Profiling iron corrosion coating on iron grains in a zerovalent iron system under the influence of dissolved oxygen

Rapid oxidation of Fe0 by O2 occurred when Fe0 grains were bathed in 0.54 mM FeCl2 solution saturated with dissolved oxygen (DO), forming a substantial corrosion coating on Fe0 grains. A sonication method was developed to strip the corrosion coating off the iron grains layer by layer. The transformation of the constituents and the morphology of the corrosion coating along its depth and over reaction time were investigated with composition analysis, X-ray diffraction and scanning electron microscopy. Results indicate that the sonication method could consistently recover >90% iron oxides produced by the Fe0-DO redox reaction. Magnetite (Fe3O4) and lepidocrocite (γ-FeOOH) were identified as the corrosion products. Initially, lepidocrocite was the preferential product in the presence of DO. As the oxide coating thickened, the inner layer transformed to magnetite, which retained as the only stable corrosion product once DO was depleted. The study confirms the phase transformations between γ-FeOOH and Fe3O4 within a stratified corrosion coating. The sonication technique exemplifies a new approach for investigating more complicated processes in Fe0/oxides/contaminants systems.