JPH0416510A - Production of oxide superconducting bulk material - Google Patents

Abstract

PURPOSE:To produce a large-sized and high-grade oxide superconducting bulk material by quenching and solidifying a melt contg. RE, Ba and Cu to obtain a formed body, semi-melting the body, cooling and further heat-treating the product under specified conditions. CONSTITUTION:A melt contg. RE (rare-earth elements including Y and their combination), Ba and Cu is quenched and solidified to obtain a plate or wire- shaped formed body. The formed body is transiently heated to 1000-1200 deg.C and semi-melted. The semi-molten formed by is slowly cooled in the atmosphere from 1000 to 850 deg.C at the rate of <=200 deg.C/hr and then slowly cooled in the atmosphere free of oxygen from 850 deg.C to room temp. at the rate of <=200 deg.C/hr. The formed body is then pressed at <=500kg/cm<2> and heated in an oxygen atmosphere from 200 to 600 deg.C in >=1hr, hence oxygen is infiltrated into the body, and the tetragonal crystal is converted to a rhombic crystal. Consequently, superconductivity is imparted to the body, and the body is not cracked. A high- grade oxide superconducting bulk material is obtained in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for obtaining a superconducting phase from a semi-molten state at high temperatures in the production of oxide superconducting bulk materials.

[Prior art] Efforts to put oxide-based superconducting bulk materials into practical use are currently focused on melting methods, such as the QMG method (Reference: J
ap, J, Apl)1. Phys, Vol. 28. N
o, 7.1989°pp 1189-1194).

This involves melting a material containing RE (rare earth elements including Y, and combinations thereof), Ba, and Cu elements, then rapidly solidifying a plate or linear molded body with a thickness of 5 mm or less and heating it at 1000°C to 1350°C. After heating to a high temperature of 200°C to a semi-molten state, at a rate of 200°C/hr or less,
By cooling it, IO'
This is a method of obtaining a critical current density (Jc) of A/cm2 or more. By this method, 10'A/c under high magnetic field.
It has become possible to obtain a critical current density of m2 or more, and there is a prospect of practical application, or there is a need to develop even higher-grade oxide bulk superconducting materials. In other words, cracks within the grains are the cause of hindering further improvement in Jc and enlargement.

[Problems to be Solved by the Invention] The present invention solves these problems and provides a method for manufacturing large-sized, high-quality oxide bulk superconducting materials.

[Means for Solving the Problems] The present invention provides RE (rare earth elements containing Y, and combinations thereof) obtained by rapid cooling from a molten state.

A molded body containing Ba and Cu elements is heated from 1000°C to 1200°C.
℃ to a semi-molten state, and then slowly cooled in the atmosphere from 1000℃ to 850℃ at a rate of 200"C/hr or less,
From 850℃ to 200℃/h in an oxygen-free atmosphere
After slow cooling to room temperature at a speed of 500 yen or less, in an oxygen atmosphere,
From 200℃ to 60℃ with a pressure of 00kg/cff12 or less
Production of an oxide superconducting bulk material characterized by heating at 0°C for 1 hr or more and then cooling to room temperature at a rate of 200°C/hr or less to prevent defects such as clutter and obtain a high Je superconductor. It's a method.

[The action phase REBa2Cu30t-x (hereinafter referred to as 123 phase) is approximately 10
60°C (RE: Nd with the highest 123 phase formation temperature
RE2BaCu is unstable at higher temperatures than
It melts and decomposes into a liquid phase (BaCu oxide) and a liquid phase (BaCu oxide). Furthermore, approximately 120 (21 at temperatures above 1°C)
One phase also decomposes and becomes RE2O3 and liquid phase. However, since the molded product heated at high temperature has a high viscosity in this semi-molten state, the shape of the molded product is almost maintained. When this semi-molten molded body is slowly cooled, a 123 phase is formed by a peritectic reaction between the 211 phase and the liquid phase. The organization formed at this time is fine21
It becomes an aggregate of several lllll11 pseudo-single crystals including one phase.

For this reason, the material produced by the present invention has extremely few grain boundaries that interfere with Jc, and not only can a high Jc be obtained in a zero magnetic field, but also a Jc that is two orders of magnitude higher than that obtained by conventional methods even in a high magnetic field. can get.

The reason for limiting the heating temperature of the compact is that below 1000°C, it will not fully melt partially, and after partially melting, it will become an aggregate of fine crystals, and the Jc will be reduced to that of a sintered body, and above 1200°C, it will not be heated at high temperatures. Sometimes, it was determined because of the large reaction with the support base (for example, platinum). In addition, these temperatures vary somewhat depending on the type of RE element, the atmosphere at the time of heating, and the charging composition. The more the temperature increases, the more likely it is to sit on the high temperature side.

After heating to a high temperature of 1000℃ to 1200℃, 100℃
The reason for slow cooling from 0℃ to 850℃ at a cooling rate of 200℃/hr or less is 200℃/hr or more!
This is because the crystal growth of the 23 phase becomes faster and the final structure becomes polycrystalline.

The reason for slowly cooling from 850° C. to room temperature in an oxygen-free atmosphere is to prevent cracks that occur during the phase transformation from tetragonal to orthorhombic. Also, at this time, 200℃/
The reason for slow cooling at a rate of hr or less is that if the dough is cooled at a faster rate than kneading, cracks will form due to the sudden change in temperature difference.

The reason why the molded body is then heated in an oxygen atmosphere is to transform the molded body from a tetragonal crystal to an orthorhombic crystal by introducing oxygen into the molded body, thereby making it a superconductor. Also, the reason for the temperature limit is that if it is lower than 200℃, oxygen cannot enter sufficiently, and if it is higher than 600℃, R
This is because some H exceeds the phase transformation temperature. The reason for the time limit is that if it is less than hr, sufficient oxygen will not enter. Furthermore, heating without applying pressure for a period exceeding 60 hours is not necessary because the diffusion of oxygen in the oxide bulk superconducting material I is saturated. At this time, further
The reason why the heat treatment is performed during pressurization is to suppress and control cracks that occur during phase transformation from tetragonal to orthorhombic crystals. The reason why this pressure is limited to 5001℃g/cm" or less is that if a pressure greater than 500kg/co+2 is applied, this pressure will cause cracks. Also, in order to prevent cracks from occurring, at least l
Pressure of 0 kg/cm2 or more is required.

[Example] An example of manufacturing an oxide bulk superconducting material by the method described above will be described below.

The molded body was obtained by melting YBa2Cu3O7-x powder and hammer quenching, with a thickness of I + nm and a width of 10
mn+, and a length of 20+ nm was prepared. This was placed on a platinum mesh and subjected to the following heat treatment in an oxygen atmosphere. After holding at 1100℃ for 1 hour, 20℃/
The temperature was raised to 1000°C at a cooling rate of 100°C, then lowered from 1000°C to 850°C at a cooling rate of 10°C/hr, and then heated to room temperature at 100°C/hr in an Ar atmosphere.
The temperature was lowered at a cooling rate of hr. After slow cooling, oxygen; in an atmosphere;
Under pressure of 300 kg/cm2, 500 hr, 10 hr
Heated. The obtained material was cut out, its structure was observed using an optical microscope, and its superconducting properties were measured, and the following results were obtained.

Group #I: A sample with very few cracks was obtained as shown in FIG. 1(a). (Figure 1(b) shows the structure diagram of a sample obtained by the conventional QMG method.) A sharp superconducting transition was exhibited at a critical temperature (C) of 95.

Critical current density (Jc): 7 as shown in Figures 2 and 3
The magnetic field dependence of Je in 7 and 4.2 was found to be better compared to the conventional QMG method.

[Effects of the Invention] As detailed above, the present invention enables the production of high-grade oxide bulk superconducting materials that have not been possible until now, and can be applied as molded products in various fields. This has a very large industrial effect.

As a specific example, l) Superconducting wire With this manufacturing method, high J can be obtained from the linear molded body.

It can be used as a long-distance power transmission line because it can be used as a wire rod and is easy to connect.

2) A high-quality magnet can be created simply by stacking several superconducting coil spiral molded bodies, touching them at the joints, and heat-treating them.

3) Superconductors of any shape can be created by simply placing a plate-shaped superconducting magnetic shielding material into a mold of any shape and heat-treating it.

We can produce high-grade magnetic shielding materials with little magnetic flux leakage.

Natogaagera 4ru.

[Brief explanation of drawings]

FIG. 1(a) is a micrograph showing the structure of the oxide bulk superconducting material produced according to the present invention. FIG. 1(b) is a micrograph showing the structure of an oxide bulk superconducting material manufactured by the conventional QMG method. Figure 2 shows the magnetic field dependence of Je at a liquid nitrogen temperature of 77,
It is a graph showing a comparison between the method of the present invention and the conventional QMG method. FIG. 3 is a graph showing the magnetic field dependence of Je at a liquid helium temperature of 4.2, comparing the method of the present invention and the conventional QMG method.

Claims (1)

[Claims] 1. A molded body obtained by rapidly cooling and solidifying a molten body containing RE (rare earth elements including Y, and combinations thereof), Ba, and Cu elements is heated to a high temperature of 1000 ° C. to 1200 ° C. to a semi-molten state, and then Slowly cool in air from 1000°C to 850°C at a rate of 200°C/hr or less, cool slowly from 850°C to room temperature at a rate of 200°C/hr or less in an oxygen-free atmosphere, and then cool at 500 kg/hr in an oxygen atmosphere. cm^
1. A method for producing an oxide superconducting bulk material, which comprises heating from 200° C. to 600° C. for 1 hr or more while applying pressure at 2° C. or less.