Study On The Growth Mechanism Of Fe-6.5wt.%Si/SiO₂ Core-shell Heterostructure During Fluidized Vapor Deposition

Ferrosilicon soft magnetic core,with excellent soft magnetic properties,is an ideal material for high-frequency motor core.With the development of high-power and high-frequency new energy devices,the demand for ferrosilicon soft magnetic powder core increases sharply.However,due to the lack of its own technology in this system,China has encountered a bottleneck in research and development,especially the eddy current loss problem in the field of high-frequency application,so it cannot form a series of products to compete with foreign enterprises.To solve the above problems,this paper adopts the new concept of"Three-dimensional epitaxial nucleation"system constructed by in-situ deposition of fluidized vapor,and uses ethyl orthosilicate as the precursor of SiO₂ insulating medium carry out surface insulating coating on Fe-6.5wt.%Si alloy particles.And Fe-6.5wt.%Si/SiO₂ composite particles are successfully prepared with controllable performance.This paper focused on the effects of microstructure,physical and chemical properties and soft magnetic properties of SiO₂ insulating coating layer via the different deposition temperature,deposition time,TEOS precursor concentration and dilution gas flow and combining with X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FTIR),et al phase analysis methods of characterization and four-probe resistivity tester and vibrating sample magnetometer instrument.This paper reveals the physical and chemical conditions for the formation of Fe-6.5wt.%Si/SiO₂ core-shell structure composite particles and the growth mechanism of SiO₂ insulating coating layer,and determines the key process parameters of preparing a complete and uniform Fe-6.5wt.%Si/SiO₂ core-shell structure.Study have found that the key to obtain complete Fe-6.5wt.%Si/SiO₂ core-shell structure particles is select appropriate process parameters via fluidized vapor deposition.The best coating process parameters for thr deposition temperature is920?960 K,deposition time 960 s,TEOS concentration 3.0 vol%,dilution gas flow rate 200?300 sccm.In the SiO₂ layer generated by the decomposition of ethyl orthoposilicate,there are four silicon groups with different degrees of polymerization and four oxygen groups corresponding to them,in addition,there are oxygen element groups interacting with the surface of Fe-6.5wt.%Si alloy particles.The formation process of Fe-6.5wt.%Si/SiO₂ core-shell structure conforms to the three-dimensional island nucleation model.The resistivity of the complete Fe-6.5wt.%Si/SiO₂ core-shell composite particles increased by three orders of magnitude compared with that of the original Fe-6.5wt.%Si alloy particles,and the saturation magnetic induction intensity was slightly lower than that of the original Fe-6.5wt.%Si alloy particles,but all showed typical soft magnetic properties,and the coercivity was almost unchanged.