低压空气中直流电弧法制备单壁碳纳米管

本文以Fe-S为催化剂、低压空气为缓冲气体采用直流电弧放电法首次大量合成低成本、高质量的单壁碳纳米管。实验结果表明在电弧放电过程中通过控制空气流量,使得电弧腔室压强保持在6～12 KPa为最优制备条件。采用扫描电子显微镜(SEM)和透射电子显微镜(TEM)对样品的形貌和结构进行表征,结果表明该方法所制备的单壁碳纳米管具有较高结晶度,管壁表面光滑、其直径为1.5～6.0 nm.采用低压空气电弧放电法有望成为低成本、大量制备高质量单壁碳纳米管的重要技术手段之一。     

Synthesis of straight multi-walled carbon nanotubes by arc discharge in air and their field emission properties

The possibility of preparing straight multi-walled carbon nanotubes (MWCNTs) on a large scale is demonstrated using direct current arc discharge with a rotating graphite anode in low pressure air. The process is time-saving, economical, and non-hazardous. It is found that the optimum air pressure for the highest yield of MWCNTs is about 60 Torr. Investigation of the internal organization of the cathode deposit reveals that many columns about 40 μm in diameter are closely packed and mechanically stable. The highest content of MWCNTs is found in the intercolumnar spaces between columns. Emitters made of the cathode deposits that contain a large number of straight nanotubes exhibit outstanding field emission properties. The turn-on electric field decreases from 1.44 to 0.93 V/μm and the field enhancement factor β increases from about 3,190 to 7,830 only after simple burning at 750 °C for 30 min in air. The results indicate that MWCNTs prepared by arc discharge in air are promising for field emission application.     

不同压力下碳纳米管的电弧法合成及其表征

采用电弧放电法在氦气/乙炔混合气氛中,在不同压力下合成了碳纳米管.运用场发射扫描电镜、场发射透射电镜、X-射线衍射仪和拉曼光谱对碳纳米管的形貌进行了表征.采用可见发射光谱对碳纳米管的形成过程进行了原位诊断研究.场发射扫描电镜结果表明,在氦气/乙炔气氛中合成的碳纳米管的长度大于50微米,许多碳颗粒沉积在碳纳米管壁上.场发射透射电镜结果表明,在0.100MPa下合成的碳纳米管的壁厚明显大于0.035MPa下合成的碳纳米管的壁厚.可见发射光谱诊断结果表明,CH和C2物种可能作为碳纳米管形成的前驱体,其中,以H原子作为无定形炭的刻蚀物种.阳极消耗速率和产物在阴极的沉积速率随着反应器中压力的增加而增加.因此,可以通过加强阳极和乙炔的蒸发速率及CH和C2物种的沉积速率而增加碳纳米管的形成速率.     

Synthesis of high quality single-walled carbon nanotubes by arc discharge method in large scale

Single-walled carbon nanotubes (SWNTs) were synthesized by a novel method. The dc arc discharge in H₂-Ar gas atmosphere with Fe₃O₄ as catalyst was used. The morphology and structures of the as-prepared SWNTs were characterized by SEM, HRTEM and Raman spectroscopy techniques. The results indicated that this new catalyst could be used to produce SWNTs with high purity and yield in large scale. The purity and yield of the SWNTs synthesized from these new catalysts were affected by the mixture buffer gas. Based on the overall ease and low-cost advantages of these new catalysts, these results suggest a potential opportunity for cost-effective and commercial production of SWNTs.     

电弧放电法制备煤基炭纳米纤维及开口竹节状碳纳米管

以中国白杨树无烟煤为原料,添加一定量煤焦油和沥青黏结剂制成炭棒作为阳极,采用直流电弧法制备竹节状碳纳米管及炭纳米纤维.用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能量散射谱(EDS)和X射线衍射(XRD)等技术对产物进行表征.结果表明:在较低氦气压力下(0.020MPa),采用不添加任何催化剂的无烟煤基炭棒进行电弧放电,在剩余阳极上制备得到竹节状碳纳米管和炭纳米纤维.所得竹节状碳纳米管多为开口状,直径在50nm左右;炭纳米纤维宏观上成绒毛球形,纤维的直径在30nm～50nm之间.     

Coral-like amorphous carbon nanotubes synthesized by a modified arc discharge

A coral-like amorphous carbon nanotube was prepared by a modified arc discharging furnace in hydrogen atmosphere with a mixture of Mo-Co₂O₃-Mg powders as catalyst at 600°C. This carbon nanotube presented a microscopic coral-like by SEM observation and amorphous structure of nanotubes by HRTEM observation. The XRD diffraction and Raman pattern presented noncrystal characteristics compared to the normal graphite structure. We believed that these results may be affected by the “synergistic” effect of catalyst, atmosphere, and temperature in the synthesis process. The possible explanations to the formation mechanism of this novel carbon nanotube have also been proposed.     

Multi-walled carbon nanotubes grow under low pressure hydrogen,air, and argon ambient by arc discharge plasma

Multi-walled carbon nanotubes (MWCNTs) were grown on cathode deposit by arc discharge plasma under H₂, Ar, and air ambient environment. The influence of ambient gas pressure on the structure and physical properties of carbon nanotube were compared. Herein, we highlight the influence of ambient environment and pressure to grow high quality carbon nanotubes. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction were used for structural characterization and yield determination. The result revealed that background gas and pressure were crucial factor for growing highly crystalline and highly graphitic with I_D/I_G ratio 0.237 obtained for MWCNTs' synthesized in H₂ environment with extreme low defects.     

Multi-walled carbon nanotubes produced by hydrogen DC arc discharge at elevated environment temperature

Multi-walled carbon nanotubes (MWCNTs) were synthesized by hydrogen DC arc discharge at elevated environment temperature. The sample collected from the soot on the inner wall of the arc discharge furnace was investigated using TEM, HRTEM and X-ray diffraction. The results show that environment temperature has a significant effect on the formation of MWCNTs in the soot in hydrogen atmosphere as well as the diameter of the tubes. When environment temperature in the furnace is higher than about 500 °C, MWCNTs can be formed on the furnace walls with a great quantity.     

The preparation of carbon nanotubes by dc arc discharge using a carbon cathode coated with catalyst

Carbon nanotubes (CNTs) were grown using a dc arc discharge process and relevant process parameters were investigated. Unlike the usual process in which a carbon anode is filled with metal catalyst powder, CNTs were prepared using a carbon cathode on which the metal catalyst had been deposited using an electroplating system. Various transition metals were investigated. The results show that multi walled carbon nanotubes (MWNTs) and single walled carbon nanotubes (SWNTs) can both be synthesized using this technique. SWNTs are detected in the soot sample collected around the cathode, whereas the MWNTs are detected mainly in the deposit sample collected from the central area of the cathode. The CNT yield varies depending on the catalyst used and the properties of a good catalyst are discussed.     

Conversion of toluene into carbon nanotubes using arc discharge plasmas in solution

In order to form nanocarbon materials, an arc discharge plasma method in hydrocarbon solvent is developed. In the case that the arc discharge is performed in toluene with nickel electrodes, tube-like nanocarbons were formed from toluene. The catalysis of the metal electrodes is found to be an important factor for the formation of the nanocarbons by the arc discharge in toluene. This method has a possibility of forming carbon nanotubes from liquid state solvents as a new carbon source by using catalyst ingredient as discharge electrodes.     

Catalyst effect on the preparation of single-walled carbon nanotubes by a modified arc discharge

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharge furnace using 500?Torr helium as buffer gas at 600?°C. The effect of the catalyst type on the production of SWCNTs was studied by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results indicated that the catalyst composition plays an important role in the production rate and purity of the SWCNTs product. Fe-Ni-Mg and Co-Ni powder catalysts demonstrated excellent catalytic effect at a catalyst content of 3?wt%. The soot production rate was up to 15?g/hr and the mean diameter of SWCNTs was about 1.3?nm.     

STM observation of asymmetrical Y-branched carbon nanotubes and nano-knees produced by the arc discharge method

The scanning tunneling microscopy (STM) observation of arc-grown Y-branched carbon nanotubes and sharp nanotube bends (nano-knees) is reported. A drilled out graphite rod filled with a nickel/yttrium particle mixture was used as the anode in an arc chamber under He atmosphere of 660-mbar pressure. Straight multi-wall nanotubes, Y-branches and nano-knees were found in a sample taken from the cathodic deposit. The asymmetrical Y-branches and complex nano-knees found in this experiment may be related to the additional use of metals or/and to induced changes of the temperature distribution on the cathode side. It is suggested that complex nano-knees could be new examples for carbon quantum dots.     

Fabrication of high quality carbon nanotubes with a simple ethanol-assisted arc discharge process

In this paper, a simplified ethanol-assisted arc discharge method was developed for the fabrication of multi-wall carbon nanotubes in high quality. Carbon nanotubes with high purity (80-90%) were obtained through controlling the current (15-25 V, 10-25 A) and ethanol concentration (70-100%). The products were characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectrometry.     

水下电弧放电法制备洋葱状富勒烯

探索了纯石墨电极在水中放电制备洋葱状富勒烯（Onion-like fullerenes，OLFs）的过程和工艺。用高分辨透射电镜（High resolution transmission electron microscope。HRTEM）对生成的OLFs进行了形貌、结构的观察与表征。分析结果表明制得的OLFs具有各种不同形状的内核。石墨化程度很高，直径分布在5nm～40nm范围内。在一定范围内随着电流强度的增大OLFs的产量和产率都有不同程度的提高。     

液苯介质放电制备洋葱状富勒烯

以液体苯(C6H6)为放电介质,石墨做电极,成功地制备了洋葱状富勒烯(Onion-like Fullerenes,OLFs)。重点考察了电流对OLFs产量的影响,利用高分辨透射电镜(HRTEM)和X-射线衍射(XRD)对所得产物进行了表征。结果表明:电流大小是影响OLFs产量的主要因素,所制OLFs直径分布可控制在10nm~30nm范围内。     

Synthesis of Mn-Al alloy nanoparticles by plasma arc discharge

Alloy nanoparticles in the Mn-Al system were prepared by the plasma arc discharge method. The influence of process parameters on the vaporization rate, composition, particle size, and magnetic properties of the as-produced nanoparticles was investigated. The Mn content was found to be higher in the nanoparticles than in the corresponding mother alloy, although the difference diminished with the reaction time. With increasing H₂ content in the reaction gas, both vaporization rate and particle size increased. With 30 at.% Mn, the average particle diameter in pure Ar was 35.2 nm, whereas that in an atmosphere with Ar:H₂ = 60:40 was 95.4 nm. With the addition of a small amount of carbon, ε-phase nanoparticles were synthesized. After heat treatment in a vacuum for 30 min at 400-600 °C, the nonmagnetic ε-phase was transformed into the ferromagnetic τ-phase and a very high coercivity of about 446 kA/m was achieved.     

空气中多壁碳纳米管的稳定性

采用化学气相沉积法(CVD),以二甲苯为碳源,二茂铁为催化剂制备了多壁碳纳米管(MWCNTs)。考察了纯化后的多壁碳纳米管在空气中的结构稳定性,利用电子显微技术及体积电阻率法研究了多壁碳纳米管在空气中的特性变化。结果表明:多壁碳纳米管在空气中存放时会被缓慢氧化而变短,氧化程度随空气中放置时间的延长而增加,15d后几乎完全转化为无定形碳。体积电阻率随氧化程度不同而不同。多壁碳纳米管在空气中不稳定,容易氧化,需要密闭保存。     

Synthesis of carbon nanotubes

Carbon nanotubes play a fundamental role in the rapidly developing field of nanoscience and nanotechnology because of their unique properties and high potential for applications. In this article, the different synthesis methods of carbon nanotubes (both multi-walled and single-walled) are reviewed. From the industrial point of view, the chemical vapor deposition method has shown advantages over laser vaporization and electric arc discharge methods. This article also presents recent work in the controlled synthesis of carbon nanotubes with ordered architectures. Special carbon nanotube configurations, such as nanocoils, nanohorns, bamboo-shaped and carbon cylinder made up from carbon nanotubes are also discussed.     

Electric field-oriented growth of carbon nanotubes and Y-branches in a needle-pulsed arc discharge unit: mechanism of the production

Carbon nano-onions, multiwall carbon nanotubes and Y-branched nanotubes are synthesised in a simple production apparatus. A pulsed plasma is generated by discharging a high voltage needle pulse between two graphite electrodes. A strong electric field is presented along anode and cathode electrodes. The pulse width is 0.3 μs. Acetone vapour, as a precursor, is introduced to the plasma through a graphite nozzle in the cathode assembly. A magnetic field, perpendicular to the plasma path, is provided. The possibility of carbon nanotube production through a short-pulsed arc discharge technique is investigated in this article. The results show that adding an electric field between electrodes prevents carbon ions’ dispersion, facilitates charge transferring between ions and electrodes, orients the growth of carbon nanotubes along the applied electric field and finally makes it possible to produce functionalised carbon nanoparticles such as Y-branch nanotubes and nanoknees. In this work, the growth mechanism of carbon nanotubes in a needle-pulsed arc-discharge reactor is discussed. And a possible explanation is provided for the synthesis of Y-branch carbon nanotubes. The products are examined by using scanning probe microscopy technique.