Study On Nial 2 O 4 Spinel Coating Of Inert Anode With Flexible Transition Layer

In the aluminum electrolytic industry, inert anode demonstrates environmental protection and energy saving advantages, and has a better application prospect. Replace the carbon anode with inert anodes was the main direction to improve the traditional electrolytic process. According to the basic requirements of the inert anode, NiAl2O4 was adopted as the coating material for its strong resistance to molten salt corrosion and semiconductor properties; Nickel foam was adopted as flexible transition layer between stainless steel substrate and ceramic coating, in order to release thermal stress generated during the process of preparation and work owing to their thermal expansion coefficient mismatch.In this paper, NiAl2O4 spinel sintering process was studied and NiAl2O4 spinel ceramic powder was prepared; A plate-shaped inert anode with nickel foam substrate and NiAl2O4 spinel coating is successfully prepared by the brazing technique and plasma spraying technique. The microstructure, phase composition and interfacial reaction of the coating were characterized and analyzed by SEM, XRD, EDS etc. The thermal stability, high electrical conductivity properties, thermal shock resistance and corrosion resistance in aluminium electrolysis were investigated. The electrical conduction mechanism of NiAl2O4 spinel, corrosion-inhibiting mechanism and the possibilities of the application were discussed. The results show that:The ratio of NiO to Al2O3, pressing scheme and sintering temperature were determined by analysing the effects of sintering temperature and body density to NiAl2O4 spinel composition. The research show that: after the spinel coating was deposited by plasma spraying, the residual Al2O3 dissolves into spinel structure and form NiAl2O4-Al2O3 solid solution, which leads to little excess of NiO in coating. NiAl2O4 spinel coating did not occur obvious physical and chemical changes between the temperature of 30℃and 1050℃. It shows that the coating had good thermal stability. Thermal shock performance of coated electrode sample with flexible transition layer is excellent, which indicated that the thermal shock resistance of NiAl2O4 coating was improved by the flexible connection layer. The results showed that for NiAl2O4 spinel coating, the electrical conductivity is 0.15s·cm-1 at 960℃. The whole coating resistance is very small as a result of the small thickness, which is lower than the resistance of graphite anode under the same surface area. NiAl2O4 spinel coating shows good salt corrosion resistance. The corrosion rate of the coating depends on the number of openings, thus reducing the porosity and increasing coating density can be effective methods to enhance the molten salt corrosion resistance of the coating.