Preparation of boron nitride/zinc phosphate nanoflower composites and anticorrosion performance of their modified epoxy coatings

To improve the anticorrosion performance of epoxy coatings, zinc phosphate nanoflowers (ZPN) modified with 3-aminopropyltriethoxysilane (KH-550) were loaded onto polydopamine (PDA)-modified boron nitride (BN) nanosheets. A composite epoxy anticorrosion coating synergistically reinforced by BN nanosheets and ZPN nanoflowers was then prepared, denoted as PDA-BN@KH-ZPN/EP. The morphology, elemental composition and dispersion stability of the composite materials were characterized by SEM, FT-IR, XRD, XPS and sedimentation tests. The coating performance was evaluated by adhesion testing, electrochemical measurements, salt spray tests and Raman spectroscopy. The results show that PDA-BN@KH-ZPN exhibits a three-dimensional hierarchical structure composed of interwoven spherical flower-like clusters and nanosheets. This structure significantly improves the dispersion stability of the filler in the epoxy system and enhances the interfacial compatibility, thereby increasing the adhesion strength and anticorrosion performance of the coating. After immersion in 3.5wt% NaCl solution for 20 d, the low-frequency impedance modulus of the PDA-BN@KH-ZPN/EP coating reached 4.05×10¹⁰ Ω·cm², remaining on the order of 10¹⁰ Ω·cm² and being markedly higher than those of the BN/EP and ZPN/EP coatings, indicating superior protective stability during immersion. After 50 d of salt spray testing, no obvious rust or corrosion propagation was observed on either the PDA-BN@KH-ZPN/EP coating or the Q235 steel substrate. The excellent anticorrosion performance of the composite coating is attributed to the synergistic enhancement mechanism involving the interfacial regulation of PDA and KH-550, the physical barrier effect of BN nanosheets and the chemical inhibition effect of ZPN. This mechanism provides efficient anticorrosion protection for the metal substrate by extending the transport path of corrosive media, suppressing interfacial electrochemical reactions and promoting the formation of a stable passivation film.