Abstract
Protective coatings are the most widely used corrosion protection method for construction materials in different environmental conditions. They isolate metals from aggressive media, making the structure more durable. Today, alongside good anti-corrosive properties, coatings need to be safe for the environment and harmless to those who apply them. The high volatile organic compound (VOC) content in conventional solvent-borne coatings presents a huge ecological problem. A solution for indispensable solvent emission reduction is the application of powder coatings. This study evaluates the corrosion performance and surface morphology of polyester and epoxy–polyester powder coatings. Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurement, salt spray chamber and humidity chamber testing followed by adhesion testing were used to investigate the protective properties of powder coatings. Scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) was used to analyse the surface morphology and chemical composition, whereas the microstructure and coating uniformity were determined by optical microscope examination. The research revealed a negative influence of coating surface texture on coating thickness and consequently a lack of barrier and adhesion properties. The epoxy–polyester powder coating showed a better performance than the polyester coating. All tested coatings showed uniform structure.
Highlights
Electrostatic powder coating originated in the USA in the 1950s
The tests performed in this study showed that the powder coatings exhibited very good The tests performed in this study showed that the powder coatings exhibited very good properties properties in humid and marine environments as well as in an alkali medium, and displayed in humid and marine environments as well as in an alkali medium, and displayed some failures
Good protective properties were displayed in the epoxy–polyester coatings, Extremely good protective properties were displayed in the epoxy–polyester coatings, which are which are intended for indoor use, while the worst performance was delivered by polyester powder intended for indoor use, while the worst performance was delivered by polyester powder coating B, coating B, intended for outdoor use, which lost of adhesion after exposure to the humid and warm intended for outdoor use, which lost of adhesion after exposure to the humid and warm atmosphere atmosphere (ISO 6270-2)
Summary
Electrostatic powder coating originated in the USA in the 1950s. It has been extensively used for painting processes in the automotive industry. The electrostatic coating process starts by electrostatically charging the powder. The electrostatic attraction between the powder particles and the object allows the powder to adhere to the surface, forming an even coating [3,4]. The application of the electrostatic powder coating is followed by a high-temperature curing process, which provides a smoothly-coated surface. The powder is charged using either a corona or tribo-charging spray gun [3]. In the case of corona-charging, the powder particles pass through an ion-rich area and become charged based on their permittivity. Since tribo-charging generates less charge on powder particles, corona-charging is generally used for electrostatic powder
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