Evaluation of the protective properties of novel chromate-free polymer coatings using electrochemical impedance spectroscopy
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The protective properties of different types of novel chromate-free polymer coatings have been evaluated by means of electrochemical impedance spectroscopy (EIS). The first set of samples included steel panels coated with pentasiloxanes where different crosslinkinglcure chemistries were compared for their effect on the protective properties of the coatings. The second set contained Al 2024-T3 coated with a poly(2,5-bis(N-methyl-N-hexylamino)phenylene vinylene (BAM-PPV) based powder coating. Samples were exposed to 0.5 N NaCl and EIS data were recorded as a function of exposure time. The EIS data suggest that the nonfluorinated pentosiloxane provided better corrosion protection than the two fluorinated pentasiloxanes and that room temperature UV cure with a photo-acid catalyst provided better corrosion protection than phenol-catalyzed thermal crosslinking. The sample with the BAMPPV coating showed very good corrosion resistance during exposure for 50 days. Delamination properties were examined by means of scribing the sample after a certain period of exposure and evaluating the resulting changes in the impedance spectra. The delaminated area was observed with SEM at the end of the test. 2007 American Chemical Society.
