Enhancement of Bi-2223 Intergrain Connections by Heat Treatment Parameters Optimization

Aiming at the improvement of current capacity in Bi
₂
Sr
₂
Ca
₂
Cu
₃
O
_10+δ
(Bi-2223) superconducting tapes, both the calcination process of precursor powders and the sintering process of Bi-2223 tapes have been modified to tune the intergrain connections. By adopting different calcination atmosphere of air and oxygen during the pre-calcination process, the phase composition of final precursor powder kept almost the same, while the particle size decreased in oxygen pre-calcinated powders, which thus led to the appearance of more secondary phases. On the other hand, due to the optimization of crystallization process of Bi-2223 phase, the microstructure with less pore density has been obtained, which proved that the increase of heating rate could obviously lead to the enhancement of intergrain connections of Bi-2223 tapes. Finally, critical current of 116 A has been achieved with the air pre-calcinated powders and 400 °C /h heating rate during HT2, which was ∼40% increase comparing with the
I
_c
of Bi-2223 tape with oxygen pre-calcinated powders and 100 °C/h heating rate in HT2 process.