MoSi_2对C_f/SiC/Ni复合材料微观结构及吸波性能的影响

以葡萄糖、Si粉、碳纤维为原料,镍为催化剂,采用水热反应-烧结法制备了C_f/SiC/Ni和C_f/MoSi_2/SiC/Ni复合吸波材料。通过X射线衍射、扫描电子显微镜、波导法分别表征了C_f/SiC/Ni和C_f/MoSi2/SiC/Ni复合材料的相组成、微观结构和吸波特性。结果表明:C_f/SiC/Ni复合材料上生长的Si C纳米线稀疏且分布不均匀;厚度为1.5 mm时,在8.20 GHz处最小反射损耗为–14.61 dB,有效吸收带宽为0.23 GHz。C_f/MoSi_2/SiC/Ni复合材料的碳纤维表面生长大量SiC纳米线,分布致密且均匀;厚度为2.0 mm时,在9.10 GHz时最小反射损耗为–34.14 dB,有效吸收带宽达2.18 GHz。与C_f/SiC/Ni复合材料相比,添加MoSi_2的C_f/MoSi_2/SiC/Ni复合材料吸波性能更好,说明MoSi_2可有效改善C_f/SiC/Ni复合材料的微观结构及吸波性能。     

NiCo2O4/BPC复合材料的制备及吸波性能研究

以紫菜为碳源、KOH活化法制备的生物质衍生多孔碳为基体,采用水热法及高温煅烧成功合成钴酸镍/生物质衍生多孔碳（NiCo₂O₄/BPC）复合材料。利用XRD、SEM对样品进行表征分析,并利用矢量网络分析仪（VNA）对其吸波性能进行测试。结果表明,NiCo₂O₄/BPC复合材料具有远远高于生物质多孔碳和钴酸镍材料的电磁波吸收性能。当匹配厚度为5.5 mm、频率为6.24 GHz时,样品的最小反射损耗值可以低至-43.20 dB,此时有效吸收带宽为3.3 GHz。该多孔结构的碳材料可有效改善纳米复合材料的阻抗匹配条件,提高材料的衰减能力,从而获得优异的微波吸收性能。     

多孔Al2O3/SiC、MoSi2/SiC复合材料的制备及吸波性能

以Si、Al₂O₃、MoSi₂微粉和生物竹材为原料,采用包埋烧结法分别制备出SiC多孔材料、Al₂O₃/SiC、MoSi₂/SiC复合材料。采用XRD、SEM及波导法测试其物相组成、显微结构及吸波性能。结果表明：MoSi₂/SiC复合材料的厚度为2 mm时有明显的吸波特性,有效吸收带宽在X波段的9.65~12.4 GHz频率范围内达2.75 GHz,且最低反射损耗为-38.27 dB。Al₂O₃/SiC复合材料孔道内的Al₂O₃与SiC晶须交缠,形成大量电偶极矩,产生介电损耗;MoSi₂/SiC复合材料除介电损耗外还存在电阻损耗,使得复合材料电磁损耗增加,是较有前途的结构功能吸波材料。     

壳核结构SiC/C纤维的制备与吸波性能的研究

采用活性碳纤维转换法制备了壳核结构SiC/C纤维,采用拉曼光谱、SEM、XRD以及热重分析等测试方法对比研究了生成SiC的厚度对壳核结构SiC/C纤维样品的热重及吸波性能的影响。结果表明:包裹SiC壳层后样品吸波性能得到提高,样品厚度为3.0 mm时,保温4 h样品的最小反射损耗在8.24 GHz处达到-17.22 dB,低于-10 dB(90%的电磁波被吸收)的频宽在2.0 mm处达到4.8 GHz(11.12~15.92 GHz);保温3 h样品的最小反射损耗在8.23 GHz处达到-14.45 dB,低于-10 dB(90%的电磁波被吸收)的频宽在2.0 mm处达到4.56 GHz(10.88~15.44 GHz);且随着SiC含量的升高,试样微波吸收性能有所增强;制备的壳核结构SiC/C纤维样品起始氧化温度提高了150 ℃以上,并且最终残余质量在50%左右,即包裹SiC纤维后样品的抗氧化能力大大提高。     

天然橡胶/丁苯橡胶/Ni/MWCNTs复合材料的结构与吸波性能

以Ni和多壁碳纳米管(MWCNTs)为填料,天然橡胶(NR)/丁苯橡胶(SBR)共混物为基体,采用机械共混法制备了性能优异的NR/SBR/Ni/MWCNTs多维复合材料,研究了填料共混及其组成对复合材料微观形貌和电磁损耗网络行为的影响。结果表明:Ni与MWCNTs共混有助于促进两者在橡胶基体中的分散,形成更优的双填料网络结构;当Ni与MWCNTs体积比为7∶3时,NR/SBR/Ni/MWCNTs复合材料在频率10.00 GHz、厚度2 mm处反射损耗可达-31.53 dB,有效吸收带宽达到3.58 GHz,阻抗匹配行为优于其他填料比例的复合材料;复合材料良好的吸波性能源于填料网络优异的阻抗匹配和多重损耗共同作用。     

多孔Al_2O_3/SiC、MoSi_2/SiC复合材料的制备及吸波性能

以Si、Al_2O_3、Mo Si_2微粉和生物竹材为原料,采用包埋烧结法分别制备出SiC 多孔材料、Al_2O_3/SiC 、Mo Si_2/SiC 复合材料。采用XRD、SEM及波导法测试其物相组成、显微结构及吸波性能。结果表明:Mo Si_2/SiC 复合材料的厚度为2 mm时有明显的吸波特性,有效吸收带宽在X波段的9.65～12.4 GHz频率范围内达2.75 GHz,且最低反射损耗为-38.27 d B。Al_2O_3/SiC 复合材料孔道内的Al_2O_3与SiC 晶须交缠,形成大量电偶极矩,产生介电损耗;Mo Si_2/SiC 复合材料除介电损耗外还存在电阻损耗,使得复合材料电磁损耗增加,是较有前途的结构功能吸波材料。     

碳纳米管/金属Ni/稀土氧化物复合材料用于增强夹层结构的吸波性能

将碳纳米管、纳米氧化镧、微米金属Ni粉、微米氧化镱分散至环氧树脂,将该环氧树脂混合物填充复合材料夹层结构的夹层,来探究该复合材料结构的吸波性能。利用网络矢量分析仪对该结构进行检测。结果表明,该复合材料结构在吸波分贝和吸波带宽方面都有提升,具有良好的吸波性能。在2.99~18.00GHz频段内,反射分贝出现三次波峰:第一个波峰的吸波带宽(-5d B)为2.55GHz,最大值出现在4.86GHz,为-23.78d B。第二个波峰的吸波带宽(-5d B)为3.75GHz,最大值出现在10.35GHz,为-21.07d B。第三个波峰吸波带宽(-5d B)为5.66GHz,最大值出现在14.04GHz,为-13.65d B。整体的吸波带宽(-5d B)达到11.96GHz,占全部测试频率的80%。另外,该复合材料结构对电磁波的损耗比例也有提升。     

片状和棒状γ-AlOOH/MWCNTs复合材料的制备及微波吸收性能研究

以Al(NO3)3·9H2O、柠檬酸钠和多壁碳纳米管(MWCNTs,Multi Walled Carbon Nanotubes)为原料,采用水热法制备了片状和棒状γ-AlOOH/MWCNTs复合材料.研究了γ-AlOOH/MWCNTs复合材料形貌结构和水热时间对材料电磁参数及微波吸收性能的影响.结果表明:片状复合材料的介电常数高于棒状复合材料,棒状复合材料具有更好的吸波性能.片状γ-AlOOH/MWCNTs复合材料在10.32 GHz处的最小反射损耗(RL,Reflection Loss)为-29.86 dB,有效吸收带宽达到3.76 GHz.棒状γ-AlOOH/MWCNTs复合材料在7.92 GHz处的最小反射损耗RL值达到-61.05 dB,同时低于-10 dB的有效吸收带宽为3.44 GHz.     

环氧树脂/玻璃纤维/石墨烯复合材料的电磁吸波性能

为了制备具有一定电磁吸波性能的结构型吸波材料,采用喷涂法制备了负载石墨烯微粒的玻璃纤维预浸料,并通过热压罐成型工艺进行固化,制备了环氧树脂/玻璃纤维/石墨烯吸波复合材料。研究了石墨烯含量对吸波复合材料电磁性能、吸波性能和力学性能的影响。通过三点弯曲测试结果可知,随着石墨烯含量的增加,环氧树脂/玻璃纤维/石墨烯吸波复合材料的弯曲强度先增大后减小,弯曲弹性模量增大,但总体变化幅度较小。矢量网络分析仪测试结果表明,随着石墨烯含量的增加,环氧树脂/玻璃纤维/石墨烯复合材料的介电常数逐渐增大,磁导率几乎不变,介电损耗正切角值逐渐增大。分析反射损耗计算结果可知,环氧树脂/玻璃纤维/石墨烯吸波复合材料的吸波性能主要由复合材料的厚度和石墨烯含量决定,随着复合材料厚度的增大,反射损耗峰值逐渐朝低频移动;随着石墨烯含量的增加,复合材料的吸波性能逐渐增大。当石墨烯质量分数为2.5%、复合材料厚度为1.7 mm时,环氧树脂/玻璃纤维/石墨烯复合材料具有最佳的吸波效果,此时反射损耗峰值为-11.8 dB,有效带宽为1.45 GHz。     

多孔集料砂浆的吸波特性

对发泡聚苯乙烯、膨胀珍珠岩、页岩陶粒等3种多孔集料填充水泥基复合材料的电磁波吸收性能进行了研究。结果表明：多孔集料提高了复合材料与自由空间的波阻抗匹配程度,还可引起电磁波多次反射和散射,从而使电磁波迅速衰减;多孔集料填充率、集料种类、集料粒径等对电磁波吸收性能有显著影响;选用的多种集料中发泡聚苯乙烯对复合材料吸波性能的...     

Facile synthesis of cobalt nanoparticles embedded in a rod-like porous carbon matrix with excellent electromagnetic wave absorption performance

A rod-like porous Co/C composite was successfully fabricated by carbonizing a Co-based MOF-74 precursor. Due to significant synergy between the porous carbon framework (dielectric loss) and cobalt nanoparticles (magnetic loss) coupled with the multiple polarization loss (interfacial or dipole polarization loss) due to the porous nature of the structure, the Co/C composites showed extremely favorable microwave absorption performance. When the as-prepared cobalt-based MOF precursor was annealed at 700 °C (S700), the supreme EM wave reflection performance was ?38.46 dB at 7.82 GHz with a coating thickness of 2.5 mm, whereas the broadest effective absorption bandwidth (3.3 GHz) was obtained with a coating thickness of 1.5 mm. Moreover, S600 samples exhibited an expansive absorption bandwidth range of 14.82 GHz (3.18–18 GHz) as the coating thickness was varied from 1.0 mm to 5.5 mm. The unique rod-like porous Co/C samples prepared in this study have significant potential for application in the field of the EM wave absorption.     

Ti3C2Tx/Ni/TiO2复合粉体的制备及吸波性能研究

采用热处理的方法制备出二维层状Ti₃C₂T_x/Ni/TiO₂复合粉体,并利用TG-DSC、SEM、XRD和XPS对样品进行表征分析,通过矢量网络分析仪测试样品的电磁参数并模拟计算不同涂层厚度下样品的反射损耗值(RL)。结果表明:随着热处理温度的升高,样品中TiO₂质量含量增加;当热处理温度为300 ℃时,在频率f=17.5 GHz下样品的RL为-35.2 dB,其有效吸波带宽超过1.7 GHz,对应的涂层厚度为4 mm。其优异的吸波性能一方面来自良好的阻抗匹配,另外一方面来自样品的介电损耗、磁损耗的协同效应。此外,样品的电磁波吸收能力可以通过其组分和微观结构进行调控。     

Synthesis of carbon-coated cobalt ferrite core–shell structure composite: A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

Cobalt ferrite has problems such as poor impedance matching and high density, which results in unsatisfactory electromagnetic wave (EMW) absorption performance. In this study, the CoFe₂O₄@C core-shell structure composite was synthesized by a two-step hydrothermal method. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and vector network analysis et al. were used to test the structure and EMW absorption properties of CoFe₂O₄@C composite. The results show that the reflection loss (RL) of the CoFe₂O₄@C composite reaches the maximum value of -25.66 dB at 13.92 GHz, and the effective absorbing band (EAB) is 4.59 GHz (11.20-15.79 GHz) when the carbon mass content is 6.01%. The RL and EAB of CoFe₂O₄@C composite are increased by 219.55% and 4.59 GHz respectively, and the density is decreased by 20.78% compared with the cobalt ferrite. Such enhanced EMW absorption properties of CoFe₂O₄@C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite, moreover, the carbon coating layer adjusts the impedance matching of the composite, and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.     

Fabrication of Ni/ZnO/C hollow microspheres decorated graphene composites towards high-efficiency electromagnetic wave absorption in the Ku-band

Developing light-weight, thin thickness and high-efficiency electromagnetic wave (EMW) absorbers is an effective strategy for dealing with the increasingly serious problem of electromagnetic radiation pollution. Herein, nickel/zinc oxide/carbon (Ni/ZnO/C) hollow microspheres decorated graphene composites were facilely prepared through the high-temperature pyrolysis of bimetallic NiZn metal-organic frameworks (MOFs) precursors. Morphological characterization results manifested that the Ni/ZnO/C microspheres with unique hollow structure were almost evenly anchored on the wrinkled surfaces of flake-like graphene. Moreover, the influences of additive amounts of graphene oxide (GO) in the MOFs precursors on the crystal structure, graphitization degree, micromorphology, magnetic properties, electromagnetic parameters and EMW absorption performance were investigated in detail. It was found that the superior EMW absorption performance could be achieved through facilely adjusting the additive amounts of GO in the precursors. As the additive amount of GO was equal to 60 mg, the obtained composite showed the comprehensive excellent EMW absorption performance. Notably, the optimal minimum reflection loss reached ?57.5 dB at 16.5 GHz in the Ku-band under an ultrathin matching thickness of merely 1.34 mm, and the broadest effective absorption bandwidth achieved 5.6 GHz (from 12.4 to 18 GHz) when the thickness was 1.5 mm. Furthermore, the underlying EMW absorption mechanisms of as-prepared composites were revealed. It was believed that our results could be valuable for the structural design and EMW absorption performance modulation for MOFs derived magnetic carbon composites.     

Effect of BaTiO3 on the microwave absorbing properties of Co‐doped Ni‐Zn ferrite nanocomposites

Coprecipitation and hydrothermal method were utilized for the synthesis of Co‐doped Ni‐Zn ferrite and barium titanate nanoparticles. The microwave absorption properties of Co‐doped Ni‐Zn ferrite/barium titanate nanocomposites with single layer structure were studied in the frequency range of 8.2–12.4 GHz.The spectroscopic characterizations of the nanocomposites were examined using X‐ ray diffraction, scanning electron microscopy, transmission electron microscopy and dynamic light scattering measurement. Thermogravimetric analysis indicated the high thermal stabilities of the composites. The composite materials showed brilliant microwave absorbing properties in a wide range of frequency in the X‐band region with the minimum return loss of ?42.53 dB at 11.81 GHz when sample thickness was 2 mm and the mechanisms of microwave absorption are happening mainly due to the dielectric loss. Compared with pure Co‐doped Ni‐Zn ferrite, Co‐doped Ni‐Zn ferrite/BaTiO₃ composites exhibited enhanced absorbing properties. The microwave absorbing properties can be modulated by controlling the BaTiO₃ content of the absorbers and also by changing the sample thicknesses. Therefore, these composites can be used as lightweight and highly effective microwave absorbers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39926.     

Development of biobased microwave absorbing composites with various magnetic metals and carbons

The preparation and characterization of a biobased electromagnetic absorbing composites derived from natural lacquer as a renewable resource with microwave‐absorption fillers, including Ni–Zn ferrite and carbonyl iron (CI) as magnetic metals and soot and carbon nanotube (CNT) as carbon materials, were investigated in terms of the gel content, hardness, drying properties, and electromagnetic absorption properties. Interestingly, composites with ferrite and CI contained up to 320 and 550 wt %, respectively, of these compounds. This quite high loading capacity of the metal fillers in a natural‐lacquer base could have been due to the high compatibility between the filler and the natural lacquer; this indicated that the natural lacquer worked as a binder for these metals. The morphology of the biobased composite was characterized by scanning electron microscopy. The electromagnetic absorption properties of composites were characterized in the frequency range from 0.05 and 20 GHz by the reflection loss (RL) measurement method in terms of the kind of fillers and filler loading. The natural lacquer did not affect the absorption properties of the fillers. Biobased composites showed over 99% electromagnetic absorption in the frequency range 3.0–4.0 GHz for 280 wt % ferrite and 8.9–9.7 GHz for 200 wt % CI. Conversely, 10 and 20 wt % soot exhibited good performance (RL < ?20 dB) between 16.5 and 17.3 and between 8.8 and 9.2 GHz, respectively. The areas with RL values of less than ?20 dB of the CNT composites were 10.4–11.0 GHz for 5 wt % and 14.6–15.2 GHz for 10 wt %. Hence, natural lacquer can be used as a binder material for electromagnetic absorption composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44131.     

Synthesis of PPy/Ni/RGO and enhancement on its electromagnetic wave absorption performance

The ternary composites of hollow tubular polypyrrole (PPy) and Ni particles based on reduced graphene oxide (RGO) were synthesized by a low-energy method. PPy and Ni particles were uniformly distributed on the surface of RGO. Specifically, multilayer interfaces existed in the hybrid, residual defects and folded structures of RGO and the hollow tubular structures of PPy made a significant contribution to electromagnetic (EM) wave attenuation. The final results showed that the strongest reflection loss (RL) value of PNR-2 sample could achieve ??47.32?dB at 5.76?GHz. The PNR-3 sample's RL value was ??18.21?dB at 15.92?GHz with the thickness of only 1.5?mm, and its corresponding effective absorption bandwidth reached 4.32?GHz (13.68–18?GHz). Hence, with the changes of PPy mass ratio, the impedance matching and attenuation were regulated to realize remarkable EM wave absorption performance including lightweight, thin thickness, wide bandwidth and strong absorption.     

One-step hydrothermal synthesis and enhanced microwave absorption properties of Ni0.5Co0.5Fe2O4/graphene composites in low frequency band

Ni_0.5Co_0.5Fe₂O₄/graphene composites were synthesized successfully via one-step hydrothermal method. The crystal structure, morphology and corresponding elemental distribution, electromagnetic parameters and microwave absorption performances of the as-prepared composites were measured by XRD, SEM, TEM and VNA, respectively. The results indicated that the microwave absorbing performance can be obviously enhanced through the addition of graphene in a suitable range, the magnetic loss plays a dominant contribution for the microwave absorption of composites. The maximum reflection loss of ?30.92?dB at 0.84?GHz with a ?10?dB bandwidth over the frequency range of 0.58–1.19?GHz is obtained when the composite contains 12?wt% graphene and the thickness of sample is 4?mm. This investigation presents a simple method to prepare Ni_0.5Co_0.5Fe₂O₄/graphene composites with excellent microwave absorption performance in the low frequency band of 0.1–3?GHz.     

Enhanced electromagnetic wave dissipation features of magnetic Ni microspheres by developing core-double shells structure

Readily oxidization of magnetic particles is a common drawback of these type of materials which reduce their electromagnetic wave dissipation performance. In this study, the magnetic core-double shells structured (Ni/SiO₂/Polyaniline) composite has been developed for protection of the core from oxidation and in consequent improvement the complex permittivity. Solvothermal and in-situ polymerization methods were utilized for decorating Ni micro-particles with SiO₂ and conductive polyaniline polymer respectively. All physico-chemical, magnetic and electromagnetic features were evaluated via XRD, FTIR, XPS, FESEM, VSM and VNA analysis. The double shells composite possesses significant performance in terms of reflection loss and effective absorption bandwidth. The results reveal that the maximum dissipation capacity of the double shells composite is – 32.5 dB at 16.5 GHz with 4.5 GHz effective absorption bandwidth and 1.5 mm thickness. Enhancement in microwave dissipation features are arises from synergistic influence of various phenomena such as interfacial polarization, multiple Debye relaxation, natural ferromagnetic resonance and proper impedance matching characteristic. Overall, developing double shells structure on magnetic Ni microsphere particles had a meaningful effect on tuning the microwave absorption performance.