Trace element effects in oxidation: The influence of cerium on grain boundary transport in nickel oxide

doi:10.1016/0167-2738(84)90163-2

Solid State Ionics

Volume 12, March 1984, Pages 343-351

https://doi.org/10.1016/0167-2738(84)90163-2 Get rights and content

Abstract

The oxidation rate of Specpure nickel in oxygen below 1000°C is considerably reduced by coating the metal thinly with cerium dioxide (CeO₂), which breaks up and becomes incorporated at low concentrations in the growing nickel oxide. Comparison with diffusion data suggests that grain boundary diffusion of nickel in nickel oxide is being reduced, despite a reduction in the oxide grain size. By use of SIMS, cerium has been shown to be segregated at grain boundaries within the outer oxide scale. Tracer experiments show that self-diffusion of nickel in these boundaries is not significantly affected by the presence of cerium. It therefore appears that the blocking effect of cerium is restricted to the inner scale, where CeO₂ is observed as a second phase. There is no known explanation for this “second phase” effect, which may account for many observations of oxidation retardation by trace elements.

Résumé

La cinétique d'oxydation du nickel (Specpure) sous oxygène en dessous de 1000°C est fortement ralentie lorsqu'on couvre le métal par une couche mince de dioxyde de cérium (CeO₂), qui se fractionne et s'incorpore en faibles concentrations à l'oxyde de nickel en cours de croissance. La comparaison aux donnés de diffusion suggère que la diffusion intergranulaire du nickel dans l'oxyde de nickel est réduite bien que la taille des grains diminue. Des analyses par SIMS ont permis de montrer que le cérium ségrégeait aux joints de grains dans la partie externe de la couche d'oxyde. Des expériences de traceur montrent que l'autodiffusion du nickel dans ces interfaces n'est pas affectée de fácon significative par la présence de cérium. Il apparait cependant que l'effet de blocage du cérium est limité à la partie interne de la couche dans laquelle le cérium est observé sous forme d'une seconde phase. Il n'existe pas d'explication de cet effet de “seconde phase” qui pourrait expliquer de nombreuses observations de retard de l'oxydation dûs à des éléments à l'état de trace.

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Citation Excerpt :
Many instances show that dilute elements have a marked influence on thermal oxidation of metals, but the level of understanding the oxidation mechanism leaves much to be desired [1–10].
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Trace element effects in oxidation: The influence of cerium on grain boundary transport in nickel oxide

Abstract

Résumé

Corros. Sci.

Corros. Sci.

Thin Solid Films

J. Mat. Sci.

Corros. Sci.

Oxid. Met.

Phil. Trans. Roy Soc. (London)

Metall. Trans.

Trans. Metall. Soc. AIME

Oxid. Met.