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Effects of Different Relative Humidities on the Corrosion of the Epoxy-Coated Galvanized Steel in the Presence of Sulfur Dioxide

“…The value of n is between 0 and 1 (0 ≤ n ≤ 1) which is related to the deviation from the ideal capacitive behaviour 34 . The CPE represents a constant phase element to replace the double-layer capacitance (Cdl) to provide a more accurate fit to the experimental results 35 . The impedance parameters that were obtained by fitting the EIS data to the equivalent circuit are listed in Table- of the capacitors is equal to the sum of the double-layer and coating capacitances.…”

Study of molybdate–phytic acid passivation on galvanised steel

“…For n>0?8, Q can be generally denoted as equivalent to a capacitance. 12,19,20 Thus, the total impedance of equivalent circuit could be expressed by following equation …”

Electrochemical Identification and Categorization of the Protective Quality of Intact and Damaged Coatings

“…When calculated from impedance spectra of a coating having defects, the time constant that appears at the highest frequencies ( T 1 = R pore ⋅C coat ) may represent the resistance of pores within the coating and the capacitance of the coating. If present, the second time constant at lower frequencies may also represent the coating where some portion differs largely from that modeled by the first ( T 2 = R pore2 ⋅C coat2 ) as is the case for an electrolyte saturated layer in EEC 2 6, 7. However, in most cases, the working area of the coating being examined is not a bilayer and the second time constant (when observed) is indicative of the electrical double‐layer that forms on any exposed metal surface, represented by a charge transfer resistance and double layer capacitance ( T 2 = R ct ⋅C dl ) 8.…”

“…However, in most cases, the working area of the coating being examined is not a bilayer and the second time constant (when observed) is indicative of the electrical double‐layer that forms on any exposed metal surface, represented by a charge transfer resistance and double layer capacitance ( T 2 = R ct ⋅C dl ) 8. When corrosion is present on the metal surface, three time constants may be observed, as seen in EEC 3, and can be attributed to an oxide layer on the metal surface ( T 3 = R ox ⋅C ox ) 7. When fitting experimental data, often constant phase elements ( CPEs ) are used in place of ideal capacitors 9.…”

“…When mechanical damage is intentionally applied to a coating system and then monitored by EIS, the analyzed spectra can be used to explain similar processes observed in weathered samples 5, 7, 10, 11. Although there are numerous types of mechanical defects that may occur in a protective coating, two general classes of failure are depicted in Figure 2: abrasion and pinhole defects (i.e.…”