Analysis of the chemical or bacterial origin of iron sulfides on steel by time of flight secondary ion mass spectrometry (ToF-SIMS)

We report here on ToF-SIMS measurements of the ³⁴S/³²S isotopic ratio on three different iron sulfide compounds, a Pyrite substrate, a troilite layer prepared by thermal sulfidation of iron in H₂S gas, and an iron sulfide prepared by interaction of a steel sample with a medium containing Sulfate-Reducing Bacteria (SRB). The measurements performed on the three kinds of surfaces show that ToF-SIMS is perfectly suitable, after fine tuning of its performance, to distinguish the origin (chemical or bacterial) of the sulfide formed on Fe based substrates from the measurement of the ³⁴S/³²S intensity ratio. This opens the way to quick and clear determination of the origin of sulfide degradation in many industrial areas.