JPH04164864A - Production of superconducting material - 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 adopting constitution of three processes comprising melting of raw material, 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 hot processing in a mixed phase state of liquid phase and crystal phase after cooling and a process of growing crystal and cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to bulk superconducting materials used in 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 application is the Ln-Ba-Cu-0 system (
Ln indicates a rare earth element), A of the University of Arkansas
+ Tl-Ba-Ca discovered by M, Hermann et al.
-Cu-0 series, B discovered the day before at the Institute of Metals and Materials Technology
It can be roughly divided into three types: 1-8r-Ca-Cu-0 system.
(These are substances with high stability and reproducibility, so they are officially recognized high-temperature superconductors, but in addition to La-8r-Nb
-0 series, Tl-8r-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 in a portion of the pot tube after being formed.

[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. It 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 constantly obtainable critical current density was as low as 103 A/cm2 (77 K). 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 aims to solve these problems and to obtain a superconducting material that has 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 manufacturing a superconducting material of the present invention is a method for manufacturing a bulk superconducting material, in which the basic step is to use raw materials (including calcined powder). It is characterized by comprising a step of melting, a step of hot working in a mixed phase state of a liquid phase and a crystalline phase after cooling, and a step of growing crystals and cooling until the whole becomes a solid phase.

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

Example-1 First, raw materials Y 203, B a C03, and CuO powder were mixed and dispersed and then calcined at 900°C in an oxygen atmosphere for 15 hours.The calcined product was then crushed and stirred and then heated at 1350°C to 145°C.
Heat to 0°C to melt. If the melting time is too long, the Y2O3 will aggregate and become non-uniformly dispersed, so it is preferable to melt the Y2O3 in a relatively short time of 3 to 10 minutes.The melt then enters the heated sheath. The sheath heating temperature is a temperature at which the melt (liquid phase) is cooled to a mixed phase state of a liquid phase and a crystalline phase, that is, 1050°C to 1150°C. Next, the casting is rolled while rotating together with the sheath. By this rolling, YBa2Cu307-x (superconducting phase: 123
Y2BaCuO5 (non-superconducting phase: hereinafter referred to as 211 phase), which serves as the nucleus for growth (hereinafter referred to as 211 phase), and the liquid phase are uniformly dispersed.
If the dispersion of the 211 phase and the liquid phase is non-uniform, the non-superconductor (21
1 phase, etc.'') phase increases and breaks the connection between the superconductor phases.

In order to grow the 123 phase continuously, it is necessary to uniformly disperse the 211 phase, but rolling under certain conditions has the effect of uniformly dispersing the 211 phase due to the mixing effect.

Next, rolling is continued at around 1000°C, i.e. 1
The product is cooled to a temperature at which phase 23 precipitates (the liquid phase must always exist), and then rolling is stopped and the product is held for a certain period of time to allow gradual cooling to allow crystal growth. This rolling causes the crystals to become oriented.

The critical current density of the superconducting material thus obtained was measured after the sheath was peeled off. 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.

Comparison of these Example materials and Comparative Example materials by X-ray diffraction, optical microscopy, SEX observation, etc. revealed that the superconducting material of the present invention had a higher degree of crystal orientation than the Comparative Example, and 123 phases grew continuously. There were few pores. In addition, although the number of pores in the comparative example in which melting was carried out was significantly smaller than that in comparative example a, elongated voids were observed. The width of this whisker 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 working also has the effect of suppressing the occurrence of IB.

In this example, YB a2Cu 307-x material was used, 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 may be used. Although hot rolling was explained as a method for this, any other method that can be hotly deformed, such as hot forging (in this case, the molten material may be introduced into the mold instead of the sheath), may be used.

[Effects of the Invention] As described above, according to the present invention, even in materials with strong anisotropy, it is possible to align the crystal orientation and continuously grow a superconducting phase, and furthermore, it is possible to suppress the generation of vacancies and 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] The basic steps in the manufacturing method of bulk superconducting materials are: melting raw materials (including calcined powder), hot processing in a mixed phase state of liquid phase and crystalline phase after cooling, and growing crystals. 1. A method for producing a superconducting material, comprising a step of cooling at the same time.