Radio Frequency Thermal Plasma: The Cutting Edge Technology in Production of Single-Walled Carbon Nanotubes (original) (raw)
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Journal of Applied Physics, 2002
A high density plasma from a methane-hydrogen mixture is generated in an inductively coupled plasma reactor, and multiwalled carbon nanotubes ͑MWNTs͒ are grown on silicon substrates with multilayered Al/Fe catalysts. The nanotubes are vertically aligned, and the alignment is better than the orientation commonly seen in thermally grown samples. A detailed parametric study varying inductive power, pressure, temperature, gas composition, catalyst thickness, and power to the substrate is undertaken. Transmission electron microscopy and Raman spectroscopy are used to characterize the nanotubes. Emission spectroscopy and a global model are used to characterize the plasma. The power in the lower electrode holding the substrate influences the morphology and results in a transition from MWNTs to nanofibers as the power is increased.
In the present study, CFD simulations are carried out to investigate the effect of thermal conductivity of the reaction chamber's graphite liners on the flow and the temperature fields in the induction thermal plasma processing system for the continuous production of single-walled carbon nanotubes (SWCNTs). The thermal conductivity of ten different graphite liners were measured at different temperatures and the thermal conductivity profiles were plotted versus temperature. These temperature-dependent profiles were then implemented into the CFD code and the temperature and flow fields were compared to our previous numerical simulations [1,4]. The results indicated that the thermal conductivity profiles of the graphite liners imposed slight variations on the flow and the temperature fields inside the reaction chamber.
Synthesis of Carbon Nanotubes in Thermal Plasma Reactor at Atmospheric Pressure
Nanomaterials, 2017
In this paper, a novel approach to the synthesis of the carbon nanotubes (CNTs) in reactors operating at atmospheric pressure is presented. Based on the literature and our own research results, the most effective methods of CNT synthesis are investigated. Then, careful selection of reagents for the synthesis process is shown. Thanks to the performed calculations, an optimum composition of gases and the temperature for successful CNT synthesis in the CVD (chemical vapor deposition) process can be chosen. The results, having practical significance, may lead to an improvement of nanomaterials synthesis technology. The study can be used to produce CNTs for electrical and electronic equipment (i.e., supercapacitors or cooling radiators). There is also a possibility of using them in medicine for cancer diagnostics and therapy.
The Journal of Physical Chemistry C, 2009
Characterization and purification studies have been performed on the single-walled carbon nanotubes (SWNTs), prepared by the large-scale (i.e., at production rates of ∼100 g h -1 ) induction thermal plasma process. The main impurities present in the as-produced soot materials are first identified by various material analyses and turn out to be amorphous carbon, graphitic carbon particles, and metal/metal-oxide catalysts, but without significant content of fullerenes. In particular, the amounts of graphitic particles present were high in comparison with those of other plasma arc or laser-grown SWNTs, and it is believed that these graphitic particles mainly originate from the remains of the feedstock materials. On the basis of this observation, different purification protocols have been explored by combining the two-step processes of thermal oxidation in air and liquid oxidation in a variety of acids. At each step of the purification, the changes in the SWNT samples are monitored by various analytical techniques, and the results reveal that the air oxidation at 350°C for 1 h, followed by refluxing in 7 M HNO 3 for 6 h, provides for the best efficiency in conducting the purification of the thermal plasma-grown SWNT. The material properties of the purified samples, such as the electrical resistivity and the specific surface area (SSA), have also been analyzed by using the Brunauer-Emmett-Teller (BET) and the four-probe methods, the measured values being ∼500 m 2 g -1 and ∼2 × 10 -3 Ω cm, respectively.
Low temperature plasma chemical vapour deposition of carbon nanotubes
Diamond and Related Materials, 2002
Carbon nanotubes have been grown on alumina-supported iron compound catalysts by 2.45 GHz microwave plasma chemical vapour deposition, without additional substrate heating, using methaneyargon gas mixtures with no added hydrogen, and with microwave powers typically up to 100 W. The conditions that produced a stable plasma were investigated by statistical selection of the values of power, pressure and gas flow rates. The conditions for abundant multi-walled nanotube formation were determined within this parameter space by SEM and TEM observations of the deposited material. The temperatures of the plasma and of the substrate in the reactor were investigated by optical emission spectroscopy and melting point samples, respectively. ᮊ
Modeling of multi-scale processes during plasma-assisted growth of carbon nanotubes
Multi-Scale Computational Framework (MSCF) has been developed for modeling nanostructured materials fabrication. This framework integrates Computational Fluid Dynamic software for reactor-scale simulations, a Kinetic Monte Carlo simulator for atomic-scale surface modeling, and a Molecular Dynamic solver for computing rates of surface reactions, and other elementary processes. In this paper, the MSCF was used to investigate the catalytic growth of carbon nanotubes (CNT) in a C 2 H 2 /H 2 inductively coupled plasma reactor. It was shown that MSCF is capable of predicting paths for delivering carbon onto catalyst/CNT interface, formation of single wall or multi-wall CNTs depending on the shape of catalyst, and transition from nucleation to the steady growth of CNTs.
Journal of Nanoparticle Research, 2009
The nucleation of the nickel nanoparticles on substrates, a critical process in the growth of carbon nanotubes, has been modeled analytically using thermodynamic and statistical theories. It was hypothesized that during the initial stages of the annealing process smaller nanoparticles with the size of about 5 nm form and, subsequently, randomly hop to make larger nanoparticles. The minimum and maximum diameter of the nickel nanoparticles can be obtained from the derived expressions. In addition, the size-dependent probability of forming the nanoparticles was examined at various temperatures and plasma power densities in chemical-vapor deposition and plasma-enhanced chemical-vapor deposition methods, respectively. The theoretical results presented agreed very well with experimental data.
Carbon, 2006
High-quality single-walled carbon nanotubes (SWCNTs) have been synthesized from H 2 -CH 4 mixtures on a MgO-supported bimetallic Mo/Co catalyst using microwave plasma-enhanced chemical vapor deposition (PECVD). Reaction parameters including temperature, H 2 :CH 4 ratio, plasma power, and synthesis time have been examined to assess their influence on SWCNT synthesis. Raman spectroscopy and high-resolution field emission scanning electron microscopy reveal that the quality, selectivity, density and predominant diameter of SWCNTs depend on the varied synthesis parameters. Results of this study can be used to optimize SWCNT synthesis conditions and products and to improve understanding of the growth of SWCNTs by PECVD.
Continuous Mass Production of Carbon Nanotubes by 3-Phase AC Plasma Processing
2004
For the synthesis of carbon nanotubes (CNTs), the plasma process is an original new approach. Hereby, the carbon mass flow is no longer limited by a physical ablation rate (which is the limiting step in the production rate of the classical nanotube processes), but is freely adjustable. Moreover, the process is operated at atmospheric pressure and the NT rich soot is extracted continuously. The feasibility for producing a large variety of different nanostructures at high selectivity including Carbon MWNTs, SWNTs, nanofibers and necklaces nanostructures is well established. From the characteristics observed, it is concluded that the AC plasma technology shows a significant potential for the continuous production of bulk quantities of carbon-based nanotubes of controlled properties and novel nanostructures. In this paper, the plasma process for continuous nanotube synthesis, typical process conditions prevailing and products are presented.
Journal of the Brazilian Chemical Society, 2013
A reforma de fontes de carbono por plasma térmico de argônio de elevada capacidade calorífica é um dos métodos mais promissores na síntese de novos materiais. Um método para a obtenção de negro de carbono e nanotubos de carbono através da pirólise do metano por plasma térmico de corrente contínua é relatado no presente trabalho. A reforma foi realizada na ausência de oxigênio utilizando um jato de plasma gerado por uma tocha de plasma de argônio. O produto sólido foi caracterizado por espectroscopia Raman e microscopia eletrônica de varredura e transmissão. Os resultados mostraram que nanotubos de carbono foram produzidos na presença de catalisadores metálicos, enquanto que a formação de negro de carbono ocorreu na ausência de catalisadores no reator. A relação I D /I G obtida a partir dos espectros Raman indicou que a amostra obtida usando o catalisador 5%Ni/Al 2 O 3 apresentou nanotubos de carbono com maior pureza em relação aos outros catalisadores (10%Ni/Al 2 O 3 e 10%Ni-5%Ce/Al 2 O 3 ) testados.