Porous SiCN(Ti) composite ceramics with good microwave absorbing performance were fabricated by pyrolysis of solid polysilazane modified by tetrabutyl titanate. The introduction of Ti not only acted as active filler to react with free carbon in the matrix to form TiC, but also played the role as catalyst to promote the formation of SiC nanowires. Finally, SiCN(Ti) composite ceramics formed a microstructure containing multi-nanophases and multi-nano heterogeneous interfaces when annealing temperature reached 1500 °C. The complex microstructure annealed at 1500 °C made composite ceramics have good matching impedance, as well as greatly increase the interfacial polarization loss and dipole polarization loss. As a result, the TiC/SiC/SiCN composite ceramics showed the excellent performance of electromagnetic wave absorption in X band. The minimum reflection loss (RL) of samples was ??17.1 dB at the thickness of 1.9 mm, and the maximum effective absorption bandwidth (EAB) of composite ceramics was 3.2 GHz when the thickness of sample was 2.1 mm, which exhibited a promising prospect as a structural and microwave absorbing integration material.
It is a focus of electromagnetic wave-absorbing materials to control the microscopic appearance and structure design of materials to achieve good absorbing performance. Herein, we synthesized the bamboo-like β-SiC whiskers with numerous stacking faults using bamboo pulp paper. The results show that the bamboo-like β-SiC whiskers stacking faults are mostly concentrated at the bamboo nodes of the whiskers which had a significant impact on conductive and polarization losses. The composite with β-SiC whiskers/paraffin mass ratio of 0.5 shows good EM wave absorption capacity with a minimum reflection loss (RLmin) of ? 46.62 dB at 2.35 mm, and the effective absorption bandwidth (EAB) is 3.4 GHz (8.3–11.7 GHz) at 2.50 mm. The conductance loss, dipole polarization, polarization relaxation loss, and interfacial polarization induced by the bamboo-like structure are the major factors to improve its microwave absorption performance. This work provides a new idea for designing biomass-derived materials for excellent microwave absorbers.
Advanced carbon materials are constantly being used in the field of microwave absorption. Herein, in order to enrich the variety and expand the application fields of graphdiyne (GDY), the wrinkled graphene (RGO) nanosheet coated and embedded with GDY porous microspheres (RGO/GDY) are prepared by GDY synthesis, ultrasonic spray, and pyrolysis. The study finds that RGO and GDY have effective synergistic effects. The suitable pores and composition, conductive network formed by overlapping 0D and 2D materials, special surface and internal morphology design, and high-temperature activation process make RGO/GDY exhibit excellent impedance matching and attenuation capabilities. Under the best amount of GDY (20 mg), the particle sizes of the microspheres (≈6 µm), and filler content (27.5%), the minimum reflection loss (RLmin) is −58 dB@8.3 GHz, and the corresponding matching thickness is 2.7 mm. The effective absorption bandwidth is 4.3 GHz as the thickness is 1.9 mm. By adjusting the thickness, the absorber can completely absorb microwaves of all the C, X, and Ku bands. The microwave absorbing mechanisms are elucidated. GDY materials are first applied to the field of microwave absorption, enhancing the absorption performance of RGO/GDY. It provides a new way to manufacture electromagnetic wave absorbers with satisfactory performance. 相似文献
CeO2/Co/C dodecahedrons composites with excellent microwave absorption performance were synthesized by using a hydrothermal method. ZIF-67/CeO2 was first prepared by introducing CeO2 into the precursor of ZIF-67 and then CeO2/Co/C composite was obtained after heat treatment. Impedance matching of the samples could be well adjusted by controlling the content of CeO2. Unique dodecahedral structure for more interfacial reflection and cerium dioxide oxygen vacancies enhance microwave absorption performance. Specifically, the CeO2/Co/C exhibited a minimum reflection loss of ?68.83 dB is observed at 5.92 GHz, while the thickness was 3.69 mm. The introduction of CeO2 effectively enhanced the impedance matching of the materials and improved the microwave absorption performance. Therefore, this CeO2/Co/C composite is a promising microwave absorber material with high performance. 相似文献
In the present study, Microwave absorbing Li-Sr, Li-Co ferrite nanoparticles and RGO/Li-Sr, RGO/Li-Co ferrite nanocomposites containing Li ferrite and reduced graphene oxide (RGO) were synthesized to further improve the microwave absorption performance of Li ferrite nanoparticles (LiFe5O8). The Li-Sr and Li-Co nanoparticles were synthesized by thermal treatment method, the RGO/Li-Sr and RGO/Li-Co nanocomposites were obtained by a polymerization method and were characterized by different techniques. The electromagnetic wave absorption properties of the samples were evaluated by vector network analyzer (VNA) in the frequency range of 2–18 GHz. The magnetic and dielectric loss, impedance matching, and electromagnetic wave absorption of the samples are significantly improved through the addition of RGO. Experimental results revealed that the RGO/Li-Co nanocomposite considerably increased microwave absorption. The minimum reflection loss (RL) of RGO/Li-Co also was found to reach −46.80 dB at the thickness of 3 mm and the effective absorption bandwidth (≤-10 dB) amounted to 6.80 GHz (from 10.52 to 17.32 GHz), which was much higher in comparison with pure Li and Li-Co ferrites nanoparticles. Due to the synergistic effect between magnetic loss and dielectric loss and the good impedance matching, the RGO/Li-Co nanocomposite may be regarded as a new candidate for microwave absorbing materials characterized with a broad effective absorption bandwidth at thin thicknesses. 相似文献
In this work, we studied the preparation and microwave absorption properties of D-xylose-derived carbon materials modified by CuFe2O4 nanoparticles and discussed the influence of the addition amount of carbon materials. It was prepared with a simple hydrothermal method, and various methods are used to characterize its microscopic morphology, chemical structure and microwave absorption properties.Results show that the modification of copper ferrite nanoparticles is effective in mitigating polarization and magnetic losses, enhancing the microwave absorption properties of the samples and absorption curves of the composite materials change from a single peak to double peaks. Comparing all samples it can be concluded that the effective absorption bandwidth of CuFe2O4 composite materials containing carbon microspheres (CuFe2O4/CMs-0.3) is 6.24 GHz. The minimum reflection loss (RL) is???50.4 dB at 14.64 GHz. The thickness of the above corresponds to 2.5 mm. This work not only provides a reference method for the preparation of microwave absorbing materials but also contributes to the understanding of absorption mechanisms.
Magnetic metals are vital microwave absorbing materials, while they face the problems of a large density and relatively narrow absorption band in practical microwave absorption applications. The combination of magnetic metals with carbon materials can effectively ameliorate the electromagnetic (EM) parameters to resolve these the problems to a certain extent. In this study, we successfully fabricated the N-doped Co/graphite C (Co/NC) composites via directly calcining a dry mixture of Co powders and melamine in an Ar atmosphere. This method is simple and low cost. The effects of the variation in the phase composition and morphology on EM parameters and the microwave absorbing property were investigated. The graphite C content in Co/NC was relatively larger than Co content. Thus, the contribution of the dielectric loss to EM energy dissipation was more than that of the magnetic loss. Compared to pure Co, the Co/NC composites exhibit superior EM wave absorbency and are easier to realize strong absorption and lightweight. A minimum reflection loss of???41.45 dB was obtained at 3.84 GHz. The effective absorbing bandwidth (EABW, RL?≤????10 dB) reached 14.80 GHz (3.20?18.00 GHz) at a coating thickness d of 1.54?5.00 mm. The maximum EABW was as large as 5.50 GHz at only 1.54 mm thick. The main reasons for the enhanced EM wave absorption performance of Co/NC were the well impedance matching and strong attenuation capability (interfacial and dipolar polarization, conduction loss, magnetic loss, and microwave multiple scattering and reflections on rough surfaces). Our study can provide a simple guideline for preparing other light carbon-based magnetic metal composites.
Graphical abstract
The Co/NC composites with melamine as C and N source more favor for realization of strong absorption and lightweight compared to Co.
With the increasing demand for microwave absorbing materials, to develop a microwave absorber with a simple synthesis process is of great significance to the field of protection. Herein we have successfully loaded iron-cobalt-nickel oxide (FeCoNiOx) onto the as-prepared polydopamine-reduced graphene oxide (PDA-rGO) through a two-step process. The preparation method has mild reaction conditions without high temperature and pressure compared with the traditional method, which is conducive to large-scale production. Based on effectively combining dielectric loss and magnetic loss mechanism, the obtained material possesses excellent electromagnetic waves absorbing performance with the minimum RL value of ?36.28 dB. The results proved that the composites can be endowed with various microwave absorption effects by the adjustion of different component ratios. In addition, the microwave absorption mechanism was dicussed in detail, and we believe that the results of our research have certain guiding significance for preparation of efficient microwave absorbers. 相似文献
The greigite (Fe3S4)/reduced graphene oxide (RGO) hierarchical structural composites (F–R) with the Fe3S4 nanoparticles attached to the RGO layers were successfully prepared via a simple one-pot solvothermal method. The microwave absorption properties were evaluated by calculating the reflection loss (RL) values. The results show that the RGO content and the filler loading of composites in paraffin mixture are very critical to the microwave absorption properties because they can improve the electromagnetic parameters. Sample F–R-3 presents the best microwave absorption capacity, in which an optimum RL value of ??62.3 dB and an effective absorption bandwidth (EAB, RL value?<???10 dB) of 3.04 GHz (14.96–18 GHz) can be obtained when the matching thickness is only 1.29 mm. Meanwhile, the widest EAB reaches 4.08 GHz (13.92–18 GHz) at the matching thickness of only 1.37 mm. Impressively, when the matching thickness is in the range of 1.2–5.5 mm, all RL peaks are below ??20 dB, and the EAB can be 14.98 GHz (3.02–18 GHz), covering the whole C, X and Ku bands. The distinguished absorption property is mainly ascribed to the combined effect of strong loss ability and good impedance matching. Apparently, the F–R composite with strong absorption ability, thin thickness and wide EAB is suitable for the efficient microwave absorber.
The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M–SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M–SAs. However, the simultaneous engineering of the morphology and electronic structure of M–SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co–SAs on N-doped hollow carbon spheres (NHCS@Co–SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co–SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8 wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co–SAs are up to −44.96 dB and 5.25 GHz, respectively, while the absorbing thickness is only 2 mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M–SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co–SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers. 相似文献
Ti3C2Tx MXenes and their composites play a vital role in the research on microwave absorbing materials. Herein, the different interlamellar spaces of Ti3C2Tx MXene materials were prepared by an etching process. The dependence of the microwave absorbing properties of the Ti3C2Tx MXene nanosheets on different interlamellar spaces was studied. The complex permittivity, dielectric loss, impedance matching characteristic and the minimum reflection loss (RL) value with the variation in interlamellar space were systematically investigated. Results showed that 40% ratio paraffin-bonded composites (S3) have a strong electromagnetic wave absorption performance and large effective absorbing bandwidth. The maximum RL reaches −36.3 dB at 4.67 GHz with the thickness of 4.5 mm, ascribed to its a high dielectric loss and good impedance matching characteristics. The RL value of Ti3C2Tx MXenes is strongly dependent on the inter-lamellar space. The enhanced microwave absorption originates from the unique 2-D structure, good impedance matching characteristics, and enhanced space-charge polarization effects. This work provides a new avenue for exploring high-performance microwave absorbers based on MXene materials. 相似文献
Electromagnetic wave (EMW) absorbing materials play a vital role in modern communication and information processing technologies to inhibit information leakage and prevent possible damages to environment and human bodies.Currently,most of EMW absorbing materials are either composites of two or more phases or in the form of nanosheets,nanowires or nanofibers in order to enhance the EMW absorption performance through dielectric loss,magnetic loss and dielectric/magnetic loss coupling.However,the combination of complex shapes/multi phases and nanosizes may compound the difficulties of materials processing,composition and interfaces control as well as performance maintenance during service.Thus,searching for single phase materials with good stability and superior EMW absorbing properties is appealing.To achieve this goal,the EMW absorbing properties of transition metal carbides TMCs (TM=Ti,Zr,Hf,Nb and Ta) and high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C which belong to ultrahigh temperature ceramics,were investigated in this work.Due to the good electrical conductivity and splitting ofd orbitals into lower energy t2g level and higher energy eg level in TMC6 octahedral arrangement,TMCs (TM=Ti,Zr,Hf,Nb and Ta) exhibit good EMW absorbing properties.Especially,HfC and TaC exhibit superior EMW absorbing properties.The minimum reflection loss (RLmin) value of HfC is -55.8 dB at 6.0 GHz with the thickness of 3.8 mm and the effective absorption bandwidth (EAB) is 6.0 GHz from 12.0 to 18.0 GHz at thickness of 1.9 mm;the RLmin value of TaC reaches-41.1 dB at 16.2 GHz with a thickness of 2.0 mm and the EAB is 6.1 GHz with a thickness of 2.2 mm.Intriguingly,the electromagnetic parameters,i.e.,complex permittivity and permeability are tunable by forming single phase solid solution or high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C.The RLmin value of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C is -38.5 dB at 9.5 GHz with the thickness of 1.9 mm,and the EAB is 2.3 GHz (from 11.3 to 13.6 GHz) atthickness of 1.5 mm.The significance of this work is that it opens a new window to design single phase high performance EMW absorbing materials by dielectric/magnetic loss coupling through tuning the conductivity and crystal field splitting energy of d orbitals of transition metals in carbides,nitrides and possibly borides. 相似文献
In this paper, CaMnO3 and Ca0.97La (or Ti)0.03MnO3 powders were synthesized using mechanical ball milling technique and sintered at 1100°C for 12 h in an air atmosphere. Results showed that all the samples are single phase with an orthorhombic symmetry. Compared with the pure CaMnO3 sample, the Ca0.97La0.03MnO3 and Ca0.97Ti0.03MnO3 samples have higher complex permittivity and better microwave absorbing properties. These changes are caused by the doping-ion incorporating in CaMnO3 lattice and Ca vacancies, which could result in abundant dipoles and the local charge accumulation. The Ca0.97Ti0.03MnO3 sample exhibited the best microwave absorption performance, i.e. the minimum reflection loss was -46.9 dB with a matching thickness of 2.2 mm and effective absorption bandwidth reached 5.2 GHz with a thickness of only 1.8 mm. This study demonstrates that the CaMnO3 would be a potential material in the microwave absorbing field and needs further research.
Lightweight and highly efficient electromagnetic absorptions are crucial for microwave absorption materials due to the fast development of information technology. Bio-derived carbon materials are ideal resistance loss-type microwave absorbers with lightweight. A honey-comb carbon structure has been obtained from peach gum by facile hydrothermal and pyrolysis processes. The skeleton of the as-derived honey-comb carbon structure is composed of carbon nanoparticles with diameters around 40 nm. The honey-comb structures were further carbonized at 850 °C (NPG-850) to have a large specific surface area of 1401.7 m2 g?1 with an average pore diameter of 3.2 nm. A minimum reflection loss (RL) of???59.4 dB was obtained by NPG-850 at a thickness of 2.0 mm with an effective absorption bandwidth (EAB, RL?<????10 dB) of 4.1 GHz (14.7–10.6 GHz). The RL value of the peach gum-derived honey-comb carbon nanostructures is much higher than the reported carbon nanostructures even with thinner thickness and less mass loading, which might due to the multi-reflection effect of the honey-comb structures and the skeleton composition.
A cobaltosic-oxide-nanosheets/reduced-graphene-oxide composite (CoNSs@RGO) was successfully prepared as a light-weight broadband electromagnetic wave absorber.The effects of the sample thickness and amount of composite added to paraffin samples on the absorption properties were thoroughly investigated.Due to the nanosheet-like structure of Co3O4,the surface-to-volume ratio of the wave absorption material was very high,resulting in a large enhancement in the absorption properties.The maximum refection loss of the CoNSs@RGO composite was-45.15 dB for a thickness of 3.6 mm,and the best absorption bandwidth with a reflection loss below-10 dB was 7.14 GHz with a thickness of 2.9 mm.In addition,the peaks of microwave absorption shifted towards the low frequency region with increasing thickness of the absorbing coatings.The mechanism of electromagnetic wave absorption was attributed to impedance matching of CoNSs@RGO as well as the dielectric relaxation and polarization of RGO.Compared to previously reported absorbing materials,CoNSs@RGO showed better performance as a lightweight and highly efficient absorbing material for application in the high frequency band. 相似文献
Fe3O4-reduced graphene oxide-polyaniline (Fe3O4–RGO–PANI) ternary electromagnetic wave absorbing materials were prepared by in situ polymerization of aniline monomer on the surface of Fe3O4–RGO nanocomposites. The morphology, structure and other physical properties of the nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, vibration sample magnetism, etc. The electromagnetic wave absorbing properties of composite materials were measured by using a vector network analyzer. The PANI–Fe3O4–RGO nanocomposites demonstrated that the maximum reflection loss was ?36.5 dB at 7.4 GHz with a thickness of 4.5 mm and the absorption bandwidth with the reflection loss below ?10 dB was up to 12.0 GHz with a thickness in the range of 2.5–5.0 mm, suggesting that the microwave absorption properties and the absorption bandwidth were greatly enhanced by coating with polyaniline (PANI). The strong absorption characteristics of PANI–Fe3O4–RGO ternary composites indicated their potential application as the electromagnetic wave absorbing material. 相似文献
Multi-walled carbon nanotube buckypaper (BP) reinforced glass fiber–epoxy (GF/EP) composites were selected to fabricate electromagnetic interference (EMI) shielding and microwave absorbing materials. Six different composite configurations with 3.0 mm thick have been conceived and tested over the X-band (8.2–12.4 GHz). Flexible and low-density (0.29 g/cm3) BP provided a high specific EMI SE of 76 dB with controlled electrical conductivity. GF/EP/BP111 and GF/EP/BP101 composites possess EMI SE as high as of 50–60 dB, which can be attributed to the number of BP inserted and variation in the wave-transmitting layer of the laminates. Furthermore, the shielding mechanism was discussed and suggested that the absorption was the dominant contribution to EMI SE. GF/EP/BP110 laminate demonstrated suitable EMI performance (~?20 dB), whereas GF/EP/BP011 composite revealed excellent microwave performance, achieving an effective ? 10 dB bandwidth of 3.04 GHz and minimum reflection loss (RL) value of ? 21.16 dB at 10.37 GHz. On the basis of these results, GF/EP/BP composites prepared in this work have potential applications as both EMI shielding and microwave absorber materials given their facile preparation and lightweight use.