Evolution over time of mackinawite generated on carbon steel by the SRB metabolic activity: an in-operando Raman study

Abstract

Mackinawite was biologically synthetized by immersing carbon steel coupons in artificial seawater containing Sulphate-Reducing Bacteria (SRB) for 6 months. These coupons were removed from the culture medium solution and some were stored in air while others were placed in SRB-free culture medium solution. In operando Raman spectroscopy was used to analyse all these coupons immediately after extraction from the incubation medium and nanocrystalline, well-crystallized and partially oxidized mackinawite was detected. The evolution of these corrosion products was also monitored as a function of ageing time with this technique. Nanocrystalline and well-crystallised mackinawite transformed into partially oxidised mackinawite, greigite and sulphate green rust for an ageing time between 4 and 72 h. After 120 h, maghemite, magnetite, lepidocrocite, goethite appeared on the coupons placed in SRB-free culture medium solution as opposed to those stored in air atmosphere. Greigite and sulphate green rust were not observed for Raman measurements performed in air.

Keywords:

• Mackinawite
• SRB
• in operando Raman spectroscopy
• ageing tests

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was funded through the PROCOMIC research project. This European project was co-funded by the Normandy County Council, the European Union within the framework of the Operational Programme ERDF/ESF 2014-2020.