Lithium Carbonate and Oxalate Salts as Corrosion Inhibitors for Magnesium Alloy AZ31 B in NaCl Solution

Abstract

The corrosion inhibition effectiveness of dissolved Li2CO3 and Li2C2O4 was studied for Mg alloy AZ31 B in 0.1 M NaCl solution. The electrochemical and corrosion inhibition properties of Li salts were studied using potentiodynamic polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and H2 evolution measurement methods. The corrosion inhibition efficiency as a function of immersion time was also investigated. The morphology and chemical composition of AZ31 B surfaces after 24 h immersion in 0.1 M NaCl with and without the addition of dissolved Li salts revealed considerable differences in corrosion properties. The role of Li+ ions, CO32- ions, and C2O42- on corrosion inhibition of AZ31 B was focused and their role in the corrosion inhibition was discussed. Li2CO3 had better corrosion inhibition efficiency compared to Li2C2O4 in 0.1 M NaCl solution at ambient temperature. The optimum concentration of Li2CO3 was 50 mM to provide the highest corrosion inhibition efficiency of 96.75 %, while the optimum concentration and inhibition efficiency for Li2C2O4 were 3 mM and 82.84 % respectively. Surface characterization of the Li2CO3 inhibited AZ31 B revealed that the enhanced corrosion protection was due to the formation of a protective layer mainly composed of MgCO3. Corrosion studies over time showed that Li2CO3 could effectively provide corrosion protection for 48 h, while Li2C2O4 became ineffective after 12 h of immersion in 0.1 M NaCl.