ELECTROCHEMICAL IMPEDANCE STUDY OF THE DEGRADATION OF ORGANIC-COATED COPPER

Electrochemical impedance spectroscopy (EIS) was used to study the cor rosion behavior of organic-coated copper plate. The organic coatings o f commercial lacquer or epoxy Epon resin 828 (Shell Co.) were evaluate d in 0.5 M sodium chloride solutions. It was found that the coating wa s saturated with water after a short period of time and a rapid increa se of coating capacitance and decrease of resistance were observed. Th e penetration of water molecules and electrolytes within the organic c oating proceeds in three steps. Firstly, water diffuses into the coati ng and saturates the free volume of the coating, causing a rapid rise of capacitance. Secondly, the electrolytes penetrate within the voids into the metal-coating interface and the corrosion of metal intensifie s; the coating resistance R-p and electrode charge transfer resistance R-ct decrease gradually during this period. The last period of time c orresponds to the constant R-p and R-ct plateaus followed by decreases of these resistances due to a loss of adhesion of polymer him on the copper substrate. The EIS procedure developed in the study proved to b e useful to characterize the degradation behavior of the copper-coatin g system. (C) 1998 Elsevier Science S.A.