【摘要】 面向海洋装备防腐蚀需求，石墨烯耐腐蚀镀层得到广泛关注和应用。为了解决传统镍基石墨烯镀层中石墨烯分散性差、与基体结合强度不足等导致镀层耐腐蚀性能难以显著提升的问题，开展了基于聚多巴胺修饰与磁场协同电沉积改善镍基石墨烯镀层的研究。采用聚多巴胺修饰以优化石墨烯的分散性和结合强度，研究不同磁场施加方式及其对电沉积镍基石墨烯镀层的影响。通过场发射扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)、电化学工作站等，对聚多巴胺修饰石墨烯及复合镀层的微观结构、元素组成和耐腐蚀性能进行系统表征分析。结果表明：聚多巴胺修饰可有效改善石墨烯在水溶液中的分散稳定性，避免其发生团聚；平行磁场协同电沉积制备的镍基石墨烯镀层的耐腐蚀性能显著优于无磁场和垂直磁场条件下制备的镀层，且耐腐蚀性能随磁场强度的增大而提升，在磁场强度为20 mT的平行磁场作用下制备的镀层腐蚀电流密度最小，为13.52μA/cm~2,表现出最佳的耐腐蚀性能。聚多巴胺修饰能够有效解决石墨烯在电沉积体系中的分散与结合难题，平行磁场协同电沉积可显著优化镍基石墨烯镀层的耐蚀性能，为高性能耐蚀镍基复合镀层的制备提供技术参考。更多还原

【Abstract】 Corrosion of marine structural materials has become a key bottleneck restricting the development and exploration of marine resources. Nickel-based graphene composite coatings are widely used for the protection of metal equipment in metallurgy, chemical industry, petroleum, and other industries due to graphene’s excellent mechanical properties, chemical inertness, high thermal conductivity, and structural stability. However, the strong van der Waals forces between graphene layers and its high surface energy make graphene prone to agglomeration and stacking. Meanwhile, its hydrophobicity leads to very poor dispersion in aqueous solutions, which severely limits its practical application in corrosion-resistant coatings. In addition, traditional electrodeposited coatings generally contain defects such as pores and cracks, which adversely affect corrosion resistance. To solve these problems, this work aimed to investigate electrodeposited nickel-based graphene corrosion-resistant coatings by combining polydopamine modification with magnetic-field-assisted electrodeposition. Polydopamine was used to modify graphene to enhance its dispersibility and bonding strength, and the effect of magnetic-field assistance on electrodeposited nickel-based graphene coatings and their corrosion resistance was investigated. Polydopamine-modified graphene(PDA@GR) was first prepared. Specifically, 0.5 g of multilayer graphene was added to 500 mL of distilled water, magnetically stirred for 10 min, and ultrasonically oscillated for 30 min. Then, 0.6 g of tris(hydroxymethyl)aminomethane(Tris) was added to adjust the pH to 8.5, followed by the addition of 1 g of dopamine hydrochloride. The mixture was magnetically stirred at room temperature for 12 h, allowing dopamine to undergo oxidative polymerization on the graphene surface to form a polydopamine coating. Ni/PDA@GR composites were then prepared. Specifically, 0.5 g of PDA@GR and 2.56 g of nickel acetate were dispersed in anhydrous ethanol, while 4.83 g of sodium hypophosphite was dissolved in anhydrous ethanol. After ultrasonic dispersion, the two solutions were mixed and stirred in a constant temperature water bath at 80 ℃ for 12 h, during which nickel ions were reduced by hypophosphite and anchored onto the polydopamine surface. Nickel-based graphene coatings were subsequently prepared. After the 45 steel substrates were ground stepwise with 400-2 000 mesh sandpaper, ultrasonically cleaned with ethanol, and subjected to electrocleaning activation, pure Ni, PDA@GR, and Ni/PDA@GR were separately dispersed into a rapid nickel plating solution to prepare a composite bath at a concentration of 2 g/L. Magnetic-field-assisted electrodeposition was conducted under three conditions: no magnetic field, parallel magnetic field(10 mT and 20 mT), and vertical magnetic field(20 mT). After deposition, the coatings were vacuum-dried at 70 ℃ for 12 h for subsequent use. Surface morphology was observed by field emission scanning electron microscopy(SEM), elemental composition was analyzed by X-ray photoelectron spectroscopy(XPS), and dispersibility in aqueous solution was evaluated by dispersion tests. A 3.5%(mass fraction) NaCl solution was used to simulate seawater for immersion tests under magnetic stirring at 1 000 r/min for 2 h. Open-circuit potential, polarization curves, and corrosion current density were measured with an electrochemical workstation to comprehensively evaluate corrosion resistance. The experimental results showed that the synergistic effect of polydopamine modification and magnetic field significantly improved the material properties and coating quality. SEM observations showed that the original graphene exhibited a layered structure with sharp edges and a few protrusions, whereas the edges of PDA@GR became smooth and rounded, confirming the successful coating of graphene by polydopamine. Obvious granular protrusions appeared on the surface of Ni/PDA@GR, verifying the effective anchoring of nickel particles. XPS analysis confirmed the successful synthesis of the Ni/PDA@GR composite. The dispersion tests showed that PDA@GR remained stably dispersed in aqueous solution for 15 h, which was markedly superior to GR, which almost completely precipitated within 1 h, and Ni/PDA@GR, which showed stratification after 2 h. This improvement was attributed to the hydrophilic groups such as catechol and amine groups in polydopamine. In terms of coating morphology, a large number of pores and cracks were observed in the coatings deposited without a magnetic field. The vertical magnetic field reduced the number of pores, but some large defects still remained. In contrast, the coatings prepared under the parallel magnetic field exhibited a dense and smooth surface with very few cracks and no large pores. The immersion tests showed that all coatings adhered firmly to the substrate without peeling, and only slight surface discoloration occurred due to galvanic reactions. Electrochemical measurements showed that, under the condition without a magnetic field, the corrosion current densities of the pure Ni coating, PDA@GR coating, and Ni/PDA@GR coating decreased to 75.93, 35.00, 16.89 μA/cm~2, respectively. For the Ni/PDA@GR coating, the corrosion current density was 16.98 μA/cm~2 under a 20 mT vertical magnetic field, 13.91 μA/cm~2 under a 10 mT parallel magnetic field, and 13.52 μA/cm~2 under a 20 mT parallel magnetic field, indicating that the parallel magnetic field significantly improved corrosion resistance and that the performance was further optimized as the magnetic field strength increased within the tested range. This study successfully solved the key problems of poor dispersion and severe agglomeration of graphene in corrosion-resistant coatings through polydopamine modification combined with magnetic-field-assisted electrodeposition. Polydopamine modification not only improved the dispersibility of graphene in aqueous solution but also enhanced the bonding strength between graphene and the substrate, while nickel particle anchoring further improved coating compactness. By inducing a microscopic magnetohydrodynamic effect, the parallel magnetic field promoted mass transfer, refined grains, reduced coating defects, and thereby significantly improved corrosion resistance. The Ni/PDA@GR composite coating prepared under a 20 mT parallel magnetic field exhibited a corrosion current density as low as 13.52 μA/cm~2 and showed better corrosion resistance than the coatings prepared without a magnetic field and under a vertical magnetic field. This study provides a novel and efficient technical route for the development of high-performance nickel-based graphene corrosion-resistant coatings, and such coatings show broad application prospects in corrosive environments such as marine engineering and chemical equipment. Further work could optimize the magnetic field parameters and explore long-term corrosion resistance under extreme service conditions.更多还原