Achieving ultra-low frequency microwave absorbing properties based on anti-corrosive silica-pinned flake FeSiAl hybrid with full L band absorption

Highlights: • Plasma technology is introduced to design dense protective layer of alloy particle. • P-FSA@SiO₂ possesses the enhanced microwave absorbing properties at ultra-low frequency. • The dense SiO₂ layer improves the anti-corrosion performance of absorber. -- Abstract: The inevitable corrosion of magnetic microwave absorber (MA) remains a great challenge to adapt oxygen-containing environment. Herein we developed a plasma-induced approach for protecting the magnetic MA by anchoring robust SiO₂ layers on their surface. Keeping the original flaky shape of FeSiAl (FSA) led to breaking the Snoek limit, which brought excellent ultra-low-frequency absorption. In detail, the ultrathin amorphous silica layer (5 nm) grew on FSA surface by the facile Stöber method at low cost firstly. Plasma technology was introduced to make these SiO₂ layers dense and attain the integrated P-FSA@SiO₂. SiO₂ layer protected FSA from the corrosive medium, which increased polarization resistance to 186.9 kΩ·cm² of P-FSA@SiO₂ (from 97.46 kΩ·cm² of pure FSA) and decreased the corrosion current to 18.45 μA/cm² (from 63.35 μA/cm²). The corrosion of the samples in acid solution also verified the electrochemical characterizations. Meanwhile, rich interface and sheet ordered structure enable P-FSA@SiO₂ exhibit enhanced microwave absorption in ultra-low-frequency through multiple reflections, magnetic loss and the interface polarization between core and shell. The minimum reflection loss of P-FSA@SiO₂ reduced from −8.0 dB (FSA) to −12.4 dB and the efficient absorption band ( < −5 dB) increased from 0.18 GHz (FSA) to 1.44 GHz. The densification SiO₂ layer coating technology opens up a fantastic avenue for devising anti-corrosion absorber.