Preparation and properties of cobalt oxides coated carbon fibers as microwave-absorbing materials

Cobalt oxides/carbon fibers (CoO_x/CFs) composites were synthesized by thermal oxidation of cobalt coated carbon fibers (Co/CFs). The scanning electron microscopy images and X-ray diffraction pattern indicate that the layers are about 0.7 μm and composed of Co₃O₄ and CoO (CoO_x), the preferred condition for preparation of CoO_x/CFs composites is to anneal Co/CFs precursors at 350 °C for 3 h in air. The coercivity, saturation magnetization and residual magnetization of the CoO_x/CFs composites are 464.8 Oe, 10.62 emu/g and 2.21 emu/g, respectively. The reflectivity of cobalt oxides coated carbon fibers (1.11-5.12 mm in thickness) is less than −10 dB over the working frequency range of 4.04-18.00 GHz and less than −20 dB over 11.54-14.77 GHz. The lowest reflectivity is −45.16 dB at 13.41 GHz when the thickness is 1.50 mm.     

Synthesis of magnetocoated tetrapod ZnO-whiskers by polymer precursor derived method

Magnetic coatings were synthesized in situ on the surface of tetrapod ZnO-whiskers (ZnOws) via a Fe-containing polymer precursor derived method. Raw ZnOws were dispersed in polymer solution prepared from FeCl₃ modified polymethylsilane. Then the dispersion was solidified and cured. When the curing temperature was high enough, the polymer to inorganic conversion occurred, and ZnOws with magnetic coatings were obtained. Results of scanning electron microscopy, energy diffraction of X-ray spectroscopy, and X-ray diffraction proved that magnetic ZnOw maintains a tetrapod morphology and Fe has been introduced on the surface of ZnOw. The appropriate pyrolysis temperature is above 800 °C. A study of the electromagnetic parameters of the composite powder proved that μ″ is between 0.1 and 0.3. The material has radar-absorbing properties. At a thickness of 2.6 mm, the calculated maximum reflection loss for the absorber is about −9.2 dB at 2-8 GHz.     

Fabrication of composite structure of carbon fibers and high density SiC nanowires

Composite structure of carbon fibers and SiC nanowires was fabricated by a simple chemical vapor deposition process, using commercial silicon dioxide and graphite powders as raw materials. The analysis of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction indicates that the synthesized SiC nanowires distribute uniformly with high density in the used carbon fiber preform, which are perpendicular to and around each carbon fiber in a radial array. The SiC nanowires located at the interface of advanced composites is very favorable to the interfacial bonding between composites matrix and carbon fibers, thereby increasing the strength of composites greatly.     

Composited BCN/carbon fibers prepared by hot-filament chemical vapor deposition

The combined BCN/carbon fibers with porous configuration have been successfully prepared by hot-filament chemical vapor deposition (HF-CVD). The composited materials consist of carbon fiber inside covered by the cylindrical BCN films. The differences in the surface morphology and the diameter of the composite fibers are related to the different reactant gases. It is demonstrated that the elements of B, C, and N are chemically bonded with atomic-level BCN hybrid in the composite fibers. The resistance of the composite fibers is about 300 Ω which is 10 times higher than that of the isolated carbon fibers (27.5 Ω). When the applying voltage increases up to 8-15 V, the BCN films have been broken down and the resistance of composite fibers decreases to the typical value of the carbon fibers. The composite fibers with porous configuration have the strongly capacity to adsorb oxygen. The findings suggest that the combined BCN/carbon fibers are favorable for achieving high performance nano-optoelectronic and sensor devices.     

Graphene oxides and carbon nanotubes embedded in polyacrylonitrile-based carbon nanofibers used as electrodes for supercapacitor

This study investigates the use of graphene oxides (GOs) and carbon nanotubes (CNTs) embedded in polyacrylonitrile-based carbon nanofibers (GO–CNT/CNF) as electrodes for the supercapacitor. GO–CNT/CNF was prepared by electrospinning, and was subsequently stabilized and activated. The specific capacitance of GO–CNT/CNF is 120.5 F g⁻¹ in 0.5 M Na₂SO₄ electrolyte, which is higher than or comparable to the specific capacitances of carbon-based materials in neutral aqueous electrolyte, as prepared in this study. GO–CNT/CNF also exhibits a superior cycling stability, and 109% of the initial specific capacitance after 5000 cycles. The high capacitance of GO–CNT/CNF could be attributed to the edge planes and the functional groups of GO, the highly electrical conductivity of CNT, and the network structure of the electrode.     

Preparation and hydrogen storage of activated rayon-based carbon fibers with high specific surface area

Activated carbon fibers were prepared from rayon-based carbon fibers by two step activations with steam and KOH treatments. Hydrogen storage properties of the activated rayon-based carbon fibers with high specific surface area and micropore volume have been investigated. SEM, XRD and Brunauer-Emmett-Teller (BET) were used to characterize the samples. The adsorption performance and porous structure were investigated by nitrogen adsorption isotherm at 77 K on the base of BET and density functional theory (DFT). The BET specific surface area and micropore volume of the activated rayon-based carbon fibers were 3144 m²/g and 0.744 m³/g, respectively. Hydrogen storage properties of the samples were measured at 77 and 298 K with pressure-composition isotherm (PCT) measuring system based on the volumetric method. The capacities of hydrogen storage of the activated rayon-based carbon fibers were 7.01 and 1.46 wt% at 77 and 298 K at 4 MPa, respectively. Possible mechanisms for hydrogen storage in the activated rayon-based carbon fibers are discussed.     

Photoluminescence study of the surface modified and MEH-PPV coated cotton fibers

In this paper, we report a study on the photoluminescence properties of pure cotton fibers from chemically surface and morphology modified and coated with MEH-PPV polymer samples by dip-coating method. The treated and coated fibers surfaces were characterized using scanning electron microscopy (SEM), luminescence and FT-IR spectroscopy. The SEM photos showed that cotton fiber surface was covered by a layer of MEH-PPV with the thickness around 1 μm. The effects on the crystalline structure and photoluminescence (PL) were studied as a function of the alkali modification conditions. It was found that the blue light intensity of the mercerized and bleached specimen is approximately two orders higher than the scoured one. The performance of fibers with MEH-PPV polymer as a coating component was investigated and an excellent white-light emission which consists of blue-, green-, and red-light-emitting bands was demonstrated.     

Preparation of vertically aligned carbon nanotube arrays grown onto carbon fiber fabric and evaluating its wettability on effect of composite

Vertically aligned carbon nanotube (CNT) arrays have been grown onto the carbon fiber fabric using a catalytic chemical vapor deposition (CCVD) method. The as-synthesized CNT arrays are about 20 μm in height, and the nanotube has a mean inner and outer diameter of 2.6 nm, 5.5 nm, respectively. The CNT-grafted carbon fabric shows a hydrophobic property with a contact angle over 145°, and the single CNT-grafted carbon fiber shows a sharp increase of dynamic contact angle in de-ionized water from original 71.70° to about 103°, but a little increase does in diiodomethane or E-51 epoxy resin. However, the total surface energy of carbon nanotube-grafted carbon fiber is almost as same as that of as-received carbon fiber. After CNTs growth, single fiber tensile tests indicated a slight tensile strength degradation within 10% for all different lengths of fibers, while the fiber modulus has not been significantly damaged. Compared with the as-received carbon fibers, a nearly 110% increase of interfacial shear strength (IFSS) from 65 to 135 MPa has been identified by single fiber pull-out tests for the micro-droplet composite, which is reinforced by as-received carbon fiber or CNT-grafted carbon fiber.     

Surface modification and submicron structure of carbon fibers through high current pulse

This paper investigated the behavior of carbon fibers subjected to a ∼20 kA, ∼5 μs high current pulse. It was found that the broken fibers and submicron particles were generated by electrical explosion process. After high current pulsed discharge, the fiber diameter increased significantly, from 5-7 μm to ∼13 μm. Also, the surface rupture of carbon fibers with valleys of hundreds of nanometers was observed. Most notably, the submicron particles appeared with two typical shapes (near-sphere and square). The high current pulsed discharge of carbon fibers can be divided into three stages, namely, heating stage, phase change stage, and explosion stage. Indeed, the electrical explosion process occurred in the last stage of ∼200 ns. The nature behind these results is closely related to the plasma development during the explosion process. The plasma expansion due to a large plasma thermal stress leads to the incomplete explosion. In the explosion stage, the current passing through the fibers exhibited a huge fluctuation, indicating plasma instabilities. Finally, the physical mechanisms, how to affect the surface morphology of carbon fibers, are presented.     

Effect of the surface roughness on interfacial properties of carbon fibers reinforced epoxy resin composites

The effect of the surface roughness on interfacial properties of carbon fibers (CFs) reinforced epoxy (EP) resin composite is studied. Aqueous ammonia was applied to modify the surfaces of CFs. The morphologies and chemical compositions of original CFs and treated CFs (a-CFs) were characterized by Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy (XPS). Compared with the smooth surface of original CF, the surface of a-CF has bigger roughness; moreover, the roughness increases with the increase of the treating time. On the other hand, no obvious change in chemical composition takes place, indicating that the treating mechanism of CFs by aqueous ammonia is to physically change the morphologies rather than chemical compositions. In order to investigate the effect of surface roughness on the interfacial properties of CF/EP composites, the wettability and Interfacial Shear Strength (IFSS) were measured. Results show that with the increase of the roughness, the wettabilities of CFs against both water and ethylene glycol improves; in addition, the IFSS value of composites also increases. These attractive phenomena prove that the surface roughness of CFs can effectively overcome the poor interfacial adhesions between CFs and organic matrix, and thus make it possible to fabricate advanced composites based on CFs.     

Effect of catalytic graphitization on the electric heating performance of electroless nickel-coated carbon fibers

Graphite possesses several desirable properties, which facilitate its applications in several materials. However, the applications of graphitic materials depend on the extent of graphitization. Generally, the heat treatment of carbon is carried out at temperatures above 3000 °C. However, in this study, the catalytic graphitization of carbon fiber (CF) with an electroless Ni–P coating was studied at low temperature. The surface morphology and structural, thermal, and electrical properties of CF with and without electroless Ni–P coating were characterized through scanning electron microscopy, X-ray diffraction, Raman spectroscopy, infrared thermal imaging, and four-probe volume resistivity testing. The results showed that the catalytic graphitization of CF considerably improved at relatively low temperatures when a Ni–P coating was present. Moreover, when the average P content was 15.88 wt%, the degree of catalytic graphitization of Ni–P-coated CF markedly increased with heat treatment at 600 °C.     

Smoothing of an atomically rough vicinal surface – STM observation and MC simulation

Smoothing of an atomically rough vicinal surface of SrTiO₃ is studied by scanning tunneling microscope (STM) observation and by Monte Carlo (MC) simulation. A complex step pattern that resembles a two-dimensional phase separation pattern is observed on the surface. Analysis of the step pattern during annealing obtained by the STM in comparison with the MC simulation reveals an asymmetry of the relaxation pattern between islands and holes. The asymmetry is attributed to the difference of the mobility of an adatom and an atomic hole, and the asymmetry is enhanced by the step edge diffusion barrier. Values of an effective bond energy and an effective diffusion barrier as well as the surface diffusion coefficient are deduced from the relaxation pattern.     

Preparation and characterization of aligned carbon nanotubes/polylactic acid composite fibers

Aligned functionalized multiwalled carbon nanotubes/polylactic acid (MWNTs-PCL/PLA) composite fibers were successfully prepared by electrospinning processing. The MWNTs bonded with the polycaprolactone chains exhibited excellent uniform dispersion in PLA solution by comparing with the acid-functionalized MWNTs and amino-functionalized MWNTs. Optical microscopy was used to study the aligned degree of the fibers and to investigate the influences of the electrodes distance on the alignment and structure of the fibers, and results showed that the best quality of aligned fibers with dense structure and high aligned degree were obtained at an electrodes distance of 3 cm. Moreover, the MWNTs embedded inside the MWNTs-PCL/PLA fibers displayed well orientation along the axes of the fibers, which was demonstrated by field emission scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

Synthesis and characterization of ZrO2/MnO2/carbon clusters nanocomposite materials

Nano-sized ZrO₂/MnO₂/carbon clusters composite materials has been successfully obtained by the calcination of a Zr(acac)₄/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere. The compositions of the resulting composite materials were determined using inductively coupled plasma (ICP) spectroscopy, elemental analysis and surface characterization by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM). The ultraviolet–visible (UV–VIS), X-ray photoelectron spectra (XPS) and electron spin resonance (ESR) spectra of the composites were also measured. ESR spectral examinations suggest the possibility of an electron transfer in the process of MnO₂ → carbon clusters → ZrO₂. The visible light-responsive oxidation–reduction ability of the calcined material was also investigated.     

Preparation and performance of photocatalytic TiO2 immobilized on palladium-doped carbon fibers

Pd-modified carbon fibers (CFs) are obtained by a facile oxidation-reduction method and then dip-coated in a sol-gel of titanium dioxide (TiO₂) to form supported TiO₂/Pd-CF photocatalysts. The morphology of the Pd-modified CFs and the amount Pd deposited are characterized by field emission scanning electron microscopy and atomic absorption spectrometry, respectively. X-ray diffraction is used to investigate the crystal structures of the TiO₂ photocatalyst. Acid orange II is used as a model contaminant to evaluate the photocatalytic properties of the photocatalyst under UV irradiation. TiO₂/Pd-CF exhibits higher catalytic activity than TiO₂/CF towards the degradation of acid orange II. Optimum photocatalytic performance and support properties are achieved when the Pd particle loading is about 10.8 mg/g.     

Phosphorus-based nanothermites: A new generation of energetic materials

Thermites are energetic materials that are classically made of a transition metal oxide mixed with a reducing metal. Contrary to explosives, thermites do not detonate because their combustion is relatively slow and their reaction by-products are often solid or liquid. The use of nanoparticles to prepare superthermites is very promising. The dramatic changes observed in their reactivity were reported by numerous recent papers dealing with the use of aluminium as fuel.Red phosphorus is widely used in pyrotechnic devices. Highly explosive compositions are classically obtained by mixing this substance with strong oxidizers such as oxygenated potassium salts (chlorate, nitrate). But to our knowledge, the idea to prepare P-nanothermites with metallic oxide nanoparticles was never reported before. In order to illustrate this new concept of energetic formulations, P-nanothermites were prepared from nickel oxide (NiO), iron oxide (Fe₂O₃), and copper oxide (CuO) nanopowders. The reactivity of these compositions was studied by thermogravimetric analysis, impact and friction tests, electrostatic discharge and high-speed cinematography. P-nanothermites are very insensitive to thermal and impact stress. Their combustion rates strongly depend on the nature of the oxide (NiO <Fe₂O₃?CuO). The SEM observation of the microstructure of the residues produced by the combustion clearly indicates that they were formed by the solidification of molten phases. In other words, the energy released by the combustion of P-nanothermites provokes the melting of the reaction products. The temperatures reached are thus high enough to cause the gasification of phosphoric anhydride produced by the combustion. For this reason, P-nanothermites can be considered gas-generating materials.     

A study on UV laser drilling of PEEK reinforced with carbon fibers

This paper deals with the application of Nd-YAG laser emitting at 355 nm to the drilling process of Carbon Fiber Reinforced Polyetheretherkethone (PEEK-CF) laminates. The combination of a modern UV-laser source with a scanning technology enabling speeds up to 4 m/s, suppresses heat affected zones (HAZ) and consequently detachment of fibers from the polymer matrix. A removal technique based on the ablation of superimposed layers of composite material is proposed and analyzed in detail as a function of energy density delivered to the surface, hatch strategy and thickness of the laminate to be drilled. The hatching technique discussed in the paper is compared with conventional laser trepanning and percussion drilling through holes for the realization of 2 mm and 0.1 mm diameter, respectively. In both the cases benefits were noticed in terms of extension of HAZ and quality of the cut edges.     

对苯二酚-甲醛碳气凝胶的制备

 溶胶-凝胶法制备了高HC比（10~40,对苯二酚与催化剂(Na₂CO_{3/sub>)的物质的量之比）的对苯二酚-甲醛有机气凝胶,并经高温碳化处理得到其碳气凝胶。借助有机气凝胶的红外光谱研究了其化学结构,说明其网孔结构形成的可能性;研究了有机气凝胶的扫描电镜图像、比表面积及孔径分布等,并得到碳化前后的一些对比数据：有机气凝胶颗粒大小30~50 nm,碳化后约为10 nm,比表面积从341.77 m²/g增大到452.75 m²/g,密度从0.170 8 g/cm^{3/sup>增大到0.335 6 g/cm3/sup>。}}     

Can solid carbon materials be lighter than water and air?

The number of possible hollow carbon molecules with a spatially closed structure is theoretically unlimited. Only a few have been studied up to now, mainly with relative small radiuses. If the structure is big enough, spatially closed, hollow, spherical, and with a monolayer shell, it will have a considerable elevating force when immersed in liquids or gases. Calculations demonstrate that it can be lighter than liquids and air when the molecule is over a certain size. Hollow multilayered carbon structures with such radiuses have already been reported. Development of new methods for synthesis of closed carbon molecules where the shell is reduced to a single layer will allow designing new materials, which are lighter than gases.