Hydrous oxide films

Electrochemistry of Hydrous Oxide Films Burke, L. D. Lyons, M. E. G. 18... 

Hydrous oxides films, many of them with electrochromic properties, have been grown on a number of other metals using potential cycling methods, for example Rh [126] and Ni [159] in alkaline solution. Film formation seems to occur via a similar mechanism to Ir on the various metals under potential cycling conditions. Further, the films exhibit the same type of potential-pH response [150,160] as that described above in the case of Ir. 

Conway and co-workers [511, 512] studied the kinetics of chlorine evolution on the hydrous oxide film formed on Ir by potential multicycling. An increase of up to 180 in Cl2 evolution rate was observed (Fig. 22), the apparent exchange current density increasing almost linearly with oxide thickness. This enhancement in Cl2 evolution rate at the Ir-solution interface was mainly attributed to an increase in microscopic surface area with... 

The essential features of the IHOAM theory are the suggestions that (1) premonolayer incipient hydrous oxide formation commences at noble metal surfaces at approximately the same potential as that at which thick hydrous oxide films are reduced and (2) the resulting oxyspecies function as mediators or inhibitors in many electro-catalytic processes. 

Corrosion control is one of the demonstrated uses of silicates in detergents since builders may be imagined as breaking the structural integrity (and increasing the rate of corrosion) of the hydrous oxide films that protect metals such as aluminum in contact with water. Other metals (e.g. zinc) and combinations of materials are sometimes attacked by alkaline detergents. 

Formation and reduction of a hydrous oxide film on platinum resulted in an increase in the charge for monolayer oxide reduction in subsequent experiments.20 Obviously the metal surface was roughened as a result of formation and subsequent reduction of the phase oxide. However, the roughness developed with this technique tended to decay under open-circuit conditions (a process that was accelerated by occasional potential sweeps for monitoring purposes). Such decay was more rapid than with platinum black deposits prepared from conventional chloroplatinic acid baths— evidence perhaps that in the former case the active metallic layer is of a more highly strained, finely divided character.128... 

Thick hydrous oxide films on gold can readily be produced, as in the case of platinum, by either dc or potential cycling techniques. 

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