to be 100 ° C / min.

In the method of the present invention, by subjecting the crystallized oxide superconductor layer to the second heat treatment step, the crystal structure is adjusted and oxygen is supplied, and characteristics such as Jc are improved.

Additional reasons for the heating temperature T ₂ in the second heat treatment step is limited to the first heating temperature T ₁ of from 20 to 150 ° C. lower temperature in the heat treatment step, temperature T ₂ is temperature T ₁ of from less than 20 ° C. lower temperature In this case, the crystal structure is not adjusted, and oxygen is not sufficiently replenished at a low temperature exceeding 150 ° C. Above temperature T ₂
Is 20 to 100 ° C. lower than the temperature T ₁ is is particularly preferred.

In the method of the present invention, the thickness of the calcined powder layer between the inner surface of the metal tube and the core material or between the core materials of the rolled material is 0.001 to 1.0 mm.
The reason is that if it is less than 0.001 mm, a slight change in the density distribution of the pre-fired powder layer may cause disconnection or degrade the performance during the elongation process. This is because the C-axis orientation of the crystal and the crystal growth in the longitudinal direction are not sufficiently performed in the first heat treatment step.

In the method of the present invention, the reason why the raw material to be filled into the metal tube is limited to the preliminarily calcined powder that is preliminarily calcined and pulverized and classified in a low oxygen atmosphere because the preliminarily calcined powder prepared by this method is in an oxygen-deficient state. Activation, resulting in a rapid reaction to the superconductor. Also, the calcined powder has a reduced melting point so that a metal with a relatively low melting point, such as Ag, can be applied to the metal tube. This is because a superconductor has advantages such as a single phase having a high Tc in an oxygen-deficient state.

In the method of the present invention, it is possible to expand the use in various ways by selecting the material or shape of the coating metal tube and the core material.For example, if a high-strength material is used for the material, thermal such Ag, in the case of using high electrical conductivity materials are those capable of acting as a stabilizing material for the quenching phenomenon, further metal pipe outside the H ₂ O and C
It also has an action of protecting the oxide superconductor layer from harmful gases such as O ₂ and an external magnetic field.

Further, if a material having high toughness is processed thinly or thinly, flexibility can be obtained, so that the present invention can be applied to a field requiring bending such as a coil and a magnet.

In addition, since the oxide superconductor is embrittled by the heat treatment, it is also useful to form the oxide superconductor into a coil, a magnet or the like in advance, and then heat-treat the coil.

Furthermore, by using a large number of thin and fine materials for the core material, the area occupied by the oxide superconductor layer can be increased, and a conductor having a large current capacity can be obtained.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

Bi: Sr: Ca: Cu atomic ratio of Bi ₂ O ₃ , SrO, CaO, CuO is 2: 2:
The mixed powder was mixed and mixed at a ratio of 1: 2, and the mixed powder was pre-fired at 850 ° C. for 3 H in an atmosphere with an oxygen partial pressure of 1.4 × 10 ⁻¹ Torr. Bi ₂ Sr ₂ CaCu ₂ O
_x calcined powder was prepared.

Then, the above-mentioned calcined powder was filled into an Ag tube in which an Ag cylindrical core material was arranged at the center of the same structure as shown in FIG. 1, and this was rolled and drawn to form circular cross sections of various diameters. distraction workpiece and without, then it was held for 30 minutes at a temperature T ₁ of the liquidus temperature near the calcined powder in the atmosphere, then cooled from the temperature to temperature T ₂ at a predetermined speed, the 30 at temperature T ₂
After holding for a time, this was cooled to room temperature to form an oxide superconductor. In the above, the temperatures T ₁ , T ₂ and the cooling rate from T ₁ to T ₂ were varied.

In the above, the thickness of the oxide superconductor layer was changed by changing the pipe diameter while keeping the core diameter constant.

Tc and Jc were measured for each of the oxide superconductors thus obtained. Jc was measured by a four-terminal method in liquid nitrogen (77K) with and without applying a magnetic field. The results are shown in Table 1 together with the thickness of the oxide superconductor layer.

As is clear from Table 1, the products of the present invention (1 to 7)
Showed high values of both Tc and Jc. In particular, even when a magnetic field was applied, Jc was maintained at a high value, and the magnetic field resistance was excellent.

On the other hand, No. 8 and 9 of the comparative method products are those in which the thickness of the calcined powder layer of the rolled material is out of the limit value of the present invention, and the former is too thick, so that the C-axis orientation and the energizing direction are different. Was not sufficiently grown, and Jc was low. In the latter, the density of the calcined powder layer became non-uniform due to strong processing to a small thickness, and Jc decreased. In No. 10, the heating temperature T ₁ in the first heat treatment step was too low and the calcined powder was not melted.
11 and 12 because the heating temperature T ₂ of the second heat treatment step had limited value outside of the present invention, also No13 the C of any crystal for the cooling rate is too fast from the heating temperatures T ₁ to T ₂ Crystal growth in the axial orientation and / or in the direction of current flow was not sufficient, resulting in low values of Tc and Jc.

〔effect〕

As described above, according to the method of the present invention, an oxide superconducting conductor having excellent superconducting characteristics such as Jc and capable of transmitting a large amount of power can be efficiently produced, and thus has a remarkable industrial effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 are cross-sectional explanatory views showing an embodiment of an oxide superconductor manufactured by the method of the present invention. 1,4 ... Metal tube, 2,3,5,6 ... Core material, 7 ... Pre-fired powder.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-243316 (JP, A) JP-A 64-72419 (JP, A) JP-A-63-277575 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01B 12/00-13/00 C04B 35/00

Claims (1)

(57) [Claims] 1. An oxide superconductor raw material powder having an oxygen partial pressure of 10 ^-5.
After calcining in an atmosphere of ~ 200 Torr, the calcined powder obtained by pulverizing and classifying the calcined powder is filled into a metal tube in which a core material is arranged at a predetermined position, and then this is stretched to form an inner surface of the metal tube. Set the thickness of the calcined powder layer between core materials or between core materials to 0.
001 to 1.0 mm, and then, after heating this stretched material at a temperature T1 or higher at which the calcined powder layer partially melts in an oxygen-containing atmosphere, 0.01 to 100 ° C / min. A first heat treatment step of cooling at a rate and a second heat treatment of heating the oxide superconductor layer crystallized through the first heat treatment step at a temperature T2 lower than the above temperature T1 by 20 to 150 ° C. in an oxygen-containing atmosphere. A method for producing an oxide superconductor, comprising sequentially performing steps.