Formation Process of the Integrated Core(Fe-6.5wt.%Si)@Shell(SiO2) Structure Obtained via Fluidized Bed Chemical Vapor Deposition

Abstract

As electromagnetic functional materials, soft magnetic composites (SMCs) have great potential for applications in high-energy electromagnetic conversion devices. The most effective way to optimize the performance of an SMC is to incorporate it into insulated ferromagnetic core-shell particles with high structural uniformity and integrity. Fluidized bed chemical vapor deposition (FBCVD) is a facile and efficient technique for the synthesis of ferromagnetic/SiO2 core-shell particles. However, the formation mechanism and conditions of integrated ferromagnetic/SiO2 core-shell structures during the FBCVD process are not fully understood. On this basis, the formation process and the deposition time required for transformation of the Fe-6.5wt.%Si substrate into the Fe-6.5wt.%Si/SiO2 composite, and finally into the Fe-6.5wt.%Si/SiO2 core-shell structure, were investigated. Deposition of the insulative SiO2 coating onto the Fe-6.5wt.%Si particles was described by the three-dimensional island nucleation theory. The SiO2 islands were initially concentrated in rough areas on the Fe-6.5wt.%Si particle substrates owing to the lower heterogeneous nucleation energy. Deposition for at least 960 s was necessary to obtain the integrated ferromagnetic/SiO2 core-shell structure. The uniformity, integrity, and thickness of the insulative SiO2 coating increased with the increasing deposition time. The results in this study may provide a foundation for future kinetics investigations and the application of FBCVD technology.

Fabrication and Soft Magnetic Properties of Fe–Si–Cr Composites with Double-Insulating Layers Suitable for High-Frequency Power Applications

“…The impact of different insulating layers on the magnetic characteristics of SMCs is currently the primary focus of research. Nonetheless, it is important to remember that external layers that are too thin may not fill the original gap, while external layers that are too thick may amplify the magnetic dilution effect, ultimately resulting in a lower magnetic phase per unit volume [6]. Therefore, it is important to examine how the thickness of exterior coatings affects the properties of SMCs so that their performance can be optimized.…”