Phase transformation in Bi-2223/AgMg alloyed PIT tapes during different sintering processing and its influence on critical current density
The effect of various sintering conditions on the phase transformation and critical current density of multifilament Bi-2223 PIT tapes with AgMg sheaths has been investigated. A two stage sintering process was used comprising a first (HT1) and second (HT2) heat treatment with an intermediate roll pass between each stage. The sintering atmosphere during each stage was a mixture of nitrogen and oxygen with a N/O percentage ratio of either 80/20% (in N80/020%) or 92.5/7.5% (in N92.5/07.5%). It was found that the conversion of 2212 precursor phase to 2223 was significantly influenced by the sintering atmosphere of HT1. Sintering in N80/020% tended to produce larger 2223 grains and a higher degree of texturing compared to sintering in N97.5/07.5%. The lower partial pressure of 0 promoted faster and more complete conversion of 2212 and smaller 2223 grain size, however, retained much more 2201 phase. It was observed that conditions of HT2 had less of an impact on the conversion of 2212 phase but influenced the proportion and size of secondary phases, specially influenced that of the lead-rich secondary phase. A possible explanation for the differences in phase transformation and the effect on the critical current was discussed. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.