Optimization of Partial Melting Process for Bi-2212 Multi-Filament Wires

Bi-2212 precursor powder was synthesized by a co-precipitation process, and 19×(36+1) multi-filament wires were prepared by traditional powder in tube (PIT) process. Both the maximum melting temperature, Tmax and cooling rate, Rc1 have been optimized during partial melting process (PMP). The texture structures of Bi-2212 grains and secondary phase distributions were observed with the scanning electron microscopy. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) were used to evaluate the thermodynamic properties of Bi-2212 wires. The phase transition process during cooling was discussed based on the analysis of both microstructure evolution and the thermodynamic investigation. It can be concluded that both Tmax and Rc1 have great influences on the distribution of pores and secondary phase, such as alkali earth cuprate (AEC). The optimized critical current density of ∼4400 A·cm−2 at 77 K and self field can be obtained with the Tmax of 892 °C and a two-step cooling process at the Rc1 of 40 °C/h.