3D Visualization of the Dissolution Products of a Metal in the Near-Electrode Layer at the Metal-Solution Interface

Abstract

A 3D profile of the layer of the metal dissolution products precipitated from a solution is reconstructed by means of reflectometry. Its nano-scale resolution in thickness enables one to investigate in situ the formation of micro- and nano-size adsorption islets, new phase nuclei, and steady-state localized superficial domains (with different rates of the metal dissolution and complex formation processes). In this way, the originally unseen structure of the metal surface defects is visualized. The digital optical images obtained with a scanner for a small probed surface spot were processed in order to clarify the pitting nature of the metal dissolution in distilled water and visualize the latent defective metal structure. Local dissolution centers (pits) appear mainly in the first 10 to 20 min and determine the corrosion rate. The technique is highly sensitive to thin layers and, consequently, to the ions in solution. All these peculiarities make the measurements of the tangential non-uniformity of the layer at the studied spot of the electrode surface highly informative. The secondary precipitated layer of dissolution products can be considered as a distributed sensor layer immobilized at defects of the metal surface. Minor changes in the solution chemistry (pH, oxygen content, etc.) lead to the change in the dissolution rate and, hence, in the thickness, structure, and composition of the secondary precipitated sensor layer.