Fabrication and corrosion resistance of magnetic field-regulated Fe3O4/BNNSs/EP composite coatings

Purpose The purpose of this paper is to develop high-performance anticorrosive epoxy coatings by regulating the orientation of two-dimensional (2D) nanosheets. This is achieved by synthesizing superparamagnetic boron nitride nanosheets (m-BNNSs) and applying a parallel external magnetic field to induce highly ordered in-plane alignment. Design/methodology/approach Few-layer BNNSs prepared via liquid-phase exfoliation were functionalized with Fe3O4 nanoparticles through in situ co-precipitation to obtain Fe3O4/BNNSs (denoted as m-BNNSs). These fillers were incorporated into an epoxy matrix with a parallel magnetic field applied during curing. Composite structures and magnetic behavior were verified by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and vibrating sample magnetometer. Electrochemical measurements and pull-off adhesion tests were conducted to evaluate the anticorrosion performance and coating-substrate bonding strength, respectively. Findings Application of a 200 mT magnetic field successfully reduced the average tilt angle of m-BNNSs from 46.1° ± 27.0° to 12.5° ± 12.0°, achieving highly ordered parallel orientation. The coating with 1.0 wt % m-BNNSs under a 200 mT field exhibited the best performance, maintaining a low-frequency impedance modulus of 1.52 × 109 Ω·cm2 after 30 days of immersion. Pull-off tests confirmed that the filler incorporation and magnetic alignment did not significantly alter the coating adhesion. However, excessive filler loading or higher field strengths (300 mT) caused possible local re-stacking and structural defects, leading to the deterioration of protective performance. Originality/value This work provides an effective strategy for regulating the orientation of inert 2D nanosheets in polymer coatings. The enhanced long-term protection is attributed to the synergistic effects of Fe3O4 spacers in suppressing restacking and the field-induced alignment in maximizing the tortuous diffusion path for corrosive species.