Behaviour and Material Properties of the Grain Boundary on the Surface of an Anode during the Formation of a Dense Layer

Abstract

EPMA was used to investigate the corrosion-evolution mechanism of a dense ceramic spinel layer on the surface of NiFe2O4-10NiO-based cermet inert anodes during electrolysis in a high-temperature molten salt electrolyte. The evolution behaviour of the grain boundary on the surface of a 22(20Ni-Cu)(NiFe2O4-10NiO) anode during the formation of a dense layer was also examined. The experimental results showed that the content of the Al element on the grain boundary at the bottom of both the NiFe2O4,NiAl2O4 and FeAl2O4 was higher than that in the core of the 22(20Ni-Cu)(NiFe2O4-10NiO) anode, and the content of the Al element between the Ni-Cu and the dense layer of NiFe2O4-NiAl2O4-FeAl2O4 was higher than that in both the NiFe2O4,NiAl2O4 and FeAl2O4. It was concluded that the production of the NiAl2O4 was due not only to the reaction of the NiO with the Al2O2F42-, but also to the oxidisation of the Ni, which then reacted with the Al2O2F42-.