Improved dielectric and electromagnetic interference shielding properties of ferrocene-modified polycarbosilane derived SiC/C composite ceramics

In order to enhance the dielectric and electromagnetic interference shielding (EMI) properties, the SiC/C composite ceramics were fabricated by pyrolysis of ferrocene-modified polycarbosilane. The microstructure evolutions, dielectric properties, EMI and microwave absorption properties of SiC/C composite ceramics were investigated. The increases of both ferrocene contents and annealing temperatures led to the increases of crystallizations of SiC and carbons. Crystallized carbons including carbon nanowires, turbostratic carbons, onion-like carbons and graphene-like carbons were obtained in the materials. The carbon nanowires were longest when the 5 wt.% ferrocene-modified polycarbosilane was annealed at 1250 °C. These carbons played a more important role than SiC in the increases of dielectric and EMI properties. The average real and imaginary permittivities of materials increased from 4.4 and 0.7 to 38.9 and 39.6, respectively. The materials exhibited high total shielding effectiveness, high absorption shielding effectiveness and low reflection shielding effectiveness, which were 36.6, 30.1 and 6.5 dB, respectively.     

Electromagnetic interference shielding effectiveness of hybrid multifunctional Fe3O4/carbon nanofiber composite

Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe₃O₄/carbon nanofiber composites in the X-band region (8.2–12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe₃O₄ content, carbonization temperature and thickness on total shielding efficiency (SE_total) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe₃O₄ (0.7 mm thick) with the dominant shielding by absorption (SE_A) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe₃O₄/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe₃O₄) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency.     

Multifunction properties of SiOC reinforced with carbon fiber and in-situ SiC nanowires

Herein, the SiC nanowires were successfully fabricated via chemical vapor infiltration (CVI) into carbon fiber felts (CFs) and then the SiOC/SiCnws/CFs composites were synthesized by precursor infiltration and pyrolysis (PIP) processes. Results indicated that the lightweight composites possessed enhanced mechanical performance, low thermal conductivity, and excellent electromagnetic wave absorption properties. Detailedly, the compressive strength reached to 22.0 MPa and 9.6 MPa after two PIP processes cycles in z and x/y directions, respectively. Meanwhile, the composites exhibited tailored electromagnetic wave absorption performance with the effective absorption bandwidth of 3.06 GHz, and the minimum reflection loss (RL_min) was -48.2 dB with a thickness of 3.6 mm. The present work has a guidance to prepare and design multifunction properties for application in harsh environment.     

Enhanced microwave-absorption properties of polymer-derived SiC/SiOC composite ceramics modified by carbon nanowires

Novel microwave-absorbing SiOC composite ceramics with dual nanowires (carbon nanowires (CNWs) and SiC nanowires) with high performances were fabricated by using the polymer-derivation method and heat treatment in Ar atmosphere. The introduction of CNWs in the amorphous SiOC ceramics promotes the ceramic crystallization into SiC nanoparticles and SiC nanowires at lower annealing temperatures, which leads to multi-phases and multiple nano heterogeneous interfaces. The distinctive architectures largely increase the interfacial and dipole polarizations of the composite ceramics. The CNWs/SiC/SiOC composite ceramics exhibit excellent microwave-absorption properties in the Ku band (12.4–18 GHz). The minimum reflection coefficient (RC) is -24.5 dB at a thickness of 1.8 mm, while the maximum effective absorption bandwidth (EAB, the corresponding frequency band in which RC is smaller than -10 dB) is 4.8 GHz at a thickness of 1.9 mm, which make the CNWs/SiC/SiOC composite ceramics promising electromagnetic-wave-absorbing materials.     

Effects of oxidation temperature on microstructure and EMI shielding performance of layered SiC/PyC porous ceramics

Herein, the influence of oxidation temperature on the oxidation behavior, microstructure and electromagnetic shielding performance of layered porous ceramics has been systematically investigated. Layered SiC/PyC porous ceramics were prepared by using low-pressure chemical vapor infiltration (LPCVI) method. The oxidized SiC/PyC layered porous ceramics exhibited a negligible mass reduction of 11.94 mg·cm^?3, which indicates the excellent high-temperature oxidation resistance of porous ceramics. The electromagnetic shielding performance of SiC/PyC porous ceramics did not exhibit any obvious change even after oxidation at high temperature from 900 to 1300 °C for 10 h. The SE_T of the layered SiC/PyC porous ceramics was 24.1, 20.0, 19.5, 19.0, 19.8 dB after oxidation at 25 °C, 900 °C, 1000 °C, 1100 °C and 1300 °C, which corresponds to a decrease of 17.01%, 19.09%, 21.16% and 17.84%, respectively. The high-temperature oxidation has rendered a more significant influence on the reflection efficiency of the layered SiC/PyC porous ceramics.     

Effect of surface treatment of carbon fiber on the electrical and mechanical properties of high-impact polystyrene composite

Carbon fiber (CF), PU(polyurethane)-coated carbon fiber (CF-PU) and Ni-coated fiber (NCF) treated with a coupling agent (CA) were used to prepare composites for high impact polystyrene (HIPS) by melt blending. The optimum concentration of the titanate CA is 1.5 phf (per hundred parts of filler) when coupled with the carbon fibers. A composite prepared by adding a CA directly into the matrix which was then reinforced with fibers was investigated for comparison. These composites were evaluated for electromagnetic interference shielding effectiveness, dispersion, and adhesion between the polymer and the filler by means of scanning electron microscopy (SEM). The addition of CA generally improved the shielding effectiveness; this is especially apparent when the matrix was pretreated with CA before compounding with the fibers. The tensile properties were also improved upon CA addition.     

Roll-to-roll processable MXene-rGO-PVA composite films with enhanced mechanical properties and environmental stability for electromagnetic interference shielding

MXene films promise potential electromagnetic interference (EMI) shielding materials, but poor scalable processability, environmental instability, and weak mechanical properties severely restrict their applications. Herein, we engineer the large-area, high-performance, and compact nacre-like MXene-based composite films through cooperative co-assembly of Ti₃C₂T_X MXene and reduced graphene oxide (rGO) in the presence of polyvinyl alcohol (PVA). The resulting MXene-rGO-PVA composite films benefit from enhanced bonding strength and extra chain bridging effect of linear PVA molecules enriched with hydroxyl groups. Therefore, the composite film achieves high tensile strength (～238 MPa) and toughness (～1.72 MJ m^?3) while having high conductivity of ～32 S cm^?1. A significant EMI shielding effectiveness (41.35 dB) is also demonstrated, with an excellent absolute shielding effectiveness of ～20,200 dB cm² g^?1 at only 12-μm thickness. Moreover, due to the synergistic effect of multiple components, the composite films maintain a stable EMI shielding performance in harsh environments (sonication, hot/cold annealing, and acid solution) with mechanical properties that fluctuate only within 10% compared to the original film. More importantly, commercial polyethylene terephthalate release liner can be applied for the film coating, facilitating continuous roll-to-roll production of large-area films and future applications.     

Electromagnetic shielding and thermal conductive properties of SiC nanowires reinforced C/(PyC-SiC)n composites

SiC was introduced as nanowires and multilayered structure matrix to modify C/C composites, then SiC nanowires reinforced C/(PyC-SiC)_n (SM-CS) composites were prepared. The electromagnetic shielding and thermal conductive properties were investigated and the further relationship between these properties and the number of cycles of preparation (N) was also studied. The results showed that total shielding effectiveness (SET) values of modified composites were all higher than 30 dB which meant more than 99.9% electromagnetic wave was shielded. And the SET values increased with the rising of N (SM-CS4--47.6 dB > SM-CS3--42.7 dB > SM-CS2--37.1 dB). With the rising of N, not only the conductivity of SM-CSN composite increased, but also the interfaces inside the matrix increased, leading to a continuous increase in reflection and absorption of electromagnetic waves. Meanwhile, the thermal diffusivities and conductivities of the SM-CS composites in the temperature range from 25 to 1500 °C were all higher than those of pure C/C composites, and they were also almost increased by N. That was because the improvement of SiC nanowires in heat transport was very large, and even exceeded the reducing of multilayered structure. Due to these good functional properties, the modified composites would exhibit excellent potential in aerospace field.     

Effect of the pyrolytic carbon (PyC) content on the dielectric and electromagnetic interference shielding properties of layered SiC/PyC porous ceramics

A novel layered SiC/pyrolytic carbon (PyC) porous ceramic was synthesized from a nickel foam substrate via low-pressure chemical vapor infiltration (LPCVI) with SiCl₃CH₃-NH₃-BCl₃-H₂-Ar. The microstructure and phase composition of the PyC deposited via Ni catalysis were investigated. In addition, the effect of the PyC content on the microstructure, conductivity, and electromagnetic shielding effectiveness of a two-layered SiC/PyC porous ceramic were discussed. Both the electrical conductivity (from 0.090 to 0.319?S/cm) and the total shielding effectiveness (from 19.2 to 29.0?dB) of the two-layer SiC/PyC porous ceramic (pore size: 200–400?µm) increased with the PyC content. The high-temperature shielding effectiveness of the sample showed an outstanding stability with temperature and remained nearly unchanged (only 2?dB variation) over the 25–600?°C temperature range.     

EMI shielding effectiveness of silver nanoparticle-decorated multi-walled carbon nanotube sheets

With the aim of exploring the excellent properties of multi-walled carbon nanotubes (MWNTs) in modern composite technologies, various macrostructures of nanotubes have been developed from one to three dimensions, e.g. fibers, networks, sheets (buckypapers) and pellets. The MWNT sheets discussed here were fabricated by a vacuum filtration procedure, a process that has potential for large-scale manufacturing. In order to further enhance the transport properties of MWNT sheets by reducing the contact resistance between nanotubes, highly conductive silver nanoparticles were introduced by an in situ photochemical reduction method. TEM analysis showed that highly acid-treated MWNTs dispersed in the presence of Triton X-100 (TX-100) under UV light was a controllable processing method for preparation of a narrow size distribution of silver nanoparticles that were anchored onto the nanotubes. The free-standing MWNT/Ag nanohybrid sheets possessed a sharp increase in electrical conductivity from 27.7 to 40.0 S/cm, which consequently led to a much improved electromagnetic interference shielding effectiveness (SE). In principle, the SE could reach 3500 dB/cm with a thickness of 110 μm, which matched the experimental results well. In addition, the nanohybrid sheets are robust and can be folded with a thickness of 30 μm, which opens a promising way to integrate MWNT sheets into conventional composite laminates.     

Ti3C2Tx-coated diatom frustules-derived porous SiO2 composites with high EMI shielding and mechanical properties

Effective electromagnetic interference (EMI) shielding materials have garnered substantial interest for their efficacy in attenuating electromagnetic wave energy, ensuring data confidentiality, ensuring the operational stability of fragile electronic systems. To begin, artificially cultured diatom frustules (DF)-derived porous silica (DFPS) skeletons were constructed as templates in this study. Porous ceramics hot-pressed at 800 °C displayed a high compressive strength with a high specific surface area due to their three-dimensional (3D) multilayered and porous structures. Then, mechanically robust Ti₃C₂T_x/DFPS composites with exceptional EMI shielding performance were fabricated by immersing porous DF-based ceramics into Ti₃C₂T_x solutions and annealing in an argon environment to increase the materials’ shielding efficiency (SE). The EMI SE of composites hot-pressed at 800 °C achieved the maximum EMI SE of 43.2 dB in the X-band and a compressive strength of 67.5 MPa, establishing a hitherto unreported balance of mechanical characteristics and shielding performance. Prolonged transmission paths, multiple dissipation, scattering and reflection of electromagnetic energy were achieved using a well-maintained hierarchical porous silica framework decorated with MXene, with adsorption caused by surface MXene serving as the primary shielding mechanism for the composites. Due to their superior overall performance, MXene/DFPS EMI shielding composites have a bright future in the aircraft sector as delicate electronic device components.     

2D Ti3C2Tx MXene/aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties

Electromagnetic shielding (EMI) materials are becoming more and more important because of the increasingly serious radiation pollution. The preparation of high mechanical strength, ultrathin, lightweight, flexible materials with excellent EMI shielding performance have so far been elusive. Here, we try to prepare an ultrathin, lightweight and flexible film with excellent EMI shielding performance using one-dimensional aramid nanofibers (ANFs) and two-dimensional few-layered Ti₃C₂T_x through a simple filtration method. The ultimate tensile strength and strain of the film are up to 116.71 MPa and 2.64%. The EMI shielding effectiveness and the specific EMI shielding efficiency are 34.71 dB and 21971.37 dB cm² g⁻¹, which will be no recession after 1000 times bending. Our results show that a practical EMI shielding material with excellent performances has been successfully prepared, which will be widely applied in wearable electronics, robot joints, and precision instrument protection and so on.     

Microstructures and enhanced flexural properties of single-crystalline HfC nanowires in-situ modified carbon/carbon composites by electrophoresis-thermal evaporation using CNTs as the template

To improve the mechanical properties of carbon/carbon (C/C) composites, in-situ synthetized single-crystalline hafnium carbide nanowires (HfCnws) were introduced into the carbon fiber preforms by electrophoresis-thermal evaporation method. The Multi-walled carbon nanotubes (MWCNTs) were utilized as the carbon source and templates for forming HfCnws. The microstructure, chemical composition and mechanical properties of the HfCnws modified carbon/carbon (HfCnws-C/C) composites were characterized. Results reveal that HfC is produced preferentially in the inner nodular parts and end parts of MWCNTs. The raising heat-treatment temperature would influence the diffusion rate of Hf atoms and then the number of nucleation sites, which further changed the aspect ratio and morphology of HfCnws. The HfCnws have refined the grain size of pyrolytic carbon (PyC), and significantly improve the flexural strength of C/C composites by 79.3%.     

Fabrication and mechanical properties of carbon fibers/lithium aluminosilicate ceramic matrix composites reinforced by in-situ growth SiC nanowires

To improve the mechanical properties of carbon fibers/lithium aluminosilicate (C_f/LAS) composites, C_f/LAS with in-situ grown SiC nanowires (SiC_nw-C_f/LAS) were prepared by chemical vapor phase reaction, precursor impregnation, and hot press sintering, consecutively. The effect of multi-scaled reinforcements (micro-scaled C_f and nano-scaled SiC_nw) on the mechanical properties was investigated. The phase composition, microstructure and fracture surface of the composites were characterized by XRD, Raman Spectrum, SEM, and TEM. The morphology of SiC_nw has a close relation with the content of Si. Microstructure analysis suggests that the growth of SiC nanowires depends on the VLS mechanism. The multi-scale reinforcement formed by C_f and SiC_nw can significantly improve the mechanical properties of C_f/LAS. The bending strength of SiC_nw-C_f/LAS reaches to 597 MPa, achieving an increase of 19% to C_f/LAS. Moreover, the samples show a maximum fracture toughness of 11.01 MPa m^1/2, achieving an increase of 46.4% to C_f/LAS. Through analysis of the fracture surface, the improved mechanical properties could be attributed to the multi-scaled reinforcements by the pull-out and debonding of C_f and SiC_nw from the composites.     

炭纤维增强水泥基复合材料(CFRC)的电磁性能

炭纤维增强水泥基复合材料(Carbon Fiber Reinforced Cement Composites,CFRC)是新发展起来的一种电磁屏蔽材料,它是防止电磁污染的防护性功能材料之一。本文阐述了炭纤维增强水泥基复合材料的制备成型工艺;分析了炭纤维掺入量和长度、水灰比和密实成型制备工艺、炭纤维分散性、养护龄期、外加剂、炭纤维表面化学气相沉积(CVD)处理等因素对CFRC力学性能、导电性能、压敏性能及电磁性能的影响。合适的炭纤维掺入量和长度、炭纤维的均匀分散、合理的水灰比和炭纤维表面处理是影响CFRC导电性能和电磁性能的主要因素。CFRC对电磁波的屏蔽效果除利用屏蔽效能从反射电磁波角度衡量外,亦可从吸收电磁波角度利用反射率进行评价。     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

The effect of honeycomb pore size on the electromagnetic interference shielding performance of multifunctional 3D honeycomb-like Ag/Ti3C2Tx hybrid structures

To solve pollution problems caused by electromagnetic waves, advanced three-dimensional (3D) honeycomb Ag/Ti₃C₂T_x hybrid materials were produced by a microwave hydrothermal method. The Ag/Ti₃C₂T_x hybrid materials retained their hollow sphere structure after the polymethyl methacrylate (PMMA) template was removed by annealing. The hybrid materials changed from hydrophilic to hydrophobic and exhibited cross-surface heat insulation and reflection-dominant electromagnetic interference shielding (EMIS) performance owing to their special honeycomb structure. This study innovatively explored the influence of different particle sizes of honeycomb holes on EMIS performance. In particular, the Ag/Ti₃C₂T_x 5 μm hybrid materials had an excellent average EMIS performance of 51.15 dB in the X-band and 56.64 dB in the K_u-band. The superior performance was due to conduction loss, interface polarization, multi-reflection, and scattering caused by the 3D porous structure of the Ag/Ti₃C₂T_x hybrid materials. In general, Ag/Ti₃C₂T_x hybrid materials with honeycomb structures retained the advantages of lightweight, hydrophobicity, and EMIS performance, illustrating the great application prospects of these materials in high-end electronic equipment.     

Synthesis and tunable electromagnetic shielding and absorption performance of the three-dimensional SiC nanowires/carbon fiber composites

Silicon-carbide nanowires (SiCnws) have been considered as dielectric loss materials for application in the field of electromagnetic wave (EMW) attenuation. In this study, SiCnws/carbon fiber (CF) composites were fabricated using precursor infiltration and pyrolysis process for the in-situ growth of SiCnws. The SiCnw fraction of the SiCnws/CF composites could be adjusted using various catalysts. At a small SiCnw fraction (38 wt%), the composites exhibited excellent EMW absorption performance with the minimum reflection loss of ? 18.3 dB when their thickness was only 1.2 mm and can cover the entire X and Ku bands by adjusting the material thickness. They transformed from EMW absorption performance to electromagnetic interference (EMI) shielding property with the increase in SiCnw fraction from 38 wt% to 73 wt%, reaching an EMI shielding effectiveness of 31.25 dB. In addition, the density of the SiCnws/CF composites was only 0.31–0.41 g/cm³, and their compressive strength can reach 0.61–0.99 MPa with excellent high-temperature stability. Therefore, the SiCnws/CF composite presents a promising EMW absorption and EMI shielding material that can be applied in harsh environments.     

Waste cotton Fabric/MXene composite aerogel with heat generation and insulation for efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials have become more and more indispensable due to serious electromagnetic-radiation pollution. Herein, waste cotton cellulose aerogels were prepared by dissolving waste cotton fabrics (WCF) in NaOH/urea aqueous solution, and MXene nanosheets were subsequently deposited on the cellulose aerogels by a facile dip coating method to obtain WCF/MXene composite aerogels. The WCF/MXene composite aerogels with highly porous network structure show remarkable electrical conductivity (8.2 Ω/sq of surface resistance), high EMI shielding effectiveness (EMI SE) in the range of 2–18 GHz (39.3–48.1 dB). The WCF/MXene aerogel possesses high SSE and SSE/t of 677.94–829.74 dB cm³ g^?1 and 3512.62–4299.17 dB cm² g^?1, respectively (2–18 GHz). In addition, the heating temperature of WCF/MXene composite aerogels reaches 199 °C when 3 V positive voltage is applied on them. The WCF/MXene composite aerogels possess excellent electromagnetic shielding effectiveness, heat generation property and insulation, which can be potentially used as multifunctional materials for EMI shielding, electrical-heating and high temperature protection.