Dislocations in Particular Oxides

The following sections relate to monoxides (Section 4.1 and 4.2), followed by dioxides (Sections 4.1-4.5), sesquioxides (Section 4.6), mixed oxides (Sections 4.7-4.9), other oxides (Section 4.10), and non-oxides (Section 4.11). 

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Pt-Rh/AROs catalysts are widely used in automotive-exhaust emission control. In these systems, Pt is generally used for the oxidation of CO and hydrocarbons and Rh is active for the reduction of nitric oxide to N2. HRTEM and AEM show two discrete particle morphologies and Pt-Rh alloy particles (Lakis et al 1995). EM studies aimed at understanding the factors leading to deactivation, surface segregation of one metal over the other and SMSI are limited. There are great opportunities for EM studies, in particular, of surface enrichment, and defects and dislocations in the complex alloy catalysts as sites for SMSI. 

THE FORMATION OF dislocation etch pits and in particular the nucleation of steps at dislocations and the motion of steps are briefly discussed. The role of dislocations in oxidation processes is summarized. 

The Peierls-Nabarro model has been used to determine properties of dislocation cores, the misfit energy and particularly changes with pressure. This is based on the assumption of a planar core which is the most able to ghde. It has direct implications for slip systems. In order to move, a dislocation must overcome an energy barrier under an applied stress. The Peierls-Nabarro model has been used to constrain dislocation core sizes and Peierls stresses in several oxides and sihcates relevant to the Earth s mantle, particularly periclase [439], ohvine [440,441], ringwoodite [80],... 

Entrapped oxygen and water vapor in lubricants can act as anti-wear additives to form protective surface films. Metals are known to catalyze decomposition of certain lubricants, and decomposition temperatures may be reduced by 60°C or more. This is particularly true of bearing surfaces, on which the surface energy may be increased by stress-induced dislocations and by freshly exposed metal surfaces. An example of the way a tribochemical surface is affected by a polymerization process is vinyl chloride. If the load is increased from 0.1 to 0.5 kg in the presence of a vinyl chloride atmosphere, the Auger spectra of iron oxide surface shows a marked increase in the concentration of vinyl chloride on the surface (Buckley, 1981). 

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