High-performance Fe–6.5wt.%Si/CaCO3 soft magnetic composites prepared via the thermal decomposition of calcium acetate

Recent studies on inorganic salt compounds are predominantly directed towards their utilisation as reinforcements for resins. However, the use of salt compounds besides phosphates as insulating layers has not been widely explored. Therefore, this study focuses on using salt compounds as insulating layers for soft magnetic composites (SMCs), revealing their numerous potential advantages. Fe–6.5wt.%Si/(CH3COO)2Ca composite powders were successfully synthesised using a hydrothermal method. Then, SMCs powders of Fe–6.5wt.%Si/CaCO3 and Fe–6.5wt.%Si/CaO, along with their corresponding SMCs, were prepared using powder heat treatment and cold press moulding techniques. The effects of calcium acetate ((CH3COO)2Ca) addition on the structure and electromagnetic properties of Fe–6.5wt.%Si/CaCO3 SMCs were further explored via an in-depth investigation of the formation mechanism of CaCO3 and CaO insulating layers on the surface of the Fe–6.5wt.%Si matrix. Results showed that (CH3COO)2Ca, as a precursor, decomposed into CaCO3 at 300 °C and CaO at 900 °C during heat treatment. Compared with the CaCO3 insulating layer on the surface of the Fe–6.5wt.%Si matrix, the CaO insulating layer exhibited a tendency for flocculent agglomeration, with lower homogeneity and integrity. Furthermore, the addition of (CH3COO)2Ca considerably influenced the thickness of the CaCO3 insulating layer in the Fe–6.5wt.%Si/CaCO3 SMCs, thereby effectively modulating the magnetic properties of the materials. The prepared Fe–6.5wt.%Si/CaCO3 SMCs had optimal magnetic properties when 4 wt.% (CH3COO)2Ca was added. Under the conditions of a 25 mT external magnetic field and 100 kHz frequency, the material exhibited a relative magnetic permeability as high as 37.2, a total loss of merely 125.06 kW/m³, a saturation magnetic induction intensity of 178.15 emu/g and an electrical resistivity of 125.4 Ω∙m. The innovative material design and the proposed preparation method considerably enhanced the comprehensive magnetic properties of Fe–6.5wt.%Si-based SMCs, opening up a new avenue for the research and development of high-frequency SMCs.