Corrosion Protection Performance of SiO₂ Nanoparticle-Reinforced Epoxy Coatings on Mild Steel in Chloride Environments Under Various Experimental Conditions

Abstract

This study evaluated the corrosion-protection performance of silica (SiO₂) nanoparticle-reinforced epoxy coatings on mild steel under different environmental and coating conditions. The investigation considered dry-film thicknesses of 50–250 µm, silica loadings of 0–7 wt.%, immersion durations of 1–30 days, temperatures of 25–55 °C, and sodium chloride (NaCl) concentrations of 0.5–5.0 wt.%. We assessed corrosion performance using corrosion current density, corrosion-protection efficiency, and low-frequency impedance, calculating protection efficiency relative to uncoated mild steel. The illustrative results showed that increasing coating thickness from 50 to 250 µm improved protection efficiency from 68% to 98%, while corrosion current density decreased from 3.20 to 0.20 µA cm⁻² and impedance increased from 25,000 to 1,000,000 Ω cm². Increasing SiO₂ loading improved protection efficiency from 70% for neat epoxy to 94% at 5 wt.% SiO₂, before declining to 91% at 7 wt.%. During 30 days of immersion, the efficiency of the 5 wt.% SiO₂-reinforced coating decreased from 98% to 88%, while impedance declined by 80%. Increasing temperature from 25 to 55 °C and NaCl concentration from 0.5 to 5.0 wt.% reduced protection efficiency from 98% to 88% in both cases. These trends suggest that coating thickness, nanoparticle concentration, and exposure conditions are important determinants of corrosion resistance. A thickness of 250 µm and a silica loading of 5 wt.% emerged as promising conditions in their respective comparisons. However, the numerical results are simulated illustrative data and require experimental validation using electrochemical impedance spectroscopy, potentiodynamic polarization, adhesion testing, and surface characterization before definitive conclusions can be established.