化学气相沉积法制备同轴核壳结构CNTs@SiC的电磁特性研究

以Si单质和功能化多壁碳纳米管(CNTs)为原料,采用化学气相沉积法(CVD)制备了CNTs@SiC同轴核壳结构复合吸波剂。CNTs@SiC的一维管状核壳结构有利于提高材料的介电性能和调节阻抗匹配性能,并能有效提高CNTs的初始氧化温度。Si与CNTs质量比是影响此复合材料电磁特性的关键参数,当m(Si) : m(CNTs) = 1:1.5时,复合材料有最好的吸波性能,当其厚度为1.7mm时,反射率小于-10dB所对应的有效带宽达到4.8GHz;当m(Si) : m(CNTs) = 1:2时,材料在X波段有最好的吸波效果,有效带宽达3GHz。所制备的CNTs@SiC复合材料不仅在常温下具有宽频强吸收的特点,其独特的一维管状核壳结构有望使材料在高温环境下仍具有优异的吸波性能。     

轻质磁性炭气凝胶的制备及电磁吸波性能研究

目的 提高炭气凝胶材料电磁吸波性能。方法 以氢氧化钠或氨水为共沉淀剂制备不同尺寸的Fe3O4颗粒,并加入间苯二酚-甲醛溶液的预聚物中,充分搅拌后快速凝胶,经老化、超临界干燥、碳化等工艺制备Fe3O4/炭气凝胶复合材料。利用SEM、TEM、激光粒度分析仪、比表面及微孔分析仪、振动样品磁强计对Fe3O4及复合材料的微观结构和静磁性能进行表征,并对复合材料的吸波性能进行分析。结果 Fe3O4/炭气凝胶复合材料具有丰富的三维网络结构,Fe3O4颗粒在炭气凝胶中呈离散性分布。Fe3O4颗粒粒径越小,Fe3O4/CA的饱和磁化强度越大,75 nm-Fe3O4/CA的饱和磁化强度最大,达到29.26 emu.g^–1;当Fe3O4粒径为75 nm时,复合材料在厚度为2.1 mm时的最小反射损耗值可达–52.43 dB;当Fe3O4粒径为120 nm时,复合材料在厚度为2.5 mm时的有效吸收带宽高达6.98 GHz。结论 Fe3O4纳米颗粒粒径对复合材料介电损耗能力和阻抗匹配有显著影响,进而影响复合材料的吸波性能。大粒径的Fe3O4颗粒会破坏炭气凝胶的三维导电网络结构,从而降低复合材料的介电损耗能力。小粒径的Fe3O4颗粒可有效改善复合材料的阻抗匹配性能。     

Zn~(2+)含量对纳米Ni_(1-x)Zn_xFe_2O_4粉末在X波段吸波特性的影响

利用溶胶-凝胶自蔓延燃烧反应制备了Ni1-xZnxFe2O4(x=0.5,0.65和0.8)铁氧体纳米粉末,将粉末分别在550、800和1050℃下退火2 h,研究了各退火样品的晶体结构及自燃烧样品在X波段(8.2～12.5 GHz)的电磁性质。XRD分析表明,随Zn2+含量的提高,在自燃烧及550℃退火后,除尖晶石主相外,还有微量的ZnO、Fe3O4杂相;经800℃及其以上较高的温度退火后,所得样品呈完好的尖晶石相。VSM及微波矢量网络测量表明,Zn2+含量影响材料的比饱和磁化强度和矫顽力以及吸波性能、复介电常数和复磁导率;适当的Zn2+含量可提高纳米晶材料的自然共振频率,展宽其吸收频带,提高其复磁导率和磁损耗性能,改善其吸波性能。当x=0.65时,纳米Ni0.35Zn0.65Fe2O4粉末的吸波性能最好。当涂层厚度d=1mm时,其在测试频段内有四个吸收峰,在频率f=11.2315 GHz处,最大吸收值为15.879 dB;在9.0～11.7 GHz,吸收值达8 dB以上,μ'值达1.0以上,μ"值基本在0.7以上;其中吸收值超过11 dB和μ"值超过1.0的带宽达1.2 GHz。     

随机分布Fe纳米线复合材料的吸波性能

在具有纳米级孔洞的多孔氧化铝模板上,用电沉积方法制备出α-Fe纳米线有序阵列组装膜.用10%NaOH将纳米线溶液解离,并使之与树脂混合均匀,制成随机分布Fe纳米线/绝缘体复合吸波材料,并对其吸波性能进行了研究.研究结果表明:随铁纳米线体积分数的提高,随机分布的Fe纳米线/绝缘体复合吸波材料的电磁参数也随之增大;用测试电磁参数计算了不同厚度的反射率,体积分数为25%随机分布的铁纳米线/绝缘体的复合吸波材料最佳吸收厚度为1.14 mm;在9.7 GHz时,反射率达-45 dB,小于-5 dB时,反射率带宽达到9 GHz;随铁纳米线/绝缘体的复合吸波材料厚度的增加,吸收峰位向低频移动;随铁纳米线体积分数的增加,其吸收率明显增大,同时最佳吸收厚度也减小.     

Co含量对MOFs衍生的片状Co/C复合材料吸波性能的影响

金属有机骨架(MOFs)衍生的磁性金属/碳复合材料在轻质吸波材料领域展现出巨大的潜力。以二维片状结构Co/Zn双金属MOFs为前驱体通过高温热解合成片状Co/C复合材料,系统研究了前驱体中Co/Zn摩尔比对复合材料形貌结构、石墨化程度、磁性能和吸波性能的影响。结果表明：金属Co纳米微粒在碳骨架中均匀分布,随着Co含量的减少,复合材料中碳组分的石墨化程度逐渐降低,铁磁特性逐渐减弱;片状Co/C复合材料的吸波性能随着Co含量的降低先增强后减弱,填充比例为30 wt%、Co/Zn摩尔比为4:1时片状Co/C复合材料具有最佳吸波性能,厚度为2.11 mm时在10.8 GHz处最小反射率为-23.09 dB,最大有效带宽(反射率小于-10 dB)在厚度为1.62 mm时达到4.96 GHz。复合材料良好的吸波性能是由于均匀分布的磁性Co纳米粒子和碳骨架的协同作用,在增强电磁波导电损耗和界面极化损耗的同时,改善了阻抗匹配性能。     

Ni纳米线的制备及其微波吸收电磁性能

以氧化铝模板的孔洞为模型利用直流电沉积法制备了Ni纳米线.采用SEM,XRD,TEM对Ni纳米线的形貌和结构进行了表征.结果表明,Ni纳米线为单晶结构,沿[111]方向择优取向.把所制备的Ni纳米线和石蜡按质量比1∶1混合均匀后,利用同轴法测量其磁导率和介电常数,同时研究了该复合材料的吸波性能,计算得到了在不同厚度下的反射率曲线.研究发现,该纳米线/石蜡复合材料是一种介电损耗材料,在约9.5 GHz处介电损耗可达0.55,具有一定的吸波性能;当厚度为3mm时,在6.5 GHz处反射率可达-18 dB.     

聚苯胺/聚苯乙烯复合材料的电磁波吸收特性

研究了导电聚合物聚苯胺(PAni)/聚苯乙烯(PS)微/纳米复合材料的电磁波吸收特性.随掺杂态PAni在复合材料中的含量增加,复合材料电导率和PAni/PS复合板的吸波能力随之提高.PAni的微观形貌对吸波性能有影响,纤维形貌PAni要比颗粒形貌PAni具有更好的吸波特性.经过优化后,厚度为1.80 mm的掺杂态PAni/PS微/纳米复合材料雷达波反射率小于10 dB的频宽达6 GHz(11.6-17.6 GHz).     

Microwave Absorbing Properties of Ni/Ferrite Mixture

采用溶胶凝胶法制备了平面六角铁氧体,并用扫描电镜 (SEM),X射线衍射仪 (XRD) 对它的形貌以及相结构进行了表征,用矢量网络分析仪 (VAZ) 研究了不同比例的Ni/铁氧体混合物的微波吸收性能。结果发现,随着混合物中的平面六角铁氧体含量增多,混合物的微波吸波吸收峰向高频方向移动,当混合物由 20%Ni + 80% 铁氧体组成时,混合物的微波吸收性能最佳。当吸波涂层厚度为 2 mm时,在12 GHz 处,最小反射率为–20 dB,小于–10 dB的带宽达到了4 GHz。当吸波涂层厚度增加时,吸收峰频率向低频移动,吸收峰值先变小,后增大。当厚度达到一定值时,混合物在 2~18 GHz 之间出现 2 个吸收峰,这对于研究宽频吸收具有重要意义。     

基于CNTs/PLA的多层宽频超材料吸波结构设计与优化

目的 解决传统超材料吸波结构密度大以及对入射角度敏感的问题。方法 采用机械搅拌法和熔融共混法制备碳纳米管/聚乳酸（CNTs/PLA）复合吸波材料，通过CST电磁仿真软件开展多层超材料吸波结构设计，利用熔融沉积3D打印制备了设计的超材料吸波结构。通过扫描电子显微镜、矢量网络分析仪对制备材料和设计结构的微观形貌和电磁特性进行表征分析。结果 在机械搅拌和熔融共混的共同作用下，碳纳米管在聚乳酸中分布均匀。碳纳米管含量为10%时，复合材料的综合性能达到最佳。当其厚度为1.7 mm时，有效带宽达到最大为3.9 GHz；当厚度为3.2 mm时，反射率达到最低值约为–53.1 dB。设计的多层超材料吸波结构均具有极佳的宽频吸波特性；当R=11 mm时，圆形多层超材料结构的吸波性能最佳，反射率最低值为–53.9 dB，有效带宽为33.1 GHz，而平均反射率为–17.1 dB。此外对于TE极化的电磁波入射角在0°～60°范围内，而对于TM极化电磁波在入射角0°～70°范围内，圆形多层超材料结构具有宽角域吸波性能。结论 将碳纳米管与聚乳酸复合，在此基础上开展多层超材料结构设计，通过微观复合材料和宏观结构设...     

镍粉/平面六角锶铁氧体复合材料微波吸收性能的研究(英文)

采用溶胶凝胶法制备了平面六角铁氧体,并用扫描电镜(SEM),X射线衍射仪(XRD)对它的形貌以及相结构进行了表征,用矢量网络分析仪(VAZ)研究了不同比例的Ni/铁氧体混合物的微波吸收性能。结果发现,随着混合物中的平面六角铁氧体含量增多,混合物的微波吸波吸收峰向高频方向移动,当混合物由20%Ni+80%铁氧体组成时,混合物的微波吸收性能最佳。当吸波涂层厚度为2 mm时,在12 GHz处,最小反射率为–20 d B,小于–10 d B的带宽达到了4 GHz。当吸波涂层厚度增加时,吸收峰频率向低频移动,吸收峰值先变小,后增大。当厚度达到一定值时,混合物在2~18 GHz之间出现2个吸收峰,这对于研究宽频吸收具有重要意义。     

纳米晶W-Ni-Fe复合粉末及其烧结过程中的固溶特性

采用溶胶喷雾干燥-热还原法制备了50W-35Ni-15Fe(质量分数,%,下同)纳米晶复合粉末。利用X射线衍射及微区组织的能谱(EDAX)分析,揭示了纳米晶W-Ni-Fe复合粉末及其烧结过程中的固溶特性。研究发现:纳米晶50W-35Ni-15Fe复合粉末中,W在γ-(Ni,Fe)相中的固溶度达到了15%,Ni、Fe元素在W中的固溶度达到了2.4%,形成了超饱和固溶体;随着温度的升高,W的超饱和固溶体W(Ni,Fe)发生Ni、Fe元素的脱溶。而W在γ-(Ni,Fe)相中的固溶度随温度的升高而进一步增加,在1300℃以后基本维持在29%左右;稀土La的加入在低温阶段对W在γ-(Ni,Fe)相中的固溶度影响不大,在1200℃以上使固溶度有一定的降低。     

Microstructure and corrosion resistance of Ti-Ni/steel composite materials

Ti-Ni composite sub-micron powders with different compositions were prepared by vacuum melting and atomization technology. These powders, after being mixed with a solution of phenolic resin and alcohol, were applied on the mold cavity wall, by which a casting-infiltration layer was introduced on the surface of ZG45 steel via reactions between the powders and molten steel under the heat released by solidification. The effects of the powders’ composition and pouring temperature on the corrosion resistance of the casting-infiltration layer were studied. An optimal casting-infiltration layer with a thickness of ∼7 mm was obtained by infiltrating the Ti-Ni composite powders containing 35wt.% Ti to ZG45 steel pouring at 1,650 °C. The casting-infiltration layer has a good metallurgic bonding with the matrix, and is mainly composed of Fe₂Ti phase and continuous γ-(Fe, Ni) solid solution. In the corrosive H₂SO₄ solution, the corrosion potential of the casting-infiltration layer is lower than the matrix, tending to form a passivation film, which lowers the dissolution rate especially when the potential rises to 0.50 V. After dipping in the 10wt.% NaCl solution for 480 h, a lot of corrosion holes appear in the ZG45 steel matrix, while there are no obvious traces of corrosion on the casting-infiltration layer.

     

Full X-Ku band microwave absorption by Fe(Mn)/Mn7C3/C core/shell/shell structured nanocapsules

New type of Fe(Mn)/Mn₇C₃/graphite nanocapsules was prepared by a modified arc discharge technique in ethanol vapor, with Fe(Mn) solid solution nanoparticles as the core, Mn₇C₃ as the inner shell, and graphite as the outer shell. The Cole-Cole semicircle approach was adopted to explain the ternary dielectric resonance, due to a cooperative consequence of the core/shell/shell interfaces and the dielectric Mn₇C₃ and C shells. A remarkable increase in the anisotropy energy led to a shift in the natural resonance frequency to 6.6 GHz. Dielectric losses come from the ternary dielectric resonance while magnetic losses were from the magnetic natural resonance. An optimal reflection loss (RL) of −142.1 dB was observed at 12 GHz for 5.0 mm thickness layer. RL exceeding −10 dB was obtained at 6.6-18 GHz for 1.4 mm thickness, covering the whole X band (8-12 GHz), Ku band (12-18 GHz), and some of C band (6.6-8.0 GHz). RL exceeding −20 dB was found at 6-10.6 GHz for 2.2 mm thickness.     

Large gap joining of Ti–6Al–4V alloy with mixed powder interlayers

Abstract

Titanium based brazing alloys containing chromium, iron, copper, and nickel as β stabilisers have been studied for joining the titanium alloy Ti–6Al–4V. Two of these alloys were selected for use in producing large gap joints. The first brazing alloy, Ti–12Zr–14Cr–12Cu–12Ni (type 1), can be used to braze Ti–6Al–4V below its β transus temperature. Joints of thickness up to 150 μm can be made in a normal brazing cycle without prolonged holding. The interlayer consists of a β titanium alloy with no precipitation of intermetallic compounds. The second brazing alloy, Ti–12Zr–14Cr–6Fe–5Cu–5Ni (type 2), has to be brazed above the β transus temperature of Ti–6Al–4V. Its powders were mixed with pure titanium and Ti–6Al–4V powders and the mixture was used as the joining interlayer. Interlayers 5 mm in thickness were used to produce joints for microstructural examination and mechanical testing. It was found that residual pores in the interlayers were related to the amount of the brazing alloy in the interlayer. A fully dense interlayer could be obtained with 60 wt-% brazing alloy in the interlayer. The as bonded joints revealed tensile strength equal to 50% of that of the base metal. Diffusional treatment of the joints improved the joint efficiency to about 70%, compared with the base metal.     

用于ETC系统的羰基铁粉二氧化钛复合吸波材料

将羰基铁粉和二氧化钛与橡胶混合,采用压延法制备了应用在工作频率为5.8GHz的电子不停车收费系统(ETC)中的吸波材料,运用矢量网络分析仪测试了材料的复磁导率与复介电常数在2.0~18.0GHz范围的频谱特性,并在微波暗室内测试了材料的反射率。结果表明,Fe与TiO2在7∶3质量比混合下性能最佳,实验探讨了样品厚度对材料吸波特性的影响,确定厚度在1.7mm时,材料吸收峰值位于ETC所工作的5.8GHz频率,实验测试了材料在电磁波从不同角度入射条件下的反射率,垂直入射情况下效果最佳,可达-30dB。     

PVP对石墨烯/Fe3O4复合吸波材料形貌及吸波性能的影响

目的研究分散剂PVP对Fe_3O_4在石墨烯表面分散性的影响,以获得吸波性能良好的吸波材料。方法采用溶剂热法制备石墨烯/Fe_3O_4复合吸波材料,通过扫描电子显微镜、X射线衍射分析仪、X射线光电子能谱、矢量网络分析仪等对石墨烯/Fe_3O_4复合吸波材料进行表征,并研究了PVP添加与否在石墨烯/Fe_3O_4复合吸波材料形貌及吸波性能的影响。结果添加PVP后的石墨烯/Fe_3O_4复合吸波材料与未添加PVP的相比,Fe_3O_4在石墨烯表面的团聚现象明显减少,尺寸显著减小。通过计算机模拟反射率,未添加PVP的石墨烯/Fe_3O_4复合吸波材料在匹配厚度d=2.00 mm时,在16.25 GHz处达到最大反射损耗-18.79 dB,复合材料反射损耗小于-10 dB的频带宽度可达4.1 GHz。添加PVP的复合材料在匹配厚度d=2.00 mm时,在16.25 GHz处达到最大反射损耗-25.88 dB,复合材料反射损耗小于-10 dB的频带宽度可达4.5 GHz,相比未添加PVP的复合吸波材料,反射损耗小于-10 dB的频带宽度增加0.4 GHz,最大反射损耗提高7.09 dB。结论 PVP能提高Fe_3O_4在石墨烯表面的分散性,并在石墨烯表面形成良好的导电网络,使复合材料的吸波性能明显提升。     

The influence of magnetic and dielectric loss on the noise absorption of iron particles-rubber composites attached to a microstrip line

Magnetic and dielectric loss are systematically controlled by using iron flake powders with various initial sizes (7 μm and 70 μm) as the absorbent fillers in the rubber matrix, and their noise absorbing characteristics have been investigated as a function of frequency and sheet thickness. Flake iron particles were prepared by the mechanical forging of spherical powders using an attrition mill. Composite sheets (thickness=0.2 mm-1.0 mm) were prepared with a mixture of iron particles and silicone rubber. Attaching the composite sheets to a microstrip line of 50 Ω, a network analyzer was used to measure the reflection and transmission parameters (S₁₁ and S₂₁, respectively). A nearly constant value of S₁₁ (about −10 dB) was observed, irrespective of particle size. However, S₂₁ is strongly dependent upon initial particle size. For the composites of 7 μm particles (with high magnetic loss), S₂₁ is reduced below −20 dB in the frequency range of 1 GHz to 10 GHz, and the corresponding bandwidth of noise absorption is not so greatly diminished by reducing the sheet thickness as low as 0.2 mm. For the composites of 70 μm particles (with high dielectric loss), however, the bandwidth is greatly reduced with a decrease in sheet thickness. It is concluded that the attenuation of conduction noise through the microstrip line is primarily controlled by the magnetic loss of the iron particles due to strong magnetic field around the microstrip line.     

Sr0.8Re0.2Fe11.8Co0.2O19(Re=La,Nd)的制备、表征及吸波性能

采用溶胶凝胶法,制备Sr0.8Re0.2Fe11.8Co0.2O19(Re=La,Nd)复合铁氧体。采用X射线衍射仪、扫描电子显微镜、振动样品磁强计和矢量网络分析仪表征粉体的结构及电磁性能。结果表明:得到的粉体为纯净的磁铅石型铁氧体,La3+掺杂样品的各项性能明显改善。在室温条件下,稀土离子掺杂后样品的Ms受到稀土离子掺杂的影响较小,Hc则明显提高;La^3+掺杂样品和Nd3+掺杂样品的Ms值接近,前者的Hc值则明显强于后者的,Sr0.8La0.2Fe11.8Co0.2O19的Ms和Hc分别为58.08A m^2/kg和362.0kA/m。稀土离子掺杂使铁氧体样品的复介电常数(ε′和ε″)增大,与Nd3+掺杂样品相比,La3+掺杂样品的介电损耗和磁损耗改善更为明显。利用传输线理论优化设计时发现,在1.2~2.4 mm之间,随着厚度的增加,Sr0.8La0.2Fe11.8Co0.2O19的反射率峰值先减少后增加,逐渐向低频移动;在厚度为2.0 mm时,其反射率峰值达到最小值为27.8 dB(11.8 GHz),小于10 dB的吸波带宽为5.2 GHz(9.5~14.7 GHz)。     

Nd元素对Ce2Co17为基体的合金吸波性能的影响

目前,具有高效、宽、薄等特点的微波吸收材料已经引起了研究人员的广泛关注。在此文中,采用真空电弧熔炼和高能球磨法制备片状NdxCe2-xCo17合金粉末并且通过相关设备研究Nd含量和匹配厚度对相组成、形貌、电磁参数和微波吸收性能的影响。结果显示,Nd0.3Ce1.7Co17粉末的最大反射率可以达到-32.36dB,同时有效带宽能扩大4倍。此外,调整Nd含量能成功优化Ce2Co17合金粉末的微波吸收性能。随着Nd含量的增加,吸收峰有向低频段移动的趋势,并且当厚度为1.8mm时,Nd0.3Ce1.7Co17 粉末在7.28 GHz处,最大反射率可以达到-30.53 dB并且有效带宽为2.24 GHz,这些表明Nd-Ce-Co合金可以用作在C波段具有低厚度、宽频和高效等特点的理想吸收材料。     

Densification behavior of nanocrystalline W–Ni–Fe composite powders prepared by sol-spray drying and hydrogen reduction process

This paper studied the densification behavior of nanocrystalline composite powders of 93W–4.9Ni–2.1Fe (wt.%) and 93W–4.9Ni–2.1Fe–0.03Y synthesized by sol-spray drying and hydrogen reduction process. The X-ray diffraction (XRD) analysis showed that γ-(Ni, Fe) phase was formed in the final obtained powders. Powders morphology characterized by scanning electron microscope (SEM) showed that the 93W–4.9Ni–2.1Fe nanocrystalline composite powders exhibited larger agglomeration and grain size compared with the 93W–4.9Ni–2.1Fe–0.03Y nanocrystalline composite powders. Both kinds of green compacts can obtain full density if sintered at 1410 °C for 1 h. When sintering temperature was above 1410 °C, the sintering density for both compacts decreased rapidly. In addition, the sintering density, densification rate and grain coarsening rate of 93W–4.9Ni–2.1Fe compacts were higher than those of 93W–4.9Ni–2.1Fe–0.03Y. The effect of trace yttrium on the densification behavior of nanocrystalline composite powders was also discussed.