Mushy-zone microstructure and concentration variation of Co-93wt.%Sb hyperperitectic alloy under TGZM effect

Skutterudite thermoelectric material, CoSb₃ is a peritectic compound, and the traditional preparation method needs several days to obtain single-phase CoSb₃ by annealing treatment. In this work, we employed temperature gradient zone melting (TGZM) to investigate the microstructure evolution of Co-93wt.%Sb alloy in mushy zone under different thermal stabilization time. Due to the existence of temperature gradient, two mushy zones between complete liquid phase region and solid phase region were observed. There exists a solute gradient across the mushy zone and the solute diffuses from the cold side to the hot side, inducing that the liquid droplet migrates up the temperature gradient. As the thermal stabilization time increases, the volume fraction of the liquid in mushy zone decreases, and the initial solid/liquid interface moves downwards paralleling to the temperature gradient. After 4h thermal stabilization time, the solute concentration is higher in liquid zone than the nominal alloy concentration, and lower in the mushy zone measured by Energy Dispersive Spectroscopy (EDS). By means of TGZM effect, the preparation time for the CoSb₃ thermoelectric materials was shortened remarkably.