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Chemical, mechanical, and thermal control of substrate-bound carbon nanotube growth
, 2006
"... Carbon nanotubes (CNTs) are long molecules having exceptional properties, including several times the strength of steel piano wire at one fourth the density, at least five times the ther-mal conductivity of pure copper, and high electrical conductivity and current-carrying capac-ity. This thesis pre ..."
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Carbon nanotubes (CNTs) are long molecules having exceptional properties, including several times the strength of steel piano wire at one fourth the density, at least five times the ther-mal conductivity of pure copper, and high electrical conductivity and current-carrying capac-ity. This thesis presents methods of CNT synthesis by atmospheric-pressure thermal chemical vapor deposition (CVD), where effective choice of the catalyst composition and processing con-ditions enables growth of tangled single-wall CNTs or structures of aligned multi-wall CNTs, on bare silicon, microstructured silicon, and ceramic fibers. Applying mechanical pressure during growth controls the structure of a CNT film while causing significant defects in the CNTs. This mechanochemisty approach is used to "grow-mold " CNTs into 3D-shaped microforms. A new reactor apparatus featuring a resistively-heated suspended platform enables rapid (~100 *C/s) temperature control and versatile in situ characterization, including laser measure-ment of CNT film growth kinetics, and imaging of stress-induced film cracking. By thermally pre-treating the reactant mixture before it reaches the substrate platform, aligned CNTs are
Energy storage in carbon nanotube super-springs
, 2008
"... A new technology is proposed for lightweight, high density energy storage. The objective of this thesis is to study the potential of storing energy in the elastic deformation of carbon nanotubes (CNTs). Prior experimental and modeling studies of the mechanical properties of CNTs have revealed nanosc ..."
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A new technology is proposed for lightweight, high density energy storage. The objective of this thesis is to study the potential of storing energy in the elastic deformation of carbon nanotubes (CNTs). Prior experimental and modeling studies of the mechanical properties of CNTs have revealed nanoscale structures with a unique combination of high stiffness, strength and flexibility. With a Young's modulus of 1 TPa and the ability to sustain reversible tensile strains of 6 % [1, 2] and potentially as high as 20 % [3-5], mechanical springs based on these structures are likely to surpass the current energy storage capabilities of existing steel springs and provide a viable alternative to electrochemical batteries. Models were generated to estimate the strain energy of CNTs subject to axial tension, compression, bending and torsion. The obtainable energy density is predicted to be highest under tensile loading, with an energy density in the springs themselves about 2500 times greater than the maximum energy density that can be reached in steel springs, and ten times greater than the energy density of lithium-ion batteries. Practical systems will have lower overall stored energy density once the mass and volume of the spring's support structure and any
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, 2006
"... The fracture strain of carbon nanotubes (CNTs) obtained by molecular dynamics is about 30%, which is much higher than the experimental results (10–13%). The present study shows that this difference results mainly from defects in CNTs. As the tensile strain reaches a few percent, defects are nucleate ..."
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The fracture strain of carbon nanotubes (CNTs) obtained by molecular dynamics is about 30%, which is much higher than the experimental results (10–13%). The present study shows that this difference results mainly from defects in CNTs. As the tensile strain reaches a few percent, defects are nucleated in the form of Stone–Wales transformation (901 rotation of a bond). A bond in the vicinity of rotated bond breaks as the tensile strain reaches about 13%, which agrees well with the experimental results. Therefore, the Stone–Wales transformation is the precursor of CNT fracture.
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"... have a wide range of technological applications such as nano-composites, nano-electro-mechanical scopy [8], scanning force microscopy [9], micro Raman spectroscopy [10], or electric field-induced tension [11]. Though there are large scatterings in the reported elastic modulus of CNTs, they are all o ..."
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have a wide range of technological applications such as nano-composites, nano-electro-mechanical scopy [8], scanning force microscopy [9], micro Raman spectroscopy [10], or electric field-induced tension [11]. Though there are large scatterings in the reported elastic modulus of CNTs, they are all on the order of 1 tera-Pascal (TPa). Aside from experimental studies, atomistic simulation tech-
Article Dialytic Separation of Bundled, Functionalized Carbon Nanotubes from Carbonaceous Impurities
, 2014
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Electromechanical Characterization of Quasi-One Dimensional Nanostructures of Silicon, Carbon, and Molybdenum
, 2010
"... Since September 2005, I have been receiving intensive training from the Materials ..."
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Since September 2005, I have been receiving intensive training from the Materials
A Hyperelastic Description of Single Wall Carbon Nanotubes at Moderate Strains and Temperatures
"... Abstract: In this work, single wall carbon nan-otubes (SWNTs) are shown to obey a hyperelastic constitutive model at moderate strains and tem-peratures. We consider the finite temperature ef-fect via the local harmonic approach. The equi-librium configurations were obtained by minimiz-ing the Helmho ..."
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Abstract: In this work, single wall carbon nan-otubes (SWNTs) are shown to obey a hyperelastic constitutive model at moderate strains and tem-peratures. We consider the finite temperature ef-fect via the local harmonic approach. The equi-librium configurations were obtained by minimiz-ing the Helmholtz free energy of a representative atom in an atom-based cell model. We show that the strain energy can be fitted by two cubic poly-nomials, which consequently produces for the lin-ear elasticity a linearly increasing tangent modu-lus below a critical strain and an almost linearly decreasing tangent modulus beyond the critical strain. To avoid the strain dependent tangent mod-ulus, we propose to use Ogden’s hyperelasticity model to describe the mechanical behaviors of SWNTs. Our results indicate a constant μ for Ogden’s hyperelastic model for moderately large strains for large tubes and below 900oK. The arm-chair tubes are shown to be much stronger and stiffer, but less ductile than the zigzag tubes. We also show that small tubes are more ductile but less stronger. Small tubes and high temperatures reveal more nonlinearity. 1
