Protective Organic Coatings Research Articles

Assessing the feasibility of laser ablation coating removal (LACR) on legacy bridge steel: Coating removal and adhesion, and effects on mechanical properties

The application of protective organic coatings is one of the most effective and commonly used corrosion mitigation strategies. To maintain the protective nature of coatings on long-term-exposed surfaces such as steel bridge components, coatings must be periodically removed and reapplied. A relatively new method called laser ablation coating removal (LACR), which incorporates a high energy nanosecond pulsed laser beam in combination with a high efficiency filtration system, allows for safe and effective removal of coatings and contamination from metal surfaces. In this study, LACR cleaning is tested on legacy bridge steel components to investigate the effect on substrate cleanliness and steel mechanical properties. These bridge sections were never blasted and contain a 20–100 μm thick mill-scale layer (iron oxide) below several coating layers (including lead-rich coatings). The top micron of the oxide layer is melted by LACR and also thermally insulates the underlying steel and prevents any melting within the metallic substrate. The resulting surfaces are analyzed using microscopy, hardness testing, tensile, and fatigue testing, and it is shown that LACR does not cause any measurable detrimental effects to the bulk mechanical properties of the bridge steel, as well as effectively removes all paint coatings. Furthermore, adhesion testing on LACR-cleaned substrates shows excellent adhesion, qualifying above adhesion requirements for coated steel.

Corrosion-Responsive Self-Healing Coatings.

Organic coatings are one of the most popular and powerful strategies for protecting metals against corrosion. They can be applied in different ways, such as by dipping, spraying, electrophoresis, casting, painting, or flow coating. They offer great flexibility of material designs and cost effectiveness. Moreover, self-healing has evolved as a new research topic for protective organic coatings in the last two decades. Responsive materials play a crucial role in this new research field. However, for targeting the development of high-performance self-healing coatings for corrosion protection, it is not sufficient just to focus on smart responsive materials and suitable active agents for self-healing. A better understanding of how coatings can react on different stimuli induced by corrosion, how these stimuli can spread in the coating, and how the released agents can reach the corroding defect is also of high importance. Such knowledge would allow thedesign of coatings that are optimized for specific applications. Herein, the requirements and possibilities from the corrosion and synthesis perspectives for designing materials for preparing self-healing coatings for corrosion protection are discussed.

Development of a warning system for defects onset in organic coatings on large surfaces

In this work, a warning system for monitoring the service status of organic coatings over large areas was developed. Taking advantage of electrochemical impedance spectroscopy (EIS) measurements, an attempt was first made to verify the repeatability of measurements made on surfaces with gradually increasing size. A threshold value of normalized impedance modulus was then set to be an easily detectable warning signal for the testing and maintenance of protective organic coatings. Monitoring continued for nearly two years, validating the threshold value for long immersion times. It was verified that the introduction of a defect could be easily detected through this system. Introducing a number of disturbing factors into the measurement did not significantly affect the results. Finally, the use of a portable potentiostat was adopted. It was found that the use of a potentiostat with smaller size but lower sensitivity equally allowed discerning the state of protection of the organic coating, with the possibility of using the measurement system for monitoring coated surfaces used in the naval industry.

Discrimination of Steel Coatings with Different Degradation Levels by Near-Infrared (NIR) Spectroscopy and Deep Learning

Assessing the current condition of protective organic coatings on steel structures is an important but challenging task, particularly when it comes to complex structures located in harsh environments. Near-infrared (NIR) spectroscopy is a rapid, low-cost, and nondestructive analytical technique with applications ranging from agriculture, food, and remote sensing to pharmaceuticals. In this study, an objective and reliable NIR-based technique is proposed for the accurate distinction between different coating conditions during their degradation process. In addition, a state-of-the-art deep learning method using a one-dimensional convolutional neural network (1-D CNN) is explored to automatically extract features from the spectrum. The characteristics of the spectrum show a downward trend over the entire wavenumber period, and two major absorption peaks were observed around 5250 and 4400 cm−1. The experimental results indicate that the proposed deep network structure can powerfully extract the complex characteristics inside the spectrum, and the classification accuracy of the training and testing data was 99.84% and 95.23%, respectively, which suggests that NIR spectroscopy coupled with a deep learning algorithm could be used for the rapid and accurate inspection of steel coatings.

Synthesis of Smart Nanofiber Coatings with Autonomous Self-Warning and Self-Healing Functions.

Organic protective coatings are widely used to protect metal structures from corrosion but they are vulnerable to undetectable damage. Without timely detection and repair, it could lead to severe consequences. How to warn and heal damaged areas simultaneously and automatically has become a challenging problem. Herein, we report an intelligent protective coating with self-warning and self-healing functions. This strategy was achieved by embedding bifunctional nanofibers containing 1,10-phenanthroline (Phen) in organic coatings. The nanofibers with Phen as a core and a poly(vinyl alcohol) (PVA)─chitosan (CS) blend solution as a shell were synthesized by coaxial electrospinning. The PVA/CS@Phen nanofiber-embedded coating displayed self-healing and high contrast indication function of the damaged area on coatings. Prominent red could warn microdamage and macrosurface damage, which occurred rapidly and healed permanently. The intelligent coating exhibited high healing performance under artificial injury with self-warning characteristics, and the cure rate was about 98.4% without external intervention. In the healing process, free amino groups of CS in the shell of nanofibers enhanced the sustained release of Phen. This convenient, economical, and efficient strategy with cooperative functions of self-warning and self-healing delivers an effective solution for prolonging the service life of protective coatings. This multifunctional coating exhibits excellent potential in the field of marine engineering applications.

Correlations between standard accelerated tests for protective organic coatings and field performance

Accelerated testing is widely used in development and pre-qualification of protective organic coatings. In this work 26 coating systems have been investigated in a 2-year C5 atmospheric exposure field test, ISO 9227 salt spray test, ISO 12944-9 cyclic ageing and ISO 16773 electrochemical impedance spectroscopy measurement of coating resistance. Of the 26 coating systems, 16 have epoxy mastic primers and 10 have zinc rich epoxy primers. In the field test, the zinc rich primer improved corrosion creep resistance from scribe by a factor of about 10. However, this is not reflected in any of the accelerated lab tests. The lab tests all show rather poor correlation to the field test with respect to corrosion creep. All the coatings had little corrosion creep from scribe in the field test, even the coating systems with epoxy mastic primers. The large focus on this parameter in coating pre-qualification testing, e.g. in ISO 12944-6 and 12944-9, may therefore not be justified.

Correlations between Standard Accelerated Tests for Protective Organic Coatings and Field Performance

Correlations between Standard Accelerated Tests for Protective Organic Coatings and Field Performance

Local oxidation of the buried epoxy-amine/iron oxide interphase

Epoxy-amine resins continue to find widespread use as the binders of corrosion protective organic coatings. In service, exposure to the environment ultimately results in oxidative deterioration of epoxy coatings, limiting the performance lifetime. Whilst the mechanisms underpinning surface oxidation have been characterized, few studies have examined polymeric degradation in the polymer/metal interphase, the integrity of which is central to performance. This is in part due to the inaccessibility of the buried interphase, which lies beyond the resolution limits of most organic analysis techniques. In this study, two innovative approaches are used to examine early stages of oxidative degradation of the buried polymer/iron oxide interphase for diglycidyl ether of bisphenol-A (DGEBA) coatings cross-linked with an aliphatic amine hardener, triethylenetetraamine (TETA). First, high fractions of iron oxide interfaces are introduced into the resin systems using synthetic hematite, Fe2O3, magnetite, Fe3O4 and goethite, Fe(O)OH powders, and the oxidation process is monitored using conventional infrared spectroscopy. Next, the buried interphase of coatings applied to iron is examined directly using nanoscale cross-sectional infrared analysis (via the photothermal infrared, PTIR, atomic force microscopy technique, known as AFM-IR). Diffusion limited oxidation is shown to initiate at the buried polymer-metal interface and progress slowly into the polymer, in accordance with pre-established mechanisms, resulting in chemical gradients of <400 nm after 28 days exposure to mild thermal aging conditions (70 °C, 14% RH).

Non-Destructive Evaluation of Hidden Defects Beneath the Multilayer Organic Protective Coatings Based on Terahertz Technology

An organic protective coating system plays an important role for the corrosion protection of offshore metallic structures. It is of practical importance to detect possible coating defects and evaluate coating performance for corrosion degradation monitoring. Reliable defect identification can provide timely and effective maintenance to avoid serious consequences. This work investigated various multilayer organic coating systems by terahertz pulse imaging technology and aimed to explore the inspection ability of terahertz non-destructive testing (THz NDT) of protective coatings. Several types of defective coating samples were measured. The comparison of measurements obtained for sites with and without defects was provided. The changes in the signals caused by the presence of defects were explained. Structural analysis, quantitative evaluation, and defect identification were carried out in detail. The results of measurements showed that corrosion defects, paint bulge defects, and paint detachment defects can be distinguished and identified in combination with the causes of defects. It can provide effective technical guidance for terahertz technology to be gradually extended to engineering applications.

Electroless codeposition of GO incorporated silane nanocomposite coating onto AZ91 Mg alloy: Effect of GO content on its morphology, mechanical and corrosion protection properties

The corrosion of Mg alloys is a significant concern in practical applications, and silane-based protective organic coatings are promising to protect the Mg alloys from corrosion. The (3-glycidyloxypropyl) trimethoxysilane/graphene oxide (GPTMS/GO) coating was developed using electroless codeposition technique on AZ91 Mg alloy such that GO sheets were grafted with silanol groups. The coating was prepared by dipping AZ91 Mg alloy in GPTMS/GO solution and then curing at 120 °C. The electrochemical measurement results showed an increased corrosion resistance of AZ91 Mg alloy in 3.5% NaCl solution. The decrease in the corrosion current density value of 0.016 µA cm−2 is attributed to the formation of a passive layer of GO grafted GPTMS on the surface of AZ91 Mg alloy. The enhanced hydrophobicity of 108°, the improved adhesion (5 A) and high hardness (52 HV) were attained due to covalent metallic siloxane bonds (MgOSi) and the laminate structure of GO developed on AZ91 substrate.

Environmentally Friendly Anticorrosive Polymeric Coatings

This paper provides a synthetic and comprehensive overview on environmentally friendly anticorrosive polymeric coatings. Firstly, the economic and environmental impact of corrosion is presented to highlight the need of anticorrosive polymeric coatings as a flexible and effective solution to protect a metal. Secondly, the implementation of regulations together with the consumer awareness for environmental considerations and protection of health are the driving force for a progressive but significant change in the sector. Therefore, within the protective organic coatings market, this article provides a review of the most recent developments in environmentally friendly solutions, including bio-based and water-borne epoxy, hyperbranched polyester for low- volatile organic compounds (VOC) coatings, waterborne polyurethane and non-isocyanate polyurethanes (NIPUs), and graphene or bio-based fillers for acrylics. Moreover, this paper outlines new trends such as smart additives, bio-based corrosion inhibitors, and functional antibiocorrosive coatings as superhydrophobics. Finally, industrially relevant applications of environmentally friendly anticorrosive polymeric coatings including solutions for marine and off-shore industries are summarized.

Thickness mapping of organic layers applied on sterling silver by means of X-ray fluorescence scanning

The application of organic protective coatings is the most commonly used strategy to avoid tarnishing of silver artefacts. Non-invasive mapping of coating thickness is a key point to evaluate the consistency and completeness of coating application and to monitor protective effectiveness over time. This work is aimed at evaluating the feasibility of acquiring thickness maps of coated silver surfaces by means of X-ray fluorescence scanning. Experimental calibration curves were built by using organic films of known thickness made of several commonly used protective coatings, (Zapon nitrocellulose lacquer, and acrylic resins Paraloid B72 and Paraloid B44). X-ray fluorescence scans were performed on coated silver sterling coupons treated by brushing or spraying polymer solutions prepared with different solvents and concentrations. Thickness maps pointed out different average thickness values among selected polymers and highlighted that almost all the coatings were unevenly spread on the surface. Application by brush provided particularly uneven coatings and brush strokes were clearly distinguishable. The accuracy of thickness measurements was calculated by means of a semi-empirical approach, and results suggest that thickness can be predicted with an uncertainty of about ±5%.

Use of Dynamic Mechanical Analysis (DMA) for Characterizing Interfacial Interactions in Filled Polymers

Dynamic mechanical analysis (DMA) provides reliable information about the viscoelastic behavior of neat and filled polymers. The properties of filled polymers are relevant to different industries as protective organic coatings, composites etc. Interfacial interactions in filled polymers play an important role in determining their bulk properties and performance during service life. In this brief review article, studies that used DMA to characterize the interfacial interactions in filled polymers have been reviewed. The available open literature provides a mixed opinion about the influence of interfacial interactions on the glass transition temperature of filled polymers. Nevertheless, it appears that in the case of strong interfacial interactions between the filler particles and the polymeric matrix, the peak value of tan δ is reduced in comparison to that of a filled polymer where these interactions are weak.

Organic zinc-rich protective coatings with improved electrochemical properties: The role of nano-powder additions

In this paper, the role of nickel-20 chromium and TiO2 nanoparticles additions for enhancement of corrosion resistance and microhardness of organic zinc-rich coatings were investigated. Three coati...

Special Issue on “Advances in Organic Corrosion Inhibitors and Protective Coatings”

This Special Issue collects new findings and recent advances in the development, synthesis, and structure–activity relationships of organic corrosion inhibitors and protective coatings.

Simplified approach to assess water uptake in protective organic coatings by parallel plate capacitor method

Water uptake in organic coatings is often determined from changes in coating capacitance obtained by analyzing electrochemical impedance spectroscopy (EIS) data. However, the method has been criticized for providing inconsistent results poorly correlating to gravimetry measurements, which may arise from the absence of a straightforward approach to treat impedance data. A simple method based on forming a parallel plate capacitor (PPC) and measuring the capacitance using commercial inductance (L), capacitance (C) and resistance (R) meter is proposed. Water content in commercial coil coated steel specimens was determined by the Brasher-Kingsbury equation from coating capacitance measured by both PPC and EIS methods. A good correlation was observed between the reference gravimetric results and water uptake measured by the PPC approach. The new method can be considered as an industrial technique applicable also for on-site determination of water content in protective coatings applied on metallic structures.

Imaging Fungal Contamination of Protective Organic Coatings

Imaging Fungal Contamination of Protective Organic Coatings

EIS and organic coatings performance: Revisiting some key points

The objective of this work is to gather historical aspects about the use of EIS for evaluation of corrosion protective organic coatings performance, emphasizing experimental care, contributions and limitations for wider technological application. Contributions are rescued from authors who made important work in development and evaluation of organic coatings with the support of electrochemical techniques. The knowledge of these fellows in organic coatings paved the way for the use of EIS in this field; particularly, some contributions of J.E.O. Mayne are reverenced. This paper does not provide a complete review of the subject, but rather outline keypoints, that were selected according to their relevance in the technological applications to which impedance measurements could contribute, as: early detection of underfilm corrosion, indirect measurement of delaminated areas, prediction of coatings service life by water uptake and modeling with analog electric devices as a tool to obtain the parameters needed for the mentioned applications. Fundamental aspects of EIS in this field have extensive literature which is referenced. The massive current use of EIS justifies this retrospective, revisiting some basics as a source for new users, sharing critical comments and reinforcing the importance of some experimental care.

Synthesis of PDA-BN@f-Al2O3 hybrid for nanocomposite epoxy coating with superior corrosion protective properties

A novel PDA-BN@f-Al2O3 nanohybrid was synthesized by depositing Al2O3 nanoparticles modified with γ -Aminopropyltriethoxysilane (KH550) on the surface of hexagonal boron-nitride (h-BN) sheets covered with polydopamine (PDA). Then, PDA-BN@f-Al2O3 hybrids was dispersed in epoxy resin to prepare composite coating samples. Many characterizations revealed that the functionalized Al2O3 successfully deposited on the surface of PDA-BN platelets and PDA-BN@f-Al2O3 hybrids showed good dispersibility in the epoxy resin, and the interfacial adhesion between hybrids and epoxy matrix was improved. Furthermore, the effects of Al2O3, h-BN and various mixtures of PDA-BN@f-Al2O3 hybrids at a low weight fraction of 1 % on the corrosion resistance of epoxy coating were studied by electrochemical measurement and salt spray test. The potentiodynamic polarization test revealed that PDA-BN@f-Al2O3 hybrids have a corrosion inhibitive performance. Moreover, the coating resistance of PDA-BN@f-Al2O3 (3:1)/epoxy was enhanced by three orders of magnitude compared with neat epoxy after 5 d immersion. This study provides a promising application prospect for the development of superior metal protective organic coatings.

Mussel-inspired UV protective organic coatings via layer-by-layer assembly

Layer-by-layer (LbL) deposition technique has been employed to design mussel-inspired UV protective organic coating using polyethylenimine-polydopamine (PEI-PDA) and poly (acrylic acid) (PAA) pairs. The photocatalytic decomposition of RhB (Rhodamine B) is studied inside the multilayer coated glass vials and a 10 BLs (Bilayers) coatings with a thickness of 1 µm reduces the degradation efficiency of the dye by a factor of 7. The nanocomposite films remain stable under a broad range of pH (pH 4 to pH 10) and temperature (250 °C). The presence of PDA in the nanocomposite films offers a substrate independent adhesion and the film has grown conformally on diverse substrates like cotton and poly(ethylene terephthalate) (PET) using spray assisted LbL coating. Moreover, a study has shown that LbL deposited films have better UV protection efficiency compared to traditional “one pot” PDA deposited films. Finally, these environmental friendly multilayer films are able to protect the degradation of conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films from long UV exposure.