Experimental Study on Phase Transformation Between MgB ₂ and MgB ₄

Abstract

Using X‐ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we have investigated the reaction between MgB 4 and Mg in its solid, liquid, and gas physical states. The XRD results indicate that the reaction of MgB 4 +Mg=2MgB 2 always occurs independently of the different states of Mg. DSC measurements show that the solid–solid reaction MgB 4 ( s )+Mg( s )=2MgB 2 ( s ), the Mg melting Mg( s )→Mg( l ), and the Mg volatilization occur in turn with increasing temperature for mixed (MgB 4 +Mg) powder with a nominal stoichiometry of MgB 2 . SEM observations indicate that the resulting synthesized MgB 2 samples, obtained from the MgB 4 +Mg mixtures, have a denser microstructure than those obtained directly from Mg+B mixtures. On the basis of XRD, DSC, and SEM results, a kinetic model for the reaction between MgB 4 and Mg is proposed.