The objective of this work was to determine the effectiveness of dissolved Li2CO3 as a corrosion inhibitor for AZ31B-H24 sheet metal when immersed in NaCl (aq) at ambient temperature. Corrosion rates were determined by gravimetric mass loss and volumetric H2 evolution measurements and the observed inhibition was investigated further using potentiodynamic polarization, scanning vibrating electrode technique and X-ray photoelectron surface analytical measurements. We show that dissolved Li2CO3 significantly inhibits corrosion as it reduces the corrosion rate by a factor of 10. The manner in which inhibition is achieved is rationalized by the role played by the surface film produced during corrosion in inhibiting both the anode (anodic dissolution) and cathode (H2 evolution) kinetics. Inhibition involves the suppression of the filament-like corrosion mode, albeit on the macro-scale, and associated cathodic activation. By process of elimination, we propose that the Li+ cations play a key role in inhibiting the anodic dissolution and associated cathodic activation that is required to drive the filament-like corrosion.
The extent of corrosion inhibition of Mg alloy ZEK100 in 100 mM NaCl (aq) imparted by dissolved Li2CO3 (aq), with a particular focus on Li incorporation into the surface film that forms under activated anodic dissolution (anodic polarization) was determined. Dissolved Li2CO3 reduces corrosion by a factor of ∼12 when added at a concentration (100 mM) just below saturation. Effective inhibition involves suppressing the transition to filament-like corrosion, and associated anode/cathode activation, initiating at local breakdown sites. Such suppression is linked to the formation of Li-doped MgO as a corrosion product film during activated anodic dissolution. When formed by anodic polarization, the film composition also significantly affects the chloride ion distribution with the film. Without Li incorporation, chloride ions tend to enrich at the film/metal interface, whereas with Li incorporation, chloride ions tend to be uniformly distributed within the film.
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