Study on hole formation during sintering reaction for Mg-B system

The MgB₂ bulks were prepared using the spherical and scrap-like magnesium powders with the same purity (99.9%) and grain size (< 45 μm) as raw materials. The two kinds of magnesium powder were mixed with amorphous boron powder with a nominal stoichiometry of MgB₂, then pressed into pellets under a pressure of 10 MPa, and sintered at 650°C, 700°C, 750°C and 800°C, respectively. The characteristics of holes for the sintered samples were described by using the immerged medium method. The results indicate that the porosities in the two kinds of MgB₂ samples are similar. Their porosities increase with the increase of sintering temperature. The scanning electron microscope observation shows that the shapes and sizes of holes in sintered sample are associated with those of the raw Mg powder. Finally, the reason of hole formation for the Mg-B system during sintering process was analyzed based on the reaction model of Mg-B system.