Inhibiting Corrosion of Mg Alloy AZ31B-H24 Sheet Metal with Lithium Carbonate

Abstract

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.

Corrosion Inhibition of Mg Alloy ZEK100 Sheet Metal by Dissolved Lithium Carbonate

“…The H 2 evolution rate is consistently lower than the mass loss rate, which is expected based on corrosion rates reported for AZ31B immersed in NaCl (aq). 55,62 The discrepancy is likely explained by a lower H 2 gas collection efficiency than the assumed 100% value. Gas bubbles sticking to the corroding surface and the glass surfaces used to construct the collection apparatus (inverted funnel and upside-down burette) are limitations of this technique.…”

“…61 We showed that this concentration, over the range from 0.0001 M to 0.1 M, inhibited corrosion of AZ31B-H24 to the greatest extent. 55 The pH of this inhibiting solution is 11.1. Similar testing was conducted in pairs of test solutions to determine combinatory effects of dissolved Li + cations, OH − anions and CO 3 2− /HCO 3 − anions on corrosion inhibition.…”

“…[46][47][48][49] Combining the beneficial effect of Li, as an alloying element, on stifling the anodic kinetics of Mg 50 and of dissolved OH − anions 51,52 and total dissolved carbonate anions (CO 3 2− /HCO 3 − ), produced by dissolving a carbonate salt, 53,54 on stifling both the anode and cathode kinetics of Mg, we investigated the inhibition extent imparted by dissolved Li 2 CO 3 (aq) on the corrosion of AZ31B-H24 in 0.1 M NaCl (aq) with promising results. 55 We showed that dissolved Li 2 CO 3 (aq) inhibits corrosion by suppressing the filament-like corrosion mode and associated anode/cathode activation at breakdown sites. We also showed that inhibition involves a reduction in both the global anode (anodic dissolution) and the global cathode (H 2 evolution) kinetics.…”

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part III—Corrosion Inhibitors and Combining Them with Other Protection Strategies

“…Similarly, in the physiological environment, due to the presence of a variety of carbonates, their influence on the corrosion rate of Mg alloys has been demonstrated to be profound [ 50 ]. The inhibition performance of dissolved bi/carbonate is highly dependent on the electrolyte pH, being more effective at alkaline pH [ 51 ], since the concentration of bi/carbonate rapidly decreases in favor of carbonic acid as the pH becomes more acidic. The inhibition effect of individual carbonates seems to be unsatisfactory for severe corrosive conditions, while the synergistic effects with other inhibitors, including Li + ions [ 51 , 52 ] and phosphates (H 2 PO 4 − /HPO 4 2− /PO 4 3− ) [ 50 ], can boost the overall reduction in corrosion rate.…”

“…The inhibition performance of dissolved bi/carbonate is highly dependent on the electrolyte pH, being more effective at alkaline pH [ 51 ], since the concentration of bi/carbonate rapidly decreases in favor of carbonic acid as the pH becomes more acidic. The inhibition effect of individual carbonates seems to be unsatisfactory for severe corrosive conditions, while the synergistic effects with other inhibitors, including Li + ions [ 51 , 52 ] and phosphates (H 2 PO 4 − /HPO 4 2− /PO 4 3− ) [ 50 ], can boost the overall reduction in corrosion rate. The environmental benignity of the carbonates also renders them suitable and unrestricted components to improve corrosion inhibition.…”