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.
Highlights
Soft magnetic composites (SMCs) have become increasingly important in materials research, because they are magnetically isotropic, highly permeable, and inhibit eddy current loss [1,2,3]
Many researchers have focused on the design and controlled synthesis of insulated ferromagnetic C-S structures and the relationships between their structures and activities [6,7]
These research achievements promoted the development of basic theory and expanded the range of applications for SMCs
Summary
Soft magnetic composites (SMCs) have become increasingly important in materials research, because they are magnetically isotropic, highly permeable, and inhibit eddy current loss [1,2,3]. Many researchers have focused on the design and controlled synthesis of insulated ferromagnetic C-S structures and the relationships between their structures and activities [6,7]. While many studies have focused on SMC characterization and measurement, few have investigated the formation mechanisms and optimal conditions for the production of C-S structures with ferromagnetic cores. Fluidized bed chemical vapor deposition (FBCVD) has been recognised as an efficient technique for the synthesis of ferromagnetic/SiO2 core-shell particles [22,23]. FBCVD is a complex two-phase gas and solid flow system, and the controlled synthesis of ferromagnetic/SiO2 C-S particles is influenced by many factors. The formation mechanism and conditions of integrated ferromagnetic/SiO2 core-shell structures during the FBCVD process are not fully understood
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