A novel sensor for evaluating coating barrier has been developed based on electrochemical impedance spectroscopy (E2S) aiming aton-site monitoring of coating failure. The aging process of three organic coatings, namely polyurethane (PU), fluorine polyurethane(F-PU) and acrylic polyurethane(A-PU) coatings in salt spray test chamber (SST) were studied based on the coating sensor and conventional electrochemical cell. Several indexes related to ELS such as the phase angle at 10 kHz and 10 Hz, the breakpoint frequency of 45°phase angle, the specific capacitance at 10 kHz and the impedance modulus of 0.1 Hz, were proposed to evaluate the severity of coating aging. It is found that the on-site sensors exhibit a similar aging curve as the conventional EIS does. Once the impedance modular at 0.1Hz is less than 106 Ohnvcm2, or the breakpoint frequency of 45° phase angle is more than 100Hz or the phase angle at 10Hz is below 40°, the coatings may age significantly and fail to protect the metal substrate. One-year test indicates that the EIS sensor can not only detect the coating aging process of seaplanes, ships and bridges, but also provide a criterion for the on-condition maintenance of coatings.
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