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.

Magnetic and microwave absorbing properties of M-type barium ferrite/graphene oxide composite microwave absorber

In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autocombustion method. X-ray diffraction （XRD）, a scanning electronic microscopy （ SEM ）, a physical properties measurement system （PPMS-9）, and a vector network analyzer were used to analyze their structure, surface morphology, magnetic and absorbing properties, respectively. The results show that the absorbing band of the composite absorbing material is widened and the absorbing strength is increased compared with the pure M-type barium ferrite. The sample with the content of doped graphene oxide of 3% has the minimum reflectivity at 10 to 18 GHz frequencies. Hence, the doped graphene oxide effectively improves the absorbing properties of M-type barium ferrite.

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.

Synthesis of flowerlike nickel particles and their microwave absorbing properties

Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.

The absorbing properties of Fe_(73.5) Cu_1 Nb_3Si_(13.5)B_9 amorphous powder/S-glass fiber-reinforced epoxy composite panels

Fe73.5Cu1Nb3Si13.5B9 （or FeCuNbSiB） powder/ S-glass fiber-reinforced epoxy composite panels were pre- pared by mold pressing method. Metallographic analysis shows that the amorphous powders are evenly distributed between the layers of S-glass fibers. The effects of the Fe- CuNbSiB powder mass fraction on the complex permittivity, complex permeability, and microwave absorption of the composite panels have been studied in the frequency range of 2.6-18.0 GHz. The complex permittivity of the composite panels with different mass fractions of the FeCuNbSiB powders shows several peaks in the 2.6-18.0 GHz fre- quency range. The complex permeability of the composites decreases with the increasing frequency in the frequency range of 8-18 GHz. The composite with FeCuNbSiB/epoxy mass ratio of 2.5：1.0 has excellent microwave absorption properties of a minimum reflection loss value -30.5 dB at 10.93 GHz for a thickness of 2 mm. A reflection loss exceeding -10 dB can be obtained in a broad frequency range of 3.2-18.0 GHz with a thickness of 1.15-5.00 mm. For the FeCuNbSiB composites, the magnetic loss is the dominant term for microwave absorption. The FeCuNbSiB powders are a possible candidate for high-performance microwave absorption filler.

Electroless plating of carbon nanotubes and their millimeter-wave absorbing properties

A method of electroless plating was utilized to deposit Cu, Ni, Co, Ag on the surface of carbon nanotubes （CNTs） respectively, in order to prepare millimeter-wave absorbing materials. Field emission scanning electron microscope （FE-SEM） and energy dispersive spectrometer （EDS） were used to observe morphologies and chemical compositions of the samples respectively. Millime- ter-wave radiometer imaging detection was employed to measure the absorbing properties of the sam- ples. FE-SEM and EDS results demonstrate the effectiveness of successful metal deposition. The re- suits of millimeter-wave radiometer imaging detection reveal that the millimeter-wave absorbing properties of electroless-silver plating are better than other kinds of samples.

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.

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.

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.

Engineering of dielectric composites on electromagnetic and microwave absorbing properties for operation in the X-band

In this study,carbon black(CB)powder-loaded polyurethane(PU)composites(CB-PU composites)were prepared by melt mixing method with different volume percentages(45,50,55,58 and 61 vol.%)of CB in the PU matrix.The prepared CB-PU composites had been further studied for surface morphology using the field-emission scanning electron microscopy(FESEM)technique.Dielectric properties in terms of real permittivity(ε′)and imaginary permittivity(ε′′)of the fabricated composites were computed using an Agilent E8364B vector network analyzer in the frequency range of 8-12 GHz(X-band).Dielectric loss factor of the prepared CB-PU composites was computed in terms of the dielectric loss tangent(tanδ_(e)=ε′′/ε′).Microwave absorbing properties were appraised in terms of the reflection loss(RL)which in turn was calculated for varying thicknesses of the prepared composites from the measured real and imaginary permittivity data.The minimum RL was observed as−20.10 dB for the absorber with a thickness of 2.2 mm and the bandwidth achieved was 1.92 GHz for RL≤−10 dB.Based on the above results these CB-PU composites have potential use as effective microwave absorbers in 8-12-GHz(X-band)frequency range.

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 absorbing properties of NdFeCo magnetic powder

NdFeCo magnetic powder was prepared by the process of smelting, high-energy ball milling and oxidation heat treating. The effects of oxidation heat treatment and Co content on phase composition and microwave absorbing properties of NdFeCo magnetic powder were investigated by an X-ray diffractometer （XRD） and vector network analyzer. The minimum reflectivity of Nd23.25Fe36.75Co40 powder before oxidation heat treatment was 4.2 dB, and that of oxidized powder decreased to -14.0 dB. The microwave absorbing properties of NdFeCo magnetic powder could be improved effectively by oxidation heat treatment. With the increase of Co content, the Fe2O3 reduced and the Nd2O3 increased; Fe3CO7 phase appeared when the content of Co increased to 40% （mass ratio）; the absorption peak was found to move towards lower frequency region first, and then it moved towards a higher frequency region. Nd23.25Fe06.75Co10 powder had better comprehensive properties in absorbing microwave in the frequency band of 3-13 GHz. The value of minimum reflectivity and absorption peak frequency, when the coating thickness （d） was 1.8 mm, were -19.7 dB and 4.8 GHz, respectively.

Influence of absorbent on electromagnetic wave absorbing property of porous concrete

Influences of ferrite content and iron ore powder content on electromagnetic wave absorbing property of porous concrete are studied.The radar cross section(RSC)of samples was tested in a microwave anechoic chamber.Results show that the optimum content of ferrite is 15%,and the minimum,maximum and average reflectivity of the sample is-46.60 dB,-10.84 dB and-23.75 dB,respectively.And the sample's improved bandwidth is 8.2 GHz.The optimum content of iron ore powder is 20%,and the minimum,maximum and average reflectivity of the sample is-34.69 dB,-9.25 dB and-20.69 dB,respectively.And the sample's improved bandwidth is 6 GHz.In conclusion,appropriate ferrite and iron ore powder can improve wave absorbing property and widen wave absorption bandwidth of porous concrete.

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.

Preparation of new sunscreen materials Ce_(1-x)Zn_xO_(2-x) via solid-state reaction at room temperature and study on their properties

Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce（SO4）2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts, drying at 80°C, and calcining.The precursor and its calcined samples were characterized using thermogravimetry and differential thermal analyses（TG/DTA）, UV-vis absorption spectroscopy, X-ray powder diffraction（XRD）, and scanning electron microscopy（SEM）.The results showed that superfine Ce1-xZnxO2-x behaved as an excellent UV-shielding material.The ZnO-doped CeO2 can facilitate the formation of crystalline state CeO2.The catalytic ability of products used in air oxidation of castor oil was investigated.The results showed that the catalytic abilities of products decreased with increasing zinc amount.

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.

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.