Electrochemical impedance models for molten salt corrosion

Citation
Cl. Zeng et al., Electrochemical impedance models for molten salt corrosion, CORROS SCI, 43(4), 2001, pp. 787-801
Citations number
18
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Material Science & Engineering
Journal title
CORROSION SCIENCE
ISSN journal
0010-938X → ACNP
Volume
43
Issue
4
Year of publication
2001
Pages
787 - 801
Database
ISI
SICI code
0010-938X(200104)43:4<787:EIMFMS>2.0.ZU;2-W
Abstract
Taking into account the chemical stability and scaling features of metals, four electrochemical impedance models were proposed to represent their elec trochemical impedance responses in molten-salt systems at the open-circuit potential. Electrochemical charge transfer for the non-active metals is the rate-limiting process. For the active metals, the transfer of ions in the scale and the diffusion of oxidants in melts become increasingly important as compared with the electrochemical process. When a non-protective scale f orms on the metal surface, the impedance diagram may present the characteri stics typical of a diffusion-controlled reaction. i.e.. a semi-circle at hi gh frequency and a line at low frequency. When a protective scale forms on the metal surface, the Nyquist plot is composed of double capacitance loops , and the transfer of ions in the scale is rate limiting. An equivalent cir cuit of double layer capacitance in series with oxide capacitance can be us ed to represent this kind of impedance response. In the case of localized c orrosion, the Nyquist plot also consists of double capacitance loops, which can be described by an equivalent circuit of double layer capacitance para llel to oxide capacitance. Impedance measurements of Pt. Ni3Al and FeAl int ermetallics in molten-salt systems were conducted to verify the proposed im pedance models. (C) 2001 Elsevier Science Ltd. All rights reserved.