Trapped Field Properties of MgB2 Bulks Prepared Via an in-situ Infiltration-Reaction Process Using Refined Boron Powders

An infiltration-reaction (IR) method can fabricate a dense MgB2 bulk under ambient pressure, thus being a promising method for mass production. However, the IR-processed MgB2 hulks are known to contain the unreacted Mg and B and the intermediate product, Mg2B25, which degrades the trapped field, B-T, and critical current density, J(c), of the bulks. To expedite the creation of the MgB2 phase during the IR process, we prepared the refined B powder by ball-milling and fabricated the MgB2 bulks by the IR method. We achieved both improved B-T and J(c) for the MgB2 bulks made from the ball-milled B powders with sub-micron size. The microstructural analysis suggested that these results originated from the refinement of MgB2 grains and the increase of the volume fraction of MgB2 phase. The refinement of the starting B powder is quite effective to enhance the magnetic properties for the IR-processed MgB2 bulks.