A Study on the Processing Variables of the BSCCO-2212 Bulk Superconductors

Bi-2212/SrSO₄ bulk superconductors were fabricated using a casting process, and the effects of the powder mixing method, annealing temperature, and SrSO₄ content on the texture, microstructure, and critical properties were evaluated. The Bi-2212 powders were mixed with SrSO₄ either by hand-mixing (HM) or planetary ball milling (PBM), followed by melting at 1100degC-1200degC, solidification, and annealing. The rod produced by PBM had a more homogeneous microstructure and smaller grain size of SrSO₄ and minor phases, resulting in increased I_c, than the rod made by HM. The I_c of the rod was also dependent on the annealing temperature with the highest I_c of 200 A being obtained at an annealing temperature of 810degC. This was attributed to the moderate density and 2212 texture as well as the smaller and less minor phase than that observed at higher temperature. In addition, the optimum SrSO₄ content was found to be 6 wt.% for an increased I_c. SEM, EPMA, and DTA analyses indicated that the differences in microstructural evolution caused the variations of the I_c with the powder mixing method, annealing temperature, and SrSO₄ addition.