Effect of CaO doping on corrosion resistance of Cu/(NiFe₂O₄-10NiO) cermet inert anode for aluminum electrolysis

Abstract

The CaO-doped Cu/(NiFe₂O₄-10NiO) cermet inert anodes were prepared by the cold isostatic pressing-sintering process, and their corrosion resistance to Na₃AlF₆-K₃AlF₆-Al₂O₃ melt was studied. The results show that the relative density of 5Cu/(NiFe₂O₄-10NiO) cermet sintered at 1 200 °C increases from 82.83% to 97.63% when 2% CaO (mass fraction) is added. During the electrolysis, the relative density of cermet inert anode descends owing to the chemical dissolution of additive CaO at ceramic grain boundary, which accelerates the penetration of electrolyte. Thus, the corrosion resistance to melts of Cu/(NiFe₂O₄-10NiO) cermet inert anode is reduced. To improve the corrosion resistance of the cermet inert anode, the content of CaO doped should be decreased and the technology of cleaning the ceramic grain boundary should be applied.

Keywords

aluminum electrolysis / Cu/(NiFe₂O₄-10NiO) cermet / CaO / inert anode / corrosion resistance

References

[1] LIU Ye-xiang. Advance on the research and development of inert anode and wettable cathode in the aluminum electrolysis [J]. Light Metals, 2001(5): 26–29. (in Chinese)

[2] LaiY.-q., QinQ.-w., DuanH.-n., LiJ., LiuY.-xiang.. Materials fabrication and corrosion behavior of NiFe₂O₄ cermet inert anode [J]. Journal of Central South University of Technology: Natural Science, 2004, 35(6): 885-890

[3] TianZ.-l., LaiY.-q., LiJ., LiuY.-xiang.. Electrical conductivity of Cu/(10NiO-NiFe₂O₄) cermet inert anode for aluminum electrolysis [J]. Journal of Central South University of Technology, 2007, 14(5): 643-646

[4] XiJ.-h., YaoG.-c., LiuY.-h., ZhangX.-ming.. Electrolysis corrosion behaviour of NiFe₂O₄-based cermet inert anode [J]. The Chinese Journal of Process Engineering, 2006, 6(5): 758-762

[5] JohnsonD. W., VogelE. M., GhateB. B.. Recent progress on mechanical properties of ferrites [C]. Proceedings of the Third International Conference on Ferrite, 1980, Tokyo, Reidel Publishing Company: 285-291

[6] GhoshA., DasS. K., BiswasJ. R., TripathiH. S., BanerjeeG.. The effect of ZnO addition on the densification and properties of magnesium aluminate spinel [J]. Ceramics International, 2000, 26(6): 605-608

[7] LiJ., ZhangG., LaiY.-q., ZhangY., TianZ.-liang.. Densification and sintering dynamics of 10NiO-NiFe₂O₄ doped CaO [J]. Journal of Central South University of Technology, 2007, 14(5): 629-632

[8] LaiY.-q., ZhangY., ZhangG., LiJ., HeY.-h., HuangB.-y., LiuY.-xiang.. Effect of CaO doping on densification of NiFe₂O₄-10NiO composite ceramics [J]. The Chinese Journal of Nonferrous Metals, 2006, 16(8): 1355-1360

[9] LaiY.-q., SunX.-g., LiJ., DuanH.-n., LiX.-z., ZhangG., TianZ.-liang.. Densification of Ni-NiFe₂O₄ cermets for aluminum electrolysis [J]. Trans Nonferrous Met Soc China, 2004, 14(3): 666-670

[10] ZhangG., LiJ., LaiY.-q., SunX.-gang.. Effect of sintering atmosphere on the relative density and conductive properties of Ni-Fe spinel ceramics [J]. Journal of Functional Materials, 2006, 36(11): 1709-1711

[11] QingQ.-w., LaiY.-q., XiaoJ., LiJ., LiuY.-xiang.. Preliminary testing of NiFe₂O₄-NiO as ceramic matrix of cermet inert anode in aluminum electrolysis [J]. Trans Nonferrous Met Soc China, 2003, 13(5): 1208-1212

[12] OlsenE., ThonstadJ.. Nickel ferrite as inert anodes in aluminium electrolysis (I): Material fabrication and preliminary testing [J]. Journal of Applied Electrochemistry, 1999, 29: 293-299

[13] ZhangG., LiJ., LaiY.-q., ZhangY., TianZ.-liang.. Effect of CaO addition on the densification and conductivity of 10NiO-NiFe₂O₄ composite ceramics [J]. Journal of Materials and Metallurgy, 2007, 6(3): 214-219

[14] JunzoT., ToyohikoI.HiroshiW. F.. Effect of additives on magnetization of ferrites [C]. Proceedings of the Third International Conference on Ferrites, 1980, Tokyo, Reidel Publishing Company: 178-181

[15] DeyoungD. H.. Solubilities of oxides for inert anodes in cryolite-based melts [C]. Light Metals, 1986, Warrendale, TMS: 299-307