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This paper discusses the influence of coatings of praseodymium, dysprosium, and yttrium oxide gels on the oxidation behaviour of Fe–20Cr alloys. The morphology of the coatings was found to vary with the rare earth (RE) element used. The oxidation rates of Fe–20Cr specimens with all three RE oxide coatings were significantly lower than that of the uncoated alloy. The extent of influence on oxidation rate decreased in the following order: Pr, Dy, Y. The scale formed in the presence of RE oxides was a very thin, adherent chromia scale. Micrographic evidence of RE oxides in the chromia scales was found, further confirming the mechanism of scale growth in the presence of REs. Chromium ion diffusion is hindered by RE oxide coatings, making oxygen ion diffusion dominant. A direct correlation between RE ion radius and the extent of influence on chromia growth at 1000°C has been found.

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