Multilayer organic–inorganic coating incorporating TiO2 nanocontainers loaded with inhibitors for corrosion protection of AA2024-T3

Organic–inorganic multilayer coating containing organically modified silicates, epoxy resins and TiO₂ nanocontainers loaded with 8-hydroxyquinoline were produced on AA2024-T3 substrates via dip coating method. The parameters of the curing temperature and time were optimized via variation in a widespread range in order to realize coatings with best anticorrosive properties. Curing temperature at 110 °C for 24 h presented the best anticorrosive behavior. The morphology of the coating was examined via scanning electron microscopy. The composition of the coatings was determined by energy dispersive X-ray analysis and Fourier transform infra-red spectroscopy. Furthermore, the coatings were exposed to corrosive environment and evaluated by electrochemical impedance spectroscopy. We demonstrate that the presence of loaded TiO₂ nanocontainers enhances the anticorrosive properties of the coatings; specifically, the total impedance values were increased about two orders of magnitude compare to the bare substrate after 400 h of exposure to aggressive environment.     

Studying the corrosion protection properties of an epoxy coating containing different mixtures of strontium aluminum polyphosphate (SAPP) and zinc aluminum phosphate (ZPA) pigments

Epoxy/polyamide coatings were loaded with different mixtures of strontium aluminum polyphosphate (SAPP) and zinc aluminum phosphate (ZPA) pigments. Moreover, a coating containing zinc phosphate (ZP) was prepared as a reference sample. The coatings were applied on St-37 steel substrates and then were exposed to 3.5 wt% NaCl solution up to 35 days. The corrosion inhibition properties of the pigments extracts were studied on bare steel samples by a potentiodynamic polarization technique after 24 h immersion. The morphological properties and corrosion resistance of the coatings were investigated by scanning electron microscope (SEM), optical microscope, electrochemical impedance spectroscopy (EIS) and salt spray tests.     

Effect of polyaniline-modified glass fibers on the anticorrosion performance of epoxy coatings

Polyaniline (PANI) and different mass ratios of polyaniline/glass fiber (GB) composites (PANI/GB, PGB) were prepared through in situ oxidative polymerization. The chemical structure of composites was investigated via Fourier transform infrared spectroscopy and X-ray diffraction. Epoxy coatings loaded with different mixtures of PANI and GB were applied on steel substrate and exposed to NaCl solution. The morphological properties and corrosion resistance of the coatings were investigated through environmental scanning electron microscopy, electrochemical impedance spectroscopy, and salt spray tests. Results showed that the addition of PANI, GB, and PGB composites caused an improvement in corrosion resistance. The greatest improvement in corrosion resistance was exhibited by the coatings loaded with mass ratio of 1:1 of PANI/GB. This enhancement was attributed to the corrosion resistance of PANI and penetration resistance of GB. Moreover, the uniform distribution of PGB composites in the epoxy resin is an important parameter affecting corrosion resistance of the coatings.     

Hollow mesoporous silica nanoparticles loaded with phosphomolybdate as smart anticorrosive pigment

Recent developments in surface science and technology open up new opportunities for the development of smart pigments through the integration of nanoscale containers loaded with active components into coatings. Regarding the external factor to trigger the inhibitor release, a change in pH is a very interesting stimulus since corrosion activity leads to local changes in pH. Although several types of nanocontainers and encapsulation approaches have been proposed and studied to meet this goal, mesoporous silica nanoparticles (MSNs) are especially interesting as they retain their solid properties as long as pH of the surrounding medium does not exceed ~11. On the other hand, the use of hollow mesoporous silica nanoparticles (HMSNs) with a large cavity inside each original mesoporous silica nanoparticle has recently gained increasing interest due to the higher loading capacity. In the present work, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, sodium phosphomolybdate, has been successfully loaded and encapsulated on HMSNs. The pH-dependent release of the corrosion inhibitor from the loaded/encapsulated HMSNs has been confirmed. In addition, an improved anticorrosive behavior of the coatings formulated with loaded/encapsulated HMSNs has been observed by Scanning Kelvin Probe (SKP).     

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.     

Protective ability of hybrid nano-composite coatings with cerium sulphate as inhibitor against corrosion of AA2024 aluminium alloy

The corrosion protective ability of hybrid oxy silane nano-composite coatings deposited on AA2024 by sol-gel technique was studied. The coatings are developed as an environmentally friendly alternative of the toxic chromium containing coatings on aluminium. A cerium salt, Ce₂(SO₄)₃, was used as inhibitor of the corrosion process. Two methods were applied to introduce the salt in the hybrid matrix: directly in the matrix, or by porous Al₂O₃ nano-particles preliminary loaded by the salt. Atomic force microscopy (AFM) was used to evaluate the superficial morphology of the coatings, while their layer structure was studied by means of scanning electron microscopy (SEM). Linear voltammetry (LVA) and electrochemical impedance spectroscopy (EIS) were used for assessment of the barrier ability. The hybrid matrix was found to possess remarkable barrier ability which was preserved even after prolonged exposure of the coatings to a model corrosive medium of 0.05 M NaCl. In all cases, the cerium salt involved either directly or by Al₂O₃ nano-particles proved to deteriorate the protective properties of the coatings and to accelerate pitting nucleation. The experimental results have shown that cerium sulphate, introduced in the by the both manners in the hybrid matrix did not efficiently inhibit the corrosion of AA2024, unlike the reported inhibiting properties of other cerium salts.     

Corrosion protection of stainless steel by a new and low-cost organic coating obtained from cashew nutshell liquid

In this work, the corrosion protection of 316L steel was promoted by an electro-synthesized polymer obtained from the technical cashew nutshell liquid (t-CNSL). Spectroscopic techniques confirmed the polymer formation. The polymer was dispersed in the ethyl acetate solvent and used to form coatings on 316L steel substrates. The coated samples were subjected to electrochemical tests in a saline environment. The coated electrode with poly(t-CNSL) polymer was exposed to the corrosive medium for 24 days, and superior corrosion protection was observed compared with the uncoated sample. The open circuit potential measurements showed that the coated sample possessed a more positive corrosion potential when compared with the uncoated substrate. The electrochemical impedance spectroscopy results indicated that the coated electrode's polarization resistance (R_p) recorded ~1.0 MΩ cm² after 24 days of exposure. A decrease in polarization resistance was observed with the exposure time due to the presence of micropores in the t-CNSL coating. The polarization curves exhibited that the coated electrode with poly(t-CNSL) has lower corrosion current density and less negative corrosion potential than the uncoated steel electrode. Therefore, t-CNSL favors the manufacture of thin poly(t-CNSL) coatings for corrosion protection purposes besides being a low-cost material.     

Impact of inhibitor loaded mesoporous silica nanoparticles on waterborne coating performance in various corrosive environments

This article is a contribution to the development of the smart, self-healing solutions in the context of corrosion protection of metallic materials based on nanotechnology. Mesoporous silica nanoparticles were successfully synthesized and loaded with two different corrosion inhibitors, 1-hydroxybenzotriazole and 8-hydroxyquinoline. Loaded particles were embedded in different concentrations in waterborne epoxy coating, and as such applied to low carbon steel substrates. A continuous immersion test in 3.5% NaCl solution, humidity chamber exposure, and salt spray exposure were performed. Successful synthesis of silica nanoparticles has been demonstrated using scanning electron microscopy and energy-dispersive X-ray spectroscopy characterization techniques. Fourier transform infrared spectroscopy was used to confirm the loading of inhibitors, while the quantity of loaded inhibitors was determined by thermogravimetric method. Anticorrosive performance of intact composite coatings was determined using electrochemical impedance spectroscopy and open-circuit potential measurements. Adhesive properties were determined using the pull-off test (ISO 4624). Significant improvement in corrosion protection performance has been demonstrated for coatings containing inhibitor-loaded nanoparticles.     

A comparative study of epoxy and polyurethane based coatings containing polyaniline-DBSA pigments for corrosion protection on mild steel

Organic coatings based on epoxy and polyurethane matrices containing polyaniline doped with dodecyl benzene sulfonic acid (Pani-DBSA) were prepared and applied over steel plates (SAE 1020). The plates were submitted to salt spray chamber for up to 30 days in order to evaluate the corrosion protection of these coatings. The properties of the coated plates were analyzed as a function of time by electrochemical impedance spectroscopy, open circuit potential, optical microscopy, and Raman spectroscopy. In general, results indicate a decrease in the electrical resistance, increase in capacitance and decrease in open circuit potential. Epoxy based coatings have improved performance when Pani-DBSA is used as pigment, whereas for the polyurethane coatings, Pani-DBSA seems to play an adverse effect. Raman spectroscopy indicates a possible chlorination of the epoxy matrix after 30 days exposure to salt spray chamber.     

Synthesis and Characterization of Cerium Molybdate Nanocontainers and Their Inhibitor Complexes

Cerium molybdate nanocontainers were synthesized using a two-step process and then loaded with 8-hydroxyquinoline (8-HQ) or with 1-H-benzotriazole-4-sulfonic acid (1-BSA). First, polystyrene (PS) nanospheres were produced using emulsion polymerization. Second, the PS spheres were coated via the sol–gel method to form a cerium molybdate layer. Finally, the nanocontainers were made by calcination of cerium molybdate coated PS nanospheres. The products were characterized by scanning electron microscopy (SEM/EDX), transmission electron microscopy, FT-infrared (FT-IR) spectroscopy, X-ray diffraction, thermogravimetric analysis (TGA), and differential thermal analysis. Moreover, nanocontainers were loaded with 8-HQ or with 1-BSA and their presence was confirmed with FT-IR. The loading of the inhibitors in the nanocontainers was estimated with TGA. The loading amount of 8-HQ was 5.22% w/w and that of 1-BSA was 16.43%. Based on the size of the nanocontainers and the assumption that they are not broken, we deduced to the amount of approximately with 1.07 × 10⁶ molecules of 8-HQ and 2.35 × 10⁶ molecules of 1-BSA per nanocontainer. Furthermore, release of 8-HQ or 1-BSA in corrosive environment was studied by potentiodynamic measurements for aluminum alloys 2024-T3 (AA2024-T3) and DC01 carbon steel (DC01-CS) samples, showing that the inhibitors are released from the nanocontainers, suppressing the corrosion activities. SEM photographs confirmed that the nanocontainers maintained their shape after suspension in 0.5 M NaCl solution for more than 72 h. Moreover, release of 8-HQ or 1-BSA in water was studied using spectrophotometer.     

A study on the anticorrosion performance of the epoxy-polyamide nanocomposites containing ZnO nanoparticles

Epoxy nanocomposites were prepared using different loadings (2, 3.5, 5 and 6.5 wt%) of ZnO nanoparticles. Nanocomposites were applied on steel substrates. Samples were immersed in 3.5 wt% NaCl solution for 1344 h. Corrosion resistance of the coatings was studied by an electrochemical impedance spectroscopy (EIS). The effects of addition of nanoparticles on the mechanical properties of the epoxy coating were studied by a dynamic mechanical thermal analysis (DMTA). Curing behavior of the coatings containing nanoparticles was studied by a differential scanning calorimeter (DSC). Atomic force microscope (AFM) was utilized to investigate the surface topography and surface morphology of the coatings. Coating resistance against hydrolytic degradation was studied by FTIR (Fourier Transform Infrared).Results showed that addition of low loadings of nanoparticles can increase T_g of the composite. Decrease in T_g and cross-linking density of the coating were observed at high loadings of nanoparticles. It was found that nanoparticles can influence the curing behavior of the epoxy coating. Nanoparticles improved the corrosion resistance of the epoxy coating. Increase in coating resistance against hydrolytic degradation was obtained using nanoparticles.     

Characterization and anticorrosive properties of poly(2,3‐dimethylaniline)/TiO2 composite synthesized by emulsion polymerization

Poly(2,3‐dimethylaniline)/TiO₂ composite (PTC) was prepared by emulsion polymerization using dodecyl benzene sulfonic acid as emulsifier and dopant. The structure of PTC was characterized by Fourier transformation infrared spectroscopy, wide‐angle X‐ray diffraction, and field emission scanning electron microscopy. Effect of TiO₂ content on the PTC properties was studied by tafel polarization curves, electrochemical impedance spectroscopy, polymerization yield, and cyclic voltammetry measurements. The results showed that the anticorrosion property and electrochemical activity of PTC reached a maximum level when the content of TiO₂ was 15%. Epoxy coatings containing poly(2,3‐dimethylaniline) (P(2,3‐DMA)) and PTC, respectively, were painted on steel and accelerated electrochemical corrosion tests were performed to evaluate the anticorrosion property of the coatings in 3.5% NaCl solution. The results showed that the PTC coating had higher corrosion resistance than that of P(2,3‐DMA). POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

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.     

Electrochemical corrosion behavior of nanocrystalline Co coatings explained by higher grain boundary density

In this paper, nanocrystalline Co coatings were prepared using pulse reverse electrodeposition method. The electrochemical corrosion behavior of nanocrystalline (NC) Co compared with coarse-grained Co (CG) coatings in different corrosion media were characterized using potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). Results showed that in the NaOH or NaCl solutions, the NC Co exhibited improved corrosion resistance when compared with CG Co coatings, which is due to the higher grain boundary density in NC materials to quickly form a stable and protective passive film. In the case of NC Co coatings in HCl or H₂SO₄ solutions, since no obviously passive process can be observed, high grain boundary density in NC Co will accelerate corrosion by providing high-density of active sites for preferential attack. The controversial experimental results on NC Co coatings in different corrosion media can be reasonably explained by the positive or negative effect of high-density network of grain boundaries in NC materials.     

Designing of corrosion resistant epoxy coatings embedded with polypyrrole/SiO2 composite

Polypyrrole/SiO₂ composite was synthesized by chemical oxidative polymerization of pyrrole using FeCl₃. The synthesized polymer composite was loaded in epoxy resin to develop coatings for mild steel substrates using powder coating technique. SEM and TEM images reveal homogenous dispersion of SiO₂ particles in polypyrrole matrix. TGA analysis confirms good thermal stability of the polymer composite. Tafel polarization and electrochemical impedance spectroscopy (EIS) results exhibit remarkably high corrosion protection efficiency of epoxy coatings with polymer composite in 3.5% NaCl solution. Corrosion studies of coatings with an artificial defect reveal the passivation of defect by the polymer composite present in the epoxy coatings. Salt spray test results revealed superior corrosion resistance offered by the polymer composite.     

Development of poly(vinylcarbazole)/alumina nanocomposite coatings for corrosion protection of 316L stainless steel in 3.5% NaCl medium

Poly(vinylcarbazole) (PVK) and PVK‐alumina (Al₂O₃) nanocomposite coatings were electrochemically coated on 316 L stainless steel (SS) substrates for corrosion protection of 316 L SS in 3.5 weight (wt) % NaCl medium. The formation of PVK and incorporation of nanoalumina particles in PVK‐Al₂O₃ nanocomposite coatings were confirmed from attenuated total reflectance‐infrared spectroscopy (ATR‐IR). Thermal analysis (TG) results showed enhanced thermal stability for the composites relative to PVK. Incorporation of Al₂O₃ nanoparticles enhanced the micro hardness of PVK coated 316 L SS. The dispersion of alumina nanoparticles was examined via scanning electron microscope (SEM) and tunneling electron microscopy (TEM) and revealed distinct features. The influence of nanoparticles on the barrier properties of PVK and PVK‐Al₂O₃ nanocomposites was evaluated in aqueous 3.5 wt % NaCl by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies. The results proved that PVK nanocomposite coatings provided better protection for 316 L SS than PVK coatings. The drastic increase in impedance values is due to the high corrosion resistance offered by the PVK nanocomposite coatings that arises due to the interaction between Al₂O₃ nanoparticles and PVK. The highest corrosion protection shown by the 2 wt % nano Al₂O₃ incorporated PVK composite coatings proved enhanced corrosion resistance compared to PVK. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44937.     

Corrosion protection by epoxy coating containing multi-walled carbon nanotubes

Epoxy coatings that contained multiwalled carbon nanotubes (MWCNTs) were prepared. Further, the effect of the MWCNTs on the hydrophobicity and water transport behavior, and hence, on corrosion resistance provided by the epoxy coating were examined using hygrothermal cyclic tests and electrochemical impedance spectroscopy (EIS). The water transport behavior of epoxy coatings with higher MWCNT content decreased to a larger extent for coatings with higher surface hydrophobicity. The corrosion protection of carbon steel coated with epoxy coating that contained MWCNTs correlated well with water transport behavior and hydrophobicity.     

SiAlON nanoparticles effect on the corrosion and chemical resistance of epoxy coating

Effect of incorporating SiAlON nanoparticles at different loading levels (0?C12?wt%) on chemical resistance of epoxy coating was investigated by immersion in basic (Na₂CO₃, pH?=?11) and salty (NaCl 3.5?wt%) (environments at 85?°C for 60?days. Epoxy resin chemical resistant coating grade based on bisphenol A was used with polyamine hardener as a curing agent. In these testes, surface morphology changes of the samples were studied and compared owing to initiation and propagation of cracks. Results indicate an enhancement in the epoxy nanocomposite chemical resistance due to the addition of small fraction of SiAlON nanoparticles. Samples containing 3 and 5?wt% of SiAlON nanopowders were considered as optimum samples compared to all the other samples, because they showed more resistances to initiation and propagation of cracks and lower permeability in chemical environment in comparison with neat resin and other samples. Also, epoxy coatings containing SiAlON nanoparticles were successfully coated on steel substrates and corrosion electrochemical behavior of these nanocomposite coatings were characterized by electrochemical impedance spectroscopy (EIS). The electrochemical monitoring of the coated steel over 35?days of immersion in 3.5?wt% NaCl solution at room temperature suggested the positive role of nanoparticles in improving the corrosion resistance of the coated steel.     

Electrospun protective self‐healing coatings for light alloys: A better understanding of the intrinsic potential of the technology

Polymeric coating systems exhibit high potentiality to provide an effective barrier against corrosion of metallic surfaces. However, these coatings can lose their protective characteristics because of their high susceptibility to damage. Thus, the addition of corrosion inhibitors is desirable and considered as an alternative route for active corrosion protection. In the present work, eco‐friendly electrospun coatings of poly(vinyl alcohol) (PVA) loaded with cerium salts have been deposited onto aluminium 6082 alloy. Two different precursors of cerium (III) (i.e., cerium nitrate and cerium acetylacetonate) were added to the electrospinning solutions and the effectiveness of the resulting nanofibrous coatings was evaluated for the healing of generated defects. The microstructural features of the electrospun coatings have been investigated by scanning electron microscopy, infraredspectroscopy, and thermal analysis. Tensile tests were performed to assess the mechanical properties of the different fibrous coatings. The electrochemical behavior of both intact and damaged coatings was evaluated in 3 wt % NaCl solution by means of electrochemical impedance spectroscopy. All the deposited PVA coatings loaded with cerium(III) salts showed remarkable corrosion resistance. In the case of artificially damaged coatings, a self‐healing effect, which stops the development of the corrosion process and provides a significant recovery of the corrosion resistance, has been observed only for coatings loaded with cerium III acetylacetonate. The release of cerium from damaged PVA fibers has been demonstrated by means of inductively coupled plasma mass spectrometry. The observed self‐healing effect has been ascribed to the formation of cerium hydroxide on the defective zone, which hindered the corrosion process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42728.     

LDH型MoO_4~(2-)缓蚀剂的合成及防腐性能

采用共沉淀法制备了镁铝氢氧化物为层板、MoO24-柱撑的LDH型MoO24-缓蚀剂(记为MoO24-LDH),利用XRD和Raman光谱对样品进行表征。通过缓释实验,讨论了LDH型缓蚀剂的释放能力以及缓蚀剂的缓蚀机理。SEM-EDS、ICP、N2吸附脱附和极化曲线测试结果表明,合成的LDH型MoO24-缓蚀剂具有很好的离子交换和吸附Cl-的性能,释放出MoO24-缓蚀剂进入电解液,24 h内对镁合金的腐蚀电流保持在9.129μA/cm2,减缓了镁合金腐蚀。添加质量分数20%MoO24-LDH颜料的环氧涂层在质量分数3.5%NaCl溶液中的EIS测试体现出较好的耐蚀作用,耐盐雾腐蚀187 h以上。