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.