Facile synthesis and influences of Fe/Ni ratio on the microwave absorption performance of ultra-small FeNi-C core-shell nanoparticles

A facile and scalable metal-organic chemical vapor deposition method is proposed for the fabrication of ultra-small FeNi-C core-shell nanoparticles. As-synthesized nanoparticles are composed of ultra-small FeNi nanocores of an average diameter of ∼ 6.2 nm and thin shells of 1–3 nm in thickness, which are stable in air atmosphere up to 210 °C. The ratio of Fe/Ni in the nanocores was tuned by varying the reaction temperature, suggesting a simple route to tailor the magnetic and microwave absorption properties of the synthesised nanostructures. These core-shell nanoparticles with a filler loading of 16.7% in paraffin wax exhibited a low minimum reflection loss (RL) of -63.7 dB, together with a great effective bandwidth (BW) of 6.5 GHz at a thickness of 2.2 mm, attributing to their ultra-small size and unique magnetic-dielectric core-shell nanostructure. Such core-shell nanoparticles should be a strong candidate as a light-weighted absorber with tunable microwave absorption performance

Achieving Tunable Microwave Absorbing Properties by Phase Control of NiCoMnSn Alloy Flakes

Microwave absorption performance of metal alloys are highly dependent on their phase structures. However, the phase control of Ni–Mn-based alloys to achieve effective microwave absorption properties has been rarely reported. In this work, Ni43Co7Mn39Sn11 alloy flakes were fabricated by balling milling method, and the contents of γ phase in the flakes were tuned by the subsequent heat treatment process. The as-fabricated Ni43Co7Mn39Sn11 alloy flakes exhibited excellent tunable microwave absorption by control of their phase structures. The optimal reflection loss was lower, up to −56.4 dB at 8.8 GHz, and was achieved at a single thickness of 2.0 mm. This can be attributed to the optimal structure of Ni43Co7Mn39Sn11 alloy flakes by phase control, and thus achieving improved attenuation property and impedance matching. This study proved Ni43Co7Mn39Sn11 alloy flakes should be a promising microwave absorption material. It is also demonstrated that phase control is an effected strategy for optimal microwave absorption properties of metal alloys and may have some reference value for related studies

Enhanced electromagnetic wave absorption of Ni-C core-shell nanoparticles by HCP-Ni phase

The strategy of phase control has been playing an important role in optimizing the electromagnetic wave (EMW) absorption properties. Here, Ni nanoparticles (NPs) with two phases, hexagonal close-packed Ni (HCP-Ni) and face-centered cubic (FCC-Ni), coated by C shells are synthesized by metal-organic chemical vapor deposition. The average size of the Ni nanocores and thickness of C shells are about 10 and 4 nm, respectively. After blended with paraffin wax at a mass ratio of 1:5, the Ni-C core- shell NPs exhibit excellent EMW absorption properties with an optimal reflection loss of -52.6 dB and a large effective bandwidth (BWeff) of 9.3 GHz. The core-shell NPs annealed in vacuum to remove the metastable HCP-Ni exhibit degraded EMW absorption properties. Comparative analyses reveal that the HCP-Ni phase in the core-shell NPs can enhance the dielectric loss and thus improve the impedance matching, suggesting that phase control should be a practicable strategy for optimizing the properties of Ni-based EMW absorption materials

Facile synthesis and excellent microwave absorption properties of FeCo-C core-shell nanoparticles

FeCo-C core-shell nanoparticles with diameters of 10 - 50 nm have been fabricated on a large scale by one-step metal-organic chemical vapor deposition using the mixture of cobalt acetylacetonate and iron acetylacetonate as the precursor. The Fe/Co molar ratio of the alloy nanocores and graphitization degree of C shells, and thus the magnetic and electric properties of the core-shell nanoparticles, can be tuned by the deposition temperature ranged from 700 to 900 oC. Comparative tests reveal that a relatively high Fe/Co molar ratio and low graphitization degree benefit the microwave absorption performance of the core-shell nanoparticles. The composite with 20 wt.% core-shell nanoparticle obtained at 800 oC and 80 wt.% paraffin exhibits an optimal reflection loss (RL) of -60.4 dB at 7.5 GHz with a thickness of 3.3 mm, and an effective absorption bandwidth (frequency range for RL≤10 dB) of 9.2 GHz (8.8-18.0 GHz) under an absorber thickness of 2.5 mm. Our study provides a facile route for the fabrication of alloy-C core-shell nanostructures with high microwave absorption performance