Novel soft magnetic composite with insulating layers formed in situ from hydrothermal carbon nanospheres and boric acid

This work addresses a method for obtaining a novel double-layered soft magnetic composite (SMC) by using carbon nanospheres and boric acid as precursors for a post-compaction formation of the insulating coatings on the surface of iron particles. Through the material’s heat treatment, the hydrothermal carbon nanospheres release oxygen groups that react with the metallic iron surface, generating a thin iron oxide layer. Additionally, the boric acid decomposes into glassy boron oxide (B ₂O ₃ ), which spreads over the iron oxide coating, hence improving the electrical insulation among the neighbor particles. The selected compounds and production method allowed for a synergetic mechanism that led to a reduction of 42% on the dynamic losses of the double-layered SMC when compared to the single-layered ones. Furthermore, the effects of the mean size and the concentration of carbon nanospheres on the magnetic behavior of the double-layered SMC showed that an optimization of the system can be achieved when using smaller carbon nanospheres providing the concentration used is high enough to guarantee the covering of the iron particles.