Wear Testing of Inert Anodes for Magnesium Electrolyzers

Inert anodes are required in magnesium electrolysis cells because electrode dimensional stability is critical. Graphite is a good inert anode material because it does not react with the molten chloride salt electrolyte. However, during a cell’s life, there is a gradual wearing of the anodes, which increases cell resistance and hinders hydrodynamics. These changes eventually jeopardize the high metal output offered by these cells and, due to increased operational costs, ultimately limit the cell’s longevity. To investigate this phenomenon, a novel approach for measuring anode wear using confocal surface profilometry was developed. Surface profilometry is well suited for this application, because, with its high resolution, it is able to measure the micron scale wear that results from a laboratory cell. Using this technique, the effects of oxide concentration and type on anode wear were studied. There was found to be a strong linear relationship between wear and oxide concentration. Comparing equimolar amounts of soluble MgOHCl and practically insoluble MgO, there was at least twice as much wear associated with the former. Also, in investigating the impact of graphite properties on anode wear, it was determined that grain size has the most significant influence on anode wear. Along with demonstrating this measurement technique, the main significance of these results is that they show that anode wear can be reduced through improved feed processing as well as graphite selection and development.