Investigation of the electromagnetic absorption properties of Ni@TiO2 and Ni@SiO2 composite microspheres with core–shell structure

Abstract

In this work, amorphous TiO₂ and SiO₂-coated Ni composite microspheres were successfully prepared by a two-step method. The phase purity, morphology, and structure of composite microspheres are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Due to the presence of the insulator SiO₂ shell, the core–shell Ni–SiO₂ composite microspheres exhibit better antioxidation capability than that of pure Ni microspheres. The core–shell Ni–SiO₂ composite microspheres show the best microwave absorption properties than those of pure Ni microspheres and Ni–TiO₂ composites. For Ni–SiO₂ composite microspheres, an optimal reflection loss (RL) as low as −40.0 dB (99.99% absorption) was observed at 12.6 GHz with an absorber thickness of only 1.5 mm. The effective absorption (below −10 dB, 90% microwave absorption) bandwidth can be adjusted between 3.1 GHz and 14.4 GHz by tuning the absorber thickness in the range of 1.5–4.5 mm. The excellent microwave absorption abilities of Ni–SiO₂ composite microspheres are attributed to a higher attenuation constant, Debye relaxation, interface polarization of the core–shell structure and synergistic effects between high dielectric loss and high magnetic loss.