Protection Properties Of Coatings Research Articles

On the Limits of the EIS Low-Frequency Impedance Modulus as a Tool to Describe the Protection Properties of Organic Coatings Exposed to Accelerated Aging Tests

This study analyzes the limitations of the low-frequency EIS impedance modulus as a tool to describe the protective properties of organic coatings subjected to accelerated aging tests. Acrylic clear-coated steel and hot-dip galvanized steel were exposed to accelerated test methods such as the neutral salt spray chamber and the Prohesion test for up to 2000 and 3000 h, respectively. During exposure, the protective properties of the coatings were monitored by EIS and visual inspection. We observed a significant discrepancy between the measured impedance modulus in the low frequency range (|Z0.01Hz|), and the actual deterioration of the metal–paint interface. The degradation of the two painted substrates is independent of the accelerated test considered. The |Z0.01Hz| values do not represent the actual degradation state of the metal–polymer interface. The manuscript discusses the reasons for the lack of agreement between EIS and visual inspection. The limitations of using the low-frequency EIS impedance modulus to describe the protective properties of organic coatings are highlighted, and several cautions for interpreting the raw EIS data are suggested. The reliability of possible thresholds of |Z0.01Hz| (e.g., failure below 106 ohm∙cm2) to define the protective performance of the coating turned out to be misleading.

Performance Assessment of Differently Dried Coating Systems for Potential Application in the Power Transformer Industry

Many companies in the power transformer industry are striving to speed up the drying process of coatings, which is why alternative drying methods are constantly being explored while maintaining the same coating protection properties. The infrared (IR) drying of protective coatings is a potential solution for their higher productivity, but has not yet been extensively investigated. In this paper, two solvent-borne coating systems, with and without zinc in the primer, from two different manufacturers, dried by infrared radiation and under atmospheric conditions, were studied. The coating systems consisted of epoxy primer, epoxy intermediate coat, and polyurethane topcoat. Anti-corrosion performance of the coatings was characterized using a salt spray chamber, pull-off adhesion testing, electrochemical impedance spectroscopy (EIS) investigation, and open circuit potential (OCP) measurement. All samples were analyzed using stereo microscope. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) for detailed study and chemical composition determination was used. The results showed that infrared technology notably reduced coating drying times while maintaining or improving anticorrosion performance properties compared to the coatings dried under atmospheric conditions.

The Effect of Trivalent Chromium Process on Al-Zn-In Pigments in Epoxy Primer on the Corrosion Protection of AA2024-T3

Active metal pigments in metal-rich coatings are oxidized preferentially and provide sacrificial protection to more-noble metallic substrates. Al-rich primer (AlRP), which contains pigment particles made from an active aluminum alloy (Al-5Zn-0.02In), uses this mechanism to provide a chromate-free epoxy primer system. To address the high self-corrosion rate of active aluminum pigments, the active aluminum pigment particles are pretreated using trivalent chromium process (TCP). In this study, the effects of different TCP treatment times were evaluated, and coating protection properties were studied. Potentiodynamic polarization tests were performed in aerated 0.1 M NaCl solution for a TCP-treated bulk active aluminum alloy and for AA2024-T3. The potentiodynamic polarization curves show that the corrosion potential of the bulk active aluminum alloy is about 500 mV lower than that of AA2024-T3. Therefore, bulk active aluminum alloy is a candidate alloy for cathodic protection of AA2024-T3. In addition, the TCP treatment reduces the corrosion rate of the bulk active aluminum alloy by one order of magnitude. AlRP-coated AA2024-T3 panel samples were scribed and exposed in corrosion chambers, and the cross section of each coating was evaluated by scanning electron microscopy and energy dispersive x-ray spectroscopy mapping. The accelerated corrosion exposure results show that AlRP coatings containing TCP-treated particles provided better protection to the scribe than the one with bare pigment particles. The adhesion of the AlRPs based on pull-off adhesion tests was similar regardless of the TCP treatment time of the pigments, but the adhesion of AlRP was reduced in comparison to a neat epoxy coating.

Comparative study on tribological and corrosion protection properties of plasma sprayed Cr2O3-YSZ-SiC ceramic coatings

In this research, the tribological and corrosion protection properties of atmospheric plasma sprayed Cr2O3-20YSZ (CZ) and Cr2O3-20YSZ-10SiC (CZS) composite coatings on 304 L stainless steel substrates were evaluated and compared to pure Cr2O3 (C) coating. Microstructural evaluations were carried out using an optical microscopy, X-ray diffraction (XRD) analysis, and a Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS). The ball-on-disk wear test was performed using an alumina counterpart at room temperature. The protective efficiency of the coatings with/without sealing treatment was evaluated by electrochemical potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl solution. Evaluation of wear tracks showed that enhancement of the wear resistance of the composite coatings was ascribed to the zirconia phase transformation toughening and the presence of more ductile tribofilms participated in pore filling during the wear. The corrosion measurements revealed that the protection properties of the coatings were strongly dependent on the porosity content so that the as-sprayed coatings due to their porous nature could not protect the substrate. However, filling the porosity using an epoxy sealant prevented the penetration of the corrosive environment into the substrate and therefore increased the protective efficiency of the coatings. Moreover, the density of the unfilled defects such as micro-cracks determines the protection properties of the sealed coatings, so that the CZ coating due to its highest toughness had the lowest micro-crack density and thus the highest protective efficiency.

Electrodeposition of polypyrrole/ metal oxide nanocomposites for corrosion protection of mild steel—A comparative study

Electrodeposition of polypyrrole (PPy) and PPy-metal oxide nanocomposites on mild steel (MS) was carried out in oxalic acid solution by constant potential technique. The protection properties of coatings were studied in 0.5 M H2SO4 solution by Tafel polarization and electrochemical impedance spectroscopy (EIS). The effect of different nanoparticles (Al2O3, ZnO, TiO2, CeO2 and SnO2) on the protection performance of the nanocomposite coatings was compared. The results reveal that PPy/Al2O3 nanocomposite provided the best performance for corrosion protection of the MS by reducing its corrosion current density by 18 times. Furthermore, corrosion protection behavior of PPy/nano-Al2O3 and PPy/micro-Al2O3 composites was compared.

Evaluation of the protective properties of multilayer coatings for steam turbine blades

The results of investigation of the protective properties of multilayer ion-plasma coatings relative to the conditions of their exploitation on steam turbines are described. It was established that the protection properties of coatings on 20X13 steel in an aggressive NaCl environment of various concentrations increase according to the sequence [Cr + (Cr,Ti)N]10 < (Ti + TiN)10 < (Cr + CrN)10. It was also found that a breach in the coating integrity can lead to the appearance of macrogalvanic couples. Their activity considerably increases (by 4–5 times) during the mechanical passivation of the surface under the conditions of drop-collision erosive wear. The greatest values of the EMF in stationary conditions are generated between the 20X13 steel and Ti + TiN coating.