| Inert anodes is very little consumed in the alumnum electrolysis process.Aluminum electrolysis occurs in a high-temperature environment.The cryolite-alumina electrolyte is high-temperature and highly corrosive,so higher requirements are imposed on the selection of anode materials.The metal alloy anodes have the advantages of good conductivity,easy preparation and low cost,but they have the problems of poor resistance to high temperature oxidation and poor corrosion.Preparing a dense,well-adhesive protective coating on a metal substrate can effectively improve its corrosion resistance.In order to improve the corrosion resistance of alloy inert anodes,a Ni-Fe alloy coating was prepared on the surface of SUS430 stainless steel by electroplating,the coating is thermally converted into a protective oxide layer at 800?in air.The high temperature oxidation behavior of Ni-Fe alloy coated and uncoated steel was studied.The anodes were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)after oxidation and electrolysis.The corrosion behavior of the coated and uncoated anodes was investigated at 800?.The research results are as follows:Ni-Fe alloy coatings of four different thicknesses were successfully prepared on the stainless steel by electroplating.When the plating time is 10 min,15 min,20 min,25 min,the coating thickness is about 5 ?m,8 ?m,10 ?m,13 ?m,respectively,and the coating thickness was uniform and well bonded to the substrate.For the Ni-Fe alloy coated and uncoated steel,the oxidation behavior at 800? shows that the oxidation of the coated and uncoated steel was mainly concentrated in the first 5 hours,and then the weight gain tends to gentle.After 25 hours of oxidation,the oxide films on the Ni-Fe alloy coating samples with different coating thicknesses formed different structures.The coated sample plated for 10 min and 15 min to form a three-layer oxide scale with an inner Cr2O3 layer,followed by(Ni,Fe)3O4 layer and the outer layer Fe2O3.The sample plated for 20 min and 25 min presented a four-layer oxide scale,consisting of inner Cr2O3 layer,followed by NiO and(Ni,Fe)3O4,and the outer layer Fe2O3.The oxide scale formed on the uncoated sample a double layer oxide layer,consisting of an inner Cr2O3 layer and MnCr2O4 layer on the top.Ni-Fe alloy coated steels with different electroplating time were studied,and the coated steels for 15 min and 20 min were selected as the inert anode.Electrolysis experiments were performed on uncoated anodes,coated anodes for 15 min and 20 min.Through cross-section SEM and EDS,XRD analysis of the electrolyzed anode,the corrosion layer of anode coated for 20min is more dense and the resistance is larger,so that the cell voltage is larger than the cell voltage of the coated anode for 15 min and the uncoated anode.The corrosion products of the uncoated anode are mainly Cr2O3 and Fe2O3.The corrosion layer is relatively loose.The difference is that the corrosion products on the surface of the electroplated Ni-Fe coating anodes contain protective Cr2O3,(Ni,Fe)3O4,Fe2O3 oxide films,the solubility of(Ni,Fe)3O4 in cryolite molten salt is small,which can alleviate the erosion of electrolyte to the matrix.It shows that the electroplated Ni-Fe coating enhances the corrosion resistance.Research on the electrolytic process of Ni-Fe coated anodes found that cracks of different degrees appeared in both corrosion layers after electrolysis for 30 minutes.With the extension of the electrolysis time,a large amount of fluoride salts accumulates at the interface between the substrate and the corrosion layer of the anode plated for 15 min,the oxide film on the coating for 20 min is relatively dense,and there is less fluorine salt at the interface between the corrosion layer and the substrate.In summary,the corrosion resistance of the anode plated for 20 min is better than that of the coated anode plated for 15 min,and the corrosion resistance of the bare steel anode is the worst. |
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