| Abstract
| - Hydrolysis of M−O−M (M = Sc−Mn) bridges was studied using quantum chemistry. A sequence of molecular clusters, containing single, double, and triple bridges, was considered for each atom type. The hydrolysis reactions of double and triple M−O−M bridges displayed substantial exothermicities, while water addition to a single bridge was generally found to be slightly endothermic. This points to entropy increase and the formation of mononuclear water complexes as decisive factors for dissociation.
- Water addition to molecular single, double and triple M−O−M bridges (M = Sc, Ti, V, Cr, and Mn) wereconsidered, and the stabilities toward stepwise hydrolysis of the oxygen bridges were studied by means of quantumchemistry. The M−O bond distances for the studied systems were compared to experiment for demonstration ofthe applicability of the B3LYP functional to the investigated systems. While substantial exothermicities werefound for the hydrolysis of double and triple M−O−M bridges, addition of water to a single bridge was generallyfound to be slightly endothermic. The lack of enthalpy drive for the (OH)yOxM−O−MOx(OH)y + H2O →2MOx-1(OH)y+2 reaction was taken to suggest that entropy increase and the formation of mononuclear watercomplexe, would be decisive factors for the dissociation. A mechanism was proposed for the observed erosion ofthe protective chromium oxide scale on high-temperature alloys at elevated temperatures and high humidities,based on the formation of CrO2(OH)2(g).
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