Dynamic Impedance-Based Monitoring of St37 Carbon Steel Corrosion in Sterilized Manganese Broth Medium

Microbiologically influenced corrosion (MIC) of metals is a serious challenge where manganese oxidizing bacteria (MOB) can play a relevant role. However, there is no consensus on how MOB influences corrosion mechanisms. This arises from the complexity of the corrosion process and the challenge of distinguishing the effects of chemicals from the biological contributions. In this work, the electrochemical characteristics of St37 carbon steel in a bacteria-free Mn broth medium were monitored for 5 h using the new Dynamic Electrochemical Impedance Spectroscopy (DEIS) technique. The results were compared with those from the classical electrochemical methods to validate the new technique. DEIS accurately tracked corrosion processes in the media and analysis of the variation of parameters such as the polarization resistance (R_p), corrosion potential (E), and constant phase elements (n, and Y₀) proved valuable insight in understanding the corrosion processes. The study reveals that, in a sterile Mn broth medium, the corrosion resistance of St37 steel improved over time due to the adsorption of yeast and (NH₄)₂Fe(SO₄)₂ on the surface. SEM and EDX results confirm the adsorption of protective deposits on the steel surface. The polarization resistance of St37 steel increased up to 12,000 Ω cm² at 5 h of measurement. The results from the DEIS technique conform with those from the classical methods. The work therefore established the DEIS technique as reliable for corrosion measurements in a dynamic system. The results obtained can serve as a suitable baseline for future MIC studies induced by MOB.