Kinetics of the alignment and the formation of the Bi(2223) platelets in the powder-in-tube processed Bi(2223)/Ag compos
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Kinetics of the alignment and the formation of the Bi(2223) platelets in the powder-in-tube processed Bi(2223)yAg composite tapes Li-jun Wu, Y-L. Wang, Weimin Bian,a) and Yimei Zhu Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973
T. R. Thurston Department of Physics, Brookhaven National Laboratory, Upton, New York 11973
R. L. Sabatini Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973
P. Haldar Intermagnetic General Corporation, Latham, New York 12110
M. Suenaga Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973 (Received 14 April 1997; accepted 2 July 1997)
The alignment and the formation of (Bi, Pb)2 Sr2 Ca2 Cu3 O10 inside an Ag sheath were investigated for tapes from four different precursor powders. Microstructural characterization along with in situ transmission x-ray diffraction experiments revealed that the kinetics depended strongly on the processing technique and the phase assemblage of the precursors. The alignment process was governed by the preferential grain growth of the Bi-cuprates along the a-b plane and the constraint applied by the sheath. The formation mechanism of (Bi, Pb)2 Sr2 Ca2 Cu3 O10 was either the intercalation or the nucleation and growth, depending on whether excessive liquid is adjacent to the platelets.
I. INTRODUCTION
Over the last several years, tremendous advances have been made in fabrication of Bi2 Sr2 Ca2 Cu3 O10yAg, [Bi(2223)yAg], tapes by the powder-in-the tube process. Presently, self field critical currents of 15 –20 kAycm2 (for the superconducting area) at 77 K are often reported for long lengths of rolled tapes.1 Moreover, a number of relatively large model devices using these tapes, such as transformers, motors, fault current limiters, and transmission cables, are currently being constructed for feasibility studies in electric utility power applications.1 In spite of these advances, further improvement of critical currents is needed to ensure the realization of these large-scale applications in the near future. Toward this goal, numerous microstructural investigations have been performed to characterize the formation of the Bi(2223) phase from various precursor powders in a Ag sheath and to correlate the observations with the critical currents of the tapes.2–14 From these studies, it is generally known that the alignment of the c-axis of the Bi(2223) platelets as well as a high fraction (nearly 100%) of the Bi(2223) phase in the core are crucial to achieving high current densities. However, these studies suggested a)
Present address: Materials Testing Centre, Northeastern University, Shenyang, Liao Ning Province, 110006, People’s Republic of China. J. Mater. Res., Vol. 12, No. 11, Nov 1997
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different possible mechanisms for the formation and alignment processes for Bi(2223) in a tape. For example, based primarily on the observation of the droplets in the interior
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