Sponsored by: Jt. EMPMD/SMD Superconducting Materials Committee, MSD Electronic, Magnetic and Optical Phenomena Committee, FEMS (Federation of European Materials Societies)
Program Organizers: U. Balachandran, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439; Paul J. McGinn, University of Notre Dame, Notre Dame, IN 46556; Stuart Abell, University of Birmingham, Edgbaston, Birmingham B152TT, UK
Monday, AM Room: B7
February 5, 1996 Location: Anaheim Convention Center
Session Chairpersons: R. Wesche, EPFL, Centre de Recherches en Physique des Plasmas, Switzerland; J. Schwartz, Florida State University, Tallahassee, FL
8:30 am Invited
DEVELOPMENT OF HTS CONDUCTOR AND COILS FOR ELECTRIC POWER APPLICATIONS: P. Haldar, G. Hoehn, Jr., Intermagnetics General Corp., Latham, NY 12110; U. Balachandran, Argonne National Laboratory, Argonne, IL 60439
Long lengths of bismuth-2223 based silver sheathed superconductors by the powder-in-tube approach have been produced, to fabricate high temperature superconducting (HTS) components for electric power applications such as generators, motors, transmission cables, transformers, SMES, etc. Prototype lengths of multi filament tapes are presently being manufactured with critical current densities useful for most electric power applications. We have recently demonstrated the fabrication of lengths approaching 1 km of Bi-2223 multi filament conductor that carried >10,000 A/cm2 at 77 K, self field. A shorter piece length (20 m) exhibited a critical current of 42 A with a corresponding Jc of 21,000 A/cm2. Work at ANL and part of the work at IGC is supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, as part of a DOE program to develop electric power technology, under Contract W-31-109-Eng-38.
8:50 am Invited
DEVELOPMENT OF Bi2Sr2Ca1Cu2Oy HTS CONDUCTORS AND COILS FOR HIGH FIELD GENERATION: K. Togano, H. Kumakura, H. Kitaguchi, National Research Institute for Metals, Tsukuba 305, Japan; M. Okada, Hitachi Research Laboratory, Hitachi 319-2, Japan; I. Kato, Hitachi Cable Ltd., Tsuchiura 300, Japan; T. Hasegawa, Showa Cable & Wire Company, Ltd., Kawasaki 210, Japan
We have concentrated on developing long lengths of Bi2Sr2Ca1Cu2Oy tape conductors and their coils aiming at the high magnetic field generation in Liq. He or by refrigerator operation. The tapes were fabricated by the powder-in-tube method (PIT) or coating process on Ag substrate tape. Multifilamentary tape processed by PIT showed good strain tolerance and uniformity of Jc along the tape. Using this multifilamentary tape, we have fabricated a compact magnet with 13mm and 45mm in inner and outer diameters, respectively, which was designed as a booster of the 20T class superconducting magnet. The coil generated 3.3T in zero bias field at 4.2K. In order to improve the strain tolerance of the coating-processed tape, a laminated tape was fabricated by sandwiching several coated tapes between Ag foil, which was heat treated continuously by being passed through a pipe furnace with precise temperature gradient. The laminated tape has good strain tolerance which is enough for coil making by "react & wind" method. Coil tests in strong bias field in Liq. He or refrigerator operation are in progress.
9:10 am Invited
CONTROLLED PROCESS OF Ag-CLAD Bi-BASED SUPERCONDUCTING TAPES: S. X. Dou, M. Ionescu, W. G. Wang, Y. C. Guo, H. K. Liu, Centre for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia; E. Babic and I. Kusevic, Dept. of Physics, Univ. of Zagreb, Zagreb, Croatia; and E. W. Collings, Dept. of Materials Science and Engr., The Ohio State University, Columbus, OH 43210-1179
A continuous forming process was successfully tested as an alternative process of the powder-in-tube process for fabrication of long length superconducting tapes. A "sandwich rolling" process has been developed to prevent the formation of sausaging and cracks in longitudinal direction of the Ag-clad Bibased superconducting tapes. High Jc for Ag/Bi-2212 tapes achieved through MTG in the alternating oxygen and nitrogen atmosphere. While N2 annealing on cooling ensures high Tc, O2 treatment during melting and slow cooling period enhances the stability of 2212 allowing for grain growth with ample liquid formation. Direct observation of the interface achieved by removing Ag sheath with Hg alloy shows highly dense, textured and thin-film like structure. Grain growth in 2223 tape must be coupled with the 2212/2223 phase transformation in order to optimise Jc- No initial drop in Jc-B for 2212 MTG tape as typical feature of 2223 tape. In high T, Jc for both 2212 and 2223 tapes is limited by intragrain Jc. The Uo for 2223 tape is larger than that for the best 2212 tape and epitaxial thin films.
9:30 am Invited
Bi2Sr2CaCu2Ox CONDUCTOR PREPARATION FOR INSERT COILS IN 20 T MAGNETS: J. Schwartz, J. Kessler, W. Wei, H. Weijers, Florida State University, National High Magnetic Field Laboratory, Tallahassee, FL
The superconducting properties of many high temperature superconductors are excellent for applications in high magnetic fields. One of these materials is Bi2Sr2CaCu2Ox. Li-doping of this superconductor greatly improves the superconducting properties. Powder-in-tube wires and tapes were prepared using Ag and AgMg tubes, Li-doped and undoped powders. Additionally, hot rolling of the tapes was performed to improve the conductor performance. Short samples were characterized by critical current measurements in high magnetic fields up to 20 T. Investigations of the ceramic microstructure were performed by SEM to correlate the critical current with the grain structure and impurities inside the core. Wind-and-react layer-wound and pancake coils were prepared to analyze the critical current in longer conductors lengths at 4.2 K and fields up to 20 T. This work was supported by the National Science Foundation through the National High Magnetic Field Laboratory, Grant No. 9016241.
9:50 am Invited
RECENT ADVANCES IN HTS COMPOSITE SUPERCONDUCTORS: J. M. Seuntiens, American Superconductor Corp., Two Technology Drive, Westborough, MA 01581
Continued progress in the performance of HTS composite superconductors has been made. Using powder metallurgical techniques that are based on scaleable processes, filament critical current densities in excess of 40,000 A/cm2 (77 K, self field) have been achieved for multifilamentary conductors. Composites have been fabricated which demonstrate the ability to twist and bend the composite without excessive degradation in critical current. A strong interest in HTS composites exists for alternating current (AC) applications. AC losses of composite conductors have been characterized to quantify eddy current, hysteresis, and coupling current losses. Microstructural analysis of the HTS composite superconductors provides insights into mechanisms that limit supercurrent, strain tolerance, and AC loss. Results of recent efforts in fabrication of multistrand conductors and coils will be presented.
10:10 am BREAK
OPTIMIZATION OF THE FABRICATION PROCESS OF Bi (2223) TAPES: G. Grasso, F. Marti, A. Jeremie, B. Hensel, R. Flükiger, Université de Genéve, Departement de Physique de la Matiere Condensee, 24, quai ErnestAnsermet, 1211 Genéve 4, Switzerland
In this work, we describe in detail the technique we have developed for the preparation of rolled, high ic Bi(2223) tapes with Ag and Ag-Mg sheaths. New results about the correlations between the critical current density and the powder heat treatment temperature and time, the cold deformation steps, as well as the tape heat treatment temperature and time are presented. Moreover, we have found that the local pressure exerted on the tapes during the rolling deformation between the heat treatments has a strong influence on the transport properties: the highest ic (77 K, 0 T) value (30 kA/cm2) was found for a local rolling pressure of 0.6 GPa. The addition of Mg to the Ag sheath has been used to improve the mechanical resistance of the tapes. We have found that the Mg addition has also remarkable effects on the principal physical properties of the tapes. Thermal transport measurements have been performed on both types of tapes. The Ag sheathed tapes have shown a thermal conductivity 2 and 7 times higher than the Ag-Mg sheathed ones at 77 K and 4.2 K, respectively. Preliminary results have shown that at 77 K the transport AC losses are about 20% lower in Ag-Mg sheathed tapes.
ALTERNATIVE SHEATH MATERIALS FOR Bi-2223: J. D. Cotton, Los Alamos National Laboratory, Los Alamos, NM 87545; G. N. Riley, Jr., American Superconductor Corp., Westborough, MA 01581
The oxide-power-in-tube (OPIT) process for producing Bi-2223 superconducting tapes has been used with considerable success. This is largely due to the good chemical compatibility of the tube material, pure silver, with the Bi2223 phase. Additionally, silver is formable, has a sufficiently high melting point, is oxygen-permeable, and has a low electrical resistivity. However, certain device designs would benefit from a sheath material which has a higher electriccal resistivity than pure silver. This presentation will report the results of our investigations into alternative ssheath alloys for processing Bi-2223. Alloys investigated include Ag-Mn, Ag-Pd and Ag-Pt. The electrical resistivity at 75 and 300 K is determined, as well as hardness, oxidation response, chemical compatibility and superconducting transition temperature.
11:00 am Invited
FABRICATION AND PROPERTIES OF SUPERCONDUCTING AgNiMg AND AgBi-2212 WIRES: R. Wesche, A. M. Fuchs, B. Jakob, G. Pasztor, EPFL, Centre de Recherches en Physique des Plasmas, CH-5232 Villigen PSI, Switzerland
Superconducting AgNiMg and Ag/Bi-2212 monocore wires of 1 and 1.5 mm diameter have been fabricated by the powder-in-tube technique from the same batch of powder. The effects of the different sheath materials on the optimum heat treatment conditions and the superconducting properties of the Bi-2212 wires have been studied. At 4.2 K and B = 0 short sample critical current densities up to 70000 A/cm2 and 100000 A/cm2 have been achieved for AgNiMg and Ag/Bi2212 wires of 1 mm diameter, respectively. For both wire diameters the critical temperature is lower in the case of the AgNiMg. The optimum heat treatment conditions have been found to depend on the sheath material. This may be a consequence of rapid oxygen diffusion through the AgNiMg sheath via grain boundaries. Finally, first results for multifilamentary AgNiMg and Ag/Bi-2212 wires will be presented.
CRITICAL CURRENT ANISOTROPY AND EFFECTIVE TEXTURE IN BSCCO-PHASE CONDUCTORS: J. Everett, M. Dhallé, M. Johnston, A. D. Caplin, Centre for High Temperature Superconductivity, Blackett Laboratory, Imperial College, London SW7 2BZ, UK
The powder-in-tube (PIT) fabrication of BSCCO-phase conductors aims to achieve a high degree of texturing, with the abplane of the crystallites parallel to the plane of the conductor. However, it is now well-known that the current distribution in these tapes is far from uniform, and that texture may play an important role in determining which are the dominant current paths. Therefore, the anisotropy of the critical current (at some voltage level) with respect to the direction of an applied magnetic field reflects the texture of the significant current pahts, which may be very different from the texture averaged through the core of the conductor, as obtained from structural studies. We report anisotropy studies of such conductors, analyze the nature of their texture, and draw inferences above the form of the current paths.
POWDER-IN-TUBE TAPES OF Tl-1223 MATERIAL PREPARED BY DIFFERENT METHODS: R. Löw, T. Riepl, G. Rößl, B. Steinberger, W. Huber, R. Stierstorfer, G. Oswald, K. F. Renk, Institut fur Angewandte Physik, Universität Regensburg, 93040 Regensburg, Germany
We have synthesized (Tl,Bi)1Srl 6Ba0.4Ca2Cu3Ox (Tl-1223) with a Tc up to 117 K
by the usual ceramic route and by a single step sol-gel process using citric
acid and ethylene glycol. These methods lead to Tl-1223 material with different
grain sizes (ceramic route about 10 m - sol-gel process about 50 m). Our
powder-in-tube tapes from material prepared by the ceramic route showed jc 5.5
x 103 A/cm2 (Ic 13 A) at 77 K and 0 T when rolled
longitudinally and transversally.
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