Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

Abstract

HIGHLIGHTS• The crystalline Fe/MnO@C core-shell nanocapsules embedded in porous amorphous carbon matrix (FMCA) was prepared by a novel confinement strategy of modified arc-discharge method.• The heterogeneous crystalline-amorphous nanocrystals disperse evenly and exhibit improvement of static magnetization and excellent electromagnetic absorption properties. • The adding MnO 2 confines degree of graphitization and contributes to form amorphous carbon. Dielectric loss and microwave absorption are achieved adjustable. ABSTRACT Crystalline Fe/MnO@C core-shell nanocapsules inlaid in porous amorphous carbon matrix (FMCA) was synthesized successfully with a novel confinement strategy. The heterogeneous Fe/ MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2-18 GHz. The addition of MnO 2 confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon. The heterogeneous materials composed of crystalline-amorphous structures disperse evenly and its density is significantly reduced on account of porous properties. Meanwhile, adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network. The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption. The optimal reflection loss (RL) is up to − 45 dB, and the effective bandwidth (RL < − 10 dB) is 5.0 GHz with 2.0 mm thickness. The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber, but also offers a general duty synthesis method for heterogeneous crystalline-amorphous composites with tunable composition in other fields.

Solvent-Free Synthesis of Ultrafine Tungsten Carbide Nanoparticles-Decorated Carbon Nanosheets for Microwave Absorption

“…S6). It is believable that this enhancement should be associated with the following two aspects: conductive loss and polarization loss [53][54][55]. Conductive loss is always generated by some residual carriers in dielectric medium, and their directional movement under an applied electric field will convert electric energy into heat energy [56].…”

“…Compared to conductive loss, polarization loss has diversified modes, i.e., electronic polarization, ionic polarization, dipole orientation polarization, and interfacial polarization [54,55]. However, electronic polarization and ionic polarization are widely accepted to be inactive for the dissipation of EM energy in gigahertz range because their relaxation time is too short (10 −12 -10 −16 s) [54,55]. Therefore, dipole orientation polarization and interfacial polarization are the two modes that can be responsible for energy consumption under 14 16 18 Frequency (GHz) current conditions.…”

A Nano-Micro Engineering Nanofiber for Electromagnetic Absorber, Green Shielding and Sensor

“…EM functional materials have always been a hot spot in the information explosion era, and their applications in ultra-long-distance energy transmission, military stealth camouflage, and anti-interference of electrical equipment cannot be ignored [12][13][14][15][16][17][18][19]. Generally, the EM absorption mechanism fatefully depends on the impedance matching level, and incident EM wave is attenuated by dielectric or/ and magnetic losses [20][21][22][23][24][25][26][27][28]. Many meritorious electromagnetic absorbing materials are emerging in recent decades, such as carbon materials, metal-based material, and polymers.…”

Porous carbon materials for microwave absorption

“…For example, EM waves emitted by mobile phones would affect the normal work of precision electronic medical devices; EM waves can also seriously interfere with aircraft communications; besides, EM waves cause long-term harm to human body health; and, in the military aspect, the development of radar detection technology based on EM waves seriously threatens the survivability of aircraft, tanks, and ships. [2][3][4] Therefore, developing advanced microwave absorption (MA) materials to eliminate unwanted EM energy has attracted great interest at the global scale. [5][6][7][8][9] Usually, ideal MA materials should be thin in thickness, light in weight, wide in bandwidth, and strong in absorption.…”