Role of nanoceria coatings on the high temperature oxidation of stainless steels: An atomistic simulation

Computer simulations using the Density Functional Theory and GAUSSIAN 03 were implemented in predicting potential mechanisms that can be associated with the high temperature oxidation of stainless steels. In particular, the role of nanoceria protective coatings on the induced diffusional mechanisms at 1273 K was satisfactorily predicted. Atomistic calculations were made on computed activation energies for oxygen inward diffusion and for iron outward diffusion through the nanoceria coating and the chromium oxide scale, respectively. In addition, it was assumed that when nanoceria coatings are present in stainless steels, cerium ions can be incorporated in the Cr2O3 scale as dopants. Computer simulations indicate that in the absence of Ce ions in the chromia scale lattice Fe outward diffusion is dominant and accounts for the relatively high oxidation rates. It was found that in a Ce-doped Cr2O3 scale the predicted activation energies exhibit appreciable changes. Under these conditions the activation energies for both, iron and oxygen diffusion increase in magnitude. However, the activation energy for O inward diffusion falls below the one corresponding to Fe outward diffusion. In turn, oxygen inward diffusion becomes rate limiting accounting for the role of nanoceria coatings on the high temperature oxidation resistance of stainless steels.