Reaction mechanism of self-propagating magnesiothermic reduction of ZrB2 powders

Abstract

Fine zirconium diboride (ZrB2) powders with high purity were successfully prepared by combustion synthesis through magnesiothermic reduction process in Mg–B2O3–ZrO2 system. The reaction mechanism was investigated by differential thermal analysis and quenching experiment. The results show that the whole magnesiothermic reduction process includes three stages: first, molten B2O3 and Mg formed above the temperature of 650 °C, and glassy B2O3 and solid ZrO2 particles were coated on the surface of the molten Mg; thus, the hollow balls can be formed when the molten Mg was exuded under capillary function. Second, ZrO2 particles reacted with molten Mg to form Zr and MgO with dissolution–precipitation mechanism, which released a large amount of heat to induce the diffusion reaction between B2O3 and Mg to form B and MgO. Last, Zr reacted with B to form ZrB2 grains. The preparation of ZrB2 by self-propagating synthesis in Mg–B2O3–ZrO2 system is a solid–liquid-liquid reaction.