The change of dielectric properties of barrier coatings during the initial state of immersion

Abstract

The initial state of immersion of seven commercially available barrier coatings was monitored using electrochemical impedance spectroscopy (EIS). Within the first spectra, a fast change of state can be detected at low frequencies. This non-stationarity can be eliminated with an evaluation procedure, known as the Z-HIT algorithm, resulting in causal spectra which can be interpreted reliably and accurately. The spectra of the coatings can be well modeled by a parallel combination of a capacity and a two step continuous time random walk (CTRW-2) as a relaxation element. The capacity represents the pure dielectric properties of the coating material which are not affected by the penetrating electrolyte solution. This part of the evaluated coating capacity remains constant during the soaking. In contrast, the parameters of the CTRW-2 change during water uptake and can be attributed to pores and free sites within the coating material. This separation into parts which are affected by the penetrating solvent and parts which can be described by an ideal dielectric material reflects the inhomogeneous nature of the coatings under test.In the entire measured frequency range the change of the dielectric properties of the investigated systems can be modeled by the same equivalent circuit which was used formerly to interpret impedance spectra of barrier coatings in the saturated state, requiring four to five adjustable parameters for simulating the experimental data.

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

“…Many authors believe that samples must be carefully selected before aging tests to obtain homogeneous data [1,2] and a more reproducible campaign. However, real paint films very often do not show a pure capacitive behavior over the whole frequency range [33,[51][52][53][54] because the application methods induce the formation of defects. In this work, we examine a range of samples, including coatings with some unavoidable weak spots, to investigate the limit of |Z| in a broader range of scenarios closer to actual application conditions.…”

Self‐healing silane coatings of cerium salt activated nanoparticles

“…a–d. Penetrating water through the pores and free sites within the coating material during the first days of the immersion (2 and 24 h), leads to a drift in experimental data and fitted results in both samples. By increasing the immersion time due to blocking the pores/defects (by precipitation of either insoluble corrosion products or the inhibition activity of the film) and consequently slowing the electrolyte diffusion into the coatings, drift is almost not observable within the spectra for both samples and the fittings are in good agreement with the experimental data.…”

Effect of the Metallic Surface Finishing on the Adhesion and Protective Properties of the Organic Films

“…The pretreatments of the metallic surface before painting are very important for the corrosion behaviour of the painted metal [1][2][3].…”