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TITLE: Zero-Direct Emission Silicon Production Via Solid Oxide Membrane Electrolysis

ABSTRACT: Currently industrial processes to produce silicon occur in batch units that are energy intensive, capital intensive, and capable of emitting harmful pollutants into the atmosphere. A new technology, solid oxide membrane (SOM) processing, seeks to produce silicon without direct emissions and with lower energy and capital costs. Previous studies have shown that this technology can produce silicon; however, the proof-of-concept cell was incapable of producing large volumes of silicon due to restrictions in the molten salt.

Current research has engineered an oxyfluoride molten salt to be more efficient in four main ways: a higher amount of silica in the molten salt, a chemistry stable with the yttria-stabilized zirconia (YSZ) membrane, a low volatility, and a high electrical conductivity. A capillary experiment found that the solubility of silica in the oxyfluoride melt was very high, matching slag phase diagrams. Two other experiments found that the volatility of the oxyfluoride salt was low while not attacking the YSZ membrane when optical basicity values matched up between the salt and the YSZ. Due to the fluoride base of the salt and the high temperature experiments, the salt was also found to have a high conductivity at 1050C (2.62 to 3.20 S/cm). Combining thesei mprovements in the salt with pre-existing techniques, silicon crystals were produced in the new SOM cell.

COMMITTEE: Advisor: Uday Pal, MSE/ME; Soumendra N. Basu, MSE/ME; Srikanth Gopalan, MSE/ME; Vinod Sarin, MSE/ME