Determination of water uptake in organic coatings deposited on 2024 aluminium alloy: Comparison between impedance measurements and gravimetry

•Complex-capacitance representation was used to follow coating capacitance variation during immersion in the electrolyte.•Impedance data were analysed assuming an exponential distribution of coating resistivity.•Chromates leaching was quantified to accurately analyse the impedance data.•Water uptake...

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Bibliographic Details
Published in:Progress in organic coatings 2017-11, Vol.112, p.93-100
Main Authors: Nguyen, Anh Son, Causse, Nicolas, Musiani, Marco, Orazem, Mark E., Pébère, Nadine, Tribollet, Bernard, Vivier, Vincent
Format: Article
Language:English
Subjects:
Aluminum alloys
Aluminum base alloys
Capacitance
Chemical Sciences
Complex-capacitance
Electrochemical impedance
Electrochemical impedance spectroscopy
Epoxy coatings
Gravimetry
Measurement
Organic coatings
Other
Permittivity
Pigments
Probability distribution functions
Resistivity distribution
Water uptake
Water-based protective coatings
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Summary:•Complex-capacitance representation was used to follow coating capacitance variation during immersion in the electrolyte.•Impedance data were analysed assuming an exponential distribution of coating resistivity.•Chromates leaching was quantified to accurately analyse the impedance data.•Water uptake was determined by gravimetric measurements and compared with calculated values from dielectric constant values.•Measured water uptake was in agreement with that calculated by employing a linear combination formula. 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 0.5M 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.
ISSN:0300-9440
1873-331X
DOI:10.1016/j.porgcoat.2017.07.004