• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.467-472
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• 2002

Long Carbon Nanotubes(CNTs) were cut by diamond lapping film followed by observation using SEM. The paste was prepared by mixing shortened CNT powder, ${\alpha}$-terpineol used as a solvent, and ethylcellulose as a binder. This paste was deposited on glass substrate by screen printing and extruded by syringe. After screen printing, several post-treatments were performed to control the alignment of CNTs perpendicular to the substrate. The deposited CNTs were scratched by sand paper or diamond lapping film. It was also treated by attachment followed by an immediate detachment using the adhesive tape. SEM observation indicates that excellent vertical alignment of CNTs could be achieved by simple post-treatments from the screen printed-CNTs paste. Similar alignment of CNTs is also observed in the as-extruded CNTs paste.

• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.35-44
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• 2009

In this study, boiling heat transfer coefficients(HTCs) and critical heat flux(CHF) are measured on a smooth square flat copper heater in a pool of pure water with and without carbon nano tubes(CNTs) dispersed at $60^{\circ}C$. Tested aqueous nanofluids are prepared using multi-walled CNTs whose volume concentrations are 0.0001, 0.001, 0.01, and 0.05%. For dispersion of CNTs, polyvinyl pyrrolidone(PVP) is used in distilled water. Pool boiling HTCs are taken from $10kW/m^2$ to critical heat flux for all nanofluids. Test results show that the pool boiling HTCs of the nanofluids are lower than those of pure water in entire nucleate boiling regime. On the other hand, critical heat flux is enhanced greatly showing up to 200% increase at volume concentration of 0.001% CNTs as compared to that of pure water. This is related to the change of surface characteristics by the deposition of CNTs. This deposition makes a thin CNT layer on the surface and the active nucleation sites of heat transfer surface are decreased due to this layer. The thin layer acts as the thermal resistance and also decreases the bubble generation rate resulting in a decrease in pool boiling HTCs. The same layer, however, maintains the nucleate boiling even at very high heat fluxes and reduces the formation of large vapor canopy at near CHF resulting in a significant increase in CHF.

• Journal of Radiation Industry
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• v.5 no.2
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• pp.137-143
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• 2011

Epoxy resins are widely used as high performance thermosets in many industrial applications, such as coatings, adhesives and composites. Recently, a lot of research has been carried out in order to improve their mechanical properties and thermal stability in various fields. Carbon nanotubes possess high physical and mechanical properties that are considered to be ideal reinforcing materials in composites. CNT-reinforced epoxy system hold the promise of delivering superior composite materials with their high strength, light weight and multi functional features. Therefore, this study used multi-walled carbon nanotubes (MWNT) and gamma rays to improve the mechanical and thermal properties of epoxy. The diglycidyl ether of bisphenol A (DGEBA) as epoxy resins were cured by gamma ray irradiation with well-dispersed MWNTs as a reinforcing agent and triarylsulfonium hexafluoroantimonate (TASHFA) as an initiator. The flexural modulus was measured by UTM (universal testing machine). At this point, the flexural modulus factor exhibits an upper limit at 0.1 wt% MWNT. The thermal properties had improved by increasing the content of MWNT in the result of TGA (thermogravimetric analysis). However, they were decreased with increasing the radiation dose. The change of glass transition temperature by the radiation dose was characterized by DMA (dynamic mechanical analysis).

• Journal of the Korean Vacuum Society
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• v.16 no.1
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• pp.33-39
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• 2007

Electrical and mechanical modifications of devices based on carbon nanotubes(CNTs) using an atomic force microscope(AFM) in the forms of cutting and reconnection of CNTs are demonstrated. In addition to the modifications, electrostatic force microscopy is used to visualize the cutting and reconnection of CNTs. In this way, AFM is shown to be a useful tool in local modifications and manipulations of CNT-based devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.297-298
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• 2005

We have fabricated twisted nematic (TN) liquid crystal cells doped by carbon nanotubes (CNTs) with different CNT wt. %. With a minute amount doping, multi-walled CNTs did not perturb the liquid crystal orientations at the off- and on-state. The hysteresis studies of voltage-dependent capacitance (V-C) under the influence of electric field generated by ac and dc voltage show that the residual do, which is tightly related to image sticking problem in liquid crystal displays, is greatly reduced due to ion trapping by CNTs. Also, the V-C hysteresis shows dependency of capacitance on concentration of multi-walled CNTs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.3
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• pp.250-254
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• 2006

Hetero-junction sheet actuator composed of carbon nanotubes and $V_{2}O_5$ nanowires were demonstrated in a bimetal configuration. The successive filtration of $V_{2}O_5$ nanowire solution followed by carbon nanotube dispersed water solution in the same way produced a dark-gray colored sheet. A significant actuation was observed in sodium chloride electrolyte solution with a bending direction to the carbon nanotube side at the positive bias voltage against the copper counter-electrode. As the frequency of the applied voltage increased, the amplitudes decreased, indicating a rather slow response of the hetero-film actuator in the electrolyte solution. The hybrid structure enabled an easy fabrication of the film actuator with the enhanced efficiencies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2713-2718
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• 2010

To improve the CNT's dispersion, we tried to chemically modify the surface of MWNT with the butyllithium and the hexyllithium solution in sonicated reactor. The functionalized-MWNTs were characterized by Fourier transform infrared spectrometer(FT-IR) and Raman spectrophotometer. Also, we investigated the amount of alkyl moiety incorporated into MWNT's surface with Thermal gravimetric analyzer(TGA) and dispersibility in various organic solvents. Finally, we could find organic content was about 5% of the functionalized MWNT and dispersibility was enhanced in some solvents having intermediate solubility parameter.

• Coupled systems mechanics
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• v.10 no.1
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• pp.39-60
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• 2021

The present paper is concerned with the study of nonlinear ultrasonic waves in a magneto thermo (MT) elastic armchair single-walled carbon nanotube (ASWCNT) resting on polymer matrix. The analytical formulation is developed based on Eringen's nonlocal elasticity theory to account small scale effect. After developing the formal solution of the mathematical model consisting of partial differential equations, the frequency equations have been analyzed numerically by using the nonlinear foundations supported by Winkler-Pasternak model. The solution is obtained by ultrasonic wave dispersion relations. Parametric work is carried out to scrutinize the influence of the non local scaling, magneto-mechanical loadings, foundation parameters, various boundary condition and length on the dimensionless frequency of nanotube. It is noticed that the boundary conditions, nonlocal parameter, and tube geometrical parameters have significant effects on dimensionless frequency of nano tubes. The results presented in this study can provide mechanism for the study and design of the nano devices like component of nano oscillators, micro wave absorbing, nano-electron technology and nano-electro- magneto-mechanical systems (NEMMS) that make use of the wave propagation properties of armchair single-walled carbon nanotubes embedded on polymer matrix.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.44-44
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• 2003

Growth mechanism of carbon nanotubes(CNTs) synthesized by chemical vapor deposition is abided by two growth modes. These growth modes are classified by the position of activated catalytic metal particle in the CNTs. Growth mode can be also affected by interaction between substrate and catalytic metal and induced energy such as thermal and plasma. We studied the reaction of catalytic metal to the substrate and growth mode of CNTs. Various substrates such as Si(100), graphite plate, coming glass, sapphire and AAO membrane are used to study the relation between catalytic metal and substrate in the synthesis of CNTs. For catalytic metal, thin film was deposited on various substrate via sputtering technique with a thickness of ∼20nm and magnetic fluids with none-sized particles were dispersed on AAO membrane. After laying process on AAO membrane, it was dried at 80$^{\circ}C$ for 8 hour. Synthesizing of CNTs was carried out at 900$^{\circ}C$ in NH3/C2H2 mixture gases flow for 10minutes.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.130-137
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• 2023

This study analyzed the effect of mixing order on the flowability, compressive strength, and flexural strength of cement composites reinforced with polyvinyl alcohol(PVA) fibers and multi-walled carbon nanotubes(MWCNTs). The experimental results showed that the addition of CNTs significantly reduced the flowability, and the flowability was considerably affected by the mixing order when CNTs were added. The compressive strength was most effectively improved when water and CNTs solution were mixed first before adding PVA fibers, and the flexural strength was highest when water and CNTs solution were mixed with PVA fibers after dry mixing. However, there was no clear correlation between the flexural toughness and the mixing order. In addition, scanning electron microscopy(SEM) image analysis was conducted to analyze the microstructure. The SEM images showed that CNTs were randomly dispersed through the specimens and contributed to the strength improvement, but the effect of the mixing order was not clearly observed. The main results of this study are expected to be useful for evaluations of workability and material performance of PVA fiber-reinforced cement composites with CNTs.