Formation of iron oxide and iron sulfide at high temperature and their effects on corrosion

Recent high temperature H2S corrosion study reported that a thermodynamically less stable iron oxide layer can also form in addition to iron sulfide. In this work, H2S corrosion experiments were conducted at 120 °C for different exposure times, ranging from 1 to 21 days. The inner layer was identified by Transmission Electron Microscopy (TEM) as Fe3O4 (magnetite); Fe3O4 was always present over time despite it being less stable than iron sulfide. The observed formation sequence of iron sulfide at high temperature was mackinawite → troilite → pyrrhotite → pyrite. The role of the different corrosion product layers in corrosion is discussed.