The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys

Howlett, P. C., Khoo, T., Mooketsi, G., Efthimiadis, J., MacFarlane, D. R. and Forsyth, Maria 2010, The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys, Electrochimica acta, vol. 55, no. 7, pp. 2377-2383, doi: 10.1016/j.electacta.2009.11.080.

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Title The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys
Author(s) Howlett, P. C.ORCID iD for Howlett, P. C.
Khoo, T.
Mooketsi, G.
Efthimiadis, J.
MacFarlane, D. R.
Forsyth, MariaORCID iD for Forsyth, Maria
Journal name Electrochimica acta
Volume number 55
Issue number 7
Start page 2377
End page 2383
Total pages 7
Publisher Elsevier
Place of publication New York, N.Y.
Publication date 2010-02-28
ISSN 0013-4686
Keyword(s) ionic liquids
magnesium alloy corrosion
impedance spectroscopy
surface film
Summary An electrochemical approach to the formation of a protective surface film on Mg alloys immersed in the ionic liquid (IL), trihexyl(tetradecyl)phosphonium–bis 2,4,4-trimethylpentylphosphinate, was investigated in this work. Initially, cyclic voltammetry was used with the Mg alloy being cycled from OCP to more anodic potentials. EIS data indicate that, under these circumstances, an optimum level of protection was achieved at intermediate potentials (e.g., 0 or 0.25 V versus Ag/AgCl). In the second part of this paper, a small constant bias was applied to the Mg alloy immersed in the IL for extended periods using a novel cell design. This electrochemical cell allowed us to monitor in situ surface film formation on the metal surface as well as the subsequent corrosion behaviour of the metal in a corrosive medium. This apparatus was used to investigate the evolution of the surface film on an AZ31 magnesium alloy under a potential bias (between ±100 mV versus open circuit) applied for over 24 h, and the film evolution was monitored using electrochemical impedance spectroscopy (EIS). A film resistance was determined from the EIS data and it was shown that this increased substantially during the first few hours (independent of the bias potential used) with a subsequent decrease upon longer exposure of the surface to the IL. Preliminary characterization of the film formed on the Mg alloy surface using ToF-SIMS indicates that a multilayer surface exists with a phosphorous rich outer layer and a native oxide/hydroxide film underlying this. The corrosion performance of a treated AZ31 specimen when exposed to 0.1 M NaCl aqueous solution showed considerable improvement, consistent with electrochemical data.
Language eng
DOI 10.1016/j.electacta.2009.11.080
Field of Research 091207 Metals and Alloy Materials
030304 Physical Chemistry of Materials
Socio Economic Objective 850602 Energy Storage (excl. Hydrogen)
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2010, Elsevier
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