Carbon Thermal Reduction Experimental Study Of Disproportionation Preparation Of High Quality Silicon

At present, there are many companies and universities which are researching a new way to get solar grade silicon by metallurgical technology. In spite of these new techniques have many differences, physical or chemical characters of silicon are used in the metallurgy process. Purification aim can be achieved by direction solidification, vacuum distillation at high temperature, oxidizing impurities, carbothermic reduction and so on.Process route in this study is shown as follow. Experimental equipment is self-designed intermediate frequency induction furnace. Pretreated silica wastes and charcoal wastes are used as raw material. High purity SiO gas can be formed by carbothermic reduction at high temperature, and SiO gas will be disproported into high purity silicon and silicon dioxide in the self-designed high purity graphite crucible when temperature go down, then solar grade silicon can be achieved after separating silicon dioxide in HF acid and directional solidification in vacuum.In this paper micromechanism and generation mechanism of the sample prepared by carbothermic reduction and disproportionation method are studied by scanning electron microscope(SEM). Phase composition of the sample is studied by X-Ray diffraction instrument(XRD) and raman spectrum instrument. Purity of the sample are studied by inductive coupled plasma spectrometer(ICP).From the study we can get the following results:(1) Sample prepared by disproportionation method is made up of nanowires and nanospheres whose diameter from 100 nanometer to 600 nanometer, and nanowires and nanospheres are made up of silicon and silicon dioxide which locate on the surface of the silicon, as a result silicon dioxide can be absolutely removed by acid leaching; (2) Silicon dioxide and B element can be absolutely removed by acid leaching,and has bad effect on removing P, Fe,Al element. B element absolutely removing mechanism is analysed;(3) Impurities such as B, P, Fe, Al content in the high purity silicon by carbothermic reduction and disproportionation method is lower than the raw materials, especially B content in the production is close to 0 ppmw. If raw material has high purity, then the production has higher purity.