Dual-functional epoxy coating with dispersed tannic acid-modified carbon nanotubes barriers and cerium-based self-repairing for corrosion protection of NdFeB magnets

Epoxy resin coatings incorporating tannic acid-modified carbon nanotubes (TCNTs) and cerium nitrate were deposited onto NdFeB magnets via air spraying to enhance corrosion resistance through synergistic filler/inhibitor effects. The composition and dispersion stability of the fillers were characterized using thermogravimetric analysis and zeta potential measurements. The morphology and microstructure of the composite coatings were analyzed by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Corrosion behavior was evaluated through full immersion tests (55 days), accelerated aging tests, and electrochemical measurements (potentiodynamic polarization, electrochemical impedance spectroscopy). The coating containing TCNTs exhibited superior corrosion resistance, achieving the highest low-frequency impedance modulus (| Z | 0.01 Hz = 4.01 × 10 9 Ω·cm²) and the lowest corrosion current density ( J corr = 8.930 × 10 −12 A·cm −2 ) after immersion. Incorporation of cerium nitrate endowed the coatings with self-repairing functionality during corrosion. The enhanced corrosion resistance of the EP(TCNTsCe ₓ )/NdFeB specimens is attributed to the combined barrier effect of uniformly dispersed TCNTs and the self-healing effect of insoluble cerium-containing corrosion products formed within the coating.