Carbon encapsulated nanoscale iron/iron-carbide/graphite particles for EMI shielding and microwave absorption (original) (raw)
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Carbon, 2020
In this work, EMI shielding behaviors in the X-band frequency have been investigated for flexible polyvinylidene fluoride (PVDF) composites containing globular- and tubular-shaped carbonaceous nanostructures embedded with mono-metallic (Ni) and bi-metallic (FeNi, CoNi, MnNi) alloy nanoparticles. Pyrolysis was carried out at two different temperatures (800 °C and 1000 °C) to synthesize carbonaceous materials with two different morphologies. Carbon nanotubes (CNTs) are predominantly seen in the samples synthesized at lower temperature (800 °C), whereas carbon globules (CGs) are observed for the samples synthesized at higher temperature (1000 °C). The PVDF-CNT composites show superior microwave shielding behavior than the PVDF-CG composites, which is attributed to the enhanced absorption of the microwave through Ohmic conduction and interfacial polarization loss. The 1-D structure of CNTs provides the required conduction path for the electrons and forms a network to trap the microwave within them via multiple scattering. The microwave absorption behavior of the composites predominantly results from the metallic nature of the embedded nanoparticles, the graphitic layer encapsulating them and the graphitic walls of the CNTs. We further demonstrate the direct correlation of the EMI shielding behavior of the nanocomposites with the morphology of carbonaceous nanomaterials and the conductivity of the embedded metallic nanoparticles.
Physical Chemistry Chemical Physics, 2019
Using composites of polyvinylidene fluoride (PVDF) and carbon nanostructures embedded with Co-nanoparticles we demonstrate that electromagnetic shielding effectiveness depends strongly on the graphitic carbon concentration and the magnetic properties of Co-particles. Cobalt nanoparticles encapsulated by graphitic carbon embedded in an amorphous carbon-matrix were synthesized by a one-pot pyrolysis method at two different synthesis temperatures, T S = 800 1C (Co-800) and 1000 1C (Co-1000). We demonstrate that T S plays an important role in determining the structure, morphology and magnetic properties of the carbonaceous matrix, the graphite layer and the Co nanoparticles. Higher amounts of graphitic carbon and high saturation magnetization were observed for the Co-1000 sample than that for the Co-800 sample. We observed that the electromagnetic interference (EMI) shielding behavior of the PVDF-Co-1000 nanocomposite shows higher shielding effectiveness than that of the PVDF-Co-800 specimen. A more inhomogeneous dielectric medium in the PVDF-Co-1000 composite results in higher dielectric loss and impedance mismatch. A direct correlation between the shielding effectiveness with dielectric permittivity and magnetic permeability is demonstrated. The synergy between the multiple reflections at the interfaces and absorption of the microwave radiation in the conducting species confirms that a higher degree of graphitization and highly magnetic particles in nanocomposites are effectively superior for EMI shielding of microwave radiation.
Journal of Electronic Materials, 2019
High-efficiency Electromagnetic Interference (EMI) shielding materials are essential in the harsh environment created by unwanted electromagnetic (EM) signals. In this work, polyvinylidenefluoride (PVDF) composites reinforced with magnetic Fe 3 O 4 nanoparticles and cost-effective conducting carbon black (CB) were derived by a solution mixing and coagulation method. Coagulation is found to be an effective method to fabricate uniform composites of materials having higher tendency to form aggregates. The three-dimensionally extending conducting network created by CB and the hopping electrons from Fe 3 O 4 result in high electrical conductivity of PVDF/CB/Fe 3 O 4 composites (PCF). The permittivity, permeability and impedance spectra in the 10 MHz-1 GHz broadband region indicate that dielectric loss is dominating over magnetic loss and is attributed to the collection of a large number of capacitive regions at the interfaces formed by CB and Fe 3 O 4 , which results in the enhanced interfacial polarization losses in PCF composites. The composites exhibit EMI shielding effectiveness (EMI SE) greater than 20 dB and their shielding mechanisms involve dielectric losses, magnetic losses and their synergistic interaction. The matching input impedance of the composites allows the radiations to enter into the material and it undergoes multiple internal reflections at the interfaces and the energy of the internally reflected radiation is subsequently absorbed by CB. These different mechanisms result in an absorption dominated EMI shielding with a total EMI SE of 55.3 dB (99.9997% of shielding) for PCF-40 composite having thickness 2 mm and an average skin depth of 0.37 mm in the X-band microwave region.
Carbon, 2014
Epoxy composites with different amounts of magnetite nanoparticles, carbon nanofibres (CNF) and magnetite decorated CNF were prepared and characterized. A simple method for the magnetite CNF decoration was developed by adsorbing preformed oleic acid capped magnetite nanoparticles over the CNF surface. A synergy between magnetite nano particles and CNF was found to have crucial effects in the electromagnetic shielding effi ciency of the prepared materials. This effect has been analysed by their electrical conductivity in terms of percolation theory and complex permittivity at high frequencies. Electromagnetic shielding mechanisms (reflection, absorption and transmission) were individually studied in the 1 18 GHz range. Results show that decoration of CNF with mag netite, notably increases permittivity and high frequency AC conductivity and enhances the electromagnetic shielding efficiency up to around 20 dB at high frequencies. It is pro posed that interfacial polarization adds an additional dissipation mechanism that may be responsible for the observed electromagnetic shielding enhancement. 1.
Electromagnetic interference shielding nature of PVDF-carbonyl iron composites
Polyvinylidene fluoride-carbonyl iron powder (PVDF-CIP) composites with different carbonyl iron powder loading were developed for electromagnetic interference shielding applications in the X band. Shielding properties improved with increase in carbonyl iron powder content and uniform electromagnetic shielding effectiveness of about 20 dB is obtained for PVDF-50 vol% carbonyl iron powder composite over the entire X band. The magnetic and dielectric loss tangent of the composite increased with increase in carbonyl iron content. It is found that the PVDF-CIP composites shield by absorption
Applied Nanoscience, 2020
The electrical properties of three-phase composite materials (CMs) graphite nanoplatelets/carbonyl iron/epoxy resin (GNP/ Fe/epoxy) with 30 wt% of Fe and (1-5) wt% of GNP were studied by measuring DC conductivity and AC impedance spectra in the frequency range up to 2 MHz. The microwave shielding properties were measured in the frequency range of electromagnetic radiation (EMR) 1-67 GHz. The Nyquist diagrams derived from measured impedance-frequency spectra for GNP/ Fe/epoxy CMs were considered within the equivalent circuit model. The significant increase of permittivity was observed for three-phase CMs with the increase of GNP content compared to two-phase GNP/epoxy CMs. For example, the real part of permittivity ′ = 700-300 and imaginary part ′′ = 4 × 10 5-300 for ternary 5 GNP/Fe/epoxy composite in the frequency range 1 kHz-2 MHz. The observed significant increase of AC conductivity for three-phase composites proved the synergetic role of Fe particles in dispersing of GNP filler in epoxy matrix and formation of micro-capacitor network (for low GNP content) as well as the conductive network for higher GNP content. The observed sufficient increase of EMR shielding (SE T in dB) beginning from 30-35 GHz for GNP content of 3-5 wt% correlates with DC electrical conductivity increase. The increase of the sample thickness d leads to the increase of shielding efficiency mainly due to the increase of EMR absorption SE A term.
The present paper reports, novel outcome comprising experimental results on electromagnetic interference (EMI) shielding and radar signal absorption characteristics of a polymer-metal composite (PMC) based on polyvinylidene fluoride (PVDF) dispersed with varying concentration of nanocrystalline iron (n-Fe). The PVDF/n-Fe composites, prepared using mechanical blending followed by hot-molding process at an optimum pressure and temperature, exhibited better filler dispersion. The relevant parameters, i.e.; microwave permittivity, permeability, shielding effectiveness (SE) and loss factors, has been calculated using scattering parameters measured in X-band (8.2–12.4 GHz) by waveguide method. The theoretical EMI SE has also been evaluated by transmission line model, assuming a single layer PMC absorbing structure backed by perfect electrical conductor, using measured material parameters as the input for meaningful comparison with the experimental results. The results so obtained, confirmed an improved shielding and absorption properties of PVDF/n-Fe composites vis-à-vis its counterpart reported in literature. The findings in this work, suggest potential futuristic applications of PMC in shielding and absorption of electromagnetic waves.
Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials
The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.
Electronic Materials Letters, 2018
With the recent developments in the millimeter and sub-millimeter wave instruments and devices, there is a need to develop electromagnetic (EM) wave absorbing materials in these frequency bands for applications like electromagnetic interference control, electromagnetic compatibility, etc. In this work, carbon nanofibers (CNF) were uniformly dispersed in a blend of poly(methyl methacrylate), polyvinylidene fluoride and cyanoacrylate for air spray coating a film on the cellulosic substrates. The samples were characterized for evaluation of their structure, morphology, electrical and EM absorption properties in 0.15-1.2 THz range by X-ray diffraction, field emission electron microscopy, I-V measurements and terahertz time domain spectroscopy. These coatings can conveniently be applied to the material surfaces by conventional air spray painting method, which makes this technique cost-effective as well as easy to deploy in various applications. The electrical conductivity enhancement in the samples has been attributed to the formation of conducting network by uniform distribution of CNFs in the insulating polymer matrix. As a result, the shielding effectiveness (SE) has been observed to improve with the increase in CNF's loading in the polymer matrix. The SE is also a function of frequency, which is attributed to the increase in the skin depth. A SE of 20 dB has been estimated in these samples for the frequencies 1 THz and higher, which is of significant importance for the use of this technique in practical applications.