Phase Regions and Kinetics of Formation of (Bi,Pb)2Sr2Ca2Cu3Ox in Ag-Sheathed Tape |
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Authors: | Yeon Soo Sung,Eric E. Hellstrom |
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Affiliation: | Applied Superconductivity Center and Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 |
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Abstract: | Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3O, (2223) tapes were made by the oxide-powder-in-tube method. Tapes were heat-treated isothermally at several different temperatures in 7.5% O2/Ar, then quenched into oil to retain the phase assemblages at the reaction temperatures. 2223 formed between ∼810° and ∼837°C. The Avrami equation was applied to describe the kinetics of 2223 formation from a mixture of Bi2Sr2CaCu2O x and nonsuperconducting phases, mainly Ca2PbO4 and CuO. The calculated Avrami exponent, n ∼ 1, indicated that the kinetics in this system could be described as a diffusion-controlled, two-dimensional nucleation and growth process. The apparent activation energy for forming 2223 was ∼2900 kJ/mol from ∼817° to ∼825°C and ∼890 kj/mol from ∼825° to ∼837°C. A temperature-time-transformation diagram was constructed based on the kinetic data; it describes the transformational behavior of this particular system. |
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