Characteristics of carbon nanotubes grown by mesh-inserted plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition (CVD) has the advantages of low temperature and vertical growth in synthesizing carbon nanotubes (CNTs), but has generally produced stubby CNTs, probably due to an ion bombardment effect. To suppress the ion bombardment, a metal mesh with the same electrical potential as that of the cathode was placed just above the substrate on the cathode. The anode was electrically grounded while the cathode and the mesh were both negatively biased, causing no plasma to occur below the mesh. The substrate was therefore separated from the plasma by the mesh so that the ion bombardment was suppressed. CNTs were grown on a 2 nm-thick Invar catalyst with different DC plasma powers of 0–112 W at 500 °C, 3.3 torr for 10 min, using C₂H₂ (28 sccm) and NH₃ (172 sccm). Compared to CNTs grown with no mesh, these CNTs showed smaller diameters and greater lengths. As the plasma power decreased, the CNTs grown with mesh were thinner and longer and resembled those grown at a higher temperature by thermal CVD. Etching these CNTs by N₂ plasma reduced their population density and considerably improved their field emission characteristics.     

聚丙烯/碳纳米管微孔注塑发泡行为及力学性能

研究了不同含量单壁碳纳米管(CNT)的加入对聚丙烯(PP)流变、热稳定性及微孔注塑发泡行为和力学性能的影响。结果表明，随着CNT含量从不足1.0 %(质量分数，下同)逐渐增加，PP熔体黏度显著增大，热稳定性逐渐提升，即使CNT的加入量仅为0.15 %也会产生团聚现象,但团聚体尺寸较小且与基体结合紧密；微孔发泡注塑样品中泡孔分布不均匀,泡孔尺寸范围在10~70 μm，直径随着CNT含量增加呈现先减小后增大；PP/CNT复合材料微孔发泡成型后，弹性模量、屈服应力下降不大，但断裂伸长率平均提升了近400 %，不同组分发泡样品间力学性能指标变化不大。     

Reinforcement role of carbon nanotubes,Part I: High‐performance epoxy resin

The reinforcement role of single‐walled carbon nanotubes (SWCNT) in a high‐performance epoxy resin is studied in this article, with the emphasis on the deformation and load transfer mechanism. Tensile tests show that introducing carbon nanotubes (CNTs) into the epoxy resin changes the tensile strength of the material, and that the increase of Young's modulus is in good agreement with the increasing of glass transition temperature (T_g) measured by differential scanning calorimetry (DSC). Residual strains in CNTs induced during curing process have been investigated both experimentally and theoretically. Raman spectroscopy study shows that load transfers more efficiently in tension than in compression. The Raman shifts of deformed CNTs under repeated loading indirectly reveals that the load can be further transferred via friction after debonding fully occurs. Thin epoxy layers were observed on the pull out ends of CNTs, which implies the existence of the immobilized epoxy layer between CNTs and bulk epoxy. POLYM. COMPOS., 36:2212–2219, 2015. © 2014 Society of Plastics Engineers     

Development of electrically conductive and anisotropic gel-coat systems using CNTs

Electrical conductivity of an unsaturated thermoset polyester based gel-coat system containing 0.05 wt.% of carbon nanotubes (CNTs) was investigated. The CNTs used were synthesized by chemical vapor deposition method by methane decomposition and Raman characterization showed that they were mostly single walled and high quality. To disperse CNTs in the gel-coat resin, 3-roll milling technique was used. It was found that as the CNTs are added to gel-coat system, resistivity value decreases significantly while neat gel-coat showed a high resistivity. By the application of an AC electrical field during curing process, it was attempted to align CNTs in the gel-coat resin and an electrically anisotropic polymer was obtained.     

Effect of surface treatment for carbon nanotubes on morphological and rheological properties of poly(ethylene oxide) nanocomposites

Poly(ethylene oxide) nanocomposites filled with functionalized multi‐walled carbon nanotubes are prepared and characterized using rheological and morphological measurements. This study investigates how the surface treatment of carbon nanotubes (CNTs) affects the CNT dispersion state. It is found that the nanocomposites have a higher effective volume fraction than the real volume fraction of the CNTs. The dispersion state of the CNTs is identified by using field emission scanning electron spectroscope and transmission electron microscope. The rheological findings indicate that there exists a percolated network structure of the CNTs in the nanocomposites, which was confirmed by electrical conductivity measurements as well as morphological observation. POLYM. ENG. SCI., 46:1350–1357, 2006. © 2006 Society of Plastics Engineers     

Effects of nitrogen doping on the structure of carbon nanotubes (CNTs) and activity of Ru/CNTs in ammonia decomposition

Nitrogen doping on carbon nanotubes (CNTs) was carried out using N₂ microwave plasma at the powers of 200 and 400 W. N₂ physisorption, XPS, XRD, TEM, and CO chemisorption were employed to investigate the effects of nitrogen doping on the structure of CNTs and the state of Ru particles supported on CNTs. The bulk structure and the surface texture of CNTs remain unchanged by such nitrogen doping. Two types of nitrogen species, pyridinic and quaternary nitrogen, were found on the surface of nitrogen doped CNTs. Pyridinic nitrogen atom may have a strong interaction with Ru. The average Ru particle size decreases with the increase of pyridinic nitrogen content. The activity of Ru/CNTs catalysts in ammonia decomposition is dependent on the dispersion of Ru particles and remaining nitrogen on the surface of CNTs.     

Dispersion and thermal conductivity of carbon nanotube composites

A mechanical method was used to shorten carbon nanotubes (CNTs) for improving dispersion without reducing their thermal conductivity. Single walled carbon nanotubes (SWCNTs) were mechanically cut to produce short and open-ended fullerene pipes. These shortened SWCNTs were then used in polymer composites. Both atomic force microscopy and scanning electron microscopy characterizations suggested that nanotube shortening significantly improved CNT dispersion. Thermal conductivity of composites containing short CNTs were found to be much better than those containing pristine CNTs.     

纳米铁/碳纳米管复合氧阴极电-Fenton降解RhB

制备了纳米铁/碳纳米管(Fe/CNTs)复合氧阴电极,通过SEM、EDS、XRD对电极进行了表征。基于该氧阴电极中性条件下电-Fenton降解Rhodamin B(RhB)溶液的试验表明,外加电压1.2 V、通入空气量0.1 m3/h、反应120 min、5mg/L的RhB溶液降解率达到92.1%,说明H2O2和离子态铁可以通过电化学还原在该氧阴极表面高效产生,RhB可通过E-Fenton反应高效去除。     

Effects of nitrogen-doped carbon nanotubes on the discharge performance of Li-air batteries

Carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (N-CNTs) were synthesized using a floating catalyst chemical vapor deposition method and characterized by scanning electron microscopy (SEM), transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. The study found that the as-prepared CNTs and N-CNTs showed different discharge capacity as cathode materials in Li-air battery. To further study the reason why N-doping improves the electrochemical performance exceptionally, the discharge products on the two kinds of nanotubes were detected by SEM, XRD and Raman. SEM study showed, for the first time, that more uniform distribution of discharge products on the surface of CNTs arising from N-doping affected the boost of discharge capacity, a result which was discussed in detail. In comparison to non-doped CNTs, nitrogen doping was considered to be a promising way to improve the performance of carbon based cathode material for Li-air batteries.     

Deposition of silver nanoparticles onto human serum albumin‐functionalised multi‐walled carbon nanotubes

To facilitate the design of carbon nanotube (CNT)‐based hybrid materials, a strategic approach for nanotube dispersion in aqueous media is required. This means that the reactants must exhibit certain selectivity towards both the nanotubes and the solvent medium. The main goal of this study was to prepare new bionanomaterials based on human serum albumin (HSA) and multi‐walled CNTs (MWCNTs), under mild conditions and without covalent modification of the nanotubes. Silver nanoparticles (AgNPs) of a controlled particle size, about 2‐nm diameter, were prepared and directly deposited onto the HSA‐functionalised MWCNTs. The characterisation of AgNP/HSA‐MWCNT hybrids prepared was carried out by scanning tunneling microscopy and transmission electron microscopy (TEM). The presence of the AgNPs was corroborated by elemental chemical analysis using TEM‐coupled energy‐dispersive X‐ray spectroscopy. The density of AgNPs coverage is discussed as a function of HSA concentration, the strength of the reducing agent, and the nature of protein employed (HSA vs. bovine serum albumin and rotavirus nucleocapsid protein VP6). © 2012 Canadian Society for Chemical Engineering     

RF-PECVD growth and nitrogen plasma functionalization of CNTs on copper foil for electrochemical applications

This work describes an efficient way to improve the adhesion, growth rate and density of CNTs on copper substrate using radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD). The adhesion of an alumina buffer layer to the copper substrate is critical for the successful growth of CNTs. Hydrogen plasma was performed on the copper substrate to reduce copper oxide from the surface. The effect of two intermediate layers (Ti, Ni), as individual or in combination, between alumina and copper substrate on the CNT growth has been investigated. Furthermore, a nitrogen plasma treatment was carried out to functionalize the obtained CNTs. Electrochemical measurements were performed using CNTs grown on a copper substrate as electrodes and LiClO₄ as electrolyte. The specific capacitance of the obtained electrodes increases from 49 up to 227 Fg^− 1 for untreated and nitrogen-plasma treated CNTs at a scan rate of 10 mVs^− 1, respectively.     

Localized fabrication of carbon nanotubes forest at a needle electrode by atmospheric pressure corona discharge

Characteristics of the growth of multi-walled carbon nanotubes (CNTs) at a localized surface of a needle-shaped graphite cathode by corona discharge were investigated with varied temperature, 400–1000 °C. For the CNTs' growth, C₂H₄ in H₂ stream was used as carbon source. The CNTs were observed in aligned form on the tip of a needle-shaped cathode under the present condition. It was observed that the temperature range for the CNTs' growth with corona discharge, 600–800 °C, was lower than that that without corona discharge, 700–1000 °C. In the relevant reaction system, strong electric field at the cathode tip enforced the CNTs to grow straightly to form the free-standing aligned CNT forest at a specifically narrow tip zone of the needle cathode.     

Zinc barrel electroplating using low cyanide electrolytes

The influence of plating conditions on the cathode efficiency of zinc barrel electroplating and the quality of deposited layers for low cyanide electrolytes is analysed. The investigations are carried out using factorial design methodology. The first part of the study shows how electrolyte components, such as brightening agent, sodium carbonate concentration, sodium hydroxide concentration, sodium cyanide concentration and zinc metal content, influence cathode efficiency and the morphology and the texture of the zinc electrodeposits. A mathematical model that fits experimental data is suggested and the pseudo three-dimensional plot of yield as a function of electrolyte composition for three significant component mixtures, brightening agent, sodium cyanide concentration and zinc metal content, is represented. The second part of the study shows how varying six process parameters influences current efficiency and metal thickness distribution. For the range studied, efficiency is affected by workload volume, current density, perforation and part size, but not by rotation speed and quantity of charge.     

Catalytic synthesis of carbon nanotubes using Ni- and Co-doped calcium tartrates

Calcium tartrate doped with Ni and/or Co has been used as a catalyst source in the chemical vapor deposition synthesis of carbon nanotubes (CNTs). Thermolysis of doped calcium tartrate in an inert atmosphere was shown to yield Ni, Co or Ni-Co nanoparticles ∼6 nm in diameter dispersed in a calcium oxide matrix. The CNT synthesis was carried out by ethanol vapor decomposition at 800 °C. The structure of the products was characterized by transmission electron microscopy and Raman spectroscopy. It was found that Ni nanoparticles embedded in CaO provide the narrowest diameter distribution of CNTs, while the bimetallic Ni-Co catalyst allows the formation of the thinnest CNTs with the outer diameter of ∼2 nm. This type of CNT is more likely to be responsible for the lowest value of the turn-on field (∼1.8 V/μm) for the emission current detected for the latter sample.     

Microstructural evolution and fracture toughness of plasma sprayed CNT reinforced Yttria-stabilized Hafnia coating

Yttria (8 wt%)-stabilized hafnia (YSH) and carbon nanotubes (CNTs) (1 wt%) reinforced yttria-stabilized hafnia (YSHC) coatings were fabricated on alumina substrate using atmospheric plasma spray technique. Raman spectra confirmed the survival of CNTs in plasma sprayed YSHC coating and indicated about graphitization of CNTs. Whereas, the FE-SEM micrograph infers the presence of few 2-D graphene platelet-like structure in plasma sprayed YSHC coating. Addition of 1 wt% CNTs has significantly increased the densification of YSH coating from 86% to 92%, whereas average hardness and elastic modulus increased by ~57% and ~16%, respectively. A phenomenal increase of ~125% in relative fracture toughness was observed in YSHC coating, which is attributed to three major factors viz. (a) Enhanced densification (b) High fraction of fully melted regions and (c) Various toughening mechanisms, like CNTs pull out, CNTs braiding, graphene splat wrapping, CNTs anchoring.     

Adsorption of Pyridine from Aqueous Solution by Surface Treated Carbon Nanotubes

Abstract

The surface treatment of multi‐walled carbon nanotubes (MWCNTs) with acid, heat, ultrasonic, and polyvinyl alcohol has been examined. The original CNTs and four treated CNTs were first used as adsorbents to remove pyridine from water and the adsorption isotherms of pyridine on CNTs were studied. At the same time, the effect of pH, temperature, and the adsorption kinetics on the adsorption of pyridine were also evaluated. The experiments show that the adsorption of pyridine on different CNTs is mainly a physical process and the data fit the Freundlich adsorption isotherm well. The short time needed to reach equilibrium as well as the high adsorption capacity of pyridine suggests that CNTs possess highly potential applications for pyridine removal from water.     

Carbon nanomaterials from eleven caking coals

Carbon nanotubes (CNTs) have been successfully produced from 10 typical Chinese caking-coals using an arc plasma technique. For comparison, one caking coal from New Zealand is also tested. The results show that all coals tested can be used to produce significant quantities of CNTs with fullerenes as by-products. The CNTs are examined using scanning electron microscope and high resolution transmission electron microscope. It has been found that the yields of CNTs are closely related to coal properties. The CNT yield increases as the fixed carbon content in coal increases or as the volatile matter content in coal decreases.     

Poly[ethylene‐co‐(acrylic acid)]‐based nanocomposites: Thermal and mechanical properties and their structural characteristics studied by Raman spectroscopy

Nanocomposites containing carbon nanotubes (CNTs) as nanofillers and poly[ethylene‐co‐(acrylic acid)] (PEAA) or a polymer miscible mixture of PEAA and poly(2‐ethyl‐2‐oxazoline) (PEOx) as a matrix were prepared by the solution‐evaporation method with minimal damage to nanotubes. CNTs were prepared by chemical vapor deposition (CVD) with ethanol as the source of carbon. Raman spectroscopy confirmed the presence of single walled carbon nanotubes (SWNTs). High resolution transmission electron microscopy (HRTEM) showed the formation of multi walled carbon nanotubes (MWNTs). Thermal and mechanical properties of the nanocomposites were studied by analyzing samples containing different amounts of CNTs. The degree of crystallinity (X_c) of the PEAA‐based nanocomposite containing a smaller amount of CNTs was larger (X_c = 17.0%) than both the one of pure PEAA (X_c = 14.6 %) and PEAA‐based nanocomposite containing higher amounts of CNTs (X_c = 15.0%). The Young's modulus, ultimate stress, deformation at break, and toughness obtained from unidirectional tensile tests of the CNTs (1 wt%)‐PEAA nanocomposite were higher than both the one of pure PEAA and CNTs (5 wt%)‐PEAA nanocomposite. When a polymer mixture of PEAA/PEOx (containing 80 wt% of PEAA) was used as a matrix, a better mechanical response was also detected for nanocomposite containing 1 wt% CNTs. The nanocomposites containing small amounts of CNTs prepared here have potential to be used as coatings of metal or glass surfaces expecting a better mechanical performance than the one of pure matrix. POLYM. COMPOS., © 2011 Society of Plastics Engineers.     

化学气相沉积法制备碳纳米管的研究进展

从催化剂、碳源气体及反应器的选择等方面综述了化学气相沉积法制备碳纳米管的研究进展 ,讨论了碳纳米管的合成机理。指出催化合成碳纳米管的研究难点在于管径的有效调控和大批量生产 ,今后的研究方向应为单层碳纳米管的有效合成     

Low temperature growth of carbon nanotubes using Ni nanopowder mixed with Ag-paste as catalyst

Growth of carbon nanotubes (CNTs) at low temperature is a critical issue in the development of CNTs for diversified applications. The screen printing method, which used silver paste mixed with CNTs and glass powder as the raw material, was usually adopted for fabricating cathode of field emission device. In this work, Ni nanopowder mixed with commercial Ag-paste was prepared and screen-printed on the glass substrate, and then subjected to sintering in air at 500 °C. Growth of CNTs was performed in a self-designed cold-walled chemical vapour deposition (CVD) chamber at 500 °C under a pressure between 1 and 10 Torr. Field emission property was tested and the turn-on field of 2.4 V/μm was obtained for the specimen containing 2.7 wt.% Ni nanopowder. CNT density can be controlled by adjusting the concentration of Ni nanopowder in silver paste. This method proposed a simple route for synthesizing CNTs at relatively low temperature in a conventional CVD system, which is capable of fabricating large area cathode with proper CNT density.