Search

The development of anti-corrosion polymeric coatings has grown exponentially in the fields of material science, chemistry, engineering, and nanotechnology during the last century and has prompted the evolution of efficient characterization techniques. Nowadays, polymeric coatings represent a well-established protection system that provides a barrier between a metallic substrate and the environment. However, the increase in complexity and functionality of these coatings requires high-precision techniques capable of predicting failures and providing smart protection. This review summarizes the state of the art for the main electrochemical techniques, emphasizing devices that track the anti-corrosion properties of polymeric coatings from the macroscale to the nanoscale. An overview of the advances in accelerated corrosion testing and the electrochemical characterization of coatings is explored, including insights into their advantages and limitations. In addition, the challenges and potential applications of the theoretical approaches are summarized based on current knowledge. Finally, this work provides the reader with the trends and challenges of designing future technologies and models capable of tracking corrosion and predicting failures. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1000 days immersion study of PMMA-silica coatings on Al alloys in 0.6 M NaCl solution. • Water uptake of less than 0.7 vol% assessed by analysis of electrochemical impedance data. • Modeling of electrochemical impedance data revealed a "less-Fickian" diffusion coefficient. • The efficient diffusion barrier against corrosive species results in high corrosion resistance. • Nanostructural changes do not significantly affect the long-term anticorrosive performance. Poly (methyl methacrylate) (PMMA)-silica coatings form a few micrometers thick anti-corrosive barrier that blocks corrosive species when exposed to harsh environments. Their excellent anti-corrosive performance stands out for protecting metal alloys immersed in seawater for long periods (>2 years), making them compliant for applications in the marine, aeronautical, and automotive industries. A key approach to understanding the degradation of high-performance coatings over time consists of analyzing their water uptake-induced structural changes. This work examines in detail the uptake and structural modification of PMMA-silica coatings on Al alloys immersed for more than 1000 days in 3.5 wt% NaCl solution. Gravimetry, thermal analysis, infrared spectroscopy and electrochemical impedance spectroscopy (EIS) were employed to monitor the evolution of coated samples. Nuclear magnetic resonance, X-ray photoelectron spectroscopy, electron and atomic force microscopies before and after immersion indicate a slight leaching-induced surface roughening due to silica hydrolysis. These findings comply with the low uptake values (∼0.6 vol%) and a less-Fickian diffusion coefficient obtained from modelling of the EIS data. The high impedance modulus (>GΩ) is related to the highly cross-linked structure, resulting in a very low permeation rate of the electrolyte. The applied methodology is of crucial importance for establishing a standardized analysis for high-performance protective coatings. [ABSTRACT FROM AUTHOR]

This study investigates the potential of lignin as a sustainable alternative to petroleum-based polyols in the production of polyurethane-silica (PU-Si) coatings with improved tribological, anticorrosive and bactericidal properties. To achieve this goal, hybrid PU-Si coatings were developed and modified by incorporating varying amounts of lignin into the PU macromer chain, which were then applied to carbon steel substrates. Analysis through Fourier-transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (13C NMR) analyses confirmed complete integration of the lignin into the PU chains. Additionally, 29Si NMR revealed that lignin incorporation acted to increase the condensation degree of the silica. Lignin had a smoothing effect in the hybrid coatings, leading to reduced roughness. Mechanical tests showed that the presence of lignin decreased the friction coefficients of the coatings, while enhancing their wear resistance and critical delamination loads, compared to the coating without lignin. The best PU-Si-lignin coating presented outstanding anticorrosive performance, achieving low-frequency impedance values up to 100 GΩ cm2, without failure for over 100 days. Furthermore, the incorporation of lignin inhibited E. coli biofilm formation. These multifunctional properties suggest that these coatings have promising applications across various industries, from infrastructure to healthcare. [Display omitted] • Explorer lignin as a renewable substitute for petroleum-based polyols in polyurethane-silica (PU-Si) coatings. • 29Si NMR analysis indicated that lignin incorporation increased the condensation degree of silica. • Lignin improved tribological, anticorrosive, and bactericidal properties of the coatings. • PU-Si-0.4Lig coating achieved low-frequency impedance values up to 100 GΩ cm2 and remained intact for over 100 days. • These coatings suggest potential uses in various sectors, including infrastructure and healthcare. [ABSTRACT FROM AUTHOR]

• Development of covalently bonded PMMA-cerium oxide hybrid anticorrosive coatings. • Homogeneous distribution of cerium oxide nanoparticles in PMMA matrix. • Transparent and defect free coatings with excellent anticorrosive performance. • Extended coating lifetime by active corrosion protection. • Efficient, environmentally compliant and active protection of metallic surfaces. Metallic alloys are extensively used in many technological applications, however their susceptibility to corrosion causes huge economical losses and can result in failure of critical components. Aiming to obtain environmentally friendly, self-healing and high efficient anticorrosive coatings, organic-inorganic hybrids consisting of poly(methyl methacrylate) (PMMA) covalently bonded to CeO 2 /Ce 2 O 3 nanoparticles have been synthetized by the sol–gel process. Cerium oxide nanoparticles were covalently conjugated with the coupling agent 2-hydroxyethyl methacrylate (HEMA) and different proportions of methyl methacrylate (MMA), and subsequently the hybrid solutions were used to deposit films on A1020 carbon steel by dip-coating. The coatings are transparent, homogeneous, free of pores, have low surface roughness (<1.6 nm), and present good thermal stability (>220 °C). Excellent anticorrosive efficiency and durability was obtained by the nanoscale dispersion of cerium oxide nanoparticles into PMMA matrix, achieving for the sample with molar ratio of 1Ce:2HEMA:25MMA an impedance modulus up to 290 GΩ cm2, 8 orders of magnitude higher than the bare carbon steel, remaining essentially unchanged during 6 months exposure to saline solution. A detailed analysis of scratched coatings evidenced that Ce ions act as self-healing agents inhibiting the progression of the corrosion process. This work demonstrates that the active corrosion inhibition and environmental compliance make these PMMA-cerium oxide coatings a very promising alternative for the conventional protection systems. [ABSTRACT FROM AUTHOR]

• Novel covalently bonded PMMA-TiO 2 and PMMA-ZrO 2 hybrid nanocomposites. • Homogeneous distribution of fiber-like TiO 2 structures and ZrO 2 nanodomains. • Transparent and defect free coatings with excellent anticorrosive performance. • Elevated thermal stability and high coating adhesion to steel substrate. • Efficient environmentally compliant protection of metallic surfaces. The covalent conjugation between the phases of organic-inorganic nanocomposites and the careful tuning of the proportion of the colloidal precursors are essential to yield homogeneous, cross-linked and dense coatings that are able to protect metallic alloys against corrosion. In this work, the sol-gel route was used to prepare organic-inorganic hybrid coatings based on poly(methyl methacrylate) (PMMA) covalently bonded to TiO 2 or ZrO 2 nanoparticles through the coupling agent 2-hydroxyethyl methacrylate (HEMA), applied for the first time as anticorrosive coatings for metallic alloy. Different formulations of the hybrids were prepared by varying the proportion of titanium isopropoxide or zirconium propoxide, methyl methacrylate and benzoyl peroxide, and applied on carbon steel by dip-coating. The optimized parameters yielded for the two hybrids transparent and homogeneous coatings, with a thickness less than 3 μm, low surface roughness (<1.8 nm) and elevated thermal stability (>200 °C). Electrochemical impedance spectroscopy assays showed that PMMA-ZrO 2 and PMMA-TiO 2 coatings exhibit corrosion resistance up to 10 GΩ cm2, 7 orders of magnitude higher than the bare carbon steel, remaining essentially unchanged for PMMA-TiO 2 during 14 days exposure to 3.5 % saline solution. The results suggest that PMMA-ZrO 2 and PMMA-TiO 2 nanocomposites are suitable for application as environmentally compliant highly efficient anticorrosive coatings. [ABSTRACT FROM AUTHOR]

• High performance methyl methacrylate-silica anticorrosive coatings with long-term stability. • Correlation of structural characteristics with electrochemical barrier properties. • Modeling of the electrolyte permeation using the two-layer Young approach. • Comparison of electrical equivalent circuits using constant phase element and Young model. This work reports a detailed investigation of the structural and electrochemical barrier properties of PMMA-silica coatings. Hybrid nanocomposites were prepared by combining the sol-gel method with the polymerization of methyl methacrylate (MMA), using the thermal initiator benzoyl peroxide (BPO), followed by the hydrolytic condensation of tetraethoxysilane (TEOS) and 3-(trimethoxysilyl)propyl methacrylate. Raman spectroscopy and thermal analysis showed that the fine-tuning of the BPO amount, a critical synthesis parameter, improved the polymerization efficiency of MMA, leading to a highly cross-linked hybrid structure. The homogeneous coatings prepared under optimized synthesis conditions presented elevated thermal stability due to improved polymerization of the organic phase. Electrochemical impedance spectroscopy (EIS) showed a quasi-ideal capacitive impedance response in 3.5% NaCl solution, with low frequency impedance modulus of up to 10 GΩ cm2, which remained essentially unchanged during 19 months of immersion. This notable barrier property was modeled by fitting the EIS curves assuming slowly expanding electrolyte uptake, using the two-layer Young approach, and by comparison with the standard equivalent electrical circuit (EEC/CPE) model. The Young model provided valuable information on the time evolution of physical parameters including the thickness of the uptake zone, the conductivity depth-profile and the dielectric constant, among others, evidencing the high performance of the coatings. [ABSTRACT FROM AUTHOR]

Hypothesis The fraction of the silica/siloxane phase is a crucial parameter, which determines the structure and thus the properties of epoxy-siloxane-silica hybrid coatings. A careful adjustment of the colloidal precursor formulation allows tuning the nanostructure towards a highly condensed and cross-linked hybrid nanocomposite, suitable as an efficient anticorrosive coating. Experiments Novel epoxy-siloxane-silica hybrids have been prepared through the curing reaction of poly(bisphenol A-co-epichlorohydrin) (DGEBA) with diethyltriamine (DETA) and (3-glycidoxypropyl)methyltriethoxysilane (GPTMS), followed by hydrolytic condensation of tetraethoxysilane (TEOS) and GPTMS. At a constant proportion of the organic phase, the effects of the varying molar proportions of siloxane (GPTMS) and silica (TEOS) on the film properties have been investigated. Findings A detailed structural analysis suggests for intermediate TEOS to GPTMS ratios a structure of highly condensed silica-siloxane domains covalently bonded to the embedding epoxy phase. The homogeneous distribution of the quasi-spherical sub-nonmetric silica-siloxane nodes is in agreement with low surface roughness (<5 nm), observed by atomic force microscopy. This dense nanostructure results in high thermal stability (>300 °C), strong adhesion to steel substrate and excellent barrier property in saline solution, with corrosion resistance in the GΩ cm 2 range. [ABSTRACT FROM AUTHOR]

Ti6Al4V is the mostly applied metallic alloy for orthopedic and dental implants, however, its lack of osseointegration and poor long-term corrosion resistance often leads to a secondary surgical intervention, recovery delay and toxicity to the surrounding tissue. As a potential solution of these issues poly(methyl methacrylate)-silicon dioxide (PMMA-silica) coatings have been applied on a Ti6Al4V alloy to act simultaneously as an anticorrosive barrier and bioactive film. The nanocomposite, composed of PMMA covalently bonded to the silica phase through 3-(trimethoxysilyl)propyl methacrylate (MPTS), has been synthesized combining the sol-gel process with radical polymerization of methyl methacrylate. The 5 μm thick coatings deposited on Ti6Al4V have a smooth surface, are homogeneous, transparent, free of pores and cracks, and show a strong adhesion to the metallic substrate (11.6 MPa). Electrochemical impedance spectroscopy results proved an excellent anticorrosive performance of the coating, with an impedance modulus of 26 GΩ cm2 and long-term durability in simulated body fluid (SBF) solution. Moreover, after 21 days of immersion in SBF, the PMMA-silica coating presented apatite crystal deposits, which suggests in vivo bone bioactivity. This was confirmed by biological characterization showing enhanced osteoblast proliferation, explained by the increased surface free energy and protein adsorption. The obtained results suggest that PMMA-silica hybrids can act in a dual role as efficient anticorrosive and bioactive coating for Ti6Al4V alloys. Unlabelled Image • Conjugation of silica and PMMA yielded homogeneous and adherent hybrid coatings. • PMMA-silica coatings provide efficient corrosion protection for a Ti6Al4V alloy. • Apatite formation in SBF solution predicts bone-bonding ability. • The coatings promote osteoblastic proliferation. • Effective protection metallic implants by bioactive anticorrosion coatings [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrids are considered an effective and environmentally compliant alternative to chromate-based anticorrosive coatings, currently banned due to the high toxicity of hexavalent chromium. In this work, hybrid nanocomposites based on poly(methyl methacrylate) (PMMA), covalently bonded to cerium oxide nanoparticles through the 2-hydroxyethyl methacrylate (HEMA) coupling agent, were tailored by carefully tuning the inorganic colloidal precursor to provide films with active corrosion protection for metallic substrates. Lithium hydroxide was exploited as oxidizing agent of cerium nitrate to form ceria nanoparticles. Precursor solutions and solid nanocomposites with different LiOH to Ce(NO 3) 3 .6H 2 O molar ratios were analyzed using spectroscopic and electron microscopy techniques and theoretical simulations. Electrochemical impedance spectroscopy (EIS) was used to study the anticorrosive performance of the coatings on carbon steel and 7075 aluminum alloy. The results showed that increasing amounts of LiOH lead to the formation of higher ceria content and larger primary nanoparticles, ranging from 1.7 to 2.8 nm. The homogenous ~20 μm-thick coatings present excellent anticorrosive performance on carbon steel and AA7075 substrates. Coatings on carbon steel with low LiOH loading (1Li:1Ce) showed long-term durability and high impedance modulus of up to 29 GΩ cm2 after 1 day in saline solution. On the AA7075 alloy, the presence of larger cerium oxide particles at higher LiOH content (3Li:1Ce) acted as effective reservoirs of cerium ions, providing high barrier coatings (395 GΩ cm2) with active corrosion protection. [Display omitted] • LiOH was used as oxidizing agent of cerium nitrate to form ceria nanoparticles. • Homogenous distribution of CeO x nanoparticles in the PMMA matrix for Li:Ce = 1. • PMMA-cerium oxide coatings exhibited excellent anticorrosive performance. • Coatings containing higher CeO 2 content showed self-healing ability. • Active protection was achieved by Ce4+ depletion forming insoluble cerium species. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid coatings deposited on different types of metallic alloys have shown outstanding anticorrosive performance. The incorporation of osteoconductive additives such as hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) into organic-inorganic hybrid coatings is promising to improve the osseointegration and corrosion resistance of Ti6Al4V alloys, which are the most widely used metallic orthopedic and dental implant materials today. Therefore, this study evaluated the capability of poly(methyl methacrylate) (PMMA)-TiO 2 and PMMA-ZrO 2 hybrid coatings modified with HA and β-TCP to act as bioactive and corrosion protection coatings for Ti6Al4V alloys. In terms of cell growth and mineralization, osteoblast viability, Ca+2 deposition and alkaline phosphatase assays revealed a significant improvement for the HA and β-TCP modified coatings, compared to the bare alloy. This can be explained by an increase in nanoscale roughness and associated higher surface free energy, which lead to enhanced protein adsorption to promote osteoblast attachment and functions on the coatings. The effect of HA and β-TCP additives on the anticorrosive efficiency was studied by electrochemical impedance spectroscopy (EIS) in a simulated body fluid (SBF) solution. The coatings presented a low-frequency impedance modulus of up to 430 GΩ cm2, 5 decades higher than the bare Ti6Al4V alloy. These findings provide clear evidence of the beneficial role of HA and β-TCP modified hybrid coatings, improving both the biocompatibility and corrosion resistance of the Ti6Al4V alloy. Unlabelled Image • Modification of PMMA-TiO 2 and PMMA-ZrO 2 coatings with hydroxyapatite and β-TCP • The coatings provided effective corrosion protection for a Ti6Al4V alloy • Osteoblastic growth and mineralization were enhanced with calcium phosphate addition • Higher surface free energy and roughness promoted osteoblast proliferation • Achievement of a bioactive and anticorrosive coating for metallic implants [ABSTRACT FROM AUTHOR]