Preparation of magnetic ZSM-5/Ni/fly-ash hollow microspheres using fly-ash cenospheres as the template

Magnetic ZSM-5/Ni/fly-ash hollow microspheres are prepared by using fly-ash cenospheres as the template. The preparation procedure mainly includes two steps, i.e., preparation of magnetic nickel/fly-ash composites by electroless plating and growth of the ZSM-5 layers on the nickel/fly-ash composites by a secondary growth method. The samples are characterized by scanning electron microscope, X-ray diffraction, nitrogen adsorption and vibrating sample magnetometer. The resulting ZSM-5/Ni/fly-ash hollow microspheres show integral hollow structure and magnetic property. They are floatable on water surface when the electroless plating time is 10 min and the hydrothermal synthesis time is 12 h at 180 °C. The floatability of these hollow microspheres can further be adjusted by changing the electroless plating and hydrothermal synthesis times. Furthermore, their magnetic property can also be managed by controlling the synthesis conditions.     

碳纳米管/聚苯胺/钴复合物的制备及其微波吸收特性研究

采用多壁碳纳米管(样品A)为原料,采用原位聚合方法制备了聚苯胺包覆的碳纳米管(样品B),再利用电镀工艺制备了碳纳米管/聚苯胺/钴复合物(样品C).通过透射电镜(TEM)、红外光谱(FTIR)和振动样品磁强计(VSM)等手段分别对样品A、B和C的形貌、微结构与磁性能进行了表征,并采用网络分析仪分别对样品A、B和C的微波吸收特性进行了研究.发现在相同的吸波剂含量(5%)下,样品B吸收峰的强度和频带宽度均比样品A减少,而样品C的吸收峰强度和吸波频带宽度均比样品A和B增大.     

Synthesis and microwave absorption properties of magnetite nanoparticles

Nanoparticles of Fe3O4 with various sizes were synthesized from FeCl3 x 6H2O, FeCl2 x 4H2O and NaOH by coprecipitation process. The crystal structure, morphology, particle size and magnetic property of the products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). It was found that the molar ratio of ferrous to ferric played an important role in the formation of Fe3O4 nanoparticles. The particle mean diameter swelled from approximately 10 to approximately 20 nm with the molar ratio range from 1:2 to 6:1. The saturation magnetization and the coercivity increased correspondingly. The complex permittivity epsilon(r) and permeability mu(r) of the Fe3O4 mixture with paraffin were measured using vector network analysis. Values of epsilon(r), and mu(r) were used to determine the reflection loss at various sample thicknesses, based on a model of microwave absorbing layer backed by a metal plate. The minimal reflection loss or the dip shifts to a lower frequency region with increasing thickness. When the thickness is 5 mm, the minimal reflection loss of Fe3O4 synthesized with the molar ratio of 6:1 and paraffin wax composites reaches -35.1 dB at 5.2 GHz and -30.2 dB at 17.6 GHz, respectively. The minimal reflection loss is attributed to the thickness of the absorber approximates an odd number multiple of a quarter of the propagation wavelength.     

Synthesis,characterization and microwave absorption properties of Fe3O4/Co core/shell-type nanoparticles

Co coated Fe₃O₄ core/shell-type nanoparticles were fabricated by hydrothermal technique and electroless plating process. X-ray powder diffraction (XRD), X-ray fluorescence spectrometer (XRF) and transmission electron microscope (TEM) were employed to investigate the crystal structure, element composition and morphology of the prepared nanoparticles. Vibrating sample magnetometer (VSM) and vector network analyzer were used to measure the magnetic properties and electromagnetic parameters of pure Fe₃O₄ and Fe₃O₄/Co core/shell-type nanoparticles, then reflection losses (RL(dB)) were calculated in the frequency range of 2–18 GHz. Magnetic studies revealed typical ferromagnetic behavior for the pure Fe₃O₄ and Fe₃O₄/Co core/shell-type nanoparticles with their saturation magnetization (M_s = 63.1 and 72.4 emu/g) and coercivity (H_c = 99.5, and 165.4 Oe), respectively. Due to the existence of the core/shell structure, the electromagnetic characteristic of the Fe₃O₄/Co nanoparticles exhibit better microwave absorption performance than the pure Fe₃O₄ in the range of 2–18 GHz, such as more powerful absorbing property and wider frequency band of microwave absorption.     

氧化铟锡(ITO)薄膜的透明吸波特性研究

利用直流磁控溅射技术室温下在柔性聚酯薄膜衬底上制备了ITO薄膜,将ITO薄膜与有机玻璃和空白聚酯薄膜等介质材料组合成复合结构,最终得到吸波能力较强的透明吸波体.该吸波体在Ku带(12～18GHz)范围波段衰减低于-10dB,峰值超过-20dB,且在可见光区透光率达到68%.     

Processing and characterization of a lightweight concrete using cenospheres

A study has been conducted in which a lightweight concrete was processed using ceramic microspheres, known as cenospheres, as a primary aggregate. The mechanical properties, including compressive strength, tensile strength, flexural strength and fracture toughness, were tested and cataloged. It was determined that the addition of high volumes of cenospheres significantly lowered the density of concrete but was also responsible for some strength loss. This strength loss was recovered by improving the interfacial strength between the cenospheres and the cement. The interfacial properties were quantified using interfacial fracture mechanics techniques. These techniques were also employed to find a suitable surface modifier with which to improve this interface. The admixture silica fume and the coupling agent Silane were found to be suitable candidates and both performed well in small-scale compression testing. Silica fume was eventually isolated as a prime candidate. The concrete produced with this admixture was tested and compared to a concrete with an equal volume fraction of cenospheres. The addition of silica fume improved the compressive strength of cenosphere concrete by 80%, tensile strength by 35%, flexural strength by 60% and fracture toughness by 41%.     

HAP/聚酯生物复合材料的制备与吸波特性

采用化学沉淀法合成了纳米羟基磷灰石粉体(HAP),与不饱和聚酯复合制备了HAP/聚酯生物复合材料,用X射线衍射和透射电镜等实验手段对纳米粉体的粒径和表面形貌进行了表征,应用微波网络S参数法测量了HAP/聚酯生物复合材料的吸波性能,结果表明:HAP粉体粒径在100nm以下,呈颗粒状,粒径分部均匀;HAP/聚酯生物复合材料在一定频率范围内具有良好的吸波性能,并简要分析了其吸波机理.     

Silica-coated iron nanoparticles: Shape-controlled synthesis,magnetism and microwave absorption properties

Body-centered cubic (bcc) phase iron nanocrystals with granular, rod-like and flaky shapes were prepared through a simple surfactant-controlled chemical reduction route. In view of extra stability and enhanced manipulative ability, thus-prepared iron nanoparticles were morphology-retained modified with a thin silica shell through a Stöber process. A serial of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), thermogravimetry (TG), vibrating sample magnetometer (VSM) and scalar network analyzer (SNA) were used to characterize the iron particles before and after silica coating. Results showed that the surface silica coating could effectively improve the oxidation resistance and microwave absorption performance of iron particles, while slightly influenced their magnetic properties. Furthermore, the flaky Fe@SiO₂ nanocapsules particles exhibited better microwave absorption performance than that of the granular and rod-like counterparts, which could be ascribed to the shape effect.     

CoxSy/C@MoS2 nanofibers: synthesis,characterization and microwave absorption investigation

Journal of Materials Science: Materials in Electronics - Microwave absorbing materials have been widely studied and applied nowadays, but their loss mechanism, especially the correlation between...     

Preparation and microwave absorbing properties of SiC microtubes

Using cotton as carbon source and template, SiC microtubes were prepared by the carbothermal reduction of a cotton-contained precursor, which was obtained by impregnating cotton in tetraethyl orthosilicate solution. To characterize the product, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and network analyzer were used. The results show that the SiC microtubes with surfaces composed of villus-like β-SiC nanowires have a length of tens to hundreds of micrometers and a diameter of several to 20 μm. SiC microtubes achieve a reflection loss below −10 dB (90% absorption) at different frequencies, and the minimum value is −23.9 dB at 17.5 GHz when its thickness is 1 mm.     

微波辐照纳米银的制备与表征

在微波辐照下,以硝酸银为银源,水为溶剂,聚乙烯吡咯烷酮(PVP)为稳定剂和还原剂,不加入其他还原剂的条件下,快速制备出纳米银胶体。利用紫外光谱法,对微波制备纳米银粒子的条件进行了一系列研究,得出了先40℃下预热15min,再微波辐照30min,微波功率为260W,AgNO3∶PVP=1∶3(质量比)为最佳制备条件。对制得的纳米银粒子进行了TEM、SPM、DTA表征,发现制得的纳米银粒子为球形粒子,粒径较小,且粒径分布较窄,为18~25nm。对PVP的作用机理研究认为:主要是由于Ag离子与PVP的配位作用和PVP的空间位阻效应,使得能够制备出纳米球形银粒子。     

Preparation, characterization and properties of MgSiN2 ceramics

MgSiN₂ ceramics with and without sintering additives were prepared by hot uni-axial pressing. For the sintered samples the lattice parameters, secondary phases, density, oxygen and nitrogen content, microstructure, oxidation resistance, hardness, elastic constants, linear thermal expansion coefficient and thermal diffusivity were determined. By suitable processing, fully dense MgSiN₂ ceramics with an oxygen content <1.0 wt % could be obtained. The size of the MgSiN₂ grains increased with increasing hot-pressing temperature and time. Transmission electron microscopy (TEM) showed the absence of grain-boundary phases and that secondary phases are present as separate grains in the MgSiN₂ matrix. Scanning thermal microscopy (SThM) thermal imaging revealed a thermal barrier at the grain boundaries. The influence of the microstructure as well as the oxygen content and defect chemistry on the thermal diffusivity is limited. Supported by some theoretical considerations it is concluded that the thermal conductivity of the MgSiN₂ ceramic samples is determined by intrinsic phonon-phonon scattering and will not exceed 35 W m^-1K^-1 at 300 K in agreement with the maximum observed value of 21–25 W m^-1 K^-1.     

Preparation, characterization and microwave absorption properties of polyaniline/Co0.5Zn0.5Fe2O4 nanocomposite

The polyaniline (PAni)/Co_0.5Zn_0.5Fe₂O₄ nanocomposite was prepared by an in situ polymerization in an aqueous solution. The products were characterized by Fourier transform infrared (FT-IR) spectrometer, ultraviolet-visible (UV-vis) spectrometer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The average particle size of the PAni/Co_0.5Zn_0.5Fe₂O₄ was estimated to be about 70 nm by TEM. The reflection loss (dB) of the nanocomposite was measured at different microwave frequencies in X-band (8.2-12.4 GHz), U-band (12.4-18 GHz) and K-band (18-26.5 GHz) by radar cross-section (RCS) method according to the national standard GJB-2038-94. The results showed the reflection loss of the PAni/Co_0.5Zn_0.5Fe₂O₄ nanocomposite was higher than that of the PAni. The maximum reflection loss of the PAni/Co_0.5Zn_0.5Fe₂O₄ nanocomposite was about −39.9 dB at 22.4 GHz with a bandwidth of 5 GHz (full frequency width at about a half of the peak response). In conclusion, this sample is a good microwave shielding and absorbing materials at higher frequency.     

Controllable synthesis and morphology-dependent microwave absorption properties of iron nanocrystals

Iron nanospheres, nanoflakes and nanofibers were synthesized via a simple pyrolysis method. When the pyrolysis temperature increased from 523 to 623 K and the flow rate of Ar carrier gas maintained at 100 sccm, the as-prepared iron nanocrystals showed a morphology evolution from isotropic nanospheres to isotropic nanofibers. The phase structures and morphologies of the composite were characterized by X-ray diffraction and scanning electron microscopy. The complex permittivity (ε′ − jε″) and permeability (μ′ − jμ″) of these composites were measured using the transmission/refection coaxial line method in the frequency range of 1–18 GHz by a vector network analyzer. The iron nanofibers exhibited superior microwave absorbing properties compared to iron nanoparticles and nanoflakes. The optimal reflection loss (RL) reached −17.8 dB at 9.9 GHz with a layer thickness of 2.0 mm. The RL below −10 dB can be obtained in the frequency range of 7.3–11.7 GHz. Considering the low cost and high efficiency; the iron nanofibers are favorable for application as microwave absorber.     

纳米镍铜铁氧体粒子的制备与微波吸收特性研究

采用溶胶 凝胶法制备了纳米镍铜铁氧体粒状材料,并对其吸波性能进行研究。实验结果表明,镍铜铁氧体有很好的微波吸收特性,在微波波段有两个吸收峰,较大的吸收峰在 9. 834GHz 处,其值为13.3dB,半峰宽度为3.612GHz。然后,把不同微量稀土铈掺杂到镍铜铁氧体当中,发现适量的稀土铈能提高镍铜铁氧体的吸波性能。较大的吸收峰向高频移动到10.049GHz,其吸收值提高到 21.906dB,半峰宽度展宽为 4.322GHz。镍铜铁氧体是一种有应用价值的新型微波吸收材料。     

Relaxation dynamics,microwave absorption,and secondary periodicity in properties of rare-earth-modified bismuth ferrites

Based on an analysis of the structure and physical properties of bismuth ferrite (BiFeO₃) modified by rare-earth (RE) elements, solid solutions characterized by the presence of spontaneous magnetization, low- and high-temperature relaxation, and maximum microwave absorption have been found. It is established that these materials exhibit a secondary periodicity in their properties. The observed effects are related to the appearance of symmetry phase transitions, specific features of the crystal chemistry of RE elements, and changes in the type of solid solutions.     

Study on microwave absorption properties of metal-containing foam glass

Materials with the properties of electromagnetic (EM) wave absorption are attractive topics. In this work, we report that EM wave absorption composites, consisting of foam glass, zinc and zinc oxide, were prepared by sintering mixture of foam glass raw material and zinc powder. Microwave reflection loss of composite was calculated based on the permittivity in the range of 8.2-12.4 GHz. The results show that zinc-containing foam glass absorbs efficiently microwaves. The sample with zinc filler to foam glass mass ratio of 3/18 had a reflection loss below −10 dB in the range of 11.3-12.4 GHz, and the minimum reflectivity was −15.6 dB at both 12.0 and 12.4 GHz. Microwave absorption performances of specimens can be controlled by changing the ratio between zinc powder and foam glass mass. The detailed mechanism of the control was investigated through X-ray diffraction (XRD) analysis and scanning electrical microscopy (SEM) observations.     

Fe基玻璃包覆微丝的吸波性能研究

实验分析了微丝的组织结构，表明微丝是非晶态的，内部芯丝表面光滑，在长度方向上厚度均匀。用矢量网络分析仪测定了微丝的电磁参数，并进行了不同填充率不同厚度的单层吸波涂层设计，结果显示微丝在微波波段10～18GHz频段范围内具有较好的衰减特性，反射率最小值为--32dB，吸波效果好。     

BaMnZnCoTi-W型铁氧体微波吸收剂的制备和特性研究

对用Ｃｏ２＋、Ｔｉ４＋部分置换Ｆｅ３＋的Ｂａ（ＭｎＺｎ）ａＣｏｂＦｅ１６－ｙＣｏ２＋０．５ｙＴｉ４＋０．５ｙＯ２７－Ｗ型平面六角晶系微波铁氧体吸收剂的制备和特性进行了研究,并对其复介电常数的实部ε′和虚部ε″、磁导率的实部μ′和虚部μ″、损耗随微波频率、Ｃｏ２＋、Ｔｉ４＋含量、涂层厚度的变化作了测试和分析,发现当ｙ＝１．０时铁氧体的吸收性能最佳,其最佳厚度为１．４０ｍｍ,吸收衰减最大达２７．５ｄＢ。