Containerless solidification of germanium by electromagnetic levitation and in a drop-tube

Containerless solidification of germanium has been realized by electromagnetic levitation and drop-tube processing, respectively. The effect of undercooling in the range of 40-426 K on the as-solidified structures of levitation melted Ge drops (similar to 8.4 mm diameter) was investigated. For undercoolings less than 300 K, the lamellar twins were grown, whereas a microstructural transition to equiaxed grains was observed at undercoolings greater than or equal to 300 K. Further increasing the undercooling to 400 K, a significant reduction in grain size was achieved. In addition to a similar microstructural development among the particles solidified during free fall in a 8.5 m drop-tube, high-undercooling-induced single crystals were found for some droplets less than 200 mu m in diameter. The results on the transition from twins to fine equiaxed grains are accounted for by theories of solidification kinetics and a dendrite break-up model.