JPH04160062A - Production of superconducting material - Google Patents

Abstract

PURPOSE:To increase critical current density and to improve mechanical strength and durability by heating a quenched block obtd. by quenching molten starting materials and by hot working the heated block in a liq.-crystal mixed phase state. CONSTITUTION:Starting materials such as Y2O3, BaCO3 and CuO are mixed, calcined in an oxygen atmosphere, pulverized, melted by heating at 1,350-1,450 deg.C for 3-10min and quenched to obtain a quenched block. This block is heated at 1,050-1,150 deg.C and hot worked in a liq.-crystal mixed phase state at 970-1,000 deg.C.

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 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, B1 discovered by the Institute of Metal Materials Technology
-3r-Ca-Cu-0 type. (
These are substances with high stability and reproducibility, so they are officially recognized high-temperature superconductors, but in addition to La-3r-Nb-0,
Kagoshima University, Hitachi, etc. have reported the Tl-3r-V-0 series and the like. ) 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 to fill a silver tube (sheath) with pre-prepared superconducting powder, as described in the Powder Metallurgy Association's 1986 Spring Conference Abstracts, pages 26-27.
The process consisted of sintering the powder inside the silver tube after forming it by wire drawing, roll rolling, etc.

[Problems to be Solved by the Invention] However, in the conventional manufacturing method, (1) the crystal orientation of a high-temperature superconductor is not controlled even though it is a material with strong anisotropy due to its crystal structure. Although it is slightly oriented by drawing or rolling, the degree of orientation is low because the powders interfere with each other and are difficult to rotate. ■Non-superconductor phases tend to precipitate at grain boundaries, etc., and superconductor phases do 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 is intended to solve these problems, and aims to provide a superconducting material that has a high critical current density, 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 process is a step of melting raw materials and a step of melting the melt. It is characterized by comprising a step of rapidly cooling to obtain a quench salt, and a step of heating the quench salt and then hot working it in a mixed phase state of a liquid phase and a crystalline phase. After hot working, an annealing treatment may be performed to further promote crystal growth and remove strain.

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

Example-1 First, raw materials Y2O3, BaCO3, and CuO powder were mixed and dispersed, and then calcined for 15 hours in an oxygen atmosphere at 900°C. Next, the calcined product is pulverized and stirred, and then heated to 1350°C to 1450°C to melt it. If the melting time is too long, Y2O3 will aggregate and become non-uniformly dispersed, so melting is preferably carried out for a relatively short time of 3 to 10 minutes. This melt is then cast into a sheath that is cooled. Since the melt is rapidly cooled at this time, it becomes a quench salt in which fine Y2O3 particles are dispersed in an amorphous phase.

Next, the quench salt was heated to 1050°C to 1150°C along with the sheath.
Roll at ℃. During rolling, Y203, which becomes the nucleus of 211 phase growth in the early stage of rolling, and further YBa2Cu307-x
(Superconducting phase: hereinafter referred to as 123 phase) 21 which is the core of growth
-1 phase is dispersed more uniformly.

As is well known, the 123 phase is the 211 phase and the liquid phase (3Bacu0
211 to become vivid due to peritectic reaction with 2+2cu○)
If the phase and liquid phase are not uniformly dispersed, non-superconductor (211 phase, etc.) phases will increase and the connection between the superconductor phases will be severed. Totally 1
In order to continuously grow the 23 phase, it is necessary to uniformly disperse the 211 phase, and rolling under predetermined conditions has the effect of uniformly dispersing the 211 phase due to the mixing effect.

Next, while rolling,
Cooled to a mixed phase state of 23 phases (main phase), 211 phases, and liquid phase,
The rolling of the noodles is stopped and the noodles are slowly cooled to room temperature. By this rolling, the C-axis of the crystals is oriented parallel to the pressing direction.

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.

Example 2 As in Example 1, a quenched mass was obtained by casting the melt into a folded sheath of 20 mm x 20 mm, height 20 mm, and thickness 2 mm. Then, cover the folded sheath and seal it. The purpose of sealing here is to prevent liquid phase from scattering during hot working. Next, use a hot press machine to
It is heated to a mixed phase state of 1 phase and liquid phase, compressed by 20%, and further 1
It is cooled to a mixed phase state of 000° C. to 970° C., that is, a 123 phase, a 211 phase, and a liquid phase, and subjected to 60% compression processing. Next, after peeling off the sheath, annealing treatment was performed at 900° C. in an oxygen atmosphere for 5 hours to obtain a superconducting material.

Table 3 The critical current density of the obtained sample was measured. The measured temperature is 7
It's on 7th. From Table 0 showing the results in Table 3, it can be seen that the critical current phase is significantly improved as in Example-1.

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, 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 processing also has the effect of suppressing the formation of whiskers.

In this embodiment, the YBa2Cu3O7-x material was explained, but any material may be used as long as it has anisotropy due to its crystal structure and can obtain a mixed phase state of a crystalline phase and a liquid phase.

[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 the raw materials, rapidly cooling the melt to obtain a quenched lump, heating the quenched lump and then heating it in a mixed phase state of liquid phase and crystalline phase. A method for producing a superconducting material, comprising a processing step.