Journal
PROGRESS IN ORGANIC COATINGS
Volume 112, Issue -, Pages 93-100Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.porgcoat.2017.07.004
Keywords
Water-based protective coatings; Electrochemical impedance; Complex-capacitance; Resistivity distribution; Water uptake
Funding
- EmconMobil Gator Chemical Engineering Alumni Term Professorship
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Electrochemical impedance spectroscopy (EIS) and gravimetric measurements on two water-based coatings, containing either SrCrO4 or a mixture of Cr(VI)-free pigments and deposited on 2024 aluminium alloy, were performed to follow the water uptake in a 0.5 M NaCl solution as a function of exposure time. To account for the observed non-ideal capacitive behaviour, the coating capacitance and dielectric constant values were extracted from the EIS data in two ways: (i) by using a complex-capacitance representation and (ii) by fitting to the EIS data a model that assumed an exponential distribution of coating resistivity. The agreement of values obtained by these independent methods served to validate the model used to account for the observed pseudo constant phase-element (CPE) behaviour of the coatings. The water uptake calculated from dielectric constant values, employing a linear combination formula, was in good agreement with that directly measured by gravimetry, using supported-films.
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