Synthesis of single-walled carbon nanotubes by induction thermal plasma

Abstract

The production of high quality single-walled carbon nanotubes (SWCNTs) on a bulk scale has been an issue of considerable interest. Recently, it has been demonstrated that high quality SWCNTs can be continuously synthesized on large scale by using induction thermal plasma technology. In this process, the high energy density of the thermal plasma is employed to generate dense vapor-phase precursors for the synthesis of SWCNTs. With the current reactor system, a carbon soot product which contains approximately 40 wt% of SWCNTs can be continuously synthesized at the high production rate of ~100 g/h. In this article, our recent research efforts to achieve major advances in this technology are presented. Firstly, the processing parameters involved are examined systematically in order to evaluate their individual inÁuences on the SWCNT synthesis. Á Based on these results, the appropriate operating conditions of the induction thermal plasma process for an effective synthesis of SWCNTs are discussed. A characterization study has also been performed on the SWCNTs produced under the optimum processing conditions. Finally, a mathematical model of the process currently under development is described. The model will help us to better understand the synthesis of SWCNTs in the induction plasma process. KEYWORDSSingle-walled carbon nanotubes (SWCNTs), large-scale continuous synthesis, radio frequency (RF) induction thermal plasma, optimization, numerical modeling Nano ResearchOver the past decade, the superlative properties of single-walled carbon nanotubes (SWCNTs) [1] have attracted much attention for their use in a wide range of applications, including microelectronic [2], biomedical [3], polymer [4], energy [5], and environmental [6] devices. Consequently, the economical production of high quality SWCNTs on a large scale has become an issue of considerable interest. To date, there have been tremendous efforts to develop new synthesis methods leading to the economical production of SWCNTs and it has been shown that SWCNTs can be produced by many 801 Nano Res (2009) 2: 800 817 different ways, such as arc discharge, laser ablation, arc-jet plasmas, chemical vapor deposition (CVD), non-equilibrium plasmas, and combustion methods.Recently, it was demonstrated that high quality SWCNTs can be continuously synthesized, on a large scale, by the method of simultaneous direct evaporation of carbon black and metal/metaloxide catalyst mixtures, using induction thermal plasma technology [7]. In this process, the high energy density of the thermal plasma is employed to generate dense vapor-phase precursors for the synthesis of SWCNTs. The main advantages of this process are that the rate of input carbon is not limited by the rate of electrode erosion and that SWCNTs are synthesized in the free space without any substrates. Before undertaking optimization efforts, it was shown that a carbon soot product which contains approximately 40 wt% of SWCNTs can be continuously synthesized at production rates of over 100 g/h.The primary goal ...

Thermal Plasma Synthesis of Nano-Sized Powders

“…Traditionally, CNTs with high purity have been obtained using the transferred DC arc discharge generated by graphite electrodes [57][58][59][60]. Due to the limitations of the batch process inherent in this type of plasma system, however, there have been many efforts to produce CNTs continuously by decomposing liquid or gas phase hydrocarbons with non-transferred DC or RF plasma torches [61][62][63][64]. For example, Choi et.…”

Radio Frequency Thermal Plasma: The Cutting Edge Technology in Production of Single-Walled Carbon Nanotubes

“…However, implementing those models into the plasma and particle models is quite challenging because of their large differences in physical scales. In the previous work by Keun Su et al (10) , a simplified model was adopted based on supersaturation of metal catalyst nanoparticles. In the model, the nucleation of SWCNTs is started when the droplet particles are supersaturated by carbon atoms.…”

“…As the electro-magnetic fields penetrate through the plasma, they lose electrical energy through joule heating. The excitation frequency is typically between 200 kHz and 40 MHz and the power levels at laboratory units vary between 30-50 kW (5) . The electrode-less operation of RF plasma torch enables the system to operate continuously and to generate final products clean from electrode erosion.…”

“…Subsequently, inside the reactor chamber under a controlled temperature gradient environment, of vapors results in the formation and growth of catalyst nanoparticle aggregates and bundles of SWCNTs on the aggregates. Studies have shown that the size distribution and chemical composition of the catalysts nanoparticles, as well as the plasma and thermo-fluid fields in the system, affect the nanotubes diameter, growth rate, morphology and microstructure (10,11) . The optimization procedure of the RF plasma system requires a more complete understanding of the SWCNT formation mechanism and its relationship with the local plasma properties and thermo-fluid field in the system (10) .…”

“…Studies have shown that the size distribution and chemical composition of the catalysts nanoparticles, as well as the plasma and thermo-fluid fields in the system, affect the nanotubes diameter, growth rate, morphology and microstructure (10,11) . The optimization procedure of the RF plasma system requires a more complete understanding of the SWCNT formation mechanism and its relationship with the local plasma properties and thermo-fluid field in the system (10) . Numerical modeling in conjunction with experimental studies can help provide a fundamental understanding of the process parameters in order to optimize the system.…”