Comparative Analysis of Corrosion Inhibition Efficiency Between Epoxy Paint and Organic Varnish Blended with Oils of Aloe vera and Elaeis guineensis Applied in Cooling Systems

Air conditioning coils are made of copper, a material known for its good corrosion resistance. However, when they are installed in high-salinity environments, they corrode, causing various problems, such as refrigerant leakage, reduced efficiency, a shortened lifespan, and increased electricity consumption. To reduce coil corrosion, a public entity in São Luís-MA uses highly toxic epoxy polyamide paint, which is also expensive. Other methods used to protect air conditioning systems from corrosion include electrophoretic coatings (E-coatings) and electropolymerization, which, while effective, are costly and require specialized equipment. Sol–gel coatings, though useful, tend to degrade at high temperatures. Azoles and benzotriazoles, although effective, pose significant toxicity risks to both humans and the environment. In this regard, to identify more sustainable and cost-effective alternatives, this study aims to compare the corrosion inhibition efficiency of toxic epoxy polyamide paint with that of organic varnish blended with several concentrations of Aloe vera and Elaeis guineensis oils applied to copper tubes used in air conditioning systems. The copper tubes were coated with the epoxy paint and organic varnish-oil mixtures and then subjected to electrochemical impedance and potentiodynamic polarization tests in a 3.5% sodium chloride (NaCl) solution to evaluate the inhibition potential. The results indicate that both natural extracts significantly inhibited corrosion (> 90%), although they were less effective than the epoxy paint. This efficiency is attributed to the chemical bonds in the oils' molecular structure, especially C‒N, C‒Cl, C=C, C=O, and CH₃, CH₂, and OH radicals, which bind to the metal surface and delay corrosion processes.