Anodic dissolution under film-free conditions

With regard to the anodic dissolution under film-free conditions in which the metal does not exhibit passivity, and neglecting the accompanying cathodic process, it is now generally accepted that the mechanism of active dissolution for many metals results from hydroxyl ion adsorption " , and the sequence of steps for iron are as follows ... 

Anodic Dissolution under Film-free Conditions... 

Firstly, they might be expected to have an effect when corrosion occurs under conditions of active (film-free) anodic dissolution and is not limited by the diffusion of oxygen or some other species in the environment. However, if the rate of active dissolution is controlled by the rate of oxygen diffusion, or if, in general terms, the rate-controlling process does not take place at the metal surface, the effect of crystal defects might be expected to be minimal. 

The detailed anodic and cathodic reactions under the self-corrosion condition are schematically presented in Fig. 1.13. In general, anodic reactions occur mainly in film-free areas whereas in film-covered areas anodic dissolution is negligible. Cathodic reactions with hydrogen evolution as a main process, can take place in both the film-free and film-covered areas, although in a film-free area much faster than on a film-covered surface. 

Not only nanometric structures such as tubes or particles are important but also the application of nanoporous materials such as the case of nanoporous gold films [48, 87] (NPG) that could be prepared by selective dissolution of silver form Au/Ag alloys under free corrosion conditions. In this case, stability of the electrode can be increased and biomolecule immobilization could happen inside the mnable pores. Due to their well-defined nanopores, anodized alumina membranes have found many applications, among them, impedimetric immunosensing [63]. 

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