A bacterial biofilm-regulated corrosion protection for magnesium-based sacrificial anode

Abstract

Magnesium (Mg) alloys are traditionally used as sacrificial anodes, but their high self-corrosion rates limit their application. In this study, a bacterial biofilm protection method was developed, and tested on Mg under potentials of −1.5 V, −1.4 V, −1.3 V, and −1.2 V vs. saturated calomel electrode (SCE), as well as with a Mg-Q235 carbon steel (CS) couple. The Mg sample was immersed in a Bacillus sp. inoculum at a bacterial concentration of 10⁵ CFU mL⁻¹ for 7 days, during which highly active biofilms were formed and the mean fluorescence efficiency reached 78.5 ± 10.9 % on the 7th day. In this case, the biofilm effectively inhibited the self-corrosion of the Mg, reducing the corrosion rate to a much low value, minimally around 11.53 ± 0.06 μA cm⁻². When the Mg started cathodic protection, the biofilm on the surface lost its blockage and thus the Mg was activated to give out a required galvanic current. The anode efficiencies of the Mg at galvanic potentials of −1.3 V and −1.4 V vs. SCE, or when the Mg was coupled with a carbon steel reached 70.9 ± 2.8 % and 73.3 ± 1.8 %, or 79.8 ± 0.9 %, respectively, significantly higher than the protective efficiencies around 50 % usually reported in literatures. Detailed biofilm-regulated protection mechanism at OCP losing its blockage for cathodic protection is also analyzed in the paper.