Final Report - Strategic Environmental Research and Development ...

The solution resistance (R sol ) value was always very small compared to R corr and was ignored.
Kramers-Kronig (K-K) transformations were applied to the measured data to assess whether or
not invalid EIS data was collected [25, 26]. Particularly, a frequency range where the EIS data
did not follow the K-K transforms was determined from the K-K analysis. The remaining valid
frequency range was then used to fit the EIS data into the EC showed in Figure 6.1. In this work,
the regression of process models was the chosen method to validate the EIS data collected and an
explanation can be found elsewhere [27].
C c
R s
R f
R p
Pore
C dl
Figure 6.1. Equivalent circuit used for modeling of EIS data.
5.6.1.3 Results
Solution
Coating
Substrate
5.6.1.3.1 Exposure testing. Figure 6.2 shows the results of the exposure testing for the 15
coating systems examined. Results are reported as time to failure (TTF) indicating the first
instance of any form of visual degradation in the coating. Three main observations can be made.
First, Metallast and PreKote conversion coatings, regardless of the primer used, failed at
exposure times of less than 196 h. Second, combinations of Alodine, Boegel and T5900
conversion coatings combined with Deft or Hentzen primers showed good corrosion resistance at
longer exposure times. In fact all of these samples, except the sample with the Alodine
conversion coating and the Hentzen primer, showed no indications of corrosion after 1000 hours
of exposure. Third, samples prepared with Sicopoxy primers all failed in 196 hours or less of
exposure irrespective of the type of conversion coating used.
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