A Study On Conductivity And Molten Salt Corrosion Behavior Of Nb₂O₅Doped Nife₂O₄Based Cermet

The exhaust emission and energy consumption in the process of traditional aluminum production can be reduced by the exploitation and application of technology based on inert anode in aluminum electrolysis. NiFe2O4based cermet is currently one of the most promising industrial inert anode materials for aluminum electrolysis. The high sintering density, good conductivity and excellent corrosion resistance in high temperature molten salt were required for this kind of materials. Supported by the National Basic Research Program (973Program) and the National High-Tech Research and Development Program (863Program), the effect of Nb2O5dopant on sintering performance, conductivities and molten salt corrosion behavior of NiFe2O4based ceramics and cermets has been studied mainly in this paper. The low temperature electrolysis and the formation mechanism of surface dense layers in this materials are also discussed. The main completed research and achieved results are as followed:(1) The Ni1-xNbxFe2O4(x=0,0.02,0.05,0.07,0.10,0.20) ceramic powders were synthetized by solid-state reaction method, and the ceramic samples were prepared by isostatic pressing-atmosphere sintering method. It was found that the sintering densification and electrical conductivities were further improved for NiFe2O4ceramics by a suitable amount of Nb2O5doping. A different thickness spinel dense layer in the surface of anode was found during960℃electrolysis. There have no prior corrosion of Nb element, and the corrosion resistance of ceramics was ameliorated by suitable Nb2O5doping.(2) The sintering performance, conductivities and corrosion resistance of NiFe2O4based cermets has been studied by Nb2O5doping. The results show that a higher sintered density of cermet was prepared in the joint action of Nb2O5and NiO. The material has good conductivity in the high temperature due to the reduction of conductive activation energy. The corrosion resistance of spinel phase in the surface of inert anode has been improved by moderate Nb2O5doping, and the dense ceramic layers which more thick and uniform were easier formed during electrolysis.(3) The molten salt corrosion behavior of NiFe2O4based cermets has been studied in electrolysis conditions with different temperature. It was found that higher temperature is in favor of the stability of electrolysis and the formation of dense layer in surface. The interaction of anode and electrolyte (especially Al2O3) was suppressed due to the lower solubility of Al2O3in lower temperature, leading to the reduction of corrosion resistance.(4) The static corrosion behavior of NiFe2O4based ceramic and cermet has been discussed, the results explain that the polarization condition is one of the necessary factors in formation of the dense ceramic layers. Under the role of nascent oxygen, the growth of spinel phase precipitates in NiO phase, the transformation of NiO phase to spinel phase, and the deposition of A12O3were the key factors in formation of the dense ceramic layers.