Realizing high-resistivity and low-loss Fe–Si–Al based soft magnetic powder cores through interfacial chemistry regulation

• Published in: Ceramics international 2023-06, Vol.49 (12), p.19870-19878
• Main Authors: Wu, Z.Y., Kang, L., Liao, X.W., Kong, H., Wang, H.C., Wang, R.
• Format: Article
• Language: English
• Subjects: High-temperature annealing; Interfacial regulation; Magnetic properties; Soft magnetic powder cores; Thickness of insulating layers
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/j.ceramint.2023.03.106

As a symbolic ceramic oxide, SiO2 is one of the most important insulating layers of soft magnetic powder cores (SMPCs). Thus, the reaction of SiO2 with Fe–Si–Al based SMPC substrates during annealing, the induced phase transition of the core-shell structure, and the influence of the latter on the magnetic characteristics of SMPCs are worth investigating. In this study, Fe–Si–Al based SMPCs were successfully synthesised using fluidised-bed chemical vapour deposition (FB-CVD) at various times, combined with an electric pressure-assisted sintering method and high-temperature annealing. The evolution of the insulating layers with different thicknesses was investigated. With increasing thickness, the insulating layers (shell) gradually transformed into Al2O3 and the Fe–Si–Al substrate (core) to Fe3Si. The newly formed Al2O3 and Fe3Si increased the coercivity and saturation magnetisation of the SMPCs, while the hysteresis loss increased with thicker insulating layers. The generated Al2O3 improved the integrity of the insulating layers, preventing possible point contact between particles, and significantly reduced the Eddy current losses. The SMPCs with the thickest insulating layers (7#) exhibited superior magnetic properties (Ms = 129.3 emu/g, resistivity = 2.51 mΩ cm, total loss = 593.1 kW/m3 at 10 mT and 100 kHz; 18.0% reduction from the maximum). Thus, a precise method of adjusting the magnetic behaviour of Fe–Si–Al based SMPCs was developed through the novel approach of building SMPCs with inorganic ceramic insulating layers, enabling a comprehensive understanding of the relationship between the thickness of insulating layers and magnetic properties, which is of significance for industrial production. [Display omitted]