JPH03163714A - Manufacture of oxide superconductive conductor - Google Patents

Abstract

PURPOSE:To manufacture efficiently an oxide superconductive conductor excellent in superconductivity by applying a second heat treatment process to a crystallized oxide superconductive conductor layer. CONSTITUTION:After a metal tube 1 filled with tentatively baked powder is given elongation processing, this elongated material is heated at a temperature T1 above the temperature, where a tentatively baked powder layer is partly melted, followed by being cooled at a speed 0.01 to 100 deg.C/min. The elongated material is crystallized by this first heat treatment process being C-axially oriented. A heating temperature T2 in a second heat treatment process is made 20 to 150 deg.C lower than heat treatment temperature T1 in the first heat treatment process. It is because, when the temperature T2 is lower than T1 by less than 20 deg.C, adjustment of crystal structure is not effected, and when T2 is lower than T1 by more than 150 deg.C, oxygen is not sufficiently performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing oxide superconducting conductors used in magnet wires, power cables, power storage links, magnetic shields, Meissner effect devices, etc. [Prior art and its problems] As is well known recently, Y-Ba-Cu-0 system, BiSr-C
Oxide superconductors such as a-Cu-0 series and Tj2-Ba-Ca-Cu-0 series were discovered. This oxide superconductor is a material with a high critical temperature (T,) that becomes superconducting when an inexpensive cooling medium such as liquid nitrogen is used, so research into practical application is progressing in various fields. The above 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-0 atoms. High critical current density (Jc
), and since grain boundaries pose an obstacle to current flow, it is important to reduce the grain boundaries in the direction of current flow.

By the way, these oxide superconductors cannot be processed like metals because they are brittle, and in order to make them into oxide superconductors of a predetermined shape, for example, the raw material that can be made into oxide superconductors must be Ag. A method is used in which the material is filled into a manufactured pipe, etc., stretched into a predetermined shape, and then subjected to a predetermined heat treatment to cause a solid phase reaction to occur in the oxide superconductor.
However, the oxide superconductor obtained in this way is composed of polycrystals with random crystal orientation, and
Since the grain boundaries are in a weakly bonded state, the current carrying resistance at the grain boundaries is large, and therefore a high Jc value cannot be obtained. In addition, a method has been proposed in which an oxide superconductor with high conformity is formed on a substrate using a vapor phase method such as a PVD method or a CVD method. It is necessary to strictly control the conditions for manufacturing by using rs. IIl
Productivity was poor, as it required a long heat treatment afterwards. [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. The goal is to provide the following. That is, in the present invention, raw material powder for an oxide superconductor is pre-sintered in an atmosphere with a low oxygen partial pressure, and then the pre-sintered powder prepared by pulverizing and classifying is placed in a metal tube in which a core material is placed at a predetermined position. The thickness of the pre-sintered powder layer between the inner surface of the metal tube and the core material or between the core materials is 0.001 to 1.
．． 0 m, and then the elongated material is heated to a temperature T higher than the temperature at which the pre-sintered powder layer partially melts. A first heat treatment step of heating at a temperature and then cooling at a rate of 0.01 to 100 °C/sxn, and a second heat treatment of heating at a temperature T2 that is 20 to 150 °C lower than the above temperature T in an oxygen-containing atmosphere. It is characterized by performing the steps sequentially. The pre-calcined powder used in the method of the present invention includes, for example, oxides, carbonates, etc. of alkaline earth metals, rare earth elements, and copper.
A predetermined amount of raw material powder for oxide superconductors such as sulfates, nitrates, sulfides, halides, alkoxides, or individual elements or alloys of each element is mixed, and 10'' to 200 To
It is a pulverized and classified material 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. are used, for example Ag, Ag-PdSAg
-AuSAg-Cu,Ag-MgSAg-PL,Ag-
1r, Au, Au-Ni, Au-Cu, Au-Ag-C
u, Au-Pd-Ag, Au-1 r, Pt, Pt-1
r, Pt-Pd, Pd%Pd-Ni, Pd-Co, N
i-Cr, Ni-Cr-Co, Ni-Fe, Ni-Fe
-CoSFe-Cr, Fe-Ni-Cr (SUS) and other materials are suitable. In the above, the metal tube and the core material may be made of different materials, but it is preferable to use the same material because it is easier to process. In the method of the present invention, the shape and structure of the metal tube and core material are such that the thickness of each part of the pre-sintered powder layer after stretching is 0.00.
There is no particular limitation as long as it falls within the range of 1 to 1.0 m, and any shape such as round, oval, or square can be used. The structure of the oxide superconducting conductor manufactured by the method of the present invention will be explained below with reference to the cross-sectional views shown in FIGS. 1 to 4. That is, the oxide superconducting conductor of the present invention shown in FIG. 1 has a cylindrical core material 2 placed at the center of a metal tube 1 with a circular cross section, and the conductor shown in FIG. 2 has a circular cross section. The conductor shown in Fig. 3 has a rectangular cross section, and has two cylindrical core members 3 with different diameters and one cylindrical core member 2 arranged concentrically in a metal tube 1. One rectangular cylindrical core material 5 and 1 is placed inside the metal tube 4 of the mold.
In order to obtain a high IC value, the conductor shown in FIG. The core materials 2 are arranged at predetermined intervals, and the gap between each metal tube and the core material is filled with pre-sintered powder 7 to make it a large conductor. Any stretching method such as rolling, extrusion, pressing, groove roll rolling, swaging, or drawing can be applied to the method of stretching the metal tube filled with the calcined powder. 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 T is, for example, Bt In the case of oxide superconductors, approximately 880 to 920
℃ or higher, which is the temperature at which at least a portion of the above-mentioned pre-fired powder layer melts. Therefore, it is desirable to determine the heating temperature T1 by conducting a thermal analysis and actually measuring the melting temperature for each set of conditions. In the method of the present invention, the temperature T. The cooling rate from
℃/■in will impair crystallization; 0
At a low speed of less than 1"C/sin, phase separation and coarsening of crystal grains occur, so it is necessary to set the speed to 0.01 to 100°C/sin. In the method of the present invention, the above-mentioned crystallized oxide superconductor layer By applying the second heat treatment step to the crystal structure, the crystal structure is adjusted and oxygen is supplied, and the properties such as Jc are further improved. The reason for limiting the temperature to 20 to 150°C lower than the heating temperature T in the process is that if temperature T2 is less than 20°C lower than temperature T1, the crystal structure will not be adjusted;
This is because oxygen supply is not sufficient at low temperatures exceeding . It is particularly preferable that the temperature T2 is 20 to 100°C lower than the temperature T1. In the method of the present invention, the thickness of the pre-sintered powder layer between the inner surface of the metal tube of the drawn material and the core material or between the core materials is set to 0.001 to 1.
．． The reason why it is limited to 0- is that if it is less than 0.001 W, slight fluctuations in the density distribution of the pre-fired powder layer may cause wire breakage during stretching or deteriorate the performance. This is because if it exceeds 0 ms, the C-axis orientation of the crystal and the crystal length in the longitudinal direction cannot 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 the advantage of having a single phase with a high Tc in an oxygen-deficient state. In the method of the present invention, it is possible to widen the range of applications by selecting the materials and shapes of the metal tube for coating and the core material. When a material with high thermal and electrical conductivity such as Ag is used, it can also act as a stabilizing material against the quenching phenomenon, and the metal tube also prevents external HtO
It also has the effect of protecting the oxide superconductor layer from harmful gases such as C and C O t and external magnetic fields. In addition, flexibility can be obtained by processing a material with high toughness into a thin or thin shape, so it can be applied to fields that require bending, such as coils and magnets. Also, since oxide superconductors become brittle when heat treated, it is also useful to form them into coils, magnets, etc. in advance and then heat treat them. Furthermore, by using a large number of thin, narrow-shaped materials for the core material and increasing the area occupied by the oxide superconductor layer, a conductor with a large current capacity can be obtained. [Example] The present invention will be explained in detail below using Examples. Biz
os, SrO%Cab%CuO:Bi:Sr:Ca:
Cu is mixed in an atomic ratio of 2:2:1:2, and the mixed powder is heated to an oxygen partial pressure of 1. 4 X 1 0-
The calcined body was calcined at 850°C for 3 hours in an atmosphere of 'Torr, and the calcined body was crushed and classified to produce Bi. Sr. Ca
CugO. A pre-calcined powder was prepared. Then, the pre-sintered powder was filled into an Ag tube with a cylindrical Ag core placed at the center of the same structure as shown in Figure 1, and then rolled and wire-drawn to form circular cross-sections of various diameters. This is then heated in the atmosphere to a temperature T. near the liquidus temperature of the pre-sintered powder. The temperature is then maintained at T. for 30 minutes, and then the temperature is increased from the above temperature to T. After cooling to temperature Tt and maintaining it for 30 hours, it was cooled to room temperature to form an oxide superconducting conductor. In the above, temperatures T1, T
The cooling rate from 8 and T to T2 was varied. In the above, the thickness of the oxide superconductor layer was varied by changing the tube diameter while keeping the core diameter constant. Tc and Jc were measured for each of the oxide superconducting conductors thus obtained. Jc was measured using the four-terminal method in liquid nitrogen (77K) with and without a magnetic field applied. The results are shown in Table 1 along with the thickness of the oxide superconductor layer. As is clear from Table 1, the method products (1 to 7) of the present invention are:
Both T and Jc showed high values. Even when a magnetic field was applied to vF, JC maintained a high value and had excellent magnetic field resistance. In contrast, comparative method product No.
、． In No. 9, the thickness of the pre-sintered powder layer of the elongated material was outside the limit of the present invention, and in the former case, the thickness was too thick, so that the C-axis orientation and the crystal elongation in the current direction were not sufficiently achieved. Jc became a low value. In addition, because the latter was subjected to strong processing to the point of thinning, the density of the pre-fired powder layer became non-uniform, resulting in a decrease in J. Further, in No. 12, the heating temperature T1 in the first heat treatment step was too low and the pre-fired powder did not melt, and in No. 12, the heating temperature Tt in the second heat treatment step was outside the limit value of the present invention. Therefore, No. 3 has a heating temperature of T, to T. Because the cooling rate to
has a low value. [Effects] As described above, according to the method of the present invention, it is possible to efficiently produce an oxide superconducting conductor that has excellent superconducting properties such as Jc and is capable of transmitting large amounts of power, and therefore has a significant industrial effect.

[Brief explanation of the drawing]

1 to 4 are cross-sectional explanatory views showing examples of oxide superconducting conductors manufactured by the method of the present invention. 1.4...Metal tube, 2,3,5.6...Core material, 7
...Preliminary calcined powder.

Claims (1)

[Claims] After pre-sintering the raw material powder of the oxide superconductor in an atmosphere with low oxygen partial pressure, the pre-sintered powder prepared by crushing and classifying it is filled into a metal tube with a core material placed in a predetermined position. This is stretched so that the thickness of the pre-sintered powder layer between the inner surface of the metal tube and the core material or between the core materials is 0.001 to 1.0 mm, and then the above-mentioned pre-sintered powder layer is applied to this elongated material. The first step is heated at a temperature T_1 higher than the temperature at which the powder layer partially melts and then cooled at a rate of 0.01 to 100°C/min.
The above temperature T_1 in the heat treatment process and in an oxygen-containing atmosphere
A method for producing an oxide superconducting conductor, comprising sequentially performing a second heat treatment step of heating at a temperature T_2 that is 20 to 150°C lower.