• Korean Journal of Materials Research
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• 제12권6호
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• pp.458-463
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• 2002

Carbon nanotubes were synthesized at various conditions using Ni-catalytic thermal chemical vapor deposition method and their characteristic properties were investigated by SEM, TEM and Raman spectroscopy. Carbon nanotubes were formed on very fine Ni-catalytic particles. The carbon nanotubes synthesized by thermal decomposition of acetylene at $700^{\circ}C$ had a coiled shape, while those synthesized at $850^{\circ}C$ showed a curved and Y-shape having a bamboo-like morphology. It was found that the carbon nanotube was also made on the fine Ni-catalytic particles formed on the surface of 100~400nm sized large ones after pretreatment with $NH_3$.ber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• Journal of the Korean Society for Railway
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• 제12권4호
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• pp.590-596
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• 2009

In this study, the failure modes and energy absorption characteristics of four different kinds of circular tubes made of carbon, glass, Kevlar and carbon-Kevlar hybrid fibres composites with epoxy resin have been evaluated. To achieve these goals, compressive tests were conducted for the tubes under 10mm/min loading speed. Based on the test results, the carbon/epoxy tube showed the best energy absorption capability, while carbon-Kevlar/epoxy tubes were worst. In the failure mode during crushing, both of the carbon/epoxy tubes and the glass/epoxy tubes were crushed by brittle fracturing mode. The Kevlar/epoxy tubes were collapsed by local buckling mode like steel, while the carbon-Kevlar hybrid tubes were collapsed by mixed mode of local buckling and lamina bending.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.93-93
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• 2000

수소화된 비정질 탄소(a-C:H)는 그 증착 조건에 따라서 여러 가지 다른 구조와 특성을 갖게 되며, 특히 DLC(diamond-like carbon) 및 CNT(Carbon nanotube)는 FED (field emission display) 개발 면에서 중요하게 연구되고 있다. 우리는 a-C:H 박막을 PECVD (plasma-enhanced chemical vapor deposition) 방법으로 증착하고 CH4 가스를 사용하였고 기판 온도는 상온-32$0^{\circ}C$ 사이에서 변화되었다. 기판은 Corning 1737 glass, quartz, Si, Ni 등을 사용하였다. 증착 압력과 R.F. power는 각각 0.1-1 Torr 와 12-60w 사이에서 변화되었다. ESR 측정은 X-band(주파수 약 9 GHz)에서 그리고 상온에서 행해졌다. 상온에서의 스핀밀도는 약한-표준피치(weak-pitch standard) 스펙트럼과 비교하여 얻을 수 있었다. 그리고 a-C:H 박막의 구조는 He-Ne laser(파장 632.8 nm)를 이용하는 micro-Raman spectroscopy로 분석하였다. 증착조건에 따른 스핀밀도의 변화 및 Raman 스펙트럼에서의 D-peak, G-peak의 위치 및 반치록, I(D)/I(G) 등을 조사하였다. 증착된 a-C:H 박막은 R.F.power가 증가할수록 대체로 스핀밀도가 증가하였으며, Raman 스펙트럼에서의 I(D)/I(G) 비율은 대체로 감소하였다. 증착된 박막들은 polymer-like Carbon으로 추정되었으며, 스핀밀도가 증가할수록 대체적으로 흑연 구조 영역이 증가됨을 알 수 있었다. 또한 glass나 Si 기판에 비해 Ni 기판위에서 polymer-like Carbon 구조는 향상되는 경향을 보였다.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.743-749
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• 1999

Recently new rehabilitation techniques have been proposed with advanced composite materials like carbon fiber, aramid, glass fiber sheet and so forth. The purpose of this paper is to investigate the mechanical characteristics of reinforced concrete columns confined with carbon fiber sheet and evaluate the degree of their strengthening effect. For the test, the specimen size of column is 15cm$\times$15cm$\times$90cm reinforced with 4 number of main bars of 10 mm diameter, tied bars of 6 mm diameter and slenderness ratio 20. Columns were wrapped with carbon fiber sheet along the column length. It is necessary to make some assumption regarding the confinement of carbon fiber sheet to apply to reinforced concrete columns under concentric loads. The strength gain effect of columns confined with carbon fiber sheet could be predicted using the proposed equation.

• Journal of the Korean Society for Precision Engineering
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• 제26권1호
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• pp.51-56
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• 2009

Recently, with the increasing lightness and miniaturization of high resolution camera phones, the demand for aspheric glass lens has increased because plastic and spherical lens are unable to satisfy the required performance. An aspheric glass lens is fabricated by the high temperature and pressure molding using a tungsten carbide molding core, so precision grinding and coating technology for the molding core surface are required. This study investigates the effect of diamond-like carbon (DLC) and rhenium-iridium (Re-Ir) coating For aspheric molding core surface. The grinding conditions of the tungsten carbide molding core were obtained by design of experiments (DOE) for application in the ultra precision grinding process of the tungsten carbide molding core of the aspheric glass lens used in 5 megapixel, $4{\times}$ zoom camera phone modules. A tungsten carbide molding core was fabricated under this grinding condition and coated with the DLC and Re-Ir coating. By measurements, the effect of DLC and Re-Ir coating on the form accuracy and surface roughness of molding coer was evaluated.

• Carbon letters
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• 제5권1호
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• pp.6-11
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• 2004

In spite of unparalleled combination of essential material properties for brake linings and clutch facings, replacement for asbestos is seriously called for since it is a health hazard. Once asbestos is replaced with other material then composition and properties of brake pad changes. In certain cases hardness of the material may be high enough to affect the rotor material. In this study, hardness of the brake pad has been controlled using suitable reinforcement materials like glass, carbon and Kevlar pulp. Brake pad formulations were made using CNSL (cashew net shell liquid) modified phenolic resin as a binder, graphite or cashew dust as a friction modifier and barium sulphate, talc and wollastonite as fillers. Influence of each component on the hardness value has been studied and a proper formulation has been arrived at to obtain hardness values around 35 on Scleroscopic scale. Friction and wear properties of the respective brake pad materials have been measured on a dynamometer and their performance was evaluated.

• Proceedings of the KIEE Conference
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1737-1739
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• 2004

Diamond-like carbon (DLC) films were prepared with RF-PECVD (Plasma Enhanced Chemical Vapor Deposition) method on coming glass and silicon substrates using methane ($CH_4$) and hydrogen ($H_2$) gases. We examined the effects of $CH_4$ to $H_2$ ratios on tribological and optical properties of the DLC films. The structure and surface morphology of the films were examined using Raman spectroscopy and atomic force microscopy (AFM). The hardness of the DLC film was measured with nano-indentor. The optical properties of DLC thin film were investigated by UV/VIS spectrometer and ellipsometry. And also, solar cells were fabricated using DLC as antireflection coating before and after coating DLC on silicon substrate and compared the efficiency.

• The Korean Journal of Ceramics
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• 제3권2호
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• pp.92-95
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• 1997

Because of the novel characteristics such as chemical stability, hardness, electrical resistivity and thermal conductivity, diamond-like carbon (DLC) film is a suitable material for the passivation layers. For this purpose, using the PECVD, DLC films were synthesized at room temperature. The adhesion and the hardness of the DLC films deposited on Si an SiO2 substrate were measured. The resistivity of 5.3$\times$$10^8$$\Omega$.cm was measured by automatic spreading resistance probe analysis method. The thermal conductivities of different DLC films were measured and compared with that of phospho silicate glass (PSG) film which is commonly used as passivation layers. The thermal conductivity of DLC film was improved by increasing hydrogen flow rate up to 90 sccm and was better than that of PSG film. The patterning techniques of the DLC film developed using the RIE and the lift-off method to form 5$\mu\textrm{m}$ line. Finally, the thermal characteristics of the power transistor with the DLC film as passiviation layer was analyzed.

• Carbon letters
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• 제6권2호
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• pp.101-105
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• 2005

Like bamboo-sprouts after rains, numerous sub${\mu}m$-sized pyrocarbon whiskers growth on the Mullite ($3Al_2O_3{\cdot}2H_2O$) substrate could be observed through a looking glass during methane pyrolysis at the temperature of $1050^{\circ}C$ in this study. If the surface of substrate would be scrubbed strongly with iron metals, then finely sticked iron particles were more effective catalytic for nm-sized whisker growth. Numerous fine flakes of pyrolytic carbon were hanging by invisible nm-whiskers as like as small spiders hanging by a spiderweb. This is the identification of nm-sized whisker growth. Therefore if the pyrolysis would be stopped at the initial stage of the whisker growth, the primary lengthening growth was nm-sized whisker. So could we vary arbitrarily sizes of whisker from nm- to ${\mu}m$-sizes. But ${\mu}m$- and nm-whiskers grown with the different growth mechanism; the former was straight and the latter has twigs, The lengthening growth of whisker was depended on the flow pattern pyrolysis species on the active sites of substrate and on the growth duration. We could obtained straight whisker length of 10~20 ${\mu}m$/min during the primary growth and laboratory spiral whisker of 30~40 ${\mu}m$-diameter/hr during the secondary growth.

• Journal of Korean Vacuum Science & Technology
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• 제3권1호
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• pp.54-58
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• 1999

We deposited diamond-like carbon (DLC) films using ion beam sputtering of a graphite target on flat substrates for use as a thin film field emitter. An n-type silicon wafer, titanium-coated silicon, and indium tin oxide (ITO) coated glass were used as a substrate. All films exhibited a sudden increase in the emission after a breakdown occurred at high voltage. The morphology of the films after the breakdown depended on the substrate. On ITO and Ti substrates, the DLC film peeled off upon breakdown, but on the Si substrate the surface melting due to breakdown resulted in the formation of various structures such as a sharp point, mound, and crater. By scanning the deformed surface with a tip anode, we found that the emission was concentrated at the deformed sites, indicating that the field enhancement due to the morphology change was responsible for the increased emission.