A new method to substantially reduce the processing time of Ag/Bi-2223 tapes

Multi-stage thermal cycling is commonly used in the processing of Ag/Bi-2223 tapes requiring a total annealing time often in excess of 100 h, which is very undesirable for large-scale production. A new process was investigated that reduced the heat treatment time for Ag/Bi-2223 tapes. In this process, the tape was quenched at the end of the Ist thermal cycle. Following either pressing or rolling, it was rapidly heated to the sintering temperature. In doing so, the usual decomposition and recovery of Bi-2223 during cooling and heating was eliminated, along with a reduced formation time for Bi-2223. By using this new procedure, the zero-field J(c) and the Bi-2223 volume fraction in tapes sintered for a total time of 20-30 h were comparable to those treated for 100 h using a conventional process. The results further confirm that a low-temperature annealing at 825 degrees C in the end of the last thermal cycle eliminates residual 2201, hence improving J(c). It was also found out that tapes containing a large number of filaments had a higher Bi-2223 volume fraction and exhibited a better J(c) vs. H performance, than for tapes with a small number of filaments, when both were processed for the same time period. (C) 1998 Elsevier Science B.V. All rights reserved.