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

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.