Mechanisms for oxidation and passive behavior of nickel in molten carbonate

The oxidation and passivation mechanism and the passive behavior of nickel in molten carbonate have been investigated with impedance measurements, quasi-stationary polarization curve measurements, and scanning electron microscopy. The oxidation of Ni probably proceeds according to a dissolution and...

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Bibliographic Details
Published in:Journal of the Electrochemical Society 1996-07, Vol.143 (7), p.2272-2280
Main Authors: VOSSEN, J. P. T, AMENT, P. C. H, DE WIT, J. H. W
Format: Article
Language:English
Subjects:
Chemistry
Electrochemistry
Exact sciences and technology
General and physical chemistry
High temperature electrochemistry (including molten salts)
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Summary:The oxidation and passivation mechanism and the passive behavior of nickel in molten carbonate have been investigated with impedance measurements, quasi-stationary polarization curve measurements, and scanning electron microscopy. The oxidation of Ni probably proceeds according to a dissolution and reprecipitation process. The slowest steps in the reaction sequence are probably dissociation of carbonate and diffusion of the formed NiO to the surface. In the passive range, it is most likely that dissolution of Ni exp 2+ proceeds after diffusion of Ni exp 2+ through the oxide layer. The Ni exp 2+ is formed at the metal/oxide interface. The slowest process is the diffusion of bivalent nickel ions through the passive scale. If only one reaction path is assumed, the formation of trivalent Ni ions probably takes place at the oxide/melt interface. This reaction is accompanied by the incorporation of an oxygen ion and Ni vacancy in the NiO lattice. The trivalent Ni ions and the Ni vacancy diffuse to the bulk of the oxide scale. The slowest step in this sequence is likely the dissociation of the carbonate ions and the subsequent incorporation of the oxygen ion in the NiO lattice.
ISSN:0013-4651
1945-7111
DOI:10.1149/1.1836993