Mechanism and Effect of the Dilution Gas Flow Rate on Various Fe–Si/SiO₂ Soft Magnetic Composites during Fluidised Bed Chemical Vapour Deposition

• Main Authors: Zhaoyang Wu, Zihan Gao, Qian Zhao, Hui Kong, Mingyang Li, Jixiang Jia
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Crystals
• Subjects: dilution gas; soft magnetic composites; evolution mechanism; magnetic performance
• Online Access: https://www.mdpi.com/2073-4352/11/8/963

The effect of the dilution gas flow rate on inorganic oxide insulating layers can improve fluidised bed chemical vapour deposition (FBCVD) in Fe–Si/inorganic-oxide soft magnetic composites and obtain excellent magnetic properties. Herein, Fe–Si/SiO₂ composite particles coated via FBCVD and deposited at a 125–350 mL/min Ar-dilution gas flow rate were prepared and sintered into soft magnetic composites. Results demonstrate that SiO₂ deposited on the Fe–Si substrate particle surface changed from submicron SiO₂ clusters (125 mL/min) to an incomplete SiO₂ film, then to a complete SiO₂ film, and finally to a porous SiO₂ film as the Ar-dilution gas flow rate increased. SiO₂ layers began to transform from the amorphous to the beta-cristobalite state with a hexagonal crystal structure between 1149.45 K and 1280.75 K. However, the SiO₂ amorphous layers’ crystallisation did not affect the Fe–Si substrate particles’ crystal structure. With the increasing Ar-dilution gas flow rate, the saturation magnetisation of Fe–Si/SiO₂ soft magnetic composites initially decreased and then increased. The electrical resistivity increased before 150 mL/min, followed by an increase between 150 and 250 mL/min and then decreased, whereas the total core loss exhibited the opposite trend. These results show that magnetic performance can be promoted by selecting a suitable dilution flow rate.