Tin dioxide-based ceramics as inert anodes for aluminium smelting: a laboratory study

Abstract

The behaviour of tin dioxide-based ceramics as inert anodes was examined in a laboratory-scale aluminium smelting cell over a range of electrolyte compositions with operating temperatures between 830 - 975°C. Anodes of a nominal composition SnO 2 (96 wt%), Sb 2O 3 (2 wt%) and CuO (2 wt%), were electrolyzed for 90 min at a current density of approx. 1 A cm -2. The corrosion rate was determined from the tin and copper concentrations in the recovered electrolyte, aluminium metal and the fume. The corrosion rates were 12.5, 1.6 and 6.5 mg (Ah) -1 in electrolytes with bath ratios 1.5 (975°C), 0.89 (903°C) and 0.74 (830°C), respectively. A four-fold increase in corrosion rate was obtained at open-circuit demonstrating the protection provided by oxygen evolution during electrolysis. A preliminary investigation of the dependence of corrosion rate on firing temperatures and additive (Sb 2O 3 and CuO) concentrations was conducted using a part-factorial design experiment. Post-electrolysis examination of the anodes using scanning electron microscopy coupled with energy dispersive spectroscopy analysis revealed a depletion of copper from the anode and a build-up of an alumina-rich surface layer under certain conditions.