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

Research paper by Jian-hua LIU, Xiao-jun LÜ, Jie LI, Ling-yun HU, Liang-xing JIANG

Indexed on: 09 Nov '16Published on: 05 Nov '16Published in: Transactions of Nonferrous Metals Society of China



Abstract

New types of refractory materials need to be developed for designing the man-made ledge of the Hall–Héroult 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.