PREPARATION OF HIGH PURITY SILICON BY ELECTROLYSIS-VACUUM DISTILLATION

Solar energy is the most abundant renewable resource and polysilicon is the major raw materials for fabricating solar cell. The preparation of polysilicon by metallurgical technique will reduce production costs significantly. In this paper, Mg-Zn-Si alloys were prepared by electrolysis that employs high purity graphite as anode, the rolling Mg-Zn alloys in magnetic field as cathode and high purity silicon dioxide as raw material in fused salt system. Then high purity silicon obtained then was separated from Mg-Zn-Si alloys by vacuum distillation. We used DD-A testing device of molten salt electrolysis and teslameter to measure parameter, such as current density, cell voltage, back electromotive force and magnetic field strength. We have studied the electromagnetic stirring effect on cathode alloy reaction, the change of back electromotive force, and current efficiency and silicon concentration in details. Finally, at 1000 degrees C, magnetic field intensity 28mT, the silicon content of 35.7% (mass fraction) in Mg-Zn-Si alloy was obtained by electrolyzing in the current density of 0.56A. cm(-2) for 4h. At 1050 degrees C, the high purity silicon of 99.98% was obtained by vacuum distillation for 3h.