Protective properties of cataphoretic epoxy coating on aluminium alloy AA6060 modified with electrodeposited Ce-based coatings: Effect of post-treatment

Ce-based conversion coatings (CeCCs) are a promising alternative to toxic chromate coatings on the metal substrates. In this work the CeCCs were electrodeposited on aluminium alloy AA6060 from aqueous solution of Ce(NO₃)₃ at different potentials (−0.95 V, −1.2 V and −1.4 V). Effect of deposition potential and post-treatment in the phosphate solution on morphology and protective properties of CeCCs with top cataphoretic epoxy coating was studied. To assess the differences between the protective systems, originating from the different CeCCs pre-treatments, electrochemical impedance spectroscopy (EIS), polarization measurements, AFM and SEM/EDS analysis were used. The EIS study was undertaken to follow the evolution of corrosion behaviour of epoxy coating/CeCCs protective systems over prolonged time of exposure to the chloride environment (3 wt.% NaCl). Results suggest significantly improved corrosion stability of epoxy coating on AA6060 with as-deposited CeCCs sub-layers with respect to the same epoxy coatings with phosphate post-treated CeCCs. The far best protective properties, i.e., the greatest value of pore resistance and the lowest value of corrosion current density were provided by the epoxy coating/CeCC protective system with CeCC deposited at −1.2 V and without post-treatment.     

聚苯胺/环氧复合阴极电泳涂料防腐蚀性能的研究

运用插层聚合的方法制备了蒙脱土／聚苯胺复合材料，并进行了表征。将该复合材料通过共混的方式加入聚酰胺／环氧阴极电泳（CED）涂料中配制成聚苯胺／环氧复合阴极电泳涂料，并利用电化学阻抗谱方法对各电泳涂层的防腐性能进行了分析。研究发现：在3．5％NaCl溶液中浸泡10d后，腐蚀介质不能到达涂层／基底金属界面，金属表面没有发生腐蚀反应。随着聚苯胺含量的增加，复合电泳涂膜的阻抗值增加，具有较好的防腐性能。当聚苯胺含量相同时，与掺杂态聚苯胺复合电泳涂膜相比，本征态聚苯胺复合电泳涂膜具有很高的阻抗值，表现出更好的防腐性能。     

Study on corrosion electrochemical behavior of several different coating systems by EIS

Corrosion electrochemical behavior of chlorinated rubber top coating (single-layer), inorganic zinc-rich primer/chlorinated rubber top coating (double-layers) and inorganic zinc-rich primer/epoxy middle paste/chlorinated rubber top coating (tri-layers) in 3.5 wt% NaCl solution was studied by electrochemical impedance spectroscopy (EIS). A series of impedance spectra of the three coating systems during immersion were measured; and their protective properties were compared according to the spectra. The experimental results showed that, the protective properties of the double-layers coating system were even worse than that of the single-layer coating system; and the tri-layers coating system had the best protective properties in the three coating systems; epoxy middle paste had played a very important role for protective properties of the composite coating system.     

颜填料体积浓度对水性环氧导静电防腐蚀涂层性能的影响

考察了颜填料体积浓度（PVC）对水性环氧导静电防腐蚀涂料涂层导静电性能和防腐蚀性能的影响,运用X射线能谱（EDX）分析了导电填料的元素组成,采用电化学阻抗谱（EIS）、扫描电镜（SEM）等手段对不同颜填料体积浓度的涂层进行了性能测试及表征,根据不同颜填料体积浓度涂层的物理机械性能、盐水浸泡实验结果和电化学阻抗谱分析,确定该水性环氧导静电防腐蚀涂料的最佳颜填料体积浓度为35%。     

Self-healing and anticorrosive properties of Ce(III)/Ce(IV) in nanoclay–epoxy coatings

The self-healing and anticorrosion effects of cerium nitrate in epoxy–clay nanocomposite coatings systems were studied. Different amounts of cerium (III) were added to epoxy–montmorillonite clay composites and the nanocomposite coatings were prepared and applied on cold rolled steel panels. Ultrasonication was applied to disperse the nanoclay into the epoxy cerium nitrate composition. Electrochemical impedance spectroscopy (EIS) was used to study the self-healing and anticorrosion behaviors of the coatings. The structure of the dry coating and the protective mechanism of the pigments in the coating were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) analysis and field emission electron microscopy (FESEM). Transmission electron microscopy (TEM) illustrated the separation of clay layers which interacted with the epoxy resin. Electrochemical impedance data indicated that the epoxy cerium (III)–montmorillonite nanocomposite coatings were superior to the epoxy coatings in corrosion protection properties. The self-healing behavior of such coatings was due to the presence of cerium nitrate that could be released at the defects within the coating and hindered the corrosion reactions at the defective sites. It was shown that the best corrosion protection was achieved with nanocomposite coatings containing 4 wt% clay and 2 wt% cerium nitrate.     

Electrochemical and sorption characteristics and thermal stability of epoxy coatings electrodeposited on steel modified by Zn–Co alloy

The corrosion behaviour, transport properties and thermal stability of epoxy coatings electrodeposited on steel and steel modified by Zn–Co alloys were investigated during exposure to 3% NaCl solution. The electrochemical impedance spectroscopy (EIS), gravimetric liquid sorption measurements and thermogravimetric analysis (TGA) were used. Zn–Co alloys were electrodeposited on steel from chloride and sulphate baths, by different current densities. From the time dependence of pore resistance and coating capacitance of epoxy coating, diffusion coefficient of water through epoxy coating and thermal stability it was shown that Zn–Co sublayer obtained from chloride solution significantly improves the corrosion stability of the protective system based on epoxy coating. Almost unchanged values of pore resistance were obtained over the long period of exposure time, indicating the great stability of this protective system, due to the existence of a passive layer consisting of basic salts.     

AZ91D镁合金表面不同树脂体系富镁涂层的保护性能

采用划叉浸泡实验,电化学交流阻抗(electrochemical impedance spectroscopy,EIS),开路电位(open circuit potential,OCP)及动电位扫描研究了不同类型的环氧树脂对于AZ91D镁合金的表面的富镁涂层的保护性能的影响。结果表明环氧618-593构成的富镁涂层防护性能较差;环氧6101-TY650制备的富镁涂层可明显改善涂层对破损处镁合金基体的保护作用,但涂层本身长期防护性能较差;环氧618-T31构成的富镁涂层对AZ91D镁合金的防护作用较强,适宜制备镁合金表面的富镁涂层。3种环氧涂料中加入镁粉颗粒制备的富镁涂层均可对缺陷处裸露的AZ91D镁合金基体提供保护,从而延长漆膜的破坏时间。涂层中的镁粉颗粒被激活后,为镁合金的基体提供了一定程度的阴极保护作用,减缓了镁合金基体的腐蚀。     

环氧树脂改性及其涂层性能研究

通过硅溶胶来改善环氧树脂E-44的性能,以改性环氧树脂为基料,制备了富锌防腐涂料。应用电化学交流阻抗法研究了涂料涂层在质量分数为3.5%的NaCl溶液中的腐蚀过程。实验结果表明,添加硅溶胶可明显改善环氧树脂性能,当硅溶胶与环氧树脂E-44质量比5∶3防腐性能最好,同时该涂层具有较好的力学性能、耐热性和耐候性。根据交流阻抗谱图(E IS)响应特征,涂层在浸泡过程可分为3个主要阶段且涂层电阻变小。     

Effect of polypyrrole–montmorillonite nanocomposites powder addition on corrosion performance of epoxy coatings on Al 5000

The synthesis of hybrid polypyrrole–montmorillonite (Ppy–MMT) nanocomposites and their effects on the improvement of the protection efficiency of the epoxy coatings on aluminum corrosion were studied. In order to understand the effect of MMT and Ppy on the corrosion inhibition performance of the epoxy coatings in 3.5% NaCl solution, the epoxy (E), epoxy blend with MMT (EM) and polypyrrole (EP) coatings were investigated by electrochemical impedance spectroscopy (EIS). It was shown that EM and EP systems could not provide a good corrosion protection for long-time applications. The results showed that the incorporation of Ppy–MMT nanocomposites inside the epoxy notably increases the resistance of the coating in comparison to the other coatings for long-time period. These phenomena can be attributed to specific morphology of the nanocomposite. The structure and morphology of nanocomposites were studied by FT-IR and XRD techniques, as well as, scanning electron microscopy (SEM).     

EIS法研究3种配套涂层体系的腐蚀电化学行为

采用电化学阻抗谱(EIS)研究了由水性无机富锌底漆、环氧中间漆和氯化橡胶面漆3种涂料配套而成的3种不同涂层体系在3.5%NaCl溶液中的电化学腐蚀行为,考察了氯化橡胶面漆、水性无机富锌底漆／氯化橡胶面漆、水性无机富锌底漆／环氧中间漆／氯化橡胶面漆这3种涂层体系的阻抗谱在浸泡过程中的演化并据此比较了3种涂层体系的防护性能。结果表明,两涂层体系的防护性能比单涂层的还要差,三复合涂层体系的防护性能最好。根据涂层腐蚀电化学阻抗谱特征推测,中间漆在三复合涂层体系中起到了使底漆和面漆结合更加紧密的桥梁作用。     

海水压力对深海用环氧涂层防护性能的影响

采用电化学阻抗谱(EIS)技术与局部交流阻抗技术(LEIS)研究了深海环境用重防腐环氧涂层H44-61在深海模拟环境(青岛海水,常压以及6 MPa交变压力)下的腐蚀电化学行为,探讨了交变压力对深海用涂层防护性能的影响。结果表明,涂层在6 MPa交变压力下的涂层电容较常压下高且涂层电阻较低,涂层的防护性能下降,但低频阻抗膜值均在10⁷ Ω·cm²以上,说明涂层仍有较好的防护性能;LEIS的研究表明交变压力下人造缺陷区域的阻抗值较小,缺陷周围涂层的剥离面积较大,说明压力交变能加快电解质溶液向涂层金属界面扩散,加速涂层下金属的腐蚀过程,降低涂层的防护性能。     

Electrochemical characterisation of protective organic coatings for food packaging

A very common material for food packaging is steel, in the form of metallic containers (cans), in particular for beverage packaging. The corrosion degradation of the packaging must be carefully controlled, not only because the packaging integrity must be preserved, but also in order to avoid any significant contamination of the food or drink, compromising the flavour. In order to increase the coating performance and the food compatibility, new organic coatings are under development with very high protective properties, with the final aim to increase the shelf life of the product. An electrochemical characterisation is often used to study the protective performance of organic coatings on metal substrate for various applications. Some different coatings for food packaging were considered in the present study, including materials with different chemical composition and different pigments content. The protective properties were quantified using electrochemical impedance spectroscopy (EIS) measurements, comparing the electrochemical substrate activity with electrochemical noise (EN) and scanning Kelvin probe (SKP) measurements. The influence of mechanical deformations on the protective properties was also investigated. The results obtained on the studied coatings confirmed the validity of the electrochemical approach and showed that, in general, the coatings containing pigments (TiO₂) have better performance than clearcoats, while comparing the different polymers, epoxy–phenolic coatings have a better corrosion protection than epoxy–melamine coatings.     

Comparisons of clear coating degradation in NaCl solution and pure water

Organic coating's degradation behavior is essential to its corrosion protective function and has been widely studied. A main function of anti-corrosive organic coatings is acting as barriers to water uptake and ion diffusion. It is of great fundamental importance to study the influence of different working fluids on the degradation of organic coatings. In this study, a 3.5 wt% NaCl solution and the pure water are adopted as the working fluids based on their distinct properties. The commercially available polyurethane and epoxy based clear coatings are chosen for evaluation. The coating degradation is monitored by electrochemical impedance spectroscopy (EIS) measurement. Equivalent circuit models are employed to interpret the EIS spectra. The time evolution of coating resistance, capacitance, and water volume fraction of the coating is analyzed. Besides the fact that the coating's barrier property is deteriorated by the percolating of both NaCl solution and pure water, we also discover that pure water leads to faster coating degradation, demonstrated by a more substantial decrease in coating resistance, a more prominent increase in coating capacitance, and a greater saturated water volume fraction.     

利用EIS高频区参数评价两种环氧涂层的性能

利用10 kHz下的相位角、10 kHz下的相对介电常数和对应于45°相位角的特征频率这3种EIS高频区的参数对两种环氧涂层体系在盐水浸泡+紫外照射的腐蚀条件下的失效过程进行了表征,并与涂层阻抗值进行了对比。测量结果表明,上述3种高频区参数的结果一致,都能够反映涂层性能的变化及相对优劣。当频率10 kHz处的相位角下降到40°,相对介电常数增大到40,或特征频率接近10 kHz时,所研究的两种环氧涂层体系的阻抗值都对应降低到10⁶ Ω•cm²左右,涂层保护性能接近失效。由于这几种EIS高频区参数能够很快测得,因此可以利用这些参数快速评价该涂层的保护性能与失效程度。     

Preliminary investigation of the impact of polymer composition on electrochemical properties of coatings as determined by electrochemical impedance spectroscopy

The influence of structural and systematic compositional variations in glycidyl carbamate (GC) functional polymers on the electrochemical properties of their coatings was studied. There are few reports which focus on the correlation of structural and compositional variations in polymer films with their electrochemical barrier properties, diffusion properties with regards to water and aqueous electrolytes, and corrosion performance. To begin to fill this knowledge gap, two sets of GC functional polymers were studied. The polymer compositions were designed to vary the extent of polar hydrophilic groups, non-polar hydrophobic groups, and reactive epoxy groups in the final coatings. Impedance responses of the coatings were found to be closely related to the structural and compositional variations of these GC polymer films. In addition, single frequency EIS experiments were used in an attempt to understand the water uptake behavior of these polymer films using NaCl solution and ionic liquid under immersed condition. The resulting transport property data of the films was correlated to their polymer structure and composition. Moreover, a novel attempt at ranking the stability of coating using capacitance measurement during a cyclic wetting–drying condition was also attempted. The information obtained from this work can potentially be used to optimize the polymer for the specific performance properties needed in the protective coating applications, saving significant time and effort in the research and development stage.     

A Comparative Study of Anticorrosion Paints Based on Silicone-Urethane Binders: a Multilayer Primer

Using zinc phosphate, micaceous iron oxide and their combination in the composition of the undercoat, a series of novel multilayer paint systems based on different silicone-urethane binders with the same R/Si and Ph/R ratio have been formulated. The developed paint systems showed excellent mechanical, adhesion and chemical properties. Scanning Electron Microscopy (SEM) analysis of the surface of the paint systems shows no fractures or holes. The electrochemical impedance spectroscopy (EIS) evaluation of the developed paint systems confirms their excellent protective and anticorrosion properties, especially for Silicone-Urethane-Urea (SPUU) based paint systems with a combination of pigments in the composition of the undercoat. SPUU-based paint systems show low water uptake. The new multilayer silicone-urethane-based paint systems can be used as a anticorrosion primer.     

Adhesion and corrosion resistance of epoxy primers used in the automotive industry

One of the most important factors in corrosion prevention by protective coatings is the loss of adhesion of the coating under environmental influence. Thus, adhesion strength is often used when characterizing protective properties of organic coatings on a metal substrate. In this work, the adhesion of different epoxy primers (pigment-free, zinc-rich and chromate-based) was examined on steel. Both the dry and wet adhesion strengths of organic primers were measured directly by a pull-off standardized procedure, as well as indirectly by the NMP test. The corrosion stability of coated samples was investigated by electrochemical impedance spectroscopy. It was shown that under dry test conditions all the samples showed very good adhesion. However, different trends in adhesion for different primers during exposure to the corrosive agent (3% NaCl solution) were observed. The lowest adhesion values were obtained for chromate-based epoxy primer; however, the change in adhesion of this protective system during immersion in 3% NaCl solution for 25 days was the smallest of all investigated samples. Electrochemical impedance measurements in 3% NaCl solution confirmed good protective properties of pigmented epoxy primers on steel, i.e., greater values of pore resistance and charge-transfer resistance, and smaller values of coating capacitance and double-layer capacitance, were obtained for these protective systems.     

Corrosion protective performances of commercial low-VOC epoxy/urethane coatings on hot-rolled 1010 mild steel

The protective properties of low-VOC epoxy/urethane paint systems of commercial grade have been investigated using a variety of techniques such as electrochemical impedance spectroscopy (EIS). One epoxy-polyamide mastic/urethane, three high-solid epoxy-amine/urethane coatings, one solvent-free epoxy-amine/urethane, one water-based epoxy-amine and one high-VOC alkyd paint system (used as paint reference system) were applied on hot-rolled 1010 mild steel panels and exposed for up to 2000 h in the salt spray cabinet (SSC) or for 1 year at an outdoor marine test site. These paints were tested for their barrier properties, corrosion-induced adhesion loss and visual defects, as well as for their flexibility and resistance to direct impact. The barrier properties increased in the following order: alkyd相似文献   

EIS and ENM measurements for three different organic coatings on aluminum

Electrochemical impedance spectroscopy (EIS) and Electrochemical noise measurements (ENM) were used to evaluate protective properties of three different organic coating systems. The coatings under investigation were two-component aerospace coatings, applied on aluminum substrate. They were immersed in a 0.5 mol l⁻¹ sodium chloride (NaCl) solution, within a controlled flow cell and were tested for 1 year.

The impedance modulus in the low frequency domain and the noise resistance were calculated and compared. From EIS data, coating capacitances and coating resistances of coating performance were estimated. The electrochemical results are in good agreement with final visual observations. The results of this study yield a performance ranking of the three different coatings.     

环氧富锌/氯化橡胶涂层体系腐蚀过程的电化学阻抗谱

采用环氧富锌作为底漆、氯化橡胶作为面漆，研究了涂层体系腐蚀过程中电化学阻抗谱(EIS)的变化。结果表明，腐蚀初期环氧富锌/氯化橡胶涂层体系中底漆的厚度比例与涂层的防护性能无关，而在腐蚀中后期，随底漆厚度比例适当增大，涂层自修复能力增强，离子等腐蚀介质在涂层中的传输速度得到显著延缓，涂层吸水率和孔隙率明显降低，涂层防护性能出现短时间升高。当环氧富锌底漆为涂层总厚度的2/3左右时，涂层体系的防护性能最好，而仅有底漆或面漆的体系则不具备良好的防护性能。