A fundamental study of an Fe-Cr(111) binary alloy-metal oxide(110)-water interfaces

Tight-binding quantum chemical molecular dynamics (QCMD) method was used to study Fe- Cr/Cr₂O₃/H₂O interfaces in a boiling water reactor (BWR) environment. The system under study comprises an Fe-Cr (111) binary alloy covered with a Cr₂O₃ (110) surface and four water molecules. Reaction at the metal and oxygen-terminating metal oxide interface causes diffusion of oxygen ions into the metal surface and segregation of the metal ions. Concurrently, the interaction at the metal oxide-water interface causes the dissociation of water molecules. As a result, dissociated hydrogen atoms diffuse into the oxide film and are trapped at the interstitial sites. Hydrogen in the oxide film reduces its protective capabilities. Atomic charge analysis shows that oxygen at the metal-metal oxide interface prefers to bond with metallic atoms in the alloy rather than in the metal oxide. Oxygen atoms gain an average charge of -0.50e during the interaction. This electron transfer process initiates oxidation of the new alloy surface. Positively charged hydrogen atoms are repulsed from the metallic atoms generating an internal stress in the oxide film. The results of the present study confirm that degradation of the oxide film takes place from both interfaces reducing the protective qualities of the film.