Preparation and Microwave Absorbing Properties of Double-layer Fine Iron Tailings Cementitious Materials

To develop the microwave absorbing(MA)properties of cementitious material mixed with mine solid waste,the iron tailings cementitious microwave absorbing materials were prepared.The iron tailings was treated into different particle sizes by planetary ball mill,and the physicochemical properties of iron tailings were tested by laser particle size analyzer and scanning electron microscope(SEM).The electromagnetic parameters of iron tailings cementitious materials were characterized by a vector network analyzer and simulated MA properties,and the MA properties of iron tailings-cement composite system with steel fiber as absorber was studied.Based on the design of the single-layer structure,optimum mix ratio and thickness configuration method of double-layer structure were further studied,meanwhile,the mechanical properties and engineering application were analyzed and discussed.The results show that the particle size of iron tailings can afiect its electromagnetic behavior in cementitious materials,and the smaller particles lead the increase of demagnetisation efiect induced by domain wall motion and achieve better microwave absorbing properties in cementitious materials.When the thickness of matching layer and absorbing layer is 5 mm,the optimized microwave absorbing properties of C1/C3 double-layer cementitious material can obtain optimal RL value of-27.61 dB and efiective absorbing bandwidth of 0.97 GHz,which attributes to the synergistic efiect of impedance matching and attenuation characteristics.The double-layer microwave absorbing materials obtain excellent absorbing properties and show great design flexibility and diversity,which can be used as a suitable candidate for the preparation of favorable microwave absorbing cementitious materials.

Microwave Absorbing Performance of RE-Fe Based Alloys

REI3Fes4Cr3（RE=Ce, Pr, Tb, Er） and Pr13_XFes4Cr3Ti（x=0, 2, 4, 6） alloy powders were prepared by are smelting method and high energy ball milling technique. The phase structure and the morphology of the alloy powders were investigated by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and their microwave absorbing properties were determined by a vector network analyzer. The results show that the alloys with light rare earths （Ce, Pr） have good low frequency absorbing property and those with heavy rare earths （Tb, Er） exhibit an improved high frequency absorbing property. The minimum refleetivity at the absorbing peak frequency of RE,FeuCr3（RE=Ce, Pr, Tb, Er） are -9.49 dB at 5.76 GHz, -22.38 dB at 7.92 GHz, -18.52 dB at 11.68 GHz and -17.59 dB at 10.24 GHz, respectively. The absorbing bandwidth under -10 dB of the Pr13FesaCr3 powder was widened from 1.91 GI-Iz to 3.89 GHz by adding 2% Ti, but the reflectivity of the alloy was increased from -22.38 dB to -14.91 riB.

Study of Microwave Absorbing Performances of Nanometer Fe-Al Solid solution

In this paper,Fe-Al solid solution was prepared by mechanical alloying technology,and Fe-Al powder was dispersed into unsaturated polyester (UP) with different contents as absorber to form mixture Fe-Al-UP.The results indicate that the alloying process is almost accomplished and most of the particles are nanometer.Meanwhile,the microwave absorbability of Fe-Al-UP samples in frequency from 0.3 MHz to 1.5 GHz was studied.The results indicate that the more the absorber,the better the absorbing property.The absorbing property of Fe-50Al-UP was slightly higher than Fe-28Al-UP.

Electromagnetic and microwave absorbing properties of FeCoB powder composites

The electromagnetic and microwave absorbing properties of FeCoB powder composites prepared by sin- gle-roller melt-spinning and mechanical milling processes were investigated in this paper. The result indicates that the flake-like powders are obtained. As milling time increases, the flake-like powder particles tend to agglomerate, causing the flake-like powders decrease gradually. The milling time plays an important role in the electromagnetic parameters which relates to the shape and size of the powder particles. The calculation shows that the sample milled for 6 h could achieve an optimal reflection loss of -11.5 dB at 5.8 GHz, with mass fraction of 83 % and a matching thickness of 1.8 mm. The result also indicates that the microwave absorbing properties of the FeCoB powder composites are adjustable by changing their thickness, and can be applied as a thinner microwave absorbing material in the range of 2-8 GHz.

Mossbauer spectroscopy studies on the particle size distribution effect of Fe–B–P amorphous alloy on the microwave absorption properties

An Fe-based nanocrystalline alloy powder is important for application in microwave absorption,and the particle size has a critical impact on the electromagnetic microwave parameters.Therefore,it is necessary to study further the effects of the particle size on such parameters and improve the microwave absorption performance of Febased nanocrystalline powers.In this study,Fe-B-P particles were prepared through a synthetic approach consisting of an aqueous chemical reduction and a ball milling treatment.We investigated the effects of ball milling on the microstructure and electromagnetic properties of Fe-B-P particles.The experimental results indicate that the Fe-B-P particles synthesized through an aqueous chemical reduction are amorphous spheres.Fe-B-P particles with an original particle size of 200-1200 nm can be milled into an irregular shape with the size reduced to\500 nm after 0.5 h of ball milling,and subsequently,the particles become smaller with increases in the milling time,with traces of Fe2O3 generated on the particle surface.The results of the Mo¨ssbauer spectra show that a portion of the small particles demonstrate a superparamagnetic property.The volume proportions of the superparamagnetic component increase from 13.1 to 15.8%as the treatment time increases.We measured the permittivity and permeability spectra of Fe-B-P particles within the frequency range of 2-18 GHz.The reflection loss(RL)is-10 dB for an absorber thickness of 1.7-5.0 mm.The RL is-20 dB for an absorber thickness of 1.9-2.7 mm.The microwave absorption properties of samples with the same thickness are improved with an increase in the treatment time and are shifted to a higher frequency,which will broaden the bandwidth of the absorption as well.

Magnetic and microwave absorbing properties of Ce-Co-based alloy powders driven with lanthanum content

The composites of Ce-Co-based alloys doped with La content were fabricated via a vacuum arc melting method.The influences of La addition on microstructure,electromagnetic parameters,magnetic property and microwave absorbing property were measured by the corresponding equipment.The morphology characteristics manifest that all samples display sheet structure,and the average particle size of alloy powders increases with increasing La content The saturation magnetization(MS) decreases with increasing La addition as a whole.The minimum reflection loss(RL) of La0.4Ce1.6Co17 alloy powder about-42.29 dB can be obtained about-42.29 dB at 7.84 GHz with the matching thickness of 1.8 mm,and the corresponding effective bandwidth can achieve about 2.24 GHz.In addition,the minimum RL frequency moves towards a lower frequency region as the La content increases.The minimum RL of La0.3Ce1.7Co17alloy powder is less than-20 dB ranging from 1.2 to 2.4 mm in the whole 4-16 GHz.The maximum bandwidth can reach about 4.88 GHz at the given thickness of 1.2 mm.In general,these all indicate that the La addition is beneficial to improving the microwave absorbing performance in both effective bandwidth and absorption intensity.

Microwave electromagnetic and absorbing properties of Dy^(3+) doped MnZn ferrites

Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM) and network analyzer(Agilent 8722ET).All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03.The average crystallite size was about 44?56 nm.The mi...

Synthesis and microwave absorbing properties of La-doped Sr-hexaferrite nanopowders via sol-gel auto-combustion method

La-doped Sr-hexaferrite（Sr（1-x）LaxFe（12）O（19））（x=0.05,0.10,0.15,0.20） nanopowders with particle size ranging from 80 to 110 nm were successfully synthesized by sol-gel auto-combustion. The phase formation temperature increases, while the particle size decreases as the Ladoping content goes up. The partial substitution of Sr^（2＋） by La^（3＋） results in the suppression effects on the growth-up of the crystallites and the enhancement of the electron hopping between Fe^（3＋） with different valences, which leads to the improvement in the dielectric loss and magnetic loss.Therefore, both the microwave absorbing abilities and absorbing frequency ranges are tuned by La-doping. The synthesized Sr-hexaferrite nanopowders with doping element content of 0.10 demonstrate the fine broad microwave absorbing properties.

Dielectric,magnetic and microwave absorbing properties of polyaniline-Co0.7Cr0.1Zn0.2Fe2O4 composites

The spinel cobalt chromium zinc ferrites（Co0.7Cr0.1Zn0.2Fe2O4） and the polyaniline（PANI）-Co0.7Cr0.1Zn0.2Fe2O4 composites were prepared by polyacrylamide gel and an in situ polymerization method,respectively.The structure of the synthesized material was characterized by X-ray diffraction（XRD） and Fourier transform infrared spectrometer（FTIR）,which shows that the spinel Co0.7Cr0.1Zn0.2Fe2O4 ferrites and the PANI Co0.7Cr0.1Zn0.2Fe2O4 composites are obtained.As a small amount of Co^2＋ in the octahedron ferrite is replaced by Cr^3＋,the lattice constant of Co0.8Cr0.2Zn0.2Fe2O4 ferrites reduces from0.8409 to 0.8377 nm.The magnetic properties of the two materials were investigated by vibrating sample magnetometer（VSM）.The VSM results confirm that the saturation magnetization（Ms）,remanent magnetization（Mr） and coercive force（Hc） of the PANI-Co0.7Cr0.1Zn0.2Fe2O4composites are 8.80 mA·m^2·g^-1,3.14 mA·m^2·g^-1 and37.22 kA·m^-1,respectively,which are smaller than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.The microwave absorbing capability of the two materials was studied by waveguide method.In the frequency range of 5-20 GHz,two reflection loss maximum values of the PANI-Co0.7Cr0.1Zn0.2Fe2O4 composites appear at 14.1 and 17.9 GHz with-13.17 and-15.36 dB,respectively,which are obviously higher than those of the Co0.7Cr0.1Zn0.2Fe2O4 ferrites.

Microwave Absorbing Properties of Magnesium-substituted MnZn Ferrites Prepared by Citrate-EDTA Complexing Method

Magnesium-substituted MnZn ferrites with composition of Mn0.4Zn0.6MgxFe（2-x）O4（x=0.00,0.05） were prepared by citrate-EDTA（ethylenediamine tetraacetic acid） complexing method.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction（XRD） analysis,scanning electron microscopy（SEM） and network analyzer（Agilent 8722ET）.All the XRD patterns showed the single phase of the spinel-type MnZn ferrite without other intermediate phase.The lattice parameter and average particle size increased with the substitution of magnesium.The microwave electromagnetic properties of the samples have been studied at the frequency range from 2 to 18 GHz.It was shown that the values of ε′ and ε″ decreased slightly with the substitution of magnesium.The values of μ′ and μ″ were improved significantly,and the peak of μ″ shifted to low frequency with Mg2＋ ions substituting.Furthermore,the reasons have also been discussed by using electromagnetic theory.The reflection loss（RL） ascended after magnesium was substituted.Magnesium-substituted ferrite had excellent microwave absorption properties.The frequency（with respect to-10 dB） started from 11.3 GHz,and the bandwidth reached about 3.5 GHz.The peak value of RL was about-19 dB at a matching thickness of 3.1 mm.

Effect of rare earths on microwave absorbing properties of RE-Co alloys

The powders of RE2Co17（RE=Y, Ce, Nd, Ho, Er） and Ho x Co100–x（x=6, 8, 10, 12） alloys were prepared by the arc melting method and high-energy ball mill process. The compositions and morphologies of the alloys were characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM）, and the microwave absorbing properties were studied by a vector network analyzer. The results showed that the alloy of Y2Co17 had better absorbing properties at low frequencies and its lowest reflectivity value was –9.5 d B at 3.8 GHz. The lowest reflectivity value of Ho2Co17 alloy was –13.7 d B at 7.02 GHz and it obtained large absorbing bandwidth. Reflectivity value less than –5 d B was from 5.1 to 10.2 GHz. When x=6 and x=8, the alloys of Ho x Co100–x consisted of Ho2Co17 phase and Co phase. They had good radar absorbing properties. With increase in Ho content, the minimum reflectivity value worsened and the absorbing peak frequency shifted toward higher frequencies. But when x=12, the absorbing peak frequency shifted toward lower frequencies but the minimum reflectivity value worsened.

Electromagnetic and microwave absorption properties of Er-Ho-Fe alloys

The ErxHo（2-x）Fe（17）（x = 0.0, 0.1,0.2, 0.3, 0.4） powders were prepared by arc melting and high energy ball milling method. The influence of the Er substitution on phase structure, morphology, saturation magnetization,electromagnetic parameters was investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）, vibrating sample magnetometer（VSM） and vector network analyzer（VNA）,respectively. The results show that the saturation magnetization increases and the average particle size increases with the increase of Er content. The minimum absorption peak frequency shifts towards a lower frequency region with the increase of Er content. The ErxHo2-xFe17 powder can achieve the minimum RL of-24.07 dB at 6.96 GHz with a thickness of 2.0 mm and the minimum RL is less than-20 dB at the thickness range from 2.0 to 3.0 mm. The minimum RL of ErxHo2-xFe17 is-37.26 dB at5.68 GHz and the frequency bandwidth of R〈-10 dB reaches about 1.2 GHz with a thickness of 2.4 mm.And the microwave absorbing properties of the composite with different weight ratios of Er0.3Ho1.7Fe17/graphene were researched. The microwave absorbing peaks of the composite shift to lower frequency with the increase of graphene content. The values of the minimum RL of ErxHo2-xFe17/graphene are close to-10 dB with absorbing coating thicknesses increased.

Novel hierarchical structure of MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites for dramatically enhanced electromagnetic absorbing properties

In order to prevent the microwave leakage and mutual interference,more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation.In this work,we have successfully prepared MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) hierarchical composites by one-pot hydrothermal method and focused on the relationship between structures and electromagnetic absorbing properties.Supported by comprehensive characterizations,M0S_(2) nanosheets were proved to be anchored on the surface and interlayer of Ti_(3)C_(2)T_(x) through a hydrothermal process.Additionally,TiO_(2) nanoparticles were obtained in situ.Due to these hierarchical structures,the MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites showed greatly enhanced microwave absorbing performance.The MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites exhibit a maximum reflection loss value of -33.5 dB at 10.24 GHz and the effective absorption bandwidth covers 3.1GHz(13.9-17 GHz)at the thickness of 1.0 mm,implying the features of wide frequency and light weight.This work in the hierarchical structure of MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites opens a promising door to the exploration of constructing extraordinary electromagnetic wave absorbents.

Preparation and microwave absorption properties of NdFeB alloys

In order to improve the microwave absorbing properties of NdFeB alloys, as-jet milled powders were further processed in a planetary mill. The phase structure, morphology and particle size of the alloy powders were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and laser diffraction-based particle size analyzer, respectively. The saturation magnetization and electromagnetic parameters of the powders were determined by a vibrating sample magnetometer （VSM） and a vector network ana-lyzer （VNA）, respectively. The results showed that the saturation magnetization decreased as the milling time increased. The mini-mum absorption peak frequency shifted towards the lower region and the reflection loss values increased with increasing the ball mill-ing time. The minimum absorption peak value of the powders milled for 15 h on the basis of jet milling reached–44.4 dB at 11.04 GHz, and the bandwidth of R〈–10 dB was 1.2 GHz with the best matching thickness of 1.8 mm.

Effects of cobalt substitution on structure and microwave absorption properties of PrNi_5 alloy

The polycrystalline samples PrNi5_xCox （x=0.0, 0.1, 0.2, 0.3, 0.4） were synthesized by arc smelting and high energy ball milling method. The phase structure, morphology, saturation magnetization and electromagnetic parameters of the alloy powders were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, vibrating sample magnetomctry （VSM） and vector network analyzer （VNA）, respectively. The results revealed that the lattice parameter a and c and unit-cell volume V increased with the increasing amount of Co substitution. The saturation magnetization increased as Co content increased. The minimum absorp- tion peak frequency shifted towards lower frequency region with the increasing amount of Co substitution. And the minimum reflec- tion loss of the PrNi5 xCox powders increased first and then decreased with the increasing amount of Co substitution. The PrNisCox alloys possessed the excellent microwave absorbing properties. The minimum reflection loss of the PrNi4.gCo0,1 alloy all could reach 20.0 all3 with the coating thickness ranging from 1.8 to 3 ram. The minimum reflection loss of PrNi4.gCoo.l powders was -36.20 d13 at 7.76 GHz, and the frequency bandwidth ofR〈10 dB reached about 1.50 GHz with the best matching condition d=2.0 ram.

Electromagnetic wave absorption properties of cobalt-zinc ferrite nanoparticles doped with rare earth elements

Traditional ferrites are of poor electromagnetic wave(EMW) absorption while doping rare earth elements(REEs) can greatly enhance their permeability to improve the EMW loss performance.In this study,Co-Zn ferrite nanoparticles doped with various amounts of REEs(Gd^(3+),Nd^(3+)and Pr^(3+)) were synthesized by a hydrothermal method,and their particle morphology and an EMW absorption performance were characterized by using transmission electron microscopy(TEM) and a Vector network analyzer(VNA).The results show that the initial spherical Co-Zn ferrite nanoparticles present an irregular quadrilateral structure after Gd^(3+)doping,and the average particle size of Co_(0.5)Zn_(0.5-x)Gd_(x)Fe_(2) O_(4) increases from 26 to 50 nm with x increasing from 0 to 0.35.At x of 0.25,the reflectivity absorbance achieves-27.94 dB at 18 GHz with the effective absorption bandwidth(EAB) of 4.08 GHz at a sample thickness of 2.5 mm.When Nd^(3+)doping amount reaches x=0.3,the minimum reflection loss(RL)is-25.63 dB at 18 GHz and EAB is 3.91 GHz.Doping Pr^(3+)(x=0.25) in the sample broadens EAB,and the minimum RL is-16.1 dB at 16.81 GHz and EAB is 7.31 GHz.This study shows that the magnetic moment produced by doping REES can form magnetic domains,which affects the incident EMW and improves the magnetic loss.It is expected that REEs-doped Co-Zn ferrite nanoparticles can be used as efficient electromagnetic shielding materials in aerospace.

Simulation and research of percolation phenomenon in T-ZnOw resin matrix composite

A novel three-dimensional lattice model of tetrapod-like zinc oxide whisker（T-ZnOw） resin matrix composite with a coordination number of 12 is constructed based on the special structure of T-ZnOw;the percolation phenomenon of the system is simulated by the Monte Carlo method,and the percolation threshold is obtained at 23.2%.The critical mixing ratio of T-ZnOw is calculated by considering the practical factors,and the result basically agrees with the reported one.Theoretical calculation shows that the critical mixing ratio mainly depends on the L/D ratio of T-ZnOw, and is also related to the size of T-ZnOw as well as the preparation method of the composite.The microwave absorbing mechanism of T-ZnOw composite is discussed,and conductivity loss and point discharge caused by the polarization effect are regarded to be two important means of energy dissipation.

Er^(3+)-substituted W-type barium ferrite: preparation and electromagnetic properties

Er3+-substituted W-type barium ferrites Ba1-xErx(Zn0.3Co0.7)2Fe16O27 (x=0.00, 0.05, 0.10, 0.15, 0.20) were synthesized by polymer adsorbent combustion method. Samples were characterized by X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and network analyzer to investigate the relationships among Er3+ concentration, crystal structure, surface morphology and electromagnetic properties. All the XRD patterns showed pure phase of W-type barium ferrite when x≤0.15, while the impurity phase of ErFeO3 appeared when x=0.20. The pure W-type barium ferrite showed a hexagonal flake shape. In addition, the microwave electromagnetic properties of samples were analyzed in the frequency range of 2-18 GHz. It was indicated that the electromagnetic properties were significantly improved when Er3+ doping content was 0.10. The reasons were also discussed using electromagnetic theory. The optimized ferrite exhibited excellent microwave absorption performance. The maximum of reflection loss (RL) reached about-27.4 dB and RL was below-10 dB at the frequency range from 8.4 GHz to 18 GHz, when the thickness was 2.6 mm.

Preparation of hollow ceramic microspheres absorbent based on self-reactive quenching technology

A1 ＋ BaO2 ＋ Fe2O3 ＋ sucrose and O2 as reaction system and feeding gas, respectively, are used to prepare hollow multiphase ceramic microspheres （HMCMs） absorbent based on self-reactive quenching technology. The morphologies, particle size distribution, hollow structure and phase compositions were characterized by scanning electron microscope （SEM）, X-ray diffraction （XRD） and size analysis. The results show that the quenching products possess high sphere-forming rate, and most of them are hollow structures. Owing to the self-burst, the particle size is between 40 and 70 μm. The phase compositions contain Al2O3, Fe3O4, Fe2O3, Ba2Fe14O22, BaO2 and BaFe4O7. The microwave absorbing tests show that the lowest reflectivity of HMCMs is -19 dB. The frequency bands less than -10 dB are from 13.0 to 15.8 GHz. The reasons for HMCMs possessing good microwave absorbing properties may be their magnetic and electrical properties as well as special hollow structure.