The Waterborne Symposium

Coatings mitigate corrosion on assets in marine environments by acting as barriers to aggressive molecules while maintaining adhesion to the asset.  Eventually, the coatings are breached or defects develop in the coatings that have the potential to act as breaches.  The performance of breached coatings no longer depends on barrier properties; instead, it depends on the adhesion strength at the polymer-substrate interface and resistance to substrate dissolution (corrosion).  Identifying polymer properties that govern the mitigation of corrosion at this polymer-substrate interface is essential to develop future corrosion control coatings.  Analysis of cathodic disbondment at the polymer-substrate using the unaided eye, scanning acoustic microscopy, fluorescence microscopy, and electrochemical analysis techniques has been reported.
Currently, literature is void regarding means to detect the earliest onset of coating failure using a non-destructive method and identify the major polymer properties that govern the mitigation of the corrosion process at the polymer-substrate interface. Confocal laser scanning microscopy (CLSM) and electrochemical frequency modulation (EFM) were employed to obtain time-lapse quantifiable acquisitions of thermoset and thermoplastic polymer clearcoat systems in the presence of an intentionally placed macroscopic breach while immersed in saline solution. CLSM enabled us to quantify the variability of delay time for micro-blister initiation, velocity of micro-blister growth from a defect, and initiation of substrate dissolution at the polymer-substrate interface. Via EFM analysis, we were able to measure the current induced by the corrosion process (e.g., micro-blistering and substrate dissolution) at the polymer-substrate interface. CLSM-EFM time-lapse acquisitions were conducted simultaneously to identify the onset of micro-blistering and substrate dissolution at the polymer-substrate interface to deconvolute the EFM signal from the corrosion process. The EFM corrosion analysis was vetted as an industrially accessible technique to evaluate a coating’s corrosion mitigation performance in the presence of a breach at the polymer-substrate interface for both clear and pigmented coatings during immersion.