engleski

The study of coal tar epoxy protective coatings by impedance spectroscopy

Steel panels coated with a coal tar epoxy composition were studied by impedance spectroscopy in the dry condition as well as during exposure to synthetic seawater and to 10% NaOH solution. In the temperature range from 0 to 20 °C the dry coating behaves as an almost ideal capacitor with a dielectric constant ranging from 3.0 to 3.2. The coal tar epoxy coating immersed in synthetic seawater showed capacitative behaviour over a long period of exposure, in the frequency range 100 Hz to 100 kHz. However, the thinner coatings (~50 μm) were subject to a permanent slow degradation and their resistance decreased to approximately 107 Ωcm2 after 7 months of continuous immersion, whereas the degradation process for thicker coatings (~125 μm) was slower and the resistance was still above 108 Ωcm2 after 9 months of continuous immersion. The water uptake showed an initial rapid rise to between 9 and 13%. The coating degradation in a 10% NaOH solution is rather more rapid and after only one day of immersion a coating resistance of 106 Ωcm2 and a water uptake of 30% was found.

steel panels; coal tar epoxy; impedance spectroscopy

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