Application of SVET/SIET Techniques to Study Healing Processes in Corroding Micro-confined Defects

Active corrosion protection based on self-healing of defects in coatings is a vital issue for development of new advanced corrosion protection systems. However, there is a significant lack of experimental protocols which can be routinely used to reveal the self-healing ability and to study the active corrosion protection properties of organic and hybrid coatings. One of the tools which allow direct observation of the corrosion activity in the micro-confined defects is Scanning Vibrating Electrode Technique (SVET). Regrettably, it is only sensitive to charged species and is unable to identify the species detected.

The present work demonstrates how micro-potentiometric and micro-amperometric mapping of different species in electrolyte near the active surface can help the interpretation of SVET data, complementing it. The microcapillary-based potentiometric pH-sensor was used to acquire distribution of OH^- ions during the corrosion processes in artificial micro-defects in pure and inhibitor-doped electrolytes. The inert metallic microelectrode was employed here to study the distribution of local oxygen concentration near the cathodic and anodic defects. The 2024 aluminium alloy coated with hybrid sol-gel film was used as a model system to study the healing of artificial defects by different organic and inorganic corrosion inhibitors.

The corrosive process was addressed from the side of the solution. The measurement of the ionic currents in solution permitted to follow the evolution of the process in time and the inhibition kinetics of a soluble inhibitor. The local distribution of pH and dissolved oxygen gave extra information about the corrosion and inhibition process. This can be very useful in studies of self-healing of coatings in defects.