Environmental humidity influence on a topcoat/Mg-rich primer system with embedded electrodes

Organic coatings are widely used to protect metal/alloy substrates from corrosion. They act by providing barrier to the transport of corrosive species such as water, ions and oxygen from the environment to the substrate. They are also sometimes dispersed with corrosion inhibitors which passivate the substrate, or metallic pigments that provide galvanic protection to the underlying substrate. Conventional coating evaluation procedure includes the use of accelerated standard tests such as ASTM B117, ASTM G85 (Prohesion), SAE J2334, QUV, QUV/Prohesion™, and other customized tests designed to simulate certain weather conditions. These methods rely on visual inspection for ranking and evaluating the protection performance of coating. The coating can, however, fail earlier than is predicted by these conventional test methods. Therefore, the use of embedded sensors in coating is a very appropriate approach to monitor and verify the state of protection offered by coating in situ. In this work, sensors embedded in coating were used to monitor the performance of coating in situ under changing humidity conditions, using electrochemical impedance spectroscopy (EIS) and electrochemical noise monitoring (ENM) methods. The ability of this unique technique to locate defects in coatings was also tested.