Numerical and Experimental Investigation of Carbon Nanotube Sock Formation
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Numerical and Experimental Investigation of Carbon Nanotube Sock Formation Guangfeng Hou1, Vianessa Ng1, Yi Song1, Lu Zhang1, Chenhao Xu1, Vesselin Shanov1, David Mast2, Mark Schulz1*, Yijun Liu1 1 Department of Mechanical and Materials Engineering, University of Cincinnati, OH 45221, United States 2 Department of Physics, University of Cincinnati, OH 45221, United States ABSTRACT Formation of the carbon nanotube (CNT) sock, which is an assemblage of nanotubes in a thin cylindrical shape, is a prerequisite for continuous production of thread and sheet using the floating catalyst growth method. Although several studies have considered sock formation mechanisms, the dynamics of the sock behavior during the synthesis process are not well understood. In this work, a computational technique is utilized to explore the multiphysics environment within the nanotube reactor affecting the sock formation and structure. Specifically the flow field, temperature profile, catalyst nucleation, and residence time are investigated and their influence on the sock formation and properties are studied. We demonstrate that it is critical to control the multiphysics synthesis environment in order to form a stable sock. Sock production rate was studied experimentally and found to be linearly dependent on the amount of effective catalyst (iron in the sock) inside the reactor. To achieve a high sock production rate, the proportion of effective iron has to be high when increasing the total amount of catalyst in the reactor. Based on the analysis, we suggest that using small size catalyst and growing longer CNTs by increasing temperature, increasing residence times etc. will increase the CNT production rate and improve the properties of CNT thread/sheet produced from the sock. INTRODUCTION Carbon nanotubes (CNTs) are a promising high-performance material due to their high mechanical, electrical and thermal properties. CNTs can be directly used in integrated circuits1, or processed into CNT thread or tape for various applications2,3. CNT thread can be produced by several methods: (i) dry spinning from a vertically aligned CNT array4, (ii) wet spinning from a CNT suspension5, and (iii) continuous direct-spinning from an aerogel-like sock in a floating catalyst type reactor6. Among these methods, the floating catalyst reactor is one of the most promising candidates for scaling up CNT production, due to high reaction rates and ease of making fibers and tapes. For CNT yarn, tape or sheet production by the floating catalyst method, a CNT sock is the prerequisite material where all the tubes within a sock are bonded through the CNT π bond interactions and possibly London forces, so that the highly porous sock can be handled, stretched and spun into a yarn. The sock formation process has been studied by numerical simulation and experimental methods7,8. The parameter space was studied for a vertical reactor9 considering the effect of carrier gas and feedstock. Several governing mechanisms for sock formation have been proposed, including thermophoresis o
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