Research on multi-scale failure model of epoxy coating based on EIS-EN combined monitoring and SiC@GO composite protection mechanism

Electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) each possess distinct advantages in coating corrosion research; however, the deep fusion of data from these two techniques and the correlation modeling with failure stages remain largely unexplored. This study employed in-situ synchronous monitoring technology combining EIS and EN to systematically track the long-term corrosion evolution of bare iron, pure epoxy coating, and SiC@GO/epoxy composite coating in 3.5 wt.% NaCl solution. Based on the synergistic evolution patterns of EIS frequency-domain parameters (phase angle inflection point, impedance modulus, CPE exponent n) and EN time-domain characteristics (current noise standard deviation σI, noise resistance Rn, pitting index PI), a novel "four-stage failure model" for coatings was innovatively constructed. The results demonstrated that the pure epoxy coating underwent a complete progression from initial protection, active zone formation, localized corrosion development, to ultimate failure; whereas the SiC@GO composite coating, benefiting from the synergistic effects of physical barrier and chemical cross-linking of multi-scale fillers, remained confined to the first two stages throughout the entire exposure period. Its impedance modulus is about four orders of magnitude higher than pure EP, and its current density is about four orders of magnitude lower. This study not only provides a new framework for EIS-EN multi-scale analysis but also offers theoretical guidance for the structural design of long-term anti-corrosion coatings.