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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.Coatings 2018, 8, 98 2 of 12 coating [1]. Today, thanks to the commercial success and wide application of powder coatings, extensive research is carried out in this field of study, in particular in the powder coating chemistry [5].Compared to liquid paints, powder coatings feature several advantages including the absence of volatile organic content, the reduction in coating material loss (up to 68%), the reduction of dust formation (from 40% to 84%) [1], high utilization rates, fast curing, the minimal health risks involved, and the elimination of hazardous wastes [7]. However, a major disadvantage of electrostatic coating technology is that the curing of the powder coating requires a significant amount of heat energy. For this reason, the future of these technologies will include the development of low temperature curable (LTC) powder coatings, whose application will enable energy saving solutions and also the ability to coat heat-sensitive substrates [8]. The second disadvantage is the lack of coating uniformity in Faraday-cage areas. Aside from several challenges needing improvement, powder coating is an environmentally-friendly coating process with good performance properties.There are numerous methods to evaluate the corrosion performance of powder coatings. Mafi et al. [5] investigated the protective behaviour of powder coatings in 3.5% w/w NaCl solution using electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurement, as well as differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Bhadu et al. [9] studied...

Inhibition efficiency of calcium gluconate, alone and in blends with sodium benzoate, on the corrosion of carbon steel in chloride solutions has been assessed by potentiodynamic polarization measurements and mass loss detection in the temperature range from 25 to 70 °C. Sodium benzoate efficient in hindering the general corrosion in chloride solutions can induce pitting of carbon steel. Along with decreasing the general corrosion calcium gluconate, an ecologically acceptable compound, eliminated the susceptibility to pitting formation. The inhibition of the anodic reaction by gluconate and benzoate, and the slowing down the cathodic reaction in solutions of calcium gluconate was confirmed.

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The inhibition effect of olive leaf extract on corrosion of carbon steel in brine solutions saturated with CO2 was investigated at 25 °C and 65 °C by means of Tafel polarization, weight loss measurements and Fourier transform infrared spectroscopy. The experimental results reveal that the olive leaf extract has a good inhibition effect on the carbon steel in CO2-saturated brine solution at both temperatures. Tafel polarization investigations revealed that olive leaf extract acted as a mixed inhibitor showing anodic and cathodic behavior. The adsorption of olive leaf extract on carbon steel surface obeyed the Langmuir adsorption isotherm. The adsorption thermodynamic parameters indicated the physisorption of olive leaf extract on carbon steel surface was a spontaneous and exothermic process with an increase in entropy. Fourier transform infrared spectroscopy spectra showed types of bonding for olive leaf extract on the carbon steel surface.