| Currently,CO2 greenhouse gas will be emitted when carbon anode is used for electrolysis in industry,while inert anode is a kind of anode with little or no consumption.The total reaction in aluminum electrolysis is:Al2O3=2Al+3/2O2.Among many materials,metal inert anode has good electrical conductivity,thermal conductivity,thermal shock resistance,low cost and easy connection with the anode bus.However,metal inert anode has poor oxidation resistance and molten salt corrosion resistance in aluminum electrolysis molten salt environment.Therefore,this paper focuses on improving the oxidation resistance and molten salt corrosion resistance of metal anodes.In this paper,the Ni-Fe layer was coated on the surface of GH3030 alloy by electroplating technology,and it was transformed into a double-layer oxide structure protective film of Cr2O3 inner layer and NiFe2O4 outer layer,so as to improve its oxidation resistance and corrosion resistance.Firstly,Ni-Fe layer with different thickness was coated on the surface of GH3030 alloy by electroplating,and then oxidized in high temperature air to study its high temperature oxidation resistance and oxide film structure.On this basis,its corrosion behavior in molten salt electrolyte of 58.25Na3AlF6-32.35AlF3-5CaF2-4.4Al2O3(wt%)at 800℃ was studied.The main results are as follows:Three kinds of Ni-Fe coatings with different thicknesses were electrodeposited on the surface of GH3030 alloy by electroplating technology.The surface of the coating was continuous and dense,and there was no obvious shedding phenomenon.The adhesion between the coating and the substrate was good,and the composition of the coating was uniform.The thickness of the coating after electrodeposition for 10 min,20 min and 30 min was about 1.5 μm,3.5 pm and 5.5 μm,respectively.The oxidation behavior of GH3030 alloy substrate and Ni-Fe coating GH3030 alloy in air at 800℃ was studied.The oxidation kinetics of GH3030 alloy and GH3030 alloy coated with Ni-Fe layer shows that the oxidation weight gain mainly occurs in the first 3 h,indicating that the oxidation layer generated by each sample has good oxidation resistance.After oxidation for 30h,only about 0.5 μm Cr2O3 layer was formed on the surface of GH3030 alloy.The thickness of the oxide layer on the surface of the samples electroplated for 10 min,20 min and 30 min was about 3 μm,8 μm and 11 μm,respectively.The oxidation film of the sample after electroplating for 10 min is composed of three-layer structure oxides,the outer layer is NiFe2O4,the middle layer is NiO,and the inner layer is Cr2O3.The oxide films of the samples after oxidation for 30 h for 20 min and 30 min were Fe2O3 layer,NiFe2O4 layer,NiO layer and Cr2O3 layer from outside to inside.The electrochemical corrosion behavior of GH3030 alloy anode after pre-oxidation(oxidation in air at 800℃ for 30 h)and 20 min Ni-Fe coated GH3030 alloy anode after pre-oxidation in molten salt electrolyte with current density of 0.5 A·cm-2 and temperature of 800℃ was studied.In order to further explore the process of electrochemical corrosion,the anode was corroded for 5 min,15 min,30 min and 60 min respectively.The results show that the cell voltage of Ni-Fe alloy coating anode with pre-oxidation plating for 20 min is more stable than that of the anode without coating,and the anti-molten salt corrosion effect of electrolysis for 5 min,15 min and 30 min is better than that of the sample without coating at the corresponding electrolysis time,while the corrosion of the two anodes is more serious when electrolysis is carried out to 60 min.In addition,it was found that the surfaces of pre-oxidized GH3030 alloy anode and Ni-Fe alloy coating anode after electroplating for 20 min at 800℃ for 60 min were NiO,NiAl2O4,NiCr2O4 and electrolyte(Na10Al6F28,AlF3).This indicates that the oxide layer of Ni-Fe alloy coating anode after pre-oxidation and electroplating for 20 min has been corroded or dropped into molten salt after electrolysis for 60 min. |
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