Abstract

The application of ledge-free sidewalls in the Hall-Héroult cells is preferred as it potentially reduces the energy requirement of aluminum production by about 30%. However, this approach requires new types of sidewall materials to replace the currently used Si3N4 bonded SiC sidewalls. In the present paper, (Ni,Mg)(Al,Fe)2O4 materials were prepared using fused magnesia, reactive alumina, nickel oxide and ferric oxide powders as starting materials. The sintering behaviors of specimens as well as their corrosion resistance to molten electrolyte have been investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM). The results show that after firing at 1400 to 1600○C, all the specimens prepared are composed of single-phase (Ni,Mg)(Al,Fe)2O4 composite spinel, whose lattice parameter increases with increasing Fe3+ ion concentration. Increasing the ferric oxide content enhances densification of the specimens, which is accompanied by the formation of homogeneously distributed smaller pores in the matrix. The corrosion tests show that corrosion layers consist of fluoride and Ni(Al,Fe)2O4 composite spinel grains are produced in specimens with Fe/Al mole ration no more than 1, whereas for specimens with Fe/Al mole ration more than 1, dense Ni(Al,Fe)2O4 composite spinel corrosion layers are formed on the surface of the specimens. The Ni(Al,Fe)2O4 composite spinel layers formed effectively improve the corrosion resistance of the specimens by inhibiting infiltration of electrolyte and hindering chemical reaction between the specimen and electrolyte.