Compact coating impedance detector for fast evaluation of coating degradation

In this paper, a prototype miniaturized impedance measurement instrument, a coating impedance detector (CID), is proposed to provide a quick estimate of the protective capacity of coatings. The performance of the CID was compared with a conventional potentiostat by measuring the impedance modulus of commercial coatings. Five coated samples with various impedance moduli were used to evaluate the efficiency and functionality of the CID. The results indicate a good correlation between the impedance moduli obtained by the CID and laboratory-type potentiostat in the range of 107-109 Ω-cm2. Furthermore, measurements associated with coating delamination demonstrate that the CID can acquire impedance data quickly while maintaining its precision. Although the CID is unable to evaluate in detail the performance of perfect coatings or provide kinetic information regarding the corrosion process occurring within the metal-coating interface, it is extremely useful to observe the changes in the coating impedance modulus in the critical range to help workers determine whether coating maintenance should be scheduled.