Superconducting properties of sintered bulk MgB2 prepared from hexane-mediated high-energy-ultra-sonicated boron

•Ultra-sonication is a cost effective novel technique to refine precursor boron powder.•MgB2 bulk made of boron ultra-sonicated in hexane showed refined grains.•Special Mg-B-O nano-grains and layers formed on pore surfaces.•MgB2 bulk prepared of boron ultra-sonicated for 30 min showed 20% Jc increment. Recently, novel low cost techniques have been employed to improve critical current density of MgB2. Ultra-sonication is one such technique. We report on the influence of hexane dispersant on particle size of ultra-sonicated cheap commercial boron and the superconducting properties of MgB2 bulks prepared using this new precursor. XRD showed major peaks corresponding to MgB2, with small fractions of MgO and unreacted Mg. Tc was close to 39 K, with a sharp transition. The highest Jc was found in the sample with boron ultra-sonicated for 30 min as high as 375, 328, and 270 kA/cm2 at 10, 15, and 20 K, respectively. SEM analysis revealed tiny particles and layers randomly dispersed in the microstructure, while EDX indicated that these particles were secondary phases of Mg, B, and O. Flux pinning diagrams showed the peak of normalized pinning force located close to b = 0.2, depicting dominance of grain boundary pinning mechanism.