JPH0451413A - Manufacture of ceramic superconductor - Google Patents

Abstract

PURPOSE:To realize a ceramic superconductor which is excellent in superconducting characteristics even in a strong magnetic field by heating and melting raw materials for the ceramic superconductor, then rapidly cooling and solidifying the melted materials to pulverize them into powder, and processing the powder into a compact, and heating and melting the compact in an oxygen-containing atmosphere to unidirectionally solidify it. CONSTITUTION:For example, powders of Y2O3, BaCO3, and CuO are used as starting materials and mixed together, and thereafter the mixed powder is calcined in the atmosphere. This calcined powder is then put into a crucible and heated and melted by means of an electric furnace. After this melted body is rapidly cooled and solidified while sandwiched between two iron plates, it is granulated with a hammer. This granulated body is put into an automatic mortar and pulverized into powder. The pulverized powder of the rapidly cooled and solidified body is pressed into a rod-shaped compact. Then this rod-shaped compact is passed through the electric furnace under atmospheric conditions and unidirectionally solidified so that a ceramic superconductor can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a ceramic superconductor suitable as a conductor for cables, magnets, current leads, current limiters, etc.

C. Prior art] In recent years, Y-BaCu-0 system, B1-3r-Ca-Cu-0 system, and Te-Ba-Ca which exhibit superconductivity at liquid nitrogen temperature have been developed.
Ceramic superconductors such as the -Cu-0 system have been discovered, and research into practical use is progressing in various fields.

By the way, these ceramic superconductors are brittle, so in order to make them into a ceramic superconductor of a desired shape, for example, a predetermined amount of raw material powders such as oxides and carbonates containing the constituent elements of the ceramic superconductor are mixed. The mixture is mixed and heated at a predetermined temperature to form a pre-sintered powder, and this pre-sintered powder is formed into a compacted compact of a desired shape by a press molding method, or the pre-sintered powder is mixed with Ag, Ag alloy, Cu, It is filled into a metal pipe with excellent thermal conductivity and electrical conductivity, such as a Cu alloy, or composited on a metal tape to form a composite material with metal, and then the powder compact or the composite material with metal is formed. Composite material compacted,
A stretching process such as swaging, drawing, or extrusion is performed to form a bulk or linear molded body of a desired shape, and then this molded body is subjected to a prescribed heat treatment to cause the pre-fired powder to react with the ceramic superconductor. Method: After kneading the pre-calcined powder and a binder and applying this onto the substrate, or after creating a green sheet using the doctor blade method and combining it with the substrate, a prescribed heat treatment is performed.
Methods such as making ceramic superconductors react have been applied.

[Problem to be solved by the invention]

However, ceramic superconductors manufactured by such conventional methods have poor superconducting properties in a magnetic field, even if they are heat-treated under the best conditions. There was a problem in that the critical current density (Jc) decreased by one to two orders of magnitude compared to the case.

[Means to solve problems]

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 manufacturing a ceramic superconductor having excellent magnetic field characteristics.

That is, the present invention heats and melts a raw material that can be made into a ceramic superconductor, rapidly cools it to solidify it, pulverizes the rapidly cooled solidified material to form a powder, and then uses the powder as it is. Alternatively, after being processed into a molded article of a desired shape, it is heated and melted in an oxygen-containing atmosphere to solidify it in one direction.

In the present invention, a heated melt of a raw material material that can be made into a ceramic superconductor is solidified by rapid cooling, a non-superconducting heterogeneous phase is precipitated in the rapidly cooled solidified material (hereinafter abbreviated as the rapidly frozen solidified material), and then this The pulverized powder obtained by pulverizing a cold solidified body is used as it is or after being formed into a desired shape, heated and melted, and unidirectionally solidified to form a C-axis oriented ceramic superconductor layer, which is effective for pinning magnetic flux. This is a method for manufacturing a ceramic superconductor that can obtain high superconducting properties even in a high magnetic field by dispersing a non-superconductor different phase material.

In the above, the different phase substance precipitated in the rapidly solidified body is, for example, YzB a in the Y-based ceramic superconductor.
It is an oxide with the composition CuO=, and is a substance that does not undergo phase transformation into a superconductor in the subsequent unidirectional solidification process, etc., and is refined by pulverization of the rapidly solidified solid, and is finely deposited within the ceramic superconductor layer. The magnetic flux is distributed throughout the area and acts as a pinning force for the magnetic flux.

In addition to the various types of ceramic superconductors mentioned above being widely used as raw materials that can be used as the ceramic superconductor used in the method of the present invention, ceramic superconductors can also be formed by heat treatment in an oxygen-containing atmosphere. Intermediates until the reacting ceramic superconductor is synthesized, such as oxides, carbonates, etc. containing elements constituting the ceramic superconductor - A mixture obtained by blending and mixing the following raw material powders to a desired composition and pre-sintering; A coprecipitation mixture, an oxygen-deficient composite oxide, an alloy of the above-mentioned constituent elements, etc. can be used.

In the method of the present invention, an electric furnace is used for melting the raw material,
Any heating furnace such as a high frequency induction furnace or an infrared heating furnace can be used.
Further, as the crucible material in which the raw material is placed, metals or ceramics that are non-reactive with the raw material, such as Pt, Au, or alloys thereof, or MgO1YSZ (Y-stabilized Z r Oz ), are used. In addition, the melting temperature is 1300 to 15 in the case of Y type.
00°C and 1,000 to 1,300°C in the case of Bi systems, but in order to increase the cooling rate, it is preferable to raise the melting temperature to reduce the viscosity of the melt.

Methods for rapidly solidifying the above-mentioned melt include a method of injecting it onto a metal plate with good thermal conductivity, a method of squeezing it with the metal plate, a single-roll method, a twin-roll method, a centrifugal quenching method, and a gas atomization method. The amorphous metal manufacturing method can be applied as is. Further, the shape of the rapidly solidified material may be any shape such as plate, foil, powder, etc.

In the method of the present invention, the method of crushing the rapidly frozen solidified material includes crushing it into granules with a hammer, then using a mortar, ball mill, or
A method of finely pulverizing with an attritor, stamp mill, etc. is suitable.

In the method of the present invention, the powder obtained by pulverizing the rapidly solidified material may be formed into a desired shape by compression molding methods such as press or CIP, or by kneading it with a binder to form a paste or by doctor blade method. In addition to forming a green sheet by applying it onto a substrate or making it into a composite, there is also a method of filling the powder as it is or compression-molding it into a metal container, and then rolling and swaging it. A method of forming the material into a desired shape by a stretching method such as , drawing, or extrusion is used.

The materials of the above-mentioned substrate or metal container include Ag, Au,
Cu, Ir, Pd, PL, or their alloys are used, and among them, Ag or Ag alloys have good oxygen permeability, so oxygen can be sufficiently supplied to the ceramic superconductor during the unidirectional solidification process, etc. High J. In addition to being able to obtain a superconductor having a high thermal conductivity, the obtained superconductor has excellent resistance to aging and is suitable for increasing the amount of current flowing.

In the method of the present invention, the method of unidirectionally solidifying the rapidly solidified crushed powder includes heating mold continuous casting in which the mold is heated to a high temperature and the heat of solidification is extracted only by cooling the produced ingot. method, Czochralski method, etc. are used.

Further, as a method for unidirectionally solidifying the molded body of the pulverized powder, for example, the molded body is continuously moved in an electric furnace heated and maintained at a temperature equal to or higher than the melting start temperature of the pulverized powder with a predetermined temperature gradient. The zone melt method is applied.

The heating and holding temperature of the electric furnace is 95% when the compact is Y-based.
About 0 to 1100°C, 850 to 100 for Bi type
Approximately 0°C, and the moving speed of the molded body is suitably 0.1~]Om+n/min, although it depends on the temperature gradient in the furnace. Furthermore, an oxygen-containing atmosphere is created in the electric furnace so that sufficient oxygen is supplied to the superconductor. Note that the superconducting properties of the unidirectionally solidified body can be further improved by further subjecting it to heat treatment to supply oxygen to the superconductor and adjust the crystal structure.

[Effect]

The method of the present invention heats and melts a raw material that can be made into a ceramic superconductor, rapidly solidifies it to precipitate a non-superconducting heterogeneous substance in the rapidly solidified material, and then crushes this rapidly solidified material to form a powder. Since this pulverized powder is unidirectionally solidified from a molten state, the resulting four ceramic superconducting bodies consist of a structure in which a different phase substance that has a pinning effect is finely distributed in the C-axis oriented ceramic superconducting layer. This results in high superconducting properties even under high magnetic fields.

〔Example〕

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

Example 1 Using powders of Y2O3, BaCO3, and CuO as starting materials, they were blended and mixed so that the atomic ratio of Y:Ba:Cu was i:2:3, and then this mixed powder was Temporary firing was carried out at 900° C. for 20 hours in the air. Next, this calcined powder was placed in a PT crucible and heated to 1350"C in an electric furnace to melt it. This molten material was then sandwiched between two iron plates to rapidly solidify it, and then this solidified material was hammered. After crushing the mixture into granules, the mixture was placed in an automatic mortar and pulverized for 100 hours to obtain a powder with an average particle size of 3 IM.

Next, the pulverized powder of the rapidly frozen solidified material was press-molded to form a 5x5xl
OOmn rod-shaped molded body, and the total length of this rod-shaped molded body is 3
0C11, maximum temperature 1000'c, temperature gradient 40°C/
Ceramic superconductor 4 is made by passing it through an electric furnace in an atmospheric atmosphere of G at a speed of 0.5 mm/min and solidifying it in one direction.
manufactured the body.

Example 2 The same calcined powder used in Example I was placed in a PT crucible and heated to 1400°C to melt it, and then rapidly solidified by twin roll method to form a foil with a thickness of 30jrm. Next, this foil was crushed into thin pieces with a hammer, and the thin pieces were placed in an automatic mortar and crushed for 100 hours to form a powder with an average particle size of 3μ,
This rapidly cooled solidified powder was press-molded into a 5X5X100
This rod-shaped molded body was made into a rod-shaped molded body of mm in diameter, and then this rod-shaped molded body was unidirectionally solidified by the same method as in Example 1 to produce four ceramic superconducting bodies.

Example 3 The same rod-shaped molded body as that produced in Example 2 was made with a total length of 30 cm.
Four ceramic superconducting bodies were manufactured by passing through an electric furnace in an atmospheric atmosphere with a maximum temperature of 1100° C. and a temperature gradient of 45° C./cm at a speed of 0.5 m/min for unidirectional solidification.

Example 4 The same rapidly frozen solidified powder produced in Example 2 was prepared with an outer diameter of 1
A hollow billet made of Ag-Pd alloy with an inner diameter of 0 mm and an inner diameter of 8 mm is filled, and this is swaged and rolled to a thickness of 0.
．． A composite tape with a width of 2 mm and a width of 3 mm was prepared, and this composite tape was unidirectionally solidified by the same method as in Example 3 to produce a ceramic superconductor.

Example 5 The rapidly cooled solidified powder produced in Example 1 was heated to 1000°C.
This melt was unidirectionally solidified by the above-mentioned heated mold continuous casting method to produce a rod-shaped ceramic superconductor having a diameter of 6 bars.

Comparative Example 1 The same calcined powder as produced in Example 1 was press-molded as it was to form a rod-shaped compact of 5 x 5 x 100 mm, and then this rod-shaped compact was unidirectionally solidified by the same method as in Example 1. A ceramic superconductor was manufactured using this method.

Comparative Example 2 The same calcined powder as that produced in Example 1 was used as it was with an outer diameter of 1
Filled into a hollow billet made of Ag-Pd alloy with an inner diameter of 8 m and swaged and rolled to a thickness of 0.2 m.
A composite tape having a width of 3 mm and a width of 3 mm was prepared, and this composite tape was unidirectionally solidified by the same method as in Example 3 to produce a ceramic superconductor.

Comparative Example 3 The composite tape produced in Example 4 was subjected to 890'CX in the air.
A ceramic superconductor was produced by heat treatment for 20 hours.

Comparative Example 4 The composite tape produced in Comparative Example 2 was exposed to 890'CX in the atmosphere.
201 (A ceramic superconductor was produced by heat treatment.

The critical current density (J, ) of each ceramic superconductor obtained in this way was measured in liquid nitrogen (77K).
Measurements were made in magnetic fields of various strengths.

The results are shown in Table 1.

As is clear from Table 1, products manufactured using the method of the present invention (Nos. 1 to 5)
is less affected by the magnetic field, even in the IT magnetic field.
It showed Jc exceeding 03A/c+fl.

Among them, those with a faster rapid solidification rate (No. 2) are faster than those with a slower solidification rate (No. 1), and those with a smaller unidirectional solidification temperature gradient (No. 2) are higher than those with a large temperature gradient (No. Compared to 3), Jc was higher in each case, but this is because the faster the rapid solidification rate, the more foreign-phase substances that act as a pinning force for the magnetic flux are generated, and the temperature gradient during unidirectional solidification is higher. This is because the smaller the C-axis orientation, the better the C-axis orientation.

Also, the Jc value of the Ag-Pd alloy sheathed one (No. 4) was higher than that of the bare one (No. 3) because the inner ceramic superconductor layer was constrained by the sheath and had a higher density. This is because it has become Further, no large difference in Jc was observed between the molded powder obtained by zone melting (No. 1) and the case obtained by unidirectionally solidifying and casting the crushed powder (No. 5). In addition, when the structures of the samples No. 1 to 5 were observed using an electron microscope, Y
B az Cu 30. It was confirmed that a different phase of Y2B a CUO3 composition with an average particle size of 0.1 cape was uniformly dispersed in the superconductor layer of the composition.

On the other hand, in the comparison method product No. 6.7, Jc began to decrease when the magnetic field exceeded 0.1 T, and it became an extremely low value in IT. This is because the calcined powder was compacted as it was, so no foreign phase substances were present in the compact. In addition, in No. 8, different phase substances were present, but the superconductor layer was not C-axis oriented, so the Jc value was low overall.

In addition, in No. 9, there is no different phase material, and the superconductor layer is not C-axis oriented, so JC is low even under a low magnetic field, and further decreases rapidly as the magnetic field strength increases.

Although the above description has been made regarding the Y-based ceramic superconductor, the method of the present invention exhibits similar effects on other ceramic superconductors such as the Bi-based and TN-based ceramic superconductors.

[Effects] As described above, according to the method of the present invention, a ceramic superconductor having excellent superconducting properties even in a strong magnetic field can be easily produced, and it has a significant industrial effect.

Claims (1)

[Claims] A raw material that can be made into a ceramic superconductor is heated and melted, rapidly cooled and solidified, and then the rapidly cooled solidified material is pulverized into powder, and then the powder is used as it is or molded into a desired shape. A method for producing a ceramic superconductor, which comprises processing the material into a body and then heating and melting it in an oxygen-containing atmosphere to solidify it in one direction.