Abstract: Coating uniform, compact and thin nanoshells on micro-sized particles is critical to various applications including anticorrosive broadband microwave absorbing materials (MAMs), yet effective processing methods remain lacking. In this work, a turbulent sol-gel method is developed to coat the desired SiO₂ nanoshells on flaky carbonyl iron (FCI) particles. The adding millimeter-sized zirconia balls, driven by the orbital shaking, squeeze the solution and create significant relative motion between the liquid and balls, which generates turbulent flows. This significantly promotes the heterogeneous nucleation rate and high nucleation density, ultimately forming highly compact and uniform SiO₂ nanoshells covering FCI particles to enhance the electromagnetic absorption and anticorrosion properties. The as-obtained core-shell particles minimize the interface polarization and retain high magnetic loss, resulting in an improved impedance matching and a reflection loss < -10 dB with a bandwidth of 6.5 GHz at a thin thickness of 1 mm. Moreover, they also show a substantial order-of-magnitude improvement in anticorrosion performance. This work provides a promising method to fabricate anticorrosive, broadband and thin-thickness MAMs. The turbulent sol-gel method developed herein offers a facile and effective approach for fabricating uniform compact nanoshells on micro-sized particles.

Key words: Magnetic absorbers, Core-shell structures, Compact nanoshells, Corrosion resistance, Microwave absorbers