The Effect of O2 Traces in H2/H2O Atmosphere on Oxide Growth on Iron and Crofer 22 APU at 550 and 600 ∘C

Journal article, 2026

The effect of O2 traces on the oxidation behavior of iron and a Fe–Cr steel interconnect material (Crofer 22 APU) in a 5% H2 + 3% H2O (bal. Ar) environment at 550 and 600 ∘C has been investigated. The reaction of O2 with H2 in the gas at 550 and 600 ∘C is slow, allowing O2 traces to reach the samples, despite an excess of H2 in the gas. Traces of unreacted O2 resulted in increased oxidation rate as well as hematite formation on iron. The rate of iron oxidation increased with the level of O2 in the range of 2–550 ppm. The acceleration of oxide growth by O2 traces is attributed to a greater oxygen activity gradient across the iron oxide scale. To remove O2 from the gas, a nickel component was positioned upstream from the samples which allowed the gas to equilibrate. Consequently, iron oxidized without hematite formation. Moreover, the use of the nickel component greatly improved the reproducibility of results for both iron and Crofer 22 APU. The use of a catalyst for the O2 + H2 reaction in H2/H2O exposures proved essential because it provides better control of experimental conditions and thereby more reliable experimental outcomes.