Impact of Pre‐Oxidation Treatments on a Recycled MgO/Steel‐Composite as Carbon Free Anode in Aluminum‐Electrolysis Environments

This study investigates the influence of three different furnace technologies on a cermet material consisting of 60 vol.% AISI 316L stainless steel and 40 vol.% recycled MgO, intended for use in aluminum electrolysis. Different furnace heating technologies were compared for pre‐oxidation of the cermets: an electric resistance furnace, a natural gas‐fired furnace, and a furnace with an integrated microwave plasma torch. The pre‐oxidized specimens were subjected to corrosion tests in a hot stage microscope with a cryolite‐containing electrolyte mixture. The influence of the atmospheres on the pre‐oxidation behavior and corrosion effects was analyzed using Raman spectroscopy, laser scanning microscopy, scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, and electron backscatter diffraction. Different oxide layers were formed, which affected the corrosion behavior. Pre‐oxidation led to improved corrosion resistance compared to non‐pre‐oxidized specimens. The infiltration depth of the electrolyte mixture and the Mg‐depletion depended on the conducted pre‐oxidation technology.