Optimized high-frequency performances in FeSiAl soft magnetic composites through nanoscale SiO2 insulating coating

Traditional SiO 2 coating technologies remain a significant challenge in simultaneously achieving high permeability, low loss and good mechanical properties of soft magnetic composites (SMCs) at high frequency. This work presents a simple approach for coating nano-SiO 2 layer on FeSiAl powder via sol-gel method with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH792) as coupling agent. Two amino groups in KH792 can form multiple hydrogen bonds, which is beneficial for enhancing the binding force between SiO 2 and FeSiAl and maintaining the integrity of the SiO 2 layer, thereby realizing good mechanical strength and suppressing eddy current losses at 100 kHz-4 MHz. By optimizing the synthesis conditions, ∼ 30 nm SiO 2 layer is uniformly and completely coated on FeSiAl powder, which can enhance the adhesion, improve the flowability of the powder, achieve a balance between the insulation layer's thickness and the distance between the powders, and form effective electrical isolation. Therefore, the optimal FeSiAl@SiO 2 SMCs deliver the crushing strength of 280 N, permeability of 63.7 (@ 1 MHz), power loss of 65.9 kW/m 3 at 100 kHz and 1697.6 kW/m 3 at 1 MHz under 50 mT, 166.4 kW/m 3 at 5 mT/4 MHz, as well as effective permeability of >60 up to 16 MHz, associated with cut-off frequency of 282.2 MHz. These favor the low temperature rise when SMCs are used as inductors. This work provided a deeper understanding of the relationship between SiO 2 layer and the mechanical and soft magnetic performances of FeSiAl SMCs.