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Potentiostatic control of ionic liquid surface film formation on ZE41 magnesium alloy

journal contribution
posted on 01.05.2010, 00:00 authored by Jim Efthimiadis, W Neil, A Bunter, Patrick HowlettPatrick Howlett, Bruce HintonBruce Hinton, D MacFarlane, Maria ForsythMaria Forsyth
The generation of potentially corrosion-resistant films on light metal alloys of magnesium have been investigated. Magnesium alloy, ZE41 [Mg−Zn−Rare Earth (RE)-Zr, nominal composition 4 wt % Zn, 1.7 wt % RE (Ce), 0.6 wt % Zr, remaining balance, Mg], was exposed under potentiostatic control to the ionic liquid trihexyl(tetradecyl)phosphonium diphenylphosphate, denoted [P6,6,6,14][DPP]. During exposure to this IL, a bias potential, shifted from open circuit, was applied to the ZE41 surface. Electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) were used to monitor the evolution of film formation on the metal surface during exposure. The EIS data indicate that, of the four bias potentials examined, applying a potential of −200 mV versus OCP during the exposure period resulted in surface films of greatest resistance. Both EIS measurements and scanning electron microscopy (SEM) imaging indicate that these surfaces are substantially different to those formed without potential bias. Time of flight-secondary ion mass spectrometry (ToF-SIMS) elemental mapping of the films was utilized to ascertain the distribution of the ionic liquid cationic and anionic species relative to the microstructural surface features of ZE41 and indicated a more uniform distribution compared with the surface following exposure in the absence of a bias potential. Immersion of the treated ZE41 specimens in a chloride contaminated salt solution clearly indicated that the ionic liquid generated surface films offered significant protection against pitting corrosion, although the intermetallics were still insufficiently protected by the IL and hence favored intergranular corrosion processes.

History

Journal

ACS applied materials & interfaces

Volume

2

Issue

5

Pagination

1317 - 1323

Publisher

American Chemical Society

Location

Washington D.C.

ISSN

1944-8244

eISSN

1944-8252

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2010, American Chemical Society