Purification of metallurgical-grade silicon in fractional melting process

The fractional melting process involves heating an alloy within its liquid–solid region, while simultaneously ejecting liquid from the solid–liquid mixture (the cake). The extent of purification obtained is comparable to that obtained in multi-pass zone refining. A new fractional melting process, in which the centrifugal force is used for separating the liquid from the cake, was developed and applied to the purification of metallurgical grade Si (MG-Si). The major impurities in MG-Si such as Fe, Ti, Al, and Cu can significantly degrade the efficiency of solar cells. So it is important to remove these metal elements from MG-Si to obtain high-quality silicon. Since these elements have low segregation coefficients in silicon, high purification is possible through the fractional melting process. By applying the fractional melting method, a mean refining ratio of 93% with a wetness of 0.038 was achieved during the refining of 2N-Si. A further increase in the refining ratio can be realized by either controlling the processing parameters or reducing the solid fraction.