Use of Goethite as an anti-corrosive Pigment

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.