Nanostructures surface passivation layer

It is well known that nanoparticulate colloidal dispersions of PANI in various paints at low concentrations cause tremendous improvements in corrosion protection [504]. PANI-NFs showed similar anticorrosive effects e.g., carbon steel coated with PANI-NFs has better corrosion protection than that with aggregated PANI. Raman spectroscopy analysis indicated that the surface of carbon steel coated with PANI-NFs formed a better passive layer, which is composed of a-ferric oxide and Fc304 [146]. The corrosion resistance performance of soya oil alkyd containing nanostructured PANI composite coatings has recently been studied [447]. An array of Fe nano wires within PANI-NTs was obtained using a two-step template synthesis [316]. This PANI-NT envelope may protect the Fe nanowires against a corrosive atmosphere. 

Nanostructured materials and coatings, in general, offer an improved performance under tribocorrosion conditions. Their overall performance is determined by the kinetics of mechanical removal of the passive layer with the applied friction, and by the kinetics of the repassivation when the frictionis stopped. However, improvements in mechanical properties such as high hardness and ductihty, etc, and in sirrface properties such as the uniform distribution of particles in the case of composite coatings, lower surface roughness, lower residual stresses, favorable textures with lower accumulation of stresses, etc, are necessary to achieve better performance. 

Useful atomic and subatomic scale information on hydroxylated oxide surfaces and their interaction with aggressive ions (e.g., Cl ) can be provided by theoretical chemistry, whose application to corrosion-related issues has been developed in the context of the metal/liquid interfaces [34 9]. The application of ah initio density functional theory (DFT) and other atomistic methods to the problem of passivity breakdown is, however, limited by the complexity of the systems that must include three phases, metal(alloy)/oxide/electrolyte, then-interfaces, electric field, and temperature effects for a realistic description. Besides, the description of the oxide layer must take into account its orientation, the presence of surface defects and bulk point defects, and that of nanostructural defects that are key actors for the reactivity. Nevertheless, these methods can be applied to test mechanistic hypotheses. 

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