Phase formation dynamics upon thermal explosion synthesis of magnesium diboride

Time-resolved X-ray diffraction was used to study the dynamics of phase formation in magnesium diboride produced by self-propagating high-temperature synthesis in the thermal explosion mode. The MgB2 phase was demonstrated to emerge without the formation of intermediate compounds. The effect of the mixture heating rate on the formation mechanism of the MgB2 phase was established. The presence of oxygen impurities has a significant impact on the kinetics and formation mechanism of MgB2. If the heating rate exceeds 150 °/min, the oxide coating is not formed around the magnesium particles, which results in the solid-phase reaction of Mg+2B=MgB2 through a reaction diffusion mechanism. Moreover, the self-ignition temperature of the mixture is lower than the melting point for magnesium. Mechanical activation of the mixture leads to variations in the kinetics of MgB2 formation, significantly increases the period of simultaneous existence of Mg and MgB2, and reduces the temperature at which the reaction occurs.