JPH03137051A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain the oxide superconductor having good crystalline orientational properties by subjecting oxide superconducting powder having specified grain size to pressure compacting. CONSTITUTION:In a method for manufacturing an oxide superconductor by subjecting oxide superconducting powder to pressure compacting, the pressure compacting is executed by using oxide superconducting powder having 20 to 100 mum grain size. The oxide superconducting powder is sieved by using a sieve, e.g., made of stainless to collect only the ones having 20 to 100 mum grain size. The pressure compacting is executed, e.g., by inserting the oxide superconducting powder having 20 to 100 mum grain size into a compacting die and applying about 2 to 7 ton/cm<2> pressure thereto for about several min.

Description

[Detailed Description of the Invention] "Industrial Application Fields" This invention is being developed for applications such as superconducting generators, superconducting power transmission, magnetic levitation transport, magnetic shielding, electrical energy storage, superconducting magnets, and particle accelerators. The present invention relates to a method for producing an oxide superconductor.

"Conventional technology" When creating a superconductor for transporting current using high-temperature superconducting powder, the value of the current density decreases significantly due to the anisotropy of the crystal structure, which is an inherent characteristic of this material. There is a problem with this. That is, it is known that oxide superconductors have a property of making it easy to pass current only in a specific direction of their crystal structure, and have anisotropy that makes it difficult to pass a current in a specific direction.

Therefore, when manufacturing an oxide superconducting conductor using oxide superconducting powder, in order to achieve a high critical current density, it is necessary to align the crystals in a specific direction in the direction where the current flows easily, that is, to orient the crystals. is necessary.

In order to achieve this crystal orientation, it is known that when pressure is applied to oxide superconducting powder to produce a compact, the crystals at least on the surface of the compact become oriented in a direction that facilitates the flow of current. There is.

``Problem to be solved by the invention'' However, conventionally, when molding is performed under similar pressure application conditions and temperatures, it is difficult to obtain a compacted compact with good orientation, and the superconducting properties are There was a problem that a stable powder compact could not be obtained. The reason for this is that the degree of orientation varies depending on the particle size of the powder used, and this difference in particle size is thought to be the reason why stable crystal orientation cannot be obtained.

The present invention has been made to solve the above-mentioned problems, and is therefore a method for producing an oxide superconductor with good crystal orientation by forming a green compact using powder with a particle size suitable for crystal orientation. The purpose is to provide

"Means for Solving the Problems" In order to solve the above problems, the present invention provides a method for producing an oxide superconductor by press-molding oxide superconducting powder. It is press-molded using powder.

The present invention will be described in detail below by giving an example in which the present invention is applied to a method for producing a Y-B a-Cu-0 based oxide superconductor.

To produce a Y-B a-1,u-0-based oxide superconductor, first, Y + B ay Cu30? An oxide superconducting powder having a composition of -5 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 superconducting powder will be described using a powder mixing method as an example. First, a mixed powder is produced by mixing a plurality of types of compound powders of elements constituting an oxide superconductor. Here, Y-B a-Cu-0
In the case of a system, Y compound powder (e.g. Y, 03 powder) and B
Add a specified amount of the compound powder of a (BaCOs powder) and the compound powder of Cu (Cuo) to Y IBatcus.
o Mixed to a composition ratio of 7-5, this mixed powder was heated to a composition ratio of 600 to 100 in the atmosphere or oxygen gas.
A bulk oxide superconductor is produced by calcining at 0°C for several hours to several tens of hours, then compacting the calcined powder, and heat-treating the compacted body at 800 to 950°C. Oxide superconducting powder can be obtained by grinding. Note that the oxide superconducting powder may be produced by directly heat-treating the calcined powder without compacting it. Note that 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, it is sufficient to cool the oxide superconducting powder with liquid nitrogen, apply a magnetic force to the powder in the liquid nitrogen, and select only the powder that has moved by repelling the magnetic force due to the Meissner effect. It is preferable to select only highly pure oxide superconducting powder in this way and use it in the method of the present invention.

Next, the oxide superconducting powder obtained in this way is sieved using a stainless steel sieve to obtain a 20-100μ
Only oxide superconducting powder with a particle size of m is collected. Incidentally, the powder having a particle size of 20 to 100 μm may be sorted into a finer particle size range, and the powder within that particle size range may be collected.

Next, oxide superconducting powder with a particle size of 20 to 100 μm is inserted into a molding die, and compression molding is performed by applying a pressure of about 2 to 7 L/cm' for several minutes to obtain an oxide superconductor. . Note that the means for pressure molding the oxide superconducting powder is as follows:
The method is not limited to the method using a molding die, but may also be a method in which oxide superconducting powder is placed on a metal substrate and pressure is applied from above and below to obtain a layered oxide superconductor oriented on the metal substrate.

In this case, an organic binder may be mixed with the oxide superconducting powder in order to prevent the powder from spilling.

Furthermore, we have developed a method in which oxide superconducting powder is provided on a metal base material, and this is pressurized little by little at fixed distances using a compressive stress applying device equipped with a compression die to form a layered oxide superconductor on the metal base material. May be adopted. Furthermore, the oxide superconducting powder can be pressure-molded by passing it through a rolling roll instead of using the same compressive stress applying device.

The oxide superconductor obtained as described above is 2(1-
Since it is obtained by consolidating oxide superconducting powder with a particle size of 100!1 mO, an oxide superconductor with oriented crystals can be obtained. Furthermore, since it is an oxide superconductor with good crystal orientation, it exhibits good critical temperature and critical current density.

In addition, since the oxide superconducting powder is press-molded by applying pressure in the -axis direction, the crystals of the oxide superconductor are aligned along the C-axis (composite perovskite constituting the oxide superconductor) along the pressurizing direction. The C-axis of the structure is oriented, and the a- or b-axis of the crystal of the oxide superconductor is oriented in a direction perpendicular to the direction of pressure. Therefore, the obtained oxide superconductor is straight in the direction of pressure.
The crystals are oriented so that current can easily flow in the i direction.

Note that it is preferable to heat-treat the oxide superconductor after pressure molding to adjust the crystal structure. This heat treatment
This can be carried out under conditions such as heating at a temperature of about 1,000° C. for several hours to several tens of hours and then slowly cooling.

By the way, in the above example, Y-B a-CuO
An example in which the method of the present invention is applied to the oxide superconductor of B i-3r-CaCu-0 has been described.
It goes without saying that the present invention may be applied to methods for producing general oxide superconductors such as TIB a-Ca-Cu-0 and the like.

"Effect" Since the oxide superconducting powder with a particle size of 20 to 100 μm, which is suitable for crystal orientation ζζ, is consolidated, the specific direction of the crystal axis of the oxide superconductor is oriented in the direction of application, resulting in an oxide superconductor with good orientation. You get a body.

"Example" Oxide superconducting powder having the composition Y + U3 atc U30, -δ was sieved through a plurality of stainless steel sieves to obtain various oxide superconducting powders having various particle sizes (particle size 10-120 μm).

Then, the oxide superconducting powder of each particle size was put into a plurality of molding dies according to the particle size, and compression molded for 3 minutes at a pressure of 2.8 t/cm'' to obtain an oxide superconductor.

The surface of the obtained oxide superconductor was irradiated with X-rays to examine the degree of crystal orientation.

FIG. 1 shows the peaks of diffraction intensity obtained by X-ray diffraction. The peaks shown in the lower part of Figure 1 are the peaks of non-oriented powder of oxide superconductor, but the peaks shown in the upper part of Figure 1 are the peaks of the highly oriented compact obtained after pressurization. It shows. Then, for each particle size and different molded object, the intensity of the peak obtained as above was determined as the degree of orientation.

As a result, characteristics as shown in FIG. 2 were obtained.

From Fig. 2, when the particle size of the oxide superconducting powder used for compaction is between 20 and 100 μm,
It was confirmed that the crystals of the compact were highly oriented.

"Effects of the Invention" As explained above, the present invention produces an oxide superconductor conductor by compacting oxide superconducting powder with a particle size of 20 to 100 μm, so the oxide superconductor has good crystal orientation. can be obtained. Therefore, it is possible to produce a good oxide superconductor with excellent superconducting properties such as critical current density.

[Brief explanation of the drawing]

Figure 1 is a graph showing the X-ray diffraction peaks of the compact obtained according to the present invention, and Figure 2 is a graph showing the particle size of the powder used and the orientation of the compact crystals in the compact obtained according to the present invention. It is a graph showing the degree. Figure 1 Figure 2

Claims (1)

[Claims] A method for producing an oxide superconductor by pressure molding oxide superconductor powder, the method comprising pressure molding using oxide superconductor powder having a particle size of 20 to 100 μm. .