Preparation of (Bi, Pb)-2223/Ag tapes by high temperature sintering and post-annealing process

A novel heat treatment process was developed to fabricate (Bi, Pb)-2223/Ag tapes with high critical current density (J(c)). The process can be divided into two parts: reformation and post-annealing. Tapes were first heated to the maximum temperature (830-860 degreesC) followed by slow cooling (reformation).

Then, tape, were annealed between 760 and 820 degreesC (post-annealing). Reformation is expected to produce a large amount of liquid phase which may heat microcracks, decrease porosity, and improve grain growth. However, since the sintering temperature is beyond the Bi-2223 single-phase region, much Bi-2212 and secondary phases will appear at the Bi-2223 brain boundaries.

During post-annealing. these phases may convert to (Bi, Pb)-2212 and even to Bi-2223. Hence, the J(c) values for these tapes are significantly improved. The microstructure and the phase composition were investigated by high-energy synchrotron XRD and SEM/EDX. Some process parameters e.g. sintering temperature. cooling rate. and post-annealing time were optimised. (C) 2002 Elsevier Science B.V.

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