还原温度对纳米Fe/石墨复合材料结构及微波吸收性能的影响

利用氧化石墨层间可吸附大量离子的特性使金属Fe3 吸附到氧化石墨层间,再通过H2还原制备了不同还原温度下的纳米Fe/石墨复合材料.采用元素分析、TEM、XRD、磁滞回线及电磁参数测定等手段系统考察了还原温度对纳米Fe/石墨复合材料的分子组成、晶体结构、磁学性能及微波吸收性能的影响.结果表明:纳米Fe/石墨复合材料的密度约2.4g/cm3;纳米Fe/石墨复合材料属于典型的软磁性材料;FeGO300、FeGO600和FeGO900的最大反射损耗量分别为-6.2dB、-8.9dB和-3.2dB.当厚度为1mm时,FeGO600的反射损耗大于-6dB的频段范围为11~18GHz,而FeGO600和FeGO900的最大反射损耗仍低于-6dB,因此FeGO600的微波吸波效果最好,600℃为制备纳米Fe/石墨复合吸波材料的最佳还原温度.     

CoFe2O4-石墨烯纳米复合材料的制备及微波吸收性能

通过原位共沉淀法即Co²⁺、Fe²⁺均匀共沉淀在氧化石墨表面的同时氧化石墨被原位热还原, 制备出CoFe₂O₄-石墨烯(CFO-GN)纳米复合材料。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能谱(EDS)、热重分析仪(TGA)、傅里叶变换红外光谱(FT-IR)和矢量网络分析仪(VNA)等对复合材料的形貌、结构、元素成分及微波吸收性能进行了表征和分析。结果表明: 钴铁氧体(CoFe₂O₄)纳米粒子均匀分散在石墨烯层间及表面, CoFe₂O₄-石墨烯纳米复合材料同时具有介电损耗和磁损耗, 表现出良好的微波吸收性能。CoFe₂O₄质量分数分别为88.62%和74.53%的CoFe₂O₄-石墨烯纳米复合材料, 当厚度为2 mm时反射损耗分别可达-11.0 dB和-12.4 dB, 反射损耗在-8 dB以下的频宽约为2.0 GHz和4.3 GHz。其中石墨烯含量相对较高的复合材料介电损耗较强, 反射损耗强度较大, 吸收频带较宽, 具有更好的微波吸收性能。     

外贴Fe3O4/CNTs杂化碳纳米纸的碳纳米管复合材料吸波性能

通过对Fe₃O₄纳米粒子接枝碳纳米管的单分散水溶液真空吸滤制备出一种新型的杂化碳纳米纸, 它与树脂浸润良好, 可以与复合材料一体成型。分别借助FE-SEM、EDS、BJH法和振动样品磁强计表征杂化碳纳米纸及其复合材料的微观形貌、元素组成、平均孔径分布和磁性能。在8.2~18 GHz频段内利用波导法测量碳纳米管共混复合材料和外贴杂化碳纳米纸/碳纳米管共混复合材料的电磁参数和吸波反射率。研究结果表明: 外贴一层杂化碳纳米纸(厚0.1 mm)后, 碳纳米管共混复合材料的磁损耗明显增加, 在8.2~18 GHz微波频段内吸波反射率基本上全部小于-10 dB(频宽大于9.7 GHz), 在15.42 GHz位置, 反射损耗峰达-43.18 dB, 远优于碳纳米管共混复合材料。     

海参状镍@聚苯胺(Ni@PANI)纳米复合材料的制备及其微波吸收性能

本文采用原位聚合法以氯化镍和苯胺为原料制备了镍@聚苯胺(Ni@PANI)纳米复合材料,研究了该纳米复合材料在2~18GHz频段内的微波吸收性能,在14GHz时测得最大反射损耗为-35dB,吸波频带宽度约4GHz,这使镍@聚苯胺纳米复合材料优于单一的聚苯胺材料和镍离子掺杂的聚苯胺材料。对其介电常数、磁导率以及界面极化情况的研究结果表明镍@聚苯胺纳米复合材料的优良的吸波性能来自于其同时具有介电损耗和磁损耗,以及界面极化增强。     

纳米铁钴合金/石墨复合材料的微波吸收性能研究

利用氧化石墨的吸附性能将Fe³⁺和Co²⁺吸附到氧化石墨层间制备出Fe³⁺Co²⁺/氧化石墨复合物, 再通过氢气还原制备出纳米铁钴合金/石墨复合材料, 采用XRD和SEM以及磁滞回线测试等手段对其晶体结构、微观形貌以及磁学性能进行表征, 探讨了FeCo合金含量对其微波吸收性能的影响。结果表明: 所制备的产物为石墨和纳米FeCo合金颗粒组成的二元复合材料, FeCo合金分散在石墨表面和层间, 粒径为30~150 nm。纳米铁钴合金/石墨复合材料是典型的软磁性材料, 饱和磁化强度随FeCo合金含量的减小而降低。随着FeCo合金含量的减少, 纳米FeCo/石墨复合材料的介电损耗逐渐增加, 磁损耗逐渐减小。FeCo合金含量适当时, 介电损耗和磁损耗的协同作用使复合材料具有较好的微波吸收性能。     

Ni(NO3)2浓度对Ni/还原氧化石墨微观结构及微波吸收性能的影响

以Ni(NO₃)₂为Ni源, 利用液相浸渍法在氧化石墨层间吸附Ni²⁺, 通过H₂热还原制备出Ni/还原氧化石墨纳米复合材料。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)及网络矢量分析仪等对样品的结构及性能进行分析和表征, 研究了Ni(NO₃)₂浓度对材料微观形貌及电磁性能的影响。结果表明, 所制备材料为纳米级Ni颗粒与RGO的复合体, 具有优良的微波吸收性能; 当Ni(NO₃)₂浓度为1.5 mol/L时, 材料电磁吸收性能最佳, 在2~18 GHz频率范围内, 材料厚度为2 mm时, 反射损耗(RL)小于-5 dB的频率范围可达9 GHz, RL_max可达-40 dB。     

铁氧体/石墨复合吸波涂层的微波吸收性能

本文将固相法制备的磁损耗型Ba0.9Sm0.1Co2Fe16O27铁氧体与电损耗型石墨相结合,通过测试两者的电磁参数,采用YRcomputor软件模拟计算了双层复合吸波涂层的反射率。结果表明：铁氧体/石墨复合吸波涂层在2～8 GHz频段有较好的吸波性能;其中,下层为含量80 wt%的Ba0.9Sm0.1Co2Fe16O27,厚度1.5 mm,上层为10 wt%的石墨,厚度1.5 mm时,该复合涂层表现出优良的微波吸收特性,反射率损耗RL〈-10 dB时,带宽约为3 GHz（3.5～6.5 GHz）,最大吸收值约为-27 dB。     

磁性多孔RGO@Ni复合材料的制备和吸波性能

以氧化石墨烯和乙酰丙酮镍为原料,用溶剂热法合成了三维多孔RGO@Ni纳米复合材料。采用X射线衍射(XRD)和X射线光电子能谱(XPS)表征了材料的晶体结构和组成,根据拉曼谱分析了材料内部的石墨化程度和结构缺陷,用扫描电镜(SEM)和透射电镜(TEM)观察了材料的形貌和微观结构。结果表明,当RGO@Ni纳米复合材料的填充量(质量分数)为25%时在最小反射损耗(RL_min)和最大有效吸收带宽(EAB)方面显示出优异的EMW吸收性能;厚度为2.2 mm的RGO@Ni纳米复合材料其RL_min为-61.2 dB,而在2.5 mm匹配厚度下覆盖的EAB范围最广,为6.6 GHz(10.5~17.1 GHz)。这种复合材料优异的微波吸收性能,归因于协同效应的增强和特殊的多孔结构。     

木基多孔炭/铁氧体复合吸波材料的制备与性能表征

以马尾松木材为原料,使用低温预处理、真空浸注和高温原位生长等手段制备了性能优异的木基多孔炭/铁氧体复合吸波材料(WPC/Fe3 O4),采用XRD、XPS、SEM、VNA等技术对复合材料的物相、成分、形貌和电磁特性等进行表征分析,初步阐述了其吸波机理.结果表明:制备的WPC/Fe3 O4具有优异的吸波性能,其反射损耗峰值达-35.6 dB,有效吸波频带宽超过5.6 GHz,并且在3～4.3 mm厚度范围内均可实现对全部Ku频段电磁波的有效吸收;WPC/Fe3 O4具有规则通直的孔隙结构和丰富的异质界面,高温下Fe3 O4纳米粒子均匀生长于木基多孔炭的孔隙和炭壁中;随着碳化温度的升高,WPC/Fe3 O4的介电常数显著增大而磁导率变化较小;WPC/Fe3 O4的电磁损耗机制主要为导电损耗、磁损耗和界面极化损耗.复合材料表现出对Ku频段电磁波的高效与宽频吸收,有望实现其在电子通讯或目标隐身等微波领域的应用.     

退火对Fe/Al_2O_3纳米复合物微波吸收性能的影响

采用球磨法制备Fe/Al2O3纳米复合物,并在氩气保护下退火,研究了退火对Fe/Al2O3纳米复合物的微观结构、磁性和微波吸收性能的影响。结果表明,退火使样品的晶粒尺寸增大,缺陷减少,微观应力得到释放;同时,退火使Al2O3的缺陷发光峰强度明显减弱,398 nm和484 nm处的发光峰发生蓝移。厚度为7.7 mm的球磨样品,其反射损耗在15.5 GHz频率处达到最大值-11.4 dB。退火使样品的介电损耗和磁损耗均增大,电磁波吸收性能明显提高,厚度为6.4 mm时反射损耗在17 GHz频率处达到最大值-35.5 dB。     

PAn/Fe3O4网状纳米复合物的合成表征及吸波性能

在十六烷基三甲基溴化胺（CTAB）存在下,采用原位化学氧化聚合法制备了聚苯胺／Fe3O4网状磁性纳米复合材料,通过改变Fe3O4纳米粒子在聚苯胺（PAn）中的含量获得了电磁性能可调的纳米复合物,采用FT—IR、XRD、SEM、TEM、电导和磁性能测试对复合物进行了表征,通过矢量网络分析仪获得了试样在2—18GHz范围的复介电常数和复磁导率,经计算获得微波反射损耗曲线,发现当样品中Fe3O4的含量为15．8wt％时,在9．0GHz处具有最大的反射损耗-17．1dB,损耗起．过-10dB的频宽为1GHz。     

树脂基Fe纳米粒子及碳纤维复合吸波平板的制备与性能

以Fe纳米粒子(Fe NPs)为吸波剂,偶联剂KH550为表面改性剂,碳纤维(CFs)作为增强及电磁波反射相,环氧树脂(ER)作为基体,制备多种吸波平板并对其综合性能及相关机制进行研究。结果表明:平板的吸波性能随Fe NPs和CFs含量的增加而提高,吸收剂浓度梯度分布有助于形成特定频段的共振吸收;平板对电磁波损耗具有明显的各向异性,表现为CFs垂直电磁波入射方向时性能优于平行情况,当Fe NPs的含量为30%(质量分数,下同),CFs为5.52%,板厚为4.56mm时,最小反射损耗为-26.8dB(4.9GHz);同时,CFs可改善平板的抗弯性能,当Fe NPs为30%时,弯曲强度相比于纯树脂时仅降低了5.81%。     

Low-temperature synthesis of manganese oxide–carbon nanotube-enhanced microwave-absorbing nanocomposites

Noting that the dielectric properties of manganese oxide make it a promising microwave-absorbing material, a low-temperature method to deposit crystalline MnO₂ over carbon nanotubes (CNTs) is developed. Adjusting the pH of the precursor solution allows control over the phases and morphologies of the synthesized manganese oxides MnO₂ and Mn₃O₄ that have minimum reflection losses of ??11 dB and ??6 dB, respectively. The synthesized CNT–MnO₂ and CNT–Mn₃O₄ nanocomposites are superior microwave absorbers than simpler physical mixtures of CNTs and manganese oxides, with reflection losses as high as ??19 dB at 9.5 GHz and ??34 dB at 4 GHz, and have wider absorption bands than pure manganese oxides. Coating CNTs with manganese oxide not only increases dielectric and magnetic losses, but also improves the impedance match between free space and the absorber. The addition of CNTs to pure MnO₂ and Mn₃O₄ improves impedance matching by enhancing the relaxation polarization and conductivity losses, magnetic loss, including contributions form eddy current and natural resonance. This facile, low-cost, scalable, high-yield method produces an enhanced microwave-absorbing nanocomposite.     

Facile synthesis and excellent electromagnetic wave absorption properties of flower-like porous RGO/PANI/Cu<Subscript>2</Subscript>O nanocomposites

Novel porous ternary nanocomposite systems containing reduced graphene oxide (RGO)/polyaniline (PANI)/cuprous oxide (Cu₂O) were prepared via one-step in situ redox method. The RGO/PANI/Cu₂O nanocomposites present a flower-like structure with an average size of 2.0 μm in diameter. The morphologies and properties of the products can be controlled by adjusting the molar ratios of aniline to Cu²⁺. When the molar ratio of aniline to Cu²⁺ is 1:1, the product exhibits excellent microwave absorption property in the frequency range of 2–18 GHz. It can be seen that the maximum reflection loss (RL) of the ternary composite is up to ?52.8 dB at 2.7 GHz with a thickness of only 2 mm, and the absorption bandwidth corresponding to ?10 dB (90% of EM wave absorption) is 13.2 GHz. The microwave absorption property of ternary RGO/PANI/Cu₂O composite is significantly improved due to its special flower-like porous structure, dielectric loss property and well impedance matching characteristics, which is 8.12 times than that of pure RGO and 5.28 times than that of pure PANI. Therefore, our study paves a new way to prepare the promising lightweight and high-performance composite materials combined with the characteristics of three components for electromagnetic absorption.     

The enhanced microwave absorption property of CoFe(2)O(4) nanoparticles coated with a Co(3)Fe(7)-Co nanoshell by thermal reduction

CoFe(2)O(4) nanoparticles were fabricated by a sol-gel method and then were coated with Co(3)Fe(7)-Co by means of a simple reduction process at different temperatures under 2% H(2) with the protection of argon to generate the dielectric-core/metallic-shell structure. The optimum reflection loss (RL) calculated from permittivity and permeability of the 80 wt% CoFe(2)O(4)/Co(3)Fe(7)-Co and 20 wt% epoxy resin composites reached - 34.4 dB, which was much lower than that of unreduced CoFe(2)O(4) and epoxy resin composites, at 2.4 GHz with a matching thickness of 4.0 mm. Moreover the RL exceeding - 10 dB in the maximum frequency range of 2.2-16 GHz was achieved for a thickness of composites of 1.0-4.5 mm with 600?°C thermal reduction process. The improved microwave absorption properties are a consequence of a proper electromagnetic match and the enhanced magnetic loss besides its dielectric loss due to the existence of the core/shell structure in CoFe(2)O(4) composites. Thus, the reductive CoFe(2)O(4) nanoparticles have great potential for being a highly efficient microwave absorber.     

Enhanced microwave absorption performance of graphene/doped Li ferrite nanocomposites

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.     

Heterostructure design of Fe3N alloy/porous carbon nanosheet composites for efficient microwave attenuation

The self-dissipation and attenuation capacity of materials play an important role in realizing efficient electromagnetic absorption,in this case,the roles of macroscopic composition and micro-structure should be emphasized simultaneously in the reasonable design of microwave absorbent.Given that,Fe₃N alloy embedded in two-dimensional porous carbon composites were fabricated via facile sol-gel and sacrificial template methods.Satisfactorily,the magnetic/dielectric materials combination and porous structure introduction are conductive to the optimization of impedance matching property,as result of the enhancement of microwave absorption capacity.In addition,sufficient magnetic loss capacity,strong conductivity as well as polarization attenuation bring about the outstanding microwave absorbing performance with an effective absorption bandwidth of 6.76 GHz and a minimum reflection loss value of-65.6 d B.It is believed that this work not only lay a foundation to achieve microwave response materials in a wide frequency range,but also emphasize the significant role of the component selection and structural design.     

Fe/Fe_(3)C/Fe_(3)O_(4)@C磁性微球的制备及吸波性能研究EI北大核心CSCD

薄、轻、宽、强是人们对高效电磁波吸收材料的追求。用食品级柠檬酸铁与蔗糖经过水热反应,高温煅烧制备Fe/Fe_(3)C/Fe_(3)O_(4)@C磁性微球,并通过改变柠檬酸铁与蔗糖的摩尔比,探究柠檬酸铁的含量对复合材料吸波性能的影响,有效地调控电磁参数,从而优化阻抗匹配。实验结果表明,当柠檬酸铁与蔗糖的摩尔比为5∶3时,具有较好的吸波性能:当厚度为2.5 mm时,最小反射损耗为-50.17 dB,小于-10 dB的有效吸收频宽为3.52 GHz,优异的电磁波吸收性能主要得益于微球丰富的界面、孔状结构和Fe/Fe_(3)C/Fe_(3)O_(4)磁学性能的协同作用。     

炭化纳米Co3O4/硅藻土复合材料制备及其性能

利用高温热解炭化制备炭化纳米Co_3O_4与硅藻土复合材料,研究其磁性和吸波性能。采用X射线衍射、扫描电镜、透射电镜、振动样品磁强计和矢量网络分析仪等测试分析技术对复合材料进行表征。结果表明:平均粒径为50nm的超顺磁性纳米Co_3O_4粒子和无定形碳均匀分散于硅藻土表面和孔隙内,形成稳定的复合体。炭化纳米Co_3O_4/硅藻土复合具有较强的超顺磁性和吸波性能,最大反射率损失为-14.7dB,<-10dB的频率范围大约为14～18GHz,带宽为4GHz。     

Preparation and microwave absorption properties of polyaniline/Mn0.8Zn0.2Fe2O4 nanocomposite in 2–18 GHz

The polyaniline/Mn_0.8Zn_0.2Fe₂O₄(PANI/MZF) nanocomposite was prepared by an in situ polymerization method. The samples were characterized by Fourier transform infrared spectrometer, X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. The complex permittivity and complex permeability for the nanocomposites were measured by wave-guide method with vector network analyzer in 2.0–18.0 GHz. The reflection losses (R _L ) of the nanocomposites were investigated according to the wave transmission theory. The results showed the maximum reflection loss of the PANI/MZF nanocomposite was about ?20.6 dB at 14.4 GHz with a bandwidth of 5.6 GHz. In conclusion, a wider absorption frequency range could be obtained by adding polyaniline contain in the MZF ferrite. The PANI/MZF nanocomposite is a good microwave shielding and absorbing materials at higher frequency.