Oxidation of iron at 400–600 °C in dry and wet O2

The oxidation of iron in dry and wet O2 at 400–600 °C has been re-investigated using gravimetry, SEM/EDX, XRD and FIB. In the presence of O2, water vapour accelerates iron oxidation at 500 and 600 °C. At 400 and 500 °C the magnetite layer is duplex and exposure to water vapour results in the formation of blades on top of a fine-grained hematite layer. At 600 °C it results in a surface without needles and blades. The increased oxidation rate at 500 and 600 °C is attributed to a smaller grain size in the hematite layer resulting in faster ion transport.