Microbiologically influenced corrosion process of archaeological iron nails from the sixteenth century

The presence of Fe and S containing compounds inside rust layers covering iron archaeological nails was suspected but their real nature was not clearly determined. However, this finding suggested that sulphate reducing bacteria (SRB) could be involved in the corrosion processes. A thorough study focused on SRB and FeS compounds potentially present inside the rust layers was achieved on other nails recently excavated. For microbial investigations, the authors used a probe targeting SRB and performed fluorescence in situ hybridisation for cells identification. This procedure revealed that SRB were present in all analysed samples. Analysis of rust revealed that FeCO3 was the major component, indicating that the nails remained in anaerobic conditions, but FeS compounds were detected on each sample. Iron sulphides were localised on a few spots in the outer part of rust layers. This shows that the presence and activity of SRB had little influence upon the corrosion system.