Electrolytic deposition of silicon and of silicon alloys Part II: Decomposition voltages of components and current efficiency in the electrolysis of the Na₃AlF₆-Al₂O₃-SiO₂mixtures

Process for Solar Grade Silicon Production by Molten Salt Electrolysis Using Aluminum-Silicon Liquid Alloy

“…whose G 0 is À146 kJ at 1300 K. 8 Table II also shows that a part of the Al was lost by reaction(s) other than reaction 4 during the experiment. That is, the actual Al loss was 8.1 g, while the Al loss due to reaction 4 was calculated to be 6.8 g even if all the Si was formed by reaction 4.…”

“…Preliminary electrolysis.-Electrolysis of SiO 2 containing the NaF-AlF 3 melt using an Al cathode and carbon anode was reported by Bøe et al 8 During their electrolysis, however, a SiO 2 tube was employed as the lining of a carbon crucible used as the container and electric lead for the Al electrode. As Nohira et al reported, 14 SiO 2 can be electrochemically reduced to Si in a CaCl 2 melt, and there is a certain possibility that a similar reaction also takes place in the present melt.…”

“…Si þ SiðIVÞ <¼> 2SiðIIÞ [8] In addition, SiO 2 might react with the melt components to become SiF 4 , as will be mentioned later. Thus, in order to confirm the behavior of the Si species in the melt, (a) 2 g of the Si lump, (b) 2 g of the Si lump and 2.3 g of SiO 2 , or (c) 2.3 g of SiO 2 was added to 17 g of the NaF-AlF 3 melt at CR ¼ 3 and maintained at around 1273 K for 3 h. Although the amount of added SiO 2 exceeded the solubility in the melt, the present condition was selected to maintain a sufficient SiO 2 concentration even if a considerable amount of SiO 2 was consumed by any of the reactions.…”

“…1 Although the aims are different from the present paper and some problems were found as will be mentioned later, Si electrodeposition using an alloy cathode was examined by other researchers and was confirmed to be essentially possible. 1,8,9 The present authors now propose a new production process for SOG-Si using molten salt electrolysis and a liquid alloy as schematically shown in Fig. 1; (a) high purity SiO 2 is added to a molten salt and electrolyzed using an Al-Si liquid alloy cathode and carbon anode, (b) the Al-Si liquid alloy having a high Si concentration is taken from the electrolytic cell and Si is obtained by precipitation or other techniques, and (c) the remaining Al-Si liquid alloy is reused as the cathode in the first step.…”

Electrochemical Production of Al-Si Alloys in Cryolitic Melts in a Laboratory Cell

“…The observed decomposition voltage of alumina was 1.25-1.45 V, which was in agreement with the values reported in, 8 when cryolitic melts saturated with alumina at 1000 °C were tested using either aluminium or aluminium-silicon alloy(12.5 wt.% Si) as a cathode. 6 When copper was used as a cathode, the decomposition voltage of alumina was 1.50 V at 1030 °C. 7 It has been reported that the decomposition potential of silica calculated based on Nernst's equation to be −1.75 V at 1040 °C.…”