熔盐电精炼硅制备多晶硅的NaF-KCl熔盐净化及净化作用

Pre-electrolysis purification of NaF-KCl electrolyte and influence for purification

采用预电解净化方法,研究了温度、电压、时间等对NaF-KCl熔盐净化的影响,结果发现温度800℃,预电解电压2.5V,预电解时间4h为熔盐净化合适条件.采用四电极法测量了800℃,净化前后NaF-KCl混合熔盐的电导率,计算了活化能,结果发现熔盐净化后电导率提高.进行了恒电位电精炼法制备多晶硅,采用XRD,SEM,EDS和ICP-ms对熔盐净化前后获得的多晶硅进行了表征,发现熔盐净化使多晶硅产品纯度明显改善,纯度达到99.99%.

Pre-electrolysis purification of electrolyte has great significance for high pure solar grade silicon. Influence of pre-electrolytic parameters, such as temperature, electrolytic voltage and time are studied. The optimized pre-electrolysis conditions are identified as：temperature is at 800 ℃, electrolytic voltage is at 2.5 V,and time is for 4 h. Electrical conductivity and activation energy of molten NaF- KCl salt electrolyte are studied by theoretical analysis and experimental verification at 800 ℃. The composition,morphology and components of the solar grade silicon after electrorefining are analysised by means of X ray diffraction, scanning electron microscopy, spectroscopy and ICP-ms. The results show that,electrical conductivity of NaF-KCl salt is increased after pre-electrolysis purification. The purity of refined solar grade silicon is 99.99 %.