基于Li0.35Zn0.3Fe2.35O4和碳纳米纤维双层吸波体的结构设计与吸收性能研究

通过静电纺丝技术和热处理制备了Li_0.35Zn_0.3Fe_2.35O₄纳米纤维和碳纳米纤维,并将它们各自均匀分散在硅橡胶基质中,测量了相应复合体在2~18GHz频率范围内的相对复介电常数和复磁导率,并根据传输线理论评估了由它们所构成的单层和双层结构吸波体的微波吸收特性。结果显示由于Li_0.35Zn_0.3Fe_2.35O₄纳米纤维与碳纳米纤维的电磁特性的有机结合,双层吸波体的微波吸收性能明显优于同厚度的单层吸波体。当以厚为1.8mm的Li_0.35Zn_0.3Fe_2.35O₄纳米纤维/硅橡胶复合体为吸收层和厚为0.2mm的碳纳米纤维/硅橡胶复合体为匹配层时,双层吸波体的反射率在13.9GHz达到一个最小值-47.8dB,反射率低于-10dB的吸收带宽为8.8GHz,频率范围为9.2~18GHz,反射率小于-20dB的频率范围为11.5~18GHz,带宽为6.5GHz,覆盖整个Ku波段。优化设计的双层吸波体有望作为一种轻质高效的Ku波段微波吸收材料。     

Nanocomposite based on epoxy and MWCNTs modified with NiFe2O4 nanoparticles as efficient microwave absorbing material

In order to make a microwave absorbent material with good dielectric and magnetic properties, well dispersed microwave absorbing hybrid epoxy polymer composites containing nickel doped Fe₃O₄ nanocrystals coated on carbon nanotubes (NiFe₂O₄‐MWCNTs/epoxy) were synthesized by the combined precipitation‐hydrothermal method in 1‐30 wt.% of nanoparticles. Nickel possess well interaction with microwave radiation and represents fine electromagnetic interference (EMI) shielding and by dopping it into ferrite spinel structures, does not show any tendency to oxidation. Well‐dispersed NiFe₂O₄–MWCNTs/epoxy nanocomposite prepared by new in‐situ polymerization method. First, NiFe₂O₄–MWCNT nanoparticles ultrasonicated in acetone and after mixing with epoxy resin ultrasonicated again. Finally, hardner added to the composite and tuned temperature for evaporating solvent. X‐ray diffraction (XRD) and energy dispersive spectroscopy (EDS) confirmed the synthesizing NiFe₂O₄ nanoparticles. Saturation magnetization value of NiFe₂O₄‐MWCNTs is about 29 emu/g with very low remanence and coercivity content, which revealed that the NiFe₂O₄‐MWCNTs is ferromagnetic nanocrystal. Transmission electron microscopy (TEM) used to characterize the distribution of NiFe₂O₄ nanocrystals on the surface of MWCNTs. The TEM images show that NiFe₂O₄ nanocrystals have a mean size of 12 nm, and completely coated on the exterior surface of MWCNTs. The obtained results of reflection loss revealed that the maximum values of reflection loss of the NiFe₂O₄‐MWCNTs/epoxy increase by enhancing the content of nanoparticles until 10 wt.% and decreases in 30 wt.%.     

基于Li_(0.35)Zn_(0.3)Fe_(2.35)O_4和碳纳米纤维双层吸波体的结构设计与吸收性能研究

通过静电纺丝技术和热处理制备了Li0.35Zn0.3Fe2.35O4纳米纤维和碳纳米纤维,并将它们各自均匀分散在硅橡胶基质中,测量了相应复合体在2~18 GHz频率范围内的相对复介电常数和复磁导率,并根据传输线理论评估了由它们所构成的单层和双层结构吸波体的微波吸收特性。结果显示由于Li0.35Zn0.3Fe2.35O4纳米纤维与碳纳米纤维的电磁特性的有机结合,双层吸波体的微波吸收性能明显优于同厚度的单层吸波体。当以厚为1.8 mm的Li0.35Zn0.3Fe2.35O4纳米纤维/硅橡胶复合体为吸收层和厚为0.2mm的碳纳米纤维/硅橡胶复合体为匹配层时,双层吸波体的反射率在13.9 GHz达到一个最小值-47.8 dB,反射率低于-10 dB的吸收带宽为8.8 GHz,频率范围为9.2~18 GHz,反射率小于-20 dB的频率范围为11.5~18 GHz,带宽为6.5 GHz,覆盖整个Ku波段。优化设计的双层吸波体有望作为一种轻质高效的Ku波段微波吸收材料。     

Synthesis and properties of iron oxide coated carbon nanotubes hybrid materials and their use in epoxy coatings

Multi‐walled carbon nanotubes (MWCNTs) were acidified with nitration mixture, and the Fe₂O₃‐MWCNTs (iron oxide coated multi‐walled carbon nanotubes) hybrid material via sol‐gel method then verified the results through scanning electron microscope, X‐ray diffraction, and thermal gravimetric analysis. We modified the hybrid material with silane coupling agent (KH560), Fe₂O₃‐MWCNTs/epoxy, MWCNTs/epoxy composites coating, and the pure epoxy coatings were respectively prepared. The properties of the composite coatings were tested through the electrochemical workstation (electrochemical impedance spectroscopy), shock experiments, and thermal gravimetric analysis. Finally, we used scanning electron microscope to observe the surface conditions of the coatings. The results show that Fe₂O₃‐MWCNTs have good dispersion in the epoxy resin, and the Fe₂O₃‐MWCNTs/epoxy composite coatings have enhanced mechanical properties and corrosion resistance. Copyright © 2015 John Wiley & Sons, Ltd.     

NZFO-PZT磁电复合纳米纤维的制备及其吸波性能

采用静电纺丝法制备(1-x)Ni_0.5Zn_0.5Fe₂O₄-(x)Pb(Zr_0.52Ti_0.48)O₃(简称为(1-x)NZFO-(x)PZT, x=0.1、0.2、0.3、0.4、0.5)磁电复合纳米纤维, 研究了PZT含量对复合纳米纤维结构、电磁特性及微波吸收性能的影响。所有样品均由尖晶石结构NZFO和钙钛矿结构PZT两相所组成。由于NZFO磁损耗与PZT介电损耗的协同效应及界面效应的加强, 适量PZT相的引入可改善复合纳米纤维吸波涂层的电磁阻抗匹配和衰减特性, 提高微波吸收性能。x=0.3和0.4的复合纳米纤维分别在低频和高频范围表现出最强的微波吸收能力。当涂层厚度为2.5~5.0 mm时, x=0.3样品的最小反射损耗在6.1 GHz处达-77.2 dB, 反射损耗小于-10 dB的有效吸收带宽为11.2 GHz(2.8~12.9和16.9~18 GHz);x=0.4样品的最小反射损耗位于18 GHz处为-37.6 dB, 有效吸收带宽达到12.5 GHz(3.3~12.5和14.7~18 GHz)。     

NZFO-PZT磁电复合纳米纤维的制备及其吸波性能

采用静电纺丝法制备(1-x)Ni_0.5Zn_0.5Fe₂O₄-(x)Pb(Zr_0.52Ti_0.48)O₃(简称为(1-x)NZFO-(x)PZT, x=0.1、0.2、0.3、0.4、0.5)磁电复合纳米纤维, 研究了PZT含量对复合纳米纤维结构、电磁特性及微波吸收性能的影响。所有样品均由尖晶石结构NZFO和钙钛矿结构PZT两相所组成。由于NZFO磁损耗与PZT介电损耗的协同效应及界面效应的加强, 适量PZT相的引入可改善复合纳米纤维吸波涂层的电磁阻抗匹配和衰减特性, 提高微波吸收性能。x=0.3和0.4的复合纳米纤维分别在低频和高频范围表现出最强的微波吸收能力。当涂层厚度为2.5~5.0 mm时, x=0.3样品的最小反射损耗在6.1 GHz处达-77.2 dB, 反射损耗小于-10 dB的有效吸收带宽为11.2 GHz(2.8~12.9和16.9~18 GHz);x=0.4样品的最小反射损耗位于18 GHz处为-37.6 dB, 有效吸收带宽达到12.5 GHz(3.3~12.5和14.7~18 GHz)。     

Facile synthesis of Fe3O4/reduced graphene oxide/polyvinyl pyrrolidone ternary composites and their enhanced microwave absorbing properties

In this paper, ternary nanocomposites of Fe₃O₄/reduced graphene oxide/polyvinyl pyrrolidone (Fe₃O₄/rGO/PVP) as a novel type of electromagnetic microwave absorbing materials were synthesized by a three-step chemical approach. First, Fe₃O₄ nanospheres were made by solvent thermal method. Successively, the Fe₃O₄ particles were assembled with rGO after having activated by para-aminobenzoic acid. PVP grafting and reduction of GO happened simultaneously in the third step. It is found that the electromagnetic absorption (EA) performance of synthesized ternary composites with suitable PVP amount had been significantly enhanced comparing to Fe₃O₄ and Fe₃O₄/rGO. Merely 15?wt% low loading in paraffin and thin as 2.8?mm can reach effective EA bandwidth (below ?10 Db) of 11.2?GHz, and the highest reflection loss reached ?67?dB at 10.7?GHz. It was demonstrated that these composites show an effective route to novel microwave absorbing material design.     

Fabrication,characterization and X-band microwave absorption properties of PAni/Fe3O4/PVA nanofiber composites materials

This work presents a study of microwave absorption properties of PAni/Fe₃O₄/PVA nanofiber composites with different ratio of Fe₃O₄ nanoparticles. The morphology of the composites nanofibers study by Field Emission Scanning Electron Microscopes (FESEM) and Transmission Electron Microscope (TEM) showed that the low content of Fe₃O₄ nanoparticles presence in the composites nanofibers indicates very much uniform surface, in the composites nanofiber without many bends, but some bends develop at higher content of Fe₃O₄ nanoparticles as indicated in the TEM image. Image-J software was used to further investigate the diameter of the composites nanofiber and found to be in the range of 152 to 195 nm. The nanofiber composites show excellent electric and magnetic properties and therefore vary with the addition of Fe₃O₄ nanoparticles in the composites nanofiber. In addition the PAni/Fe₃O₄/PVA composites nanofibers were further characterized by X-ray diffraction spectra (XRD) and Four Transformation infrared spectra (FTIR). The XRD pattern shows the presence of PAni nanotubes containing Fe₃O₄ nanoparticles by indicating peaks at 23.4⁰ and 35.43⁰ which was further supported by FTIR analysis. Microwave vector network analyzers (MVNA) were used to estimate the microwave absorption properties of the composites nanofibers. The absorption parameters was found to be −6.4 dB at 12.9 GHz within the range of X-band microwave absorption frequency, this reflection loss is attributed to the multiple absorption mechanisms as a result of the improved of impedance matching between dielectric and magnetic loss of the absorbent materials demonstrating that these materials can be used as protective material for electromagnetic radiation.     

One‐step in situ growth of magnesium ferrite nanorods on graphene and their microwave‐absorbing properties

The magnesium ferrite nanorods/graphene (MgFe₂O₄ NR/G) composites were prepared by a facile one‐step surfactant‐assisted solvothermal method. The structure and morphology of as‐prepared composite materials were characterized by electron microscopy, energy dispersive spectrometry, Raman spectrometry, X‐ray diffraction, FT‐IR and X‐ray photoelectron spectroscopy. The homogeneous MgFe₂O₄ nanorods with a typical diameter of about 100 nm were well distributed on graphene. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss (RL) of ?40.3 dB was observed at 14.9 GHz with a thickness of 3 mm, and the effective absorption frequency (RL  <   ? 10 dB) ranged from 12.0 to 18.0 GHz, indicating the remarkable microwave absorption performance of the MgFe₂O₄ NR/G composites. The absorbing property of as‐obtained composites was better than that of the pure MgFe₂O₄ nanorods. The synergistic effect of MgFe₂O₄ and graphene was responsible for the enhanced absorbing performance.     

NiFe2O4/T-ZnOw复合材料的制备及电磁波吸收性能

采用铁氧体化学镀在四角氧化锌晶须(T-ZnOw)表面包覆NiFe2O4镀层,制备了NiFe2O4/T-ZnOw复合材料。利用X射线衍射仪、扫描电镜、能谱分析仪对镀覆前后T-ZnOw的结构、形貌等进行了表征。利用矢量网络分析仪研究了NiFe2O4/T-ZnOw复合材料的电磁波吸收性能。结果表明,化学镀覆后,在T-ZnOw表面包覆了尖晶石型NiFe2O4镀层,生成了NiFe2O4/T-ZnOw复合材料,该材料为磁损耗型材料。化学镀覆过程中T-ZnOw的装载量会影响复合材料的介电常数和磁导率,当T-ZnOw装载量为0.2g时,所制备的复合材料具有最大的介电常数、磁导率、介电损耗和磁损耗,当吸收层厚度达到3 mm时,反射率在14 GHz处达到-11 dB。     

Microwave absorbing properties of Fe3O4–poly(3, 4‐ethylenedioxythiophene) hybrids in low‐frequency band

A facile method is proposed to obtain microwave absorbing materials (MAMs), which possess strong microwave absorption properties in low‐frequency range. By simply mechanical mixing, the obtained Fe₃O₄–poly (3,4‐ethylenedioxythiophene) (PEDOT) hybrids exhibit more excellent microwave absorbing properties than that of Fe₃O₄ or PEDOT individually. The analysis on the microwave absorbing properties of the Fe₃O₄–PEDOT hybrids indicates that the excellent microwave absorbing properties are ascribed to several factors, like the dielectric loss, the interface polarization, eddy current effect, natural ferromagnetic resonance, and the impedance as well as the thickness of the coating. The Fe₃O₄–PEDOT hybrids with appropriate mass ratios of PEDOT to Fe₃O₄ (represented by (PEDOT)/(Fe₃O₄)) show superior microwave absorbing property at low frequency. When the thickness is 4 mm, the reflection loss of the sample reached ?15.8 dB at 3.2 GHz with (PEDOT)/(Fe₃O₄) of 3 and ?31.4 dB at 4.5 GHz with (PEDOT)/(Fe₃O₄) of 2, respectively. The obtained Fe₃O₄–PEDOT MAMs will have a promising application in the practical industry and commerce affairs. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Fe3O4‐doped sepiolite on the flammability and thermal degradation properties of epoxy composites

As‐received sepiolite/epoxy systems and Fe₃O₄‐doped sepiolite/epoxy systems were prepared, and the contents of sepiolite and Fe₃O₄‐doped sepiolite were kept as 2 and 4 wt%, respectively. Compared with sepiolite, the effect of Fe₃O₄‐doped sepiolite on the flame retardancy, combustion properties, thermal degradation, thermal degradation kinetics and thermomechanical properties of epoxy resin was investigated systematically by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Some interesting results had been acquired. The addition of sepiolite decreased heat release rate, total smoke production and smoke production rate, and obviously improved LOI values of epoxy composites. Compared with sepiolite, the addition of Fe₃O₄‐doped sepiolite further reduced parameters mentioned above of epoxy composites, and further enhanced LOI values and char residues after cone test. There might be a synergistic effect between sepiolite and Fe₃O₄ on flame retardant epoxy composite. TGA results indicated that the addition of sepiolite had a slight effect on the thermal degradation of epoxy composites; however, the addition of Fe₃O₄‐doped sepiolite accelerated the thermal degradation of epoxy composites. DMA results showed that the addition of both sepiolite and Fe₃O₄‐doped sepiolite increased the glass transition temperature (T_g) of epoxy composite. The results obtained in this paper supplied an effective solution for developing excellent flame retardant properties of polymeric materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,characterization and microwave absorption properties of polyaniline/Sm-doped strontium ferrite nanocomposite

Sm-doped strontium ferrite nanopowders (SrSm_0.3Fe_11.7O₁₉) and their composites of polyaniline (PANI)/SrSm_0.3Fe_11.7O₁₉ with 10 wt% and 20 wt% ferrite were prepared by a sol–gel method and an in-situ polymerization process, respectively. The structure, magnetic properties and microwave absorption properties of the samples were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and vector network analyzer, respectively. The particle size of SrSm_0.3Fe_11.7O₁₉ was about 35 nm by using XRD. The ferrite successfully packed by PANI. PANI/SrSm_0.3Fe_11.7O₁₉ possessed the best absorption property with the optimum matching thickness of 3 mm in the frequency of 2–18 GHz. The value of the maximum reflection loss (RL) were −26.0 dB at 14.2 GHz with the 6.5 GHz bandwidth and −24.0 dB at 13.8 GHz with the 7.9 GHz bandwidth for the samples with 10 wt% and 20 wt% ferrite, respectively.     

Facile synthesis of multifunctional multiwalled carbon nanotubes/Fe3O4 nanoparticles/polyaniline composite nanotubes

With an average diameter of 100-150 nm, composite nanotubes of polyaniline (PANI)/multiwalled carbon nanotubes (MWNTs) containing Fe₃O₄ nanoparticles (NPs) were synthesized by a two-step method. First, we synthesized monodispersed Fe₃O₄ NPs (d=17.6 nm, σ=1.92 nm) on the surface of MWNTs and then decorated the nanocomposites with a PANI layer via a self-assembly method. SEM and TEM images indicated that the obtained samples had the morphologies of nanotubes. The molecular structure and composition of MWNTs/Fe₃O₄ NPs/PANI nanotubes were characterized by Fourier transform infrared spectra (FTIR), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and Raman spectra. UV-vis spectra confirmed the existence of PANI and its response to acid and alkali. As a multifunctional material, the conductivity and magnetic properties of MWNTs/Fe₃O₄ NPs/PANI composites nanotubes were also investigated.     

Double-Layered Plasmonic–Magnetic Vesicles by Self-Assembly of Janus Amphiphilic Gold–Iron(II,III) Oxide Nanoparticles

Janus nanoparticles (JNPs) offer unique features, including the precisely controlled distribution of compositions, surface charges, dipole moments, modular and combined functionalities, which enable excellent applications that are unavailable to their symmetrical counterparts. Assemblies of NPs exhibit coupled optical, electronic and magnetic properties that are different from single NPs. Herein, we report a new class of double-layered plasmonic–magnetic vesicle assembled from Janus amphiphilic Au-Fe₃O₄ NPs grafted with polymer brushes of different hydrophilicity on Au and Fe₃O₄ surfaces separately. Like liposomes, the vesicle shell is composed of two layers of Au-Fe₃O₄ NPs in opposite direction, and the orientation of Au or Fe₃O₄ in the shell can be well controlled by exploiting the amphiphilic property of the two types of polymers.     

Facile Preparation of Snowflake-Like MnO2@NiCo2O4 Composites for Highly Efficient Electromagnetic Wave Absorption

Snowflake-like MnO₂@NiCo₂O₄ composites were successfully fabricated by employing crossed snowflake-like MnO₂ nanorods as cores and one-dimensional (1D) NiCo₂O₄ nanoneedles as shells. Impressively, the MnO₂@NiCo₂O₄ composites exhibited a highly efficient electromagnetic wave (EMW) absorbing capability, and the minimum reflection loss (RL) value reached −58.4 dB at 6.8 GHz for a thickness of 4.0 mm. The reasons for the improved EMW absorption capability of snowflake-like MnO₂@NiCo₂O₄ composites were analyzed. The unique core–shell structure, good impedance matching, and high dielectric loss were all found to be important contributors. Moreover, the interfacial polarization mainly stemmed from the heterostructure, a microcurrent generated from the 1D MnO₂ nanorods and NiCo₂O₄ nanoneedles under alternating electromagnetic fields, and the synergistic effect from the different components were all beneficial to improve the EMW absorption performance. These results demonstrated that snowflake-like MnO₂@NiCo₂O₄ composites could be utilized as promising materials for practical EMW absorbing applications.     

Ultrafast Preparation of Monodisperse Fe3O4 Nanoparticles by Microwave‐Assisted Thermal Decomposition

Thermal decomposition, as the main synthetic procedure for the synthesis of magnetic nanoparticles (NPs), is facing several problems, such as high reaction temperatures and time consumption. An improved a microwave‐assisted thermal decomposition procedure has been developed by which monodisperse Fe₃O₄ NPs could be rapidly produced at a low aging temperature with high yield (90.1 %). The as‐synthesized NPs show excellent inductive heating and MRI properties in vitro. In contrast, Fe₃O₄ NPs synthesized by classical thermal decomposition were obtained in very low yield (20.3 %) with an overall poor quality. It was found for the first time that, besides precursors and solvents, magnetic NPs themselves could be heated by microwave irradiation during the synthetic process. These findings were demonstrated by a series of microwave‐heating experiments, Raman spectroscopy and vector‐network analysis, indicating that the initially formed magnetic Fe₃O₄ particles were able to transform microwave energy into heat directly and, thus, contribute to the nanoparticle growth.     

Supercritical Carbon Dioxide Assisted Deposition of Fe3O4 Nanoparticles on Hierarchical Porous Carbon and Their Lithium‐Storage Performance

A composite of highly dispersed Fe₃O₄ nanoparticles (NPs) anchored in three‐dimensional hierarchical porous carbon networks (Fe₃O₄/3DHPC) as an anode material for lithium‐ion batteries (LIBs) was prepared by means of a deposition technique assisted by a supercritical carbon dioxide (scCO₂)‐expanded ethanol solution. The as‐synthesized Fe₃O₄/3DHPC composite exhibits a bimodal porous 3D architecture with mutually connected 3.7 nm mesopores defined in the macroporous wall on which a layer of small and uniform Fe₃O₄ NPs was closely coated. As an anode material for LIBs, the Fe₃O₄/3DHPC composite with 79 wt % Fe₃O₄ (Fe₃O₄/3DHPC‐79) delivered a high reversible capacity of 1462 mA h g^?1 after 100 cycles at a current density of 100 mA g^?1, and maintained good high‐rate performance (728, 507, and 239 mA h g^?1 at 1, 2, and 5 C, respectively). Moreover, it showed excellent long‐term cycling performance at high current densities, 1 and 2 A g^?1. The enhanced lithium‐storage behavior can be attributed to the synergistic effect of the porous support and the homogeneous Fe₃O₄ NPs. More importantly, this straightforward, highly efficient, and green synthetic route will definitely enrich the methodologies for the fabrication of carbon‐based transition‐metal oxide composites, and provide great potential materials for additional applications in supercapacitors, sensors, and catalyses.     

磁性纳米Pd/Fe3O4催化剂的制备及其在Heck反应中的应用

通过使用聚乙烯吡咯烷酮作为稳定剂,合成了磁性Pd/Fe₃O₄纳米颗粒催化剂。对该催化剂进行粉末X射线衍射、透射电子显微镜、感应耦合等离子体和磁性表征。将Pd/Fe₃O₄催化剂用于Heck反应,检测其催化性能。测试结果表明Pd纳米颗粒负载在Fe₃O₄纳米颗粒上,而且催化剂的尺寸<20 nm,并在Heck反应中表现了极好的催化性能。此外,催化剂可以通过磁场回收利用, 且催化活性没有显著的降低。     

Electromagnetic properties and microwave absorption enhancement of Ba0.85RE0.15Co2Fe16O27-polyaniline composites: RE = Gd,Tb, Ho

The Gd-, Tb-, and Ho-doped W-type hexagonal ferrite Ba_0.85RE_0.15Co₂Fe₁₆O₂₇ was fabricated by a facile route of low-temperature sol–gel self-propagating combustion. Furthermore, a combination of dielectric loss phase polyaniline and magnetic loss phase Ba_0.85RE_0.15Co₂Fe₁₆O₂₇ as the microwave absorber in a core-shell architecture has been synthesized. The effect of different lanthanide ions Gd, Tb, and Ho on their microstructure, static magnetic properties, electromagnetic properties, and microwave reflection loss have been systematically studied. Our results show that the Ho-doped ferrite has the low microstructure parameters (a, c, and V) and high saturation magnetization (Ms) attributed to its ionic radius and magnetic moment. Moreover, it was found that the Ho-doped composite exhibited excellent microwave absorbing property with a minimum reflection loss (RL) of about ?15.1 dB at 9.4 GHz. The reflection loss of composite increases up to almost triple upon the combination of polyaniline and doped ferrite. Such lightweight and highly effective absorbers via combining the organic and inorganic phase into a core-shell architecture are highly desirable for microwave absorber in various applications. Figure

The synthesis and properties of the PANI/REBF composites