JPH0451414A - Manufacture of ceramic superconductor - Google Patents

Abstract

PURPOSE:To realize a ceramic superconductor which is excellent in its superconductive characteristics even in a strong magnetic field by mixing specified quantities of powders of a raw material and a nonsuperconductive material together, for preparing the ceramic superconductor, then processing the mixed powder into a compact, and melting it while heating for solidification. 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. Then a nonsuperconductive material which is composed of Y2O3 is added thereto, and mixed together by means of an automatic mortar so as to produce mixed powder. This mixed powder is pressed into a rod-shaped compact. The rod-shaped compact is passed through an electric furnace under atmospheric conditions for zone melting, then 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.

[Conventional technology]

In recent years, Y-BaCu-○ system, B1-3r-Ca-Cu-0 system, and T1-Ba-Ca, which exhibit superconductivity at liquid nitrogen temperature, have been developed.
-Exceeds ceramics such as Cu-0 series.

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 press molding or the like, or the pre-sintered powder is mixed with Ag, Ag alloy, Cu, , fill a pipe made of a metal with excellent thermal conductivity and electrical conductivity, such as a Cu alloy, as it is, or melt it and fill it, or composite it on a metal tape to form a composite material with metal, or pre-sinter it. After kneading the powder and a binder to form a base and applying it onto a substrate, or preparing a green sheet using a doctor blade method and combining it with the substrate, The composite material is subjected to stretching processes such as rolling, swaging, bowing, extrusion, etc. to form a bulk or linear molded body of a desired shape, and then this molded body is subjected to a prescribed heat treatment and subjected to the above-mentioned pre-sintering. A method of reacting powder with ceramic superconductors has 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.For example, 1 tesla =
(T), there is a problem in that the critical current density (JC) decreases by one to two orders of magnitude compared to the case without a magnetic field.

[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, in the present invention, a powder of a raw material that can be made into a ceramic superconductor and a powder of a non-superconducting material are blended in predetermined amounts and mixed to form a mixed powder, and then this mixed powder is used as it is or by molding. It is characterized in that it is processed into a molded product of a desired shape, then heated and melted in an oxygen-containing atmosphere to solidify in one direction.

In the present invention, powder of a raw material that can be made into a ceramic superconductor is mixed with powder of a non-superconducting material that has a magnetic flux pinning effect to form a mixed powder, and the mixed powder can be used as it is or processed by molding. Ceramic superconductors are made into a desired shape, heated and melted, and unidirectionally solidified, resulting in fine distribution of non-superconducting substances in the C-axis oriented ceramic superconductor layer, which provides high superconducting properties even in high magnetic fields. This is a method for manufacturing various bodies.

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 addition, as the non-superconducting material that has a magnetic flux pinning effect, any thermally stable material that is non-reactive with the ceramic superconductor that is the matrix and does not transform into a superconductor even during the subsequent unidirectional solidification process etc. can be used. However, for Y-based superconductors, y□o-based Y 20 s and Y-Ba
-Cu-0 series Y2BaCuO5 oxide, and for Bi-based superconductors, Cu-0 series, 5r-Ca-Cu-0 series,
CaCu-0-based oxides are particularly preferred.

In the method of the present invention, methods for mixing powder of a raw material that can be made into a ceramic superconductor and powder of a non-superconducting material having a magnetic flux pinning effect to form a mixed powder include a mortar, a ball mill, a stamp mill, Any mixing grinder such as an attriter is applicable.

In addition, the mixed powder obtained as described above is directly heated and melted to form a melt, which is then molded while solidifying in one direction, or the mixed powder is kneaded with a binder to form a paste. Alternatively, green sheets can be formed using the doctor blade method, and these can be coated or composited onto a substrate, or the powder can be compressed as it is or compressed using a compression molding method such as press or CIP, etc., and placed in a metal container. This is made into a composite molded body of any shape such as a disc shape, a rod shape, a round wire, a flat wire, a polygonal shadow line, etc. by a stretching method such as rolling, swaging, drawing, or extrusion. It may be heated to a temperature higher than the melting temperature to melt and then solidify in one direction.

The materials for the above substrate or metal container include Ag, Au, and C.
u, Ir, Pd, Pt or alloys thereof, etc. are used,
Among them, Ag or Ag alloy has good oxygen permeability, so oxygen can be sufficiently supplied to the ceramic superconductor during the unidirectional solidification process, etc., and a superconductor with a high Jc can be obtained, as well as having high thermal conductivity. The obtained superconductor has excellent quench resistance and is suitable because it can increase the amount of current flow.

In the method of the present invention, a method for unidirectionally solidifying the mixed powder as it is is a heated mold continuous casting method in which the mold is heated to a high temperature and the heat of solidification is extracted only by cooling the produced ingot. , the Czochralski method, etc. are used. Further, as a method for unidirectionally solidifying a pre-molded body of mixed powder, for example, the above-mentioned molded body is heated and maintained in an electric furnace at a temperature higher than the melting start temperature of the mixed powder with a predetermined temperature gradient. A continuously moving 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
Appropriately, the moving speed of the molded body is approximately 0.1 to 10 mm/min, although it depends on the temperature gradient in the furnace.

In the unidirectional solidification step, an oxygen-containing atmosphere is created to ensure 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.

The structure of the unidirectionally solidified compact is such that the raw material undergoes a heat-melting reaction to become a C-axis oriented superconductor, and a non-superconductor material is finely distributed in the ceramic superconductor layer.

[Effect]

In the method of the present invention, a powder mixture of a powder of a raw material that can be made into a ceramic superconductor and a powder of a non-superconductor material that has a magnetic flux pinning effect is produced by unidirectional solidification from a molten state. Therefore, the resulting four ceramic superconducting bodies react with the ceramic superconductor in which the raw materials are C-axis oriented, and have a structure in which the non-superconducting material is finely distributed in the ceramic superconducting layer, and therefore, the strong magnetic field Among these, highly advanced superconducting properties are exhibited.

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

Example 1 As starting materials, powders of Y,03, BaCo3, and CuO were used, and the atomic ratio of Y:Ba:Cu was 1:2:
3 and mixed, and then this mixed powder was calcined at 900° C. for 20 hours in the air. Next, 2% of a non-superconducting substance of the composition y x O2 was added to this calcined powder.
The mixture was added and mixed using an automatic mortar to prepare a mixed powder, and then this mixed powder was press-molded into 5 x 5
A rod-shaped molded product with a diameter of 100 mm was made. Next, this rod-shaped molded body was made into a material with a total length of 30 cm and a maximum temperature of 1000°C at the center.
The inside of the electric furnace in an atmospheric atmosphere with a temperature gradient of 40°C/cm was heated to 0.
Four ceramic superconducting bodies were produced by passing through the melt at a speed of 5 m/min, zone melting, and solidifying in one direction.

Example 2 Y2B a was applied to the same pre-calcined powder as that produced in Example 1.
Add 3% of a non-superconductor substance having a CuOs composition and mix using an automatic mortar to prepare a mixed powder, press-form this mixed powder into a rod-shaped molded body of 5 x 5 x 10 mm,
Next, this rod-shaped molded body was made into a material with a total length of 30 cm and a maximum temperature of 1 at the center.
Ceramic superconducting 4
manufactured the body.

Example 3 A mixed powder was prepared by the same method as in Example 1, and this mixed powder was filled into a hollow Vilent made of Ag-Pd alloy with an outer diameter of 10 mm and an inner diameter of 8 bars, and was subjected to swaging and rolling processing. Composite tape with a thickness of 0.2 mm and a width of 3 m,
This composite tape was unidirectionally solidified by the same method as in Example 1 to produce four ceramic superconducting bodies.

Example 4 A mixed powder was prepared by the same method as in Example 2, and this mixed powder was filled into an Ag-Pd alloy billet with an outer diameter of 10 mm and an inner diameter of 8 mm, and the billet was swaged and rolled to give a thickness. A composite tape 7 with a length of 0.2 mm and a width of 3+ nm was unidirectionally solidified by the same method as in Example 2 to produce four ceramic superconducting bodies.

Example 5 Bi20i, PbO1SrCO+, Ca as starting materials
Using powders of COs, CuO, and Bj:Pb
:Sr:Ca:Cu has an atomic ratio of 3.2:0.4
:2:2;3, then this mixture is pre-sintered in the atmosphere at 800°C for 20 hours, and the pre-sintered body is crushed and classified to obtain a pre-sintered powder with a particle size of 1-. was created. Next, add (Sr, Ca)2CusO+J to this calcined powder.
A mixed powder was prepared by adding 2% of a powder of a non-superconducting material having a composition of Il and mixing in an automatic mortar.

Next, this mixed powder was filled into a hollow AgPd alloy billet with an outer diameter of 10III11 and an inner diameter of 8, which was swaged and rolled to form a composite tape with a thickness of 0.2 m and a width of 3 holes. The composite tape is passed through an electric furnace with a total length of 30 cm, a maximum temperature of 950°C at the center, and a temperature gradient of 45° (7 cm) in an atmospheric atmosphere at a speed of 0.5 mm/min to zone melt and solidify in one direction to form a ceramic superconductor. We manufactured several bodies.

Example 6 The mixed powder prepared in Example 1 was heated to 1000°C to melt it, and this melt was unidirectionally solidified by the above-mentioned heated mold continuous casting method to form a rod-shaped ceramic superconductor with a diameter of 6 mm. We manufactured several bodies.

Comparative Example 1 A ceramic superconductor was produced in the same manner as in Example 1, except that the calcined powder was directly formed into a compact without adding Y2O3 powder and unidirectionally solidified.

Comparative Example 2 A ceramic superconductor was produced in the same manner as in Example 3, except that the calcined powder was directly formed into a compact without adding Y2O3 powder and unidirectionally solidified.

Comparative example 3 In Example 5, the pre-fired powder was (Sr, Ca).

A ceramic superconductor was produced in the same manner as in Example 5, except that the compact was directly solidified without adding Cu or OX powder.

The critical current density (J) of each of the ceramic superconductors thus obtained was measured in liquid nitrogen (77K) 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 6)
shows that the effect of the magnetic field is small (J, even in the IT magnetic field, is more than 30% of the J in the absence of a magnetic field. Among them, A
Composite tape sheathed with g-alloy (No. 3.4)
Compared to the rod-shaped body (Nol, 2), JC has a higher density of 10' in the IT magnetic field due to the higher density of the inner ceramic superconductor layer.
The value was high, exceeding A/d. In addition, as for the raw materials, Bi-based (No. 5) is more I than Y-based (No. 1 to 4).
It showed a high J in a strong magnetic field of T.

Also, the temperature gradient during unidirectional solidification is smaller (N).

2.4) was richer in C-axis orientation than the larger one (Nol, 3) and had a higher value of J.

Also, mixed powder is zone-melted after molding (N.

No major difference in Jc was observed between 1) and the one obtained by directly melting the mixed powder and unidirectionally solidifying and casting it (No. 6).

When the structures of the samples Nos. 1 to 6 were observed using an electron microscope, it was confirmed that non-superconducting substances with an average particle size of 0.1-1 were uniformly dispersed in the superconductor layer. On the other hand, for the comparative method products (Nos. 7 to 9), Jc decreased significantly as the magnetic field strength increased because there was no non-superconducting material that pinned the magnetic flux, and J , it decreased to 10% or less.

Although Y-based and Bi-based ceramic superconductors have been described above, the method of the present invention exhibits similar effects on other ceramic superconductors such as Tl-based.

〔effect〕

As described above, according to the method of the present invention, it is possible to easily produce a ceramic superconductor having excellent superconducting properties even in a strong magnetic field, and it has a significant industrial effect.

Claims (1)

[Claims] Predetermined amounts of raw material powder that can be made into a ceramic superconductor and powder of a non-superconducting material are blended and mixed to form a mixed powder, and then this mixed powder is used as it is or is molded into a desired shape. 1. A method for producing a ceramic superconductor, which comprises forming a molded body, followed by heating and melting in an oxygen-containing atmosphere to solidify in one direction.