Corrosion behaviors of 2205 duplex stainless steel in biotic and abiotic NaCl solutions

Abstract

Biofilms on metal surfaces are important in microbiologically influenced corrosion processes. In this study, the corrosion behaviors of 2205 duplex stainless steel (DSS) in 3.5% biotic and abiotic NaCl solutions were explored with scanning Kelvin probe force microscope (SKPFM), electrochemical techniques, and X-ray photoelectron spectroscope (XPS). The results of SKPFM showed that the development process of sulfate-reducing bacteria (SRB) biofilms on 2205DSS was a slow and dynamic process and SRB preferentially attached to the ferrite phase. In the bacterial medium, the pittings of 2205DSS were narrower and deeper and the occlusion degree of pittings was aggravated. XPS and electrochemical measurement results showed that 2205DSS passivation film was sulfureted and that the corrosion current density was increased significantly by SRB metabolism. The voltaic potential measurement results indicated that the biofilm increased the potential difference on the steel surface. In the logarithmic and stable growth phases of SRB, the corrosion mechanism of 2205DSS was dominated by cathode depolarization. In the decline phase of SRB, starved SRB was more corrosive and the corrosion mechanism of 2205DSS was dominated by the extracellular electron transfer process, in which electrons were directly provided by ferrite.