Correlation Between Corrosion Rate and Electrochemical Parameters of Anode Process on the Metallic Electrode in Molten Oxyfluorides

Using metallic anodes enables oxygen evolution during the aluminum reduction in electrolysis cells with vertical electrodes. Although they are considered non-consumable compared to carbon ones, they tend to corrode in molten fluoride media, and the corrosion products end up in aluminum as impurities. The big challenge for the industry is finding the best conditions (anode and bath composition, temperature, and current density) that provide the lowest corrosion rate. The most reliable way to characterize the corrosion rate is to perform an electrolysis test and determine the mass of anode components in the produced aluminum. This method is highly time- and resource-demanding. This paper investigates the connection between the electrochemical parameters of the anode process, which can be measured in minutes, and the results of long-term electrolysis tests. Several parameters, such as exchange current density on clean and oxidized surfaces, were studied in the low-temperature KF-NaF-AlF₃-Al₂O₃ melt at 800 °C. A linear dependency between exchange currents and corrosion rate was found.