Degradation Of Organic Coatings Research Articles

Degradation of Various Organic Coatings via UV-Generated Sulfate Radicals.

Degradation of organic coatings is essential for recycling valuable substrates. Despite the development of strategies for this purpose, the resulting degradations are typically constrained by the composition of the coating. This paper presents a simple strategy utilizing radicals induced by UV for the degradation of diverse organic coatings. The sulfate radicals, generated from UV-exposed ammonium persulfates, induce the degradation of various organic coatings, including layer-by-layer assembled coating composed of alginate and chitosan polymers as well as polydopamine coating. This strategy also facilitates the separation of two adhered substrates by degrading the adhesive polymer layer positioned between them. This novel approach enables the complete degradation of various organic coatings in aqueous conditions without imposing restrictions on their composition, leading to the recovery of the original surface properties of the substrate.

Thermo-chemo-mechanical influences of impingement flow on the degradation of organic coatings in the underwater zone of offshore wind turbines

Thermo-chemo-mechanical influences of impingement flow on the degradation of organic coatings in the underwater zone of offshore wind turbines

Superhydrophobic composite coatings in bacterial culture media: Durable antibacterial activity and enhanced corrosion resistance

Degradation of organic coatings caused by microorganisms limits the application of anti-corrosive coatings in harsh marine environments. In this study, a novel superhydrophobic coating was developed to prolong the durability and integrity in marine environments. Superhydrophobic basalt scales were obtained using a set of simple methods, including chemical etching by a concentrated NaOH solution and fluorination using 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES). Then, the superhydrophobic basalt scales were arranged on top of the epoxy resin base to produce the superhydrophobic composite coating (3 μL water droplet; contact angle of 164.9°). After 21 days of immersion in Pseudomonas aeruginosa (P. aeruginosa) inoculated media, the results of antibacterial testing and electrochemical characterization in an erosive environment showed that superhydrophobicity significantly inhibited the adhesion of the P. aeruginosa cells and enhanced the corrosion resistance of the composite coating.

Degradation of epoxy coatings exposed to impingement flow

Organic coatings are widely used for the corrosion protection of metals. Despite a wide range of work on the degradation of organic coatings, few studies have contributed to understand the influence of the fluid flow on the degradation of organic coatings. In this study, an epoxy coating is exposed to a vertical impingement flow of a 3.5 wt% NaCl solution with a variety of flow rates. The coating degradation is monitored by electrochemical impedance spectroscopy (EIS). Equivalent circuit models are employed to interpret the EIS spectra. Atomic force microscopy (AFM) was employed to study the influence of fluid flow on the surface topology of the coating samples. We found that the coating’s barrier property deteriorates more drastically when exposed to higher flow rates for impingement flow. Coating thickness and surface roughness are significantly affected by the fluid shear and the flow rate. It is concluded that the impingement flow substantially impacts the barrier properties of epoxy coatings owing to its influence on the electrochemical properties of the coating layers and the fluid shear it creates on the coating surface.

Behavior of fluorine coatings on steel bridges at different temperatures upon exposure to a direct heat source

Protective coatings are commonly used for the corrosion protection of steel structures. To protect steel bridges from weather and unexpected damage (e.g., fires or explosions), fluorine-based coatings are commonly applied as a top layer. Although the safety of infrastructure should be considered via risk assessment and maintenance, few studies have been conducted on the degradation of organic coatings under harsh environments and accidental events. Therefore, we examined the effect of direct heat exposure on organic (fluorine-based) coatings. To simulate the conditions produced by an explosion, specimens were subjected to surface temperatures of 100, 200, 300, 400, and 500 °C for 10 s through direct exposure to heat. Surface changes to the post-exposure fluorine coats were characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, nanoindentation, gloss, color differentiation, laser microscopy, and thermogravimetric analysis. Overall characterization of the coatings through electrochemical impedance spectroscopy revealed that surface changes began to occur at 300 °C and detachment of the bulk coating occurred at 400 °C or higher. Our results successfully clarify the behavior of fluorine coatings under different temperatures to a degree that is relevant to critical public safety issues in civil infrastructure.

A comparative study on UV degradation of organic coatings for concrete: Structure, adhesion, and protection performance

Organic coatings have been widely used to protect concrete structures from the aggressive environment and improve their reliability. However, there is a lack of clear understanding on how environmental stressors contribute to the degradation and, ultimately the loss of protection function of organic coatings. In this study, comparative degradation studies were carried out on two kinds of coatings, namely polyurea and epoxy coatings, with the major focus on the relationship between their bulk degradation, loss of adhesion and the deterioration of protection performance. Samples were all subjected to ultraviolet (UV)-condensation exposure up to about 1440 h. The changes in the surface morphology, internal pore structure, wettability and chemical structure of aged coating surface were characterized via scanning electronic microscopy (SEM) laser scanning confocal microscopy (LSCM), static contact angle measurements, and Fourier Transform Infrared Spectroscopy (FT-IR) respectively, while the water resistance and adhesion strength between coatings and concrete were studied by water sorption and pull-off tests separately. The results showed that UV irradiation induced significant morphological and chemical changes in the epoxy coatings, while the changes in the polyurea coating were minor. However, due to the higher loss in adhesion, it was interestingly found that the chloride resistance of polyurea coating was reduced even more pronouncedly than that of epoxy coating after aging. This study has clearly demonstrated the strong dependence of the protection performance of coatings for concrete on their adhesion loss besides the bulk degradation induced by the aging process.

Diffusion cell investigations into the acidic degradation of organic coatings

Diffusion cell investigations into the acidic degradation of organic coatings

Diffusion cell investigations into the acidic degradation of organic coatings

Protective organic coatings work by preventing contact between an aggressive environment and a vulnerable substrate. However, the long required lifetime of a barrier coating provides a challenge when attempting to evaluate coating performance. Diffusion cells can be used as a tool to estimate coating barrier properties and lifetime. In this work, a diffusion cell array was designed, constructed, and compared to previous designs, with simplicity being the most important design parameter. Sulfuric acid diffusion through five different coatings was monitored using a battery of cells, and a mathematical model was developed to simulate the experimental data and to study diffusion mechanisms. The diffusion cells allowed an objective and fast analysis of coating barrier properties. It was found that sulfuric acid deteriorated these properties as it diffused through the films. This was also expressed in the modeling results, where a three-step time dependency of the diffusion coefficient was required to simulate both acid breakthrough time and the subsequent steady-state flux. A vinyl ester-based coating proved to be the most effective barrier to sulfuric acid diffusion, followed by a polyurethane coating. Amine-cured novolac epoxies provided the least effective protection.

Mechanisms of degradation of organic coatings

Abstract An overview of protection mechanisms of organic coatings for metallic constructions and products is given. The barrier effect of coatings and protection in local defects are discussed. Basic degradation mechanisms of organic coatings such as anodic and cathodic delamination in vicinity of defects, osmotic and cathodic blistering, mechanical stress assisted blistering, loss of adhesion and chalking are described. Appropriate laboratory tests are proposed for each degradation mode.

Development of Wireless and Passive Corrosion Sensors for Material Degradation Monitoring in Coastal Zones and Immersed Environment

Wireless and fully energetically passive corrosion sensors inspired from the chipless Radio-Frequency IDentification (RFID) technology are presented for the monitoring of degradation of infrastructures located in coastal zones and underwater environments. The device consists of a reader and a remote passive sensor. This study presents two radio-frequency (RF) corrosion-sensitive resonators that can be integrated in such a device. The first is sensitive to a loss of metal due to its degradation, and the second is sensitive to the corrosion potential of metals, with respect to a reference electrode. The RF characterization of these two resonators demonstrates unambiguously the sensitivity of the method to corrosion of metal, passivation of steel as well as degradation of organic coatings. Then, their integration in a demonstrator including antennas is considered. The main parameters that influence the RF wave propagation and thus the reading distance are discussed. Following the presented results, the proposed method is considered as a reliable and versatile tool which should be able to be deployed in immersed, tidal, and splash zones, for example, for offshore facilities monitoring.

Flow accelerated degradation of organic clear coat: The effect of fluid shear

Flow accelerated organic coating degradation has been received attention, but the degradation mechanism is still not completely understood. In this study, we focus on investigating the influence of fluid shear on the degradation of organic coatings. A commercially available epoxy based clear coating was exposed to the laminar flow, and a 3.5 wt% NaCl solution was employed as the working fluid with a variety of flow rates. The change in the composition of the working fluid during the coating immersion was characterized by Fourier Transform Infrared Spectrometer (FTIR) and conductivity measurement. The effect of fluid shear is also demonstrated by the change in coating thickness. The barrier properties of organic coatings were monitored inline by Electrochemical Impedance Spectroscopy (EIS) measurement. The time evolution of coating resistance, capacitance, and permittivity obtained from the equivalent circuit model was studied to demonstrate the internal composition change of the coatings due to the flowing fluid. In this study, the experiments and analysis confirmed that flowing fluid promotes the release of coating materials from the coating into the surrounding working fluid while it accelerates the transport of water and ions into the coating.

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 3.5wt% 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.

Failure mechanism of organic coatings overlaid on arc sprayed coatings

A general mechanism of corrosion degradation of organic coatings overlaid on Al and Zn–Al–Mg–RE (rare earth) coatings was investigated. The metallic coatings were prepared by the high velocity arc spraying (HVAS) technology. Artificial defects were introduced in the organic coatings and the samples were immersed in 5 wt-%NaCl aqueous solution. After 430 h, the different microstructures of corrosion products in the defects were studied by scanning electron microscopy. The microstructure of corrosion products of the HVAS Zn–Al–Mg–RE coating was more compact than that of the HVAS Al coating. The compact corrosion products were better barriers against chloride ions and water permeation, and the defects in the system were blocked by the corrosion products.

Monitoring of the AC-DC-AC Degradation of Organic Coatings Using Embedded Electrodes

Abstract The application of embedded sensors is presently being developed to serve as a reliable corrosion sensing technique used for structures protected by organic coatings. Results are presented...

Study of degradation of organic coatings in seawater by using EIS and AFM methods

AbstractIn this article, electrochemical behaviors and their topography observation for four organic coatings used in seawater, by using both electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) methods to study environment behaviors of different coatings as well as the effects of their film formation, pigments, and fillers on anticorrosion behaviors, were measured. The results show that polyurethane, epoxy, and chlorinated rubber coatings all present one capacitive loop in their tested EIS which contains phenomenally only one time constant, whereas alkyd coating presents two capacitive semicircle arcs. With two capacitive loops, the capacitive semicircle in the high frequency range represents barrier layer property, but the semicircle in the low frequency range represents corrosion reaction of metals under the film. Polyurethane coating used in seawater has well anticorrosion property in seawater immersion test. The appearance features of different layers are visible different between different layers of tested coatings at their surface topography. The property of polyurethane paint film coated on metal is better than other layers, and film of alkyd coating has many pits at its surface by observing the layer's images. AFM photos imaged have also been used to further detail surface topography for four organic coatings, and to approve effects of topography of these coatings on its electrochemical behaviors, from two views of both height and phase modes. It is beneficial to explain deeply the environment behaviors and degradation mechanism of organic coatings. To further study failure of these organic coatings and dynamic processes of corrosion of metal under the film, two equivalent circuit models, according to these tested EIS, have been suggested to explain the corrosive kinetics of these four coatings. To polyurethane, epoxy, and chlorinated rubber coatings used in seawater which have good protection effects for substrate metal, the diffusion process for water, from their layer's surface to interface of film/metal, is mainly controlled factor for degradation. However, the electrochemical reaction process has may become a control procedure for corrosion of alkyd coated metal. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Degradation of Organic Coatings on Steel Investigated by Dynamic Electrochemical Impedance Spectroscopy

Degradation of the organic coatings on steel has been investigated by the dynamic impedance measurements. The dynamic impedance was displayed on 3-dimension plots, whose axes were real and imaginary components and time. The time variation of the film resistance related to the permeation of water was monitored to discuss the corrosion mechanisms of coated steel.

Degradation of Organic Coatings on Steel Investigated by Dynamic Electrochemical Impedance Spectroscopy

not Available.

Degradation of organic coatings in a corrosive environment: a study by scanning Kelvin probe and scanning acoustic microscope

Degradation of pigmented epoxy coatings on a steel substrate during exposure to aerated 3% NaCl solution has been investigated using the scanning Kelvin probe (SKP) and scanning acoustic microscopy (SAM). A method for processing SKP potential maps has been used to visualize the distribution of anodic and cathodic current. It was observed that rust deposited at the defects, or later beneath the coating, acted as a cathodic reactant, leading to development of new anodes beneath the coating. Exposure of rusty samples to moist air (rather than salt solution) during SKP mapping is shown to lead to more noble potentials at the defect that influence the electrochemistry of under-film processes.

Understanding the Degradation of Organic Coatings Using Local Electrochemical Impedance Methods : I. Commonly Observed Features

Local electrochemical impedance mapping (LEIM) was used to investigate local underfilm corrosion occurring on organic-coated AA2024-T3 exposed to chloride solution. Films (5-20 μm thick) of neat epoxy, polyurethane, and vinyl resins were studied. Frequently observed features in the LEI maps included: an unexpected decrease in admittance in early stages of development, trenching at the periphery of admittance peaks, both increases and decreases in peak height over time, changes in peak width over time, different amplitudes in admittance over different regions of multilobed blisters, and different admittance magnitudes for different types of defect. These LEIM features could provide significant insight into and documentation of the local breakdown processes of coated metals, if they truly represent electrochemical phenomena associated with changes at the interface. These features were observed on each of the coating chemistries studied. Proposed origins and supportive evidence of these LEIM features is presented. © 2003 The Electrochemical Society. All rights reserved.

Investigating Localized Degradation of Organic Coatings : Comparison of Electrochemical Impedance Spectroscopy with Local Electrochemical Impedance Spectroscopy

The degradation of polyester coil-coated galvanized steel was compared using both conventional (macroscopic) and localized electrochemical impedance techniques on the same specimen and within a time interval (hours) much shorter than the total immersion period (days). Specimens containing a central 250 μm laser-ablated defect in the organic coating layer were immersed in a 10 mM NaCl solution for up to 30 days. The local multifrequency impedance was determined by placing a novel impedance probe, either directly above the coating defect or above an area of intact coating. In addition, single frequency impedance mapping of the specimen surface was carried out at 1 kHz and compared with optical microscopy of the surface. The results demonstrate clearly that macroscopic electrochemical impedance provides a surface-averaged measurement of the properties of the coating, plus any defects, and that where several time constants are apparent, they are not uniquely separable into physical processes. Thus, macroscopic impedance spectra convolute the separate responses of the coating and defect together. However, local electrochemical impedance can effectively separate the local properties of the organic coating from the local electrochemical behavior at a coating defect. © 2003 The Electrochemical Society. All rights reserved.