JPH04342911A - Manufacture of tape-like ceramic superconductive conductor - Google Patents

Abstract

PURPOSE:To provide a ceramic superconductive conductor excellent in a superconductive characteristics such as Jc and the like. CONSTITUTION:Upon the degressive forming of a tape-like composite wire rod 3, in which raw materials to be formed into a ceramic superconductive conductor is covered with a metallic material, is performed by an uniaxial depressing method such as a pressing method, a roll rolling method, etc., a degressive forming jig, such that it is formed in a convex-like shape having a predetermined curvature in the width direction, is used as at least one degressive forming jig, for example at the work surfaces of the pressurizing plates 1 in contact with the tape-like composite wire rod 3. Since degressive forming jigs with convex work surfaces are used, depressing forces are sufficiently exerted at the central portions at which the raw material substance layer 4 in the tape-like composite wire rod 3 is compisited, so that the resulting ceramic superconductive conductor has high density ceramic superconductive layers and excellent C-axis orientation, therefore excellent superconductive characteristics such as Jc or otherwise can be provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic superconductor having excellent superconducting properties and suitable as a conductor for magnets and cables.

0002

[Prior art and its problems] In recent years, as is well known, Y-Ba
-Cu-O system, Bi-Sr-Ca-Cu-O system, Tl-
Ceramic superconductors such as Ba-Ca-Cu-O system were discovered. Since this ceramic superconductor is a material with a high critical temperature (Tc) that becomes superconducting when an inexpensive cooling medium such as liquid nitrogen is used, research for practical use is actively progressing in various fields. By the way, these ceramic superconductors cannot be processed like metals because they are brittle, and in order to make them into ceramic superconductors of a predetermined shape, for example, the raw material that can be made into ceramic superconductors must be made of Ag. A method is applied in which the material is filled into a pipe or the like to form a composite billet, which is then processed to reduce its area to form a composite wire, and then this composite wire is subjected to a prescribed heat treatment to cause the raw material to react with the ceramic superconductor. ing. However, the ceramic superconductor manufactured in this manner has a problem in that high superconducting properties cannot be obtained even if the ceramic superconductor is in the form of a thin tape with a thickness of several hundred micrometers.

0003

[Means for Solving the Problems] The present invention has conducted extensive research in view of the above circumstances, and has found that the cause of the problem is that when reducing the area of a tape-shaped composite wire, the press plate of the processing jig, the rolling roll, etc. The ends of the composite wire are bent and come into contact with each other, so that the central portion of the composite wire where the raw materials are composited is not sufficiently rolled down;
As a result, it was discovered that the density and C-axis orientation of the ceramic superconductor layer produced by reaction are reduced by heat treatment, and after further research, the present invention was completed. That is, the present invention provides a method for manufacturing a tape-shaped ceramic superconductor, in which a tape-shaped composite wire in which a raw material that can be made into a ceramic superconductor is coated with a metal material is subjected to a desired number of steps of surface reduction processing and heat treatment. The area-reducing process of the composite wire rod is performed by forming the processed surface of at least one area-reducing jig in contact with the tape-shaped composite wire rod into a convex shape with a predetermined curvature in the width direction, so that the raw material of the tape-shaped composite wire rod is This is a method for manufacturing a tape-shaped ceramic superconductor, characterized in that it is carried out by a uniaxial rolling method in which a rolling force is applied to the composite central portion. In the method of the present invention, when reducing the area of a tape-shaped composite wire whose raw material layer is coated with a metal material by a uniaxial reduction method such as a press method or a roll roll method, the method uses a press plate in the press method or a roll roll in the rolling method. The processing surface that comes into contact with the tape-shaped composite wire is formed into a convex shape with a predetermined curvature, so that the central portion where the raw materials of the tape-shaped composite wire are composited is sufficiently rolled down. That is. In the above, the curvature R when forming the machining surface of the machining jig into a convex shape is:
20 to 200 when the width of the tape-shaped composite wire is 2 to 3 mm
It is preferable that the curvature R is approximately mm, and the wider the width, the larger the curvature R is.

Next, a method for reducing the area of a tape-shaped composite wire will be specifically explained with reference to the drawings. FIG. 1 is a perspective explanatory view showing an example of an aspect of surface reduction processing using a press method. The processed surface of the upper pressing plate 1 of the upper and lower pressing plates 1 and 2 is formed into a convex shape with a predetermined curvature in the width direction. According to this press machine, the upper and lower pressing plates 1 and 2 do not come into contact with each other at their ends, and the tape-shaped composite wire 3 is pressed so that the center portion thereof hits the top of the convex pressing plate 1. As a result, the raw material layer 4 is sufficiently reduced. In addition, in this pressing method, by continuously feeding the tape-shaped composite wire 3 while sequentially wrapping it between the press plates 1 and 2, it is possible to reduce the area of a long material having a uniform thickness. Figure 2 A and B are
FIG. 2 is a longitudinal and cross-sectional explanatory view showing an example of an aspect of area reduction processing by a rolling method, respectively. The processed surface of the lower roll 6 of the two upper and lower rolls 5, 6 is formed into a convex shape with a predetermined curvature in the width direction.
By rolling so that the top of the convex rolling roll 6 hits the center of the tape-shaped composite wire 3 without contacting each other at the ends, the raw material layer 4 is sufficiently rolled down. The case where one of the processed surfaces of the pair of upper and lower press plates or rolling rolls is formed in a convex shape has been described above, but it is also possible to use one in which both the upper and lower surfaces are formed in a convex shape. In the method of the present invention, the characteristics of the obtained ceramic superconductor are improved by performing the steps of area reduction and heat treatment two or more times, and by performing the heat treatment at a temperature that is high enough to sinter the raw material. It is preferable. The heat treatment in the final step is performed in an oxygen-containing atmosphere to sinter the raw material and react the raw material to the ceramic superconductor, and the heating temperature is 800°C to 800°C in the case of Bi-based superconductors.
This is done at a high temperature of 70°C.

In the method of the present invention, the tape-shaped composite wire can be produced, for example, by filling a metal pipe with a raw material that can be made into a ceramic superconductor, and then stretching the material. In addition to the above-mentioned Bi-based, Y-based, etc. ceramic superconductors themselves, the raw materials that can be used as the ceramic superconductor include ceramics from mixtures of compounds such as oxides and carbonates containing constituent elements of the ceramic superconductors. Intermediates before being synthesized into superconductors, such as compounds of the constituent elements of ceramic superconductors or alloys of the above constituent elements, can be used, and these precursors can be converted into ceramic superconductors by heat treatment in an oxygen-containing atmosphere. It is something that reacts. Further, as the material of the metal pipe for filling the raw material, any metal material having high thermal and electrical conductivity can be used, but Ag and Ag alloys are particularly preferable because they have excellent oxygen permeability. Further, the method of filling the raw material into the metal pipe includes tapping the powdered raw material as it is, or molding the raw material powder into a predetermined shape by a hydrostatic method such as CIP,
Alternatively, a method such as sintering and filling this molded body may be used. Further, the metal molded body used for forming a composite wire, for example, a metal pipe, may have any shape such as circular or square cross section, and the number of holes may be plural. In addition, in order to stretch the composite billet obtained by filling the raw material into the perforations of the metal molded body into a tape-shaped composite wire,
Hot extrusion, swaging, rolling, drawing, HIP, C
Any processing method such as IP may be applied.

[0006]

[Operation] In the method of the present invention, a tape-shaped composite wire made of a raw material that can be made into a ceramic superconductor and coated with a metal material is subjected to a desired number of steps of area reduction and heat treatment. The area-reducing process of the tape-shaped composite wire is carried out by forming the processed surface of at least one area-reducing jig that contacts the tape-shaped composite wire into a convex shape with a predetermined curvature in the width direction, thereby reducing the area of the raw material of the tape-shaped composite wire. Since the process was carried out using a uniaxial rolling method in which a rolling force is applied to the central part where the substances are composited, the ceramic superconductor produced by heat-treating the obtained tape-shaped composite wire in an oxygen-containing atmosphere is a ceramic superconductor. The superconductor layer has a high density and is C-axis oriented, and has high superconducting properties.

[0007]

[Examples] The present invention will be explained in detail below using examples. Example 1 Bi2 O3, PbO, SrCO3, CaCO3
, CuO powder is mixed so that the atomic ratio of Bi:Pb:Sr:Ca:Cu is 1.8:0.4:2:2:3, and the resulting mixed powder is exposed to the atmosphere. Inside 800℃ x 5
Calcinate for 0 hours, and crush this calcined body to an average particle size of 5μ.
m of calcined powder, and then this calcined powder with an outer diameter of 25 mm.
Filled in an Ag pipe with mmφ and inner diameter of 15mmφ,
A composite billet was produced. Next, this composite billet was swaged to form a composite material having a diameter of 3 mm, which was then rolled to form a tape-shaped composite wire material having a width of 5 mm and a thickness of 0.5 mm. Next, this composite wire was cut into a length of 100 mm, which was pressed with two upper and lower press plates to form a reduced-area material with a thickness of 0.2 mm and a length of approximately 250 mm, and then heated at 830°C in the atmosphere. A tape-shaped ceramic superconductor was produced by heat treatment for 100 hours. Incidentally, of the above-mentioned two upper and lower pressing plates, the upper pressing plate had a processed surface formed into a convex shape with various curvatures. In addition, the lower pressing plate used had a flat processed surface.

Example 2 The same 3 mmφ composite material used in Example 1 was rolled into a tape-shaped composite wire with a width of 5 mm and a thickness of 0.8 mm, and this was heated in the atmosphere at 830°C for 50 hours. After the heat treatment, the obtained composite wire was cut into a length of 100 mm, and subjected to area reduction processing and heat treatment in the same manner as in Example 1 to produce a tape-shaped ceramic superconductor. Example 3 Width 5 mm and thickness 0.8 m manufactured in the same manner as Example 2
After heating a tape-shaped composite wire rod of 830° C. for 50 hours in the air, it was further rolled to a thickness of 0.5 mm, and then heated again in the air at 830° C. for 50 hours.
After heat treatment for 0 hours, the obtained tape-shaped composite wire was cut into a length of 100 mm, and subjected to area reduction processing and heat treatment in the same manner as in Example 2 to produce a tape-shaped ceramic superconductor. Example 4 Produced in the same manner as Example 3, heated at 830°C x 5 in the atmosphere.
After 0 hours of heat treatment, a tape-shaped composite wire with a thickness of 0.5 mm and a length of 1 m was sequentially wrapped between the two upper and lower pressing plates used in Example 3 while being continuously fed and pressed. A long tape-shaped ceramic superconductor having a thickness of 0.2 mm and a length of 2.5 m was manufactured.

Example 5 A tape-shaped composite wire material with a thickness of 0.5 mm and a width of about 5 mm, produced in the same manner as in Example 1, was subjected to area reduction processing by roll rolling to obtain an area reduction processed material with a thickness of 0.2 mm. A ceramic superconductor was manufactured by the same method as in Example 1, except for the following. The rolling rolls had an outer diameter of 200 mm, the rolling speed was 5 m/min, and the lower rolling rolls had various curvatures in the width direction on their processed surfaces. Note that the processed surface of the upper rolling roll was left flat. Example 6 The tape-shaped composite wire with a thickness of 0.8 mm produced in Example 2 was heat-treated in the atmosphere at 830°C for 50 hours, and then the tape-shaped composite wire was subjected to area reduction processing by the same method as in Example 5. A tape-shaped ceramic superconductor was produced by heat treatment. Example 7 The tape-shaped composite wire with a thickness of 0.5 mm produced in Example 3 was heat-treated in the atmosphere at 830°C for 50 hours, and then the tape-shaped composite wire was subjected to area reduction processing by the same method as in Example 5. A ceramic superconductor having a thickness of 0.2 mm was produced by heat treatment. Example 8 The tape-shaped composite wire with a thickness of 0.5 mm produced in Example 3 was heat-treated in the atmosphere at 830°C for 50 hours, and then the processed surfaces of both the upper and lower rolling rolls were made convex on this tape-shaped composite wire. In addition to surface reduction processing using a rolling roll formed in
A tape-shaped ceramic superconductor was manufactured in the same manner as in Example 5.

Comparative Example 1 In Examples 1 to 4, the tape-shaped composite wire material was processed into a tape shape by the same method as in Examples 1 to 4, except that the tape-shaped composite wire material was subjected to surface reduction processing using two pressing plates with flat processing surfaces. A ceramic superconductor was manufactured. Comparative Example 2 In Examples 5 to 8, tape-shaped ceramics were produced in the same manner as in Examples 5 to 8, except that the tape-shaped composite wire rod was subjected to surface reduction processing using rolling rolls with flat processing surfaces for both the upper and lower rolling rolls. A superconductor was manufactured. Jc of each tape-shaped ceramic superconductor thus obtained was measured in liquid nitrogen (77K) under zero magnetic field. The results are shown in Table 1 for Examples 1 to 4 and Comparative Example 1, and in Table 2 for Examples 5 to 8 and Comparative Example 2, together with the main manufacturing conditions.

[0011]

[Table 1]

0012

[Table 2]

As is clear from Tables 1 and 2, the products produced by the method of the present invention (NO1-17, NO25-41) had high Jc values. Above all, Jc improved as the heat treatment was performed during the area reduction process. This is thought to be because the superconductor phase generated by the heat treatment was pulverized and finely distributed in the subsequent area reduction process. Also, the curvature of the processing surface of the processing jig is 200
Up to mm, the larger the curvature, the higher the Jc, and this is because the larger the curvature, the more uniform the reduction of the raw material layer. Curvature is 2
The reason why it started to decrease when it exceeded 00 mm is because the machined surface became nearly flat and the effect of creating a convex surface diminished. In addition, in the case of the press method, the higher the press pressure, the higher the value of Jc in the case of the roll rolling method, in which both the upper and lower rolling rolls were provided with curvature. On the other hand, the comparative example products (NO18 to 24, NO42 to 44) all have low Jc, and this is because the pressing plate or rolling roll is curved and insufficient rolling force is not applied to the central part of the composite wire. This is because the density and C-axis orientation of the ceramic superconductor layer decreased.

[0014]

[Effects] As described above, according to the method of the present invention, a ceramic superconductor layer having a high density and excellent C-axis orientation can be obtained, and therefore a ceramic superconductor having high superconducting properties such as Jc can be obtained, and it can be used industrially. It has a remarkable effect.

[Brief explanation of drawings]

FIG. 1 is a perspective explanatory view showing an example of an embodiment of the pressing method of the surface reduction processing method in the method of the present invention.

FIG. 2 is an explanatory view in longitudinal and transverse sections showing an embodiment of the rolling method of the area reduction method in the method of the present invention.

[Explanation of symbols]

1, 2 Press plate 3 Tape-shaped composite wire 4 Raw material layer 5,6 Rolling roll

Claims (1)

[Claims] Claim 1. A method for producing a tape-shaped ceramic superconductor, in which a tape-shaped composite wire made of a metal material coated with a raw material that can be made into a ceramic superconductor is subjected to a desired number of steps of surface reduction processing and heat treatment. The area-reducing process of the wire rod is performed by forming the processed surface of at least one area-reducing jig in contact with the tape-shaped composite wire into a convex shape with a predetermined curvature in the width direction, so that the raw material of the tape-shaped composite wire is composite. A method for manufacturing a tape-shaped ceramic superconductor, characterized in that the process is carried out by a uniaxial rolling method in which a rolling force is applied to the rolled central portion.