Superconductor technology: apparatus – material – process – High temperature – per se – Having tc greater than or equal to 150 k
Patent
1991-01-02
1993-11-16
Lieberman, Paul
Superconductor technology: apparatus, material, process
High temperature , per se
Having tc greater than or equal to 150 k
505725, 505742, 505733, C01F 1102, C01F 1700, C01G 302, C30B 100
Patent
active
052623912
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an oxide superconductor composed of oxides of RE, Ba and Cu. More particularly, the present invention relates to a bulk material or wire rod having a high critical current density, in which the crystal direction is controlled over a broad region by the unidirectional solidification process of the melting method, and a process for the preparation thereof.
BACKGROUND ART
The conventional process for the preparation of a metallic superconductor wire rod or magnet is roughly divided into two types. In the case of an alloy type material, a superconductive magnet is prepared by forming the alloy type material into an ultrafine multi-core wire mainly by utilizing a plastic deformation of the metal and winding the wire into a coil. A typical example in practical use at present is an Nb-Ti alloy. In contrast, in the case of an intermetallic compound, which has a poor workability compared with the alloy type material, a process is adopted in which the starting metal is worked to some extent to form a wire rod, the wire rod is wound into a coil, the coil is subjected to a post heat treatment to obtain a superconductive phase, and a magnet is formed (the surface diffusion process, the bronze process, and the in-situ process). Attempts to apply the technique of forming wire rods of these metallic materials to oxide superconductors have been proposed (Jpn. J. Appl. Phys., Vol. 26, No. 5, 1987, pp. L865-L866), but these attempts have no substantial practical utility because the superconductive phase in the interior of the wire is composed of a polycrystal and the crystal directions are not dispersed and are not uniform.
For a practical utilization of the oxide superconductor material, a material having a high critical current density, which is prepared by the melting method, must be formed into a long wire rod or a bulk material having a large area, but since this material has a single crystal texture, it is very difficult to obtain a superconductive phase by the conventional method adopted for metal materials, which comprises wire drawing or rolling and post heat treatment. To obtain a magnetic material from such a material, a plastic working of which is difficult, it is important to increase the length or area of an oxide superconductor having a high Jc value at a high magnetic field. In view of this problem, a primary object of the present invention is to provide an oxide superconductor of the RE-Ba-Cu-O type and a process for the preparation thereof.
DISCLOSURE OF THE INVENTION
In accordance with one aspect of the present invention, there is provided an oxide superconductor comprising an oxide of RE (which represents at least one member selected from the group consisting of rare earth elements including Y), Ba and Cu, which consists of a superconductor having a texture where crystal directions of the 123 phase in the matrix are uniform, large angle grain boundaries having an azimuth difference larger than 20.degree. are not present and the 211 phase is finely dispersed, or an aggregate thereof, wherein the superconductor is formed into a plate or wire and the c-axis of the crystal of the formed body is uniform within .+-.30.degree. to the normal of the plate face of the formed body or in the range of from 60.degree. to 120.degree. to said normal. In accordance with another aspect of the present invention, there is provided a process for the preparation of the above-mentioned oxide superconductor, which comprises inserting a formed body obtained by quenching, solidifying and forming a melt containing said elements of RE, Ba and Cu, into a heating furnace and moving a region of a temperature at which grains are formed in the 123 phase of the matrix of the formed body, i.e., through a region of a temperature of from 1050.degree. to 910.degree. C., having a temperature gradient of at least 2.degree. C., at a speed lower than 0.4 cm/hr from the top end of the formed body to the rear and thereof. According to this process, the nucleation in the 123 phase is controlled
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Y. Yamada, et al., "Critical Current Density of Wire Type Y-Ba-Cu Oxide Superconductor", J. J. of Applied Physics, vol. 26, No. 5, May 1987, pp. L865-866.
D. Dimos, et al., "Orientation Dependence of Grain-Boundayr Critical Currents in YBa.sub.2 Cu.sub.3 O.sub.7--.delta. ", Physical Reveiw Letters, vol. 61, No. 2, Jul. 1988, pp. 219-222.
Matsuda Shouichi
Miyamoto Katsuyoshi
Morita Mitsuru
Sawano Kiyoshi
Boyd John
Lieberman Paul
Nippon Steel Corporation
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