Abstract
Core-shell particles with integration of ferromagnetic core and dielectric shell are attracting extensive attention for promising microwave absorption applications. In this work, CoNi microspheres with conical bulges were synthesized by a simple and scalable liquid-phase reduction method. Subsequent coating of dielectric materials was conducted to acquire core-shell structured CoNi@TiO2 composite particles, in which the thickness of TiO2 is about 40 nm. The coating of TiO2 enables the absorption band of CoNi to effectively shift from Ku to S band, and endows CoNi@TiO2 microspheres with outstanding electromagnetic wave absorption performance along with a maximum reflection loss of 76.6 dB at 3.3 GHz, much better than that of bare CoNi microspheres (54.4 dB at 17.8 GHz). The enhanced EMA performance is attributed to the unique core-shell structures, which can induce dipole polarization and interfacial polarization, and tune the dielectric properties to achieve good impedance matching. Impressively, TiO2 coating endows the composites with better microwave absorption capability than CoNi@SiO2 microspheres. Compared with SiO2, TiO2 dielectric shells could protect CoNi microspheres from merger and agglomeration during annealed. These results indicate that CoNi@TiO2 core-shell microspheres can serve as high-performance absorbers for electromagnetic wave absorbing application.
Highlights
From contacting each other, which contributes to the dielectric dissipation[27], suppresses eddy current[28] and avoids decay-induced performance degradation
A facile and efficient method was developed to prepare composite microspheres with CoNi as cores and TiO2 as shells, in which CoNi cores can contribute to the magnetic loss, while TiO2 shells can contribute to the dielectric loss
CoNi microspheres with conical bulges were successfully synthesized via a simple liquid-phase reduction method
Summary
From contacting each other, which contributes to the dielectric dissipation[27], suppresses eddy current[28] and avoids decay-induced performance degradation. Zhang et al synthesized core-shell Ni-TiO2 composite microspheres with enhanced microwave absorption properties, which arises from multiple interfacial polarization and high thermal conductivity of rutile TiO232. The significantly improved dielectric loss of SiO2@Fe3O4 composite is attributed to the dipolar polarization and interfacial polarization[33]. TiO2 is attractive as a coating material to enhance the microwave absorption performance since it owns high dielectric constant[40]. It is expected that the interface between the magnetic core and TiO2 shell could produce some intriguing interactions, which could extremely enhance EMA properties of ferromagnetic particles. The purpose of this work was to design and fabricate core-shell composites to achieve materials with outstanding EMA performance. Our findings give insights into the understanding of the effects of core-shell structure on the microwave absorption performance, which can be extended to other ferromagnetic metals and ferrites for EMA applications
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