High-Energy Ball Milling and Synthesis Temperature Study to Improve Superconducting Properties of ${\rm MgB}_{2}$ Ex-situ Tapes and Wires

MgB
₂
monofilamentary nickel-sheathed 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. In the first part of the paper it will be shown the effect of milling on tapes realized with powders synthesized at 900degC. The milling time and the milling revolution speed were tuned in order to maximize the critical current density (J
_c
) in field: the maximum J
_c
value of 6times10
⁴
A/cm
²
at 5 K and 4 T was obtained for the tape prepared with powders milled for 144 h at 180 rpm. In the second part of the paper we study the effect of the powders synthesis temperature in a wire configuration. Various synthesis temperature were investigated (730degC-900degC) finding a best J
_c
value for the wire prepared with powders synthesized at 745degC. 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.