Macro-Micro-Coupling Simulation and Space Experiment Study on Zone Melting Process of Bismuth Telluride-Based Crystal Materials

Zone melting is one of the main techniques for preparing bismuth telluride-based crystal thermoelectric materials. In this research, a macro-micro-coupled simulation model was established to analyze the distribution of temperature and heat flow during the zone melting process. The simulation results show the melting temperature tends to affect the length of the melting zone, while the moving velocity of the melting furnace tends to affect the curvature of the melting and solidification interface. There are two small plateaus observed in the temperature curve of the central axis of bismuth telluride ingot when the moving velocity of the heat source is higher than 20 mm/h. As the moving velocity of the heat source increases, the platform effect is becoming more obvious. Based on the simulation results, the zone melt experiments were carried out both under microgravity condition on the Tiangong II space laboratory and conventional gravity condition on the ground. The experimental results indicate that the bismuth telluride-based crystal prepared in microgravity tends to possess more uniform composition. This uniform composition will lead to more uniform thermoelectric performance for telluride-based crystals. In the space condition, the influence of surface tension is much higher than that of gravity. The bismuth telluride ingot is very vulnerable to the influence of surface tension on the surface morphology during the solidification process. If the solidification process is not well controlled, it will be easier to produce uneven surface morphology