A COMPARATIVE-STUDY OF THE AVAILABLE ELECTROCHEMICAL METHODS FOR THE INVESTIGATION OF EPOXY AND FLUOROPOLYMER COATINGS DETERIORATION

The corrosion behaviour of phosphatized galvanized steel coated with b oth epoxy films of different thickness and fluoropolymer films has bee n studied by means of a.c. impedance spectroscopy (EIS), break-point f requency, potentiodynamic measurements and faradaic distortion methods as well as by the salt spray test. It was observed that the degradati on of protective films appears after a long-lasting initial period but once the process starts, the area of defects increases with exposure time. The rate of degradation depends both on type of polymer and of f ilm thickness for the same type of polymer. The same behaviour can be observed from the decrease in pore resistance and charge-transfer resi stance (EIS) and increase in double-layer capacitance (a.c. impedance measurements) and corrosion current (potentiodynamic measurements and harmonic analysis).