JPH03137050A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain the oxide superconductor having high degree of orientation and excellent in superconducting characteristics such as critical current density by pressurizing oxide superconducting powder in a uniaxial direction under the pressure in a specified range. CONSTITUTION:Oxide superconducting powder is pressurized in a uniaxial direction under the pressure in the range of >=2 to <7 ton/cm<2>. The pressurizing time is preferably regulated to about 1 to 10 min. By the pressure compacting, a (c)-axis in the crystals of a green compact (an oxide superconductor) is oriented along the pressurizing direction, and an (a)-axis and a (b)-axis in the crystals of the oxide superconductor are oriented in the direction orthogonal to the pressurizing direction. The oxide superconductor after subjected to the pressure compacting is preferably subjected to heat treatment as well to arrange the crystalline structure. For example, the method of heating at about 600 to 1,000 deg.C for several hr to several tens hr and executing slow cooling is adopted.

Description

Detailed Description of the Invention "Industrial Application Field J The present invention is applicable to superconducting generators, superconducting power transmission, magnetic levitation transport,
This invention relates to a method for manufacturing oxide superconductors that are applied to magnetic shields, energy storage, superconducting magnets, particle accelerators, etc.

"Conventional technology" In recent years, the critical temperature (
Various oxide-based superconductors exhibiting extremely high values of Tc) are being discovered.

By the way, when a conductor for current transport is made using such oxide superconductor powder, the critical current density is significantly reduced due to the anisotropy of the crystal structure, which is a unique characteristic of this oxide superconductor material. There is a problem that the value decreases. In other words, in the crystal structure of an oxide superconductor, the a-axis,
The critical current value in the b-axis direction is more than an order of magnitude larger than the critical current value in the c-axis direction, and therefore an oxide superconductor in which the axial directions in the crystal structure are randomly arranged has a sufficiently high critical current density. It cannot be obtained.

Therefore, in order to obtain a high critical current density, it is necessary to align the orientation of the crystals (a-axis, b-axis directions), that is, to align them in the direction in which the current flows.

"Problem to be Solved by the Invention" However, in the method of producing an oxide superconductor from oxide superconductor powder, when the powder is pressed to form a green compact, the surface of the compact is Although it is predicted that superconductors will be oriented in a direction that facilitates flow, the specific conditions for this have not been elucidated, and therefore, the reality is that a sufficiently oriented superconductor has not yet been obtained.

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for producing an oxide superconductor that has a high degree of orientation and therefore has excellent superconducting properties such as critical current density.

In the method for producing oxide superconductor of the present invention, the oxide superconductor powder is prepared in an amount of 2 ton/ax" or more and 7 ton/cm
The solution to the above problem was to pressurize in a uniaxial direction with a pressure in the range below .

Hereinafter, the present invention will be explained in detail by giving an example in which the present invention is applied to a method for manufacturing a Y-B a-Cu-○-based oxide superconductor.

In order to manufacture Y-B a-Cu-0 based oxide superconductor, first, Y + B atc u307-a? ,i;
An oxide superconducting powder having a composition is prepared.

In order to manufacture this oxide superconducting powder, any conventionally known method such as a powder mixing method or a coprecipitation method may be used. Here, a method for producing an oxide superconductor powder will be described using a powder mixing method as an example. First, a plurality of types of compound powders of elements constituting the oxide superconductor are mixed and mixed to produce a mixed powder. Here Y −B a
-Cu-0 system, Y compound powder (e.g. Y t
O3 powder), Ba compound powder (BaCO, powder), and Cu compound powder (Cuo powder) are mixed in predetermined amounts so as to have a composition ratio of Y + B atc 1130, and this mixed powder is The calcined powder is calcined for several hours to several tens of hours at 600 to 1000°C in the air or oxygen gas, and then the calcined powder is consolidated to form a compacted body with a
A bulk oxide superconductor is produced by heat treatment at 50°C, and an oxide superconductor powder is obtained by pulverizing this oxide superconductor. Note that the oxide superconducting powder may be produced by directly heat-treating the calcined powder without compacting it.

Further, since the oxide superconducting powder produced as described above contains impurity powder or powder with poor superconducting properties, it is preferable to remove these powders and use only powder with high purity. To remove impurity powder, the oxide superconducting powder may be cooled with liquid nitrogen, a magnetic force may be applied to the powder in the liquid nitrogen, and only the powder that has moved due to the Meissner effect due to the repulsion of the magnetic force may be selected. It is preferable to select only highly pure oxide superconducting powder in this way and use it in the present invention.

Next, the particle size of the oxide superconducting powder thus obtained is adjusted. The particle size of the superconducting powder is 20 to 100
It is preferable to make it about μ shoulder because it has excellent compressibility.

Next, the oxide superconducting powder with adjusted particle size is filled into a molding die to form a powder of 2 ton/ax” or more and 7 ton/cm.
Compression molding is performed by applying pressure in the uniaxial direction at a pressure in the range of less than 2 ton/cm to obtain a compact (oxide superconductor).In this case, if the compression molding pressure is less than 2 ton/cm, This is not preferable because sufficient orientation is not observed in the oxide superconductor, and if pressure is applied at a pressure of 7 ton/cm" or more, cracks may occur in the obtained oxide superconductor, which is not preferable. Pressurizing time It is said that a time of about 1 to 10 minutes is suitable, but a time of about 1 to 3 minutes is sufficient as a substantial pressurizing time to obtain good orientation.

The green compact (oxide superconductor) obtained in this way is
Since pressure was applied to the oxide superconducting powder in a uniaxial direction during pressure molding, the crystals of the oxide superconductor were aligned along the C axis (the C axis of the diagonal perovskite structure that constitutes the oxide superconductor). The a-axis or b-axis of the crystal of the oxide superconductor is oriented in a direction perpendicular to the direction of pressurization.

Note that the means for pressurizing the oxide superconducting powder is not limited to a method using a molding die as long as it can be pressurized in the -axial direction; Pressure may be applied to obtain a layered oxide superconductor oriented on a metal substrate. in this case,
An organic binder may be added to the oxide superconducting powder in order to prevent the powder from spilling off the metal substrate.

Alternatively, a layered oxide superconductor may be formed on the metal substrate by placing oxide superconducting powder on the metal substrate and applying pressure little by little at regular intervals using a compressive stress applying device equipped with a compression die. good. Furthermore, instead of the compressive stress applying device described above, the oxide superconducting powder may be passed through a rolling roll to pressurize and compact the oxide superconducting powder.

Further, it is preferable to further heat-treat the green compact (oxide superconductor) after pressure molding to improve the crystal structure. Here, as the heat treatment, a method of heating at a temperature of, for example, about 600 to 1000° C. for several hours to several tens of hours and then gradually cooling is adopted.

In such a method for producing an oxide superconductor, the amount of oxide superconducting powder is 2 ton/c1 or more and 7 ton/cz'
Since the pressure was applied in the uniaxial direction at a pressure in the range below, the crystals can be sufficiently distributed, and thus have good superconducting properties.

In addition, in the above example, Y-B a-Cu-0
An example was shown in which the method of the present invention was applied to a B i-3r-Ca-Cu-0 series oxide superconductor.
It may be applied to a manufacturing method of general oxide superconductors such as T iB a-Ca-Cu-0 type.

"Operation" According to the method for producing a superconductor of the present invention, the oxide superconducting powder is used in an amount of 2 ton/cm" or more 7 ton/ctn'
Since the pressure is applied in a uniaxial direction at a pressure in a range of less than 100 mL, it is possible to obtain an oxide superconductor with good orientation in which the crystal axes are oriented in the direction of application or in a direction perpendicular thereto.

"Example" An oxide superconducting powder having a composition of Y, Ba2CLI307-a was prepared, and its particle size was adjusted to a particle size of 25 to 75 μm.

Next, a predetermined amount of the oxide superconducting powder after particle size adjustment was put into a molding tie, and compression molded for 3 minutes at each pressure of 1 to 7 ton/cx2. A υ-defective oxide superconductor was obtained.

The surface of the oxide superconductor thus obtained was irradiated with X-rays to determine the degree of crystal orientation, and the results are shown in FIG.

FIG. 1 is a diagram showing the peaks of diffraction intensity obtained by X-ray diffraction, and the peaks shown on the upper side of FIG. The peak shown at the bottom shows the diffraction intensity of the superconducting powder before pressurization.

From the results shown in FIG. 1, it was confirmed that the superconductor according to the present invention exhibited high diffraction intensity and was therefore well oriented.

Further, FIG. 2 shows the relationship between applied pressure and degree of orientation.

From Fig. 2, it was confirmed that the materials pressurized at a pressure in the range of 2 to 6 ton/cx'' were well oriented.Also, the materials pressurized at less than 2 ton/ax'' were oriented well. It was found that sufficient orientation could not be obtained.

Furthermore, when the pressure was applied to 7 ton/ax" or higher, cracks occurred in the obtained oxide superconductor.

"Effects of the Invention" As explained above, the method for producing an oxide superconductor of the present invention is characterized in that the oxide superconducting powder is
Since the pressure is applied in a uniaxial direction at a pressure in the range of less than 100 ton/am, the crystals become sufficiently oriented by the pressurization, and therefore an oxide superconductor having good superconducting properties can be produced.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the X-ray diffraction peak of the oxide superconductor obtained by the present invention, and FIG. 2 is a graph showing the applied pressure and the degree of orientation of the oxide superconductor.

Claims (1)

[Claims] Oxide superconducting powder, 2ton/cm^2 or more 7ton
A method for producing an oxide superconductor, characterized by applying pressure in a uniaxial direction at a pressure in a range of less than n/cm^2.