Carbon@SiC(SiCnws)-Sc2Si2O7 ceramics with multiple loss mediums for improving electromagnetic shielding performance

Multiple loss media can be applied, not only to improve the performance of microwave absorption materials, but also to promote the electromagnetic (EM) shielding efficacy of materials. In this study, multiple loss mediums (C, SiC, and SiCnws) were introduced into Sc₂Si₂O₇ ceramics to synthesise carbon@SiC(SiCnws)-Sc₂Si₂O₇ ceramics by H₂ reduction and CVI technology. After 1–3 CVI process cycles, the open porosity decreases from 34.7 %±0.5 % to 8.4 %±0.3 % filled with multiple loss media. The results show that CH₃SiCl₃ provides the raw material for synthesising SiC(SiCnws) and carbon in ceramics, resulting in adjustable EM shielding properties. Furthermore, the EM shielding mechanism consists mainly of the combined synergistic effect of C, SiC, and SiCnws, which contributes to the reflective shielding efficacy, and promotes the absorption shielding effectiveness, including dipole polarization loss, and interface polarization loss. Subsequently, carbon@SiC(SiCnws)-Sc₂Si₂O₇ ceramics with a multiple loss medium of 31.2 wt% ±0.22 wt% achieve a total EM shielding effectiveness value of 31.8 dB (99.92 % electromagnetic waves are attenuated) with an X-band thickness of 2 mm. Therefore, carbon@SiC(SiCnws)-Sc₂Si₂O₇ ceramics are a promising novel composite, applicable in future EM shielding in high temperature environments.     

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.     

Enhanced electromagnetic wave absorption properties of a novel SiC nanowires reinforced SiO2/3Al2O3·2SiO2 porous ceramic

To realize the broad-bandwidth and high-efficiency absorption characteristics, a novel SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ porous ceramic was successfully fabricated by method of precursor infiltration pyrolysis (PIP). Polycarbosilane (PCS) and ferrocene (Fe(C₅H₅)₂) were used as the precursor and catalyst to incorporate SiC nanowires into the SiO₂/3Al₂O₃·2SiO₂ porous ceramic. The curvy SiC nanowires formed three-dimensional (3D) networks with a proper nanometer heterostructure, thereby consuming the microwave energies. The influence of SiC nanowires contents on the microwave absorption properties was investigated. The results indicate that the SiC nanowires contents can be tuned by controlling the PIP cycles, thereby modifying the dielectric properties of as-prepared composite ceramics. The dielectric and electromagnetic wave absorption performances are gradually enhanced with an increasing of SiC nanowires contents. The SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramic exhibits excellent electromagnetic wave absorption abilities when the SiC nanowires content is 23.9% (PIP5). The minimum reflection coefficient (RC_min) of the composite ceramic is −30 dB at 10.0 GHz, corresponding to more than 99.9% of the electromagnetic wave consumption. The effective absorption bandwidth (EAB) can cover the frequency ranges of 8.2–12.4 GHz (the entire X-band) at the thickness of 5.0 mm. In general, the novel SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramic can be considered as a promising electromagnetic wave absorbing material.     

Construction of Si3N4/SiO2/SiC–Y2Si2O7 composite ceramics with gradual impedance matching structure for high-temperature electromagnetic wave absorption

Good impedance matching is vital in upgrading the performance of electromagnetic (EM) wave-absorbing materials. In this study, Si₃N₄/SiO₂/SiC–Y₂Si₂O₇ composite ceramics were synthesized by sintering and chemical vapor infiltration (CVI) technology with gradual impedance matching. The relationship between the microstructure of the as-prepared composite ceramics and EM wave absorption characteristics was thoroughly explored. It was found that the amorphous Si₃N₄, SiO₂, and SiC layers were constructed with a gradual impedance matching structure, which not only improved impedance matching but also increased the number of nano interfaces. More importantly, SiC nanocrystals effectively increased the conduction loss, and the presence of defects and nanoscale heterogeneous interfaces further increased the polarization loss. Consequently, the as-prepared composite ceramics displayed enhanced EM wave absorption properties, with a minimum reflection coefficient (RC_min) value of less than ?20 dB over a temperature range of 25 °C (RT)-300 °C, and an effective absorption bandwidth (EAB) maintained at 4.2 GHz with the thickness range of 3.75–4.75 mm. These results demonstrated the practical significance of high-performance EM wave absorption materials that can be applied in high-temperature and water vapor environments.     

Enhanced EMW absorption properties of SiCN/Fe/Ni ceramics modified with Fe/Ni bimetal

The SiCN/Fe/Ni ceramics codoped with iron acetylacetonate (FA) and nickle acetylacetonate (NA) was synthesized by polymer-derived ceramics (PDCs) method in this study. The microstructure, phase composition and electromagnetic wave (EMW) absorption properties of the samples were analyzed. The polarization loss and conduction loss of materials were analyzed by the direct current (DC) multimeter and the contribution rate of polarization loss was more than 94% in the whole frequency band. The results showed that C, SiC, Fe₂Si, Ni₃Si, γ- (Fe, Ni) and CNTs were formed after pyrolysis which provided lots of heterogeneous interface and enhanced the interfacial polarization. Meanwhile, Ni could enter the lattice of Fe and formed a unique electronic configuration, which reinforced the conductivity and stability of Fe. In addition, the in-situ generated Fe₂Si and Ni₃Si provided magnetic loss and conduction loss. The RL_min value of SiCN/Fe/Ni-3 ceramic was ?52.06 dB at 1.54 mm and the effective absorption band (EAB, RL ≤ ?10 dB) reached 4.21 GHz (13.79–18 GHz, 1.43 mm).     

Polymer-derived Co2Si(Co)/SiCN composite ceramics with tunable microwave absorption properties

In this paper, Co₂Si(Co)/SiCN composite ceramics were synthesized by simple precursor-derived ceramics method. The phase composition, morphology, and microwave absorption properties of Co₂Si(Co)/SiCN composite ceramics at different pyrolysis temperatures (1000–1400°C) were studied. When pyrolysis temperature was 1300°C, carbon nanowires (CNWs), Co₂Si, Si₂N₂O, SiC and Si₃N₄ were in situ generated and the best electromagnetic wave (EMW) absorption performance was obtained. The minimum reflection loss reached−50.04 dB at 4.81 mm, and the effective absorption bandwidth broadened to 3.48 GHz (14.52–18 GHz) at 1.31 mm. The excellent EMW absorption performance mainly comes from the coexistence of multiple loss mechanisms, including the magnetic loss of Co₂Si, the conduction loss of CNWs, and the heterogeneous interfaces polarization between varieties of nanocrystals and amorphous ceramic matrix. By adjusting the sample thickness from 1 to 5 mm, the effective absorption of S1300 can cover the entire X and Ku bands, from 3.36 to 18 GHz. This study provides a simple way to synthesize high performance ceramic-based microwave absorbing materials.     

Enhanced electromagnetic microwave absorption of SiC nanowire-reinforced PDC-SiC ceramics catalysed by rare earth

Rare earth elements can modulate the dielectric constant of materials and significantly improve their dielectric properties. Herein, SiCnws/SiC ceramics were prepared through polymer derived ceramics (PDCs) technology with rare earth Sc particles as the catalyst. The Sc particles promote the precipitation of SiC and C from the matrix. Furthermore, the SiCnws, grown via the vapour-liquid-solid (VLS) mechanism, construct the three dimensional (3D) network structure to improve impedance matching and loss characteristics. Remarkably, the SiCnws/SiC ceramics minimum reflection coefficient (RC_min) achieved a value of ?33.2 dB at 9.4 GHz with a thickness of 2.75 mm, and the effective absorption bandwidth (EAB) was 4.2 GHz covering the whole X band. When microwaves permeated into the SiCnws/SiC ceramics, those trapped in the 3D network structure underwent a variety of microwave energy dissipation processes, including multiple reflections, scattering, and interface and dipole polarisation. Consequently, SiCnws-reinforced PDC-SiC ceramics catalysed by rare earth emerge as a promising new approach to enhance electromagnetic (EM) wave absorption performance.     

Enhanced electromagnetic wave absorption performance of SiCN(Fe) fibers by in-situ generated Fe3Si and CNTs

The SiCN(Fe) fibers with excellent one-dimensional microstructure and electromagnetic wave (EMW) absorption performance were synthesized by combining polymer-derived ceramics (PDCs) method and electrospinning. The in-situ generation of Fe₃Si and CNTs by adding ferric acetylacetonate (FA) into the raw materials effectively improved the dielectric properties, magnetic properties and the impedance matching performance of the SiCN(Fe) fibers. The EMW absorption performance of SiCN(Fe) fibers were mainly based on dipole polarization loss, interface polarization loss and eddy current loss. The RL_min value of SiCN(Fe) fibers reached ?47.64 dB at 1.38 mm and the effective absorption band (EAB, RL ≤ ?10 dB) reached 4.28 GHz (13.72–18 GHz, 1.35 mm).     

Enhanced electromagnetic absorption properties of Fe-doped Sc2Si2O7 ceramics

Doping transition metal elements in a crystal causes distortion and defects in the lattice structure, which change the electronic structure and magnetic moment, thereby adjusting the electrical conductivity and electromagnetic properties of the material. Fe-doped Sc₂Si₂O₇ ceramics were synthesized using the sol-gel method for application to microwave absorption. The effect of Fe-doped content on the electromagnetic (EM) and microwave absorption properties was investigated in the Ku-band (12.4–18 GHz). As expected, the dielectric and magnetic properties improve substantially with increasing Fe content. Fe doping causes defects and impurity levels, which enhance polarization loss and conductance loss, respectively. Fe replaces Sc atoms in the ScO₆ octahedral structure, creating a difference in spin magnetic moments, which increases the magnetic moment. Moreover, the magnetic coupling of Fe and O atoms occurs at the Fermi level, which benefits magnetic loss. In particular, when the Fe content is 6%, the fabricated Fe-doped Sc₂Si₂O₇ ceramics show an absorption property with absorption peaks located at 14.5 GHz and a minimum reflection loss (RL_min) of ?12.8 dB. Therefore, Fe-doped Sc₂Si₂O₇ ceramics with anti-oxidation and good microwave absorption performance have a greater potential for application in high-temperature and water-vapor environments.     

MXene-derived TiC/SiBCN ceramics with excellent electromagnetic absorption and high-temperature resistance

Demand for high-performance electromagnetic (EM) wave absorbing materials with high-temperature resistance is always urgent for application in a harsh environment. In this contribution, two-dimensional material, Ti₃C₂T_x MXene, was introduced into a hyperbranched polyborosilazane. After pyrolyzation, the as-prepared TiC/SiBCN ceramics present excellent EM wave absorption in X-band. The TiC nanograins appearing after annealing provide multilevel reflection and interface polarization. Dipole polarization formed at interface defects, in company with interfacial polarization, also makes a great contribution to enhanced EM wave absorption. The TiC/SiBCN nanocomplex prepared with 5 wt% Ti₃C₂T_x MXene possesses a minimum reflection coefficient of −45.44 dB at 10.93 GHz and abroad bandwidth 8.4 and 12.4 GHz, almost covering the entire X-band. Tuning the thickness in the range of 2.35-2.54 mm, the effective absorption band can achieve the entire X-band. And the EM wave absorbing performance has been maintained to a large extent at 600°C with the minimum reflection coefficient of −26.12 dB at 12.13 GHz and the effective absorption bandwidth of 2 GHz. Last but not the least, TiC/SiBCN ceramics offer a good thermal stability in argon as well as in air atmosphere, making it possible to serve in high-temperature detrimental environments. This study is expected to provide a new perspective for the design of high-performance absorbing materials that are able to be used in harsh environments, especially in high temperatures.     

Efficient fabrication of carbon/silicon carbide composite for electromagnetic interference shielding applications

Ceramic matrix composites are typically prepared by a costly, time-consuming process under severe conditions. Herein, a cost-effective C/SiC composite was fabricated from a silicon gel-derived source by Joule heating. The β-SiC phase was generated via carbothermal reduction, and the carbon fabric showed a well-developed graphitic structure, promoting its thermal and anti-oxidation stabilities. Owing to the excellent dielectric loss in carbon fabric, SiC and SiO₂ as well as the micropore structure of the ceramic matrix, the absolute electromagnetic interference shielding (EMI) effectiveness (SSE/t) reached 948.18 dB?cm²?g^-1 in the X-band, exhibiting an excellent EMI SE. After oxidation at 1000 °C for 10 h in the air, the SSE/t of the composite was only reduced to 846.02 dB?cm²?g^-1. The C/SiC composite promises the efficient fabrication of high-temperature resistant materials for electromagnetic shielding applications.     

Effects of ZrSiO4 content on properties of SiO2-based ceramics prepared by digital light processing

SiO₂-based ceramic cores are widely used in the preparation of gas turbine engine hollow blades due to their excellent chemical stability and easy removal after casting. In this paper, ZrSiO₄ reinforced SiO₂-based ceramics were fabricated using digital light processing (DLP) technology. The results showed that the addition of ZrSiO₄ reduced the cure depth due to its high UV light absorptivity and refractive index. When the content of ZrSiO₄ increased to 15 wt%, the cristobalite content reached the maximum, and radial shrinkage reached the minimum of 1.4%. ZrSiO₄ grains could hinder the propagation of cracks, enhancing the room-temperature flexural strength. At 1550 °C, fracturing across SiO₂ grains in SiO₂-based ceramics led to the great improvement of high-temperature flexural strength. When the content of ZrSiO₄ reached 15 wt%, the flexural strength at room temperature and high temperature was 11.5 MPa and 36.7 MPa, respectively. Therefore, the SiO₂-based ceramics prepared using DLP technology have good room temperature and high temperature properties, and are expected to be used for hollow blade casting.     

Enhanced energy storage performance of nanocomposites filled with paraelectric ceramic nanoparticles by weakening the electric field distortion

Polymer-based dielectric nanocomposites, which combines the high dielectric constant of ceramic materials and the high breakdown strength of polymer materials, has emerged as one of the most effective progress for the advanced dielectric energy storage materials. To improve energy storage performance, the core-shell structured SiO₂@SrTiO₃ paraelectric nanoparticles are used as fillers in constructing the polymer-based nanocomposites. Hence, this paper systematically investigates the impacts of filler content on energy storage performance and breakdown strength, and provides insight into the polarization behavior of different composites filled with paraelectric and ferroelectric nanoparticles (SiO₂@BaTiO₃), respectively. Combined finite element simulations, it is shown that the dielectric constant of the paraelectric ceramic is more similar to the polymer matrix, resulting in weakening the electric field distortion in the dielectric. Furthermore, due to the paraelectric characteristics of SrTiO₃ nanoparticles and the diminution of interface polarization, the remnant polarization of the nanocomposites can be significantly reduced. The polymer-based dielectric nanocomposites exhibit more impressive energy storage, of 11.42 J/cm³ at 350 MV/m with 2.5 vol% paraelectric SiO₂@SrTiO₃ nanoparticles, which is superior to the composite filled with ferroelectric nanoparticles. Overall, this finding not only establishes a new direction for the structural design of fillers but also provides insight into an underlying mechanism to control interface polarization in the dielectric composites.     

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.     

Polymer-derived Co2Si@SiC/C/SiOC/SiO2/Co3O4 nanoparticles: Microstructural evolution and enhanced EM absorbing properties

In this work, porous core-shell structured Co₂Si@SiC/C/SiOC/SiO₂/Co₃O₄ nanoparticles were fabricated by a polymer-derived ceramic approach. The in situ formation of mesopores on the shell, microstructural, and phase evolution of resulting nanoparticles were investigated in detail. The obtained nanoparticles-paraffin composites possess a very low minimum reflection coefficient (RC_min) −60.9 dB, broad effective absorption bandwidth 3.50 GHz in the X-band and 15.5 GHz in the whole frequency range (from 2.5 to 18 GHz). The results indicate outstanding electromagnetic wave (EMW) absorbing performance among all the reported cobalt-based nanomaterials, due to the reasons as follows: (a) The unique core-shell structure as well as complex phase composition of SiC/C/SiOC/SiO₂/Co₃O₄ in the shell, result in a large number of heterogeneous interfaces in the nanoparticles; (b) Nanoparticles have both dielectric and magnetic loss; (c) Mesopores in the shell prolong the propagation path of EMW, thereby increasing the absorption/reflection ratio of EMWs. Thanks to the material structure design, the resulting core-shell structured cobalt-containing ceramic nanoparticles have great potential for thin and high-performance EMW absorbing materials applied in harsh environment.     

Improved electromagnetic absorbing properties of Si3N4–SiC/SiO2 composite ceramics with multi-shell microstructure

Porous Si₃N₄–SiC composite ceramic was fabricated by infiltrating SiC coating with nano-scale crystals into porous β-Si₃N₄ ceramic via chemical vapor infiltration (CVI). Silica (SiO₂) film was formed on the surface of rod-like Si₃N₄–SiC grains during oxidation at 1100 °C in air. The as-received Si₃N₄–SiC/SiO₂ composite ceramic attains a multi-shell microstructure, and exhibits reduced impedance mismatch, leading to excellent electromagnetic (EM) absorbing properties. The Si₃N₄–SiC/SiO₂ fabricated by oxidation of Si₃N₄–SiC for 10 h in air can achieve a reflection loss of ?30 dB (>99.9% absorption) at 8.7 GHz when the sample thickness is 3.8 mm. When the sample thickness is 3.5 mm, reflection loss of Si₃N₄–SiC/SiO₂ is lower than ?10 dB (>90% absorption) in the frequency range 8.3–12.4 GHz, the effective absorption bandwidth is 4.1 GHz.     

In-situ synthesis of ternary layered Y3Si2C2 ceramic on silicon carbide fiber for enhanced electromagnetic wave absorption

A novel ternary layered ceramic of Y₃Si₂C₂ was successfully in-situ synthesized on the surface of home-made third-generation KD-SA SiC fiber for the first time by molten salt method aimed at improving the electromagnetic wave (EMW) absorption. After in-situ synthesis of Y₃Si₂C₂ ceramic layer on SiC fiber (SiC_f/Y₃Si₂C₂), significantly improved EMW absorption performance was obtained. The minimum reflection loss (RL_min) of ?16.97 dB was reached in SiC_f/Y₃Si₂C₂ composites at the thickness of only 2.19 mm, and the effective absorption bandwidth (EAB) was up to 5.44 GHz (12.56–18 GHz) at a thin thickness of 2.64 mm. The improvement in EMW absorption of SiC_f/Y₃Si₂C₂ is mainly attributed to enhanced dielectric loss and conduction loss resulting from increased heterogeneous interfaces and multiple reflections and scattering originating from net structure. The SiC_f/Y₃Si₂C₂ could be a promising EMW absorber for application in high-performance EMW absorbing materials.     

Microstructure and enhanced electromagnetic wave absorbing performance of Zn0.6Ni0.3Cu0.1Fe2O4 ferrite glass-ceramic

Here we introduce a controllable route for the efficient synthesis of Zn_0.6Ni_0.3Cu_0.1Fe₂O₄ ferrite glass-ceramic with enhanced electromagnetic wave (EMW) absorbing performance. By adding a certain amount of Zn, Ni, Cu and Fe oxides into the SiO₂–Al₂O₃–B₂O₃–CaO-R₂O glass system, the microstructure of three-dimensional dendritic ferrites combined with amorphous SiO₂-rich phase is constructed through a high-temperature melt and quenching route. The good EMW absorption performance is attributed to the unique combination of amorphous glass and spinel ferrite, which improves the impedance matching of the material and absorbs EMW by the dielectric loss and magnetic loss. Moreover, the dendritic ferrite crystal phase is compounded with the SiO₂-rich amorphous phase to form grain boundaries and crystal-amorphous interfaces, which enhances the interfacial polarization and builds multiple transmission-absorption mechanisms. The results show that the reflection loss peak value of the glass-ceramics containing 60 wt% Zn_0.6Ni_0.3Cu_0.1Fe₂O₄ spinel is ?42.16 dB with the sample thickness of 2 mm, and the effective absorption band range (reflection loss ≤ -10 dB) is 3.76 GHz (13.6–17.36 GHz) at 1.5 mm. This approach presents a scalable and low-cost solution that may be applied to the design of high-efficiency EMW consumption components in the future.     

Lightweight and resilient SiOC/SiC foam with efficient electromagnetic wave absorption and high-temperature stability

Integrating multiple functions such as high electromagnetic (EM) wave absorption, thermal insulation, and resilience into one material is critical, especially for applications in harsh environment. SiC ceramic has received considerable attention as high-temperature wave absorber, but its applications are limited by common wave absorption performance and brittleness of ceramics. Here by incorporating SiO₂ with SiC in a unique three-dimensional network structure, SiOC/SiC foam consisting of abundant SiOC thin flakes interconnected by numerous long interweaving SiC nanowires have been prepared. The foam shows high EM wave absorption with minimum reflection loss of −30.23 dB, broad effective absorption bandwidth of 5.4 GHz, and a nearly complete compressive resilience from 10% strain. Besides, the foam displays high-temperature resistance up to 1400°C in air and good thermal insulation performance. Such multifunctional material is promising for applications in advanced aerospace industry under extreme conditions.     

Simultaneously enhancing mechanical and microwave absorption properties of Cf/SiC composites via SiC nanowires additions

C_f/SiC composite is an excellent structural and functional material, silicon carbide nanowires (SiCnws) are not only a toughening material but also a great application in the field of microwave absorption. In this study, SiCnws are grown on the surface of carbon fiber (C_f) by polymer impregnation and pyrolysis, and the SiC matrix was prepared by chemical vapor osmosis method. The SiCnws are introduced to enhance the mechanical and microwave absorption properties simultaneously. After 3 impregnations, the flexural strength of the composite was 107.35 ± 10 MPa. When the thickness is 1.86 mm, the minimum reflection loss value is ?41.08 dB, and the effective absorption bandwidth (RL ≤ ?10 dB) is 3.86 GHz. Furthermore, the microwave absorption mechanism of the material is discussed. This work provides a new method to prepare lightweight, stable and high-performance microwave absorption materials, and these materials are expected to be used in high temperature environments.