Microwave absorption properties of carbonyl iron-based paint coatings for military applications

The paper explores the possibilities of using carbonyl iron in the form of a powder for the manufacture of radar-absorbing paints-reducing the radar signature of the objects that they cover.The attenuation values in the range of 4-18 GHz for various coating thicknesses,ranging from 0.5 to 2.00 mm with 0.5 mm increment,and for different absorber content-75%and 80%,as well as the use of two different binders in the form of epoxy resins with hardeners,were investigated.For the frequency of 18 GHz and a 1.5 mm thick coating with a 75%absorber content,Epidian 112 resin and Saduramid 10/50 hardener used as a binder,and the maximum attenuation level obtained equalled 20.2 d B at 16 GHz.Additionally,the absorber particle size ranging from 3 to 4μm and its higher mass content resulted in achieving the reflection loss above-12 d B in the entire 8-12.5 GHz range for layers between 1-and 1.5 mm thickness.The qualitative assessment of the tested samples in the context of camouflage in the radar range was also performed,using statistical analysis.

Influence of shape anisotropy on microwave complex permeability in carbonyl iron flakes/epoxy resin composites

To explore the mechanism of carbonyl iron flake composites for microwave complex permeability, this paper investigates the feature of the flakes. The shape anisotropy was certified by the results of the magnetization hysteresis loops and the Mossbauer spectra. Furthermore, the shape anisotropy was used to explain the origin of composite microwave performance, and the calculated results agree with the experiment. It is believed that the shape anisotropy dominates microwave complex permeability, and the natural resonance plays main role in flake.

Effects of Silane Coupling Agent on Microstructure and Mechanical Properties of EPDM/Carbonyl Iron Microwave Absorbing Patch

The effects of types and amounts of silane coupling agent on mechanical properties of vuleanized rubber microwave absorbing patch （VRMAP） were studied. The mechanisms of silane coupling agent＇s effects on mechanical properties of rubber microwave absorbing patch （ RMAP ） and microvave absorbing patch＇s （MAP＇s） mierostrueture were also discussed by using SEM and FT-IR. The experimental results show that the tensile strength of RMAP could be increased through adding the filler of carbonyl iron powder （CIP） modified by silane coupling agent. RMAP fiUed with CIP, which was treated by silane coupling agent KH550, possessed a high tensile strength of 11.5 MPa, which was 448% more than that of MAP whose filler wus not modified by any coupling agent. It was found that the optimal amount of KH550 was 1.0 phr to 100.0 phr carbonyl iron powder. The effects of different modifying techniques on RMAP＇s mechanical properties were also inrestigated. It is indieated that MAP whose filler is modified by the wet process has the highest tensile strength, but it is not the optimal modiifying technique due to complieated wet process. On the contrary, the dry process was very simple, and VRMAP possessed fairly high mechanical properties, therefore, it was the perfect modifying process.

Microwave Absorption Properties of the Carbonyl Iron/EPDM Radar Absorbing Materials

Employing carbonyl iron powder and Ethylene-Propylene-Diene Monomer （EPDM） as the absorbent and matrix, rubber radar absorbing materials （RAM） were prepared. Effects of the carbonyl iron volume fraction and the thickness of the RAM on the microwave absorption properties in the frequency range of 2.6-18GHz were studied, and a mathematical analysis was made using the electromagnetic theory. The experimental results indicate that the minimum reflectivity of the radar absorbing materials continuously decreases with the increase of the carbonyl iron volume fraction, and the absorption peak also moves towards the low frequency for the same thickness of the RAM. The minimum reflectivity of the 3.0 mm RAM is -21.7dB at 3.5 GHz when the volume fraction of carbonyl iron is 45%. The reflectivity of the RAM is not in direct proportional to the thickness of the RAM, when the RAM has the same volume fraction of the carbonyl iron. The reflectivity of the RAM presents a regular trend at a given carbonyl iron volume fraction in the frequency range of 2.6-18 GHz. With the increase of the thickness, the maximum absorption peak moves towards low frequency band, the minimum reflectivity firstly decreases and then increases, and the absorption bandwidth for reflectivity〈-10 dB firstly increases and then decreases. The microwave absorption properties of the RAM are determined by the thickness and the composition of the radar absorbing materials. Theoretical analysis indicates that the reflectivity of the RAM is determined by the matching degree of the air＇s characteristic impedance and the input impedance.

Effect of deposition temperature on SrFe12O19@carbonyl iron core–shell composites as high-performance microwave absorbers

The SrFe12O19@carbonyl iron(CI) core–shell composites used in microwave absorption are prepared by the metal–organic chemical vapor deposition(MOCVD). The x-ray diffractometer, scanning electron microscope, energy dispersive spectrometer, and vector network analyzer are used to characterize the structural, electromagnetic, and absorption properties of the composites. The results show that the SrFe12O19@CI composites with a core–shell structure could be successfully prepared under the condition: deposition temperatures above 180℃, deposition time 30 min, and gas flow rate 30 m L/min.The electromagnetic properties of the composites change significantly, and their absorption capacities are improved. Of the obtained samples, those samples prepared at a deposition temperature of 180℃ exhibit the best absorption performance.The reflection loss of SrFe12O19@CI(180℃) with 1.5 mm–2.5 mm in thickness is less than-10 dB in a frequency range of 8 GHz–18 GHz, which covers the whole X band and Ku band.

Enhancement of Heat-Resistance of Carbonyl Iron Particles by Coating with Silica and Consequent Changes in Electromagnetic Properties

Silica-coated carbonyl iron particles （CIPs） are fabricated with the Stober method to improve their heat-resistance and wave-aSsorption properties. The morphology, heat-resistance, electromagnetic properties and microwave absorption of raw-CIPs and silica-coated CIPs are investigated using a scanning electron microscope, an energy dispersive spectrometer, a thermal-gravimetric analyzer, and a network analyzer. The results show that the heat-resistance of silica-coated CIPs is better than that of raw CIFs. The reflection losses exceeding -lOdB of silica-coated CIPs are obtained in the frequency range 9.5-12.4 GHz for the absorber thickness of 2.3 mm, and the same reflection losses of uncoated CIPs reach the data in the lower frequency range for the same thickness. The enhanced microwave absorption of silica-coated CIPs can be ascribed to the combination of proper electromagnetic impedance match and the decrease of dielectric permittivity.

Model of In Situ Composite of Cobalt(Ⅱ)-Phthalocyanine and Carbonyl Iron for Organic/Inorganic Nanocomposites

Cobalt-phthalocyanine/iron nanocomposite particles have been obtained using method of composite in situ, with the mixture of carbonyl iron and solution of cobalt ( Ⅱ ) - phthalocyanine (Co-Pc) ultrasonic dispersing in N,N-dimethyl-formamide (DMF). Structure characterization of their inner and surface have relation with method of carbonyl iron joined in the mixture, contents of carbonyl iron and Co-Pc in the mixture of Co-Pc ultrasonic dispersing in DMF. With a method of composite in situ controlling reasonable experiment condition, it can be obtained that cobalt-phthalocyanine/iron nanocomposite particles has completely been covered with Co-Pc, they had structure of Chinese gooseberry in inner and mere made up of almost regular spherical shape and the average diameter is 1. 4 μm.

Electromagnetic Characterization of Recyclable Polymer Nanofibers Based on PSU/Carbonyl Iron

This study investigated and defined the optimal processing parameters for the electrospinning of polysulfone polymer solutions with N,N-dimethylacetamide.Variation of parameters such as solute concentration,electrical voltage,and working distance were correlated with the quality of the obtained nanofibers using morphological characterization via scanning electron microscopy(SEM).Carbonyl iron additive was dispersed in the polymer solutions,using ultrasonic tip,and the material processed via electrospinning with aforementioned parameters defined.Nanofibers with the property of interaction with electromagnetic waves were obtained.The dispersion of different concentrations of the additive and electromagnetic characterizations in the X-band of microwaves(8.2 and 12.4 GHz),using vector network analyzer(VNA)and rectangular waveguide,allowed the identification of the materials electromagnetic behaviors.Scattering parameters allowed the calculation of reflected and transmitted energy by the material.

Rheological properties of magnetorheological fluid prepared by gelatincarbonyl iron composite particles

Gelatincarbonyl iron composite particle was prepared by micro emulsion method. The analysis of scanning electron microscope(SEM) shows that the ultrafine particles are spheroids coated by gelatin, and the average sizes of particles are 310μm. The specific saturation magnetization σ_s is 130.9A·m2/kg, coercivity H_c is 0.823A/m, and residual magnetism r is 4.98Am2/kg for the composite particles. It is shown that the particles possess properties of soft magnetic. The yield stress of magnetorheological fluid(MRF) with composite particle reaches 70kPa at 0.5T magnetic induction. Magnetorheological effects are superior in lower magnetic field intensity and the subsidence stability of the MRF is excellent compared with pure carbonyl iron powder.

Reactivity of Fe3(CO)(12) with Alkynes R-C≡C-R＇： Syntheses and Crystal Structures of Substituted Cyclic Ketones and Carbonyl Iron Complexes

The reactivity of carbonyl iron cluster with alkynes has been studied by the thermal reaction of Fe_3（CO）_（12） with R-C≡C-R＇（R = Fc（Ferrocenyl）; R′ = Ph（Phenyl）, Fc, H）. The hexacarbonyldiiron cluster with ferracyclopentadiene ring（μ_2, η~4-C_4Ph_4）Fe_2（CO）_6（1） and one tetraphenyl substituted cyclopentadienone（Ph_4C_4CO）（2） were simultaneously obtained by the reaction of Fe_3（CO）_（12） with alkyne（Ph-C≡C-Ph）. Only one ferrole cluster（μ_2, η~4-C_4Fc_2H_2）Fe_2（CO）_6（3） was separated by using Fc-C≡C-H as alkyne. One tri-carbonyl iron complex（η~4-C_4Fc_4CO）Fe（CO）_3（4） and an unexpected new cyclic ketone compound 2,2,4,5-tetraferrocenylcyclopenta-4-en-1,3-di-one [Fc_4C_3（CO）_2]（5） were obtained by using Fc-C≡C-Fc as alkyne. A new complex（η4-2,4-diphenyl-3,5-diferrocenylcyclopenta-2,4-dien-1-one）-tricarbonyl iron（η~4-C_4Ph_2Fc_2CO）Fe（CO）_3（6） was synthesized by the reaction of Fe_3（CO）_（12） with Fc-C≡C-Ph. The structures of compounds 1~6 were determined by X-ray single-crystal diffraction and spectroscopic characterization. The crystal structures of two new compounds 5 and 6 were analyzed. Our experimental results reveal the structural models of the reaction products are affected by the kinds of substituents from alkynes R-C≡C-R′.

Electromagnetic Waves Absorbing Characteristics of Composite Material Containing Carbonyl Iron Particles

Results of measurements of permeability, permittivity and radar absorption properties of composites on basis of carbonyl iron particles R-10 brand are presented in this paper. The calculations and experimental studies have shown that in the super high frequency (SHF) and extremely high frequency (EHF) ranges on the basis of two-layer structures with different content of carbonyl iron particles can create a radar absorbing coatings with a reflectivity of less than -10 dB over a wide bandwidth from 3.1 to 17.1 GHz and from 27 to 37 GHz. Absorbing properties of composites are saved in terahertz frequency range from 250 to 525 GHz.

Surface structural engineering of carbonyl iron powder for enhancing microwave absorption and anti-oxidation performance

Surface structural engineering is desirable in modifying the surface performance of carbonyl iron powder(CIP)to enhance microwave absorption(MA)and anti-oxidation performance.Herein,the surface shape-dependent CIP absorbers are designed via surface coating with zinc oxide(ZnO)nanoparticles and then a thermal annealing treatment.The morphology of ZnO nanoparticles which can be easily regulated by controlling the annealing temperature ultimately affects the MA performance of CIP coating with ZnO nanoparticles(CIP@ZnO).The core-shell CIP@ZnO particles with cubic cone ZnO nanoparticles exhibit ex-cellent MA performance and thermal stability in comparison to the original CIP.Specifically,the CIP@ZnO annealed at 350 ℃(CIP@ZnO-350)samples which have the cubic cone ZnO nanoparticles exhibit a min-imum reflection loss(RLmin)of-55.35 dB at a thickness of 2.1 mm and a maximum effective absorp-tion bandwidth(EAB)of 7.09 GHz at a thickness of 2.0 mm.In addition,the antioxidant property of the CIP@ZnO composite particles is abruptly enhanced,which breaks the restriction of the application of CIP at high temperatures.The superior MA performance of CIP@ZnO particles with cubic cone ZnO nanoparti-cles comes from the enhancement in surface shape-dependent multiple microwave scattering,interfacial polarization,and electromagnetic-dielectric synergism between ZnO and CIP.

Effects of Multi-walled Carbon Nanotubes on the Electromagnetic Absorbing Characteristics of Composites Filled with Carbonyl Iron Particles

The electromagnetic （EM） wave absorbing property of silicone rubber filled with carbonyl iron particles （CIPs） and multi-walled carbon nanotubes （MWCNTs） was examined. Absorbents including MWCNTs and spherical/ flaky CIPs were added to silicone rubber using a two-roll mixer. The complex permittivity and complex permeability were measured over the frequency range of 1-18 GHz. The two EM parameters were verified and the uniform dispersion of MWCNTs and ClPs was confirmed by comparing the measured reflection loss （RL） with the calculated one. As the MWCNT weight percent increased, the RL of the spherical CIPs/silicone rubber composites changed insignificantly. It was attributed to the random distribution of spherical ClPs and less content of MWCNTs. On the contrary, for composites filled with flaky ClPs the absorption bandwidth increased at thickness 0.5 mm （RL value lower than -5 dB in 8-18 GHz） and the absorption ratio increased at lower frequency （minimum -35 dB at 3.5 GHz）. This effect was attributed to the oriented distribution of flaky CIPs caused by interactions between the two absorbents. Therefore, mixing MWCNTs and flaky CIPs could achieve wider-band and higher-absorption ratio absorbing materials.

Infrared emissivity and microwave absorbing property of epoxy-polyurethane/annealed carbonyl iron composites coatings

The microwave absorption property and infrared emissivity have been investigated for the single-layer coating made of the epoxy-polyurethane resin and carbonyl iron powders with variation of annealing treatment. Microwave-absorbing property was investigated by measuring the complex permittivity and complex permeability of the absorber in the frequency range from 2 to 18 GHz. Infrared emissivity value was measured using IR-2 Infrared Emissometer in the wavelength range of 8-14 μm. After annealing, the Fe （110） peak became sharp, and the crystallization improved significantly. Annealing treatment could reduce the sttrface energy of powders, improve compatibility between fillers and adhesives, and result in increase of the density of the coating. The lowest value of infrared emissivity （0.419） was obtained from the coating made of the carbonyl iron powder annealed at 700℃ for 1 h. With the variation of the annealing temperature, the magnetic and dielectric properties of the carbonyl iron particle were changed. The maximum reflection loss decreased and the matching frequency shifted to lower frequency with increasing the annealing temperature of carbonyl iron particles, which coincided with the variation of the complex permeability and permittivity according to the annealing temperature. Magnetic loss factor and dielectric loss factor of carbonyl iron particles were improved with increasing the annealing temperature in the 2-18 GHz range.

Fast Determination of Essential Oil from Dried Menthol Mint and Orange Peel by Solvent Free Microwave Extraction Using Carbonyl Iron Powder as the Microwave Absorption Medium

An improved solvent free microwave extraction, in which a kind of microwave absorption medium （carbonyl iron powder） was used, was applied to the extraction of essential oil from dried menthol mint and orange peel without addition of any solvent and pretreatment. It took much less time of extraction （30 min） than microwave-assisted hydrodistillation （90 min） and conventional hydrodistillation （180 min）. The kinds of chemical compositions in essential oil extracted by different methods were almost the same and such improved solvent free microwave extraction can be a feasible way in extraction of essential oil from dried plant materials.

Electromagnetic parameters and microwave-absorption properties for the mixtures of mechanically milled spherical and flaky carbonyl iron powders

The electromagnetic parameters were measured for the mixtures of mechanical milled carbonyl iron powders （CIPs） with different mass ratios of spheroid-like particles to flake-shape particles. The results indicate that mixing the sphere-like CIP particles with flake-shaped CIPs can be used to adjust effectively the electromagnetic parame- ters and enhance the absorption property in high frequency. In addition, a theoretic simulation based on the principle of superposition was carried out and compared with the microwave measurement results, indicating that the simple principle of superpo- sition can not reflect truly the internal interaction mechanism in the composites with different particle shapes.

Large-scale synthesis of fluorine-free carbonyl iron-organic silicon hydrophobic absorbers with long term corrosion protection property

Environmentally-friendly magnetic metallic absorbers with high-performing antioxidant property,thermal stability,and anticorrosion capability have attracted great attention in real-world applications.A surface modification technology of magnetic metallic absorbers with dense and inert materials has been an effective strategy to solve the aforesaid problem.Herein,fluorinefree core–shell carbonyl iron-organic silicon absorbers(CI@SiO_(2)/1,1,1,3,3,3-hexamethyl disilazane(HMDS))were fabricated via a facile one-pot synthesis using tetraethyl orthosilicate(TEOS)and HMDS as the precursor of protective layer(SiO_(2)/HMDS),and CI@SiO_(2)/HMDS hybrid reveals its long-term corrosion resistance and excellent microwave absorption performance with a minimum reflection loss value of−44.3 dB and an effective absorption bandwidth of 5.3 GHz at a thin thickness of 2.0 mm after immersion in 5.0 wt.%NaCl acidic solutions for 2,160 h.Meanwhile,CI@SiO_(2)/HMDS hybrid can still achieve the maximum radar cross-sectional(RCS)reduction values about 16.5 dB·m^(2) at the detectionθof 0°.The exceptional microwave absorption performance and structural stability are largely due to the extraordinary wave-transparent property and shielding ability against corrosive medium of SiO_(2)/HMDS hydrophobic protective layer with a contact angle of 132.5°.The research paves the way for the large-scale and batch production of high-performance magnetic metallic absorbers and increases their survivability and reliability in the harsh environments.

Electromagnetic and Microwave Absorption Properties of Carbonyl-Iron/Fe91Si9 Composites in Gigahertz Range

Carbonyl-iron/Fe91Si9 composites for thin microwave absorbers were firstly prepared by a simple blending technique. The patterns of carbonyl-iron and Fe91Si9 were characterized by scanning electron microscope (SEM). The complex permittivity, permeability and microwave absorption properties of the composites were studied in the frequency range of 2 - 7GHz by a HP8720B vector network analyzer. Complex permittivity and permeability decrease gradually with increasing weight percentage of Fe91Si9 in the composites, the variation of permittivity was very large but the variation of permeability was very small. The composites exhibited excellent microwave absorption properties with increasing Fe91Si9 content. The reflection loss (RL) values less than –20 dB were obtained in the 3.7 - 6.7 GHz frequency range for the paraffin matrix composites with 80 wt% carbonyl-iron/Fe91Si9 powders (weight ratio of carbonyl-iron to Fe91Si9 was 1:1), with thickness of 4.0 - 2.4 mm, respectively. The optimal RL of –45 dB was observed at 5.2 GHz with a matching thickness (dm) of 3.0 mm. The excellent microwave absorption properties were attributed to a better electromagnetic impedance match and a higher electric resistivity.

Syntheses and Crystal Structures of Two New Iron-sulfur Carbonyl Complexes: [Fe_2(SC_6H_4Cl)_2(CO)_6]·0.5(Et_2O) and [Fe_3(SC_6H_4NH_2)_6(CO)_6]·2(MeOH)

Two new iron-sulfur carbonyl complexes, [Fe2（SC6H4Cl）2（CO）6]·0.5（Et2O） 1 and [Fe3（SC6H4NH2）6（CO）6]·2（MeOH） 2, have been prepared and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. Crystal data for 1： monoclinic, C2/c, a = 18.4439（8）, b = 11.0999（5）, c = 25.1830（10）A°, β = 97.0370（10）°, V = 5116.8（4） A°^3, Z = 8, C20H13Cl2Fe2O6.50S2, Mr = 604.02, Dc = 1.568 g/cm^3, μ = 1.540 mm^-1, F（000） = 2424, the final R = 0.0545 and wR = 0.1454 for 3443 observed reflections with I 〉 2σ（I）; 2： monoclinic, P21/n, a = 12.350, b = 26.3050（11）, c = 16.057A°, β = 97.891 （3）°, V = 5166.9（2）A°^3, Z = 4, C44H44Fe3N6O8S6, Mr = 1144.76, Dc = 1.472 g/cm^3, μ = 1.128 mm^-1, F（000） = 2352, the final R = 0.0442 and wR = 0.1197 for 7978 observed reflections with I 〉 2σ（I）. Complex 1 contains one iron dimer, in which two tricarbonyliron（Ⅰ） fragments are bridged together by two 4-chlorophenylthiolate ligands, whereas complex 2 contains a linear tri-iron cluster, in which two terminal tricarbonyliron（Ⅱ） fragments and the central Fe（Ⅱ） atom are linked together by six 4-aminophenylthiolate bridging ligands.

CIPs@Mn_(0.8)Zn_(0.2)Fe_(2)O_(4)-CNTs复合材料低频吸波性能研究

随着5G无线通信与低频雷达侦察技术的飞速发展,低频电磁波辐射已成为当代的严重问题。目前,中高频段吸波材料的研究已趋于成熟,而设计低频段吸波材料仍面临巨大的挑战,亟待研究者们解决。基于四分之一波长相消机制,本研究设计了0.5~3 GHz低频段复合吸波材料。采用简单的一步水热法,诱导铁氧体在羰基铁粉与碳纳米管表面生长,制备出CIPs@Mn_(0.8)Zn_(0.2)Fe_(2)O_(4)-CNTs三元复合材料,对比研究了碳纳米管含量对材料吸收峰频率的影响。实验结果表明,引入碳纳米管,一方面为材料带来了界面极化、偶极极化等额外的损耗机制,增加了材料的衰减系数;另一方面基于四分之一波长相消机制,高介电与高磁导率的耦合,使材料在低频段获得良好的阻抗匹配。最终,在4 mm厚度下,样品分别在2.11与1.75 GHz处,获得了–40.8与–32.1 dB的反射损耗,–10 dB带宽分别为1.70~2.70 GHz和1.40~2.20 GHz。该复合材料制备工艺简单,低频吸收性能良好,具有很大的应用潜力,为开发更有效的低频吸波材料提供了新的思路和方法。