Interaction of thermally pretreated carbon nanomaterials with water vapor

We used temperature-programmed desorption-mass spectrometry to verify whether low-molecular-weight products can form by reacting thermally pretreated single-walled and multi-walled carbon nanotubes (SWNTs and MWNTs, respectively) with water vapor. The reactivity of MWNTs toward water is similar to the reactivity of graphite, whereas acid-oxidized SWNTs behave like polymerized C60 fullerene. We think the main factors influencing the reactivity are molecular surface curvature and the presence of pyrolyzable defect groups, which create highly strained bonds upon their elimination.     

核壳结构碳包覆Ni纳米材料的合成及电磁性能分析

以淀粉为炭基质,硝酸镍为金属纳米颗粒前躯体,在氢气保护下进行控温炭化制备出准球形的碳包覆Ni纳米颗粒,采用HRTEM、EDX和XRD对产物进行表征,纳米颗粒呈核壳结构,粒径分布比较窄,金属颗粒为单晶Ni。通过波导法对所制备的碳包覆Ni纳米材料电磁性能进行分析,采用矢量网络仪测试分析其在18～26.2GHz频率范围内电磁参数,并阐述材料结构与电磁性能之关联。     

Structural changes in fibrous carbon nanomaterials produced by adding sulfur during chemical vapor deposition

Vapor-grown carbon fibers (VGCFs), platelet graphite nanofibers (PGNFs), turbostratic carbon nanofibers (CNFs), and carbon spheres were continuously produced by the thermal decomposition of ethanol in the presence of an Fe catalyst and a sulfur promoter at 1100 degrees C under a nitrogen/hydrogen atmosphere in a vertical chemical vapor deposition reactor. The sulfur concentration dramatically affected the morphology and microstructure of the carbon materials produced. A large amount of sulfur in the catalytic precursor led to the direct pyrolysis of hydrocarbons and the formation of carbon spheres (Fe:S = 1:10) while a lower amount of sulfur led to the formation of fibrous carbon materials, including VGCFs (Fe:S = 1:0.2), PGNFs (Fe:S = 1:2), and turbostratic CNFs (Fe:S = 1:5). The degree of poisoning of the catalysts determined the precipitation of the graphene layers, allowing the different types of carbon material to form.     

Synthesis of fibrous carbon nanomaterials from ethanol vapor on a nickel catalyst

The processes underlying the synthesis of fibrous carbon nanomaterials via nickel-catalyzed pyrolysis of ethanol vapor are investigated. The IR spectra of the gas released from the reactor during synthesis indicate that, in the initial stages of the process, ethanol molecules decompose into simpler species: CH₄, CO, and H₂. In the temperature range 400–600°C, carbon monoxide disproportionation plays a key role in carbon deposition. Varying the process conditions, one can obtain carbon nanofibers of various thicknesses or carbon nanotubes.     

Flow induced orientated morphology and properties of nanocomposites of polypropylene/vapor grown carbon fibers

Nanocomposite filaments composed of isotactic polypropylene (iPP) and vapor grown carbon fibers (VGCF) were prepared by melt mixing extrusion, followed by melt drawing. The effect of composition and flow on the morphology was investigated by X-ray diffraction and high resolution scanning electron microscopy. Apparently in the drawn filaments, the presence of nanofibers resulted in a higher degree of orientated morphology and - as revealed by differential scanning calorimetry - higher degrees of crystallinity and crystallization kinetics enhancement. The amount of the orientated crystals increased as a result of VGCF addition, suggesting that the nanofibers obstructed the motion of polymer chains after the cessation of stretching force resulting in the delayed relaxation of stretched polymer segments. Significant stiffness improvements were observed due to the nanofibers and high draw ratios of the filaments. These results indicate that the orientated VGCF aligned in the flow direction, joined by fiber-induced crystallization of the surrounding iPP matrix, generate a strong stiffening effect.     

Processing and characterization of aligned vapor grown carbon fiber reinforced polypropylene

This investigation describes a method for aligning vapor grown carbon nano-fibers suspended in a polymer flow during extrusion to produce an improved thermoplastic composite. A twin-screw extruder was used to shear mix and extrude fiber/polypropylene mixtures through a converging-annular die that generates fiber alignment along the flow direction. The degree of fiber alignment was quantified by using X-ray diffraction. It was shown that fiber alignment could be improved by increasing the residence time in the die channel. Tensile specimens were fabricated by molding the extruded strands and the strength properties of the aligned samples increased with fiber content. The tensile strength improved with greater fiber orientation, however, more fiber alignment had little affect on the modulus. The addition of vapor grown carbon nano-fiber also increased the thermal conductivity and decreased the electrical resistivity.     

Diameter controlled chemical vapor deposition synthesis of single-walled carbon nanotubes

In this study, we systematically investigated the influence of catalyst preparation procedures on the mean diameter of single-walled carbon nanotubes (SWNTs) synthesized by the alcohol catalytic chemical vapor deposition (ACCVD) process. It was found that the SWNT diameter is dependent upon both reduction temperature and time, with lower reduction temperature and/or shorter reduction time resulting in smaller diameter SWNTs. The morphology of the SWNTs also changed from vertically aligned to randomly oriented when the reduction temperature was below 500 degrees C. We also found that introducing a small amount of water during the catalyst reduction stage significantly decreased the mean diameter of the SWNTs. Lastly, we report on the use of a new binary catalyst system in which rhodium was combined with cobalt. This new Co/Rh combination produced SWNTs of smaller diameter than the conventional Co/Mo catalyst.     

炭化聚苯乙烯/聚苯胺核-壳聚合物颗粒制备中空炭球

以磺化聚苯乙烯球为模板,苯胺为碳源,利用模板法制备了中空炭球结构.采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、傅立叶-红外光谱(FT-IR)和热重分析(TGA)对所制的样品进行了表征.结果表明:所制中空炭球的壁厚为35nm且粒径均匀,中空炭球的形貌和壳层厚度受聚苯乙烯模板磺化度的影响....     

Multi-walled carbon nanotubes fabricated by electrospinning of acrylonitrile/nylon solution and subsequent carbonization

The poly(acrylonitrile) (PAN) nanofiber web interpenetrated nylon-6 nanofiber supporters were prepared by electrospinning of an acrylonitrile (AN)/nylon-6 solution. It was realized that the average diameters of PAN and nylon-6 nanofiber were 20 and 100 nm, respectively, and that the PAN nanofibers constructed spider-mat networks which were supported by the robust nylon-6 nanofiber pillars. After stabilization and carbonization above 600 degrees C, both hollow-shaped and bamboo-shaped multi-walled carbon nanotubes (MWCNTs) were formed with the diameter range from 5 to 20 nm. The morphology and structure of MWCNTs had been further investigated by the combination techniques of transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffraction (XRD) and elemental analyzer (EA).