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Sintering Behaviour of Mg(Al_xFe_1-x)₂O₄ Materials and their Corrosion in Na₃AlF₆-AlF₃-K₃AlF₆ Electrolyte

Y.B. Xu, Y.W. Li, J.H. Yang, S.B. Sang, Q.W. Qin

Journal of Ceramic Science and Technology, Vol. 8, No. 2 (2017), pp. 193-200

DOI: 10.4416/JCST2016-00081

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Abstract

The development of new electrolysis technology in the aluminium industry calls for new sidewall materials since the frozen ledge would no longer exist. In the present paper, Mg(AlxFe1-x)2O4 materials were prepared and characterized, and corrosion tests in a Na3AlF6-AlF3-K3AlF6 bath were conducted. The results show that reaction sintering occurs in the MgAl2O4-MgO-Fe2O3 system in the range of 1000 to 1600 °C. Firstly, MgO reacts with Fe2O3 to produce MgFe2O4 phase at 1000 °C, which in turn reacts with MgAl2O4 to form Mg(AlxFe1-x)2O4 composite spinel at temperatures above 1200 °C. As a result, mass transfer and densification in the specimens are enhanced as the amount of the Fe2O3 increases. After being fired at temperatures above 1200 °C, all the specimens prepared are composed of single-phase Mg(AlxFe1-x)2O4 composite spinel, the lattice parameter of which increases with increasing Fe3+ ion concentration. The corrosion results show that corrosion resistance of the specimens increases progressively with the Fe2O3 content owing to the improved chemical stability of the Mg(AlxFe1-x)2O4 composite spinel and the enhanced densification of the specimens. And for the specimens with a Fe/(Al+Fe) mole fraction more than 0.5, a dense and stable ceramic layer forms on surface of the specimens during the corrosion test, which further improves their corrosion resistance.

Keywords

Sidewalls, Mg(AlxFe1-x)2O4, dense layer, electrolyte, corrosion resistance

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