The role of oxygen transport in oxidation of Fe-Cr alloys

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Abstract
A nuclear technique has been used to study the oxidation of Fe-Cr alloys having Cr contents of 16, 19, 28, 38, 50 and 100 wt.%. The yield of the lgO(p, α)l5N reaction was used to determine the 180 distribution in the oxide scale. Specimens were oxidized at 850°C and 950°C first in natural oxygen and then in 18O and vice versa. Any diffusion of oxygen would have shown as a mixing of the oxygen isotopes in the scale. The evidence indicates that bulk oxygen diffusion plays a negligible role in the oxidation reaction. Evidence for penetration of oxygen through the existing scale is found for the alloys of high Cr content (≥ 38%) oxidized at 950°C and it seems that this is due to cracking of the scale giving short-circuit gas diffusion paths.