Scalable mechanochemical synthesis of bifunctional MnZn ferrite/expanded graphite composites for efficient microwave absorption and corrosion resistance

Abstract

Long-term stability of microwave-absorbing materials in marine environments requires bifunctional absorbers with strong absorption and excellent corrosion resistance. To address the challenges of complex preparation process and low scalability associated with existing bifunctional materials, this study proposes an efficient solution: utilizing low-cost raw materials (MnCO₃, ZnO, Fe₂O₃, and expanded microcrystalline graphite - EMG) to prepare manganese-zinc ferrite (MZF)/EMG composite absorbers via a high-temperature mechanochemical method, enabling shortened processing and large-scale production. The mechanical forces during ball milling introduce defects into the EMG fragments and form heterogeneous interfaces with nano-sized MZF particles. Incorporating an optimized amount of EMG enhances the dielectric loss of the composite material without significantly compromising magnetic losses, thereby achieving favorable impedance matching and excellent microwave absorption. Furthermore, since EMG not only forms an impermeable barrier but also constructs tortuous diffusion pathways, it significantly enhances the corrosion resistance of the composite material. Experimental results demonstrate that with 4 wt% EMG content, the composite exhibits outstanding dual functionality: an effective absorption bandwidth of 4.56 GHz at 1.47 mm, a minimum reflection loss of -60.00 dB at 1.77 mm, and a corrosion potential significantly increased by 282 mV compared to pure MZF. This design leverages the inherent advantages of MZF (excellent magnetic properties and chemical stability) and EMG (three-dimensional structure, high dielectric loss, and chemical inertness). The resulting Mn₀.₈Zn₀.₂Fe₂O₄/EMG composite absorbers, which are simple to process and scalable to produce, offer new insights for developing and applying multifunctional materials in marine environments