The Effect of Erosion on Corrosion Protection Properties of Coal Tar Epoxy Coating

In this work, the effect of erosion on corrosion behavior of coal tar epoxy coating was evaluated usingelectrochemical impedance spectroscopy (EIS) measurements. The surface morphology of the coatingwas examined by scanning electron microscope (SEM) after 10, 20, 30, 45 and 60 min of erosion processat an impact angle of 90º. After 10 min of erosion process, the Nyquist plots showed just a single largecapacitive semicircle and the phase Bode plots exhibited a line close to −80o in the middle frequencyregion, thereby indicating high corrosion resistance (about 109 Ωcm2). After 20 and 30 min of erosionprocess, the diameter of the Nyquist semicircle was decreased with time and two semicircles appearedafter 45 min. Furthermore, SEM observations revealed that the protection performance of coating wasdecreased by an increase in time of erosion due to the formation of holes and electrolyte penetration intothe coating. Finally, after 60 min of erosion process, the coating was partially removed and the substrate appeared.