• Computers and Concrete
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• v.25 no.4
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• pp.343-354
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• 2020

In this paper, vibration characteristics of chiral double-walled carbon nanotubes entrenched on Kelvin's model. The Eringen's nonlocal elastic equations are being combined with Kelvin's theory to observe small scale response. A nonlocal model has been formulated to explore the frequency spectrum of chiral double-walled CNTs along with diversity of indices and nonlocal parameter. Wave propagation is proposed technique to establish field equations of model subjected to four distinct end supports. The significance of scale effect in relevance of length-to-diameter and thickness- to- radius ratios are discussed and displayed in detail.

• Advances in concrete construction
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• v.13 no.6
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• pp.471-479
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• 2022

In this paper, vibrational attributes of double-walled carbon nanotubes (CNTs) has been studied based upon nonlocal elastic shell theory. The implication of small scale is being perceived by establishing nonlocal Love shell model. The wave propagation approach has been operated to frame the governing equations as eigen value system. The comparison of local and nonlocal model has been overtly explored by means of scaling parameter. An appropriate selection of material properties and nonlocal parameter has been considered. The influence of changing mechanical parameter Young's modulus has been studied in detail. The dominance of end condition via nonlocal parameter is explained graphically. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.

• Steel and Composite Structures
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• v.43 no.6
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• pp.797-808
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• 2022

This paper presents an investigation on the free vibration characteristics of functionally graded nanocomposite double-beams reinforced by single-walled carbon nanotubes (SWCNTs). The double-beams coupled by an interlayer spring, resting on the elastic foundation with a linear layer and shear layer, and is simply supported in thermal environments. The SWCNTs gradient distributed in the thickness direction of the beam forms different reinforcement patterns. The materials properties of the functionally graded carbon nanotube-reinforced composites (FG-CNTRC) are estimated by rule of mixture. The first order shear deformation theory and Euler-Lagrange variational principle are employed to derive the motion equations incorporating the thermal effects. The vibration characteristics under several patterns of reinforcement are presented and discussed. We conducted a series of studies aimed at revealing the effects of the spring stiffness, environment temperature, thickness ratios and carbon nanotube volume fraction on the nature frequency.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1081-1086
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• 2005

Dynamic behavior of carbon nanotubes (CNTs) in an electric field is directly observed by in-situ transmission electron microscopy (TEM). The CNT field emitters examined by in-situ TEM are multiwalled, double-walled and single walled CNTs. Threshold fields for electron emission and sustainable emission currents depending on the structure of CNTs are presented, and degradation mechanism of the CNT field emitters is discussed. In addition to the microscopy studies on individual CNTs, our recent development in surface treatment of CNT layers grown by chemical vapor deposition, which brings about high density of emission current and high uniformity, is also presented.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.17.2-17.2
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• 2011

Double-walled carbon nanotubes (DWCNTs) were grown with vertical alignment on a Si wafer by using catalytic thermal chemical vapor deposition. This study investigated the effect of pre-annealing time of catalyst on the types of CNTs grown on the substrate. The catalyst layer is usually evolved into discretely distributed nanoparticles during the annealing and initial growth of CNTs. The 0.5-nm-thick Fe served as a catalyst, underneath which Al was coated as a catalyst support as well as a diffusion barrier on the Si substrate. Both the catalyst and support layers were coated by using thermal evaporation. CNTs were synthesized for 10 min by flowing 60 sccm of Ar and 60 sccm of H2 as a carrier gas and 20 sccm of C2H2 as a feedstock at 95 torr and $750^{\circ}C$. In this study, the catalyst and support layers were subject to annealing for 0~420 sec. As-grown CNTs were characterized by using field emission scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, and atomic force microscopy. The annealing for 90~300 sec caused the growth of DWCNTs as high as ~670 ${\mu}m$ for 10 min while below 90 sec and over 420 sec 300~830 ${\mu}m$-thick triple and multiwalled CNTs occurred, respectively. Several radial breathing mode (RBM) peaks in the Raman spectra were observed at the Raman shifts of 112~191 cm-1, implying the presence of DWCNTs, TWCNTs, MWCNTs with the tube diameters 3.4, 4.0, 6.5 nm, respectively. The maximum ratio of DWCNTs was observed to be ~85% at the annealing time of 180 sec. The Raman spectra of the as-grown DWCNTs showed low G/D peak intensity ratios, indicating their low defect concentrations. As increasing the annealing time, the catalyst layer seemed to be granulated, and then grown to particles with larger sizes but fewer numbers by Ostwald ripening.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.194-198
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• 2008

Several methods for improving dispersion of carbon nanotubes (CNTs) have been investigated. CNTs modified by acids and hydrogen peroxide ($H_2O_2$) showed improved dispersion. From SEM micrographs and photos of dispersion, CNTs modified with nitric acid and $H_2O_2$, showed no agglomeration in solution even standing for 4 months, which means successfully improved dispersion property. TEM micrographs of surface modified single CNT treated with 69% $HNO_3$ in boiling acid solution as the optimum method were obtained. For confirmation of CNTs' application to EDLC electrode materials, characteristics of EDLC have been analyzed by cyclic voltammetry curve, specific capacitance of unit cell, electrode discharge curves and AC impedance curve. From the results, it could be confirmed that electrochemical properties of CNTs were enhanced after surface modification with 69% $HNO_3$ acid treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2005.02a
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• pp.129-129
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• 2005

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.200-200
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• 2012

We investigated a flexible transparent film using the spinning multi-walled carbon nanotubes (MWCNTs). Spin-capable MWCNTs on iron catalyzed on a SiO2 wafer was grown by chemical vapor deposition, which was performed at $780^{\circ}C$ using C2H2 and H2 gas. The average diameter and length of MWCNTs grown on the substrate were ~15 nm and $250{\sim}300{\mu}m$, respectively. The MWCNT sheets were produced by continuously pulling out from well-aligned MWCNTs on a substrate. The MWCNT sheet films were produced simply by direct coating on the flexible film or grass. The thickness of sheet film was remarkably decreased by alcohol spraying on the surface of sheet. The alcohol splay increased transmittance and decreased electrical resistance of MWCNT sheet films. Single and double sheets were produced with sheet resistance of ~699 and ${\sim}349{\Omega}/sq$, respectively, transmittance of 81~85 % and 67~72%, respectively. The MWCNT sheet films were heated through the application of direct current power. The flexible transparent heaters showed a rapid thermal response and uniform distribution of temperature. In addition, MWCNT yarns were prepared by spinning a bundle of MWCNTs from vertically super-aligned MWCNTs on a substrate, and field emission from the tip and side of the yarns was induced in a scanning electron microscope. We found that the field emission behavior from the tip of the yarn was better than the field emission from the side. The field emission turn-on voltages from the tip and side of MWCNT yarns were 1.6 and $1.7V/{\mu}m$, respectively, after the yarn was subjected to an aging process. Both the configuration of the tip end and the body of the yarn were changed remarkably during the field emission. We also performed the field emission of the sheet films. The sheet films showed the turn on voltage of ${\sim}1.45V/{\mu}m$ during the field emission.

• Journal of Magnetics
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• v.17 no.1
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• pp.9-12
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• 2012

Attempts to dope carbon nanotube (CNT) with impurities in order to control the electronic properties of the CNT is a natural course of action. Boron is known to improve both the structural and electronic properties. In this report, we study the field emission properties of Boron-doped double-walled CNT (DWCNT). Boron-doped DWCNT films were fabricated by catalytic decomposition of tetrahydrofuran and triisopropyl borate over a Fe-Mo/MgO catalyst at $900^{\circ}C$. We measured the field emission current by varying the doping amount of Boron from 0.8 to 1.8 wt%. As the amount of doped boron in the DWCNT increases, the turn-on-field of the DWCNT decreases drastically from 6 V/${\mu}m$ to 2 V/${\mu}m$. The current density of undoped CNT is 0.6 mA/$cm^2$ at 9 V, but a doped-DWCNT sample with 1.8 wt% achieved the same current density only at only 3.8 V. This shows that boron doped DWCNTs are potentially useful in low voltage operative field emitting device such as large area flat panel displays.

• Composites Research
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• v.30 no.3
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• pp.215-222
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• 2017

The effect of a multi walled carbon nanotubes (MWNCT) on the adhesive properties and thermal properties of epoxy were studied by double lap-shear tests. Epoxy/MWCNT resins were prepared from a different amount of the MWCNT incorporated into the epoxy resins (araldite 2011). Steel plates and carbon fiber reinforced plastics (CFRP) were chosen as materials. Mechanical tests were performed by a universal testing machine (UTM). The analysis of thermal properties were conducted by a thermogravimetric analyzer (TGA) and a differential scanning calorimetry (DSC). The fracture surface morphology was examined using a scanning electron microscopy (SEM) and optical microscope. Compared to neat epoxy, it was found that the mechanical properties of epoxy/MWCNT resins are increased.