Refinement and carbon incorporation effects on the superconducting properties of MgB2 through wet milling process of low purity boron powder

► Wet milling effects of B powder on the superconducting properties were investigated. ► The C substitution for the B site in MgB2 occurred due to a toluene medium. ► A shift of MgB2 peaks in XRD and a variation of Jc-B slopes proved C incorporation. ► The B particle size reduction could induce a small grain size in the MgB2 formation. ► Jc and Hc2 were enhanced by increased grain boundary pinning and lattice disorder.