Phase separation of a microsized powder mixture of Si and SiC by Cu-Si alloying

In this paper, a novel Cu-Si alloying method has been studied to separate Si from a microsized Si and SiC powder mixture based on the difference in the melting point and density between solid SiC powders and a liquid Cu-Si alloy. The principle of this method is that Si and Cu powders selectively melt to form a liquid phase at a certain temperature, while SiC powders remain in a solid phase and flow up to the surface due to its lower density relative to the liquid Cu-Si phase. Effects of Si/SiC ratios and Cu fractions in the mixture on separation efficiencies of Si were investigated. For Si/SiC mixtures with an 80 wt% ( and above) Si, the highest separation efficiency was achieved when the mass ratio of Cu to Si was between 5 and 9. Under these conditions, a solid Cu-Si alloy ingot and up-floated green SiC powders were obtained. The microstructure of alloy ingots comprised of a predominant Cu3Si phase and a scattered pure Si phase. There were not SiC inclusions in the ingot and the carbon content was only 102 ppmw. The recovery ratio of Si was about 90%. The Cu-Si alloying method can separate Si from SiC/Si mixtures effectively, and is a potential approach to recycle Si from cutting slurries in the photovoltaic industry.