CHEMICAL-REACTIONS AND TRANSPORT CURRENT IN THE BI2223 PHASE

To get high transport capacities in magnetic field with Ag sheathed co nductors, the Bi2223 phase must be free of residual phases, well-cryst allized, the lamellas being parallel with the current lines and very d ense. In a research context on multifilamentary conductor (1), a preli minary study has been done on bulk material (1 x 4 x 40 mm3 bars) to o ptimize the frabrication parameters of the multifilamentary tapes. A l ot of samples, corresponding to the different operating conditions hav e been electrically characterized and analyzed by EDS so as to get som e correlations between microstructure and superconducting performances : determination, concentration and repartition of residual phases, cry stallinity, orientation and compacity of the Bi2223 phase. We also exa mined the interactions between the ''refractory phases'', (Ca, Sr)2CuO 3; (Ca, Sr) CuO2; CuO and the liquid phase, Bi2212 enriched with Bi an d Sr + (Ca, Sr)2PbO4 which promote the recombination into pure and wel l recristallized Bi2223 phase. Maximum transport current capacities at 77 K-O T were 11 A/mm2 for a commercial powder and 17 A/mm2 (47 A) fo r a laboratory type powder, the values being around 50 A/mm2 for the c orresponding multifilamentary conductors.