李 墨宸 理工総研が募集する次席研究員
LI Mochen Researcher
理工学術院総合研究所 野田 優研究室
Waseda Research Institute for Science and Engineering
Carbon nanotube (CNT) is an important allotrope of low-dimensional carbon materials and exhibits a series of intriguing structure-dependent features. Chemical vapor deposition (CVD) is a promising techniques to realize their large-scale synthesis. We have synthesized sub-millimeter-long, 99 wt%-pure few-wall CNTs and single-wall CNTs on ceramic beads using fluidized-bed technology using acetylene as carbon source. However, the supply of low concentration C2H2in these studies requires the use of a carrier gas at a high flow rate (90 times of the C2H2flow rate), resulting in problems associated with heating the gas and significant greenhouse gasemissions. Therefore, the purpose is (A) to synthesize SWCNTs at high carbon yield (the conversion ratio of carbon in the feed to that in the product) using high concentrationC2H4, and (B)to understand the relation between CNT array growth and catalyst structure.
In this study, applicantproposes to synthesize SWCNTs at high carbon yield using high concentration C2H4by fluidizedbed CVD and to study the relation between CNT array growth and catalyst structure. The detailed experimental methods are:(1) Synthesis of SWCNTs using high concentration C2H4The Fe/AlOxcatalyst will be sputter-deposited on the surface of ceramic beads using inhouse-developed drumsputtering system . The growth of SWCNTs will be carried out using a heat-exchange fluidized bed reactor . The sufficient heating and mixing of ceramic beads underproper gas flowrate is essential for the stable growth of SWCNTs at high carbon yield. The total gas flow rate and beads size will be optimized to enable the state change of beads from fixed bed to fluidized bed state during synthesis, thusensuring the sufficient heating of samples and enough space for CNT growth among beads. Additionally, applicant proposes to mix ceramic beads by rotating the reactor instead of feedingg as at large flowrate ;thus, small gas flow rate is needandtar generation at down stream can be prevented.
(2) Influence of catalyst structure on growth lifetime of CNT arrays The Fe-saturated AlOxsupportlayer is proposed to be constructed in order toreduce the bulk diffusion of Feinto AlOxlayer.The bottom Felayer with thickness gradient will be sputter-depositedon SiO2/Si substratesusinga combinatorial methodbya radio frequency magnetron sputtering. Then, the Fe/AlOxcatalyst will be sputtered. Finally, the prepared samples will be cut perpendicular to the thickness gradientand used for CNT growth. The concentration gradientof Fe and be preciselycontrolled by adjusting the thickness of bottom Fe layer and AlOxlayer. The effective growth of CNTs with longer catalyst lifetime is expected to beachieved.
Expected results and impactsApplicant expect to synthesize high-purity (> 99wt%), sub-millimeter-long SWCNTs (specific surface area>1000 m2/g) at high carbonyield(>50 %) using unsaturated hydrocarbon in FBCVD reactor. For the growth of SWCNTs by constructing Fe-saturated AlOxlayer, the growth lifetime of catalyst is expected to be prolonged to longer than 40 min.