Study On Preparation Of Nickel Ferrite Spinel Nanopowder And Its Application On Inert Anode

There are many problems in electrolytic production of aluminium in traditional Hall-Heroult aluminium-electrolytic cells such as high energy consumption, high carbon consumption, high cost and serious environmental pollution as a result of adopting consumable carbon anodes. Research groups in aluminium industry have been focusing on the investigation of inert anodes because they can overcome the problems mentioned above. Nickel ferrite-based cermets have become the key study object of inert anode for its high strength, good stability at elevated temperature, good corrosion resistance and so on. Considering the high brittleness and poor thermal shock resistance of NiFe2O4-based ceramic inert anode, it has not been used in electrolytic production of aluminium for it doesn't meet the requirements of aluminium electrolysis process. In order to improve the bending strength and impact toughness of NiFe2O4-based ceramic inert anode, the preparation of nickel ferrite spinel nanopowder and its effect of bending strength and impact toughness have been researched in this paper.In this paper, NiFe2O4 nanopowder was prepared by low-temperature solid-state reaction. The precursor of NiFe2O4 spinel nanopowder was prepared by rubbing the reactants FeSO4·7H2O, NiSO4·6H2O, NaOH and dispersant sufficiently at room temperature. The reaction mechanism was studied by the XRD analysis of the precursor. Then the precursor was calcined at different temperature for different holding time. The effects such as content of dispersant, calcining temperature and holding time on the particle size (D50) and morphology were researched emphatically through the orthogonal experiment designed using Lg(34) orthogonal table. According to the range analysis of the orthogonal experiment, the important order of factors was determined as content of dispersant, holding time and calcining temperature successively. The NiFe2O4 spinel nanopowder prepared by adding 20wt% NaCl (dispersant) in the rubbing process and calcining at 800℃for 1.5 hour was of pure cubic spinel structure and uniform distribution with the average size of the grains about 75 nm.Two-step sintering process was adopted to prepare NiFe2O4-based inert anode in this research. In the process of synthesizing NiFe2O4 spinel, Fe2O3 and NiO powders as raw materials added additive of MnO2 and V2O5 were synthesized at 1000℃. Through crushing and screening, adding nanopowder, particle gradation and compression molding, the nickel ferrite-based ceramic inert anode was sintered secondarily at 1250℃for 6h. The effect of addition level of nanopowder on the density and porosity, bending strength and impact toughness was investigated emphatically. The results showed the addition of NiFe2O4 nanopowder had significantly increased the bending strength and impact toughness of NiFe2O4-based ceramic inert anode. Inert anodes had the best comprehensive properties while adding 60wt% nanopowder. The values of density and porosity were 4.62g/cm3 and 5.2% respectively, the value of bending strength was 53.39MPa and the value of impact toughness was 3.19J/cm2.