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.