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Abstract

The anodic polarization of a rotating cylindrical carbon anode in A1₂O₃-Na₃A1F₆ and A1₂O₃-Na₃A1F₆ and A1₂O₃-Na₃A1F₆-LiF electrolytes has been examined. The anodic polarization has been measured at temperatures of 840°C, 990°C., 1020°C. and 1040°C. and at 2 wt.% and 5 wt.% alumina concentrations. An expression has been derived to explain the experimental Tafel slopes of 0.07 ± 0.02 Volts found at the current densities of 0.2 - 1.0 A./cm.². The diffusion polarization has been estimated by measuring the polarization decreases found on rotating the anode at speeds up to 4900 r.p.m.. Diffusion polarization accounts for less than 10% of the total anodic polarization for anodic current densities less than 0.25 A./cm.². A semi-empirical expression has been derived for the diffusion-polarization as a function of the anodic current density and the alumina concentration for electrolytes operated at greater than 40°C above their liquidus temperatures.