Improved high-frequency and anti-corrosion performance of FeNi soft magnetic composites through regulating SiO2 shell growth in a dual silicon source involved route

Optimizing dense insulating shells plays a crucial role in developing high-frequency soft magnetic composites (SMCs) working in acidic and salty environments. Herein, raspberry-like and litchi-like SiO2 shells are fabricated on FeNi particles by using both 3-aminopropyl triethoxysilane (APTES) and tetraethyl orthosilicate. It is found that low dosages of APTES lead to raspberry-like shells consisting of internal SiO2 layer and attached SiO2 particles. While high dosages of APTES result in litchi-like shells, owing to a much higher coordinated growth rate between the inner layer and SiO2 particles. With regard to corrosion resistance performance, the litchi-like shell contributes to a more positive corrosion potential of -0.076 V, a lower corrosion current density of 2.512 x 10(-6) A/cm(2), a higher corrosion protection efficiency of 96.70 % and a lower ion concentration in the HCl etching solution. As for magnetic properties, higher resistivity of 1.46 x 10(8) Omegam, lower eddy current loss with mu ' of 13.98 and lower tan delta of 0.01148 at 2000 kHz can be realized by the dense litchi-like shell structure. This work not only demonstrates detailed growth mechanisms of different SiO2 shells, provides FeNi SMCs with desirable high frequency and anti-corrosion performance, but also offers deeper insights into functional shell design.