Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Heating – annealing – or sintering
Patent
1997-06-19
2000-06-13
Yamnitzky, Marie
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Heating, annealing, or sintering
505230, 505231, 505236, 505430, 505431, 29599, 428688, 428702, 428930, H01L 3924, H01B 1200
Patent
active
060749911
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Process for producing an elongated superconductor with a bismuth phase having a high transition temperature and a superconductor produced according to this process.
BACKGROUND OF THE INVENTION
The invention concerns a process for producing an elongated single- or multi-core superconductor having at least one conductor core embedded in an Ag matrix, which conductor core has a bismuth-containing superconductor material with a 2212 or 2223 type high-T.sub.c phase. The process comprises the following steps: made of the precursor of the superconductor material, cross-section-reducing treatment, and melting in an oxygen-containing atmosphere to form the high-T.sub.c phase.
The invention also concerns a superconductor manufactured by this process.
A similar process and a superconductor produced by this process are known from "Supercond. Sci. Technol.," Vol. 5, 1992, pp. 591-598.
Known superconducting metal oxide compounds with high transition temperatures T.sub.c of over 77 K, which are therefore also referred to as high-T.sub.c superconductor materials (for short: HTSL materials), include in particular cuprate based on bismuth material Bi--Sr--Ca--Cu--O (BSCCO) or B(Pb)--Sr--Ca--Cu--O (B(P)SCCO) system. In this system, two superconducting phases appear, which differ by the number of copper-oxygen lattice planes (layers) of the crystal unit cell. A superconducting phase with the approximate composition Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8+y, (referred to as a 2-layer/85-K or 2212-phase) has a transition temperature T.sub.c of approximately 85 K, while the transition temperature of a superconducting phase with the approximate composition Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10+x, (referred to as a 3-layer or 100-K or 2223 phase) is approximately 110 K.
Attempts have been made to manufacture elongated superconductors in wire or tape form with these HTSL materials. A process considered suitable for this purpose is referred to as "powder-in-tube" technology, known in principle from the manufacture of superconductors with the traditional superconducting material Nb.sub.3 Sn (see, for example, German Auslegeschrift 1 257 436). According to this method, a powder made from a precursor of the HTSL material, which in general contains little or none of the desired superconducting high-T.sub.c phase, is filled into a tubular carrier or into a matrix made of normally conducting material, in particular of Ag or an Ag alloy. The structure thus obtained is then brought to its final dimensions by means of forming processes, which may be interrupted by at least one heat treatment. Then the wire- or tape-shaped raw conductor is subjected to at least one annealing operation, performed at least partially in an oxygen-containing atmosphere, e.g., air, to adjust or optimize its superconducting characteristics or to form the desired high-T.sub.c phase (see, for example, "Supercond. Sci. Technol.," Vol. 4, 1991, pp. 165-171).
If a plurality of such tape- or wire-shaped high-T.sub.c superconductors or their conductor precursors are bundled together, conductors with a plurality of superconducting cores, referred to as multi-core or multi-filament conductors, can be obtained, which offer a series of advantages for technical applications (see the article by M. Wilhelm et al. entitled "Fabrication and Properties of Multifilamentary BiPbSrCaCuO-2223 Tapes" of the "International Symposium on Superconductivity" (ISS'93), Hiroshima, Japan, Oct. 26-29, 1993).
It is known from the aforementioned reference from "Supercond. Sci. Technol.," Vol. 5 that the textural properties of such reaction-annealed tape conductor cores can be improved, thereby increasing the critical currents, and the dependence of the critical current densities on the magnetic field can be reduced by partial melting and subsequent controlled crystallization of the ceramic. The corresponding process is known as the PFDR (phase formation-decomposition-recovery) process. According to this process, a nitrate mixture of suitable composition is calcined at 830.degre
REFERENCES:
patent: 5661114 (1997-08-01), Otto et al.
Liu, H. et al., "Microstructure and defects in Ag-clad Bi-Pb-Sr-Ca-Cu-O wires prepared through a controlled melt process," Supercond. Sci. Technol., 5, Oct. 1992, pp. 591-598.
Wilhelm, M. et al., "Fabrication and Properties of Multifilamentary BiPbSrCaCuO-2223 Tapes," Proceedings ISS '93 Hiroshima, Oct. 26-29, 1993.
Database WPI Week 9240, Derwent Publ. Ltd., London, GB; AN-92-327129 & JP-A-04 233 109 (Mitsubishi Cable, Ind. Ltd.), Aug. 1992.
Database WPI Week 9413, Derwent Publ. Ltd., London, GB; AN-94-106540 & JP-A-06 056 426 (Sumitomo Metal Ind. Ltd.), Mar. 1994.
Database WPI Week 9225, Derwent Publ. Ltd., London, GB; An-92-203497 & JP-A-04 132 111 (Mitsubishi Cable Ind. Ltd.), May 1992.
Y. Yamada et al., "Microstructural study of Bi(2223)/Ag tapes with J.sub.c (77K,OT) values of up to 3.3.times.10.sup.4 A cm.sup.-2 ", Supercond.Sci.Technol. 4(1991) 165-171.
Helldorfer Helmut
Jenovelis Alexander
Roas Bernhard
Wilhelm Manfred
Siemens Aktiengesellschaft
Xu Hong J.
Yamnitzky Marie
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