Rare earth oxide coatings to decrease high temperature degradation of chromia forming alloys

Abstract

The addition of small quantities of reactive elements such as rare earths (RE) to chromia or alumina forming alloys improves the high temperature oxidation resistance. Traditionally, these elements are alloying additions or are added as oxides to form a dispersion. The alloys can also be coated with RE oxides. Several methods can be used to coat alloy substrates with RE oxides and the sol-gel process is considered to be quite efficient, as it generates the very small oxide particles. This paper presents the influence of surface coatings of Ce, La, Pr, and Y oxide gels on the oxidation behavior of an Fe-20Cr alloy at 1000 °C. The morphology of the rare earth (RE) oxide coatings varied with the nature of RE. The oxidation rate of RE oxide coated Fe-20Cr was significantly less than that of the uncoated alloy. The extent of influence the RE oxide coating exercised on the oxidation rate decreased in the following order: La, Ce, Pr, Y. The scale formed in the presence of RE oxide was very thin, fine grained and adherent chromia. A direct correlation between rare earth ion radius and the extent of influence on chromia growth rate at 1000 °C was observed.

High temperature oxidation resistance of rare earth chromite coated Fe-20Cr and Fe-20Cr-4Al alloys

“…Growth of chromium dioxide or aluminium oxide on the coated alloy specimens was inhibited by incorporation of La 2+ ions in the growing scale. This La ion segregates to the grain boundaries in the scale and blocks substrate-cation diffusion, thus inhibiting scale growth 11 . This blocking effect is due to the higher ionic radius of the La ion, compared with the ionic radii of the substrate cations.…”

An Insight into Geometries and Catalytic Applications of CeO2 from a DFT Outlook

“…The nanocrystalline ceria coatings were observed to enhance the oxidation resistance character by 90% compared to those cases of uncoated and microceria-coated steels. Likewise, Fernandes and Ramanathan [40] reported the effect of surface coatings of Ce, La, Pr, and Y oxide gels on the oxidation behavior of a Fe-20Cr alloy at 1000 • C. Alloying small quantities of rare earth elements to chromia or alumina enhances their high-temperature oxidation resistance. Usually, rare earth elements are added or doped with oxides to form a protective layer for chromia and alumina alloys.…”

Obtenção de revestimento à base de Mn e Co por dip-coating sobre aço inoxidável ferrítico

“…Diversas técnicas têm sido empregadas para a obtenção de revestimentos, entre eles, materiais de elementos reativos (21), perovskitas ( 22) e óxidos do tipo espinélio (23).…”