Kinetics analysis for the sintering of bulk MgB2 superconductor

The pertaining kinetic characteristics during the sintering of bulk polycrystalline MgB2 superconductors is essentially important for the improvement of properties. Here Differential Thermal Analysis was adopted to record the heat effect during the preparation of bulk MgB2 samples. The reaction between Mg and B powders starts before the melting point of pure Mg and the evolution for the fractions of MgB2 were determined as a function of sintering temperatures. After fitting with different kinetic mechanism functions assumed, the sintering process of bulk MgB2 superconductors was attributed to a solid-state interface-reaction controlled mechanism with an apparent activation energy of 4.54 x 10(5) J mol(-1). Combined with microstructural observations by scanning electron microscopy and phase identification by X-ray diffraction, the formation process of MgB2 phase was classified into two different stages: (i) solid-solid reaction stage, in which Mg and B powder starts to react and the growth of MgB2 grain is restricted by the pinning effects of pores; (ii) solid-liquid reaction stage, in which the molten Mg melt promotes the reaction process and the regular hexagon bulk MgB2 grain forms in a solution-reprecipitation and growth mode.