AN ALTERNATE FUSED ELECTROLYTE/SOLVENT SUITED TO THE SOFC-TYPE ANODE FOR ELECTRO WINNING ALUMINUM

摘要

Unlike cryolite-base melts where the acid-base range is greatly restricted by the formation of complex oxyfluoride anions, oxides dissolve in fused sodium sulfate melts to form simple cations and oxyanions, and such melts enjoy a wide acid-base range. Extensive previous measurements of oxide solubilities in fused sodium sulfate at 1200K show that in a very basic melt (where NaAlO_2 becomes stable) the solubility of alumina is about 8 mol %, while those for zirconia and yttria are very much lower. Therefore, at a temperature suited to use the YSZ electrolyte, the chemical compatibility required for the SOFC-type inert anode should be satisfied. However, liquid Al is not compatible with fused sodium sulfate, but should react to form a sodium-aluminum sulfide phase. A preliminary experiment indicated very slow reaction between Al and sodium sulfate. The YSZ electrolyte is known to support oxide ion titration under such melt conditions. Therefore, the application of a SOFC-type inert anode might be realized upon a change in the solvent for alumina to sodium sulfate. Novel modular vertical anode geometries are suggested.