Abstract:
This study aims to explore the impact of sieving the crystalline boron precursor applied after its ball milling on the critical current density (Jc) of MgB2 produced by the in-situ reaction. Various analytical techniques, such as X-ray diffraction, magnetization measurements, and microstructure analysis were employed to systematically investigate the bulk polycrystalline MgB2 samples. SEM revealed that grains of ball-milled B powder had a nanoscale size. Sieving made the powder more uniform in size. The purity of the refined powder was tested using X-ray diffraction, and four different precursor combinations were evaluated. MgB2 bulk had a homogeneous, dense microstructure composed of MgB2 nanocrystals, in contrast to the bulk MgB2 prepared of as-purchased B. The latter exhibited uneven microstructure containing both crystalline and porous non-crystalline portions. The improved inter-grain connectivity and microstructural homogeneity after ball milling led to an increase of self-field Jc at 20 K from 71.2 kA/cm2 to 144.6 kA/cm2. After sieving the B precursor before and after ball milling, a further increase of Jc by 18% and 8% was achieved.
