Impedance sensor for the early failure diagnosis of organic coatings

A miniature impedance sensor used for field diagnosis of the early failure of coatings has been developed based on microelectronics and electrochemical impedance spectroscopy (EIS). The aging process of polyurethane-based coatings in salt spray test chamber was studied using the impedance sensor. Several critical indexes related to EIS such as phase angle ( θ 10Hz , θ 15kHz ), breakpoint frequency ( f b ), specific capacitance ( C 10Hz , C 15kHz ), and impedance modulus ( Z 0.1Hz ) were proposed to evaluate the severity of coating degradation. The results indicated that the impedance sensor could accurately monitor the degradation process of coatings, and once Z 0.1Hz < 10 6 Ω cm 2 , f b > 100 Hz, or θ 10Hz < 20°, the coating may be regarded as completely degraded and fails to protect the metal substrate.