Trapped Field Properties of MgB$_{2}$ Bulks Prepared Via an in-situ Infiltration-Reaction Process Using Refined Boron Powders

An infiltration-reaction (IR) method can fabricate a dense MgB
$_{2}$
bulk under ambient pressure, thus being a promising method for mass production. However, the IR-processed MgB
$_{2}$
bulks are known to contain the unreacted Mg and B and the intermediate product, Mg
$_{2}$
B
$_{25}$
, which degrades the trapped field,
$B_\mathrm{T}$
, and critical current density,
$J_\mathrm{c}$
, of the bulks. To expedite the creation of the MgB
$_{2}$
phase during the IR process, we prepared the refined B powder by ball-milling and fabricated the MgB
$_{2}$
bulks by the IR method. We achieved both improved
$B_\mathrm{T}$
and
$J_\mathrm{c}$
for the MgB
$_{2}$
bulks made from the ball-milled B powders with sub-micron size. The microstructural analysis suggested that these results originated from the refinement of MgB
$_{2}$
grains and the increase of the volume fraction of MgB
$_{2}$
phase. The refinement of the starting B powder is quite effective to enhance the magnetic properties for the IR-processed MgB
$_{2}$
bulks.