| There are many problems in traditional aluminum electrolysis such as high energy consumption and serious environmental pollution as a result of adopting consumable carbon anodes. Inert anode can overcome problems mentioned above and have become the research hot spot in the aluminum industry. Now, NiFe2O4 spinel, which is regarded as the most industrial application material for inert anode, has good stability at elevated temperature and low solubility in fluoride melt, but its industrial application in aluminum electrolysis has been restricted by the poor toughness poor mechanical properties and did not meet the industrial requirements of resistance to molten salt. In the paper, NiFe2O4 ultrafine powder has been added into the NiFe2O4 substrate to improve its comprehensive performance. The preparation of ultrafine powder has been first studied, then added different amounts of ultrafine powder into the substrate and its effect on the properties of anode materials was studied, finally determined the appropriate addtion of NiFe2O4 ultrafine powder.In this paper, NiFe2O4 ultrafine powder was prepared by low-temperature solid-state reaction. Put the reactants which are ferrous sulfate (FeSO4·7H2O), nickel sulfate (NiSO4·6H2O), sodium hydroxide (NaOH) and dispersant which is sodium chloride (NaCl) on the ceramic mortar. The precursor was prepared by rubbing the reactants and dispersant sufficiently at room temperature, and then calcined to obtain ultrafine powder. The effects of the dispersant content, preparation technology, calcining temperature and holding time on the powder's phase composition, particle size distribution and morphology were researched emphatically through single-factor experiment, then determined the optimum process parameters of preparation of NiFe2O4 ultrafine powder. Results showed that the powder, prepared by first calcining the precursors using 20% NaCl as dispersant in the process of grinding at 800? for 1 hour subsequently vacuumizing and filtrating have single phase, high crystallinity and are mostly polyhedral in shape with the particle size range of 30-65 nm. The preparation technology of ultrafine powder adopts that the precursors were first calcined and then vacuumized and filtrated. Low-temperature solid-state reaction was restricted by conditions of thermodynamics and kinetics. Reaction of FeSO4·7H2O,NiSO4·6H2O and NaOH at room temperature is the reaction which gibbs free energy change is less than zero. Many factors promote the reaction, such as the crystal water from reactants, grinding and the finer reactants.Two-step sintering process was adopted to prepare NiFe2O4-based inert anode in this research. NiFe2O4 spinel base material was synthesized form Fe2O3 and NiO powders as raw materials and MnO2 and V2O5 as additives at 1000?. Through crushing and screening adding different content of NiFe2O4 ultrafine powder in the particle gradation, mixing and drying, compression molding at 160MPa, the NiFe2O4-based inert anode, its size was 60×12×Xmm,was gained by second-sintering at 1300? for 6 h. The effect of addition level of NiFe2O4 ultrafine powder on the combination properties of NiFe2O4-based inert anode was investigated emphatically. The results showed that the addition of NiFe2O4 ultrafine powder had increased the line contraction of green bodies and reduced its apparent activation energy in the initial stage of sintering. The more NiFe2O4 ultrafine powder added, the line contration of inert anode was greater and the sintering activation energy was lower, then the dense sintered bodies gained higher density. The appropriate addition level of NiFe2O4 ultrafine powder was beneficial to reduce the porosity of inert anode, increase its density, improve its mechanical performance, reduce its static corrosion rate. NiFe2O4-based inert anodes had the best comprehensive properties while adding 30wr% ultrafine powder in the particle gradation: The values of porosity and bending strength were 3.51% and 42.47MPa respectively; The values of fracture toughness were 3.12MPa·m1/2; Static corrosion rate reduced to 0.000858g·cm-2·h-1. |
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