Insight into microbiologically induced corrosion performance of magnesium in tryptic soy broth with S.aureus and E.coli

In this research,microbiologically induced corrosion(MIC)performance of magnesium in tryptic soy broth with S.aureus or E.coli were systematically explored.The results showed that magnesium in biotic solution presented higher mass loss,thicker degradation product layer and more severe pitting corrosion compared to abiotic solution after 24 h of immersion.Electrochemical measurements including EIS spectra and polarization curve further suggested that the corrosion rate of Mg in biotic solution increased during the early stage owing to the decrease of p H,which was originated from the consumption of glucose and the resulting accumulation of acidic metabolites.However,corrosion rate subsequently decreased because of the reduction of acidic metabolites and production of alkaline compound as well as the corrosion protection provided by the corrosion product and biofilm.Moreover,the corrosion rate of magnesium in high concentration of S.aureus and E.coli solution was larger than that in low concentration of S.aureus and E.coli solution,respectively during the initial stage,but subsequently presented a reverse variation.In addition,more severe corrosion of magnesium was observed in S.aureus solution in comparison with E.coli solution.These results suggested that the MIC performance of magnesium was closely related to the concentration and species of bacteria.

Effect of sulphate-reducing bacteria on the electrochemical impedance spectroscopy characteristics of 1Cr18Ni9Ti

The electrochemical characteristics of 1Cr18Ni9Ti in sulphate-reducing bacteria （SRB） solutions and the biofilm of SRB on the surface of the 1Cr18Ni9Ti electrode were studied by electrochemical, microbiological, and surface analysis methods. Electrochemical impedance spectroscopy （EIS） of 1Cr18Ni9Ti was measured in the solutions with and without SRB at the culture time of 2, 4, 8 d, respectively. The measurement used two test methods, the nonimmersion electrode method and the immersion electrode method. It was found that the polarization resistance （Rp） of 1Cr18Ni9Ti in the solutions without SRB is the greatest for each test method. When using the nonimmersion electrode method, Rp shifts negatively at first and then positively, and the time constant is only one. Although using the immersion electrode method, the Rp shifts positively at first and then negatively, and the time constant also changes when the biofilm forms. The biofilm observed through SEM is with pores. It was demonstrated that SRB has accelerated corrosion action on 1Cr18Ni9Ti. The protection effect of the biofilm on the electrode depends on the compact degree of the film.