Synthesis and Microwave Absorption Properties of Yolk–Shell Microspheres with Magnetic Iron Oxide Cores and Hierarchical Copper Silicate Shells

Abstract

Yolk-shell microspheres with magnetic Fe3O4 cores and hierarchical copper silicate shells have been successfully synthesized by combining the versatile sol-gel process and hydrothermal reaction. Various yolk-shell microspheres with different core size and shell thickness can be readily synthesized by varying the experimental conditions. Compared to pure Fe3O4, the as-synthesized yolk-shell microspheres exhibit significantly enhanced microwave absorption properties in terms of both the maximum reflection loss value and the absorption bandwidth. The maximum reflection loss value of these yolk-shell microspheres can reach -23.5 dB at 7 GHz with a thickness of 2 mm, and the absorption bandwidths with reflection loss lower than -10 dB are up to 10.4 GHz. Owing to the large specific surface area, high porosity, and synergistic effect of both the magnetic Fe3O4 cores and hierarchical copper silicate shells, these unique yolk-shell microspheres may have the potential as high-efficient absorbers for microwave absorption applications.

Preparation and microwave absorption mechanisms of the NiZn ferrite nanofibers

“…Then, the nonreflecting condition of the characteristic impedance matching can be generally expressed as e r = l r . Consequently, many studies were focused on the efficient complementarities between the complex permittivity and the complex permeability [36][37][38]. However, it is difficult to find such an ideal microwave absorber and the characteristic impedance matching is limited since the interface effects and coating thickness are not considered.…”

Dependency of tunable microwave absorption performance on morphology-controlled hierarchical shells for core-shell Fe3O4@MnO2 composite microspheres

“…Up to now, it has no exact answers, and even there are very few correlative literatures accessible yet. Just hierarchical core-shell and yolk-shell Fe 3 O 4 /CuSilicate composite microspheres for microwave absorption application have been reported, but the detailed absorption mechanism is missing [16,17]. Manganese dioxides (MnO 2 ) has been regarded as one of the most attractive microwave dielectric materials by reason of its low cost, environment friendly nature, strong dielectric loss and broad frequency bandwidth [18][19][20][21].…”

Mesoporous Fe/C and Core–Shell Fe–Fe3C@C composites as efficient microwave absorbents

“…[22,23] Recently, the core-shell composites, combining dielectric loss and magnetic loss materials M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT effectively, have been reported as one of the hot topics of MAMs because they greatly improve microwave absorbability. [24][25][26] Besides, the core-shell structure is an effective method to protect the magnetic metal cores from oxidation in air atmosphere by coating the air-stable materials on them. Considering the practical application of MAMs, carbon is one of the best candidates for the shell materials due to its dielectric loss characteristic and chemical stability.…”