An in-situ sensor, based on electrochemical impedance spectroscopy (EIS), has been developed that can detect the absorption of moisture in polymeric systems. In the case of a coated metal, moisture intrusion into the coating foretells corrosion of the substrate so that the sensor is sensitive to the very early stages of corrosion. In an adhesive bond, the sensor monitors ingress of moisture into the bondline that causes plasticization of the adhesive and hydration of an aluminum adherend. Thus, it is able to warn of impending bond degradation before delamination or even substantial weakening of the bond occurs.

For a composite, the sensor detects low concentrations of absorbed moisture that can induce delamination and other damage during repair operations. The two versions of the sensor, a permanent electrode and a hand-held probe, give identical results to conventional three-electrode measurements that require immersion in the laboratory or clamp-on liquid cells. In contrast, the sensor is suitable for identical measurements under ambient service conditions as well as during laboratory accelerated testing. Applications of the in-situ sensor include development/screening of coatings, health monitoring of coatings and adhesive bonds to enable condition-based maintenance of structures, and inspection of composite structures prior to repair.

In-Situ Sensor to Detect Moisture Intrusion and Degradation of Coatings, Composites, and Adhesive Bonds, G.D. Davis, C.M. Dacres, and L.A. Krebs, DACCO SCI Inc.