A comparative study on the dielectric response and microwave absorption performance of FeNi-capped carbon nanotubes and FeNi-cored carbon nanoparticles

Abstract

The mechanisms responsible for the dielectric response of C-based microwave absorbers remain a long-standing theoretical question. Uncovering these mechanisms is critical to enhance their microwave absorption performance. To determine how different C forms alter the dielectric response of C-based absorbers, FeNi-capped carbon nanotubes (FeNi-CNTs) and FeNi–cored carbon nanoparticles (FeNi-CNPs) are synthesized, and a comparative study of their dielectric responses is then carried out in this study. The as-synthesized FeNi-CNTs and FeNi-CNPs have similar magnetic properties and complex permeabilities, but differ in complex permittivities. It is shown that FeNi-CNTs have a much stronger dielectric loss than FeNi-CNPs. At a thickness of 2.8 mm, a low optimal reflection loss of −32.2 dB and a broad effective absorption bandwidth of 8.0 GHz are achieved for FeNi-CNTs. Meanwhile, equivalent circuit models reveal that the CNT network of the FeNi-CNTs could introduce an electrical inductance that can effectively improve its dielectric loss capability. This study demonstrates that designing a composite with a tailored C form and composition is a successful strategy for tuning its microwave absorption performance. Furthermore, the equivalent circuit modeling is an effective tool for analyzing the dielectric response of the microwave absorbers, as is expected to be applicable for other metal-C composites.

Influences of Metal Core and Carbon Shell on the Microwave Absorption Performance of Cu–C Core–Shell Nanoparticles

“…Theoretically, under the action of an altering electromagnetic field, the excited electrons are expected to generate within these nanoparticles. 27 Both Cu−C and C nanoparticles can form four kinds of polarized dipoles (as shown in Figure 4b,f), which can be assigned to four surface plasmon resonance modes. 51 First, nanoparticles with large air−C or metal−C interfaces can provide numeral polarization sites and thus exhibit enhanced resonance effects.…”

“…55,56 The resultant conduction loss usually plays an important role in the MA. 27 According to the free electronic theory, the conduction loss can be expressed as 41,57 = f…”

“…Tremendous efforts have been paid to designing and fabricating advanced microwave absorption (MA) materials featured by thin thickness, light weight, strong absorption, and a wide effective bandwidth. − Among MA materials reported previously, core–shell nanocomposites are highly expected to be promising candidates due to their small sizes, large surface areas, and unique microstructures and electromagnetic properties. − To date, many core–shell nanocomposites have been developed, including carbon (C)-coated Fe, − Co, , Ni, and their alloys, − or oxide-based nanostructures. ,− The intriguing MA performances of these nanocomposites motivate strong expectations on understanding the MA mechanisms of nanocomposite absorbers. , For example, Wang et al found that the MA performance of Ni–C core–shell nanoparticles (NPs) could be tuned by the thickness of C shells . Kuang et al investigated the effects of metal cores and C shells on the MA performance of FeCo–C and FeNi–C core–shell nanoparticles by experimental results and equivalent circuit models and found that the morphology of C shells and magnetic alloyed cores have significant influences on their MA performances. , However, for the above-mentioned magnetic core–shell nanoparticles, the small size effects, complicated core–shell interface effects, and potential synergy effects with the magnetic loss of the nanocores may affect the measured MA properties. It is a significant challenge to isolate the effects of various factors and completely clarify the underlying mechanisms .…”

Hard Carbon Embedded with FeSiAl Flakes for Improved Microwave Absorption Properties

“…Therefore, the curve of ε ′ vs. ε ″ is a semicircle named the Cole–Cole semicircle. A larger radius and more semicircles indicate a stronger Debye dipolar and a stronger dielectric loss [ 30 , 31 ]. The large Deby dipolar values of S3 and S4 were from the high content of hard carbon.…”

Microwave-Boosted One-Step Synthesis of Nanocrystal N-Doped 2D Carbon/Ni Composite with High Electromagnetic Absorption Performance

“…Carbonaceous materials have always been the most popular electromagnetic absorbing materials because of their adjustable performance, relatively low density, abundant resources, convenient preparation, and low cost [7][8][9][10][11][12]. Compared with oxides, the soft magnetic metals Ni and Co have higher magnetization, which leads to high Snoek limit and magnetic permeability in the high-frequency region, resulting in strong magnetic loss [13].…”