Na_3AlF_6-LiF熔盐体系中硅的电沉积行为

Electrodeposition Behavior of Silicon from Na_3AlF_6-LiF Melts

研究了Na3AlF6-LiF体系中硅沉积的电化学行为及影响因素,并分别采用电解沉积和电解精炼方法获得了单质硅.结果表明:Si(IV)的电化学还原过程分步进行,在有单质硅存在的情况下,还发生反应Si(IV)+Si=2Si(II);一般情况下Al的析出电位比Si要负,但在电极表面Si离子匮乏的情况下,Al会与Si共沉积;固态电极上恒流电解沉积硅呈颗粒状并与电解质夹杂,通过分离可以获得单质硅,所获硅纯度高于99.9%.电解精炼在大电流密度条件下可以稳定进行,阳极电流效率高于95%,电解精炼硅纯度比直接电沉积硅纯度有明显提高.

A fundamental electrochemical study of Si in Na3AlF6-LiF melts and electrowinning and electrorefining in a small-scale laboratory cell was conducted. Cyclic voltammograms showed that the reduction of Si proceeds by two successive electron transfers and the presence of the Si（II） species in the melt was confirmed. Galvanostatic electrolysis showed that the deposited silicon crystal does not form any dense or massive layer at the graphite cathode as other metals do, but it is generally dispersed in the deposit around the cathode. The co-deposition of Al and Si is possible when the reduction potentials are more negative than-1.8 V versus Pt. The purity of the deposited Si was higher than 99.9%. This study demonstrates the feasibility of very pure Si production by electrochemical methods.