Mitigation of microbiologically influenced corrosion of MS 1010 mild steel by a silver–hydrazone complex

Microbiologically influenced corrosion (MIC) poses a significant challenge to the durability of mild steel in saline and industrial environments, where microbial colonization and biofilm formation can accelerate localized corrosion. In this study, the effectiveness of a silver-based hydrazone complex, [(Ag)(L)]NO 3 , in mitigating MIC of MS 1010 mild steel was investigated using Bacillus megaterium SKR7 as a biofilm-forming bacterial strain. The corrosion-inhibition performance of the complex was evaluated under both biotic and abiotic conditions and compared with that of AgNO 3 . Weight-loss measurements demonstrated that exposure to SKR7 increased the corrosion rate from 0.33138 to 0.89948 mm y −1 , confirming the pronounced influence of bacterial colonization on steel degradation. Addition of 50 ppm [(Ag)(L)]NO 3 reduced the corrosion rate under biotic conditions to 0.22961 mm y −1 , corresponding to an inhibition efficiency of 74%, compared with 69% for AgNO 3 . Electrochemical impedance spectroscopy further demonstrated an increase in charge-transfer resistance from 96.852 Ω cm 2 for the uninhibited biotic system to 361.15 Ω cm 2 in the presence of the silver complex. Potentiodynamic polarization measurements showed a decrease in corrosion current density from 10.0001 to 3.3759 μA cm −2 , accompanied by an increase in polarization resistance from 163.44 to 634.93 Ω. These results indicate that [(Ag)(L)]NO 3 effectively suppresses the electrochemical corrosion processes associated with bacterial exposure, with a predominantly anodic contribution to the inhibition behavior. SEM observations further revealed substantial surface deterioration and biofilm-associated deposits on the uninhibited steel, whereas the inhibitor-treated surfaces exhibited comparatively reduced localized damage. Overall, the results demonstrate that the silver–hydrazone complex provides effective protection of MS 1010 mild steel against microbiologically influenced corrosion and performs more effectively than AgNO 3 under the investigated conditions.