Segregation and removal of transition metal impurities during the directional solidification refining of silicon with Al-Si solvent

Segregation behavior of transition metal impurities (Fe and Ti) during the Al–Si solvent refining of silicon was investigated. A directional solidification with induction heating was employed to agglomerate Si crystals and simultaneously to enhance elimination of impurities. The inductively coupled plasma optical emission spectrometry (ICP-OES) results show that the concentration of transition metal impurities increased gradually from bottom to top of the sample during solidification. The morphology of iron-containing intermetallics has undergone a transformation from plate β-Al5FeSi to script α-Al8Fe2Si and needle-like Al–Fe–Si, while that of titanium-containing intermetallics maintained as plate TiSi2. The acid leaching results demonstrate that an aqua regia was effective to remove the iron-containing phases embedded in Si enrichment zone, while a hydrofluoric acid (HF) should be more efficient to eliminate titanium-containing phases. Therefore, it suggests that a combination of aqua regia and HF could be employed to efficiently remove transition metal impurities during Al–Si solvent refining.