Study On Structure Evolution And Its Impact Factors Of NiFe₂O₄Based Cermet Inert Anodes During Electrolysis Process

Abstract:The application of inert anode and wettable cahtode in the aluminum electrolysis industry has become an important research topic because of its eliminating the greenhouse gas emissions and the problems of environmental pollution. And the inert anode is the key to the development of this new technology. Supported by the project of National Natural Science Foundation (No:51222403) and based on the previous research,17Ni-(NiFe2O4-10NiO) cermet inert anode was adopted, the changes of the anode surface phase structure and morphology in the Na3AlF6-AlF3-Al203melts were studied; and then, the influence of the electrolytic process (electrolytic temperature, the concentration of A12O3and the current density) on the anode surface phase structure evolution are further investigated. The main conclusions can be summarized as follows:1) The original phase NiO on the surface of17Ni-(NiFe2O4-10NiO) cermet inert anode and the phase NiO, which was generated because of the reaction between the nascent oxygen and the metal phase during the electrolysis process, not only can produce the NiAl2O4through reacting with A12O3in the melt but can also transfer into the phsae NiFe2O4with Fe2O3. At the same time, under some conditions, the two new biological phases can form a dense and stable corrosion layer with anodic original ceramic phase, which can enhance the corrosion resistance of materials because it has a stronger corrosion resistance to the melt than that of the phase Ni and the phase NiO.2) During the electrolysis process of17Ni-(NiFe2O4-10NiO) cermet inert anode, among the factors of the current density,the concentration of A12O3in the melt and the electrolysis temperature, the influence of current density on new biological phase of NiAl2O4and NiFe2O4is the most, and the electrolysis temperature is little. The new biological phase of NiAl2O4and NiFe2O4on the surface of NiFe2O4based cermets inert anode increase with the increase of the current density, and the dense corrosion resistance layer becomes thick. But when the current density is too high, it would be affected greatly by the concentration of A12O3in local area of the anode and the new biological would reduce. The higher the concentration of Al2O3, the easier the phase of NiAl2O4and NiFe2O4is generated on the surface of the anode. And the change of the temperature has no effect on the generation of NiAl2O4.3) In Na3AlF6-AlF3-Al2O3melt at960℃, when the concentration of A12O3is above7.5%and the current density is1.5A/cm2, the new biological phase of NiAl2O4and NiFe2O4on the surface of17Ni-(NiFe2O4-10NiO) cermet anode can form a stable dense layer of about120μm with the common action of the original ceramic phase. This would improve the corrosion resistance of the anode. In this dissertation, there are the pictures25, the tables6and the references82.