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

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.