SiO2纳米壳的厚度对羰基铁/SiO2核壳复合粒子的性能影响

以聚乙烯毗咯烷酮作表面改性剂，用溶胶-凝胶法，通过控制反应时间，在羰基铁粒子表面均匀快速地包覆不同厚度的SiO2纳米壳层，并研究了SiO2纳米壳层厚度对羰基铁／SiO2核壳复合粒子的抗热氧化性能、静磁性能、微波介电常数和吸波性能的影响．结果表明：增加SiO2纳米壳层的厚度，羰基铁／SiO2核壳复合粒子的抗热氧化能力提高，比饱和磁化强度出现最大值，矫顽力和剩余磁化强度出现最小值，微波介电常数单调降低；用其制备的吸波涂层材料在壳层厚度为15nm时，反射损耗≤-8dB的带宽达到最大值，超过10GHz，     

碳包覆铁/丙烯酸树脂水性纳米复合涂料的制备及电磁波吸收性能

以"壳/核"型碳包覆铁(Fe(C))纳米颗粒为填料、水性丙烯酸树脂为基体,制备了纳米复合电磁波吸收涂料.采用不同含量的十二烷基苯磺酸钠(SDBS)对纳米颗粒改性,提高了纳米颗粒在基体中的分散性.选用吸收剂填充量为25%(质量分数)的涂料,测定了不同厚度涂层的电磁波吸波性能.涂层具有很好的吸波性能,当厚度为5mm时,反射损耗峰值为-17.2dB,吸收带宽为3.2GHz(7～10.2GHz).首次用实验结果证明了传输线理论对铁磁性纳米颗粒吸波性能的模拟结果.     

FeCo/SnO_(2)复合纳米纤维的制备及其吸波性能EI北大核心CSCD

用静电纺丝和氢气还原法制备FeCo/SnO_(2)复合纳米纤维并使用X射线衍射、扫描电子显微镜、振动样品磁强计和矢量网络分析仪等手段分析表征其结构、形貌、磁性及电磁特性,研究了SnO_(2)含量对复合纳米纤维的吸波性能的影响。结果表明,添加适量的SnO_(2)可显著提高FeCo纳米纤维的吸波性能。用SnO_(2)摩尔含量为20%的复合纳米纤维制备的厚度仅为1.4 mm的涂层,在频率10.95 GHz处最小反射损耗(RL)为-40.2 dB,有效吸收带宽(RL≤-10 dB)为2.64 GHz (9.75-12.39 GHz),厚度减小到1.0 mm的涂层其最大有效吸收带宽为4.16 GHz,频率范围为13.84~18.00 GHz。涂层吸波性能优异的主要原因,是阻抗匹配的改善、磁性FeCo合金与介电SnO_(2)的电磁损耗协同作用、加强的界面极化驰豫以及纳米纤维形成的三维网络结构产生的多重反射与散射。     

石墨烯-镍纳米复合材料的辐射制备及其电磁行为研究

通过伽马辐射技术实现氧化石墨烯的辐射还原和Ni纳米粒子的负载,制备出石墨烯-镍(RGO-Ni)纳米复合材料。通过透射电镜对不同氧化石墨烯和镍盐比例下制备的RGO-Ni纳米复合材料的形貌进行分析。电磁结果显示,负载Ni纳米粒子后,复合材料的电损耗和磁损耗提高。反射率计算结果表明,RGO-Ni-1在厚度2mm、频率7GHz时达到最大的反射损耗-21.98dB。     

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。     

磁功能化多孔生物质炭复合材料的制备及吸波性能

采用高温炭化和水热法制备了兼具介电损耗和磁损耗特性的磁功能化生物质炭(Fe_3O_4/多孔生物质炭)吸波材料。在200℃水热条件下,随着FeCl_3浓度的增加,PLSC表面生成的聚集态Fe_3O_4纳米晶粒有所增加,颗粒大小规整,平均粒径约为200 nm。通过矢量网络分析仪探讨了磁材料含量、复合材料的形貌结构对吸波性能的影响,并分析了多重损耗吸波机理。结果表明,在2～18 GHz范围内,当FeCl_3浓度为4 mmol时制备的磁功能化生物质炭复合吸波材料具有最佳的吸波性能,在厚度为2 mm时,其在11.42 GHz处的最大反射损耗值可达-42.2 dB,有效频宽达3.14 GHz (反射损耗小于-10 dB)。     

电磁波吸收剂BaTiO_3/MWCNT及其与PAN杂化纤维的制备与性能研究

采用溶剂热法制备出一种包含BaTiO_3和多壁碳纳米管(MWCNTs)的复合吸波剂.通过透射电镜分析吸波剂的形貌发现:粒径为15～30 nm的BaTiO_3颗粒均匀地包覆在MWCNTs的外壁.电磁波吸收性能分析表明:BaTiO_3/MWCNT纳米复合吸波剂的反射损耗(RL)要大于BaTiO_3和MWCNTs,这是由于其有更好的阻抗匹配和更高的复合磁导率.当单层材料的计算厚度为2mm时,BaTiO_3/MWCNT纳米复合吸波剂的RL在9.6～13.1 GHz的频段中超过了-10dB,同时在10.4 GHz处达到最大值-37.5 dB.为了研究BaTiO_3/MWCNT纳米复合吸波剂与聚丙烯腈(PAN)基体的相容性和其杂化纤维的可纺性,采用静电纺丝成型制备吸波剂含量为10wt%的PAN杂化纤维.通过X射线衍射和扫描电子显微镜分析发现:BaTiO_3/MWCNT纳米复合吸波剂成功与PAN纤维杂化,吸波剂的结构在成型过程中没有变化,吸波剂的添加并未影响纤维形貌.     

静电纺制备Fe3O4/PEK-C纳米复合膜及其吸波性能

静电纺丝技术是一种新颖、高效且简单的制备连续纳米纤维的方法,纳米复合纤维膜的优异特点赋予了纳米吸波剂新的吸波通道。本文采用静电纺丝工艺制备Fe3O4/PEK-C纳米复合纤维膜,利用SEM和TGA表征纳米复合纤维膜的微观形貌和热稳定性,用矢量网络分析仪测试样品在8.2~12.4 GHz的电磁参数与吸波性能。结果表明,Fe3O4/PEK-C纳米复合纤维膜呈现出超细纤维彼此交织构成的立体网络结构,其热稳定性、复介电常数和复磁导率均随着Fe3O4含量的增加而增加,介电损耗和磁损耗得到加强。当纳米复合纤维膜的厚度为1.8 mm时,其反射损耗在整个测试波段均处于-5 dB以下,-10 dB以下有效吸收频宽为2 GHz,频率在8.6 GHz处吸收强度达到最大值-15.4 dB。预期可作为隐身复合材料的吸波功能层。     

纳米碳酸钙表面原位聚合包覆

通过超重力场制备了纳米碳酸钙,对纳米碳酸钙进行超声波分散,然后进行原位乳液聚合,采用分步聚合的方式,在纳米碳酸钙表面包覆了丙烯酸酯类共聚物,制得了纳米碳酸钙表面原位聚合包覆产物.采用TEM、DSC、TGA和表面电子能谱(ESCA)对纳米碳酸钙表面原位聚合包覆产物进行了表征.结果表明:制备的纳米碳酸钙粒子粒径在20nm左右,通过原位乳液聚合包覆后,粒径在40～80nm,包覆后的纳米碳酸钙复合粒子表面几乎不含Ca元素,表明纳米碳酸钙被良好包覆,并形成了以纳米碳酸钙为核、PBA为中间层、MMA和EA,St共聚物为壳的三层结构有机-无机纳米复合粒子.     

膨胀石墨基纳米镍、铁、钴化学镀制备复合吸波材料

为了获得薄、轻、宽、强等性能理想的吸波材料,采用化学镀的方法在膨胀石墨表面镀覆纳米镍、镍钴、镍铁钴,制备了复合吸波材料.SEM和EDs分析证实,膨胀石墨表面镍层、镍钴层、镍铁钴层的镀覆厚度约为70～150 nm.采用HP8722ES矢量网络分析仪测量了复合吸波材料在2～18 GHz内的复介电常数(ε=ε'-jε")和复磁导率(μ=μ'-jμ").用吸收屏理论公式计算了反射率损耗(R.L)、匹配频段(fm)及匹配厚度(dm).结果表明,当dm=0.3 mm时,镀覆镍铁钴层的复合吸波材料最低的反射损耗达-28 dB,对应的fm=13.5 GHz,R>L<-10 dB时频宽达7.5 GHz.本法制备的复合吸波材料符合"轻、薄、宽、强"的现代要求.     

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。     

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。     

Magnetic and Microwave-absorption Properties of Graphite-coated (Fe, Ni) Nanocapsules

The structure, magnetic and microwave-absorption properties of graphite-coated (Fe, Ni) alloy nanocapsules, synthesized by the arc-discharge method, have been studied. High-resolution transmission electron microscopy shows that the nanocapsules have a core/shell structure with (Fe, Ni) alloy as the core and graphite as the shell. All (Fe, Ni) alloy nanocapsules/paraffin composites show good microwave-absorption properties. The optimal reflection loss (RL) was found for (Fe70Ni30)/C nanocapsules/paraffin composites, being -47.84 dB at 14.6 GHz for an absorber thickness of 1.99 mm, while the RL values exceeding -10 dB were found in the 12.4- 17.4 GHz range, which almost covers the Ku band (12.4-18 GHz). For (Fe70Ni30)/C nanocapsules/paraffin composites, RL values can exceed -10 dB in the 11.4-18 GHz range with an absorber thickness of 1.91 mm, which cover the whole Ku band.     

镀镍碳纳米管的微波吸收性能研究

用竖式炉流动法制备了碳纳米管,碳纳米管的外径40nm～70nm,内径7nm～10nm,长度50μm～1000μm,呈直线型,用化学镀法在碳纳米管表面镀上了一层均匀的金属镍。碳纳米管吸波涂层在厚度为0.97mm时,在8GHz～18GHz,最大吸收峰在11.4GHz(R=-22.89dB),R<-10dB的频宽为3.0Hz,R<-5dB的频宽为4.7GHz。镀镍碳纳米管吸波涂层在相同厚度下,最大吸收峰在14GHz(R=-11.85dB),R<-10dB的频宽为2.23Hz,R<-5dB的频宽为4.6GHz。碳纳米管表面镀镍后虽然吸收峰值变小,但吸收峰有宽化的趋势,这种趋势对提高材料的吸波性能是有利的。碳纳米管作为偶极子在电磁场的作用下,会产生耗散电流,在周围基体作用下,耗散电流被衰减,从而雷达波能量被转换为其它形式的能量。     

配比及热处理气氛对纳米Fe/石墨复合材料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Fe3+吸附到氧化石墨层间,再通过还原法制备了纳米Fe/石墨复合材料.采用元素分析、电磁参数测定等手段系统考察了硝酸铁与氧化石墨的配比及热处理气氛对纳米Fe/石墨复合材料分子组成和微波吸收性能的影响.结果表明,纳米Fe/石墨复合材料属于典型的软磁性材料;FeGO31H600的最大反射损耗为-6dB,而FeGO21H600的最大反射损耗达到了-9dB,故FeGO21H600的微波吸收效果最好;当厚度为1mm时,FeGO21600反射损耗大于6dB的频段范围为14～18GHz,而FeGO21H600反射损耗大于6dB的频段范围为11～18GHz,比FeGO21600低且宽,故FeGO21H600的微波吸收效果比FeGO21600的好.     

One-step synthesis,electromagnetic and microwave absorbing properties of α-FeOOH/polypyrrole nanocomposites

One-step synthesis of α-FeOOH/polypyrrole (PPy) nanocomposites is reported for the first time via a facile one-step chemical method in the presence of OH⁻, Fe²⁺, Fe³⁺ and pyrrole monomer. α-FeOOH nanorods are in situ formed in PPy matrix and the content of α-FeOOH nanorods increases with decreasing the molar ratio of pyrrole to Fe²⁺ ([Py]/[Fe²⁺] ratio). The electromagnetic and microwave absorbing properties of the nanocomposites are investigated as a function of the [Py]/[Fe²⁺] ratio. The results show that the PPy nanocomposites exhibit good conductivity (up to 16.10 S/cm) and antiferromagnetic behavior. The reflection loss evaluation based on the absorbing wall theory at the thickness of 2 mm shows that the nanocomposite at [Py]/[Fe²⁺] = 1.0 exhibits the best microwave absorbing property in the 2–18 GHz. And the corresponding reflection frequency range under −10 dB and −5 dB is 4.2 GHz and 5.8 GHz, respectively.     

Structural, magnetic and electromagnetic wave absorption properties of SrFe12O19/ZnO nanocomposites

Microwave absorption of nanocomposites of strontium ferrite and zinc oxide has been investigated. M-type strontium ferrite powders synthesized by a sol–gel method were combined with different concentrations of ZnO using a new method. The samples were characterized by various experimental techniques including TGA/DTA, X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and vector network analyzer. Reflection loss of nanocomposites has been measured in two frequency ranges of 8–12 GHz (X-band) and 12–18 GHz (Ku-band). The saturation magnetization of the nanocomposites decreased with increasing concentration of ZnO, but reflection loss in the Ku frequency band is enhanced by up to 5 dB for 15 % of ZnO in the nanocomposites.     

Hierarchical structures based on Li<Subscript>0.35</Subscript>Zn<Subscript>0.3</Subscript>Fe<Subscript>2.35</Subscript>O<Subscript>4</Subscript>/polyaniline nanocomposites: synthesis and excellent microwave absorption properties

For the first time, the hierarchical structures of Li_0.35Zn_0.3Fe_2.35O₄(LZFO)/polyaniline nanocomposites were successfully synthesized by interfacial polymerization. Firstly, the LZFO particles were prepared by the sol–gel method, and subsequently the PANI nanorods, composed of nanoneedle-like PANI, were grafted on the surface of the LZFO. A novel microtopography, urchin-like, of LZFO/PANI was prepared by a simple, efficient and controllable two-step method. The crystal structure, chemical bonding states and morphology of samples were characterized by means of Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Scanning and Transmission electron microscopy (SEM/TEM). The bandwidth of reflection loss exceeds 10 dB in the frequency was 5.56 GHz (3.36–8.48, 10.32–10.76 GHz), and the maximum reflection loss can reach ??49.4 dB at 4.96 GHz with the thickness of 5.1 mm. The enhanced microwave absorption properties of LZFO/PANI nanocomposites are mainly ascribed to the multi-level structure and the improved impedance matching, and make it a potential candidate for microwave absorption materials.     

Synthesis of covalently bonded reduced graphene oxide-Fe3O4 nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic (EM) wave absorbers,covalently bonded reduced graphene oxide-Fe3O4 nanocomposites (rGO-Fe3O4),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe3O4 nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe3O4 nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe3O4 is 2∶1 (sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss (RL) reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth (RL＜-10 dB) is 6.32 GHz (11.68-18.0 GHz) with a matching thickness of 2.1 mm.Furthermore,radar cross section (RCS) simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption performance.This work provides a possible method for preparing efficient EM wave absorbers.     

非连续体吸波平板的设计制备及吸波机理分析

通过吸波体内导电媒质的“孤岛”化设计, 制备了单层非连续体平板吸波材料, 并分析了不同炭黑含量和不同试样厚度对吸波效能的影响以及电磁波的损耗机理。发现随着CB/ ABS 颗粒中炭黑含量和试样厚度的增加, 在8～18 GHz 频段内, 非连续体试样的反射损耗增加。当炭黑质量含量达到30 %时, 平板的反射损耗在8. 5～18 GHz 宽频范围内都超过- 10 dB , 在15～18 GHz 均高于- 15 dB。当试样厚度达到20 mm 时, 其反射损耗在8～18 GHz 频率范围内超过- 15 dB。结果表明, 非连续体试样较热压致密试样吸波效能有较大提高, 是很有潜力的吸波结构。