Metallic, oxygen-containing reaction products after polarisation of iron in H2S saturated saline solutions

Abstract

Corrosion of Fe in H2S containing solutions is a general problem in oil production. Here, layers rich in the the tetragonal FeS modification mackinawite were grown by polarisation of iron 200 mV above the corrosion potential in H2S saturated acetic saline solution. These layers have no band gap above room temperature thermal energy, hence behave metallic. The sulfide layers are duplex layers, with an inner, oxide-rich and an outer, oxide-poor region. Strain induced by differences in oxygen content may be responsible for the poor adhesion between the two layers, which leads to eventual loss of the outer layer.