Effect of trivalent rare earth dopants in nanocrystalline ceria coatings for high-temperature oxidation resistance

Nanocrystalline ceria (NC) and La3+-doped nanocrystalline ceria (LDN) particles synthesized by the micro-emulsion method were coated onto AISI 304 stainless steel (SS) in order to study their high-temperature oxidation resistance properties at 1243 K in dry air for 24 h. Results were compared with those for micro-ceria (MC) coatings. The coated samples showed 90% improvement in oxidation resistance compared to uncoated and MC coated steels as seen from SEM cross-sectional studies. X-ray diffraction (XRD) analysis showed the presence of chromia in both NC and 20 LDN (NC doped with 20 at.% La3+) samples which is absent in uncoated steels. From secondary ion mass spectrometry (SIMS) depth profiles, Fe, Ni depletion zones were observed in LDN-coated samples, indicating diffusion through the oxide layer. The role of oxygen vacancies in the nanoceria coatings on the formation of protective chromia layers is discussed.