Interfacial design of Al-rGO/Fe3O4 nanocomposite pigments for long-term corrosion resistance of epoxy coatings

The long-term corrosion protection of steel structures in aggressive environments remains a critical challenge for modern coating systems, particularly where durable barrier performance and interfacial stability are required. Although epoxy coatings are widely employed for corrosion mitigation, their effectiveness is often compromised by intrinsic micro-defects, limited durability, and inadequate control over coating–metal interfacial processes. To address these limitations, this work proposes a rational interface-engineering strategy based on a ternary Al-rGO/Fe 3 O 4 nanocomposite pigment, designed to synergistically enhance electrochemical inhibition and barrier durability. The corrosion inhibition behavior of individual pigments was first screened in solution using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), followed by a systematic evaluation of epoxy coatings incorporating Al-rGO/Fe 3 O 4 at different loadings. The results demonstrate that the ternary nanocomposite exhibits superior intrinsic electrochemical inhibition, while the corrosion protection performance of the epoxy coatings is highly sensitive to pigment loading. An optimal loading of 2.5 wt% achieves the lowest corrosion current density (0.00186 μA.cm -2 ), the highest inhibition efficiency (98.07%), and maintains exceptionally high low-frequency impedance (|Z| 0.01Hz ≈ 10 10 –10 11 Ω.cm 2 ) throughout the 28-day immersion period in 3.5 wt% NaCl solution. In contrast, excessive loading (3.0 wt%) leads to pigment agglomeration and interfacial defects, resulting in progressive degradation of long-term corrosion protection. The enhanced corrosion resistance at the optimal loading is attributed to a synergistic, multi-scale barrier mechanism, in which rGO nanosheets and Al flakes create highly tortuous diffusion pathways, while Fe 3 O 4 nanoparticles effectively seal microvoids and reinforce interfacial integrity. Complementary PDP and EIS analyses further reveal that corrosion protection is governed by an interface-controlled inhibition mechanism, balancing short-term electrochemical kinetics and long-term barrier stability. This study provides a clear design guideline for nanocomposite pigment loading in epoxy coatings and offers a promising strategy for developing durable, high-performance anticorrosion systems for long-term service in harsh environments.