Microwave Absorption Properties of Polyester Composites Incorporated with Heterostructure Nanofillers with Carbon Nanotubes as Carriers

Carbonaceous nanomaterials such as carbon nanotubes （CNTs）, magnetic metal nanomaterials and semicon- ductor nanomaterials are superior candidates for microwave absorbers. Taking full advantage of the features of CNTs, nanophase cobalt and nanophase zinc oxide, whose main microwave absorption mechanisms are based on resistance loss, magnetic loss and dielectric loss, we fabricate CNT/Co and CNT/ZnO heterostructure nanocom- posites, respectively. By using the CNTs, CNT/Co nanocomposites and CNT/ZnO nanocomposites as nanofillers, composites with polyester as matrix are prepared by in situ polymerization, and their microwave absorption per- formance is studied. It is indicated that the synergetic effects of the physic properties of different components in nano-heterostructures result in greatly enhanced microwave absorption performance in a wide frequency range. The absorption peak is increased, the absorption bandwidth is broadened, and the maximum peak shifts to a lower frequency.

High microwave absorption performances for single-walled carbon nanotube–epoxy composites with ultra-low loadings

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption perfor- mances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites （1.3-mm thickness） with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appro- priate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.

Electroless Plating of Carbon Nanotubes with Copper

A simple chemical method was employed to coat carbon nanotubes with a layer of copper. Due to the hydrophobic nature, large surface curvature, small diameter and large aspect ratio, it is difficult to gain continuous electroless plating layer on the surface of carbon nanotubes. In this paper, a series methods (oxidization, sensitization and activation) are used to add active sites before electroless plating, and the adjustment of the traditional composition of copper electroless plating bath and operating condition can decelerate electroless plating rate. The samples before and after coating were analyzed using transmission electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the surface of carbon nanotubes was successfully coated with continuous layer of copper, which lays a good foundation for applying carbon nanotubes in composites.

Electroless plating Ni-P matrix composite coating reinforced by carbon nanotubes

Ni-P matrix composite coating reinforced by carbon nanotubes (CNTs) was deposit ed by electroless plating. The most important factors that influence the content of carbon nanotubes in deposits,such as agitation,surfactant and carbon nanot ubes concentration in the plating bath were investigated. The surface morphology,structure and properties of the Ni-P-CNTs coating were examined. It is found that the maximum content of carbon nanotubes in the deposits is independent of carbon nanotubes concentration in the plating bath when it is up to 5 mg/L. The test results show that the carbon nanotubes co-deposited do not change the str ucture of the Ni-P matrix of the composite coating,but greatly increase the ha rdness and wear resistance and decrease the friction coefficient of the Ni-P-C NTs composite coating with increasing content of carbon nanotubes in deposits.

Microwave Absorption Properties of Carbon Nanotubes-Epoxy Composites in a Frequency Range of 2 - 20 GHz

In this work, multi-walled carbon nanotubes (MWCNTs)-epoxy composites with MWCNTs (outer diameter less 8 nm) loadings from 1 to 10 wt% were fabricated. The microstructures, dielectric constant, and microwave absorption properties of the MWCNTs-epoxy composite samples were investigated. The measurement results showed that the microwave absorption ratio of the MWCNTs-epoxy composite strongly depend on the MWCNT loading in the composites. The microwave absorption ratio up to 20%-26% around 18-20 GHz was reached for the samples with 8-10 wt% MWCNT loadings. The high absorption performance is mainly attributed to the microwave absorption of MWCNTs and the dielectric loss of MWCNTs-epoxy composites.

Preparation and tribological performances of Ni-P-multi-walled carbon nanotubes composite coatings

Multi-walled carbon nanotubes （MWNTs） were wet-milled in the presence of ammonia and cationic surfactant and then used as reinforcements to prepare Ni-P-MWNTs composite coatings by electroless plating. The tribological performances of the composite coatings under dry condition were investigated in comparison with 45 steel and conventional Ni-P coating, Micrographs show that short MWNTs with uniform length and open tips were obtained through the wet-milling process. The results of wear test reveal that the Ni-P-MWNTs composite coatings posses much better friction reduction and anti-wear performances when compared with 45 steel and Ni-P coating. Within the MWNTs content range of 0.74%-1.97%, the friction coefficient and the volume wear rate of the composite coatings decrease gradually and reach the minimum values of 0.08 and 6.22x10-15 m3/（N.m）, respectively. The excellent tribological performances of the composite coatings can be attributed to the introduction of MWNTs, which play both roles of reinforcements and solid lubricant during the wear process.

The effects of a static magnetic field on the microwave absorption of hydrogen plasma in carbon nanotubes: a numerical study

We theoretically investigate the microwave absorption properties of hydrogen plasma in iron-catalyzed high- pressure disproportionation-grown carbon nanotubes under an external static magnetic field in the frequency range 0.3 GHz to 30 GHz, using the Maxwell equations in conjunction with a general expression for the effective complex permittivity of magnetized plasma known as the Appleton Hartree formula. The effects of the external static magnetic field intensity and the incident microwave propagation direction on the microwave absorption of hydrogen plasma in CNTs are studied in detail. The numerical results indicate that the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes can be obviously improved when the exter- nal static magnetic field is applied to the material. It is found that the specified frequency microwave can be strongly absorbed by the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes over a wide range of incidence angles by adjusting the external magnetic field intensity and the parameters of the hydrogen plasma.

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.

Composition Dependent Magnetic Properties of Ni-Co-P Coated Carbon Nanotubes

Carbon nanotubes were coated with a layer of nickel-cobalt-phosphorus （Ni-Co-P） alloy with different compositions of Ni/Co through electroless plating. The effects of the concentration ratio of Co^2＋ to Ni^2＋, bath temperature, and pH on deposition rate are discussed. The prepared carbon nanotubes covered with Ni-Co-P were characterized and analyzed by fieldemission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and a vibrating sample magnetometer. The results show that the deposition rate reached the maximum when the concentration ratio of Co^2＋ to Ni^2＋ is 1 and the pH is 9; the deposition rate increases with the increase of bath temperature. The measurements of the magnetic properties of the obtained carbon nanotubes covered with Ni-Co-P indicate that the magnetic properties greatly depend on the concentration ratio of Co^2＋ to Ni^2＋, and the magnetic saturation reaches the maximum value when the Co^2＋ to Ni^2＋ ratio is 1. In addition, there are two peaks in the coercivity curve at Co^2＋ to Ni^2＋ ratios of 1/2 and 4/1, while the two peaks in the magnetic conductivity curve are located at Co^2＋ to Ni^2＋ ratios of 1/4 and 4/1.

NiCoZn/C@melamine sponge-derived carbon composites with highperformance electromagnetic wave absorption

NiMZn/C@melamine sponge-derived carbon(MSDC)composites(M=Co,Fe,and Mn)were prepared by a vacuum pump-ing solution method followed by carbonization.A large number of carbon nanotubes(CNTs)homogeneously attached to the surfaces of the three-dimensional cross-linked of the sponge-derived carbon in the NiCoZn/C@MSDC composite,and CNTs were detected in the NiFeZn/C@MSDC and NiMnZn/C@MSDC composites.Ni_(3)ZnC_(0.7),Ni_(3)Fe,and MnO in-situ formed in the NiFeZn/C@MSDC and NiMnZn/C@MSDC composites.The CNTs in the NiCoZn/C@MSDC composite efficiently modulated its complex permittivity.Thus,the composite exhibited the best performance among the composites,with the minimum reflection loss(RL_(min))of-33.1 dB at 18 GHz and thickness of 1.4 mm.The bandwidth for RL of≤-10 dB was up to 5.04 GHz at the thickness of 1.7 mm and loading of 25wt%.The op-timized impedance matching,enhanced interfacial and dipole polarization,remarkable conduction loss,and multiple reflections and scat-tering of the incident microwaves improved the microwave absorption performance.The effects of Co,Ni,and Fe on the phase and mor-phology provided an alternative way for developing highly efficient and broadband microwave absorbers.

Highly enhanced microwave absorption for carbon nanotube/barium ferrite composite with ultra-low carbon nanotube loading

Barium ferrite(BaFe_(12)O_(19))is considered as potential microwave absorption(MA)material thanks to the large saturation magnetization,high Curie temperature,and excellent chemical stability.The integration of carbon nanotube(CNT)can improve the dielectric loss of BaFe_(12)O_(19)for further enhanced MA perfor-mance,nevertheless,the MA performance is still not desirable because of the poor CNT dispersion in the CNT/BaFe_(12)O_(19)composites,which usually prepared via the ball-milling method,unless high CNT loading was used.Herein,according to the thermal stability of CNT in different atmosphere and the formation mechanism of BaFe_(12)O_(19)from precursor,CNT was introduced in the precursor of BaFe_(12)O_(19)uniformly during auto-ignition process and calcined under different atmosphere.When CNT loading is only 2.0 wt%,the CNT/BaFe_(12)O_(19)composites obtained exhibits a minimum reflection loss(RL_(min))of-43.9 dB and effective bandwidth(with RL<-10 dB)of 3.9 GHz with the thickness of 1.5 mm,which are much supe-rior to-10.2 dB and 2.2 GHz for pure BaFe_(12)O_(19),and-13.6 dB and 2.5 GHz for CNT/BaFe_(12)O_(19)composite prepared by ball-milling method.These results may pave the way to design high-performance BaFe_(12)O_(19)based microwave absorbers.

Growing CoNi nanoalloy@N-doped carbon nanotubes on MXene sheets for excellent microwave absorption

Recently,two-dimensional MXene materials have attracted numerous attention in electromagnetic wave shielding/absorption.Hybridizing magnetic materials and constructing multi-dimensional structures in MXene is highly beneficial to improve electromagnetic wave absorption properties.Herein,we demonstrate a strategy for in situ growing 0 D CoNi nanoalloy-encapsulated 1 D N-doped carbon nanotubes on a2 D Ti_(3)C_(2)T_(x)MXene sheet through an electrostatic assembly process followed by a high-temperature pyrolysis process.The resultant 201-structured MXene-CoNi@N-doped carbon nanotube(MXene-CoNi@NCNT)composites displayed high surface areas(55.6-103.7 m^(2)/g),moderate magnetism(19.8-24.6 emu/g),and excellent thermal oxidation stabilities(≥ 307℃).In addition,the unique 2 D/0 D/1 D architectures entrusted the composites with abundant interfaces,various defects,and numerous nitrogen dopants.Taking advantage of the special 201 structure and the existence of both magnetic and dielectric loss,the MXeneCoNi@NCNT composite showed great impedance matching and strong attenuation performance.A strong reflection loss of-55.3 dB was achieved when the coating thickness was 2.1 mm,and a wide effective absorption bandwidth of 4.3 GHz was achieved at a thickness of 1.5 mm,much superior to that of similar absorbers.This work demonstrates a novel strategy for designing electromagnetic wave absorbers with magnetic and dielectric losses accompanied by multiple dimensional structures.

Study of Electroless Ni-P-CNTs Composite Plating

The electroless Ni-P-carbon nanotubes composite plating was studied on the copper substrate. Metallurgical microscope, scanning electronic microscope, X-ray diffractometer and micro hardness tester were used to study the structure, constitution and performance of the electroless Ni-P-carbon nanotubes composite deposit. Experiential results show that, with the increment of carbon nanotubes content in electroless plating solution, the grain size on the sample surface decreases whereas the density of grains and the hardness for composite deposit increases. Moreover, adding carbon nanotubes not only improves the degree of crystallization for the composite deposit but also helps their transformation from the amorphous state to the nanocrystal state.

Grow defect-rich bamboo-like carbon nanotubes on carbon black for enhanced microwave absorption properties in X band

Due to the limited electromagnetic wave(EMW)loss capacity and agglomeration,carbon black(CB)gradually fails to meet the increasingly harsh demanding conditions.Herein,defect-rich bamboo-like carbon nanotubes(CNTs)were grown on CB by the process of chemical vapor deposition.CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces.What’s more,the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching,thereby causing an effective microwave absorption(MA).Meanwhile,the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability.The influence of CNTs with different growth time on MA performance has been explored.Profiting from the structural merits,the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property,which has the minimum reflection loss of-53.6 d B and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm,covering almost the entire X band.The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB,which provides a rational strategy for the design of high-efficient microwave absorption materials.

Robust microwave absorption in silver-cobalt hollow microspheres with heterointerfaces and electric-magnetic synergism:Towards achieving lightweight and absorption-type microwave shielding composites

Lightweight and high-efficiency microwave shielding materials based on high absorption loss are the hotspot of current research.Herein,the silver-cobalt bimetallic hollow microspheres(Ag-Co-HM)with low reflection loss and broadband absorption efficiency were fabricated and then used to construct bimetallic hollow structures in polydimethylsiloxane/carbon nanotube composites(PDMS/CNT)to obtain the lightweight and absorption-type microwave shielding composites.The microwave absorption of Ag-Co-HM and the microwave shielding effectiveness(SE T)of the PDMS/CNT/Ag-Co-HM composites was evaluated and discussed.The Ag-Co-HM with a molar ratio(Co/Ag)of 2.07 exhibited a low reflection loss as-46.6 dB at a thickness of 2.6 mm,and an effective absorption bandwidth of 8.40 GHz.The SE T of the PDMS/CNT composites was greatly enhanced by the incorporation of the Ag-Co-HM.Furthermore,the absorption coefficient(A)was also improved by adding the Ag-Co-HM and was much higher than the reflection coefficient.The composites exhibited absorption-type microwave shielding composites.For example,the average microwave SE T of 59.4 dB and A value of 0.78 are achieved in the PDMS/CNT/Ag-Co-HM composites containing 5 wt%CNTs and 10 wt%Ag-Co-HMs,which are much higher than the cor-responding values of 33.7 dB and 0.63 in the PDMS/CNT composites with only 5 wt%CNTs.In addition,the hollow structure of Ag-Co-HM endows the PDMS/CNT/Ag-Co-HM composites to have a low density.

Studies of Electromagnetic Properties of MWCNTs after Electroless Plating with Co-Fe Alloy

A method of electroless plating is utilized to deposit Co-Fe alloy on the surface of multi-walled carbon nanotubes （MWCNTs）,and electromagnetic parameters of MWCNTs with and without electroless plating are discussed. The MWCNTs covered by Co-Fe is a desirable light absorbent in wide wave band by utilizing electroless plating process in experiments. Field-emission scanning electron microscope （FESEM） and field-emission transmission electron microscope （FETEM） images as well as energy dispersive spectroscopy （EDS） results are presented to show the morphology,components and electromagnetic parameters of MWCNTs. Electromagnetic properties of MWCNTs are enhanced after electroless plating observed from contrast of results be-tween MWCNTs with and without plating. In conclusion,the covering Co-Fe on the surface of MWCNTs in 2-18 GHz frequency range has better electromagnetic properties. When the material is in the 6.5 GHz electromagnetic waves,the reflection loss is up to -10 dB,and the bandwidth more than -4 dB is 5 GHz. The excellent electromagnetic properties make it probable for MWCNTs to be utilized as absorbent in electromagnetic shielding materials.

Attachment of Gold Nanoparticles to Carbon Nanotubes

Carbon nanotubes were initially chemically modified with an H2SO4-HNO3 treatment,and subsequently activated with Pd-Sn catalytic nuclei via a one-step activation approach. Theseactivated nanotubes were used as precursors for obtaining gold nanoparticles-attached nanotubes viasimple electroless plating. This approach provides an efficient method for attachment of metalnanostructures to carbon nanotubes. Such novel hybrid nanostructures are attractive for manyapplications.

Synthesis,field emission and microwave absorption of carbon nanotubes filled with ferromagnetic nanowires

Carbon nanotubes filled with ferromagnetic metal nanowires (M-CNTs) were synthesized by using chlorine-contained benzene (e.g.trichlorobenzene) as precursor.The wall thicknesses of M-CNTs synthesized by trichlorobenzene are much thinner than those by precursor without Cl (e.g.benzene).As-synthesized thin-walled M-CNTs exhibit remarkably enhanced field electron emission performance with a low turn-on field of 0.3 V/μm and better field-emission stability.Microwave-absorption coatings were made by dispersing as-synthesized M-CNTs into epoxy resin matrix.It is found that the reflection losses in S-band (2-4 GHz),C-band (4-8 GHz) and X-band (8-12 GHz) are enhanced in the order of FeCoNi-CNTs 【 FeNi-CNTs【 FeCo-CNTs.The areal density of as-prepared coatings is only 2.35 kg/m2 when the coating thickness is 2.0 mm.This demonstrates that M-CNTs are promising to be used as lightweight and wide-band microwave absorbers.

Recent progress of nanomaterials for microwave absorption

Microwave absorbing materials have received considerable interest over the years for their applications in stealth,communications,and information processing technologies.These materials often require functionalization at the nanoscale so to achieve desirable dielectric and magnetic properties which induce interaction with incident electromagnetic radiation.This article presents a comprehensive review on the recent research progress of nanomaterials for microwave absorption,including the basic mechanism of microwave absorption(e.g.,dielectric loss,magnetic loss,dielectric/magnetic loss coupling),measurement principle(e.g.,fundamentals of analysis,performance evaluation,common interaction pathways:Debye relaxation,Eddy current loss,natural resonance,size and shape factors),and the advances and performance review in microwave absorption(e.g.,absorption bandwidth,reflection loss values,absorption peak position)using various nanomaterials,such as carbon nanotubes,carbon fibers,graphenes,oxides,sulfides,phosphides,carbides,polymers and metal organic frameworks.Overall,this article not only provides an introduction on the fundamentals of microwave absorption research,but also presents a timely update on the research progress of the microwave absorption performance of various nanomaterials.

碳纳米管增强硬质合金的制备及性能研究

为改善硬质合金中增强体碳纳米管(carbon nanotubes,CNTs)的团聚问题,采用化学镀Ni方法对CNTs进行表面改性,利用气压烧结工艺制备了WC-10Co-CNTs硬质合金和WC-10CoCNTs/Ni硬质合金。对镀Ni前后CNTs的表面形貌、结构及成分进行了分析表征,并研究了CNTs和CNTs/Ni对硬质合金组织及性能的影响。结果表明,CNTs经化学镀改性处理后,表面包覆了致密的纳米Ni颗粒,团聚现象明显改善;在WC-10Co中添加CNTs或CNTs/Ni后可以有效地细化硬质合金的晶粒,降低孔隙率;和未添加的比较,添加质量分数0.1%的CNTs的硬质合金和添加质量分数0.1%的CNTs/Ni的硬质合金抗弯强度分别提高了17.5%和28.2%,热扩散系数分别提高了23.5%和42.8%。