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<p>This study systematically compares the protective performance and failure mechanisms of epoxy anticorrosion coatings in 3.5 wt.% NaCl solution using basalt flakes of two origins, natural ore (N-series) and artificially formulated (A-series), and two fineness levels, 325 mesh and 500 mesh, as fillers. Electrochemical impedance spectroscopy (EIS), equivalent circuit fitting, water uptake kinetics, and surface/interface characterization were employed to evaluate the effects of flake origin and particle size on coating barrier properties, diffusion resistance, and substrate electrochemical response. The results show that 500-mesh flakes significantly outperform 325-mesh flakes, with the heat-treated, artificially formulated 500-mesh flakes (A<sub>500</sub>) exhibiting the best performance. In this case, the low-frequency impedance remained high over extended immersion, while both the charge transfer resistance (<i>R</i><sub>ct</sub>) and coating pore resistance (<i>R</i><sub>po</sub>) increased markedly and the apparent water diffusion coefficient decreased substantially under continuous saline immersion conditions. Mechanistic analysis indicates that finer flakes achieve higher packing density and form more tortuous diffusion pathways, whereas heat treatment is suggested to improve flake–epoxy interfacial conformity and reduce the likelihood of interfacial microvoid connectivity. These effects act synergistically to enhance the coating barrier function and long-term protective capability. Furthermore, kinetic and theoretical impedance models for finite-layer diffusion in coatings are presented.</p>

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Synergistic Effects of Heat Treatment and Fineness in Natural Versus Artificially Formulated Basalt Flakes: Corrosion Protection Mechanisms from EIS and Water Uptake Diffusion Kinetics

  • 期刊论文

  • 发表日期：

    2026年6月20日

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  • Bing Bai,
  • Rui Ding,
  • Yi-wen Zhang,
  • Hao-han Cao,
  • Xiao Liu,
  • Jie Liu

摘要

This study systematically compares the protective performance and failure mechanisms of epoxy anticorrosion coatings in 3.5 wt.% NaCl solution using basalt flakes of two origins, natural ore (N-series) and artificially formulated (A-series), and two fineness levels, 325 mesh and 500 mesh, as fillers. Electrochemical impedance spectroscopy (EIS), equivalent circuit fitting, water uptake kinetics, and surface/interface characterization were employed to evaluate the effects of flake origin and particle size on coating barrier properties, diffusion resistance, and substrate electrochemical response. The results show that 500-mesh flakes significantly outperform 325-mesh flakes, with the heat-treated, artificially formulated 500-mesh flakes (A500) exhibiting the best performance. In this case, the low-frequency impedance remained high over extended immersion, while both the charge transfer resistance (Rct) and coating pore resistance (Rpo) increased markedly and the apparent water diffusion coefficient decreased substantially under continuous saline immersion conditions. Mechanistic analysis indicates that finer flakes achieve higher packing density and form more tortuous diffusion pathways, whereas heat treatment is suggested to improve flake–epoxy interfacial conformity and reduce the likelihood of interfacial microvoid connectivity. These effects act synergistically to enhance the coating barrier function and long-term protective capability. Furthermore, kinetic and theoretical impedance models for finite-layer diffusion in coatings are presented.