Effects of annealing time and size of BSCCO-2212 rods and tubes prepared by a casting process

We fabricated BSCCO-2212 (2212) rods using a casting process and evaluated the effects of annealing time and size to improve critical current (I_c). Diameters of rods were 1.0 cm and 1.6 cm and annealing was performed from 60 h to 200 h at 800 °C. The I_c of rods increased with increasing annealing time, probably due to increased grain size of 2212. Annealing time of the highest I_c for the smaller rod was shorter (150 h) than that of the larger rod (200 h). This size effect seems to be related to different grain sizes of the intermediate phases such as 2201 and secondary phases in the ingot. In addition, we successively fabricated 2212 tubes from the rod by making a hole in the center region which contained inhomogeneous microstructures. This method was simple and I_c did not significantly decrease. However, critical current density (J_c) improved when as much as 60% of the diameter in the center region was machined out of the rod.