EIS Study On The Failure Process Of Three Kinds Of Composite Coatings And Rapid Detection Methods

Failure analyses of three kinds of heavy-duty anticorrosive composite coatings under the influence of ultraviolet ray (UV)/salt brine or salt brine dipping were studied in this dissertation, electrochemical impendence spectroscopy (EIS) and Physical methods (FTIR, SEM) were used to characterize the invalidation mechanism of the coating systems. Coating resistance, coating capacitance, porosity, water uptake, composite coatings/matrix desquamation rate and protective performance were also studied by using electrochemical parameter, and it was fitted and calculated by equivalent circuit and the ZsimpWin software. The main contents are listed as follows: 1. The performance of acrylic polyurethane/micaceous ferric oxide epoxy/zinc-rich epoxy composite coating and aliphatic urethane/ micaceous ferric oxide epoxy/zinc-rich epoxy composite coating in 3.5% NaCl solution under ultra-violet radiation were studied with methods of EIS, SEM and FTIR. For aliphatic polyurethane coating, the coating resistance decreased and the coating capacitance and porosity increased more quickly than acrylic polyurethane coating. The acrylic polyurethane composite coatings showed better performance than aliphatic polyurethane composite coatings. IR spectra showed that under UV irradiation conditions, the failure mechanism of the two polyurethane coatings was the transformation of sec-amide to primary amides. In contrast to aliphatic polyurethane coating, in acrylic polyurethane coating the C-O bonds fractured more slowly, which lead to better coating performance.2. Failure process of three kinds of different anticorrosion composite coatings systems composed of zinc-rich epoxy, micaceous ferric oxide epoxy and fluorocarbon in 3.5% NaCl solution were studied by EIS. The variation of electrochemical parameter, such as |Z| 0.01HZ,coating resistance,coating capacitance,porosity and water uptake, were used to analyze and compare influence of primer, intermediate coat and top coat on protective performance. It showed resistance to corrosion medium penetration ability of micaceous ferric oxide epoxy is better than that of epoxy zinc-rich primer and fluorine carbon paint, it also combined epoxy zinc-rich primer and fluorine carbon paint closely, and it played an important role for three composite coatings systems protection performance. During the early stage of corrosion, micaceous ferric oxide epoxy has big contribution to increase protective performance of composite coatings; during the middle and later stages of corrosion, epoxy zinc-rich primer can significantly delayed corrosive medium ions transmission in coatings and improved impedance values, and the ability of primer self-repair improved composite coatings protective performance effectively;3. Two kinds of different thickness of composite coatings in 3.5% NaCl solution were studied by EIS to analyze theirs failure process, the variation of the phase and |Z| 0.01HZ in middle frequency area with corrosion time was used to analyze the coatings'shielding performance, three kinds of methods, such as coating resistance and capacitance, porosity and Break-point frequency (fb) in 45°phase were also used to analyze composite coatings/matrix desquamation rate, and compared protective performance of composite coatings systems. The results showed that, when the thickness of two kinds different composite coatings systems change into 2 times, they can use 10HZ phase change to evaluate rapidly composite coatings, phase angle in 10HZ decreases below 20°, the corrosive medium infiltration caused corrosion electrochemical reactions under the coating, coating performance obviously decreased, and it has been destroyed. While the results of using three other methods to evaluate coating properties and the relative merits is in accordance with 10HZ phase change analysis, Samples performance from good to bad in order:4#) 2#> 3#> 1#。...