JPH03129611A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To manufacture a superconductive substance of a high critical current density efficiently by filling a metallic pipe with calcined powder, drawing it to form the internal calcined powder layer into a specified thickness, and subjecting the internal layer to the first and second heat treatments in succession at the respective specified temperatures. CONSTITUTION:A metallic pipe is filled with a calcined substance and drawn to form the internal calcined powder layer into a draw processed material of a specified thickness. The powder layer is subjected to first and second heat treatment in succession respectively at specified temperatures. The thickness of the draw processed material here is made 0.001-1.0mm. The first heat treatment is performed at a temperature higher than T1 at which the calcined powder layer partially melts and followed by cooling at the cooling speed of 0.001-100 deg.C/min. The temperature of the second heat treatment T2 is specified to be a temperature 20-150 deg.C lower than T1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an oxide superconducting conductor used in magnet wires, power cables, power storage links, magnetic shields, Meissner effect devices, and the like.

[Conventional technology and its problems]

As is known recently, Y-Ba-Cu-0 system, B15r-C
a-CL! -Oxide superconductors such as ○ series and Tl-Ba-CaCu- ○ series were discovered. This oxidized Th superconductor is
The critical temperature at which superconductivity occurs with inexpensive cooling media such as liquid nitrogen (
As it is a substance with high Tc), research on its practical application is progressing in various fields.

The above-mentioned oxide superconductor has a layered perovskite crystal structure, so it has strong crystal anisotropy, and current flows easily in the a-b plane containing Cu-○ atoms. This is a necessary requirement to obtain a high critical current density (J,), and since grain boundaries become a hindrance to current flow, it is important to reduce grain boundaries in the direction of current flow.

By the way, these oxide superconductors cannot be processed like metals because they are slow, and in order to make them into oxide superconductors in a predetermined shape, it is necessary to use raw materials that can be made into oxide superconductors, for example. A method is used in which Ag pipes are filled and stretched into a predetermined shape, and then subjected to a predetermined heat treatment to cause a solid phase reaction to occur in an oxide superconductor.

However, the oxide superconductor obtained in this way has a polycrystalline structure with random crystal orientation, and because the grain boundaries are in a weakly bonded state, the current carrying resistance at the grain boundaries is large.
Therefore, there was a problem that a high J value could not be obtained.

In addition, a method has been proposed in which a highly oriented oxide superconductor is formed on a substrate using a vapor phase growth method such as PVD or CVD. It is necessary to strictly control the conditions for manufacturing by epitaxial growth on the film, and the productivity is poor, such as requiring a long heat treatment after film formation.

[Means and effects for solving the problem] The present invention was made as a result of intensive research in view of the above situation, and its purpose is to provide a method for efficiently manufacturing an oxide superconducting conductor with excellent superconducting properties. Our goal is to provide the following.

That is, in the present invention, the raw material powder of an oxide superconductor is pre-sintered in an atmosphere with a low oxygen partial pressure, and then the pre-sintered powder prepared by pulverization and classification is filled into a metal tube, and then this is stretched. The inner pre-sintered powder layer is made into an elongated material with a thickness of 0.001-1.0 nm, and then the elongated material is heated to a temperature higher than that at which the pre-sintered powder layer partially melts. A first heat treatment step of heating at a temperature T and then cooling at a rate of 0.01 to 100 °C/min, and a second heat treatment step of heating at a temperature T2 that is 20 to 150 °C lower than the temperature T1 in an oxygen-containing atmosphere. It is characterized by sequentially performing heat treatment steps.

The calcined powder used in the method of the present invention includes, for example, oxides, carbonates, etc. of alkali metals, rare earth elements, and copper.
A predetermined amount of raw materials for oxide superconductors such as sulfates, nitrates, sulfides, halides, alkoxides, or their respective elements or alloys are mixed and heated to 10'' to 200 Torr.
It is a pulverized and classified substance obtained by heating to 500 to 1000°C in an atmosphere with an oxygen partial pressure of be.

In the method of the present invention, the metal tube filled with the pre-sintered powder and the core material placed in the metal tube are made of metal that is non-reactive with the oxide superconductor and has excellent electrical and thermal conductivity. For example, Ag, Ag-Pd, Ag
-AuSAg-Cu.

Ag-Mg, Ag-Pt, Ag-1rSAuSAu-
Ni, Au-Cu, Au-Ag-Cu, Au-Pd-A
g5Au-1r, PC, Pt-1r.

PC-PdSPd, Pd-Ni, , Pd-Co, , Ni
-Cr, Ni-Cr-Co, Ni-Fe, Ni-F
Those made of materials such as e-Co and Fe-Cr5Fe-Ni-Cr (SUS) are suitable.

As a method for stretching the metal tube filled with the calcined powder, any stretching method such as rolling, extrusion, pressing, groove roll rolling, swaging, and drawing can be applied.

In the method of the present invention, the pre-sintered powder layer as the inner layer of the drawn material is crystallized with C-axis orientation in the first heat treatment step, and the heating temperature T1 is, for example, Bi-based. Approximately 880 to 920 in the case of oxidized proboscis superlight conductor
℃ or higher, which is a temperature at which at least a portion of the above-mentioned pre-fired powder layer melts.

In the method of the present invention, it is preferable to determine the heating temperature T by conducting thermal analysis and actually measuring the melting temperature for each condition such as composition, and the cooling rate from temperature T1 is 100%.
If the temperature exceeds 0.01°C/min, crystallization will be impaired;
(If the speed is lower than :/win, phase separation and coarsening of crystal grains will occur, so it is necessary to set the speed to 0.01 to 1 OO'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 the properties such as j6 are further improved.

The reason why the heating temperature T2 in the second heat treatment step is limited to a temperature 20 to 50 degrees Celsius lower than the heating temperature T in the first heat treatment step is that when the temperature T2 is less than 20 degrees Celsius lower than the temperature T, This is because the crystal structure is not adjusted and oxygen is not sufficiently supplied at low temperatures exceeding 150'C. It is particularly preferable that the temperature T2 is 20 to 100° C. lower than the temperature T.

In the method of the present invention, the reason why the thickness of the pre-sintered powder layer of the drawn material is limited to 0.001 to 1.0-1.
If it is less than m1, it is not possible to obtain a large current capacity, and slight fluctuations in the density distribution of the pre-fired powder layer may cause wire breakage or performance deterioration during stretching.
Also 1. This is because if the OM is exceeded, the C-axis orientation of the crystal and the crystal growth in the elongated direction will not be sufficiently achieved in the first heat treatment step.

In the method of the present invention, the raw material to be filled into the metal tube is limited to pre-sintered powder that has been pre-sintered in a low-oxygen atmosphere, pulverized and classified, because the pre-sintered powder prepared by this method is in an oxygen-deficient state. As a result, the melting point of the calcined powder decreases, allowing the application of metals with relatively low melting points such as Ag to metal tubes. This is because superconductors have advantages such as the formation of a single phase with high T in an oxygen-deficient state.

In the method of the present invention, it is possible to widen the range of applications by selecting the material of the metal tube for coating.
In addition, when a material with high thermal and electrical conductivity such as Ag is used, it can also act as a stabilizing material against the quench phenomenon. It also has the effect of protecting the oxide superconductor layer from the field.

Furthermore, flexibility can be obtained by processing a material with high toughness into a thin layer, so it can be applied to fields that require bending, such as coils and magnets.

Furthermore, since oxide superconductors become brittle when subjected to heat treatment, it is also useful to shape the bottom of the coil, magnet, etc. in advance and then heat treat it.

〔Example〕

The present invention will be explained in detail below using examples.

BjzO*, Sr○, Cab, CuO@B i :Sr
:Ca:Cu is mixed in an atomic ratio of 2:2:1:2, and the final powder is heated to an oxygen partial pressure of 1.2X.
Temporarily baked at 850°C for 3 hours in an atmosphere of 10-' Torr,
This pre-fired body is pulverized and classified to produce BizSr with an average particle size of 8-
A calcined powder of zCaCux○ was prepared.

The above pre-sintered powder is filled into an Ag tube, which is rolled and wire-drawn to form rectangular elongated materials of various thicknesses, which are then exposed to the liquid phase of the above-mentioned pre-sintered powder in the atmosphere. The temperature T is maintained near the linear temperature for 30 minutes, and then the temperature T is increased from the above temperature at a predetermined speed.

After cooling to temperature T2 and maintaining it for 30 hours, it was cooled to room temperature to form an oxide superconducting conductor. In the above, the temperatures T1 and T2 and the cooling rate from T1 to T2 were varied.

For each oxide superconductor obtained in this way, Tc and Jc were measured. eJc was measured using liquid nitrogen (77K
), measurements were made using the four-probe method with and without a magnetic field applied. The results are shown in Table 1 along with the thickness of the oxide superconductor layer, that is, the inner layer thickness of the drawn material.

As is clear from Table 1, the method products (1 to 7) of the present invention are:
Both Tc and Jc showed high values. In particular, even when a magnetic field was applied, the JC maintained a high value and had excellent magnetic field resistance characteristics.

On the other hand, in the comparison method product No. 8.9, the thickness of the pre-sintered powder layer of the elongated material was outside the limit value of the present invention, and the former was too thick, so the C-axis orientation and current direction were changed. The crystal growth of J was not sufficiently achieved, resulting in a low value of J. In addition, since the latter was subjected to strong processing until it became thin, the density of the pre-fired powder layer became non-uniform, resulting in wire drawing interruption lines. Also, in No. 10, the heating temperature T+ in the first heat treatment step was too low and the pre-fired powder did not melt, and in No. 11.12, the heating temperature T+ in the second heat treatment step was too low. Since it was outside the limit value of the present invention, it was also N.

In No. 13, the cooling rate from the heating temperature T1 to Tt was too fast, so the C-axis orientation of the crystal and/or the crystal growth in the direction of current flow were not sufficiently achieved in all cases, resulting in low values of T9 and J. Ta.

〔effect〕

As described above, according to the method of the present invention, it is possible to efficiently produce oxide superconducting conductors having excellent superconducting properties such as jo, and therefore it has a significant industrial effect.

Claims (1)

[Claims] After pre-sintering the raw material powder for oxide superconductor in an atmosphere with low oxygen partial pressure, the pre-sintered powder is pulverized and classified, and the prepared pre-sintered powder is filled into a metal tube. The fired powder layer is made into an elongated material with a thickness of 0.001 to 1.0 mm, and then this elongated material is heated at a temperature T_1 higher than the temperature at which the pre-sintered powder layer partially melts. After that, a first heat treatment step of cooling at a rate of 0.01 to 100 °C/min, and a second heat treatment step of heating at a temperature T_2 that is 20 to 150 °C lower than the temperature T_1 in an oxygen-containing atmosphere are sequentially performed. A method for producing an oxide superconducting conductor, characterized by: