High-energy ball milling and synthesi temperature study to improve   superconducting properties of MgB2 ex-situ tapes and wires
  MgB2 monofilamentary nickel-sheated tapes and wires were fabricated by means of the ex-situ powder-in-tube method using either high-energy ball milled and low temperature synthesized powders. All sample were sintered at 920 C in Ar flow. The milling time and the revolution speed were tuned in order to maximize the critical current density in field (Jc): the maximum Jc value of 6 x 10e4 A/cm2 at 5 K and 4 T was obtained corresponding to the tape prepared with powders milled for 144h at 180rpm. Vorious synthesis temperature were also investigated (730-900 C) finding a best Jc value for the wire prepared with powders synthesized at 745 C. We speculate that this optimal temperature is due to the fluidifying effect of unreacted magnesium content before the sintering process which could better connect the grains. 
Gennaro Romano, Maurizio Vignolo, Valeria Braccini, Cristina Bernini,   Andrea Malagoli, Matteo Tropeano, Carlo Fanciulli, M...