JPH04164865A - Method for manufacturing superconducting materials - Google Patents

Abstract

PURPOSE:To obtain a superconducting material having high critical current density, excellent mechanical strength and durability (environmental resistance) in production of a superconducting material in bulk by using constitution fundamentally consisting of four processes of melting a raw material, casting melt into a mold and cooling, hot processing and then cooling. CONSTITUTION:In production of a superconducting material in bulk, fundamental processes consist of a process of melting a raw material (including calcined powder), a process of casting melt into a sheath material or a mold, cooling and crystallizing, a process of hot processing in a mixed phase state of liquid phase and crystal phase after heating and a process of growing crystal and cooling. When the melt is cast, the sheath material or the mold is provided with temperature gradient in a fixed direction and cooled to preferably raise a critical current density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to bulk superconducting materials used for power transmission lines, antennas, superconducting magnets, superconducting bearings, energy storage (load leveling), and the like.

[Prior art] The so-called high-temperature superconductor, whose critical temperature exceeds the liquid nitrogen temperature of 77 K and is expected to find wide applications, is the Ln-Ba-Cu-o system (Ln is Tl-Ba-Ca discovered by A. M. Hermann et al. of the University of Arkansas
-Cu-0 series, B discovered by the Institute of Metal Materials Technology
It can be roughly divided into three types: 1-8r-Ca-Cu-0 system.
(These are materials with high stability and reproducibility, so they are officially recognized high-temperature superconductors, but there are also other materials such as La-3r-Nb-
0 series, Tl-3r-V-0 series, etc. have been reported by Kagoshima University, Hitachi, etc. ) The conventional manufacturing method of superconducting materials using these materials will be explained using wire rods, which are typical examples of bulk (a word opposed to thin films used in devices) superconducting materials.

The basic process is as described in the Powder Metallurgy Association's 1986 Spring Conference Lecture Abstracts, pages 26-27, a silver tube (sheath) is filled with pre-prepared superconducting powder, and then wire-drawn, roll-rolled, etc. The process consisted of sintering the powder inside the ladle tube after forming.

[Problems to be solved by the invention] However, in conventional manufacturing methods, ■ Although high-temperature superconductors are materials with strong anisotropy due to their crystal structure, the crystal direction is not controlled; The degree of orientation is low because the powders interfere with each other and are difficult to rotate, although the degree of orientation is low due to rolling and rolling. does not grow continuously
■Since the powder is sintered after being molded, there are many pores and the density is low.

Due to these reasons, the critical current density that can be constantly obtained is as low as 10'A/cm2 (77K). Furthermore, when there are many pores, not only does the mechanical strength become weak, but also the surface area becomes large, which makes it easy to deteriorate and deteriorates the durability (environmental resistance).

The present invention is intended to solve these problems and to easily obtain a superconducting material having a high critical current density and excellent mechanical strength and durability (environmental resistance).

[Means for Solving the Problems] In order to solve the above problems, the method for producing a superconducting material of the present invention is a method for producing a bulk superconducting material, in which 1) the basic step is a step of melting raw materials; Consisting of a process of casting the melt into a sheath material or mold and cooling it to crystallize it, a process of hot working in a mixed phase state of liquid phase and crystalline phase after heating, and a process of growing crystals and cooling them 2) Melting It is characterized by cooling the sheath material or mold by applying a temperature gradient in a certain direction when visiting the object.

[Example] The present invention will be described in detail below with reference to Examples.

Example-1 First, raw materials Y2O3, B a C03, and Cu○ powder are mixed and dispersed and then calcined at 900°C for 15 hours in an oxygen atmosphere.The calcined product is then crushed and stirred and then heated to 1350°C to 1450°C.
Heat to melt. If the melting time is too long, Y2O3 will aggregate and become non-uniformly dispersed, so it is preferable to melt it in a relatively short time of 3 to 10 minutes.Next, this melt is placed inside a sheath with a temperature gradient in a certain direction. It is then poured into a mold and partially aligned in the crystal direction to crystallize it. It is preferable that the crystals do not grow large and are in a fine state.The zero-th order is heated together with the sheath to around 1-000°C, that is, to a mixed phase state of 123 phase, 211 phase, and liquid phase, and then rolled.The zero-th stage rolling is stopped for a certain period of time. After being held, it is slowly cooled to obtain a superconducting material.

The critical current density of the superconducting material thus obtained was measured by the sheath peeling diameter. The measured temperature is 77°C. The results are shown in Table 2 together with the comparative examples in Table 1.

As shown in Tables 1 and 2, it can be seen that the superconducting material produced by the manufacturing method of the present invention has a significantly improved critical current density.

In Example A, the temperature of the sheath is not controlled, and in Example B, a temperature gradient is applied to the sheath in a fixed direction. It can be seen that by cooling the sheath with a temperature gradient in a certain direction and partially aligning the crystal directions, the critical current density becomes higher, which is more preferable.

Comparison of these Example materials and Comparative Example materials by X-ray diffraction, optical microscopy, SEM observation, etc. showed that the superconducting material of the present invention had a higher degree of crystal orientation than the Comparative Example, with 123 phases growing continuously and voids. There were few holes. In addition, in the comparative example in which melting was performed, the number of pores was significantly smaller than in comparative example a, but elongated n (voids) were observed. The width of this 18 is almost the same as that of comparative example a, but the length is several tens to hundreds of times longer, which may be fatal in some cases. It can be said that hot processing also has the effect of suppressing the generation of scale.

In this example, the YBa2Cu3O7-x material was explained, but any material that has anisotropy due to its crystal structure and that can obtain a mixed phase state of a crystalline phase and a liquid phase is sufficient. In addition, any other hot plastic deformation processing such as hot forging (in this case, casting may be performed directly into a mold instead of a sheath) may be used.

[Effects of the Invention] As described above, according to the present invention, even in materials with strong anisotropy, the crystal orientation can be aligned and superconducting phases can be grown continuously, and the generation of vacancies can be suppressed to achieve high density. As a result, superconducting materials with high critical current densities can be obtained. In addition, suppressing the generation of pores not only increases mechanical strength but also leads to a decrease in surface area, which reduces deterioration and improves durability (environmental resistance).

that's all Applicant: Seiko Epson Corporation Representative Patent Attorney Kizobe Suzuki and 1 other person

Claims (1)

[Claims] 1) In the method for manufacturing bulk superconducting materials, the basic process is the process of melting raw materials (including calcined powder), casting the melt into a sheath material or mold, and cooling and crystallizing. 1. A method for producing a superconducting material, comprising the following steps: a step of heating and then hot working in a mixed phase state of a liquid phase and a crystalline phase, and a step of growing crystals and cooling. 2) A method for producing a superconducting material according to claim 1, characterized in that when the melt is cast, a temperature gradient is applied to the sheath material or the mold in a certain direction for cooling.