Impedance analysis of the distributed resistivity of coatings in dry and wet conditions
Résumé
A commercial coating (epoxy-polyaminoamide waterborne paint) deposited on a 2024 aluminium alloy
was characterized by impedance measurements,
first in dry conditions and then as a function of the
immersion time in NaCl solutions (wet conditions). The behaviour of the dry coating was close to that of
an ideal capacitor and could be accurately modelled with the power-law model corresponding to a
constant phase element (CPE) behaviour. Upon immersion in NaCl solutions, the behaviour of the wet
coating became progressively less ideal, i.e. farther from a capacitive behaviour. This result provided
support to the hypothesis that an inhomogeneous uptake of the electrolyte solution was the cause of the
often observed non-ideal responses of wet coatings. The experimental EIS data recorded for immersion
times up to 504 hours were compared with models assuming either a power-law or an exponential
variation of the coating resistivity along its thickness, respectively implying a phase angle independent of
frequency or slightly dependent on it.
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