Aluminium electrolysis experiments have been carried out in a fluoride electrolyte with higher density than that of liquid aluminium, whereby the metal produced floated on top of the electrolyte. The composition in weight-% was: NaF: 18, AlF_3: 48, CaF_2:16 and BaF_2:18. The "slurry cell" concept was adopted by adding excess alumina, which was kept in suspension by the gas-induced convection created by an inert anode well immersed into the electrolyte. No special problems were encountered when platinum anodes and TiB_2 cathodes were used. Current efficiencies in the range of 80-90% were achieved, which is comparable to the current efficiency typical for laboratory experiments with Hall-Heroult electrolyte in cells of similar size as in this experiment. Tin oxide anodes that were tried in some cases underwent catastrophic corrosion. This is probably related to the relatively low solubility of alumina in this electrolyte, giving rise to a limiting current condition at the anode. By optimizing the electrolyte composition with respect to increased alumina solubility it is assumed that this problem can be alleviated.
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