Electrochemical Impedance Spectroscopy (EIS) is a non-destructive and powerful technique for characterizing corrosion systems, allowing for the evaluation of surface reaction mechanisms, mass transport, kinetic evolution, and corrosion levels of materials. This study aims to analyze the progression of corrosion using EIS, with a focus on the influence of organic coating thickness. For this purpose, layers of high-purity epoxy paint were applied to carbon steel plates with thicknesses of 50 µm, 80 µm, and 100 µm. During the research, a direct correlation was observed between coating thickness and corrosion resistance, emphasizing the importance of identifying the optimal thickness for each type of coating. Additionally, it was found that thicker coatings may experience electrode penetration due to the tensions generated during deposition, resulting in cracks between the layers, while thinner coatings allow electrolyte penetration as they do not provide adequate protection to the base steel. Therefore, the 80 µm thickness demonstrated greater resistance to corrosion compared to the other tested thicknesses.

The development of self-healing coatings represents a promising approach to enhance the durability of metal substrates exposed to corrosive environments, demanding thorough in situ investigations. In this study, poly(urea–formaldehyde–melamine) (PUF) microcapsules containing linseed oil (LO) were synthesized via in situ polymerization to act as healing agents in protective coatings. The microcapsules were characterized using scanning electron microscopy (SEM), optical microscopy (OM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The capsules exhibited a regular spherical morphology with an average diameter of 96 µm and an LO encapsulation efficiency of 81 wt%. TGA confirmed their thermal stability up to 200 °C, while FTIR verified the successful encapsulation of LO. For performance evaluation, 10 wt% of the microcapsules was incorporated into an epoxy matrix and applied to carbon steel. Corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in 0.1 mol/L of NaCl solution over 500 h. The coating with microcapsules exhibited a |Z|_0.01 of 10⁶ Ω·cm², higher than the 10⁴ Ω·cm² observed for the coating without microcapsules, indicating improved barrier properties. Raman spectroscopy confirmed the auto-oxidation of LO at damaged areas, evidencing the self-healing mechanism. Although full barrier recovery was not achieved, the system effectively delayed corrosion progression.

Layered double hydroxides (LDHs) have garnered significant attention in recent years due to their unique structure, which enables the intercalation and controlled release of corrosion inhibitors in response to specific stimuli relevant to corrosion processes. In this study, LDH microparticles intercalated with sebacate (SB) were synthesized to function as a corrosion inhibitor through on-demand release. The microparticles were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis (TGA). TGA demonstrated that LDH has high thermal stability and that the actual SB content in LDH/SB was estimated to be between 21.2 and 27.6 wt %. The effectiveness of calcium and aluminum-based LDHs intercalated with SB as a corrosion inhibitor was evaluated on aluminum AA5005 substrates, both in bare form and coated with an acrylic layer. Accelerated weathering tests revealing a reduction of approximately 40% of the corroded area and a marked reduction in filiform corrosion during constantly high relative humidity. A dilute electrolyte cyclic fog/dry test also demonstrated a significant reduction in corrosion in dry/wet cyclic aging. The SB species demonstrated potential as a corrosion-inhibiting component under the studied conditions by enhancing the corrosion resistance of the aluminum alloy. This performance was confirmed through electrochemical characterization, including potentiodynamic polarization measurements performed using an Ag/AgCl (3 mol·L^–1 KCl) reference electrode. The pitting potential (E _pit) values, referred to this reference electrode, showed an increase when SB and LDH–SB were used. The blank sample presented an E _pit of 0.08 V, while the samples containing SB and LDH–SB presented E _pit values of 0.50 and 0.36 V, respectively.