Corrosion behavior of nickel-iron alloys in molten carbonate

Journal Article · Mon Jan 01 04:00:00 EST 1996 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1836387· OSTI ID:201391

Vossen, J P.T.; Janssen, A H.H. ^[1]; Wit, J H.W. de ^[2]

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1. Netherlands Energy Research Foundation ECN, Petten (Netherlands)
2. Delft Univ. of Technology (Netherlands)

At an Fe content of approximately 25%, characteristics of Fe-rich and Ni-rich behavior could be observed. At cathodic potentials of {minus}1,500 mV carbonate decomposition and, when scanning anodically, carbon reoxidation proceeds faster on the Fe-rich alloys than on Ni-rich alloys. The first oxidation reaction of the metal is the oxidation of Fe: a cubic solid solution of FeO and {alpha}-LiFeO{sub 2} is formed. This reaction is followed by the oxidation of FeO to {alpha}-LiFeO{sub 2}. At a more anodic potential a cubic solid solution of {alpha}-LiFeO{sub 2} and NiO and {alpha}-LiFe{sub 5}O{sub 8} are formed. On the surface of the 25, 50, and 75% Fe alloys a dual layer is present on the surface. The outer layer is {alpha}-LiFe{sub 5}O{sub 8}, the inner layer is a cubic solid solution of NiO and {alpha}-LiFe{sub 5}O{sub 8}. At very anodic potentials {alpha}-Fe{sub 2}O{sub 3} is formed. This compound is formed slowly on the Fe-rich alloys and its formation cannot be observed in a cyclic voltammogram. The corrosion products identified are roughly in agreement with the thermodynamic equilibrium diagram of Yokokawa et al. The first reduction reaction that proceeds is the reduction of trivalent Ni ions in the scale. This reaction is followed by the reduction of {alpha}-LiFe{sub 5}O{sub 8}. In a later stage the NiO in the cubic solid solution is reduced. At potentials of approximately {minus}1,300 mV LiFeO{sub 2} in the cubic solid solution also is reduced. At more cathodic potentials the reduction of bivalent and trivalent Fe ions in the oxide proceeds until contact loss between the metal and the oxide occurs. Then, probably dissolved Ni and Fe are reduced to the metallic state.

• Sponsoring Organization: USDOE
• OSTI ID: 201391
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 1 Vol. 143; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
36 MATERIALS SCIENCE
BATTERY SEPARATORS
BINARY ALLOY SYSTEMS
CORROSION
DISSOLUTION
FERRITES
IRON ALLOYS
IRON OXIDES
LITHIUM COMPOUNDS
MOLTEN CARBONATE FUEL CELLS
NICKEL ALLOYS
NICKEL OXIDES
REDOX REACTIONS
VOLTAMETRY