熔盐电解法制备硅纳米线的过程机理

Process Mechanism of Silicon Nanowires Preparation by Electrolytic Method in Molten Salt

采用FESEM、XRD和EDS分析了纳米二氧化硅烧结片在900℃的CaCl2熔盐中浸泡后结构和组成的变化,结果表明,由于纳米尺寸效应和CaCl2熔盐对二氧化硅的熔融(软化)具有助熔作用,纳米二氧化硅烧结片在900℃的CaCl2熔盐中由固态转变为熔融或半熔融态。根据对900℃的CaCl2熔盐中-1.2V恒电位电解不同时间电极片上反应区的结构和组成分析结果,提出了纳米二氧化硅电极片的硅/熔融二氧化硅/熔盐三相界面沿极片径向方向均匀推进的电解还原过程。通过对900℃的CaCl2熔盐中-1.2V恒电位电解5和15min电解产物的形貌、结构和成份分析,提出了硅纳米线在熔盐中的电化学成核与生长机理。

The structure and composition of the sintered pellet and the pellet immersed in molten CaCl2 at 900 ℃ were characterized by FESEM,XRD and EDS.The results show that the sintered pellet has a usual porous morphology.On the other hand,the pellet immersed in molten CaCl2 at 900 ℃ demonstrates a network structure.The network pellet remains amorphous SiO2 as indicated by XRD and EDS.The softening or melting temperature of nanometer silica is expected to be much lower than that of bulk silica.Furthermore,the CaCl2 as a fluxing agent can lower the softening or melting temperature of silica.Therefore,it is suggested that the network structure after immersing is formed through partially softening or melting process of nano-SiO2 in molten CaCl2 at 900 ℃.The structure and composition of the product obtained by electrolysis at-1.20 V for different time in molten CaCl2 at 900 ℃ were analyzed as well.The reduction process of silica pellet is explained by the model of the propagation of the Si/melted SiO2/CaCl2 three-phase interlines.The silicon nanowire electrochemical nucleation and growth mechanism is proposed.