On the Limits of the EIS Low-Frequency Impedance Modulus as a Tool to Describe the Protection Properties of Organic Coatings Exposed to Accelerated Aging Tests

Abstract

This study analyzes the limitations of the low-frequency EIS impedance modulus as a tool to describe the protective properties of organic coatings subjected to accelerated aging tests. Acrylic clear-coated steel and hot-dip galvanized steel were exposed to accelerated test methods such as the neutral salt spray chamber and the Prohesion test for up to 2000 and 3000 h, respectively. During exposure, the protective properties of the coatings were monitored by EIS and visual inspection. We observed a significant discrepancy between the measured impedance modulus in the low frequency range (|Z0.01Hz|), and the actual deterioration of the metal–paint interface. The degradation of the two painted substrates is independent of the accelerated test considered. The |Z0.01Hz| values do not represent the actual degradation state of the metal–polymer interface. The manuscript discusses the reasons for the lack of agreement between EIS and visual inspection. The limitations of using the low-frequency EIS impedance modulus to describe the protective properties of organic coatings are highlighted, and several cautions for interpreting the raw EIS data are suggested. The reliability of possible thresholds of |Z0.01Hz| (e.g., failure below 106 ohm∙cm2) to define the protective performance of the coating turned out to be misleading.

Cardanol‐based polybenzoxazine coatings: Crosslinking structures, hydrophobicity and corrosion protection properties

“…The Bode plots of the polybenzoxazine samples immersed in 3.5 wt% NaCl solution for different times are given in Figure 6. Among those results, the impedance mode value at low frequency (|Z| 0.01Hz ) is usually considered as a semi‐quantitative indicator of the barrier performance of coatings 25,26 . As shown in the Bode impedance plots (Figure 6A,C) and phase angle plots (Figure 6B,D), the |Z| 0.01Hz of PC‐aptes and PC‐s coatings gradually decrease with the increase of immersion time, while the corresponding phase angle curves also demonstrate significant changes.…”

Microgrid-Patterned Ni Foams as Current Collectors for Ultrafast Energy Storage Devices

“…Typically, EIS results are categorized into two domains: (i) the low-frequency region, represented by a straight line, referred to as the Warburg impedance, and (ii) the high-frequency region, represented by a semicircle [27]. The low-frequency region is dominated by ion diffusion resistance at the electrode/electrolyte interface, whereas the high-frequency region represents from electron transfer resistance across the elec-trode/electrolyte interface [28,29]. As shown in Figure 7a, YP50F/40MP-Ni exhibited the steepest slope with a value of 30.96 (YP50F/bare Ni: 20.35, YP50F/24MP-Ni: 25.86, and YP50F/60MP-Ni: 28.37), confirming that it has the lowest ion-diffusion resistance for electric double layer formation at the electrode/electrolyte interface [30,31].…”

Comparative study between natural and artificial weathering of acrylic‐coated steel, aluminum, and galvanized steel

“…Beyond the EIS results, which could be a black box analysis, [ 39 ] a visual inspection of the corrosion morphology deposits shows a different damage mechanism between the different experiments.…”

“…As far as EIS is concerned, although this technique is often employed to monitor the degradation of organic coatings exposed in accelerated aging cabinets and outdoors, it has not been revealed to provide a reliable description of the degradation extent occurring on the investigated samples. The paint's high dielectric and barrier properties might likely have shielded the breakdown of the polymer/metal interface [ 39 ] when the coated panels are exposed in the accelerated aging cabinets. In fact, we recorded relatively high electrochemical impedance values (Figures 6 and 7) even in the presence of a significant accumulation of corrosion products at the metal/polymer interface.…”