Corrosion Resistance Ability Of Memersion Analysis

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Moreover, the phase angle at high frequency is always used to evaluate the corrosion resistance ability of coatings[28–30]. As shown in Bode phase plot (Fig. 6), the phase angle at 105 Hz decreased, and the peak at the high frequency moved to a middle-high frequency region with the erosion process, indicating the gradual decline in the corrosion protection ability of the coatings. One time constant can be observed in the Bode phase plots of the pristine PBA, PBA/α-ZrP-3%, and PBA/α-ZrP-5% coating, indicating that the coating did not corrode during the 8-day immersion. Unlike the other coatings, PBa/α-ZrP-10% exhibited two time constants. The time constant appearing at high frequency range is associated to the coating layer, whereas that at…show more content…
However, this equivalent circuit could no longer provide a satisfactory fitting result with the elapse of time. As the electrolyte solution, water and oxygen gradually penetrated through the coating and even arrived at the coating/substrate interface, a different equivalent circuit Model b taking account of the appearance of electrochemical corrosion reaction at the metal interface was used, as shown in Fig. 7b. Specifically, the Cdl in parallel with the Rct in model b represents the Faradic reaction. In terms of the coating system where diffusion impedance appeared, Model c (Fig. 7c) was adopted to fit the impedance data. The Warburg diffusion behavior attributed to the deterioration of the coating protection and the continual diffusion in the coating system. Based on these fitting models, Rc and Cc of different coatings at a function of immersion time are shown in Fig. 8. The Rc gradually dropped with immersion time, which is another evident sign for the invalidated resistance against corrosive species transfer through the pores of coating. Besides, the Cc increased with prolonging immersion time because of the higher local dielectric constant of water than that of the polymer. PBA/α-ZrP-5% and PBA/α-ZrP-10% coatings exhibited higher Rc values, suggesting that the incorporation of >5 wt% α-ZrP in PBA matrix effectively decreased the corrosion reactions on the coated metal surface. Further, the Cc value of nancomposite coatings is relatively lower compared

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