Environmental scanning electron microscope observations of H 2 S attack on the protective oxide on an Ni‐Fe alloy

Protective oxide layers on metals are frequently attacked by corroding agents. In this study, the attack of H 2 S on the protective oxide on 60 wt‐%Ni‐40 wt‐%Fe was studied. The oxide layer was prepared in a UHV system and the sulphidation was done in an environmental scanning electron microscope at an elevated temperature. The single crystal Ni‐Fe sample had a (100) surface which was oxidized by O 2 exposure at about 800 K to produce an epitaxial Fe 2 O 3 film. The breakup of the oxide was found to begin by pitting along surface features which are believed to correspond to atomic steps or step bunches. The areas where the oxide was more uniform were found to show better resistance toward the sulphidation.