Self-healing epoxy coatings loaded with inhibitor-containing polyelectrolyte nanocapsules

The self-healing polymer coatings containing organic corrosion inhibitors are intensively investigated as an alternative for highly toxic Cr(VI)-based systems. Protective self-healing coatings are realized by embedding “smart” containers, able to release a corrosion inhibitor under some specific conditions occurring when the corrosion process starts (e.g. on pH change) or upon a mechanical damage. In this study a system with the corrosion inhibitors (2-methylbenzothiazole (BT) and 2-mercaptobenzothiazole (MBT)) encapsulated inside the polyelectrolyte nanocapsules embedded in the water-based epoxy coatings is tested for its self-healing performance. The nanocontainers were prepared by the electrostatic adsorption of polyelectrolytes directly on the oil phase drops containing the inhibiting agent. The results for BT emulsion droplets and the mixture of BT and MBT encapsulated by docusate sodium salt/poly(diallyldimethylammonium chloride) (AOT/PDADMAC) and docusate sodium salt/poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (AOT/PDADMAC/PSS) surface complexes are presented.The X-ray Photoelectron Spectroscopy (XPS) was used to confirm the release of the inhibitor from the scratched coating. The influence of the nanocapsules on the barrier properties and self-healing performance of the epoxy coatings were tested by electrochemical impedance spectroscopy (EIS) in NaCl solution, the salt spray test (SST) according to ISO9227 and filiform corrosion test (FFT) according to EN ISO 3665. Potential blistering was rated according to EN ISO 4628-2.     

Silica nanocontainers for active corrosion protection

Novel self-healing protective coatings with nanocontainers of corrosion inhibitors open new opportunities for long-term anticorrosion protection of different metallic materials. In this paper a new type of functional nanoreservoir based on silica nanocapsules (SiNC) synthesized and loaded with corrosion inhibitor 2-mercaptobenzothiazole (MBT) in a one-stage process is reported for the first time. Unlike conventional mesoporous silica nanoparticles, SiNC possess an empty core and shell with gradual mesoporosity, arising from the particular conditions of the synthetic route adopted, which confers significant loading capacity and allows prolonged and stimuli-triggered release of the inhibiting species. The kinetics of inhibitor release was studied at different pH values and concentrations of NaCl. The results show a clear dependence of the release profiles on corrosion relevant triggers such as pH and Cl(-) concentration. When SiNC loaded with MBT are dispersed in NaCl solution, there is a significant decrease of the corrosion activity on aluminium alloy 2024. More importantly, when SiNC-MBT is added to a conventional water-based coating formulation, the modified coating hampers corrosion activity at the metal interface, better than in the case of direct addition of corrosion inhibitor. Furthermore, self-healing is observed before and after artificially inflicting defects in the modified coatings. As a result, the developed nanocontainers show high potential to be used in new generation of active protective coatings.     

Salt spray and EIS studies on HDI microcapsule-based self-healing anticorrosive coatings

Anticorrosive property of hexamethylene diisocyanate microcapsule-based self-healing coatings was systematically investigated by salt spray and EIS measurements. The influences of microcapsule diameter, weight fraction and coating thickness on the anticorrosive performance of the scratched samples were studied under salt spray condition, which revealed the thicker coatings with larger microcapsules at 10 wt.% demonstrated the best anticorrosion behavior. Additionally, the kinetics of self-healing process characterized by EIS measurement was parametrically analyzed in an equivalent circuit when the scratched coating was exposed to salt solution. A simplified model was established to explain the influences of these factors with consideration of scratch dimension.     

Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor

To improve the corrosion protection of sol–gel derived hybrid silica/epoxy coatings containing boehmite nanoparticles, inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles. The morphology and chemical structure of the deposited films were studied by Scanning Electron Microscopy (SEM) and Fourier Transformed Infra-red Spectroscopy (FT-IR). The anticorrosion and self-healing properties of the coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS). The high corrosion resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites.     

Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor

To improve the corrosion protection of sol–gel derived hybrid silica/epoxy coatings containing boehmite nanoparticles, inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles. The morphology and chemical structure of the deposited films were studied by Scanning Electron Microscopy (SEM) and Fourier Transformed Infra-red Spectroscopy (FT-IR). The anticorrosion and self-healing properties of the coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS). The high corrosion resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites.     

Encapsulation of aliphatic amines into nanoparticles for self-healing corrosion protection of steel sheets

A noble approach based on the encapsulation of corrosion inhibitors has been presented, which are capable of improving the active corrosion protection without negatively influencing the barrier properties of the coating layers. Polymeric nanocapsules loaded with six types of amine corrosion inhibitors were synthesized by multi-stage emulsion polymerization. Depending on the basicity and water solubility of amines, different amounts of releasable corrosion inhibitors were encapsulated into the polymer capsules. Encapsulated organic amines were generally well released under alkaline conditions, and linear amines were more easily released from inside capsules than branched ones. The nanocapsules were incorporated into the coating resin and were coated on cold-rolled steel sheets to investigate corrosion protection efficiencies. The corrosion inhibitive efficiencies of the nanocapsule-containing coating layers were evaluated by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). In this study, it was revealed that the intrinsic properties of the amines as well as their encapsulation/release behaviors determined the barrier property and self-healing protection capability of the coating layer.     

Improvement of anti-corrosive properties of epoxy-coated AA 2024-T3 with TiO2 nanocontainers loaded with 8-hydroxyquinoline

Epoxy coatings containing TiO₂ nanocontainers were applied on aluminium alloy (AA) 2024-T3 for corrosion protection. The nanocontainers were loaded with the corrosion inhibitor 8-hydroxyquinoline (8-HQ). Epoxy coatings were deposited via the dip-coating process. The morphology of the coatings was examined by scanning electron microscopy (SEM). The composition of the films was determined by energy dispersive X-ray analysis (EDX). Electrochemical impedance spectroscopy (EIS) was employed for the characterization of the corrosion resistance of these coatings. The total impedance values were measured as a function of time exposure in corrosive environment. We observed a continuous increase of the total impedance value with the time of exposure suggesting a possible self-healing effect due to the release of the inhibitors from the nanocontainers. Furthermore, addition of loaded nanocontainers into the coatings leads to the enhancement of the barrier properties of the coatings. Conclusively, we observed an improvement of the performance of the coatings due to the loaded nanocontainers.     

Epoxy coating with self-healing capability based on a 2-mercaptobenzothiazole-loaded CeO2 nanocontainer

In this study, we demonstrated a facile approach for the synthesis of nanocontainers using the encapsulation of a 2-mercaptobenzothiazole (MBT) inhibitor; these nanocontainers were capable of responsively releasing a corrosion inhibitor and of self-healing performances. The anticorrosive performance of the CeO₂ nanocontainers was investigated with electrochemical impedance spectroscopy (EIS) measurement in a saline electrolyte via the incorporation of different weight percentages (0.5, 1, and 2 wt %) of synthesized nanocontainer in epoxy (EP) resin. The EIS results show that the loading of 1 wt % CeO₂ nanocontainer containing MBT inhibitor in the epoxy (EP) coating [EP/NC MBT–CeO₂ (1%)] provided the highest R_coat, the lowest constant phase element of coating, and the optimum release of MBT at different operating pHs. The highest coating resistance R_coat values of this coating (7.81 × 10⁷ Ω cm²) were about 12 and 8573 times greater than those considered for EP–CeO₂ and EP coatings, respectively. Different releases of the MBT inhibitor were detected at various pHs. We found that the coating operating in acidic media exhibited a better self-healing performance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47297.     

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.     

Multifunctional,environmental coatings on AA2024 by combining anodization with sol-gel process

The present work proposes the development of multifunctional composite coatings on AA 2024 by combining anodization and sol-gel process. To render the surface of AA 2024 with maximum corrosion resistance, eco-friendly citric-sulfuric acid (CSA) electrolyte with low sulphur content was used for anodization at 20 V for a duration of 30 min. The obtained anodized layer was porous. Ambient curable hybrid sol-gel coating with 8-hydroxy quinoline (8-HQ) as corrosion inhibitor was used as a sealant for the porous anodized layer to enhance the corrosion resistance with self-healing properties. Surface pre-treatments were carried out using sand blasting and alkaline etching to ensure high surface activity prior to anodization. The surface morphology and chemical composition of samples with and without coatings were characterized by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopic analysis (EDX). Adhesion strength and wettability of the coatings were measured by tape adhesion test and water contact angle analysis respectively, which revealed excellent binding strength and hydrophobic nature. The corrosion resistance of the coatings was evaluated using electrochemical impedance spectroscopic (EIS), potentiodynamic polarization and salt spray tests. The results revealed improved corrosion resistance of anodized + 8-HQ sealed AA2024. Moreover, when the coated samples were scribed and exposed to the corrosive medium, the SEM/EDX mapping confirmed presence of corrosion inhibitors at the location of the defect, thereby confirming the self-healing property. Hence, the proposed system is a chromium-free, environment friendly multifunctional system exhibiting excellent self-healing corrosion protection and can be a promising substitute for chromic acid anodization.     

咪唑啉季铵盐缓蚀剂改性蒙脱土/水性环氧纳米复合涂料

以油酸、二乙烯三胺和氯化苄为原料,合成了油酸基咪唑啉季铵盐缓蚀剂。通过FTIR、¹HNMR对其结构进行了表征,并离子交换至钠基蒙脱土(DK0)层间,制备了缓蚀剂改性蒙脱土(QACDK0)。通过XRD、TGA和UV-Vis对其结构、组成及层间缓蚀剂释放性能进行了表征。结果表明,咪唑啉季铵盐缓蚀剂约占QACDK0质量的38.96%,并将蒙脱土层间距由1.28 nm(DK0)扩大至3.98 nm(QACDK0)。利用DLS及Zeta电位对添加有QACDK0的水性环氧树脂进行了稳定性测试,其Zeta电位为–27.8 m V,具有较高的稳定性。电化学阻抗谱(EIS)测试表明,在腐蚀介质中浸泡30 d后,基于QACDK0制备的清漆漆膜仍具有2.29×10⁸?·cm²的高阻抗,表明涂层具有较好的耐腐蚀性。并且在耐中性盐雾测试中,QACDK0对应的防腐色漆耐盐雾时间最长,验证了该涂层具有良好的耐盐雾性能。     

Investigation on anticorrosion performance of nano and micro polyaniline in new water-based epoxy coating

In this research, a micro polyaniline (MicroPAni) and a dispersion of nano polyaniline particles (NanoPAni) were used as anticorrosion additive in a new water-based epoxy coating. Both materials were added directly to a new water-based hardener (RIPI-W.B.H.). The resulted mixtures were homogenized and sonicated for size reduction and better particle dispersion. The average particle size of polyaniline in the hardener was determined using dynamic light scattering (DLS). Transmission electron microscopy (TEM) was used to observe the particle size of polyaniline in the final dried film. After applying the coatings on metal surface, anticorrosion performance and adhesion properties of the coatings were compared together with a reference coating using salt spray and cross-cut adhesion tests. The results showed that anticorrosion performance of coating containing NanoPAni was better than the one for coating containing MicroPAni. In addition, investigation on the morphology of metal-coating interface by scanning electron microscopy (SEM) technique in samples containing polyaniline after salt spray test showed stable oxide layer formation on metal surface, which will enhance the corrosion resistance.     

Synergic enhancement of the anticorrosion properties of an epoxy coating by compositing with both graphene and halloysite nanotubes

The aim of this research was to improve the corrosion resistance of metal surfaces with polymer coatings. Both graphene and halloysite nanotubes (HNTs) were introduced together into the epoxy resin coating for the enhanced barrier protection of the metallic surface. The anticorrosion behaviors of different coatings were comparatively evaluated by the potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), and neutral salt spray (NSS) tests. The potentiodynamic polarization curves showed that the coating containing 0.5 wt % HNTs and 0.8 wt % graphene (H05G08EP) together had the most positive corrosion potential and the minimum corrosion current density. The EIS results revealed that graphene endowed the composite coatings with excellent electrochemical performance for anticorrosive purposes. The NSS tests indicated that H05G08EP endured the longest NSS time. These results suggest that H05G08EP had the best corrosion resistance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47562.     

Electrochemical investigations of polypyrrole aluminum flake coupling

Polypyrrole (PPy) Al flake composite (PAFC) was synthesized by chemical oxidation of pyrrole in the presence of Al flake and was used to formulate a corrosion inhibiting primer. The anticorrosion performance of the PAFC coating for AA 2024-T3 was evaluated by accelerated salt spray, scanning vibrating electrode technique (SVET), galvanic coupling measurement and electrochemical impedance spectroscopy (EIS). The PAFC primer showed an enhanced anticorrosion ability for AA 2024-T3 compared to the Al flake primer and provided cathodic protection for AA 2024-T3 as evidenced by galvanic coupling measurement. A possible corrosion protection mechanism provided by the PAFC and the role of PPy in the formulation were discussed.     

铝合金表面电解沉积稀土转化膜工艺研究

研究了一种通过电解沉积方法在防锈铝LF21表面上生成铈盐转化膜的工艺,应用正交实验研究了有关因素对成膜过程的影响并获得了最佳的技术参数用极化曲线、交流阻抗和中性盐雾试验等方法测试了该工艺形成膜层的耐蚀性能及其组成一结果表明：经过电解沉积稀土转化膜处理后,防锈铝的阳极腐蚀过程受到了阻滞,自然腐蚀电位负移;与经过化学转化膜处理后相比,其耐蚀性能有显著提高,可通过400h的中性盐雾实验,亲水性能亦有明显提高。     

Enhancement of anticorrosion protection via inhibitor-loaded ZnAlCe-LDH nanocontainers embedded in sol–gel coatings

Inhibitor-loaded ZnAlCe layered double hydroxide (LDH) nanocontainers were prepared through the co-precipitation method. Vanadate and molybdate were used as guest inhibitors intercalating in the interlayer galleries of ZnAlCe-LDHs. The samples were characterized in terms of morphology, structure, and release behavior by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and inductively coupled plasma (ICP) techniques. To investigate inhibition behavior, the LDHs particles were embedded in a hybrid sol–gel (SiO _x /ZrO _x ) layer on aluminum alloy 2024 measured by electrochemical impedance spectroscopy (EIS). The EIS results show that the sol–gel coating with inhibitor-loaded ZnAlCe-LDH particles exhibits high corrosion resistance due to the active inhibition by the dissolution of ZnAlCe-LDHs and inhibitor anions and the exchange behavior of LDHs. Compared with the addition of ZnAlCe-MoO₄-LDHs, the coating embedded with ZnAlCe-V₂O₇-LDHs exhibited better anticorrosion abilities and provided effective protection after a long immersion time.     

[V10O28]6-柱撑纳米水滑石在AZ31镁合金有机防腐涂层中的应用

研制了一种以钒酸盐阴离子([V10O28]6-)柱撑纳米水滑石防腐颜料替代铬酸盐,用于AZ31镁合金腐蚀防护的有机涂层.研究了水滑石在不同浓度的NaCl溶液里的吸附和离子交换性能,以及钒酸盐缓蚀剂的极化曲线:考察了该水滑石防腐颜料的添加比例对镁合金环氧防腐涂层性能的影响,并通过电化学交流阻抗(EIS)测试技术对各试样进行了性能检测.结果表明,添加了20%(质量分数)水滑石的环氧涂层对镁合金具有较好的防腐作用.     

Incorporation of silica network and modified graphene oxide into epoxy resin for improving thermal and anticorrosion properties

In this study, the silica network and functionalized graphene oxide (GO) were incorporated into the epoxy coating systems, which was aimed to improve the thermal property and corrosion resistance of epoxy coatings. First, tetraethyl orthosilicate (TEOS) oligomers and epoxy hybrid was fabricated through sol–gel method. Then the (3-aminopropyl) triethoxysilane (APTES) modified graphene oxide (FGO) was added into the epoxy hybrid composite to obtain anticorrosion coatings. Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), Raman spectrum, and X-ray photoelectron spectrum were conducted to evaluate the structural information of GO and APTES modified GO nanosheets. The results indicated that the APTES successfully grafted onto the surface of GO sheets. Besides, TGA curves, electrochemical measurements and salt spray test were also carried out to characterize the thermal performance and corrosion resistance of GO based epoxy coatings. The TGA results revealed that the thermal performance of epoxy coating containing silica network and FGO nanofiller (ES/FGO) was significantly strengthened compared to pure epoxy. The initial degradation temperature of epoxy coating was increased from 300 to 343.7°C after incorporation of silica component and FGO. The EIS measurements demonstrated that the impedance modulus of ES/FGO was significantly higher than neat epoxy, which indicated that the corrosion resistance of epoxy was substantially strengthened after introduction of silica component and FGO. The corrosion rate and inhibition efficiency of epoxy composite coatings were also shifted from 1.237 × 10⁻⁷ mm/year and 76.6% (for neat epoxy) to 1.870 × 10⁻⁹ mm/year and 99.6% (for ES/FGO), respectively. The salt spray test also revealed that the silica and FGO can improve the corrosion resistance of epoxy coating. Additionally, the dispersion of GO sheets was also enhanced after the modification of APTES siloxane.     

Mica/polypyrrole (doped) composite containing coatings for the corrosion protection of cold rolled steel

Micas/polypyrroles (PPys) doped with molybdate, p-toluene sulfonate, dodecyl benzene sulfonate, and 2-naphthalene sulfonate composite pigments were synthesized by chemical oxidative polymerization and characterized in coatings for corrosion protection on cold rolled steel substrate by various electrochemical techniques. Synthesized composite pigments were characterized for morphology by scanning electron microscopy, which indicated physical formation of PPy on the surface of mica. Chemical composition of the composite pigments was analyzed by X-ray photoelectron spectroscopy which chemically confirmed doped PPy formation on the mica surface. Coatings were formulated at 20% pigment volume concentration (composite pigments or as-received mica pigment) and were applied on cold rolled steel substrate. Coatings were exposed to salt spray test conditions (ASTM B117) for 30 days and were periodically assessed for corrosion with electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), and potentiodynamic polarization. EIS and circuit modeling results demonstrated higher coating resistance (R _c) for mica/PPy (doped) composite coatings as compared to as-received mica pigment containing coating after 30 days of salt spray exposure. Lower current density and more positive corrosion potential values were observed for mica/PPy (doped) composite coatings as compared to mica pigment-based coating in potentiodynamic polarization measurements, indicating improved corrosion protection for cold rolled steel substrate. OCP measurements revealed more positive values for mica/PPy (doped) composite coatings as compared to mica pigment-based coating suggesting superior corrosion protection for mica/PPy (doped) composites.     

Synthesis of tungstate doped polyaniline and its usefulness in corrosion protective coatings

A study has been made on the corrosion protection performance of tungstate doped polyaniline containing vinyl coating on steel. The tungstate doped polyaniline was chemically synthesized and characterized by FTIR, XRD, UV-VIS and TGA studies. The corrosion protection performance of vinyl coating containing tungstate doped polyaniline on steel was assessed in 3% NaCl by electrochemical impedance studies (EIS). The coating has been found to offer protection more than 60 days in salt spray and immersion in 3% NaCl. FTIR studies have shown that the formation of iron–tungstate complex along with the passive film on steel.