Regulation and control of insulated layers for intergranular insulated Fe/SiO₂ soft magnetic composites

In this work, the intergranular insulated Fe/SiO₂ soft magnetic composite cores with tunable insulating layer thickness were prepared by a modified Stöber method combined with the spark plasma sintering technology. Most of the conductive Fe particles could be coated uniformly by insulated SiO₂ using the modified Stöber method, and the high compact and intergranular insulated cores could be obtained quickly by the spark plasma sintering process. The intergranular insulated Fe/SiO₂ composite cores exhibited much higher electrical resistivity, lower core loss, better frequency stability of permeability and large higher quality factor than that of raw Fe core without insulated SiO₂. The thickness of SiO₂ insulating layer, electrical and magnetic properties of intergranular insulated Fe/SiO₂ composite cores could be readily controlled by adjusting the tetraethyl orthosilicate concentration. The thickness of SiO₂ insulating layer and resistivity of Fe/SiO₂ composite cores first increased and then dropped with increasing the tetraethyl orthosilicate concentration, while the permeability and core loss changed in the opposite direction. Fe/SiO2 composite core showed the optimal performance when the tetraethyl orthosilicate concentration was 0.135 mol l⁻¹, which exhibited better frequency stability at high frequencies, much higher electrical resistivity, higher quality factor and lower core loss.