Study On The Electrolytic Corrosion And Surface Anti-corrosion Layer Of NiFe₂O₄Based Cermet Inert Anodes In Na₃AlF₆-K₃AlF₆-AlF₃Melts

The new aluminum electrolysis technology based on inert electrode could eliminating green-house gas release and greatly decrease energy consumption, so it becomes the important frontier topic. The inert anode is the key and the precondition for successfully empoldering the new aluminum electrolysis technology. The research of the thesis is supported by the "863project", Based on the research of our institute, with22%(Cu-Ni)/(NiFe2O4-10NiO) cermet as inert anode, research the corrosion resistance of NiFe2O4-based inert anode in the K3AlF6-Na3AlF6-AlF3melts under different temperature; then to the phenomenon it can generate a dense anti-corrosion layer on the surface of NiFe2O4based cermet during electrolysis condition, carry out thermodynamic analysis, and then study the formation condition. The main conclusions can be summarized as follows:1) The corrosion rate of NiFe2O4based cermet in the K3AlF6-Na3AlF6-AlF3melts with electrolysis temperature decrease presents first decrease and then rise; under the same electrolysis temperature, in different electrolyte inert anode presents different corrosion resistance. When the electrolysis temperature is920℃、900℃、870℃and850℃, corresponding the lowest annual corrosion rate is0.479cm、0.388cm、0.198cm and0.286cm respectively.2) Analysis results show, under electrolysis condition22%(Cu-Ni)/(NiFe2O4-10NiO) cermet can react with nascent state oxygen and electrolyte. then generate aluminum compound like FeAl2O4, NiAl2O4, CuAl2O4which have greater mole volume, these substance made the anode surface more density, it can be in favor of slowing down the inert anode corrosion. But the new formation substance will be corroded with electrolysis.3) Although rising the electrolysis temperature, it is in favor of the dense anti-corrosion layer formation on the surface of NiFe2O4based cermet, but at the same time, the corrosion of new formed substance can speed up, this is bad for slow down inert anode corrosion; Increasing alumina concentration in the electrolyte, it is in favor of the dense anti-corrosion layer formation on the surface of anode, decrease the corrosion rate of inert anode; Increasing the anode current density, it is in favor of the dense anti-corrosion layer formation on the surface of anode, slow down anode corrosion, but too high current density, it can speed up surface dense anti-corrosion layer corrosion, then speed up anode corrosion. In the K3AlF6-Na3AlF6-AlF3melts which KR is18%, AlF3concentration is26%, When electrolysis temperature is870℃, anode current density is1.25A/cm2, alumina concentration in electrolyte is5.2%, it will be in favor of dense anti-corrosion layer formation on anode surface, the lowest annual corrosion rate reachs to0.014cm.