EIS characterisation of new zinc-rich powder coatings

A zinc-rich powder coating, applied onto steel substrate, was studied using electrochemical impedance spectroscopy (EIS). Before immersion when coating is dry, EIS spectra revealed that the percolation threshold was reached. Then, an equivalent circuit including a transmission line was applied to model electrochemical response. In this model, which considers isolated and semi-isolated zinc particles within the binder, it was found that both phases were equally distributed in the coating.     

Preparation of environmental friendly coatings based on natural shellac modified by diamine and its applications for copper protection

An environmental friendly coating based on natural product—shellac was prepared by using aliphatic diamine as a crosslinking agent and ethanol as a solvent. The amide group appeared in FTIR spectra in the modified shellac structure suggested the 1,3-propanediamine could successfully react with the acid groups in shellac. The enhancement in anticorrosive performance of the modified shellac could be observed directly from the color changes of the surface images of copper, copper coated with shellac and modified shellac after 60 h salt spray test. The EIS results indicated that after 24 h immersion in 0.5 M NaCl solution, the ionic Cl⁻ and water had reached the copper electrode and the shellac lost its protection to copper. However, the corrosive behavior of the copper electrode coated with modified shellac immersed in 0.5 M NaCl solution for 24 h still showed a characteristic of middle period of immersion and the coating layer hindered the ionic and water penetrating onto the surface of the copper; while after 72 h immersion, the modified shellac began to lose its protection to copper. The improvement in anticorrosive performance of modified shellac was attributed to the formation of network structure and the introduction of hydrophobic aliphatic group in shellac structure, which slowed down the speed of the ionic and water moving onto the copper surface.     

Evaluation of a high resistance paint coating with EIS measurements: Effect of high AC perturbations

Electrochemical impedance spectroscopy (EIS) was used to evaluate a high resistance paint coating immersed in 10% sodium chloride solution. Although this method was valuable in evaluating this type of coating there were many fluctuations in measured data at low AC perturbations. In this work the role of high AC perturbation to fit EIS data of high resistance coating with equivalent electrical circuit (EEC) was studied. EIS measurements showed that these fluctuations could be reduced by high AC perturbation. The impedance plots showed best fitting at 400 mV AC perturbation at the initial time of immersion and at 100 mV AC perturbation after 90 days of immersion. The coating resistance and coating capacitance were extracted from the Bode and Nyquist plots during the period of 90 days of immersion.     

EIS characterization of thick flawed organic coatings aged under cathodic protection in seawater

Electrochemical impedance spectroscopy (EIS) was used to monitor, up to 20 months, the degradation kinetics of four thick organic coatings under cathodic protection in seawater. EIS experiments were realized onto a flawless zone, which surrounds an artificial hole of the coating using the Luo's cell or a removable cell. EIS spectra were analyzed first with classic equivalent circuits and then with an approach involving the dipolar relaxation of polymer layer. These two models were unable to explain the experimental data, especially for a long immersion experiments. Taking into account the presence of vacuoles, namely pre-existing air pockets that will be then filled by electrolyte, modified equivalent circuits were used and a good representation of experimental data was obtained. The parameters extracted allowed the coating degradation to be followed. It was found that a solvent-free coating exhibited the best compatibility with cathodic protection.     

Protective performance of epoxy resin modified with coal tar coating studied by electrochemical impedance spectroscopy

The effect of different amounts of titanium powder, used as additive, on the protective performance in aqueous 3.5 wt.% sodium chloride solution of coal tar epoxy resin cured with polyamine has been studied by electrochemical impedance spectroscopy (EIS). In this paper, the electrochemical impedance spectra and breakpoint frequency (f_b) of the coating as a function of titanium content and immersion time, and the electrical resistance of the coating by calculating permittivity of the coating were analyzed and discussed. It is shown that EIS performance of the coating can be explained by change of the permittivity of the coating with time, and the protective performance (the protective life) is determined by the breakpoint frequency of the coating in given system.     

Resistance of metallic substrates protected by an organic coating containing glass flakes

The resistance against corrosion of an epoxy-polyamine-based coating immersed in a 3 wt.% sodium chloride solution was investigated by electrochemical impedance spectroscopy (EIS). The organic coating contained glass flakes as pigment in order to enhance its barrier characteristics. The data show that this coating is more strongly adhered and exhibits higher protection characteristics when applied onto carbon steel substrates than on galvanized steel. Though the capacitance of the coating (C_C) does not show any appreciable variation with immersion time, the resistance (R_PO) of the film is observed to increase with time upon immersion. The analysis of the data sustains that the organic film behaves as a porous, non-barrier coating. Two time constants are observed even at earlier exposures, and the improved corrosion resistance developed after the coating system was exposed to the test electrolyte is considered to originate from the precipitation of corrosion products within the pores in the film.     

Studying the influence of nano-Al2O3 particles on the corrosion performance and hydrolytic degradation resistance of an epoxy/polyamide coating on AA-1050

The aim of this work was studying the effects of addition of Al₂O₃ nanoparticles on the anticorrosion performance of an epoxy/polyamide coating applied on the AA-1050 metal substrate. For this purpose, the epoxy nanocomposites were prepared using 1, 2.5 and 3.5 (w/w) pre-dispersed surface modified Al₂O₃ nanoparticles. Field-emission electron microscope (FE-SEM) and ultraviolet–visible (UV–Vis) techniques were utilized in order to evaluate the nanoparticles dispersion in the epoxy coating matrix. The anticorrosion performance of the nanocomposites was studied by electrochemical impedance spectroscopy (EIS) (in 3.5 wt% NaCl solution for 135 days immersion) and salt spray test for 1000 h. The coating resistance against hydrolytic degradation was also studied by optical microscope and Fourier-transform infrared spectroscopy (FTIR). Results obtained from FE-SEM micrographs and UV–visible spectra showed that the nanoparticles dispersed in the coating matrix uniformly with particle size less than 100 nm even at high loadings. Results revealed that nano-Al₂O₃ particles could significantly improve the corrosion resistance of the epoxy coating. Nanoparticles reduced water permeability of the coating and improved its resistance against hydrolytic degradation.     

Excellent corrosion protection performance of epoxy composite coatings filled with silane functionalized silicon nitride

Silicon nitride was firstly used as anticorrosive pigment in organic coatings. An effective strategy by combining inorganic fillers and organosilanes was used to enhance the dispersibility of silicon nitride in epoxy resin. The formed nanocomposites were applied to protect Q235 carbon steel from corrosion. The anticorrosive performance of modified silicon nitride with silane (KH-570) was investigated by electrochemical impedance spectroscopy (EIS), water absorption and pull-off adhesion methods. With the increase of immersion time, the corrosion resistance as well as adhesion strength of epoxy resin coating and unmodified silicon nitride coating decreased significantly. However, for the modified silicon nitride coating, the corrosion resistance and adhesion strength still maintained 5.7×10¹⁰ Ω cm² and 7.6 MPa after 2400-h and 1200-h immersion, respectively. The excellent corrosion resistance performance could be attributed to the chemical interactions between KH-570 functional groups and silicon nitride powders, which mainly came from the easy formation of Si-O-Si bonds. Furthermore, the modified silicon nitride coating formed a strong barrier to corrosive electrolyte due to the hydrophobic of modified silicon nitride powder and increased bonds.     

Interfacial factors in corrosion protection: an EIS study of model systems

The effects of the liquid–coating interface and coating–metal interfaces on corrosion protection of a coated aluminum sheet (Alclad 7075-T6) were investigated using electrochemical impedance spectroscopy (EIS) of selected model systems. Parylene C was deposited on a solvent-cleaned aluminum sheet to prepare the coated aluminum sheet. Parylene C does not adhere well to most smooth surfaces: a freestanding film can easily be peeled off the substrate, although it does not peel off by itself during EIS measurements. When an ultra-thin layer of plasma polymer (ca. 50 nm) is deposited on the substrate, however, Parylene C adheres very strongly to the sheet. The top surface of Parylene C coating was modified via deposition of an ultra-thin layer of either a very hydrophobic or a very hydrophilic plasma polymer. The EIS Bode plot for the first run showed a typical good barrier coating regardless of the nature of the two interfaces under consideration. However, it was found that the impedance value in the lower frequency region decreases with increased immersion time, and the time-dependent change is greatly influenced by the nature of the two interfaces. A hydrophilic top surface increased the rate of time-dependent change, while good adhesion of Parylene C to the metal decreased the extent of time-dependent change. With a hydrophobic top surface and good adhesion to the substrate, EIS characteristics of a Parylene C coated sheet remained unaffected for 18 days (the longest time employed in this study). The decrease in impedance in the low frequency region converges to the Bode plot for a freestanding Parylene C film. The early decline of EIS characteristics can be correlated to the (pre-corrosion) micro-delamination of the coating.     

Cerium cinnamate as an environmentally benign inhibitor pigment for epoxy coatings on AA 2024-T3

An environmentally friendly inhibitor, cerium cinnamate (CeCin), was studied as an additive to an epoxy coating. The effects of corrosion inhibition on AA 2024-T3 provided by cerium cation and cinnamate anion were investigated by electrochemistry impedance spectra (EIS) and polarization tests. It was found that cerium ion and cinnamate group have synergistic inhibiting effects. The EIS results show that CeCin is an effective inhibitor pigment for improving the corrosion resistance of epoxy coatings on AA2024-T3, as reflected by the much higher coating resistance than that of the blank epoxy coating. The inhibiting effect of CeCin during the onset of corrosion in defects of the epoxy coating was verified using scanning vibrating electrode technique (SVET), which is in agreement with the EIS results.     

无溶剂重防腐环氧涂料的制备与研究

采用中低相对分子质量树脂体系以及改性脂环胺固化剂,以化学、物理防锈颜料,体质填料为粉料体系制备无溶剂重防腐环氧涂料。通过 EIS、划线盐雾剥离、耐 3. 5% NaCl溶液和 10% NaOH溶液、混合溶液浸泡后的附着力,研究了涂层屏蔽性、耐碱性、湿态附着力。结果表明：铁钛粉、 绢云母粉、长石粉粉料体系涂层屏蔽性、耐碱性最佳;改性脂环胺固化剂屏蔽性好,湿态附着力性能优异;采用 EIS、划线盐雾剥离,耐 3. 5% NaCl溶液、 10% NaOH溶液浸泡以及混合溶液浸泡后附着力下降程度来评价涂层屏蔽性、耐碱性、湿态附着力性能具有一定的可参考性,研究结果与涂层耐阴极剥离实验性能正相关,可用于涂层耐阴极剥离性能的早期评价与判断。     

Comparison of electrochemical behavior of CrN single-layer coating and Cr/CrN nanolayered coating produced by cathodic arc evaporation physical vapor deposition

The aim of the present work is to study the CrN single-layer coating and the Cr/CrN nanolayered coating by cathodic arc evaporation physical vapor deposition (CAE-PVD) on AISI 304 stainless steel and to assess the electrochemical behavior of the coatings. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were utilized to study the morphology and microstructure of the coatings. The mechanical behavior of the coatings was studied by the nanoindentation technique. The electrochemical behavior of the formed coatings in 3.5 wt.% NaCl solution was investigated via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests. Based on the microscopic images, it was realized that both CrN and Cr/CrN coatings were formed having a dense structure on the substrate. The results of EIS measurements showed gradual changes in the polarization resistance of the Cr/CrN nanolayered coating during the immersion time. However, significant changes in the polarization resistance of the CrN single-layer coating were seen by increasing immersion time comparing with the Cr/CrN coating. The higher polarization resistance of the Cr/CrN coating can be attributed to the effects of the interface between the layers in comparison to the CrN coating.     

纳米Ag·SiO2添加剂对涂料在金黄色葡萄球菌环境中防腐性能的影响

研究了添加不同颜基比(P/B)纳米Ag.SiO2对环氧树脂涂层在金黄色葡萄球菌环境中防腐性能的影响。利用原子力显微镜(AFM)观察了涂层在金黄色葡萄球菌溶液中浸泡前的表面形貌,测试了涂层浸泡前后的交流阻抗谱(EIS)。结果表明:添加纳米Ag.SiO2由于增加了涂层多孔性而导致其阻抗不同程度下降,P/B为0.3%时涂层的阻抗降至106Ω.cm2以下,基本失去了保护作用;在金黄色葡萄球菌溶液浸泡过程中纳米Ag.SiO2的杀菌作用开始显现,浸泡后未添加纳米Ag.SiO2涂层的耐蚀性能直线下降,而P/B为0.1%时涂层的耐蚀性能基本保持不变。     

聚苯胺颗粒对水性环氧树脂涂层防腐性能的影响

以盐酸为掺杂剂、过硫酸铵为氧化剂、咪唑类离子液体为稳定剂,采用化学氧化聚合法合成了导电聚苯胺(PANI)颗粒,将其分散到水性环氧树脂(ER)中制成聚苯胺水性环氧防腐涂层,研究了聚苯胺颗粒对涂层防腐性能和机械性能的影响。结果表明,添加聚苯胺显著提高了水性环氧涂层的阻隔性能,信号频率f=0.01 Hz时,PANI/ER涂层的阻抗(|Z|f=0.01Hz)均高于纯ER涂层。添加5.0wt% PANI时ER涂层阻隔性能最好,浸泡0~168 h时|Z|f=0.01Hz稳定在约8.0×108 Ω?cm2,浸泡168 h后|Z|f=0.01Hz=7.5×108 Ω?cm2,远高于ER和其它PANI/ER体系。中性盐雾实验结果表明,聚苯胺赋予了涂层钝化腐蚀的能力,显著提高了涂层的防腐性能,且其添加量越高,防腐性能越好。弯曲和冲击实验结果表明,涂层的机械性能随聚苯胺含量增加先上升后降低,当聚苯胺添加量不超过5.0wt%时,涂层的机械性能优异,附着力和韧性均较好;PANI添加量增至7.0wt%时,ER涂层的脆性明显变大,机械性能下降。聚苯胺在水性环氧体系中的最宜添加量为5.0wt%,此时涂层的机械性能良好,综合防腐性能最优。     

Effects of coating thickness and surface treatment on the corrosion protection of diglycidyl ether bisphenol-A based epoxy coated carbon steel

The corrosion resistance of carbon steel specimens was compared, using different surface treatment methods such as blasting and zinc phosphate treatment on carbon steel followed by application of different coating thickness. Specimen surface morphology was observed by SEM. The corrosion performance of epoxy coated carbon steel was examined by electrochemical impedance spectroscopy (EIS), along with immersion test in 0.5N-NaCl solution and NORSOK M 501 cyclic test, respectively. EIS results showed that higher thickness of epoxy coating and zinc phosphate treatment on carbon steel showed better corrosion protection than rest of the specimens. Specimens with no treatment and blasting treatment followed by epoxy coating, showed poor corrosion protection. Results of NORSOK M 501 cyclic test showed similar trend as those of EIS results however degradation of specimens was more severe than those from immersion test.     

富锌涂层在模拟海水中的失效机制

在筛选试验涂层体系基础上,通过浸泡、盐雾、阴极剥离、腐蚀电位监测和微观形貌分析,对12种舰船常用的无机富锌和有机富锌配套体系的腐蚀失效行为和机理进行研究。结果表明:在NaCl模拟海水条件下,无机富锌耐阴极剥离性能差;基于无机富锌涂层与有机富锌涂层配套体系的阻抗谱,环氧富锌涂层将比无机富锌具有明显的防护效果。     

Influence of silane coupling agent on corrosion-resistant property in low infrared emissivity Cu/polyurethane coating

Surface of copper (Cu) powder was chemically modified using silane coupling agent (KH550) in order to improve the interfacial interaction between Cu and polyurethane (PU) polymer, and therefore, expectable corrosion resistance of the Cu/PU coating with low infrared emissivity was acquired. Infrared spectra reveal an obvious interaction between Cu and PU induced by the addition of KH550. The corrosion behavior of Cu/PU coating has been investigated with potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results have shown that the proper amount of KH550 is benefit to the dispersion of Cu and induces the strong chemical interfacial interaction, which often keeps the low infrared emissivity and increases the corrosion resistance of the Cu/PU coating.     

Microstructure and electrochemical characterization of trivalent chromium based conversion coating on zinc

A trivalent chromium based conversion coating (CCC), based on chromium nitrate solution with Co(II) ions, was developed on Zn substrate. The corrosion resistance of the trivalent CCC, measured in deaerated pH 8.0 borate buffer + 0.01 M NaCl solution using anodic polarization and electrochemical impedance spectroscopy (EIS), was very sensitive to both immersion time and bath pH. Micro-cracks were found on the surface of the CCC. Besides, the density of micro-crack and the coating thickness also depended on immersion time and bath pH. With increasing the coating thickness its pitting potential increased and passive current density decreased. The trivalent CCC formed on Zn for 40 s in pH 1.7 bath showed the best corrosion resistance, and the pitting potential increased significantly from −355 mV_SCE for Zn to 975 mV_SCE for the trivalent CCC on Zn. To explain the corrosion behavior of the trivalent CCC using EIS analysis, a modified equivalent circuit, which considered the micro-cracks in the coating and chromium corrosion product (CCP) deposited in the micro-cracks, was designed and the variation of each electrical parameter was examined. Especially, its corrosion behavior was well described by the variation of the resistance of CCP (R_ccp).     

Effect of saccharin addition on the corrosion resistance of polypyrrole coatings

Electropolymerization baths for polypyrrole coating typically consist of two main constituents: monomer and counter-ion. By adding saccharin as the third constituent, a new branch emerges in electropolymerization that will yield coatings with modified properties. In the present study, polypyrrole is galvanostatically deposited onto carbon steel in an aqueous solution containing 0.2 M pyrrole and 0.1 M oxalic acid as the supporting electrolyte with (0.25, 0.5, 2.5 g/l) and without saccharin addition. Determination of the corrosion resistance of coatings in 0.1 M NaCl solution shows that in the presence of 0.5 g/l saccharin, a more noble corrosion potential and a greater corrosion resistance are obtained. Electrochemical impedance spectroscopy (EIS) revealed that the corrosion process was under infinite diffusion control of ions during prolonged immersion. The results indicate that the lower diffusion rate of ions in the coating produced in the presence of 0.5 g/l saccharin is responsible for its better corrosion resistance. Atomic force microscopy (AFM) shows that greater compaction of the coating produced in the presence of 0.5 g/l saccharin could be the reason for its higher corrosion resistance.