| Carbon is the common anode material used in industrial aluminum electrolysis.In the electrolysis process,greenhouse gases CO2,CF4 and C2F6 were generated and emitted due to the consumption of carbon anodes,which deteriorated the environmental pollution.The inert anode insteading of the graphite anode can effectively reduce the emissions of greenhouse gas and achieve the goal of sustainable and green development.Therefore,inert anode materials attracted the focus of research in the industrial aluminum electrolysis.In this research,the Fe-Ni/Fe-Cr/Ni-Cr binary alloys with different mass ratio were prepared by vacuum induction melting method.The electrochemical behavior of the alloy in 9.4wt.%NaF-33.6wt.%KF-52wt.%AlF3-5wt.%Al2O3 molten salt at 800? was characterized by linear voltammetry,impedance method and chronopotentiometry.The corrosion mechanism of Fe-Ni/Fe-Cr/Ni-Cr binary alloys in NaFKF-AlF3-Al2O3 molten salt at 800? was proposed via the characterization of the alloys after electrochemical reactions and reaction products by X-ray diffractometry,scanning electron microscopy,and chemical analysis.The self-corrosion potential of Fe-Ni alloys is in the range of 1.08-1.22 V in NaF-KF-AlF3-Al2O3 molten salt at 800?,and the self-corrosion current density reach to the maximum when the nickel content is 50%.Impedance spectroscopies show that local corrosion occurs on the Fe-Ni alloys surface and the charge transfer resistance increases in local corrosion region with the increase of Ni content.When the Ni content reaches 57%,the charge transfer resistance reaches the maximum,which indicates the local corrosion region possesses the better corrosion resistance to fluoride molten salt than the other alloys.The linear voltammetry results indicate with the increase of voltage,Fe-Ni alloys occurs active-dissolution reaction on the surface.When the oxygen evolution reaction occurs,a passivation film is formed on the surface of the alloys.After the pre-oxidization of Fe-Ni alloys,such oxides,including NiFe2O4,Fe2O3,NiO,etc are formed on the alloys surface.Impedance spectroscopies indicate that pre-oxidized Fe-Ni alloys also undergoes local corrosion due to the dissolution oxide film in molten salt.The linear voltammetry results present that the passivation reaction occurs on Fe-Ni alloys surface when the evolution of oxygen occurs.The electrolysis is conducted for 3 h by chronopotentiometry.The cell voltage is stabilized within 8-9.5 V.The purity of the obtained aluminum can reach 98.69%.The self-corrosion potential of Fe-Cr alloys is in the range of 0.98-1.07 V in NaF-KF-AlF3-Al2O3 molten salt at 800?,and the self-corrosion current density reach to the minimum when the chromium content is 25%.Impedance spectroscopies show that local corrosion occurs on the Fe-Cr alloys surface and the charge transfer resistance reach to the minimum when the chromium content is 25%.It indicates the local corrosion region possesses a better corrosion resistance to fluoride molten salt than the other alloys.The linear voltammetry results indicate a passivation film is formed on the surface of the alloys when the evolution of oxygen reaction.After the pre-oxidization of Fe-Cr alloys,such oxides,including Fe2O3,Cr2O3,etc are formed on the alloy surface.The impedance results indicate that pre-oxidized Fe-Cr alloys also undergoes local corrosion because of the dissolution of oxide film in molten salt.The linear voltammetry results present that when oxygen is evolution,a passivation reaction occurs in the Fe-Cr alloy surface.The electrolysis is conducted for 3 h by chronopotentiometry.The cell voltage of 60Fe-40Cr alloy increased sharply after electrolysis for 2 h,and the cell voltage of other alloys is relatively stable.The purity of the obtained aluminum can reach 98.12%.The self-corrosion potential of Ni-Cr alloys is 0.98 and 1.07 V for 85Ni-15Cr and 75Ni-25Cr alloy in NaF-KF-AlF3-Al2O3 molten salt at 800?,and the self-corrosion current density is the minimum when the chromium content is 25%.Impedance spectroscopies show that local corrosion occurs on the Ni-Cr alloys surface and the charge transfer resistance are the minimum,when the chromium content is 25%,the local corrosion region possesses a better corrosion resistance to fluoride molten salt than the other alloy.The linear voltammetry results indicate that with the increase of voltage,85Ni-15Cr alloy occurs active dissolution reaction on the surface.When the oxygen is evolved,a passivation film is formed on the surface of 75Ni-25Cr alloy.After the pre-oxidization of Ni-Cr alloys,such oxides Cr2O3 is formed on the alloy surface.Impedance spectroscopies indicate that pre-oxidized Ni-Cr alloys also undergoes local corrosion because of the dissolution of oxide film in molten salt.The linear voltammetry results present that when oxygen is evolved,a passivation reaction is occoured on the surface of Ni-Cr alloys.The electrolysis is conducted for 3 h by chronopotentiometry.The cell voltage of the alloys is around 8.5 V.The purity of the obtained aluminum can reach 97.12%. |
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