Interpretation of EIS data from accelerated exposure of coated metals based on modeling of coating physical properties

Constant-phase-element behavior caused by inhomogeneous water uptake in anti-corrosion coatings

“…(3). The  ratio is close to 10 for the Brasher and Kingsbury formula, and below 2 for both the series combination and the Maxwell approximation, in agreement with Hinderliter et al [11]. The permittivity profiles computed according to Eq.…”

“…1a, the pores are Fig. 1a, in which the local electrolyte volume fraction increases as  increases, is similar to the one proposed by Hinderliter et al [11] who, however, clearly separated an outer electrolyte-affected coating region from an inner pristine coating region and therefore did not consider pores that reach the substrate.…”

“…(2) and (3) for the same  w ,  c ,  w and  c values as those considered in reference [11], are shown in Fig. 3.…”

“…Taking into account that, in each elemental layer parallel to the interfaces, each position is occupied by either the coating material or the electrolyte, these two media may be assumed to be in parallel to each other. Therefore, the overall conductivity ( =  -1 ) and permittivity () may be obtained as linear combinations of the conductivities and permittivities of the two media (coating and electrolyte) with coefficients equal to the respective volume fractions [11], i.e.,…”

“…However, those authors did not propose any specific resistivity or permittivity profiles. Inhomogeneities in the coating properties have been considered by Hinderliter et al [11,12] who related these inhomogeneities with electrolyte uptake in the coating and, taking into account various geometries for the electrolyte-filled coating defects, developed physical models of substrate/coating/electrolyte systems. Roche et al [13,14] observed the formation of an interphase region, next to the substrate/coating interface, with properties significantly different from those of the bulk coating material.…”