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Synthesis and Characterization of Catalytically Grown Long Carbon Nanotube Arrays

Cho, Wondong
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337889014

Abstract Details

2012, PhD, University of Cincinnati, Engineering and Applied Science: Chemical Engineering.
This study is focused on synthesis of centimeter long carbon nanotube (CNT) arrays by a water-assisted catalytic chemical vapor deposition (CVD) process, and elucidating their growth mechanism. In order to surpass current limitations and achieve centimeter long CNT arrays, the growth kinetics and related mechanism were systematically examined to understand the relationship among growth variables, catalyst nanoparticles, and CNT structures. Knowledge about the growth rate, activation energy, and growth mechanism/model is generated through kinetics study and characterization of CNT growth. First, a real time photography method was developed to study growth kinetics. Using this method, we found that the growth of centimeter long CNT arrays revealed root growth mode. The length of the CNT arrays increased linearly with growth time for all the tested temperatures followed by an abrupt growth termination. It was demonstrated that Fe-lanthanide catalysts prolonged the catalyst lifetime and enhanced catalyst activity, which led to growing of centimeter long CNT arrays. Particularly, Fe-Gd catalyst yielded the longest catalyst lifetime and CNT growth length. Fe-only catalyst revealed very uniform particle size distribution with large particles (40 nm) while Fe-lanthanide catalysts showed wide range of particle size distribution. The composition of Fe on the surface of catalyst reduces in all catalysts as increasing the annealing time. Especially, the Fe composition in Fe-only catalyst decreased much faster than Fe-lanthanide catalysts. Hence, it has been found that Fe-lanthanide catalysts with non-uniform particle size distribution from in the range of 1 to 1.5 nm Fe film produced centimeter long CNTs. During heating followed by 15 annealing of the substrate, the catalyst particle size distribution and composition are determined by surface migration/solid diffusion and mixing of the metals in each layer. Then, the particle size distribution is steadily maintained while the composition of catalysts on the surface decreases slightly during CNT growth. Growth termination is caused by many complex reasons such as surface migration and loss of catalysts, formation of cementite and deposition of amorphous carbon on catalysts. A new model of growth termination of vertically aligned centimeter long CNTs is presented based on experimental results. In order to grow centimeter long CNTs, it is important to maintain balanced conditions, especially water and hydrogen concentration and a moderate growth rate and clean catalyst surface. The catalyst lifetime is prolonged by increasing the hydrogen partial pressure up to 0.1 volume concentration. Moreover, adding small amounts of water (180 ppm) increases the catalyst lifetime dramatically. We obtained the following optimized recipe: 560 mmHg of argon, 60 mmHg of hydrogen, 140 mmHg of ethylene, and 900 ppm of water. Based on the findings in this work, we were able to grow the longest vertically aligned CNT arrays reported so far, with length of 21.7 mm, growth rate of 27.47 ¿¿¿¿m/min and activation energy of 212.2 kJ/mol.
Vesselin Shanov, PhD (Committee Chair)
Junhang Dong, PhD (Committee Member)
Mark Schulz, PhD (Committee Member)
Peter Panagiotis Smirniotis, PhD (Committee Member)
216 p.
Nanotechnology
centimeter long carbon nanotube array; growth mechanism; growth termination mechanism; in situ observation; Fe-lanthanide catalysts; characterization of catalyst;

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Citations

  • Cho, W. (2012). Synthesis and Characterization of Catalytically Grown Long Carbon Nanotube Arrays [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337889014

    APA Style (7th edition)

  • Cho, Wondong. Synthesis and Characterization of Catalytically Grown Long Carbon Nanotube Arrays. 2012. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337889014.

    MLA Style (8th edition)

  • Cho, Wondong. "Synthesis and Characterization of Catalytically Grown Long Carbon Nanotube Arrays." Doctoral dissertation, University of Cincinnati, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337889014

    Chicago Manual of Style (17th edition)

ucin1337889014
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© 2012, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.