Two-step sintering of magnesium aluminate spinels and their corrosion in Na3AlF6-AlF3-CaF2-Al2O3 bath

New types of refractory materials need to be developed for designing the man-made ledge of the Hall-Heroult cell for aluminum electrolysis, which are currently constructed by frozen ledge. Magnesium aluminate spinel (MAS) as potential candidate materials was prepared by two-step sintering. The densification and grain growth of the MAS were investigated by the Archimedes drainage method and scanning electron microscope (SEM). All the specimens were corroded in a Na3AlF6-AlF3-CaF2-Al2O3 bath to assess the corrosion resistance. The results show that a MAS material with a high relative density of 99.2% and a homogeneous microstructure is achieved under two-step sintering conditions. The corrosion mechanisms of MAS in Na3AlF6-AlF3-CaF2-Al2O3 bath are mainly proposed by dissolution of MAS, formation of aluminum oxide, and diffusion of fluorides. The MAS prepared by two-step sintering exhibits good corrosion resistance to the Na3AlF6-AlF3-CaF2-Al2O3 bath.