Fernando Cotting

The mitigation of metallic corrosion remains a critical socio-economic and technical challenge, necessitating the transition toward sustainable and high-performance protective materials. This study explores the valorization of jarosite—a hazardous industrial waste from zinc hydrometallurgy—as a functional pigment in organic coatings. Formulations were developed using epoxy and alkyd matrices, with jarosite concentrations maintained below the Critical Pigment Volume Concentration (CPVC ~ 30%) to ensure full polymeric encapsulation. The pigment was characterized by a polymodal particle size distribution (1.1–22 μm) and high surface area (12.2 m²/g), contributing to a dense packing effect. The anticorrosive performance was evaluated through Electrochemical Impedance Spectroscopy (EIS), salt spray exposure, and pull-off adhesion tests. SEM/EDS analysis revealed that the irregular prismatic morphology of jarosite crystals is consistent with the formation of a tortuous diffusion pathway, suggesting delayed electrolyte diffusion. EIS results showed that the epoxy-jarosite system maintained superior barrier properties, with low-frequency impedance modules (|Z|_0.01 Hz) remaining above 10¹⁰ Ω.cm² for 5–8 wt% loadings throughout 100 days of immersion. Leaching assessments via ICP-OES revealed divergent immobilization behavior between the binder systems: while the epoxy matrix achieved effective retention of Pb and Cd below the quantification limit, the alkyd matrix exhibited a measurable release of Cd (40 µg/L), indicating partial immobilization efficiency under highly saline conditions.

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.

Previous results on the use of recycled polyethylene terephthalate (rPET) in the formation of corrosion-resistant films showed the possibility of providing a low-cost solution to some corrosion problems in the industry. However, to the best of our knowledge, no work has yet studied the thermomechanical incorporation of plasticizers on PET films for anticorrosion applications. Thus, in this work, a thermomechanical route was tested, for the first time, aiming at the production of anticorrosive PET-based adhesive films. A series of characterization methods were used to investigate the influence of the plasticizer addition to the thermal, mechanical, electrochemical and anticorrosive properties of the PET-based films produced. It was found that the 100% PET sample showed better mechanical and corrosion resistance performance compared to the plasticized ones, being comparable to or even better than benchmark tapes commercialized by 3M, maintaining impedance values consistently above 10 GΩ.cm2 for frequencies below 1 Hz and phase angle near 90º over a broad range of frequencies in the EIS tests.

Carbon steel is widely used as a metallic material, despite its limited corrosion resistance. To enhance its anti-corrosion properties, organic coatings such as epoxy are commonly applied due to their barrier mechanism. This study investigates the corrosion resistance of epoxy coatings reinforced with various ratios of iron oxides and goethite as anticorrosive pigments. The research aims to evaluate the adhesion and anticorrosive properties of waste mineral goethite (α-FeOOH) pigments in comparison to micaceous and red iron oxides. Coating morphology and chemical element distribution were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Electrochemical characterization techniques—including electrochemical impedance spectroscopy (EIS), linear and potentiodynamic polarization, and accelerated salt spray corrosion tests—were employed. Additionally, coating adherence was assessed via pull-off tests. Results demonstrated that goethite-based paints exhibited anticorrosive performance comparable to industrially used red and micaceous iron oxides, regardless of pigment concentration. The results of EIS showed that the 5% goethite formulation reached an impedance modulus of |Z|₀.₀₁Hz ≈ 10¹¹ Ω·cm² after 90 days. However, salt spray results showed that the area with corrosion products around the incision in the painted test specimens was quantified, showing the smallest reduction in corroded areas for the samples with 10 and 20% goethite concentration applied to the coating. These findings highlight the potential of mining waste goethite as a sustainable and effective anticorrosive pigment when properly optimized.

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.

Nowadays, there has been an urgency in the search for sustainable energy sources, such as those derived from biomass. This search is not only limited to minimizing greenhouse gas emissions but is also related to the increasing scarcity of fossil fuels. This work aims to investigate and analyze the production of bio-hydrocarbons from fatty acids through the simulation of the deoxygenation reaction by the DWSim software. In this simulation, a continuous catalytic deoxygenation reactor of the stirred tank with fluidized bed type was selected, aiming to understand the influence of operating parameters on this reaction. The parameters evaluated were temperature, pressure, hydrogen feed, and catalyst mass. For this simulation, hydrogen and stearic acid were chosen as feedstocks, focusing on the heptadecane and octadecane production. The rate law was chosen based on an extensive literature review, as well as reaction conditions. The kinetic model used as a reference was based on reactions of stearic acid and hydrogen in the presence of NiMo/Al2O3 as a catalyst. A stearic acid feed of 2.4 x 104 m3 year-1 was used as a base, representing the average feed of fatty raw material practiced in biodiesel plants located in the state of Minas Gerais, Brazil. From the variation of these parameters for a sensitivity analysis, with conversion as the key response, the following optimal operating conditions were defined: temperature of 650 K, pressure of 50 bar, molecular hydrogen feed of 4.1 x 10-3 m³ s-1, and catalyst mass of 8 kg. Under these new circumstances, the conversion of stearic acid reached a value of 99.23 %. The simulation of this reaction allowed us to understand the effect of the main reaction parameters on the reaction products, proved to be an important and robust tool to be used in projects and feasibility analyses of plants and biorefineries.

There has been a great interest in developing zinc-based composites for biological applications. Mixing bioactive particles and obtaining a well-dispersed structure is not straight forward though. The present study reports a novel processing route in which zinc particles are mixed with hydroxyapatite and bioactive glass particles and consolidated at room temperature using high-pressure torsion. The composites display good dispersion of second phase particles, enhanced strength and an increased corrosion rate in the Hank’s balanced salt solution. The incorporation of these particles can be used to tailor the corrosion rate of zinc. It is shown that the surface layer of the corrosion product in the zinc-bioactive particle composites is richer in calcium and phosphorous than the pure zinc counterpart.