Degradation Of Coatings Research Articles

Wood coating failures against natural and accelerated climates

Monitoring, assessment and prediction of service life of materials are a serious challenge for the building and construction sector. According to ISO 15686 (2008), laboratory testing must be performed alongside field testing to evaluate different degradation outcomes. Coated wooden specimens, used for building façades, were exposed to different ageing conditions in (a) a vertical climate simulator, (b) a horizontal Atlas solar simulator and (c) against natural outdoor exposure conditions. Wood specimens were from Norway spruce grown at two locations in southern Norway. Wooden boards were surface finished by a primer and red acrylate paint. Ageing cycles in the laboratory include exposure to ultraviolet and infrared radiation, water spray, freezing and thawing. Non-destructive surface evaluation techniques were used to monitor and verify the effect of ageing stresses on coatings. Before and after exposure, the coated surfaces were graded visually. Short- and long-term exposures are observed to cause physical degradation such as flaking, cracking and blistering. Blistering on the knots occurs during initial phases of exposure. Different correlations are observed between the CIELab/CIE 1976 coating total colour difference and partial colour difference for artificially aged coated surfaces, naturally aged coated surfaces, and artificially aged uncoated surfaces. Fourier transform infrared spectra suggest possible degradation of wood or coatings during the ageing cycles and a higher content of carbonyl groups in aged acrylate coating. Arrhenius temperature and humidity acceleration factor shows higher rate of deterioration of cellulose, lignin and acrylate in humid conditions.

Melting and Crystallization of Silicate Systems Relevant to Thermal Barrier Coating Damage

The melting and crystallization behaviors of model calcium–magnesium–alumino‐silicate (CMAS) compositions relevant to the degradation of thermal barrier coatings (TBCs) were investigated. A primary goal was to establish a baseline for studies on CMAS reactions with TBC materials, reported separately, and their potential to mitigate degradation. Ternary calcium alumino‐silicate (CAS) compositions investigated melt below their equilibrium solidus owing to their metastable phase constitution. Additions of MgO or FeOx have significant effects on the melting behavior, depending on the C:A:S proportions. Amorphization on cooling is commonplace, with MgO, AlO1.5, and especially FeOx promoting crystallization. The behaviors of amorphous and crystalline versions of the same CMAS are different and depend on heating/cooling rates, with attendant implications for their interaction with TBCs.

Environmental/thermal barrier coating systems deposited on Nb/Nb5Si3 based alloy

Coupons of a Nb-silicide-based alloy with the nominal composition of 47Nb–25Ti–8Hf–2Cr–2Al–16Si (at-%) were coated with Co-, Ni- and FeB-modified M7Si6-based layers using pack-cementation. Subsequently, on one side of the coated samples, environmental/thermal barrier coatings (E/TBCs) of yttria partially stabilised zirconia (YSZ) and gadolinium zirconate were deposited by electron beam physical vapour deposition. The lifetimes of the different E/TBC systems were determined performing thermal cycling tests at 1100 and 1200°C in air. At 1100°C, lifetimes approaching 1000 cycles (corresponding to 1000 h of high temperature exposure) were measured. However, severe oxidation occurred at the edges and rear side of the samples (areas without ceramic topcoat) due to local degradation of the oxidation protective coatings, resulting in substantial material recession with prolonged testing. When thermally cycled at 1200°C, the E/TBC systems exhibited lifetimes exceeding 200 cycles. The sample with FeB containing bond coat and Gd2Zr2O7 topcoat survived even 400 cycles at this exposure temperature.

各塗装鋼板の塗膜劣化現象とインピーダンス値との相関関係に関する研究

各塗装鋼板の塗膜劣化現象とインピーダンス値との相関関係に関する研究

Microstructural Degradation of Thermal Barrier Coatings on an Integrated Gasification Combined Cycle (IGCC) Simulated Film-Cooled Turbine Vane Pressure Surface Due to Particulate Fly Ash Deposition

Research is being conducted to study the degradation of thermal barrier coatings (TBC) employed on IGCC turbine hot section airfoils due to particulate deposition from contaminants in coal syn-thesis gas (syngas). West Virginia University (WVU) had been working with US Department of Energy, National Energy Technology Laboratory (NETL) to simulate deposition on the pressure side of an IGCC turbine first stage vane. To simulate the contaminant deposition, several TBC coated, angled film-cooled test articles were subjected to accelerated coal fly ash, which was injected into the flow of a combustor facility with a high pressure (approximately 4 atm) and a high temperature (1560 K) environment. To investigate the degradation of the TBCs due to particulate deposition, non-destructive tests were performed using scanning electron microscopy (SEM) evaluation and energy dispersive X-ray spectroscopy (EDS) examinations. The SEM evaluation was used to display the microstructure change within the layers of the TBC system directly related to the fly ash deposition. The SEM micrographs showed that deposition-TBC interaction made the YSZ coating more susceptible to delamination and promoted a dissolution-reprecipitation mechanism that changed the YSZ morphology and composition. The EDS examination provided elemental maps of the shallow infiltration depth of the fly ash and chemical composition spectrum results which showed yttria migration from the YSZ into the deposition.

Passivation of Zinc Coatings by Inhibition Chrome-Based Systems

The anticorrosion resistance of metal (inorganic) coatings is defined by the system of anode and cathode protection. As zinc coatings do not load the environment in such an extent like organic paint systems, current trend is to maximally prolong the service life of a zinc coating. This paper is focused on analysis of the speed of corrosion degradation of zinc coatings. The individual samples were prepared by the method of hot-dipping and galvanizing. Inhibition systems were applied only to electrolyte-applied zinc coating. There were prepared three different passivating methods: (1) slim-layer passivation with the content of Cr (III), (2) slim-layer passivation with the inhibitor Cr (VI) and (3) thick-layer passivation with Cr (III). The thickness of anticorrosion coatings has been measured by both destructive and non-destructive methods. The weight of the applied anticorrosion substrate was measured in compliance with the ČSN EN ISO 3892 standard. Ductile characteristics were analysed according to the ČSN EN ISO 1519 standard. The total evaluation of anticorrosion resistance was processed according to the ČSN EN ISO 9227 standard (salt-spray test). Based on the results of corrosion tests, the individual coatings can be analysed and their corrosion resistance can be evaluated. The service life of the zinc coating can be prolonged by sealing off the zinc coating by an appropriate inhibitor which supports the self-healing effect of the whole anticorrosion substrate.

Polarization calibration techniques and scheduling for the Daniel K. Inouye Solar Telescope

AbstractThe Daniel K. Inouye Solar Telescope (DKIST), formerly Advanced Technology Solar Telescope when it begins operation in 2019 will be by a significant margin Earth's largest solar research telescope. Science priorities dictate an initial suite of instruments that includes four spectro-polarimeters. Accurate polarization calibration of the individual instruments and of the telescope optics shared by those instruments is of critical importance. The telescope and instruments have been examined end-to-end for sources of polarization calibration error, allowable contributions from each of the sources quantified, and techniques identified for calibrating each of the contributors. Efficient use of telescope observing time leads to a requirement of sharing polarization calibrations of common path telescope components among the spectro-polarimeters and for those calibrations to be repeated only as often as dictated by degradation of optical coatings and instrument reconfigurations. As a consequence the polarization calibration of the DKIST is a facility function that requires facility wide techniques.

Effect of silane modified nano ZnO on UV degradation of polyurethane coatings

Abstract Nanosized ZnO modified by 2-aminoethyl-3-aminopropyltrimethoxysilane (APS) was prepared using the precipitation method. Modified nano ZnO by silane (ZnO-APS) was characterized by XRD, SEM, TEM and UV–vis measurements. The degradation of the polyurethane coating, the polyurethane coatings containing 0.1 wt% nano ZnO and the polyurethane coatings containing nano ZnO-APS at two concentrations (0.1 and 0.5 wt%) during QUV test was evaluated by gloss measurement and electrochemical impedance spectroscopy. The coating surface after QUV test was observed with SEM. The results show that nano ZnO-APS has spherical structure with particle size around 10–15 nm. Nano ZnO improved the UV resistance of the PU coating and surface treatment by APS enhanced the effect of nano ZnO. The presence of nano ZnO-APS at 0.1 wt% concentration significantly improved the UV resistance of polyurethane coating.

THE IMPACT OF CLIMATE PARAMETERS ON THE SURFACE OF BUILDINGS’ WALLS

The durability of surface layers of enclosures (outside walls of buildings) is highly influenced by stresses occurring in the plane of contact between finishing materials and that of the enclosure. Damage to external walls depends on a high moisture content, which in turn depends on high water absorption during driving rains. One example of such damage is damage due to direct water penetration in homogeneous walls. The other negative effects of a high moisture content are impaired heat insulation and accelerated degradation. This article investigates the external layer of walls and the durability of different paints. In case of bi-laminar system “paint film-the wall being painted” two opposite processes take place: the water flow rate from the outside towards the wall, and the water vapor flow rate of the wall to the outside. The optimum selection of paint is necessary. An investigation of the durability of wall surface paints in a climatic chamber is instructive only after intermediate investigations and measurements of the substrates’ physical and mechanical properties that aid in predetermining durability. The influence of moisture deformations upon degradation of coatings depends on the porosity of surface materials being coated, and on the origin and macrostructure of the coating.

Electrochemical Impedance Spectroscopy for Coating Evaluation using a Micro Sensor


 
 
 This paper discusses a micro-linear polarization resistance (μLPR) sensor modified to perform coating evaluation by means of electrochemical impedance spectroscopy (EIS). A circuit model is used with the EIS data to measure solution resistance, pore resistance, charge transfer resistance, intact coating capacitance, and double layer capacitance. These measurements allow the end user to monitor degradation of protective coatings in real-time, through non-destructive means. This is demonstrated through an accelerated aging test using a coated metal plate with a modified μLPR sensor. A metal panel made from aluminum alloy 7075-T6 was coated with 2 mils of an epoxy-based polymer coating and 2 mils of high solids polyurethane. The sensor was adhered to the face of the coated panel in a manner that allowed the electrolyte solution consisting of 3.5% NaCl to flow between the sensor and the coated surface of the panel. EIS measurements were acquired every hour for a total of 35 hours and at the conclusion of the test, changes in key parameters within the circuit model identified the initial time and mechanism of coating degradation, in this case, delamination
 
 

Effects of cation substitution and temperature on the interaction between thermal barrier oxides and molten CMAS

Abstract The effectiveness of candidate rare earth (RE) bearing oxides to mitigate degradation of thermal barrier coatings by molten silicates is determined by the constitution and crystallization kinetics of the reaction products. The relationships between the oxide composition, test temperature, and reaction product constitution were investigated using sintered pellets of hafnates or zirconates containing YbO1.5, GdO1.5, or LaO1.5. The results suggest that the composition of the reprecipitated ZrO2- or HfO2-based phase, typically fluorite, is a useful indicator of the effectiveness of the silicate crystallization reactions. Meanwhile, the composition of the primary crystalline reaction product, typically a RE oxy-apatite, is relatively insensitive to the experimental variables considered herein. The observed trends indicate that the larger RE cations are more potent in rapidly crystallizing the silicate melt and that their relative effectiveness increases with the REO1.5 concentration in the coating material.

Interfacial degradation of thermal barrier coatings in isothermal and cyclic oxidation test

The degradation mechanisms of thermal barrier coatings (TBCs) were investigated in different thermal fatigue condition in terms of microstructural analyses. The isothermal and cyclic oxidation tests were conducted to atmospheric plasma sprayed-TBCs on NIMONIC 263 substrates. The delamination occurred by the oxide layer formation at the interface, the Ni/Cr-based oxide was formed after Al-based oxide layer grew up to <TEX>${\sim}10{\mu}m$</TEX> in the isothermal condition. In the cyclic oxidation with dwell time, the failure occurred earlier (500 hr) than in the isothermal oxidation (900 hr) at same temperature. The thickness of Al-based oxide layer of the delaminated specimen in the cyclic condition was <TEX>${\sim}4{\mu}m$</TEX> and the interfacial cracks were observed. The acoustic emission method revealed that the cracks generated during the cooling step. It was considered that the specimens were prevented from the formation of the Al-based oxide by cooling treatment, and the degradation mode in the cyclic test was dominantly interfacial cracking by the difference of thermal expansion coefficients of the coating layers.

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.

A detailed insight into drug delivery from PEDOT based on analytical methods: effects and side effects.

The possibility to release drugs from conducting polymers, like polypyrrole or poly(3,4-ethylenedioxythiophene) (PEDOT), has been described and investigated for a variety of different substances during the last years, showing a wide interest in these release systems. A point that has not been looked at so far however is the possibility of other substances, next to the intended ones, leaving the polymer film under the high voltage excursions during redox sweeping. In this study we target this weakness of commonly used detection methods by implementing a high precision analytical method (high-performance liquid chromatography) that allows a separation and subsequently a detailed quantification of all possible release products. We could identify a significantly more complex release behavior for a PEDOT:Dex system than has been assumed so far, revealing the active release of the monomer upon redox activation. The released EDOT could thereby be shown to result from the bulk material, causing a considerable loss of polymer (>10% during six release events) that could partly account for the observed degradation or delamination effects of drug-eluting coatings. The monomer leakage was found to be substantially higher for a PEDOT:Dex film compared to a PEDOT:PSS sample. This finding indicates an overestimation of drug release if side products are mistaken for the actual drug mass. Moreover the full picture of released substances implements the need for further studies to reduce the monomer leakage and identify possible adverse effects, especially in the perspective of releasing an anti-inflammatory substance for attenuation of the foreign body reaction toward implanted electrodes. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 1200–1207, 2015.

A simulation approach to study photo-degradation processes of polymeric coatings

Chemical degradation of polymer coatings via a photo-oxidative pathway, denoted as photo-degradation, results in physical changes which, in spite of the long service life of coatings, eventually lead to failure of the material. Conventional molecular simulations cannot cope with this process with its wide range of time and length scales, related to the rare occurrence of ‘degradation events’ as compared to the time scale of structural relaxation of the polymer chains. Therefore a combination of suitable simulation techniques is needed to overcome this problem. By coupling a kinetic Monte Carlo simulation to a Dissipative Particle Dynamics method, a novel simulation approach has been developed that makes it possible to take into account chemical and physical pathways of the photo-degradation process. For a model polyester-urethane coating photo-degradation under inert conditions was studied with and without taking structural relaxation into account as well as by varying the ratio of reaction rate constants. For the model coating studied, taking physical relaxation into account proved to be essential for modeling the photo-degradation process.

Degradation of BSA Coating on Magnetite Nanoparticles

Magnetic nanoparticles used in biomedicine have to be biocompatible what can be achieved by the modification of the magnetic particle surface with an appropriate biocompatible substance. In the work protein bovine serum albumin (BSA) was chosen to modify the surface of magnetite nanoparticles. BSA coated magnetite nanoparticles (MFBSA) with different feed weight ratios of BSA to the magnetite Fe3O4were prepared and thermally characterized using thermogravimetric analysis.

Evaluation of corrosion resistance of aluminium coating with and without annealing against molten carbonate using electrochemical impedance spectroscopy

An arc ion plating (AIP) was used to fabricate a FeAl layer on 310S stainless steel to protect the sealing area being corroded by the molten carbonate in molten carbonate fuel cells (MCFCs). The degradation of aluminide coatings comes from both the corrosion of the coating in contact with the molten carbonate and the aluminium depletion due to the interdiffusion of aluminium and the substrate. The in-situ forming of aluminide in molten carbonate at 650 °C could be a possible way to reduce the inward diffusion of aluminium in the conventional pre-annealing at 850 °C. Electrochemical impedance spectroscopy (EIS) measurements were performed to model the corrosion of this pre-formed FeAl coating in comparison with the one formed in-situ in molten (0.62 Li+0.38 K)2CO3 at 650 °C. Although α-LiAlO2 is the corrosion product in both cases, the impedance spectra show distinct rate-limiting steps; the former is controlled by the charged particles passing through the scale, while the latter by their diffusion in the melt. The microstructure of the scale might be the reason for the difference in corrosion mechanism.

Degradation of TiN Coatings on Inconel 617 and Silicon Wafer Substrates Under Pulsed Laser Ablation

The degradation behavior of TiN coatings on Inconel 617 and silicon (Si) wafer substrates was compared following Nd:YAG pulsed laser ablation to apply thermomechanical stress. Surface cracks and pores were observed on the TiN coating on the Inconel 617 after five pulses, and melting of the coating was occurred over ten pulses. The TiN coating on the Si wafer also showed surface cracks and pores, but there was no surface melting. As the pulses were increased, the surface roughness of the TiN coating on Inconel 617 increased more than the TiN coating on the Si wafer, and interfacial cracking was the dominant degradation behavior on the Si wafer. The hardness of the TiN coating decreased below 50% of its initial value (2200 HK) after five pulses on the Inconel 617, whereas over 70% of the initial value (2400 HK) was maintained on the Si wafer. The TiN coating on Inconel 617 showed diffusion of substrate atoms to the surface, while Si was not found in the TiN coating on the Si wafer even after 25 pulses. It was determined that the decrease in hardness was influenced by the cracking behavior and the diffusion of atoms from the substrate.

Numerical study on interfacial delamination of thermal barrier coatings with multiple separations

Coating film generally fails by spalling on cooling after prolonged thermal cycling. Cross-section SEM images show that numerous separations exist at the coating–substrate interface even in the as-processed condition. Upon cooling from the high deposition temperature to room temperature, the difference in the thermal expansion coefficients between the substrate and the coating film makes these multiple isolated separations grow, coalescence and linking up, and, finally leads to coating buckling upon a critical size. In this paper, the interfacial degradation of thermal barrier coatings with multiple separations is investigated by combining the virtual crack closure technique with the user element subroutine “UEL” of Abaqus. The effects of interfacial separation morphology on the energy release rate (ERR) are quantified. Results show that the propagation and coalescence of local separations will dramatically alter the load capacity of the studied structures. It revealed that the larger the initially bonded zone is, the larger the steady ERR value is and the later the local maximum ERR value appears. It is believed that the concerted modeling technique will greatly benefit the understanding of the mechanics associated with the linking-up of subcritical flaws to form a critical flaw size for buckling.

Degradation of TiAlN coatings by the accelerated life test using pulsed laser ablation

The degradation behaviors of TiAlN coatings were evaluated by an accelerated life test under thermo-mechanical loading using a Nd:YAG pulsed laser ablation system. Pulse laser levels were chosen based on finite element analysis, and failure was determined when the specimen hardness decreased below 50% from its initial value. The accelerated life test was conducted on both TiAlN and TiN coatings deposited on an Inconel 617 substrate. The predicted lifetimes were obtained through statistical analysis of the failure time data. Surface and cross-sectional microstructural observations of the ablated spots were made to identify the cause for the difference in lifetimes since the TiAlN coating lasted longer than the TiN coatings by a factor of ~1.7. Pores formed on the TiAlN coating surface by the repeated laser ablation, and surface cracking and delamination of the coating layers were observed on the ablated spots in the failed specimens. The TiN coating also showed surface cracks with fewer surface pores than the TiAlN coating, but spalling of the coating layer occurred due to bursting of the substrate. Secondary ion mass spectrometry (SIMS) depth profiling revealed that surface oxidation increased in the TiN coating as the number of laser pulses increased, while the TiAlN coating showed less surface oxidation. The surface oxidation and spalling of the coating layer is considered to be the dominant influence on the decrease in hardness of the TiN coating. The TiAlN coating retains its hardness longer due to its lower thermal conductivity and higher oxidation resistance, as compared to the TiN coating.