Reaction Behavior of Stratified SiO2 Granules during Electrochemical Reduction in Molten CaCl2

Abstract

The electrochemical reduction behavior of stratified SiO 2 granules in molten CaCl 2 at 1123 K (850℃) was investigated to develop a new process for producing solar-grade silicon. The cross sections of the electrolyzed electrode prepared from a graphite crucible filled with SiO 2 granules were observed and analyzed. The visual and SEM observations indicate that the overall reduction proceeds via two different routes. In one route, the reduction proceeds along the granule surfaces from the SiO 2 near the conductor to the distant SiO 2. In the other route, the reduction proceeds from the granule surface to the core of each granule. The reduction along the granule surfaces is faster than that from the surface to the core. Fine SiO 2 granules are expected to be favorable for a high reduction rate.

High purity silicon materials prepared through wet-chemical and electrochemical approaches

“…In order to evaluate potential throughput of the process, we investigated the kinetic characteristics of the reduction process [22,23]. For this purpose, we used a small electrode consisted of a graphite crucible and an alumina tube [22] because it is convenient to conduct many experiments varying parameters, e.g.…”

“…For this purpose, we used a small electrode consisted of a graphite crucible and an alumina tube [22] because it is convenient to conduct many experiments varying parameters, e.g. diameter of SiO 2 granules, electrolysis potential and time.…”

“…From the crosssectional observation of the electrodes, it was shown that the reaction proceeded continuously from the surface of the SiO 2 granules to the inside of the granules. It was also found that the smaller diameter of SiO 2 granules is favorable to proceed the reaction effectively [22]. The time dependence of the reduction rate was investigated by measuring the weight change of the samples.…”

Electrochemical preparation of silicon nanowires from porous NiO/SiO2 blocks in molten CaCl2

“…Preparation of solar-grade silicon by the electrochemical reduction of solid SiO 2 in molten CaCl 2 has been studied for many years [11][12][13][14]. The electrochemical reduction process of SiO 2 to Si was proposed to proceed through the dynamic conductor/insulator/electrolyte three-phase interline mechanism [15].…”

Electrodeposition of Continuous Silicon Coatings from the KF-KCl-K2SiF6Melts

“…A common disadvantage of the silicon layers obtained with this technique is their high porosity. In most cases 1,3,4 silicon of the required quality cannot be obtained. Moreover, its subsequent processing is expensive.…”