Method of preparing oxide superconducting wire

Abstract: Disclosed herein is a method of preparing an oxide superconducting wire comprising the steps of coating a powder material for forming an oxide superconductor with a metal, performing deformation processing on the metal-coated powder material thereby obtaining a tape-type wire material, superposing a plurality of such tape-type wire materials, performing first heat treatment on the plurality of superposed tape-type wire materials while simultaneously diffusion-bonding the metallic coats to each other, then performing deformation processing on the plurality of superposed tape-type wire materials, and performing second heat treatment on the plurality of deformation-processed tape-type wire materials. Preferably the oxide superconductor to be obtained is a bismuth oxide superconductor having a 2223 composition in a composition of Bi-Sr-Ca-Cu or (Bi,Pb)-Sr-Ca-Cu, and the powder material consists of a superconducting phase, which is mainly composed of a 2212 phase, and non-superconducting phases.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of preparing an oxide superconducting wire, and more particularly, it relates to an improvement for increasing the critical current density of the as-formed oxide superconducting wire. Description of the Background Art In relation to an oxide superconducting wire, it has been recognized possible to attain a high critical current density by coating a powder material for forming an oxide superconductor with a metal, strongly working the metal-coated powder material into a thin tape by deformation processing, and combining such working with heat treatment. A superconducting wire which is applied to practical use must have a high critical current density, a high critical current and excellent mechanical properties. If only a high critical current and excellent mechanical properties are required for such an oxide superconducting wire, a thick tape may be employed as the material. In this case, however, the critical current density of the as-formed oxide superconducting wire disadvantageously remains at a low level. EP-A-0357779 discloses a method of preparing an oxide supercontacting wire which comprises the steps of coating a powder material for forming an oxide superconducter with a metal, performing deformation processing on that metal-coated powder material thereby obtaining a tape-type wire material performing first heat treatment on that tape-type wire material, then performing deformation processing on that tape-type wire material and performing second heat treatment on that deformation-process tape-type wire material. Further it is stated that several tape-shaped wires are stacked and subjected to rolling, whereby heat is not applied at all. If however the stacked wires are not mutually bonded, the wires deviate in the withwise direction when the wires are rolled, so that the load of rolling is not sufficiently exerted on the wires, and it is very likely that the load of rolling is applied unevenly to the wires. EP-A-0356969 and Appl. Phys. Lett. 54 (1989), April 17, Nr. 16, New York, US, pp. 1582-1584, M. Mimura et al. disclose a similar method of preparing an oxide superconducting wire which only is comprised of a single tape-type wire SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method of preparing an oxide superconducting wire, which has a high critical current density and a high critical current, as well as excellent mechanical properties. According to the present invention, the method of preparing an oxide superconducting wire, comprising the steps of: coating a powder material for forming an oxide superconductor with a metal; performing deformation processing on said metal-coated powder material thereby obtaining a tape-type wire material; superposing a plurality of said tape-type wire materials with each other; performing first heat treatment on said plurality of superposed tape-type wire materials; wherein metallic coats are diffusion-bonded to each other in said first heat treatment step; then performing deformation processing on said plurality of superposed tape-type wire materials; and performing second heat treatment on said plurality of deformation-processed tape-type wire materials. According to a prefered embodiment of the present invention, the method of preparing an oxide superconducting wire comprises the steps of: A method of preparing an oxide superconducting wire in accordance with claim 1, wherein said oxide superconductor to be obtained is a bismuth oxide superconductor having a 2223 composition in a composition of Bi-Sr-Ca-Cu or (Bi, Pb)-Sr-Ca-Cu, and said powder material consists of a superconducting phase, being mainly composed of a2212 phase, and non-superconducting phases. According to the present invention, the plurality of tape-type wire materials are so superposed with each other that strong working can be performed on the individual tape-type wire materials while ensuring a high critical current and excellent mechanical properties, whereby it is possible to attain a high critical current density. In the first heat treatment step, the metallic coats are diffusion-bonded to each other so that deformation processing can thereafter be homogeneously carried out. When the powder material is degassed before the same is coated with the metal, homogeneous properties can be attained over the longitudinal direction of the as-formed oxide superconducting wire. Thus, it is possible to obtain a long oxide superconducting wire having excellent properties. The present invention is particularly effectively applied to a method of preparing an oxide superconducting wire which contains a bismuth oxide superconductor. In this case, the bismuth oxide superconductor has a 2223 composition in a composition of Bi-Sr-Ca-Cu or (Bi,Pb)-Sr-Ca-Cu and particularly high properties are attained when the powder material consists of a superconducting phase, which is mainly composed of a 2212 phase, and non-superconducting phases. DESCRIPTION OF THE PREFERRED EMBODIMENTS Oxides and carbonates were so mixed that Bi, Pb, Sr, Ca and Cu were in the ratios 1.84:0.42:2.02:2.23:3.01, and this mixture was heat treated to prepare a powder material consisting of a 2212 phase and non-superconducting phases. This powder material was degassed under a decompressed atmosphere of 2 Torr at 700°C for 3 hours. This powder material was coated with a silver pipe, which in turn was drawn into a diameter of 1 mm, and then rolled into a thickness of 0.2 mm. Eight tape-type wire materials obtained in the aforementioned manner were stacked with each other to form a laminate. This laminate was heat treated at 840°C for 50 hours, and rolled at a degree of 40 %. This laminate was thick and integrated by the heat treatment, and exhibited excellent mechanical properties. The laminate was again heat treated at 840°C for 50 hours. The as-formed oxide superconducting wire was cut into a length of 20 m, and subjected to evaluation of properties. As the result, this wire exhibited excellent properties in liquid nitrogen, with a critical current density of 22000 A/cm 2 and a critical current of 240 A. The superconducting wire was easy to handle also after heat treatment.

Claims: A method of preparing an oxide superconducting wire, comprising the steps of: coating a powder material for forming an oxide superconductor with a metal; performing deformation processing on said metal-coated powder material thereby obtaining a tape-type wire material; superposing a plurality of said tape-type wire materials with each other; performing first heat treatment on said plurality of superposed tape-type wire materials; wherein metallic coats are diffusion-bonded to each other in said first heat treatment step; then performing deformation processing on said plurality of superposed tape-type wire materials; and performing second heat treatment on said plurality of deformation-processed tape-type wire materials. A method of preparing an oxide superconducting wire in accordance with claim 1, wherein said powder material is degassed before the same is coated with a metal. A method of preparing an oxide superconducting wire in accordance with claim 1, wherein said oxide superconductor to be obtained is a bismuth oxide superconductor having a 2223 composition in a composition of Bi-Sr-Ca-Cu or (Bi,Pb)-Sr-Ca-Cu, and said powder material consists of a superconducting phase, being mainly composed of a 2212 phase, and non-superconducting phases.

Inventors: HIKATA TAKESHI, MUKAI HIDEHITIO, SATO KENICHI, HIKATA, TAKESHI, MUKAI, HIDEHITIO, SATO, KENICHI, HIKATA, TAKESHI, C/O OSAKA WORKS OF SUMITOMO, Mukai, Hidehitio, c/o Osaka Works of Sumitomo, SATO, KENICHI, C/O OSAKA WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1991
Main classification: H01L39
IPC codes: B21F19, B21F15, B22F3, H01B12, H01B13, C22C1, H01L39