Electrochemical Noise Monitoring of the Cathodic Protection of Mg-Rich Primers

The cathodic protection of aluminum substrates by Mg-rich primers is due to the mixed potential that develops between the more active Mg particles in the binder and the substrate. The open circuit potential provides a measure of the protection of the primer with values changing from a mixed potential value of –1.0 V(SCE) to values consistent with the bare aluminum substrate. The use of electrochemical noise method is presented here to monitor the performance of a Mg-rich primer beneath a topcoat. Embedded sensors located between the topcoat and primer were used to perform measurements in a reverse configuration for sensors on separate panels and sensors on the same panel under immersion. The open circuit potential was measured to track the cathodic protection behavior of the Mg-rich primer. Analysis of the measured current and potential noises and the calculated noise resistance, localized index, and shot noise parameters is presented. The influence of a scribe introduced to the panels on the noise measurement is demonstrated. The results and analysis were used to address the feasibility of noise measurement for in-situ monitoring of the cathodic protection provided by the Mg-rich primer.