Ni 0.36 Al 0.10 Cu 0.30 Fe 0.24 Metallic Inert Anode for the Electrochemical Production of Fe-Ni Alloy in Molten K 2 CO
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INTRODUCTION
MOLTEN salt electrolysis is a typical electrochemical metallurgy process for metal extraction. Graphite is usually used as anode, such as the Hall–He´roult process for Al and FFC method for Ti.[1] The emission of carbon dioxide and carbon monoxide are hardly avoided.[2–8] In response to the challenges on climate changes and environmental pollution, it is necessary to develop the inert anode as an alternative to graphite for molten salt electrolysis.[9–15] For an outstanding inert anode, it should not react with the molten salts and possesses a high electrical conductivity. At present, three kinds of materials, including ceramics, cermets, and metals, were considered to be the most promising candidates as inert anodes.[9] For example, tin oxide and NiFe2O4-Cu are the representative ceramic and cermet for inert anodes, respectively.[16] Although ceramics have been favored due to significant chemical inertness, their applications are limited by low electrical conductivity.[9] Therefore, metals and alloys with outstanding advantages, such as
DONGHUA TIAN, MINGYONG WANG, HANDONG JIAO, XUEFENG SHE, JIUSAN XIAO, and SHUQIANG JIAO are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mails: [email protected], [email protected] YANPING ZHOU is with the Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, P.R. China. Manuscript submitted June 2, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
high electrical conductivity, good thermal shock resistance, and easy fabrication, are considered as the most promising inert anode material.[9,10,17,18] A lot of researchers have reported that precious metals (such as Pt, Ir, Ru) can resist the corrosion of molten salts.[9] However, high cost and scarce resources are the key issues. Therefore, a cost-affordable inert anode is still a challenge. Yin et al.[17] confirmed that the dissolution potentials of metal anodes in CaCl2-CaO melt follow the order: Fe, Cu, Ag, Co, Ni, Mo, and Pt. For metal anode, a metal oxide film is usually formed on the surface during electrolysis to protect the bulk of anode. Multi-metal alloy anode can exhibit better anti-corrosion ability due to the formation of composite metal oxides. Ni-based alloys, such as Ni-Fe,[19] Ni-Cu,[20] Ni-Cr,[21] and Ni wire,[22] were widely studied as the candidate of inert alloy. It is proved that NiFe2O4 on the surface of anode can effectively inhibit the dissolution of Ni-Fe-based alloys in molten fluoride and chloride salts.[16,23] The addition of metal aluminum will form the aluminum oxide with the dense structure on the surface of the metal, which will further improve the corrosion property of metal alloys.[24,25] Shi compared the electrochemical corrosion property of various copper-nickel superalloys (such as Cu-Ni-Al, Cu-Ni-Fe, and Cu-Ni-Cr) during aluminum electrolysis.[18] Cu-Al-Ni anodes possessed the best anti-corrosion ability.[18] Very recently, Alzamanigroup[26] investigated the effe
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