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Sintering of Magnesia and Iron Oxide in Air and Flowing Nitrogen and its Corrosion Process by Molten Electrolyte
Y.B. Xu, Y.W. Li, J.H. Yang, S.B. Sang, Q.W. Qin
The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, 430081 Wuhan, PR China
received December 9, 2015, received in revised form January 25, 2016, accepted February 10, 2016
Vol. 7, No. 3, Pages 249-256 DOI: 10.4416/JCST2015-00085
Abstract
In the present paper, novel sidewall materials for aluminum reduction cells were prepared in air and nitrogen using magnesia and magnetite powders. The sintering behavior of the specimens and their corrosion resistance to electrolyte have been investigated. The results show that Fe3O4 phase is transformed into Fe2O3 at high temperatures in air, which in turn reacts with the MgO added to form MgFe2O4. For the specimens prepared in nitrogen, most of the Fe3O4 is reduced to FeO in specimens without MgO while all the specimens with added MgO are composed of FexMg1-xO only. The densification of the specimens prepared in both air and nitrogen decreased with the MgO content. The corrosion tests showed that corrosion layers were produced in all the MgO-added specimens while the corrosion process was inhibited in case of formation of composite spinel layer on the surface of the specimens during the tests. Moreover, since MgFe2O4 exhibits higher chemical stability than that of FexMg1-xO in electrolyte and a protective composite spinel layer with dense structure can be more easily formed in specimens prepared in air, the specimens prepared in air generally exhibited better corrosion resistance than that of the specimens prepared in nitrogen. The corrosion processes were also analyzed and discussed based on thermodynamic calculations.
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Keywords
Sidewalls, MgO-Fe2O3(FeO), composite spinel, electrolyte, corrosion resistance
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