Specific Surface Area of Carbon Fine Particles Including Single-Walled Carbon Nanotubes Synthesized by Hot-Filament Plas
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Specific Surface Area of Carbon Fine Particles Including Single-Walled Carbon Nanotubes Synthesized by Hot-Filament Plasma Assisted Chemical Vapor Deposition Ryuhei Yamada1, Yasuhiro Masaki1 and Yasuaki Hayashi1 1
Kyoto Institute of Technology Matsugasaki, Sakyo-ku, Kyoto 606-8585, JAPAN, [email protected] ABSTRACT Carbon fine particles including single-walled carbon nanotubes (SWNTs) were synthesized by hot-filament and plasma assisted chemical vapor deposition. Specific surface area was evaluated for carbon fine particles synthesized under optimized conditions along with purified SWNTs and multi-walled carbon nanotubes (MWNTs) for comparison. The value of specific surface area for the synthesized carbon fine particles was smaller than the SWNTs, but larger than the MWNTs. Pore size distribution was analyzed with desorption isotherms by the DH method. Although smaller pores are included in the purified SWNTs than the synthesized carbon fine particles, pores of size larger than several nm were included more in the synthesized carbon fine particles. 1. INTRODUCTION Single-walled carbon nanotubes (SWNTs) are expected to be applied to material for hydrogen storage, platinum catalyst support in fuel cell electrode, or electric-double-layer-capacitor (EDLC) electrode because of their large surface area. They are synthesized by arc-discharge [1], laser ablation [2], and chemical vapor deposition (CVD) [3]. Gas phase synthesis methods are expected for the mass production of SWNTs, however, fine particles containing SWNTs are transported by gas flow or convection, so that they cannot continue to stay for more than a few seconds in a reaction zone, where SWNTs are grown through the extraction of carbon from catalytic metal particles during the decrease of temperature. We developed a new gas phase synthesis method, which applies a direct-current or a radio-frequency glow discharge plasma for the suspension of negatively charged fine particles containing catalytic metal and carbon nanotubes [4,5]. Carbon fine particles synthesized by the method are expected to have larger surface area due to ion bombardment in plasma. In this paper, we show the results of evaluation of specific surface area of synthesized carbon fine particles including SWNTs and analysis of their pore size distribution along with purified SWNTs for comparison.
2. EXPERIMENT Figure 1 shows schematic views of the system of hot-filament plasma assisted chemical vapor deposition (CVD) and its growth mechanism. RF plasma was generated between grounded filaments and an RF-induced copper plate. Filaments were heated up to 1800-2000 ℃. 40-80 % ethylene diluted in hydrogen containing the vapor of ferrocene ( Fe(C5H5)2 ) was allowed to flow toward the hot-filaments. The pressure in the chamber was maintained 2.66 kPa (20 Torr). The plate of RF electrode was set 20 mm downstream from the hot filaments and placed perpendicular to the flow of reaction gas. Power up to 50 W was applied to the RF plate with the filaments heated for about one hour. Prepared carbon fine-p
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