The performance of SnO 2 ceramic anodes doped with copper and antimony oxides was examined in cryolite alumina melts under anodic polarization at different cryolite ratios, temperatures, times, and current densities. The corroded part consists of a narrow strong corrosion zone at the anode surface with damage of the intergrain contacts and a large increase in porosity, a wider moderate corrosion zone with a smaller porosity increase, and a Cu depletion zone, where the ceramic retains its

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... microstructure and a slight porosity increase occurs due to the removal of the Cu-rich inclusions. Mechanical destruction of the anode was never observed in the 10-100 h tests. A microstructural model of the ceramic was suggested, consisting of grains with an Sb-doped SnO 2 grain core surrounded by an ϳ200 to 500 nm grain shell where SnO 2 was simultaneously doped with Sb and M n+ ͑M = Cu 2+ ,Fe 3+ ,Al 3+ ͒. The grains were separated by a few nanometers thick Cu-enriched grain boundaries. Different secondary charge carrier ͑holes͒ concentrations and electric conductivities in the grain core and grain shell result in a higher current density at the intergrain regions that leads to their profound degradation, especially in the low temperature acidic melt.