Anodic degradation of beta″-alumina in contact with mercury

The anodic degradation of beta/beta" -alumina of different compositions was studied in cells of the type Cu/Rodar alloy/Hg /beta" - alumina/NaNO3/Pt/Cu at 350 C. Single voltage sweeps were applied from the open-circuit voltage to different voltages of reversal at relatively low sweep rates (mainly 0.1-1 mV/s). The current-voltage curves display an initial rise of current with voltage between about 2.8 and 3.5V, vs. a Na reference electrode, followed by a small change of the current at voltages to 4.0V. The anodic current is attributed to the formation of HgO at the interface Hg/solid electrolyte. The oxygen is supplied by the anodic degradation of the ceramic. The oxide is decomposed at a slow rate during the cathodic sweep. Structural studies were carried out by light microscopy, x-ray diffraction, and analytical electron microscopy at the end of the electrochemical runs. These investigations supplied confirming evidence for the chosen predominant reaction and yielded additional information on how the degradation proceeds from a structural point of view.