51312-01653-Attempting to locate defects in coating using embedded electrodes

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Product Number: 51312-01653-SG

ISBN: 01653 2012 CP

Author: Gordon P. Bierwagen

Publication Date: 2012

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Organic coatings are widely used to protect various metallic structures from corrosion. They are intended to prevent the substrate from interacting with ions oxygen and electrolytes from the environment. Most often protective organic coating consists of two layered systems with a primer and a topcoat. The topcoat acts as a barrier to the outer environments whereas primer may be loaded with sacrificial pigments or corrosion inhibitor for protection against corrosion. The use of embedded sensors in coatings has facilitated in-situ monitoring of coating performance. Electrochemical impedance spectroscopy (EIS) and electrochemical noise method (ENM) in conjunction with embedded sensors/electrodes have been successfully tested for in-situ monitoring of electrochemical changes in coating under prohesion and B117 conditions. However the ability of the sensors to locate defects or corrosion of the substrate is yet to be explored. Initial attempts at finding defects in coatings by embedded electrodes in humidity/moisture condition did not provide very encouraging results. Such study could however aid in understanding the efficiency of sensor to locate defects in the coatings and facilitate timely repair. In this study sensors were adhered on top of an epoxy primer pigmented with Mg particles on a large 30 mm x30 mm aluminum AA 2024 T3 substrate. A topcoat was then applied such that the sensors were embedded between the primer and the topcoat. Six sensors were attached on six corners of the panel. Defects (scribe) were created between some sensor configurations. The panel was then exposed to B117 condition and in situ-EIS and ENM measurements were performed. EIS were performed using the sensor-sensor and sensor-substrate configuration whereas ENM was performed using the two sensors as two working electrodes and the substrates as the reference electrode. A comparison of the EIS and ENM data between scribed region and intact (unscribed) region was made and changes in the electrochemical behavior between them examined for differences which would help locate the scribe-damaged area.