6/22/2023 0 Comments Ag charge with chlorideTransport of ions through the corrosion product layer is essential for continuous corrosion. A mixed conduction mechanism can occur at intermediate current densities. exponential relationship between current density and potential. The low field conduction mechanism takes place at low current density range ( 100 mA/cm 2) in which AgCl exhibited intrinsic conductivity, i.e. Depending on the magnitude of the applied anodic current density, the growth of AgCl follows either a low field or a high field or a mixed low and high field conduction mechanism. This behavior is attributed to the Ohmic resistance of the AgCl layer. The growth of continuous AgCl film under galvanostatic condition results in a shift of the applied potential to the more positive direction. However details of the inner structure of AgCl layer were not available and in many cases were reported with speculations. Several attempts have been made to characterize the inner structure of the continuous AgCl layer with various cross sectioning techniques including mechanical polishing followed by etching, sharp scalpel cutting and breaking by liquid N 2. At longer anodic polarization exposure, the morphology of AgCl top layer changes to a mosaic structures. The top view of the continuous AgCl film is comprised of dense, fine particles. The thickness of the non-continuous layer is fairly constant, and is less than 0.5 μm. Morphology of non-continuous AgCl patches was described having rounded smooth surfaces without manifestation of any crystal orientation. Gradually a thick AgCl film was observed on silver electrode at longer exposure time. At a certain overpotential more positive than the Ag/AgCl reversible potential, multi-layer AgCl grows laterally via nucleation and growth. The formation of the monolayer AgCl follows an adsorption-desorption mechanism. on the order of tens of micrometers, the dissolution of silver substrate was mediated by the Ohmic resistance of AgCl layer.Ī precursor monolayer of AgCl was reported to be formed at potentials below the thermodynamic Ag/AgCl reversible potential. on the order of a micrometer, the dissolution of silver substrate was under mixed activation-Ohmic control. The decrease of AgCl layer conductivity during film growth were attributed to the clogging of micro-channels or decrease in charge carrier concentration inside the micro-channels. As the film grew, the spaces between AgCl patches closed and ion transport was primarily via micro-channels running through AgCl patches. The ionic transport path through this newly formed continuous film was via spaces between AgCl patches. Patches of silver chloride expanded laterally on the substrate until a continuous film formed. AgCl was found to form at bottom of scratches on the surface which may be the less effective sites for diffusion or the favorable sites for heterogeneous nucleation. The precipitation and growth of AgCl on silver in physiological NaCl solution were investigated.
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