Papers by Keyword: Microwave Absorption Property

Abstract: The BaFe₁₂O₁₉ nanoparticles was prepared by sol-gel method in different temperature (750°C,850°Cand 950°C), and then BaFe₁₂O₁₉/polyaniline nanocomposites was synthesized by in situ polymerization. The XRD, FTIR spectra, SEM and vector network analyzer were used to analyze the "" chemical component, morphology and microwave absorption property of the nanocomposites. The result show that BaFe₁₂O₁₉ can be generated at 750°C without any impurity ,and its size increased with increase of calcination temperature.BaFe₁₂O₁₉ nanoparticle was coated with polyaniline partially, and we can get it have interaction with polyaniline through FTIR spectra. While the ferrite calcined at 850°C,the thickness of the absorbing material is 4.5mm,the nanocomposites have the largest reflection loss of-17.6 dB at 6 GHz,and its reflection loss values less than−10 dB in the range of 5-7.4GHz.

Abstract: Polyaniline (PAni) Nanocomposites Containinganiline (Ani) Monomer and Hexanoic Acid (HA) Dopant were Successfullysynthesized by Using Chemical Oxidation Method. Titanium Dioxide (TiO₂)and Different Dimension of Multiwall Carbon Nanotubes (MWNT) Have been Added Inorder to Improve the Dielectric Permeability and Magnetic Permittivityproperties of the Pani Nanocomposites. Fourier Transform Infrared (FTIR) Andultraviolet-Visible (UV-Vis) Spectra Confirmed the Chemical Structure of Paninanocomposites. Conductivity and Magnetization Behavior were Investigated Byresistivity Meter and Vibrating Sample Magnetometer (VSM). Microwave Absorptionstudies were Carried out by Microwave Vector Network Analyzer (MVNA) from 0.5to 18 Ghz. among all the Pani Nanocomposites, Pani Nanocomposites with MWNT (D = 10-2- Nm, l = 5-15 μm) Shows Agood Reflection Loss (RL = -58 Db) at 7 Ghz with a Sharp and Narrow Peak due Tohigher Values of Magnetization (0.074 Emu/g) Andmoderate Electrical Conductivity (1.11 x 10^-2 S/cm)

Abstract: The low-grade ludwigite is one of the complex and refractory ores. Based on the high energy consumption and inefficient in the grinding process and according to the microwave-assisted grinding principle, this paper studied the microwave absorption property of ludwigite and researched the effect of microwave heating on the grinding efficiency of it. The non-microwaved and microwaved samples were characterized with regard to the chemical components, mineral compositions, macroscopic structure and microstructure, grinding efficiency by methods of the chemical analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and grain size analysis, etc. The results indicated that ludwigite, with good microwave absorption property, was suitable for microwave processing. The grindability of microwaved ludwigite was related to the microwave power and microwave heating temperature. By the microwave heating temperature attained 500~650°C, many macro-cracks and micro-cracks were produced by thermal stress between different mineral interfaces, which resulted in the decrease of strength of ludwigite and easy levigation, but the mineral compositions had no obviously changed, which would not affect the subsequent magnetic separation. It was concluded that short, high-power treatments were most effective but over-exposure of the sample led to reductions in efficiency. Under the same conditions, the grinding efficiency of ludwigite was improved 24.54% higher than untreated ore, which significantly improved the grinding efficiency and reduced energy consumption.

Abstract: The electroless Ni-Plated technique was used to fabricate the coupled and activated Glass beads /Carbon Fiber. The microstructure of Ni-P-GBs/CFs was analyzed by IR, SEM, EDS, and the microwave absorption properties were characterized by Vector Network Analyzer. The results showed that Ni-p alloy layer is dense and continuous after electro less plating. When the mass ratio is 3:2(GB/CFs), and mass percent of mixed dusty materials is 22.5%, the average loss value is lower than -5 dB in the frequency range of 2～18 GHz, while the greatest loss value is up to -12.4dB in the 15.1 GHz.

Abstract: The core-nanoshell composite materials doped with Nd were prepared by a solid-state reaction method. The core is magnetic fly-ash hollow cenosphere, and the shell is the nanosized ferrite doped with Nd. The thermal decomposition process of the sample was carried out by the thermogravimetry and differential thermal analysis ( TG-DTA ). The morphology and components of the composite materials were investigated by the X-ray diffraction analysis ( XRD ), scanning electron microscope ( SEM ) and energy disperse spectroscopy ( EDS ). The microwave absorption property was investigated by vector network analyzer ( VNA ). The results indicated that the exchange-coupling interaction happens between ferrite of magnetic fly-ash hollow cenosphere and nanosized ferrite coating. The exchange-coupling interaction enhances magnetic loss of composite materials. So, in the frequency between 1 MHz and 1 GHz, the absorbing effectiveness of the core-nanoshell composite absorbers can achieve –31 dB, it is better than single material and is consistent with requirements of the microwave absorbing material at the low-frequency absorption.

Abstract: M-typical SrFe12O19 ferrites and FeNi3 nanoplatelets were successfully prepared by the sol-gel method and solution phase reduction method, respectively. The crystalline and morphology of particles were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The composite coatings with SrFe12O19 ferrites and FeNi3 nanoplatelets in polyvinylchloride matrix were prepared. The microwave absorption properties of these coatings were investigated in 2-18GHz frequency range. The results showed that the M-typical SrFe12O19 ferrites and FeNi3 nanoplatelets were obtained and they presented irregular sheet shapes. With the increase of the coating thickness, the absorbing peak value moves to the lower frequency. The absorbing peak values of the wave increase along with the increasing of the content of FeNi3 nanoplatelets filling fraction. When 40% SrFe12O19 ferrites is doped with 20% mass fraction FeNi3 nanoplatelets to prepare composite with 1.5mm thickness, the maximum reflection loss is -24.8 dB at 7.9GHz and the -10 dB bandwidth reaches 3.2GHz.

Abstract: Alumina/carbon nanotubes (Al2O3/CNTs) composite coating was synthesized by plasma spray employing mixtures of Al2O3-coated CNTs and nano-sized α-Al2O3 at atmosphere. This coating was characterized for the microstructure and the composition by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), thermo gravimetric analysis (TG), differential scanning calorimetry analysis (DSC) and scanning electron microscopy (SEM). The results show that the thickness of the coating is about 0.5mm and the constituent elements were changed to α-Al2O3, CNTs and γ-Al2O3 duo to the superhigh temperature during the plasma spray process. The great mass of the mixtures were melted well and the CNTs were dispersed uniformly in the melted ceramic. The oxidation resistance and the microwave absorption properties were discussed simply to describe the functions of the composite coating.

Abstract: Both the complex permittivity and permeability of nanometer SiC and nanometer SiC/CNTs composite were investigated by Hewlett-Packard 8510B Network Analyzer. The results show that the complex permittivity of nanometer SiC/CNTs composite is much higher than that of nanometer SiC. Reflection curves of nanometer SiC and nanometer SiC/CNTs composite calculated with electromagnetic wave transmission-line theory show that the addition of CNTs at 6 wt%, 12 wt% and 18 wt% in nanometer SiC absorber can improve its microwave absorption properties strongly. There is a relationship between the mass fraction of CNTs and microwave absorption ability. With increase of the mass fraction of CNTs, its microwave absorption ability firstly increased then decreased. From the simulation, it was found that nanometer SiC with 12 wt% CNTs gave the optimum microwave absorption. The corresponding frequency of maximum reflection loss value of nanometer SiC/CNTs composite gradually moves to the low frequency range with increase of thickness. The maximum reflection loss value of nanometer SiC/CNTs composite (CNTs content is 12 wt%) was -25.74dB at the corresponding frequency of 11.60 GHz with a bandwidth under -5 dB (68% absorption) is 7.16 GHz when the thickness is 2.0 mm.

Abstract: The Co2Z hexaferrites powders, Ba3Co2Fe24O41, were synthesized by the molten salt method. The results indicated that the ferrite powders possess hexagonal shape and are well separated from one another. The composite with 40vol% Co2Z content has shown a minimum reflection loss of -24dB at 9.5GHz with a -20dB bandwidth over the extended frequency range from 8.3 to 10.2GHz in a quite thin sample with a thickness of 3.0mm. The molten salt method could be a potential way to enhance the properties of the composites filled with hexagonal ferrite powders for electromagnetic applications.