Dielectric and microwave absorption properties of CB doped SiO2f/PI double-layer composites

Carbon black (CB) with contents of 5.5?wt% and 15?wt% filled quartz glass fiber reinforced polyimide (SiO_2f/PI) composite were designed and prepared. A double-layer absorbing material was designed using the two composites materials as a matching layer and an absorption layer, respectively. The microwave absorption property of single-layer and double-layer composites is calculated according to transmission line theory. The results show that the microwave absorbing property of double-layer composite is better than that of single-layer at the same thickness. When the 5.5?wt%CB doped SiO_2f/PI composite is used as the matching layer with a thickness of 0.7?mm and 15?wt%CB doped SiO_2f/PI composite is used as the absorption layer with a thickness of 0.9?mm, the RL (reflection loss) of the composite reaches a minimum value of ?46.18?dB at 16.07?GHz. Meanwhile, the bandwidth of RL?≤??5?dB is 5.87?GHz and the bandwidth of RL?≤??10?dB is 3.95?GHz.     

Enhanced microwave absorbing properties of lightweight films based on polyaniline/aliphatic polyurethane composites in X band

Polymer blends based on nanostructured polyaniline (PANI) doped with hydrochloric acid (HCl) and para‐toluene sulfonic acid (PTSA) introduced into aliphatic polyurethane matrix (PU) are synthesized to produce flexible thin composite films for microwave absorbers. The effects of dopant type, PANI content and film thickness on morphologies, dielectric and microwave absorption properties in the X‐band are studied. It reveals that real and imaginary parts of the complex permittivity are proportional to filler concentrations and type of doped PANI. The PANI‐PTSA/PU films show higher permittivity and better microwave absorbing properties than PANI‐HCl/PU for the same weight fraction of PANI. The minimum reflection loss RL_(dB) values for the PANI‐PTSA/PU are ?37 dB at (20% PANI and 11.6 GHz) and ?30 dB at (15% PANI and 11.3 GHz) for thicknesses of 1.2 and 1.6 mm, respectively. These high values of reflection losses make the obtained lightweight and flexible composites promising radar absorbing materials (RAM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40961.     

Synthesis and microwave absorbing characteristics of flake‐like polypyrrole filled composites in X‐band

Polypyrrole (PPy)/montmorillonite (MMT) nanocompounds were prepared by in situ chemical oxidative polymerization of pyrrole in the presence of MMT. The results indicate PPy is intercalated into MMT interlayers and the morphology of obtained PPy in nanocompounds is changed to flake‐like rather than granular particles as pristine PPy. The resultant PPy/MMT nanocompounds and pristine PPy were used as microwave absorbing filler separately to prepare microwave absorbing PPy/MMT and PPy epoxy composites. The results indicate PPy/MMT epoxy composites exhibit much better microwave absorbing properties than those filled by pristine PPy. The maximum reflection loss of 20 wt% PPy/MMT filled composite is −32.63 dB at 10.55 GHz with a matching thickness of 2.8 mm, and the effective absorption bandwidth with the reflection loss below −10 dB is from 8.6 GHz to 12.4 GHz, which almost covers the whole X‐band. We postulated that the morphology change of PPy in PPy/MMT and its better dispersion may be responsible for the enhancement of microwave absorption. POLYM. COMPOS., 37:532–538, 2016. © 2014 Society of Plastics Engineers     

Ecofriendly and cost-effective composites of titanium slag and carbonyl iron for lightweight and tunable microwave absorption

For obtaining the ecofriendly microwave absorbing composites, flake carbonyl iron was mixed to the flotation carbon waste of titanium slag by ball-milling processes. The composites of 4 h ball-milling present excellent microwave absorbing performance of minimum reflected loss (RL) of ?54.9 dB at 7.8 GHz with thickness of 2.6 mm. The same composites provide the performance of RL < ?10 dB with the thickness from 1.2 mm to 5 mm at corresponding matching frequency from 3.3 GHz to 18 GHz. It means that the absorbing peak can be tunable at the wide frequency range with only adjusting the thickness. The strong absorbing intensity and wide tunable frequency range are attributed to the proper impedance matching of dielectric property from flotation carbon waste of titanium slag and magnetic property from carbonyl iron. Also, this work provides a research approach for handling industrial waste which contains carbon.     

Facile synthesis of coral cauliflower-like polypyrrole hemispheres toward screening electromagnetic interference pollution

In this study, coral cauliflower-like polypyrrole (PPy) hemispheres are synthesized on an alumina substrate via a simple chemical oxidative polymerization route. The stony coral-like morphology of PPy hemispheres acts as a conducting trap in absorbing electromagnetic (EM) radiation via multiple internal reflections. A PPy thin film deposited at 0.2 M pyrrole concentration shows a minimum reflection loss (RL) of −30.80 dB (99.9% microwave absorption) at the frequency of 14.2 GHz, and the highest total shielding effectiveness achieved is −18.3 dB at 16.8 GHz at 4.38 μm film thickness. The thin films exhibit excellent microwave absorption ability at low thicknesses, and the effective absorption bandwidth (RL < –10 dB) attains a high value of 2.2 GHz in the frequency range of 13–15.2 GHz. These findings can help researchers to enhance the EM wave absorption characteristics in a broad frequency region using lightweight intrinsically conducting polymers.     

Preparation and investigation of structural,magnetic, and microwave absorption properties of aluminum‐doped strontium ferrite/MWCNT/polyaniline nanocomposite at KU‐band frequency

Aluminum‐doped strontium hexaferrite nanoparticle SrAl_1.3Fe_10.7O₁₉ was prepared by sol–gel method and polyaniline (PANi) multiphase magnetic nanocomposite SrAl_1.3Fe_10.7O₁₉/MWCNT/PANi was synthesized through a sonochemical method by in situ polymerization. The morphology, structure, and magnetic properties of the nanocomposites are investigated by field emission scanning electron microscopy, X‐ray powder diffraction, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. The electromagnetic interference shielding efficiency was evaluated in the KU‐band (12.4–18 GHz). The reflection loss (RL) value showed that the composites have an excellent absorbing property in the KU‐band, minimum ?24.93 dB at 16.40 GHz with a bandwidth of 2.81 GHz (shielding effectiveness up to 10 dB) at a matching thickness 6.5 mm. The RL value of the SrAl_1.3Fe_10.7O₁₉/MWCNT nanocomposite was ?15.92 dB at 15.84 GHz with a bandwidth of 1.66 GHz (with a shielding effectiveness up to 10 dB). These results disclose the remarkable microwave shielding ability of SrAl_1.3Fe_10.7O₁₉/MWCNT/PANi in KU‐band due to the interactive effect of the three components. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45135.     

Three-dimensional architecture of absorbers for enhancement of the absorbing properties of MWNTs

The microwave absorbers, which can attenuate and dissipate the incident electromagnetic wave, have attracted much more attentions due to their great potential applications in military stealth and civil healthcare. In this study, the three-dimensional (3D) architecture absorber of multiwalled carbon nanotubes@polystyrene (MWNTs@PS) was designed and synthesized by the combination of PS microspheres with MWNTs via self-assembly of electrostatic adsorption. The morphology and dispersity of absorbers were characterized via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The aim of this study is to explore the influence of the 3D architecture of absorbers on the enhanced absorbing performance of MWNTs. The results of SEM and TEM demonstrated that 3D architecture constructed via MWNTs attaching on the surface of PS microspheres were established, which is in favor for MWNTs to build more electron transportation pathways and enhance the multiinterface polarization. Compared with one-dimensional (1D) absorbers of PS/MWNTs, the 3D MWNTs@PS exhibited excellent absorbing properties, the maximum reflection loss (RL) was −34.2 dB at 10.6 GHz with a thickness of 2.00 mm and the frequency bandwidth of RL below −10 dB (90% absorption) was 3.0 GHz. In contrast, the maximum RL of 1D PS/MWNTs and pristine MWNTs were −19.1 dB at 11.5 GHz and −7.7 dB at 8.8 GHz, respectively. The results implied that the construction of 3D architecture has crucial influence on the enhanced absorbing performance of MWNTs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47566.     

Ionic liquids as dispersing agents of graphene nanoplatelets in poly(methyl methacrylate) composites with microwave absorbing properties

Graphene nanoplatelets (GNP) is noncovalently functionalized with imidazolium-, pyridinium-, and vinyl-pyridinium-based ionic liquids containing bromide or bis(trifluoromethyl-sulfonyl)imide (TFSI) as the counteranions, and used to prepare poly (methyl methacrylate) (PMMA) nanocomposites by solution casting approach followed by compression molding technique. The PMMA composites loaded with 1.9 and 1.8 wt% of GNP in PMMA/GNP composite and PMMA/GNP/ionic liquids, respectively, were characterized by melting viscosity, thermogravimetric analysis and AC electrical conductivity (σ_AC). The microwave absorption properties at the X-band (8.2–12.4 GHz) frequency were measured for systems with 1 mm thickness using the metal-backed configuration. PMMA nanocomposites loaded with GNP/N-dodecyl-4-vinyl-pyridinium.TFSI (C₁₂ViPy.TFSI) displayed higher thermal stability and higher σ_AC. This system also presented the best response in terms of microwave absorbing properties, with minimum reflection loss (RL) of around −6 dB at 8.7 GHz. Triple layered composite structures with layers of different conductivities and different stacking orders were also investigated in terms of reflection loss. Broadband absorption with minimum RL ≤ −10 dB (90% of electromagnetic attenuation) in the frequency between 10.2 and 12.4 GHz and better absorbing effectiveness were observed for the PMMA/GNP-PMMA/GNP/C₁₂ViPy.TFSI-PMMA/GNP/C₁₂ViPy.Br triple-layered system with 3 mm thickness.     

导电聚苯胺的合成及电磁学性能、吸波性能研究

分别采用溶液聚合、乳液聚合、正相和反相微乳液聚合法合成了不同掺杂、不同电导率(电导率范围10^-5-10S／cm)的聚苯胺，测试了导电聚苯胺的电磁学参数和吸波性能。结果证明：制得的聚苯胺在2～12GHz范围内有较好的吸波性能，在2．12GHz范围内，雷达波反射率绝对值大于10dB的频宽范围大于7．5GHz，最大吸收率达到30dB。     

Magnetically recoverable CoFe1.9Gd0.1O4 ferrite/polyaniline nanocomposite synthesized via green approach for radar band absorption

The gadolinium substituted cobalt ferrite (CoFe_1.9Gd_0.1O₄) nanoparticles and CoFe_1.9Gd_0.1O₄/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe_1.9Gd_0.1O₄ nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe_1.9Gd_0.1O₄ ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe_1.9Gd_0.1O₄ ferrite nanoparticles and CoFe_1.9Gd_0.1O₄/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe_1.9Gd_0.1O₄/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.     

对负离子对氧化石墨烯/聚苯胺电磁性能的影响

以过硫酸铵为引发剂,控制掺杂质子浓度为1 mol/L,分别以Cl–、CSA–(樟脑磺酸根)和SO42–为对负离子,通过原位化学氧化聚合法制备得到掺杂态氧化石墨烯/聚苯胺复合材料.采用SEM、FTIR和XRD对复合材料进行形貌和结构表征,采用四探针法、矢量网络分析仪分别测试复合材料的电磁参数,并计算材料的阻抗和反射损耗(RL).结果表明,3种复合材料均呈现聚苯胺纳米椎体包覆氧化石墨烯片层的三明治形貌.对负离子为SO42–时,复合物的电导率最高为5.500 S/cm,同时介电损耗能力最强.而樟脑磺酸掺杂复合物的驻波比在14.2 GHz处可达到1.1,更接近行波状态,具有最佳阻抗匹配性能.其最佳反射损耗为–30 dB(9.93 GHz,2.75 mm),有效吸波频宽(RL<–10 dB的频率范围)最高可至4.85 GHz(12.30～17.15 GHz,2 mm).     

Electromagnetic and microwave absorption properties of FeSiAl and flaky graphite filled Al2O3 composites with different FeSiAl particle size

The increasing electromagnetic interference problems have drawn much attention to microwave absorbing materials. To satisfy the needs of practical application, FeSiAl and flaky graphite filled Al₂O₃ composites were sintered by hot-pressing for microwave absorption application. The effect of FeSiAl particle size on the electromagnetic and microwave absorption properties was investigated in the X-band (8.2–12.4 GHz). The results show that the dielectric properties enhance significantly with increasing FeSiAl particle size, which is attributed to the increased interfacial polarization and conductance loss. As a result of the favorable impedance matching and appropriate electromagnetic attenuation, the reflection loss (RL) of the composites filled with 25–48 μm flaky FeSiAl achieves -15.2 dB at 10.6 GHz and the effective absorption bandwidth (RL < -10 dB) is 1.2 GHz in 10.0–11.2 GHz with a matching thickness of 1.0 mm. It indicates that FeSiAl and flaky graphite filled Al₂O₃ composites are potential candidates for thin-thickness microwave absorbing materials, and the microwave absorption properties can be enhanced by adjusting absorbent particle size.     

Fabrication of novel polyaniline/flowerlike copper monosulfide composites with enhanced electromagnetic interference shielding effectiveness

Novel polyaniline (PANI)/flowerlike CuS composites with improved electromagnetic interference (EMI) shielding effectiveness (SE) were prepared through the in situ polymerization of PANI into the flowerlike CuS microspheres. X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible optical absorption spectroscopy, thermogravimetric analysis, electrical conductivity testing, and EMI SE testing were used to characterize the as‐obtained products. The results reveal that the flowerlike CuS was uniformly coated by a PANI shell. Most importantly, compared with the original CuS and pure PANI, the novel PANI/flowerlike CuS composites exhibited a remarkably enhanced SE. With a thickness of 3 mm, the optimal EMI SE of the PANI–CuS composites reached ?45.2 dB at 2.78 GHz, and an improved shielding efficiency below ?18 dB was also obtained over the frequency range from 300 kHz to 3 GHz. This suggested that these novel PANI/flowerlike CuS composites have promising applications in the field of shielding materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45232.     

Fabrication of hierarchical PANI@W-type barium hexaferrite composites for highly efficient microwave absorption

Hexagonal barium ferries is a promising and efficient microwave (MW) absorbing material, but the low dielectric loss and poor conductivity have limited their extensive applications. In this work, a simple tactic of coating conductive polymer PANI on hexaferrite BaCo₂Fe₁₆O₂₇ is presented, wherein the dielectric properties are customized, and more significantly, the electromagnetic loss is greatly enhanced. As displayed from structural characterizations, PANI were coated equably on the surface of hexaferrite grains by an in-situ polymerization process. The outcomes exhibit the as-prepared PANI@hexaferrite composite has remarkable electromagnetic wave absorption capacity. When the thickness is 6.0 mm, the minimal RL of ?40.4 dB was achieved at 2.9 GHz. The effective absorption bandwidth (RL < ?20 dB) of 0.65 GHz, 0.53 GHz, 0.65 GHz, 0.52 GHz, 0.46 GHz and 0.39 GHz was achieved separately when the thickness ranges from 4 to 9 mm. The highly efficient MW absorbing performance of PANI@hexaferrite composite were the consequence of multiple loss mechanisms and perfect impedance matching. It is demonstrated that the PANI@hexaferrite composite with excellent MW absorption performance is expected to be potential MW absorbers for extensive applications.     

Effect of preparation conditions on mechanical,dielectric and microwave absorption properties of SiC fiber/mullite matrix composite

Silicon carbide fiber-reinforced mullite matrix (SiC_f/Mu) composites were fabricated via an infiltration and sintering method. Effects of sintering parameters on microstructure, mechanical, dielectric and microwave absorption properties of SiC_f/Mu composites have been investigated. The flexural strength is significantly improved with increasing sintering temperature, and the highest flexural strength of 213?MPa is obtained in vacuum at 1000?°C for 2?h. The performances of composites with different holding time are further studied at 1000?°C. The flexural strengths of composites sintered at 1000?°C for 2 and 4?h reach 213 and 219?MPa, respectively. The failure displacement of the composite sintered at 1000?°C for 4?h reaches 0.39?mm. The excellent microwave absorption properties are achieved for the composite sintered at 1000?°C for 2?h. The minimum reflection loss (RL) reaches ?38?dB with a thickness of 2.9?mm?at 12?GHz and the effective absorbing bandwidth (RL?≤??10?dB) with a thickness of 3.4?mm covers the whole X?band, which indicate that SiC_f/Mu composite is a good candidate for microwave absorbing materials. These results provide valuable solutions to obtaining structural-functional materials for microwave absorption applications in civil and military areas.     

Fabrication of carbon-doped ZnCo2O4 yolk-shell microspheres compounded with magnetic graphene for enhanced electromagnetic wave absorption performance

Carbon-doped ZnCo₂O₄ (ZnCo₂O₄/C) yolk-shell microspheres are synthesized by a method of thermally decomposing precursor and then successfully compounded with magnetic graphene (MG) via co-precipitation in combination with a reduction pathway. The fabrication processes and characterizations (XRD, XPS, TEM, EDS and SEM) are described and explained in detail. It is confirmed that amorphous carbon (in situ decomposition from PVP) is uniformly doped into ZnCo₂O₄ yolk-shell microspheres. In addition, the reflection loss (RL) and electromagnetic (EM) wave absorption mechanisms of as-prepared ZnCo₂O₄/C/MG composites are calculated and analyzed exhaustively. The results show that absorption bandwidth with RL exceeding −10 dB reaches up to 4.48 GHz with a matching thickness of 3.5 mm while the maximum RL is up to −52.9 dB at 7.52 GHz with a matching thickness of 3.9 mm. Enhanced EM wave absorption performance can be attributed to good dielectric and magnetic loss, excellent impedance matching, diverse interfacial polarization and multiple reflections caused by special structures.     

High temperature microwave absorbing properties of plasma sprayed La0.6Sr0.4FeO3-δ/MgAl2O4 composite ceramic coatings

Microwave absorbing materials (MAM) which can be used in high temperature and oxidation environments are strongly demanded in application, for conventional MAM fail due to various factors at high temperature. In this work, ceramic coatings composed of La_0.6Sr_0.4FeO_3-δ and MgAl₂O₄ have been successfully prepared via atmospheric plasma spraying and the microwave absorbing properties at high temperature are first reported. When the coatings of LSF/MAS matched with the metal substrate on thermal expansion, they can be treated repeatedly in the temperature range of 300 K–1173 K without peeling off. Meantime, the ceramic coatings with thickness of 1.5 mm showed considerable microwave absorption in the range of 8 GHz–18 GHz at high temperatures between 673 K–1173 K. The absorption bandwidth of LSF30 was 3.5 GHz for RL < −10 dB and 8 GHz for RL < −5 dB in the temperature range of 673 K–1173 K. LSF/MAS possesses the advantages of thin thickness and broad bandwidth at high temperatures, suggesting great potential as MAM in ultra-temperature environment.     

聚苯胺/蒙脱土纳米复合微波吸收材料的制备及表征

以十二烷基苯磺酸(DBSA)作为乳化剂和掺杂剂,通过乳液聚合的方法制备了DBSA掺杂聚苯胺/蒙脱土(PANI/MMT)纳米复合材料,采用X射线衍射仪、傅立叶变换红外光谱仪、四探针电导率仪和矢量网络分析仪进行了初步表征。经测量和计算发现,PANI/MMT纳米复合材料与石蜡质量比为1∶1的2mm厚试样在2~18GHz范围内具有微波吸收性能,在13~14GHz范围内反射损耗小于-10dB,在13GHz处的最大反射损耗为-10.3dB。     

Microwave‐absorbing properties of linear low‐density polyethylene/ethylene–octene copolymer/carbonyl iron powder composites

Using linear low‐density polyethylene (LLDPE)/ethylene–octene copolymer (POE) as a polymer matrix and carbonyl iron powders (CIPs) as filler, we prepared polymer matrix composites with microwave‐absorbing properties by means of melt blending. Scanning electron microscopy and transmission electron microscopy were used to characterize the samples. The absorbing properties of the composites were measured with the arch method in the range of frequency 2.0–18.0 GHz. The results indicate that the absorbing peaks moved to low frequency as the CIP content in composites increased and that there was an appropriate CIP content in LLDPE/POE/CIP composites to achieve the best absorbing effectiveness. The electromagnetic parameters of the composites were determined with the transmission/reflection method in the range 2.6–17.8 GHz. The experimental results show that there were both dielectric loss and magnetic loss in the LLDPE/POE/CIP composites. Therefore, the microwave absorption of the LLDPE/POE/CIP composites was attributed to the combining contributions of the dielectric loss and magnetic loss. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electromagnetic wave absorbing properties of Cr2AlB2 powders and the effect of high-temperature oxidation

The electromagnetic (EM) wave absorbing properties of Cr₂AlB₂ powders and those after high-temperature oxidation were investigated. Coupling of magnetic and dielectric loss enables Cr₂AlB₂ with good absorption properties. The minimum reflection loss (RL) value is −44.9 dB at 8.5 GHz with a thickness of 2.7 mm, and the optimized effective absorption bandwidth (E_AB) is 4.4 GHz (13.0-17.4 GHz) with a thickness of 1.6 mm. After oxidation at 750, 900, and 1000°C for 2 h, the minimum RL values, respectively, are −23.9 dB (17.5 GHz, 1.5 mm), −41.4 dB (16.5 GHz, 1.5 mm), and −39.5 dB (8.0 GHz, 3.0 mm); and the corresponding E_AB values, respectively, are 3.8 GHz (13.6-17.4 GHz, 1.7 mm), 4.1 GHz (13.5-17.6 GHz, 1.6 mm), and 4.4 GHz (13.0-17.4 GHz, 1.7 mm). With an absorber thickness of 1.5-4.0 mm, the E_AB with a RL value of less than −10 dB can be tuned in a broad-frequency range 5.0-18.0 GHz, which basically covers C (4-8 GHz), X (8-12 GHz), and Ku (12-18 GHz) bands. These results demonstrate that Cr₂AlB₂, as a high-efficient and oxidation-resistant absorber, is a promising candidate for microwave absorption applications and can retain good EM wave absorbing properties after high-temperature oxidation.